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Bradycardia

Bradycardia, also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from various pathologic processes, it is commonly a physiologic response to cardiovascular conditioning or due to asymptomatic type 1 atrioventricular block.

Resting heart rates of less than 50 BPM are often normal during sleep in young and healthy adults and athletes. In large population studies of adults without underlying heart disease, resting heart rates of 45-50 BPM appear to be the lower limits of normal, dependent on age and sex. Bradycardia is most likely to be discovered in the elderly, as age and underlying cardiac disease progression contribute to its development.

Bradycardia may be associated with symptoms of fatigue, dyspnea, dizziness, confusion, and frank syncope due to reduced forward blood flow to the brain, lungs, and skeletal muscle. The types of symptoms often depend on the etiology of the slow heart rate, classified by the anatomic location of a dysfunction within the cardiac conduction system. Generally, these classifications involve the broad categories of sinus node dysfunction (SND), atrioventricular block, and other conduction tissue diseases. However, bradycardia can also result without dysfunction of the native conduction system, arising secondary to medications including beta blockers, calcium channel blockers, antiarrythmics, and other cholinergic drugs. Excess vagus nerve activity or carotid sinus hypersensitivity are neurological causes of transient symptomatic bradycardia. Hypothyroidism and metabolic derangements are other common extrinsic causes of bradycardia.

The management of bradycardia is generally reserved for patients with symptoms, regardless of minimum heart rate during sleep or the presence of concomitant heart rhythm abnormalities (See: Sinus pause), which are common with this condition. Untreated SND has been shown to increase the future risk of heart failure and syncope, sometimes warranting definitive treatment with an implanted pacemaker. In atrioventricular causes of bradycardia, permanent pacemaker implantation is often required when no reversible causes of disease are found. In both SND and atrioventricular blocks, there is little role for medical therapy unless a patient is hemodynamically unstable, which may require the use of medications such as atropine and isoproterenol and interventions such as transcutenous pacing until such time that an appropriate workup can be undertaken and long term treatment selected. While asymptomatic bradycardias rarely require treatment, consultation with a physician is recommended, especially in the elderly.

The term "relative bradycardia" can refer to a heart rate lower than expected in a particular disease state, often a febrile illness. Chronotropic incompetence (CI) refers to an inadequate rise in heart rate during periods of increased demand, often due to exercise, and is an important sign of SND and an indication for pacemaker implantation.

The word "bradycardia" is from the Greek βραδύς bradys "slow", and καρδία kardia "heart".

Normal cardiac conduction
The heart is a specialized muscle containing repeating units of cardiomyocytes, or heart muscle cells. Like most cells, cardiomyocytes maintain a highly regulated negative voltage at rest and are capable of propagating action potentials, much like neurons. While at rest, the negative cellular voltage of a cardiomyocyte can be raised above a certain threshold (so-called depolarization) by an incoming action potential, causing the myocyte to contract. When these contractions occur in a coordinated fashion, the atria and ventricles of the heart will pump, delivering blood to the rest of the body.

Normally, the origination of the action potential causing cardiomyocyte contraction originates from the sinoatrial node (SA node). This collection of specialized conduction tissue is located in the right atrium, near the entrance of the superior vena cava. The SA node contains pacemaker cells that demonstrate "automaticity" and can generate impulses that travel through the heart and create a steady heartbeat.

At the beginning of the cardiac cycle, the SA node generates an electrical action potential that spreads across the right and left atria, causing the atrial contraction of the cardiac cycle. This electrical impulse carries on to the atrioventricular node (AV node), another specialized grouping of cells located in the base of the right atrium, which is the only anatomically normal electrical connection between the atria and ventricles. Impulses coursing through the AV node are slowed before carrying on to the ventricles, allowing for appropriate filling of the ventricles before contraction. The SA and AV nodes are both closely regulated by the autonomic nervous system's fibres, allowing for adjustment of cardiac output by the central nervous system in times of increased metabolic demand.

Following slowed conduction through the atrioventricular node, the action potential produced initially at the SA node now flows through the His-Purkinje system. The bundle of His originates in the AV node and rapidly splits into a left and right branch, each destined for a different ventricle. Finally, these bundle branches terminate in the small Purkinje fibers that innervate myocardial tissue. The His-Purkinje system conducts action potentials much faster than can be propagated between myocardial cells, allowing the entire ventricular myocardium to contract in less time, improving pump function.

Classification

Most pathological causes of bradycardia result from damage to this normal cardiac conduction system at various levels: the sinoatrial node, the atrioventricular node, or damage to conduction tissue between or after these nodes.

Sinus node
Bradycardia caused by the alterations of sinus node activity is divided into three types.

Sinus bradycardia
Sinus bradycardia is a sinus rhythm of less than 50 BPM. Cardiac action potentials are generated from the SA node and propagated through an otherwise normal conduction system, but they occur at a slow rate. It is a common condition found in both healthy individuals and those considered well-conditioned athletes. Studies have found that 50–85% of conditioned athletes have benign sinus bradycardia, as compared to 23% of the general population studied. The heart muscle of athletes has a higher stroke volume, requiring fewer contractions to circulate the same volume of blood. Asymptomatic sinus bradycardia decreases in prevalence with age.

Sinus arrhythmia
Sinus arrhythmias are heart rhythm abnormalities characterized by variations in the cardiac cycle length over 120 milliseconds (longest cycle - shortest cycle). These are the most common type of arrhythmia in the general population and usually have no significant consequences. They typically occur in the young, athletes or after administration of medications such as morphine. The types of sinus arrhythmia are separated into the respiratory and non-respiratory categories.

Respiratory sinus arrhythmia
Respiratory sinus arrhythmia refers to the physiologically normal variation in heart rate due to breathing. During inspiration, vagus nerve activity decreases, reducing parasympathetic innervation of the sinoatrial node and causing an increase in heart rate. During expiration, heart rates fall due to the converse occurring.

Non-respiratory sinus arrhythmia
Non-respiratory causes of sinus arrhythmia include sinus pause, sinus arrest, and sinoatrial exit block. Sinus pause and arrest involve slowing or arresting of automatic impulse generation from the sinus node. This can lead to asystole or cardiac arrest if ventricular escape rhythms do not create backup sources of cardiac action potentials.

Sinoatrial exit block is a similar non-respiratory phenomenon of temporarily lost sinoatrial impulses. However, in contrast to a sinus pause, the action potential is still generated at the SA node but is either unable to leave or delayed from leaving the node, preventing or delaying atrial depolarization and subsequent ventricular systole. Therefore, the length of the pause in heartbeats is usually a multiple of the P-P interval, as seen on electrocardiography. Like a sinus pause, a sinoatrial exit block can be symptomatic, especially with prolonged pause length.

Sinus node dysfunction
A syndrome of intrinsic disease of the sinus node, referred to as sick sinus syndrome or sinus node dysfunction, covers conditions that include symptomatic sinus bradycardia or persistent chronotropic incompetence, sinoatrial block, sinus arrest, and tachycardia-bradycardia syndrome. These conditions can be caused by damage to the native sinus node itself and are frequently accompanied by damaged AV node conduction and reduced backup pacemaker activity. The condition can also be caused by dysfunction of the autonomic nervous system that regulates the node and is commonly exacerbated by medications.

Atrioventricular node
Bradycardia can also result from the inhibition of the flow of action potentials through the atrioventricular (AV) node. While this can be normal in young patients due to excessive vagus nerve tone, symptomatic bradycardia due to AV node dysfunction in older people is commonly due to structural heart disease, myocardial ischemia, or age-related fibrosis.

Atrioventricular block
Atrioventricular blocks are divided into three categories, ranked by severity. AV block is diagnosed via surface ECG, which is usually sufficient to locate the causal lesion of the block without the need for an invasive electrophysiology study.

In 1st degree AV block, electrical impulses originating in the SA node (or other ectopic focus above the ventricles) are conducted with significant delay through the AV node. This condition is diagnosed via ECG, with PR intervals in excess of 200 milliseconds. The PR interval represents the length of time between the start of atrial depolarization and the start of ventricular depolarization, representing the flow of electrical impulses between the SA and AV nodes. Despite the term "block," no impulses are fully lost in this conduction but are merely delayed. The location of the causal lesion can be anywhere between the AV node and the His-Purkinje system but is most commonly found in the AV node itself. Generally, isolated PR prolongation in 1st degree AV block is not associated with increased mortality or hospitalization.

2nd degree AV block is characterized by intermittently lost conduction of impulses between the SA node and the ventricles. 2nd degree block is classified into two types. Mobitz type 1 block, otherwise known by the eponym Wenckebach, classically demonstrates grouped patterns of heartbeats on ECG. Throughout the group, the PR interval gradually lengthens until a dropped conduction occurs, resulting in no QRS complex seen on surface ECG following the last P wave. After a delay, the grouping repeats, with the PR interval shortening again to baseline. Type 1 2nd degree AV block due to disease in the AV node (as opposed to in the His-purkinje system) rarely needs intervention with pacemaker implantation.

2nd degree, Mobitz type 2 AV block is another phenomenon of intermittently dropped QRS complexes after characteristic groupings of beats seen on surface ECG. The PR and RR intervals are consistent in this condition, followed by a sudden AV block and dropped QRS complex. Because type 2 blocks are typically due to lesions below the AV node, the ability for ventricular escape rhythms to maintain cardiac output is compromised. Permanent pacemaker implantation is often required.

Junctional rhythms
An AV-junctional rhythm, or atrioventricular nodal bradycardia, is usually caused by the absence of the electrical impulse from the sinus node. This usually appears on an electrocardiogram with a normal QRS complex accompanied by an inverted P wave either before, during, or after the QRS complex.

An AV-junctional escape beat is a delayed heartbeat originating from an ectopic focus somewhere in the AV junction. It occurs when the rate of depolarization of the SA node falls below the rate of the AV node. This dysrhythmia may also occur when the electrical impulses from the SA node fail to reach the AV node because of SA or AV block. This is a protective mechanism for the heart to compensate for an SA node that is no longer handling the pacemaking activity and is one of a series of backup sites that can take over pacemaker function when the SA node fails to do so. This would present with a longer PR interval. An AV-junctional escape complex is a normal response that may result from excessive vagal tone on the SA node. Pathological causes include sinus bradycardia, sinus arrest, sinus exit block, or AV block.

Ventricular
Idioventricular rhythm, also known as atrioventricular bradycardia or ventricular escape rhythm, is a heart rate of less than 50 BPM. This is a safety mechanism when a lack of electrical impulse or stimuli from the atrium occurs. Impulses originating within or below the bundle of His in the AV node will produce a wide QRS complex with heart rates between 20 and 40 BPM. Those above the bundle of His, also known as junctional, will typically range between 40 and 60 BPM with a narrow QRS complex. In a third-degree heart block, about 61% take place at the bundle branch-Purkinje system, 21% at the AV node, and 15% at the bundle of His. AV block may be ruled out with an ECG indicating "a 1:1 relationship between P waves and QRS complexes." Ventricular bradycardias occurs with sinus bradycardia, sinus arrest, and AV block. Treatment often consists of the administration of atropine and cardiac pacing.

Infantile
For infants, bradycardia is defined as a heart rate less than 100 BPM (normal is around 120–160 BPM). Premature babies are more likely than full-term babies to have apnea and bradycardia spells; their cause is not clearly understood. The spells may be related to centers inside the brain that regulate breathing which may not be fully developed. Touching the baby gently or rocking the incubator slightly will almost always get the baby to start breathing again, which increases the heart rate. The neonatal intensive-care unit standard practice is to electronically monitor the heart and lungs.

Causes
Bradycardia arrhythmia may have many causes, both cardiac and non-cardiac.

Non-cardiac causes are usually secondary and can involve recreational drug use or abuse, metabolic or endocrine issues, especially hypothyroidism, an electrolyte imbalance, neurological factors, autonomic reflexes, situational factors, such as prolonged bed rest, and autoimmunity. At rest, although tachycardia is more commonly seen in fatty acid oxidation disorders, acute bradycardia can occur more rarely.

Cardiac causes include acute or chronic ischemic heart disease, vascular heart disease, valvular heart disease, or degenerative primary electrical disease. Ultimately, the causes act by three mechanisms: depressed automaticity of the heart, conduction block, or escape pacemakers and rhythms.

In general, two types of problems result in bradycardias: disorders of the SA node and disorders of the AV node.

With SA node dysfunction (sometimes called sick sinus syndrome), there may be disordered automaticity or impaired conduction of the impulse from the SA node into the surrounding atrial tissue (an "exit block"). Second-degree sinoatrial blocks can be detected only by use of a 12-lead ECG. It is difficult and sometimes impossible to assign a mechanism to any particular bradycardia, but the underlying mechanism is not clinically relevant to treatment, which is the same in both cases of sick sinus syndrome: a permanent pacemaker.

AV conduction disturbances (AV block; primary AV block, secondary type I AV block, secondary type II AV block, tertiary AV block) may result from impaired conduction in the AV node or anywhere below it, such as in the bundle of His. The clinical relevance pertaining to AV blocks is greater than that of SA blocks.

Beta blocker medicines also can slow the heart rate and decrease how forcefully the heart contracts. Beta-blockers may slow the heart rate to a dangerous level if prescribed with calcium channel blocker-type medications. Bradycardia is also part of the mammalian diving reflex.

Diagnosis
A diagnosis of bradycardia in adults is based on a heart rate of less than 60 BPM, although some studies use a heart rate of less than 50 BPM. This is usually determined either by palpation or ECG. If symptoms occur, a determining electrolytes may help determine the underlying cause.

Management
The treatment of bradycardia depends on whether the person is stable or unstable.

Stable
Emergency treatment is not needed if the person is asymptomatic or minimally symptomatic.

Unstable
If a person is unstable, the initial recommended treatment is intravenous atropine. Doses less than 0.5 mg should not be used, which may further decrease the rate. If this is ineffective, intravenous inotrope infusion (dopamine, epinephrine) or transcutaneous pacing should be used. Transvenous pacing may be required if the cause of the bradycardia is not rapidly reversible.

In children, giving oxygen, supporting their breathing, and chest compressions are recommended.

Epidemiology
In clinical practice, elderly people over age 65 and young athletes of both sexes may have sinus bradycardia. The US Centers for Disease Control and Prevention reported in 2011 that 15.2% of adult males and 6.9% of adult females had clinically defined bradycardia (a resting pulse rate below 60 BPM).

Records

 * Daniel Green holds the world record for the slowest heartbeat in a healthy human, with a heart rate measured in 2014 of 26 BPM.
 * Martin Brady holds the Guinness world record for the slowest heart rate, with a certified rate over a minute duration of 27 BPM.
 * During his career, professional cyclist Miguel Indurain had a resting heart rate of 28 BPM.

title: Bradycardia


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Canada Day

Canada Day (Fête du Canada, ), formerly known as Dominion Day (Fête du Dominion), is the national day of Canada. A federal statutory holiday, it celebrates the anniversary of Canadian Confederation which occurred on July 1, 1867, with the passing of the British North America Act, 1867, when the three separate colonies of the United Canadas, Nova Scotia, and New Brunswick were united into a single dominion within the British Empire called Canada.

Originally called Dominion Day (Le Jour de la Confédération), the holiday was renamed in 1982, the same year that the Canadian constitution was patriated by the Canada Act, 1982, which severed the vestiges of legal dependence on the Parliament of the United Kingdom. Canada Day celebrations take place throughout the country, as well as in various locations around the world attended by Canadians living abroad.

Commemoration
Canada Day is often informally referred to as "Canada's birthday", particularly in the popular press. However, the term "birthday" can be seen as an oversimplification, as Canada Day is the anniversary of only one important national milestone on the way to the country's full sovereignty, namely the joining on July 1, 1867, of the colonies of Canada (divided into Ontario and Quebec), Nova Scotia, and New Brunswick into a wider British federation of four provinces. Canada became a "kingdom in its own right" within the British Empire, commonly known as the Dominion of Canada.

Although a British dominion, Canada gained an increased level of political control and governance over its own affairs, the British parliament and cabinet maintaining political control over certain areas, such as foreign affairs, national defence, and constitutional changes. Canada gradually gained increasing sovereignty over the years—notably with the passage of the Statute of Westminster in 1931—until finally becoming completely sovereign with the passing of the Constitution Act, 1982, which served to fully patriate the Canadian constitution.

Under the federal Holidays Act, Canada Day is observed on July 1, unless that date falls on a Sunday, in which case July 2 is the statutory holiday. Celebratory events will generally still take place on July 1, even though it is not the legal holiday. If it falls on a weekend, businesses normally closed that day will usually dedicate the following Monday as a day off.

History
The enactment of the British North America Act, 1867 (today called the Constitution Act, 1867), which confederated Canada, was celebrated on July 1, 1867, with the ringing of the bells at the Cathedral Church of St James in Toronto and "bonfires, fireworks, and illuminations, excursions, military displays, and musical and other entertainments", as described in contemporary accounts. On June 20 of the following year, Governor General the Viscount Monck issued a royal proclamation asking for Canadians to celebrate the anniversary of Confederation, However, the holiday was not established statutorily until May 15, 1879, when it was designated as Dominion Day, alluding to the reference in the British North America Act to the country as a dominion. The holiday was initially not dominant in the national calendar; any celebrations were mounted by local communities and the governor general hosted a party at Rideau Hall. No larger celebrations were held until 1917, and then none again for a further decade—the gold and diamond anniversaries of Confederation, respectively.

In 1946, Philéas Côté, a Quebec member of the House of Commons, introduced a private member's bill to rename Dominion Day as Canada Day. The bill was passed quickly by the lower chamber but was stalled by the Senate, which returned it to the commons with the recommendation that the holiday be renamed The National Holiday of Canada, an amendment that effectively killed the bill.

The Canadian government began in 1958 to orchestrate Dominion Day celebrations. That year, then-Prime Minister John Diefenbaker requested that Secretary of State Ellen Fairclough organize appropriate events, with a budget of $14,000. Parliament was traditionally in session on July 1, but Fairclough persuaded Diefenbaker and the rest of the federal cabinet to attend. Official celebrations thereafter consisted usually of trooping the colour ceremonies on Parliament Hill in the afternoon and evening, followed by a mass band concert and fireworks display. Fairclough, who became Minister of Citizenship and Immigration, later expanded the bills to include performing folk and ethnic groups. The day also became more casual and family oriented.

Canada's centennial in 1967 is often seen as an important milestone in the history of Canadian nationalism and in Canada's maturing as a distinct, independent country, after which Dominion Day became more popular with average Canadians. Into the late 1960s, nationally televised, multi-cultural concerts held in Ottawa were added and the fête became known as Festival Canada. After 1980, the Canadian government began to promote celebrating Dominion Day beyond the national capital, giving grants and aid to cities across the country to help fund local activities.

Some Canadians were, by the early 1980s, informally referring to the holiday as Canada Day, a practice that caused some controversy: Proponents argued that the name Dominion Day was a holdover from the colonial era—an argument given some impetus by the patriation of the Canadian constitution in 1982—and others asserted that an alternative was needed as the term does not translate well into French. Conversely, numerous politicians, journalists, and authors, such as Robertson Davies, decried the change at the time and some continue to maintain that it was illegitimate and an unnecessary break with tradition. Others claimed dominion was widely misunderstood and conservatively inclined commenters saw the change as part of a much larger attempt by Liberals to "re-brand" or re-define Canadian history. Columnist Andrew Cohen called Canada Day a term of "crushing banality" and criticized it as "a renunciation of the past [and] a misreading of history, laden with political correctness and historical ignorance".

The holiday was officially renamed as a result of a private member's bill that was passed through the House of Commons on July 9, 1982, two years after its first reading. Only 12 members of parliament were present when the bill was taken up again, 8 fewer than the necessary quorum; however, according to parliamentary rules, the quorum is enforceable only at the start of a sitting or when a member calls attention to it. The group passed the bill in five minutes, without debate, inspiring "grumblings about the underhandedness of the process". It met with stronger resistance in the Senate. Ernest Manning argued that the rationale for the change was based on a misperception of the name and George McIlraith did not agree with the manner in which the bill was passed, urging the government to proceed in a more "dignified way". However, the Senate did eventually pass the bill, regardless. With the granting of royal assent, the holiday's name was officially changed to Canada Day on October 27, 1982, and first celebrated under that name July 1, 1983.

As the anniversary of Confederation, Dominion Day, and later Canada Day, was the date set for a number of important events, such as the first national radio network hookup by the Canadian National Railway (1927); the inauguration of the Canadian Broadcasting Corporation's cross-country television broadcast, with Governor General Vincent Massey's Dominion Day speech from Parliament Hill (1958); the flooding of the Saint Lawrence Seaway (1958); the first colour television transmission in Canada (1966); the inauguration of the Order of Canada (1967); and the establishment of "O Canada" as the country's national anthem (1980). During the Canada's sesquicentennial in 2017, the Bank of Canada released a commemorative $10 banknote, which was expected to be broadly available by Canada Day.

The COVID-19 pandemic led to the cancellation in 2020 of all in-person Canada Day festivities nationwide, due to social distancing and restrictions on public gatherings. Some were converted to virtual events. The same cancellations occurred the following year; though, some also for political reasons. In-person festivities in Ottawa returned in 2022, being re-located from Parliament Hill to LeBreton Flats due to construction associated with the Parliament Hill Rehabilitation project.

Other events fell on the same day coincidentally, such as the first day of the Battle of the Somme in 1916—shortly after which Newfoundland recognized July 1 as Memorial Day to commemorate the Newfoundland Regiment's heavy losses during the battle —and the enactment of the Chinese Immigration Act in 1923, leading Chinese-Canadians to refer to July 1 as Humiliation Day  and boycott Dominion Day celebrations with shop closures, flying the Canadian flag on half-mast, or hanging wreaths in front of home and shop entrances until the act was repealed in 1947. Canada Day also coincides with Quebec's Moving Day, when many fixed-lease apartment rental terms expire. The bill changing the province's moving day from May 1 to July 1 was introduced by a federalist member of the Quebec National Assembly, Jérôme Choquette, in 1973, in order not to affect children still in school in the month of May.

Activities

Most communities across the country host organized celebrations for Canada Day, typically outdoor public events, such as parades, carnivals, festivals, barbecues, air and maritime shows, fireworks, and free musical concerts, as well as citizenship ceremonies. There is no standard mode of celebration for Canada Day; Jennifer Welsh, a professor of International Relations at the University of Oxford, said about this: "Canada Day, like the country, is endlessly decentralized. There doesn't seem to be a central recipe for how to celebrate it—chalk it up to the nature of the federation."

In the national capital of Ottawa, concerts and cultural displays are held on the front lawn of Parliament Hill, as organized by Canadian Heritage, which include the main "noon show" and an evening programme. The event traditionally begins with the singing of "God Save the King" and "O Canada" in English and French followed by a flyover by the Snowbirds. Typically the governor general and prime minister officiate, though the monarch or another member of the royal family may also attend or take the governor general's place. Smaller events are mounted in other parks around the city and in neighbouring Gatineau, Quebec. In provincial capitals, official celebrations are often held at the provincial legislative building, usually in the presence of the lieutenant-governor and/or premier of the province.

International celebrations

Canadian expatriates will often organize Canada Day activities in their local area on or near the date of the holiday. Examples include Canada D'eh, an annual celebration that takes place on June 30 at Lan Kwai Fong, in Hong Kong; Canadian Forces' events on bases in Afghanistan; at Trafalgar Square outside Canada House in London, England; in Mexico, at the Royal Canadian Legion in Chapala, and at the Canadian Club in Ajijic. In China, Canada Day celebrations are held at the Bund Beach by the Canadian Chamber of Commerce in Shanghai and at Canadian International School in Beijing, sponsored by the Canada China Business Council.

Criticism and protest
Given the federal nature of the anniversary, celebrating Canada Day can be a cause of friction in the province of Quebec, where the holiday is overshadowed by the province's Saint-Jean-Baptiste Day (Fête nationale), on June 24. For example, the federal government funds Canada Day events at the Old Port of Montreal—an area run by a federal Crown corporation—while the Fête nationale parade is a grassroots effort that has faced difficulties in operating due to limited funding from the federal government and a lack of corporate sponsors. Canada Day has attracted a negative stigma among some indigenous peoples in Canada and their sympathizers, who feel that it is a celebration of the colonization of indigenous land by the British. Criticism of Canada Day celebrations were particularly prominent during Canada's sesquicentennial in 2017, with allegations that the commemorations downplayed the role of indigenous peoples in the country's history and the hardships they face in the present day.

The same grievances were aired four years later, after possible unmarked graves of indigenous children were found in late-June 2021, at the site of an Indian residential school in British Columbia. If not already cancelled or modified due to restrictions related to the COVID-19 pandemic, Canada Day festivities were cancelled in various communities in British Columbia, New Brunswick, and Northern Saskatchewan, while indigenous protest group Idle No More announced its intent to organize peaceful rallies in multiple major cities. Some politicians supported the cancellations, while others expressed concern that activists were attacking "the very idea of Canada itself" and hampering progress toward reconciliation.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Canada Day


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Claudine (book series)

The Claudine series consists of four early novels by French authors Colette and Henry Gauthier-Villars, published 1900–1904. Written in diary form, they describe the growth to maturity of a young girl, Claudine. Aged fifteen at the beginning of the first book, Claudine à l'école, the series describes her education and experiences as she grows up. All the books are written in first-person with the first three having Claudine herself as the narrator. The last in the series, Claudine s'en va, introduces a new narrator, Annie.

The novels were written in the late 19th century in collaboration with Colette's first husband, the writer Henry Gauthier-Villars, better known by his pen name "Willy". There has been much speculation over the degree of involvement of both Colette and Willy in the writing of the Claudine novels, particularly as Willy was known for often using ghostwriters. Consequently, although the novels were originally attributed to Willy only and published under his name alone, they were later published under both names. After the death of Willy, Colette went to court to challenge her former husband's involvement in any of the writing, and subsequently had his name removed from the books. This decision however was overturned after her death, as Willy's son from a prior relationship, Jacques Gauthier-Villars, successfully sued to have his father's name restored.

The Claudine novels are thought to be roughly autobiographical.

List of books

 * Claudine à l'école (1900) – Claudine at School
 * Claudine à Paris (1901) – Claudine in Paris
 * Claudine en ménage (1902) – Claudine Married
 * Claudine s'en va (1903) – Claudine and Annie

title: Claudine (book series)


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Coronary artery disease

Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the cardiac muscle due to build-up of atherosclerotic plaque in the arteries of the heart. It is the most common of the cardiovascular diseases. Types include stable angina, unstable angina, and myocardial infarction.

A common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Occasionally it may feel like heartburn. Usually symptoms occur with exercise or emotional stress, last less than a few minutes, and improve with rest. Shortness of breath may also occur and sometimes no symptoms are present. In many cases, the first sign is a heart attack. Other complications include heart failure or an abnormal heartbeat.

Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet, depression, and excessive alcohol consumption. A number of tests may help with diagnoses including: electrocardiogram, cardiac stress testing, coronary computed tomographic angiography, biomarkers (high-sensitivity cardiac troponins) and coronary angiogram, among others. Ways to reduce CAD risk include eating a healthy diet, regularly exercising, maintaining a healthy weight, and not smoking. Medications for diabetes, high cholesterol, or high blood pressure are sometimes used. There is limited evidence for screening people who are at low risk and do not have symptoms. Treatment involves the same measures as prevention. Additional medications such as antiplatelets (including aspirin), beta blockers, or nitroglycerin may be recommended. Procedures such as percutaneous coronary intervention (PCI) or coronary artery bypass surgery (CABG) may be used in severe disease. In those with stable CAD it is unclear if PCI or CABG in addition to the other treatments improves life expectancy or decreases heart attack risk.

In 2015, CAD affected 110 million people and resulted in 8.9 million deaths. It makes up 15.6% of all deaths, making it the most common cause of death globally. The risk of death from CAD for a given age decreased between 1980 and 2010, especially in developed countries. The number of cases of CAD for a given age also decreased between 1990 and 2010. In the United States in 2010, about 20% of those over 65 had CAD, while it was present in 7% of those 45 to 64, and 1.3% of those 18 to 45; rates were higher among males than females of a given age.

Signs and symptoms
The most common symptom is chest pain or discomfort that occurs regularly with activity, after eating, or at other predictable times; this phenomenon is termed stable angina and is associated with narrowing of the arteries of the heart. Angina also includes chest tightness, heaviness, pressure, numbness, fullness, or squeezing. Angina that changes in intensity, character or frequency is termed unstable. Unstable angina may precede myocardial infarction. In adults who go to the emergency department with an unclear cause of pain, about 30% have pain due to coronary artery disease. Angina, shortness of breath, sweating, nausea or vomiting, and lightheadedness are signs of a heart attack, or myocardial infarction, and immediate emergency medical services are crucial.

With advanced disease, the narrowing of coronary arteries reduces the supply of oxygen-rich blood flowing to the heart, which becomes more pronounced during strenuous activities during which the heart beats faster and has an increased oyxgen demand. For some, this causes severe symptoms, while others experience no symptoms at all.

Symptoms in females
Symptoms in females can differ from those in males, and the most common symptom reported by females of all races is shortness of breath. Other symptoms more commonly reported by females than males are extreme fatigue, sleep disturbances, indigestion, and anxiety. However, some females do experience irregular heartbeat, dizziness, sweating, and nausea. Burning, pain, or pressure in the chest or upper abdomen that can travel to the arm or jaw can also be experienced in females, but it is less commonly reported by females than males. On average, females experience symptoms 10 years later than males. Females are less likely to recognize symptoms and seek treatment.

Risk factors
Coronary artery disease is characterized by heart problems that result from atherosclerosis. Atherosclerosis is a type of arteriosclerosis which is the "chronic inflammation of the arteries which causes them to harden and accumulate cholesterol plaques (atheromatous plaques) on the artery walls". CAD has a number of well determined risk factors that contribute to atherosclerosis. These risk factors for CAD include "smoking, diabetes, high blood pressure (hypertension), abnormal (high) amounts of cholesterol and other fat in the blood (dyslipidemia), type 2 diabetes and being overweight or obese (having excess body fat)" due to lack of exercise and a poor diet. Some other risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet, depression, family history, psychological stress and excessive alcohol. About half of cases are linked to genetics. Smoking and obesity are associated with about 36% and 20% of cases, respectively. Smoking just one cigarette per day about doubles the risk of CAD. Lack of exercise has been linked to 7–12% of cases. Exposure to the herbicide Agent Orange may increase risk. Rheumatologic diseases such as rheumatoid arthritis, systemic lupus erythematosus, psoriasis, and psoriatic arthritis are independent risk factors as well.

Job stress appears to play a minor role accounting for about 3% of cases. In one study, females who were free of stress from work life saw an increase in the diameter of their blood vessels, leading to decreased progression of atherosclerosis. In contrast, females who had high levels of work-related stress experienced a decrease in the diameter of their blood vessels and significantly increased disease progression. Having a type A behavior pattern, a group of personality characteristics including time urgency, competitiveness, hostility, and impatience, is linked to an increased risk of coronary disease.

Blood fats
The consumption of different types of fats including trans unsaturated, saturated and trans in a diet "influences the level of cholesterol that is present in the bloodstream". Unsaturated fats originate from plant sources (such as oils). There are two types of unsaturated fats, cis and trans isomers. Cis unsaturated fats are bent in molecular structure and trans are linear in structure. Saturated fats originate from animal sources (such as animal fats) and are also molecularly linear in structure. The linear configurations of unsaturated trans and saturated fats allow them to easily accumulate and stack at the arterial walls when consumed in high amounts (and other positive measures towards physical health are not met).

 * Fats and cholesterol are insoluble in blood and thus are amalgamated with proteins to form lipoproteins for transport. Low density lipoproteins (LDL) transport cholesterol from the liver to the rest of the body and therefore raise blood cholesterol levels. The consumption of "saturated fats increases LDL levels within the body, thus raising blood cholesterol levels".
 * High density lipoproteins (HDL) are considered 'good' lipoproteins as they search for excess cholesterol in the body and transport it back to the liver for disposal. Trans fats also "increase LDL levels whilst decreasing HDL levels within the body, significantly raising blood cholesterol levels".

High levels of cholesterol in the bloodstream lead to atherosclerosis. With increased levels of LDL in the bloodstream, "LDL particles will form deposits and accumulate within the arterial walls, which will lead to the development of plaques, restricting blood flow". The resultant reduction in the heart's blood supply due to atherosclerosis in coronary arteries "causes shortness of breath, angina pectoris (chest pains that are usually relieved by rest), and potentially fatal heart attacks (myocardial infarctions)".

Genetics
The heritability of coronary artery disease has been estimated between 40% and 60%. Genome-wide association studies have identified over 160 genetic susceptibility loci for coronary artery disease.

Transcriptome
Transcripts associated with CAD (TRACs) - FoxP1, ICOSLG, IKZF4/Eos, SMYD3, TRIM28, and TCF3/E2A that are likely markers of regulatory T cells (Treg), consistent with known reductions in Tregs in CAD.

The RNA changes are mostly related to ciliary and endocytic transcripts, which in the circulating immune system would be related to the immune synapse. The immune synapse is the contact-dependent mode of communication between T cells and B cells, on one side, and a variety of antigen-presenting and immunomodulating cells on the other side. One of the most differentially expressed genes, fibromodulin (FMOD, increased 2.8-fold in CAD). Several other regulated transcripts encode for proteins related to the structure and function of the immune synapse. Nebulette, the most down-regulated transcript (2.4-fold), is an important 'cytolinker' that connects actin and desmin to facilitate cytoskeletal function and vesicular movement. The endocytic pathway is further modulated by changes in tubulin, which is a key microtubule protein, and fidgetin, which is a tubulin-severing enzyme that is a GWAS marker for cardiovascular risk. Protein recycling would be modulated by changes in the proteasomal regulator SIAH3, and the ubiquitin ligase MARCHF10. On the ciliary aspect of the immune synapse, several of the modulated transcripts are related to ciliary length and function. Steriocilin (STRC) has been studied principally in outer sensory hair cells, and mutations lead to deafness. Steriocilin is a partner to mesothelin (MSN), a related super-helical protein, whose transcript is also modulated in CAD. Likewise, DCDC2, a double-cortin protein, is a known modulator of ciliary length. In the signaling pathways of the immune synapse, there were numerous transcripts that related directly to T cell function and the control of differentiation. Butyrophilin (BTN1A1) is a known co-regulator for T cell activation. Fibromodulin is a well-known modulator of the TGF-beta signaling pathway, which is a primary determinant of Tre differentiation. Further impact on the TGF-beta pathway is reflected in concurrent changes in the BMP receptor 1B RNA (BMPR1B), because the bone morphogenic proteins are members of the TGF-beta superfamily, and likewise impact Treg differentiation. As noted, several of the transcripts (TMEM98, NRCAM, SFRP5, SHISA2) are known elements of the Wnt signaling pathway, which is major determinant of Treg differentiation.

Other

 * Endometriosis in females under the age of 40.
 * Depression and hostility appear to be risks.
 * The number of categories of adverse childhood experiences (psychological, physical, or sexual abuse; violence against mother; or living with household members who used substances, mentally ill, suicidal, or incarcerated) showed a graded correlation with the presence of adult diseases including coronary artery (ischemic heart) disease.
 * Hemostatic factors: High levels of fibrinogen and coagulation factor VII are associated with an increased risk of CAD.
 * Low hemoglobin.
 * In the Asian population, the b fibrinogen gene G-455A polymorphism was associated with the risk of CAD.
 * Patient-specific vessel ageing or remodelling determines endothelial cell behaviour and thus disease growth and progression. Such 'hemodynamic markers' are thus patient-specific risk surrogates.

Pathophysiology
Limitation of blood flow to the heart causes ischemia (cell starvation secondary to a lack of oxygen) of the heart's muscle cells. The heart's muscle cells may die from lack of oxygen and this is called a myocardial infarction (commonly referred to as a heart attack). It leads to damage, death, and eventual scarring of the heart muscle without regrowth of heart muscle cells. Chronic high-grade narrowing of the coronary arteries can induce transient ischemia which leads to the induction of a ventricular arrhythmia, which may terminate into a dangerous heart rhythm known as ventricular fibrillation, which often leads to death.

Typically, coronary artery disease occurs when part of the smooth, elastic lining inside a coronary artery (the arteries that supply blood to the heart muscle) develops atherosclerosis. With atherosclerosis, the artery's lining becomes hardened, stiffened, and accumulates deposits of calcium, fatty lipids, and abnormal inflammatory cells – to form a plaque. Calcium phosphate (hydroxyapatite) deposits in the muscular layer of the blood vessels appear to play a significant role in stiffening the arteries and inducing the early phase of coronary arteriosclerosis. This can be seen in a so-called metastatic mechanism of calciphylaxis as it occurs in chronic kidney disease and hemodialysis. Although these people have kidney dysfunction, almost fifty percent of them die due to coronary artery disease. Plaques can be thought of as large "pimples" that protrude into the channel of an artery, causing partial obstruction to blood flow. People with coronary artery disease might have just one or two plaques, or might have dozens distributed throughout their coronary arteries. A more severe form is chronic total occlusion (CTO) when a coronary artery is completely obstructed for more than 3 months.

Microvascular angina is a type of angina pectoris in which chest pain and chest discomfort occur without signs of blockages in the larger coronary arteries of their hearts when an angiogram (coronary angiogram) is being performed. The exact cause of microvascular angina is unknown. Explanations include microvascular dysfunction or epicardial atherosclerosis. For reasons that are not well understood, females are more likely than males to have it; however, hormones and other risk factors unique to females may play a role.

Diagnosis
The diagnosis of CAD depends largely on the nature of the symptoms. The first investigation when CAD is suspected is an electrocardiogram (ECG/EKG), both for stable angina and acute coronary syndrome. An X-ray of the chest, blood tests and resting echocardiography may be performed.

For stable patient but who are symptomatic there are several non-invasive tests to diagnose CAD depending on pre assessment of the risk profile. Non invasive imaging include; Computed tomography angiography (CTA) (anatomical imaging, best test in patients with low risk profile-to "rule out" the disease), positron emission tomography (PET), single-photon emission computed tomography (SPECT)/nuclear stress test/myocardial scintigraphy and stress echocardiography (the three latter can be summarized as functional non invasive methods and are typically better to "rule in"). Exercise ECG or stress test is inferior to non-invasive imaging methods due to risk of both false negative and false positive test results. The use of non-invasive imaging is not recommended on individuals who are exhibiting no symptoms and are otherwise at low risk for developing coronary disease., citing

 * Invasive testing with coronary angiography (ICA) can be used when non-invasive testing is inconclusive or show a high event risk.
 * Invasive testing with coronary angiography (ICA) can be used when non-invasive testing is inconclusive or show a high event risk.
 * Invasive testing with coronary angiography (ICA) can be used when non-invasive testing is inconclusive or show a high event risk.

The diagnosis of microvascular angina (previously known as cardiac syndrome X – the rare coronary artery disease that is more common in females, as mentioned, is a diagnosis of exclusion. Therefore, usually, the same tests are used as in any person with the suspected of having coronary artery disease:
 * Intravascular ultrasound
 * Magnetic resonance imaging (MRI)

Stable angina
Stable angina is the most common form of ischemic heart disease, and is associated with reduced quality of life and increased mortality. It is caused by epicardial coronary stenosis which results in reduced blood flow and oxygen supply to the myocardium. Stable angina is characterized as short-term chest pain during physical exertion caused by an imbalance between myocardial oxygen supply and metabolic oxygen demand. Various forms of cardiac stress tests may be used to induce both symptoms and detect changes by way of electrocardiography (using an ECG), echocardiography (using ultrasound of the heart) or scintigraphy (using uptake of radionuclide by the heart muscle). If part of the heart seems to receive an insufficient blood supply, coronary angiography may be used to identify stenosis of the coronary arteries and suitability for angioplasty or bypass surgery.

In minor to moderate cases, nitroglycerine may be used to alleviate acute symptoms of stable angina or may be used immediately prior to exertion to prevent the onset of angina. Sublingual nitroglycerine is most commonly used to provide rapid relief for acute angina attacks and as a complement to anti-anginal treatments in patients with refractory and recurrent angina. When nitroglycerine enters the bloodstream, it forms free radical nitric oxide, or NO, which activates guanylate cyclase and in turn stimulates the release of cyclic GMP. This molecular signaling stimulates smooth muscle relaxation, ultimately resulting in vasodilation and consequently improved blood flow to regions of the heart affected by atherosclerotic plaque.

Stable coronary artery disease (SCAD) is also often called stable ischemic heart disease (SIHD). A 2015 monograph explains that "Regardless of the nomenclature, stable angina is the chief manifestation of SIHD or SCAD." There are U.S. and European clinical practice guidelines for SIHD/SCAD. In patients with non-severe asymptomatic aortic valve stenosis and no overt coronary artery disease, the increased troponin T (above 14 pg/mL) was found associated with an increased 5-year event rate of ischemic cardiac events (myocardial infarction, percutaneous coronary intervention, or coronary artery bypass surgery).

Acute coronary syndrome
Diagnosis of acute coronary syndrome generally takes place in the emergency department, where ECGs may be performed sequentially to identify "evolving changes" (indicating ongoing damage to the heart muscle). Diagnosis is clear-cut if ECGs show elevation of the "ST segment", which in the context of severe typical chest pain is strongly indicative of an acute myocardial infarction (MI); this is termed a STEMI (ST-elevation MI) and is treated as an emergency with either urgent coronary angiography and percutaneous coronary intervention (angioplasty with or without stent insertion) or with thrombolysis ("clot buster" medication), whichever is available. In the absence of ST-segment elevation, heart damage is detected by cardiac markers (blood tests that identify heart muscle damage). If there is evidence of damage (infarction), the chest pain is attributed to a "non-ST elevation MI" (NSTEMI). If there is no evidence of damage, the term "unstable angina" is used. This process usually necessitates hospital admission and close observation on a coronary care unit for possible complications (such as cardiac arrhythmias – irregularities in the heart rate). Depending on the risk assessment, stress testing or angiography may be used to identify and treat coronary artery disease in patients who have had an NSTEMI or unstable angina.

Risk assessment
There are various risk assessment systems for determining the risk of coronary artery disease, with various emphasis on different variables above. A notable example is Framingham Score, used in the Framingham Heart Study. It is mainly based on age, gender, diabetes, total cholesterol, HDL cholesterol, tobacco smoking, and systolic blood pressure. When it comes to predicting risk in younger adults (18–39 years old), Framingham Risk Score remains below 10–12% for all deciles of baseline-predicted risk.

Polygenic score is another way of risk assessment. In one study the relative risk of incident coronary events was 91% higher among participants at high genetic risk than among those at low genetic risk.

Prevention
Up to 90% of cardiovascular disease may be preventable if established risk factors are avoided. Prevention involves adequate physical exercise, decreasing obesity, treating high blood pressure, eating a healthy diet, decreasing cholesterol levels, and stopping smoking. Medications and exercise are roughly equally effective. High levels of physical activity reduce the risk of coronary artery disease by about 25%. Life's Essential 8 are the key measures for improving and maintaining cardiovascular health, as defined by the American Heart Association. AHA added sleep as a factor influencing heart health in 2022.

Most guidelines recommend combining these preventive strategies. A 2015 Cochrane Review found some evidence that counseling and education to bring about behavioral change might help in high-risk groups. However, there was insufficient evidence to show an effect on mortality or actual cardiovascular events.

In diabetes mellitus, there is little evidence that very tight blood sugar control improves cardiac risk although improved sugar control appears to decrease other problems such as kidney failure and blindness.

Diet
A diet high in fruits and vegetables decreases the risk of cardiovascular disease and death. Vegetarians have a lower risk of heart disease, possibly due to their greater consumption of fruits and vegetables. Evidence also suggests that the Mediterranean diet and a high fiber diet lower the risk.

The consumption of trans fat (commonly found in hydrogenated products such as margarine) has been shown to cause a precursor to atherosclerosis and increase the risk of coronary artery disease.

Evidence does not support a beneficial role for omega-3 fatty acid supplementation in preventing cardiovascular disease (including myocardial infarction and sudden cardiac death). There is tentative evidence that intake of menaquinone (Vitamin K2), but not phylloquinone (Vitamin K1), may reduce the risk of CAD mortality.

Secondary prevention
Secondary prevention is preventing further sequelae of already established disease. Effective lifestyle changes include:
 * Weight control
 * Smoking cessation
 * Avoiding the consumption of trans fats (in partially hydrogenated oils)
 * Decreasing psychosocial stress
 * Exercise

Aerobic exercise, like walking, jogging, or swimming, can reduce the risk of mortality from coronary artery disease. Aerobic exercise can help decrease blood pressure and the amount of blood cholesterol (LDL) over time. It also increases HDL cholesterol.

Although exercise is beneficial, it is unclear whether doctors should spend time counseling patients to exercise. The U.S. Preventive Services Task Force found "insufficient evidence" to recommend that doctors counsel patients on exercise but "it did not review the evidence for the effectiveness of physical activity to reduce chronic disease, morbidity, and mortality", only the effectiveness of counseling itself. The American Heart Association, based on a non-systematic review, recommends that doctors counsel patients on exercise.

Psychological symptoms are common in people with CHD, and while many psychological treatments may be offered following cardiac events, there is no evidence that they change mortality, the risk of revascularization procedures, or the rate of non-fatal myocardial infarction.

Antibiotics for secondary prevention of coronary heart disease

Antibiotics may help patients with coronary disease to reduce the risk of heart attacks and strokes. However, the latest evidence suggests that antibiotics for secondary prevention of coronary heart disease are harmful with increased mortality and occurrence of stroke. So, the use of antibiotics is not currently supported for preventing secondary coronary heart disease.

Neuropsychological Assessment
A thorough systematic review found that indeed there is a link between a CHD condition and brain dysfunction in females. Consequently, since research is showing that cardiovascular diseases, like CHD, can play a role as a precursor for dementia, like Alzheimer's disease, individuals with CHD should have a neuropsychological assessment.

Treatment
There are a number of treatment options for coronary artery disease:
 * Lifestyle changes
 * Medical treatment – commonly prescribed drugs (e.g., cholesterol lowering medications, beta-blockers, nitroglycerin, calcium channel blockers, etc.);
 * Coronary interventions as angioplasty and coronary stent;
 * Coronary artery bypass grafting (CABG)

Medications

 * Statins, which reduce cholesterol, reduce the risk of coronary artery disease
 * Nitroglycerin
 * Calcium channel blockers and/or beta-blockers
 * Antiplatelet drugs such as aspirin

It is recommended that blood pressure typically be reduced to less than 140/90 mmHg. The diastolic blood pressure however should not be lower than 60 mmHg. Beta blockers are recommended first line for this use.

Aspirin
In those with no previous history of heart disease, aspirin decreases the risk of a myocardial infarction but does not change the overall risk of death. Aspirin therapy to prevent heart disease is thus recommended only in adults who are at increased risk for cardiovascular events, which may include postmenopausal females, males above 40, and younger people with risk factors for coronary heart disease, including high blood pressure, a family history of heart disease, or diabetes. The benefits outweigh the harms most favorably in people at high risk for a cardiovascular event, where high risk is defined as at least a 3% chance over a five-year period, but others with lower risk may still find the potential benefits worth the associated risks.

Anti-platelet therapy
Clopidogrel plus aspirin (dual anti-platelet therapy) reduces cardiovascular events more than aspirin alone in those with a STEMI. In others at high risk but not having an acute event, the evidence is weak. Specifically, its use does not change the risk of death in this group. In those who have had a stent, more than 12 months of clopidogrel plus aspirin does not affect the risk of death.

Surgery
Revascularization for acute coronary syndrome has a mortality benefit. Percutaneous revascularization for stable ischaemic heart disease does not appear to have benefits over medical therapy alone. In those with disease in more than one artery, coronary artery bypass grafts appear better than percutaneous coronary interventions. Newer "anaortic" or no-touch off-pump coronary artery revascularization techniques have shown reduced postoperative stroke rates comparable to percutaneous coronary intervention. Hybrid coronary revascularization has also been shown to be a safe and feasible procedure that may offer some advantages over conventional CABG though it is more expensive.

Epidemiology
As of 2010, CAD was the leading cause of death globally resulting in over 7 million deaths. This increased from 5.2 million deaths from CAD worldwide in 1990. It may affect individuals at any age but becomes dramatically more common at progressively older ages, with approximately a tripling with each decade of life. Males are affected more often than females.

It is estimated that 60% of the world's cardiovascular disease burden will occur in the South Asian subcontinent despite only accounting for 20% of the world's population. This may be secondary to a combination of genetic predisposition and environmental factors. Organizations such as the Indian Heart Association are working with the World Heart Federation to raise awareness about this issue.

Coronary artery disease is the leading cause of death for both males and females and accounts for approximately 600,000 deaths in the United States every year. According to present trends in the United States, half of healthy 40-year-old males will develop CAD in the future, and one in three healthy 40-year-old females. It is the most common reason for death of males and females over 20 years of age in the United States.

After analysing data from 2 111 882 patients, the recent meta-analysis revealed that the incidence of coronary artery diseases in breast cancer survicors was 4.29 (95% CI 3.09–5.94) per 1000 person-years.

Names
Other terms sometimes used for this condition are "hardening of the arteries" and "narrowing of the arteries". In Latin it is known as morbus ischaemicus cordis (MIC).

Support groups
The Infarct Combat Project (ICP) is an international nonprofit organization founded in 1998 which tries to decrease ischemic heart diseases through education and research.

Industry influence on research
In 2016 research into the archives of the Sugar Association, the trade association for the sugar industry in the US, had sponsored an influential literature review published in 1965 in the New England Journal of Medicine that downplayed early findings about the role of a diet heavy in sugar in the development of CAD and emphasized the role of fat; that review influenced decades of research funding and guidance on healthy eating.

Research
Research efforts are focused on new angiogenic treatment modalities and various (adult) stem-cell therapies. A region on chromosome 17 was confined to families with multiple cases of myocardial infarction. Other genome-wide studies have identified a firm risk variant on chromosome 9 (9p21.3). However, these and other loci are found in intergenic segments and need further research in understanding how the phenotype is affected.

A more controversial link is that between Chlamydophila pneumoniae infection and atherosclerosis. While this intracellular organism has been demonstrated in atherosclerotic plaques, evidence is inconclusive as to whether it can be considered a causative factor. Treatment with antibiotics in patients with proven atherosclerosis has not demonstrated a decreased risk of heart attacks or other coronary vascular diseases.

Myeloperoxidase has been proposed as a biomarker.

Plant-based nutrition has been suggested as a way to reverse coronary artery disease, but strong evidence is still lacking for claims of potential benefits.

Several immunosuppressive drugs targeting the chronic inflammation in coronary artery disease have been tested.

title: Coronary artery disease


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Caesium

Caesium (IUPAC spelling; cesium in American English) is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 C, which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoric and reacts with water even at −116 C. It is the least electronegative element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite. Caesium-137, a fission product, is extracted from waste produced by nuclear reactors. It has the largest atomic radius of all elements whose radii have been measured or calculated, at about 260 picometers.

The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in photoelectric cells. Caesium is widely used in highly accurate atomic clocks. In 1967, the International System of Units began using a specific hyperfine transition of neutral caesium-133 atoms to define the basic unit of time, the second.

Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids, but it has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Nonradioactive caesium compounds are only mildly toxic, but the pure metal's tendency to react explosively with water means that caesium is considered a hazardous material, and the radioisotopes present a significant health and environmental hazard.

Physical properties
Of all elements that are solid at room temperature, caesium is the softest: it has a hardness of 0.2 Mohs. It is a very ductile, pale metal, which darkens in the presence of trace amounts of oxygen. When in the presence of mineral oil (where it is best kept during transport), it loses its metallic lustre and takes on a duller, grey appearance. It has a melting point of 28.5 C, making it one of the few elemental metals that are liquid near room temperature. Mercury is the only stable elemental metal with a known melting point lower than caesium. In addition, the metal has a rather low boiling point, 641 C, the lowest of all metals other than mercury. Its compounds burn with a blue or violet colour.

Caesium forms alloys with the other alkali metals, gold, and mercury (amalgams). At temperatures below 650 °C, it does not alloy with cobalt, iron, molybdenum, nickel, platinum, tantalum, or tungsten. It forms well-defined intermetallic compounds with antimony, gallium, indium, and thorium, which are photosensitive. It mixes with all the other alkali metals (except lithium); the alloy with a molar distribution of 41% caesium, 47% potassium, and 12% sodium has the lowest melting point of any known metal alloy, at −78 C. A few amalgams have been studied: is black with a purple metallic lustre, while CsHg is golden-coloured, also with a metallic lustre.

The golden colour of caesium comes from the decreasing frequency of light required to excite electrons of the alkali metals as the group is descended. For lithium through rubidium this frequency is in the ultraviolet, but for caesium it enters the blue–violet end of the spectrum; in other words, the plasmonic frequency of the alkali metals becomes lower from lithium to caesium. Thus caesium transmits and partially absorbs violet light preferentially while other colours (having lower frequency) are reflected; hence it appears yellowish.

Allotropes
Caesium exists in the form of different allotropes, one of them a dimer called dicaesium.

Chemical properties
Caesium metal is highly reactive and pyrophoric. It ignites spontaneously in air, and reacts explosively with water even at low temperatures, more so than the other alkali metals. It reacts with ice at temperatures as low as −116 C. Because of this high reactivity, caesium metal is classified as a hazardous material. It is stored and shipped in dry, saturated hydrocarbons such as mineral oil. It can be handled only under inert gas, such as argon. However, a caesium-water explosion is often less powerful than a sodium-water explosion with a similar amount of sodium. This is because caesium explodes instantly upon contact with water, leaving little time for hydrogen to accumulate. Caesium can be stored in vacuum-sealed borosilicate glass ampoules. In quantities of more than about 100 g, caesium is shipped in hermetically sealed, stainless steel containers.

The chemistry of caesium is similar to that of other alkali metals, in particular rubidium, the element above caesium in the periodic table. As expected for an alkali metal, the only common oxidation state is +1. Some slight differences arise from the fact that it has a higher atomic mass and is more electropositive than other (nonradioactive) alkali metals. Caesium is the most electropositive chemical element. The caesium ion is also larger and less "hard" than those of the lighter alkali metals.

Compounds

Most caesium compounds contain the element as the cation, which binds ionically to a wide variety of anions. One noteworthy exception is the caeside anion, and others are the several suboxides (see section on oxides below). More recently, caesium is predicted to behave as a p-block element and capable of forming higher fluorides with higher oxidation states (i.e., CsFn with n > 1) under high pressure. This prediction needs to be validated by further experiments.

Salts of Cs+ are usually colourless unless the anion itself is coloured. Many of the simple salts are hygroscopic, but less so than the corresponding salts of lighter alkali metals. The phosphate, acetate, carbonate, halides, oxide, nitrate, and sulfate salts are water-soluble. Its double salts are often less soluble, and the low solubility of caesium aluminium sulfate is exploited in refining Cs from ores. The double salts with antimony (such as ), bismuth, cadmium, copper, iron, and lead are also poorly soluble.

Caesium hydroxide (CsOH) is hygroscopic and strongly basic. It rapidly etches the surface of semiconductors such as silicon. CsOH has been previously regarded by chemists as the "strongest base", reflecting the relatively weak attraction between the large Cs+ ion and OH−; it is indeed the strongest Arrhenius base; however, a number of compounds such as n-butyllithium, sodium amide, sodium hydride, caesium hydride, etc., which cannot be dissolved in water as reacting violently with it but rather only used in some anhydrous polar aprotic solvents, are far more basic on the basis of the Brønsted–Lowry acid–base theory.

A stoichiometric mixture of caesium and gold will react to form yellow caesium auride (Cs+Au−) upon heating. The auride anion here behaves as a pseudohalogen. The compound reacts violently with water, yielding caesium hydroxide, metallic gold, and hydrogen gas; in liquid ammonia it can be reacted with a caesium-specific ion exchange resin to produce tetramethylammonium auride. The analogous platinum compound, red caesium platinide, contains the platinide ion that behaves as a.

Complexes
Like all metal cations, Cs+ forms complexes with Lewis bases in solution. Because of its large size, Cs+ usually adopts coordination numbers greater than 6, the number typical for the smaller alkali metal cations. This difference is apparent in the 8-coordination of CsCl. This high coordination number and softness (tendency to form covalent bonds) are properties exploited in separating Cs+ from other cations in the remediation of nuclear wastes, where 137Cs+ must be separated from large amounts of nonradioactive K+.

Halides
Caesium fluoride (CsF) is a hygroscopic white solid that is widely used in organofluorine chemistry as a source of fluoride anions. Caesium fluoride has the halite structure, which means that the Cs+ and F− pack in a cubic closest packed array as do Na+ and Cl− in sodium chloride. Notably, caesium and fluorine have the lowest and highest electronegativities, respectively, among all the known elements.

Caesium chloride (CsCl) crystallizes in the simple cubic crystal system. Also called the "caesium chloride structure", this structural motif is composed of a primitive cubic lattice with a two-atom basis, each with an eightfold coordination; the chloride atoms lie upon the lattice points at the edges of the cube, while the caesium atoms lie in the holes in the centre of the cubes. This structure is shared with CsBr and CsI, and many other compounds that do not contain Cs. In contrast, most other alkaline halides have the sodium chloride (NaCl) structure. The CsCl structure is preferred because Cs+ has an ionic radius of 174 pm and 181 pm.

Oxides

More so than the other alkali metals, caesium forms numerous binary compounds with oxygen. When caesium burns in air, the superoxide is the main product. The "normal" caesium oxide forms yellow-orange hexagonal crystals, and is the only oxide of the anti-cadmium chloride type. It vaporizes at 250 °C, and decomposes to caesium metal and the peroxide caesium peroxide at temperatures above 400 °C. In addition to the superoxide and the ozonide caesium ozonide, several brightly coloured suboxides have also been studied. These include, , , (dark-green ), CsO, , as well as. The latter may be heated in a vacuum to generate. Binary compounds with sulfur, selenium, and tellurium also exist.

Isotopes
Caesium has 41 known isotopes, ranging in mass number (i.e. number of nucleons in the nucleus) from 112 to 152. Several of these are synthesized from lighter elements by the slow neutron capture process (S-process) inside old stars and by the R-process in supernova explosions. The only stable caesium isotope is 133Cs, with 78 neutrons. Although it has a large nuclear spin ($7⁄2$+), nuclear magnetic resonance studies can use this isotope at a resonating frequency of 11.7 MHz. The radioactive 135Cs has a very long half-life of about 2.3 million years, the longest of all radioactive isotopes of caesium. 137Cs and 134Cs have half-lives of 30 and two years, respectively. 137Cs decomposes to a short-lived 137mBa by beta decay, and then to nonradioactive barium, while 134Cs transforms into 134Ba directly. The isotopes with mass numbers of 129, 131, 132 and 136, have half-lives between a day and two weeks, while most of the other isotopes have half-lives from a few seconds to fractions of a second. At least 21 metastable nuclear isomers exist. Other than 134mCs (with a half-life of just under 3 hours), all are very unstable and decay with half-lives of a few minutes or less.

The isotope 135Cs is one of the long-lived fission products of uranium produced in nuclear reactors. However, this fission product yield is reduced in most reactors because the predecessor, 135Xe, is a potent neutron poison and frequently transmutes to stable 136Xe before it can decay to 135Cs.

The beta decay from 137Cs to 137mBa results in gamma radiation as the 137mBa relaxes to ground state 137Ba, with the emitted photons having an energy of 0.6617 MeV. 137Cs and 90Sr are the principal medium-lived products of nuclear fission, and the prime sources of radioactivity from spent nuclear fuel after several years of cooling, lasting several hundred years. Those two isotopes are the largest source of residual radioactivity in the area of the Chernobyl disaster. Because of the low capture rate, disposing of 137Cs through neutron capture is not feasible and the only current solution is to allow it to decay over time.

Almost all caesium produced from nuclear fission comes from the beta decay of originally more neutron-rich fission products, passing through various isotopes of iodine and xenon. Because iodine and xenon are volatile and can diffuse through nuclear fuel or air, radioactive caesium is often created far from the original site of fission. With nuclear weapons testing in the 1950s through the 1980s, 137Cs was released into the atmosphere and returned to the surface of the earth as a component of radioactive fallout. It is a ready marker of the movement of soil and sediment from those times.

Occurrence

Caesium is a relatively rare element, estimated to average 3 parts per million in the Earth's crust. It is the 45th most abundant element and 36th among the metals. Caesium is 30 times less abundant than rubidium, with which it is closely associated, chemically.

Due to its large ionic radius, caesium is one of the "incompatible elements". During magma crystallization, caesium is concentrated in the liquid phase and crystallizes last. Therefore, the largest deposits of caesium are zone pegmatite ore bodies formed by this enrichment process. Because caesium does not substitute for potassium as readily as rubidium does, the alkali evaporite minerals sylvite (KCl) and carnallite may contain only 0.002% caesium. Consequently, caesium is found in few minerals. Percentage amounts of caesium may be found in beryl and avogadrite, up to 15 wt% Cs2O in the closely related mineral pezzottaite , up to 8.4 wt% Cs2O in the rare mineral londonite , and less in the more widespread rhodizite. The only economically important ore for caesium is pollucite, which is found in a few places around the world in zoned pegmatites, associated with the more commercially important lithium minerals, lepidolite and petalite. Within the pegmatites, the large grain size and the strong separation of the minerals results in high-grade ore for mining.

The world's most significant and richest known source of caesium is the Tanco Mine at Bernic Lake in Manitoba, Canada, estimated to contain 350,000 metric tons of pollucite ore, representing more than two-thirds of the world's reserve base. Although the stoichiometric content of caesium in pollucite is 42.6%, pure pollucite samples from this deposit contain only about 34% caesium, while the average content is 24 wt%. Commercial pollucite contains more than 19% caesium. The Bikita pegmatite deposit in Zimbabwe is mined for its petalite, but it also contains a significant amount of pollucite. Another notable source of pollucite is in the Karibib Desert, Namibia. At the present rate of world mine production of 5 to 10 metric tons per year, reserves will last for thousands of years.

Production
Mining and refining pollucite ore is a selective process and is conducted on a smaller scale than for most other metals. The ore is crushed, hand-sorted, but not usually concentrated, and then ground. Caesium is then extracted from pollucite primarily by three methods: acid digestion, alkaline decomposition, and direct reduction.

In the acid digestion, the silicate pollucite rock is dissolved with strong acids, such as hydrochloric (HCl), sulfuric, hydrobromic (HBr), or hydrofluoric (HF) acids. With hydrochloric acid, a mixture of soluble chlorides is produced, and the insoluble chloride double salts of caesium are precipitated as caesium antimony chloride, caesium iodine chloride , or caesium hexachlorocerate. After separation, the pure precipitated double salt is decomposed, and pure CsCl is precipitated by evaporating the water.

The sulfuric acid method yields the insoluble double salt directly as caesium alum. The aluminium sulfate component is converted to insoluble aluminium oxide by roasting the alum with carbon, and the resulting product is leached with water to yield a solution.

Roasting pollucite with calcium carbonate and calcium chloride yields insoluble calcium silicates and soluble caesium chloride. Leaching with water or dilute ammonia yields a dilute chloride (CsCl) solution. This solution can be evaporated to produce caesium chloride or transformed into caesium alum or caesium carbonate. Though not commercially feasible, the ore can be directly reduced with potassium, sodium, or calcium in vacuum to produce caesium metal directly.

Most of the mined caesium (as salts) is directly converted into caesium formate (HCOO−Cs+) for applications such as oil drilling. To supply the developing market, Cabot Corporation built a production plant in 1997 at the Tanco mine near Bernic Lake in Manitoba, with a capacity of 12000 oilbbl per year of caesium formate solution. The primary smaller-scale commercial compounds of caesium are caesium chloride and nitrate.

Alternatively, caesium metal may be obtained from the purified compounds derived from the ore. Caesium chloride and the other caesium halides can be reduced at 700 to 800 °C with calcium or barium, and caesium metal distilled from the result. In the same way, the aluminate, carbonate, or hydroxide may be reduced by magnesium.

The metal can also be isolated by electrolysis of fused caesium cyanide (CsCN). Exceptionally pure and gas-free caesium can be produced by 390 °C thermal decomposition of caesium azide, which can be produced from aqueous caesium sulfate and barium azide. In vacuum applications, caesium dichromate can be reacted with zirconium to produce pure caesium metal without other gaseous products.
 * + 2 → 2  + 2 +

The price of 99.8% pure caesium (metal basis) in 2009 was about 10 $/g, but the compounds are significantly cheaper.

History
In 1860, Robert Bunsen and Gustav Kirchhoff discovered caesium in the mineral water from Dürkheim, Germany. Because of the bright blue lines in the emission spectrum, they derived the name from the Latin word caesius, meaning bluish grey. Caesium was the first element to be discovered with a spectroscope, which had been invented by Bunsen and Kirchhoff only a year previously.

To obtain a pure sample of caesium, 44,000 litre of mineral water had to be evaporated to yield 240 kg of concentrated salt solution. The alkaline earth metals were precipitated either as sulfates or oxalates, leaving the alkali metal in the solution. After conversion to the nitrates and extraction with ethanol, a sodium-free mixture was obtained. From this mixture, the lithium was precipitated by ammonium carbonate. Potassium, rubidium, and caesium form insoluble salts with chloroplatinic acid, but these salts show a slight difference in solubility in hot water, and the less-soluble caesium and rubidium hexachloroplatinate ((Cs,Rb)2PtCl6) were obtained by fractional crystallization. After reduction of the hexachloroplatinate with hydrogen, caesium and rubidium were separated by the difference in solubility of their carbonates in alcohol. The process yielded 9.2 g of rubidium chloride and 7.3 g of caesium chloride from the initial 44,000 litres of mineral water.

From the caesium chloride, the two scientists estimated the atomic weight of the new element at 123.35 (compared to the currently accepted one of 132.9). They tried to generate elemental caesium by electrolysis of molten caesium chloride, but instead of a metal, they obtained a blue homogeneous substance which "neither under the naked eye nor under the microscope showed the slightest trace of metallic substance"; as a result, they assigned it as a subchloride. In reality, the product was probably a colloidal mixture of the metal and caesium chloride. The electrolysis of the aqueous solution of chloride with a mercury cathode produced a caesium amalgam which readily decomposed under the aqueous conditions. The pure metal was eventually isolated by the Swedish chemist Carl Setterberg while working on his doctorate with Kekulé and Bunsen. In 1882, he produced caesium metal by electrolysing caesium cyanide, avoiding the problems with the chloride.

Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical fields. Very few applications existed for caesium until the 1920s, when it came into use in radio vacuum tubes, where it had two functions; as a getter, it removed excess oxygen after manufacture, and as a coating on the heated cathode, it increased the electrical conductivity. Caesium was not recognized as a high-performance industrial metal until the 1950s. Applications for nonradioactive caesium included photoelectric cells, photomultiplier tubes, optical components of infrared spectrophotometers, catalysts for several organic reactions, crystals for scintillation counters, and in magnetohydrodynamic power generators. Caesium is also used as a source of positive ions in secondary ion mass spectrometry (SIMS).

Since 1967, the International System of Measurements has based the primary unit of time, the second, on the properties of caesium. The International System of Units (SI) defines the second as the duration of 9,192,631,770 cycles at the microwave frequency of the spectral line corresponding to the transition between two hyperfine energy levels of the ground state of caesium-133. The 13th General Conference on Weights and Measures of 1967 defined a second as: "the duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of caesium-133 atoms in their ground state undisturbed by external fields".

Petroleum exploration
The largest present-day use of nonradioactive caesium is in caesium formate drilling fluids for the extractive oil industry. Aqueous solutions of caesium formate (HCOO−Cs+)—made by reacting caesium hydroxide with formic acid—were developed in the mid-1990s for use as oil well drilling and completion fluids. The function of a drilling fluid is to lubricate drill bits, to bring rock cuttings to the surface, and to maintain pressure on the formation during drilling of the well. Completion fluids assist the emplacement of control hardware after drilling but prior to production by maintaining the pressure.

The high density of the caesium formate brine (up to 2.3 g/cm3, or 19.2 pounds per gallon), coupled with the relatively benign nature of most caesium compounds, reduces the requirement for toxic high-density suspended solids in the drilling fluid—a significant technological, engineering and environmental advantage. Unlike the components of many other heavy liquids, caesium formate is relatively environment-friendly. Caesium formate brine can be blended with potassium and sodium formates to decrease the density of the fluids to that of water (1.0 g/cm3, or 8.3 pounds per gallon). Furthermore, it is biodegradable and may be recycled, which is important in view of its high cost (about $4,000 per barrel in 2001). Alkali formates are safe to handle and do not damage the producing formation or downhole metals as corrosive alternative, high-density brines (such as zinc bromide solutions) sometimes do; they also require less cleanup and reduce disposal costs.

Atomic clocks
Caesium-based atomic clocks use the electromagnetic transitions in the hyperfine structure of caesium-133 atoms as a reference point. The first accurate caesium clock was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. Caesium clocks have improved over the past half-century and are regarded as "the most accurate realization of a unit that mankind has yet achieved." These clocks measure frequency with an error of 2 to 3 parts in 1014, which corresponds to an accuracy of 2 nanoseconds per day, or one second in 1.4 million years. The latest versions are more accurate than 1 part in 1015, about 1 second in 20 million years. The caesium standard is the primary standard for standards-compliant time and frequency measurements. Caesium clocks regulate the timing of cell phone networks and the Internet.

Definition of the second
The second, symbol s, is the SI unit of time. The BIPM restated its definition at its 26th conference in 2018: "[The second] is defined by taking the fixed numerical value of the caesium frequency $Δν_{Cs}$, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be $7⁄2$ when expressed in the unit Hz, which is equal to s−1."

Electric power and electronics
Caesium vapour thermionic generators are low-power devices that convert heat energy to electrical energy. In the two-electrode vacuum tube converter, caesium neutralizes the space charge near the cathode and enhances the current flow.

Caesium is also important for its photoemissive properties, converting light to electron flow. It is used in photoelectric cells because caesium-based cathodes, such as the intermetallic compound, have a low threshold voltage for emission of electrons. The range of photoemissive devices using caesium include optical character recognition devices, photomultiplier tubes, and video camera tubes. Nevertheless, germanium, rubidium, selenium, silicon, tellurium, and several other elements can be substituted for caesium in photosensitive materials.

Caesium iodide (CsI), bromide (CsBr) and fluoride (CsF) crystals are employed for scintillators in scintillation counters widely used in mineral exploration and particle physics research to detect gamma and X-ray radiation. Being a heavy element, caesium provides good stopping power with better detection. Caesium compounds may provide a faster response (CsF) and be less hygroscopic (CsI).

Caesium vapour is used in many common magnetometers.

The element is used as an internal standard in spectrophotometry. Like other alkali metals, caesium has a great affinity for oxygen and is used as a "getter" in vacuum tubes. Other uses of the metal include high-energy lasers, vapour glow lamps, and vapour rectifiers.

Centrifugation fluids
The high density of the caesium ion makes solutions of caesium chloride, caesium sulfate, and caesium trifluoroacetate useful in molecular biology for density gradient ultracentrifugation. This technology is used primarily in the isolation of viral particles, subcellular organelles and fractions, and nucleic acids from biological samples.

Chemical and medical use
Relatively few chemical applications use caesium. Doping with caesium compounds enhances the effectiveness of several metal-ion catalysts for chemical synthesis, such as acrylic acid, anthraquinone, ethylene oxide, methanol, phthalic anhydride, styrene, methyl methacrylate monomers, and various olefins. It is also used in the catalytic conversion of sulfur dioxide into sulfur trioxide in the production of sulfuric acid.

Caesium fluoride enjoys a niche use in organic chemistry as a base and as an anhydrous source of fluoride ion. Caesium salts sometimes replace potassium or sodium salts in organic synthesis, such as cyclization, esterification, and polymerization. Caesium has also been used in thermoluminescent radiation dosimetry (TLD) : When exposed to radiation, it acquires crystal defects that, when heated, revert with emission of light proportionate to the received dose. Thus, measuring the light pulse with a photomultiplier tube can allow the accumulated radiation dose to be quantified.

Nuclear and isotope applications
Caesium-137 is a radioisotope commonly used as a gamma-emitter in industrial applications. Its advantages include a half-life of roughly 30 years, its availability from the nuclear fuel cycle, and having 137Ba as a stable end product. The high water solubility is a disadvantage which makes it incompatible with large pool irradiators for food and medical supplies. It has been used in agriculture, cancer treatment, and the sterilization of food, sewage sludge, and surgical equipment. Radioactive isotopes of caesium in radiation devices were used in the medical field to treat certain types of cancer, but emergence of better alternatives and the use of water-soluble caesium chloride in the sources, which could create wide-ranging contamination, gradually put some of these caesium sources out of use. Caesium-137 has been employed in a variety of industrial measurement gauges, including moisture, density, levelling, and thickness gauges. It has also been used in well logging devices for measuring the electron density of the rock formations, which is analogous to the bulk density of the formations.

Caesium-137 has been used in hydrologic studies analogous to those with tritium. As a daughter product of fission bomb testing from the 1950s through the mid-1980s, caesium-137 was released into the atmosphere, where it was absorbed readily into solution. Known year-to-year variation within that period allows correlation with soil and sediment layers. Caesium-134, and to a lesser extent caesium-135, have also been used in hydrology to measure the caesium output by the nuclear power industry. While they are less prevalent than either caesium-133 or caesium-137, these bellwether isotopes are produced solely from anthropogenic sources.

Other uses
Caesium and mercury were used as a propellant in early ion engines designed for spacecraft propulsion on very long interplanetary or extraplanetary missions. The fuel was ionized by contact with a charged tungsten electrode. But corrosion by caesium on spacecraft components has pushed development in the direction of inert gas propellants, such as xenon, which are easier to handle in ground-based tests and do less potential damage to the spacecraft. Xenon was used in the experimental spacecraft Deep Space 1 launched in 1998. Nevertheless, field-emission electric propulsion thrusters that accelerate liquid metal ions such as caesium have been built.

Caesium nitrate is used as an oxidizer and pyrotechnic colorant to burn silicon in infrared flares, such as the LUU-19 flare, because it emits much of its light in the near infrared spectrum. Caesium compounds may have been used as fuel additives to reduce the radar signature of exhaust plumes in the Lockheed A-12 CIA reconnaissance aircraft. Caesium and rubidium have been added as a carbonate to glass because they reduce electrical conductivity and improve stability and durability of fibre optics and night vision devices. Caesium fluoride or caesium aluminium fluoride are used in fluxes formulated for brazing aluminium alloys that contain magnesium.

Magnetohydrodynamic (MHD) power-generating systems were researched, but failed to gain widespread acceptance. Caesium metal has also been considered as the working fluid in high-temperature Rankine cycle turboelectric generators.

Caesium salts have been evaluated as antishock reagents following the administration of arsenical drugs. Because of their effect on heart rhythms, however, they are less likely to be used than potassium or rubidium salts. They have also been used to treat epilepsy.

Caesium-133 can be laser cooled and used to probe fundamental and technological problems in quantum physics. It has a particularly convenient Feshbach spectrum to enable studies of ultracold atoms requiring tunable interactions.

Health and safety hazards
Nonradioactive caesium compounds are only mildly toxic, and nonradioactive caesium is not a significant environmental hazard. Because biochemical processes can confuse and substitute caesium with potassium, excess caesium can lead to hypokalemia, arrhythmia, and acute cardiac arrest, but such amounts would not ordinarily be encountered in natural sources.

The median lethal dose (LD50) for caesium chloride in mice is 2.3 g per kilogram, which is comparable to the LD50 values of potassium chloride and sodium chloride. The principal use of nonradioactive caesium is as caesium formate in petroleum drilling fluids because it is much less toxic than alternatives, though it is more costly.

Caesium is one of the most reactive elements and is highly explosive in the presence of water. The hydrogen gas produced by the reaction is heated by the thermal energy released at the same time, causing ignition and a violent explosion. This can occur with other alkali metals, but caesium is so potent that this explosive reaction can be triggered even by cold water.

It is highly pyrophoric: the autoignition temperature of caesium is −116 C, and it ignites explosively in air to form caesium hydroxide and various oxides. Caesium hydroxide is a very strong base, and will rapidly corrode glass.

The isotopes 134 and 137 are present in the biosphere in small amounts from human activities, differing by location. Radiocaesium does not accumulate in the body as readily as other fission products (such as radioiodine and radiostrontium). About 10% of absorbed radiocaesium washes out of the body relatively quickly in sweat and urine. The remaining 90% has a biological half-life between 50 and 150 days. Radiocaesium follows potassium and tends to accumulate in plant tissues, including fruits and vegetables. Plants vary widely in the absorption of caesium, sometimes displaying great resistance to it. It is also well-documented that mushrooms from contaminated forests accumulate radiocaesium (caesium-137) in the fungal sporocarps. Accumulation of caesium-137 in lakes has been a great concern after the Chernobyl disaster. Experiments with dogs showed that a single dose of 3.8 millicuries (140 MBq, 4.1 μg of caesium-137) per kilogram is lethal within three weeks; smaller amounts may cause infertility and cancer. The International Atomic Energy Agency and other sources have warned that radioactive materials, such as caesium-137, could be used in radiological dispersion devices, or "dirty bombs".

title: Caesium