Emeline Maisonneuve

Anaïs Dugas

Stéphanie Friszer

Cécile Toly-Ndour

Laura Cariot

Ferdinand Dhombres

Anne Cortey

Agnès Mailloux

Bruno Carbonne

Jean-Marie Jouannic

Effect of intravenous immunoglobulins to postpone the gestational age of first intrauterine transfusion in very severe red blood cell alloimmunization: A case-control study 2) RUNNING HEAD Antenatal immunoglobulins to postpone IUT 3) AUTHORS

Keywords:

BACKGROUND

Early intrauterine transfusion (IUT) is associated with a higher risk of fetal loss. Our objective was to evaluate the efficiciency of intravenous immunoglobulins (IVIG) to postpone the gestational age at first IUT beyond 20 weeks of gestation (WG) compared to the previous pregnancy in case of very severe red blood cell (RBC) alloimmunization.

STUDY DESIGN AND METHODS

Very severe RBC alloimmunization was defined by a high titer of antibodies and a previous pregnancy complicated by a first IUT before 24 WG and/or perinatal death directly related to alloimmunization.

We performed a single-center case-control study. Cases and controls were patients respectively treated with weekly IVIG infusions started before 13 WG, and without.

RESULTS

Twenty cases and 21 controls were included. Gestational age (GA) at first IUT was postponed after 20 WG in 18/20 (90%) of patients treated with IVIG and in 15/21 (71%) in the control group (p=0.24). Compared to the previous pregnancy, the GA at first IUT was postponed by a median of 22 [+11; +49] days in the IVIG group and occurred in average 2 days earlier [-17 ; +12] in the non-treated group (p=0.02).

There was no difference between number of IUT and need for exchange-transfusion.

IVIG treatment was associated with a significant decrease of antibodies' quantitation.

2

CONCLUSION

In our series, IVIG tends to differ first IUT beyond 20 WG and have a significant effect in postponing the gestational age of the first IUT in patients with very severe RBC alloimmunization.

ACKNOWLEDGMENTS:

The CNRHP members who performed ultrasound examinations, intrauterine transfusions and in-hospital management and coordinated intravenous immunoglobulin treatment: Vanina Castaigne, Evelyne Cynober, Hélène Delaby, Stéphanie Huguet-Jacquot, Bertrand Lafon, Paul Maurice, Pauline Thomas, Luce Tulpin.

TEXT (2926 words / 3500) INTRODUCTION

Intrauterine transfusion (IUT) is currently the only treatment option for fetal anemia complicating severe red blood cell (RBC) alloimmunization in pregnancy. However, IUT is associated with procedure-related complications, such as fetal distress leading to premature delivery or perinatal death. The rate of fetal complications is estimated to be 2.7% per procedure and 7.8% per fetus. [START_REF] Zwiers | Intrauterine transfusion and noninvasive treatment options for hemolytic disease of the fetus and newbornreview on current management and outcome[END_REF] Despite improved ultrasonographic resolution, the puncture of umbilical vessels before 20-22 weeks of gestation can be technically challenging and a 9 to 10 fold increased risk of fetal loss per IUT has been reported when IUT is performed before 20 weeks of gestation (WG). [START_REF] Zwiers | Complications of intrauterine intravascular blood transfusion: lessons learned after 1678 procedures[END_REF][START_REF] Yinon | Early intrauterine transfusion in severe red blood cell alloimmunization[END_REF][START_REF] Scott | Revisiting the use of intravenous immune globulin (IVIG) for Kell alloimmunization[END_REF] The study of Zwiers et al. is the largest during the last two decades assessing the effect of Intravenous Immunoglobulins (IVIG) on the possibility to postpone the first IUT after 20 weeks. [START_REF] Zwiers | Postponing Early intrauterine Transfusion with Intravenous immunoglobulin Treatment; the PETIT study on severe hemolytic disease of the fetus and newborn[END_REF] They compared 24 pregnancies treated with IVIG to 28 pregnancies without treatment. They found an adjusted 4-day between-group difference in favour of the IVIG group, but it was not significant. In addition, a metaanalysis has concluded that no information is currently available from randomized trials to indicate whether the antenatal use of IVIG is effective in the management of severe fetal RBC alloimmunization. [START_REF] Wong | Antenatal immunoglobulin for fetal red blood cell alloimmunization[END_REF] Since 2012, our center offers IVIG to patients with very severe alloimmunization, i.e. with a very high level of red cells antibodies at the beginning of pregnancy and a history of IUT before 24 WG during the previous pregnancy or perinatal death directly related to alloimmunization. [START_REF] Maisonneuve | Postponing early intrauterine transfusion with intravenous immunoglobulin treatment: the PETIT study on severe hemolytic disease of the fetus and newborn[END_REF] Our primary objective was to assess if IVIG could postpone the gestational age (GA) of first IUT beyond 20 WG as compared with the previous pregnancy without IVIG administration, or possibly allow to avoid IUT until 36 WG. Our secondary objectives were to compare the number of days gained before first IUT, perinatal outcomes (live birth rates after 28 WG and 32 WG), the number of fetal and total transfusions, and the evolution of antibodies' quantitation between patients treated with and without IVIG respectively.

MATERIALS AND METHODS

Patients

The perinatal data of patients with severe RBC alloimmunization managed between 2005 and 2020 in our French referral center (CNRHP: Centre National de Référence en Hémobiologie Périnatale) were retrospectively reviewed. The inclusion criteria were patients who delivered between January 2005 and December 2020 in our center, presenting very severe RBC alloimmunization. Very severe alloimmunization was defined as anti-D (RH1) antibody level above 15 IU/mL or anti-c (RH4) above 20 IU/ml or anti-Kell (KEL1) antibody titer ≥ 256 and at least one of the following: previous pregnancy marked by IUT performed before 24 WG; intrauterine fetal death (IUFD) or neonatal death directly related to alloimmunization. [START_REF] Zwiers | Postponing Early intrauterine Transfusion with Intravenous immunoglobulin Treatment; the PETIT study on severe hemolytic disease of the fetus and newborn[END_REF][START_REF] White | Guideline for blood grouping and red cell antibody testing in pregnancy[END_REF] The exclusion criteria were: chromosomal anomalies or congenital malformations, multiple pregnancies and inappropriate follow-up at previous pregnancy.

Management of patients with very severe RBC alloimmunization in our center

Maternal-fetal incompatibility was assessed respectively by non-invasive fetal RHD, KEL1 or RHc genotyping in case of anti-D (RH1) (Jacques Boy, France), anti-Kell (KEL1) or anti-c (in-house CNRHP test) alloimmunization. [START_REF] Sciellour | Noninvasive fetal RHD genotyping from maternal plasma. Use of a new developed Free DNA Fetal Kit RhD[END_REF][START_REF] Silva | Mise en place du génotypage RHc foetal non invasif au Centre national de référence en hémobiologie périnatale (CNRHP)[END_REF] Antibodies' titration was performed by a standardized tube procedure, in saline medium and with the indirect antiglobulin test using an anti-IgG reagent, RH:1,2,3,4,5 (DCcEe positive) RBC for anti-D and anti-c antibodies and KEL:1,2 (heterozygous K positive) RBC for anti-Kell antibody. In addition to titration by indirect antiglobulin test, anti-D and anti-c quantitation by continuous-flow hemagglutination was performed on Astoria White Horse Scientific or AMS Alliance Evolution III autoanalyzer, using RH:1,2,3,4,5 (DCcEe positive) RBC to assess for a reactivation of maternal immunization with more accuracy. [START_REF] Toly-Ndour | Clinical input of anti-D quantitation by continuous-flow analysis on autoanalyzer in the management of high-titer anti-D maternal alloimmunization[END_REF] Maternal blood sampling was collected every 2 weeks, just before starting weekly immunoglobulin infusion.

Since 2012, IVIG have been offered in our center to patients with the aim to postpone or avoid the first IUT in cases with very severe RBC alloimmunization. IVIG were started from 11 WG with a regimen of 1g/kg weekly. Our protocol for IVIG includes an infusion with an initial flow ≤1mL/kg/hour during 30 minutes. If the medication is well tolerated, the flow is increased gradually with a maximum of 4mL/kg/hour. The IVIG used in this study were: TEGELINE (50mg/mL) from 2012 to 2015, and CLAIRYG (50mg/mL) from 2015 to 2020. In case of body mass index over 30kg/m 2 , the therapeutic dose of IVIG for immunomodulation was reduced from 20% to avoid renal complication related to increase of oncotic pressure and blood viscosity. [START_REF] Ansm | Immunoglobuline humaine normale: résumé et caractérisqtiques du produit[END_REF] IVIG were continued throughout the pregnancy, until the first IUT. If there was no sign of fetal anemia during pregnancy, IVIG were continued until delivery. The patients (cases and controls) did not receive other treatment, such as plasmapheresis or corticosteroids.

Middle Cerebral Artery -Peak Systolic Velocity (MCA-PSV) measurements were performed using Voluson E8 or Voluson 730 Expert (General Electrics, Zipf, Austria) or Applio (Toshiba Medical Systems, Tokyo, Japan). Each MCA Doppler measurement was interpreted as multiples of median (MoM) for gestational age. [START_REF] Mari | Noninvasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization. Collaborative Group for Doppler Assessment of the Blood Velocity in Anemic Fetuses[END_REF][START_REF] Friszer | Determination of optimal timing of serial in-utero transfusions in red-cell alloimmunization[END_REF] The decision to perform fetal blood sampling, immediately followed by IUT in most cases, was made on the observation of a sharp increase in MCA-PSV above 1.5 MoM, confirmed by a second ultrasound examination within 1-2 days. For the second IUT, we used the MCA-PSV values in association with predictable decrease of haemoglobin concentration, and performed the MCA-PSV weekly. Then, for the following IUTs, we used only the predictable fall of haemoglobin and performed MCA-PSV measurements before and after IUT as previously reported. [START_REF] Friszer | Determination of optimal timing of serial in-utero transfusions in red-cell alloimmunization[END_REF] In our center, IUTs were performed from 17 WG if moderate to severe fetal anemia was suspected.

[15] Severely anemic fetuses were transfused with adult donor packed red blood cells, cross matched with the mother, with a hematocrit between 70 and 80%. During both periods, the patients were monitored equally often and thoroughly and there was no changes in policy and procedures related to decisions to proceed with a IUT.

Delivery was scheduled at 37 WG, by induction of labour or elective caesarean section, according to obstetrical conditions.

Data collection

For each patient, data of previous and index pregnancies were collected: GA at first IUT, evolution of antibodies quantitation, number of IUTs and transfusions after birth, IUFD after IUT, rates of live births after 28 WG, and 32 WG, hemoglobin on fetal blood sampling at first IUT and on umbilical cord at birth, rates of exchangetransfusion, side effects of IVIG. The decrease in antibodies' quantitation (between quantitation at first trimester and quantitation at first IUT or at the end of pregnancy if no IUT had occurred) was calculated for anti-D (RH1) and c (RH4) alloimmunizations.

Study design and statistical analysis

We conducted a single center case-control study. The group of cases consisted of patients treated with weekly IVIG infusions for very severe RBC alloimmunization and who delivered between 2012 and 2020. Our control group consisted of patients not treated by IVIG who delivered between 2005 and 2012 and one patient followed in 2019 who declined IVIG treatment.

We compared the number of pregnancies in which an IUT was performed beyond 20 weeks. In addition, we calculated for each patient the difference between GA at index and previous pregnancies (in days). If a patient had 2 pregnancies treated with IVIG, these two pregnancies with IVIG were compared with the control pregnancy without IVIG. Other secondary outcomes were also compared between cases and controls: live births beyond 28 WG, beyond 32 WG, and the number of total transfusions (in utero and postnatal transfusions), and need for exchange transfusion. One of the secondary outcomes was a composite outcome including: postponing the GA at first IUT of more than two weeks as compared with the previous pregnancy without IVIG, and a live birth after 28 WG or no need for IUT until 36 WG.

Bivariate analyses of significant effects were based on Chi-square test and Fisher's exact test to compare categorical variables; Fisher Exact Test was used when the assumptions of the χ 2 test were violated. The associations between IVIG treatment and the outcomes were studied by bivariate analyses that used generalized estimated equations to take the non-independence of observations for pregnancies from the same patient into account ( +12] in the non-treated group (p=0.02) (Figure 2 and table 3). There was no statistical difference between rates of live births after 28 WG (80% with IVIG vs 81% without) and 32 WG (75% with IVIG vs 76% without). The antibodies' quantitation was significantly decreased in pregnancies treated with IVIG (-43% with IVIG vs +35% without, p <0.01). Apart from three patients (15%) presenting with moderate headache after IVIG first infusion, no severe side effects were observed.

Among the 20 patients treated, two patients had no evidence of fetal anemia during the entire pregnancy with IVIG, whereas their fetuses had presented with very severe HDFN in previous pregnancies. The first patient with anti-D (RH1) alloimmunization had 4 IUTs during the previous pregnancy (23, 25, 28 and 32 WG) and the child required 2 postnatal transfusions. For the index pregnancy, no IUTs were needed. Induction of labor was decided at 36 WG for preeclampsia. Her child required only one postnatal transfusion at day 26. The second patient presented with anti-c (RH4) alloimmunization with a history of intrauterine fetal death with hydrops at 32 weeks during the first pregnancy. At her second pregnancy, an IUT was performed at 21 WG for severe fetal anemia (hemoglobin at 5.0 g/dL without hydrops) and it was complicated by IUFD the following day. The index pregnancy treated with IVIG was uneventful. Labor was induced at 37 WG and her child required one postnatal transfusion at day 14.

Discussion

In this case-control study, we found that IVIG treatment significantly delayed the onset of severe fetal anemia and the need for IUT in patients with very severe RBC alloimmunization. In addition, two fetuses of patients treated with IVIG did not require any IUT during the index pregnancies, whereas they had required very early IUT during a previous pregnancy.

In spite of this delay, we did not observe significant difference in the proportion of first IUT after 20 WG in 18/20 (90%) of patients treated with IVIG as compared to 15/21 (71%) in the control group (p=0.24).

The strength of our study relies on our single center homogenous management of patients with very severe alloimmunization in which we perform approximately 70 IUT per year and 40% of the IUT in France. [START_REF] Girault | Intrauterine blood transfusion: Status report of 4years of practice in France (2011-2014)[END_REF] Moreover, the protocol of IVIG infusions was exactly the same for all patients with an early homogenous GA at onset of 11-13 WG and duration of treatment until first IUT or delivery if no IUT was needed. The main limitation of the study is the small number of patients, since this is a very rare condition. Nevertheless, although the results of our study involve few patients, they are of utmost importance since we included only very severe HDFN cases with a high rate of poor outcome. Indeed, an additional 2 weeks offers a significant improvement in the technical conditions of IUT performance, with a larger umbilical cord and increased fetal cardiac tolerance.

The use of IVIG in severe RBC alloimmunization was introduced three decades ago following the publication of small case-series. [START_REF] Margulies | High-dose intravenous gamma globulin: does it have a role in the treatment of severe erythroblastosis fetalis?[END_REF][START_REF] Gottvall | Alloimmunization pregnancy treated with high dose intravenous immunoglobulin. Effects on fetal hemoglobin concentration and anti-D concentrations in the mother and fetus[END_REF][START_REF] Voto | High-dose gammaglobulin (IVIG) followed by intrauterine transfusions (IUTs): a new alternative for the treatment of severe fetal hemolytic disease[END_REF] These studies found a beneficial effect on reducing the severity of fetal hemolytic disease, but IVIG were started during the second or third trimester, with heterogeneous regimen. Moreover, these studies were performed before the use of MCA-PSV Doppler and thus do not correspond to the current standard of care. [START_REF] Mari | Noninvasive diagnosis by Doppler ultrasonography of fetal anemia due to maternal red-cell alloimmunization. Collaborative Group for Doppler Assessment of the Blood Velocity in Anemic Fetuses[END_REF] Our results are comparable with those of the multicenter retrospective study conducted by Zwiers et al. when taking into account only patients treated with IVIG started before 13 WG. We used the same definition of very severe alloimmunization and criteria for IVIG treatment, in particular the history of first IUT before 24 WG. [START_REF] Zwiers | Postponing Early intrauterine Transfusion with Intravenous immunoglobulin Treatment; the PETIT study on severe hemolytic disease of the fetus and newborn[END_REF] The main limitation of their study is the heterogeneity of the IVIG-group, with IVIG infusions started at different GA, variable IVIG dose and frequency regimen, and sometimes a combination with plasmapheresis. They considered the "onset of fetal anemia" as primary outcome, with no clear definition of this outcome. In our study, we preferred to compare the GA of first IUT, because this outcome is more accurate and pragmatic. Indeed, this primary outcome proved to be reliable in our study since hemoglobin levels at first IUT were similar in both groups.

In their study, Zwiers et al. showed a significant effect of IVIG to postpone the GA of first IUT only when they considered the subcohort in which immunoglobulin treatment was started before 13 weeks. We believe that it is important to start IVIG at 11-13 WG and to continue weekly infusions until the first IUT, because IVIG have multiple actions in order to reduce the immune conflict. They reduce the production of maternal antibodies, shorten their half-life, act on their transplacental transfer and saturate the reticuloendothelial system in order to curb the destruction of the fetus' red cells. [START_REF] Hadley | A comparison of in vitro tests for predicting the severity of haemolytic disease of the fetus and newborn[END_REF] We monitored patients' antibodies every 2 weeks and noticed that their concentrations decreased gradually under IVIG, which is in favour of an effect of IVIG on maternal antibodies, which could reduce the transplacental transfer of maternal antibodies. In the two cases with no IUT during index pregnancy, antibodies quantitation dropped by more than half with IVIG.

We chose the composite outcome "postponing GA of first IUT of more than two weeks resulting in a live birth after 28 WG" as a secondary outcome, because considering only GA of first IUT could be considered as a surrogate marker. [START_REF] Scott | Revisiting the use of intravenous immune globulin (IVIG) for Kell alloimmunization[END_REF] On the one hand, the pathophysiological effect of this non-invasive treatment has to be demonstrated in a significant offset of the first IUT. On the other hand, survival without morbidity is the most meaningful outcome and is what is useful for patients and physicians.

Yinon et al. calculated the number of patients needed to demonstrate a positive effect of IVIG in survival. They found that, in order to show a 50% reduction in perinatal mortality from 20 to 10% with a power of 80%, 438 patients should be recruited, which remains challenging even in a multicentre study. Therefore, management of early severe RBC alloimmunization will continue to be based on small case series. [START_REF] Yinon | Early intrauterine transfusion in severe red blood cell alloimmunization[END_REF] Even if they were pooled in a meta-analysis, all data remain retrospective. However, given the very elevated cost of IVIG and its human plasmatic origin, a well-designed prospective study seems necessary to assess the effect of IVIG in postponing the GA of first IUT as well as increasing perinatal survival.

Adverse effects may occur with IVIG, such as headache, migraines, fushing or nausea. Besides, a novel strategy to inhibit transplacental alloantibody transfer with maternal M281 monoclonal antibody therapy is under evaluation but has not yet been tested on pregnant women. [START_REF] Castleman | Medical therapy to attenuate fetal anaemia in severe maternal red cell alloimmunisation[END_REF] CONCLUSION Among patients with very severe RBC alloimmunization, we found that IVIG tend to differ first IUT beyond 20 WG and have a significant effect in postponing the gestational age of the first IUT of more than 2 weeks and resulting in a live birth after 28 WG. Moreover, in some rare cases, IVIG treatment allows to avoid IUT completely during pregnancy. Monitoring antibodies quantitation may be a predictor of treatment efficiency. The blue lines show the two patients for whom no intrauterine transfusion was needed.

The dotted line ( ) indicates the birth for the index pregnancies without intrauterine transfusion, but with postnatal transfusion. ) with intensity between 0 and 4+ † † Exchange transfusion consists in removal of the patient blood (full of bilirubin) and replacing it by donor blood (a mix of packed red blood cell and fresh frozen plasma) up to 2 blood mass It is indicated when bilirubinemia reaches threshold defined by gestational and post-natal age in hours provided by the American Academy of Pediatrics. † † † Reactivation of alloimmunization is an increase of the antibodies quantitation higher than 30% between two subsequent measurments. ‡ Three patients presented headache after IVIG first infusion only.

The associations between IVIG treatment and the outcomes were studied by bivariate analyses that used generalized estimated equations to take the nonindependence of observations for pregnancies from the same patient into account.

  The authors have no conflict of interest to disclose.

Figure 1 :SevereFigure 2 :

 12 Figure 1: Flowchart of the study Legend: IUFD: intrauterine fetal death; IUT: intrauterine transfusion; IVIG: Intravenous immunoglobulins; RBC: red blood cells; TOP: termination of pregnancy; WG: weeks of gestation

  3 patients had 2 pregnancies in the control group and 4 patients had 2 pregnancies in the cases group). Continuous variables were compared with Wilcoxon Rank Sum tests. P values were used to estimate the strength of association with each parameter. Statistical significance was set at p<0.05. Statistical analyses were performed with R 3.5.1 statistical software. gestational age (GA) at first IUT was postponed after 20 WG in 18/20 (90%) of patients treated with IVIG and in 15/21 (71%) in the control group (p=0.24). GA at first IUT was postponed of more than 14 days resulting in a live birth after 28 WG in 63% (10/16) of patients treated with IVIG and in 18% (2/11) of the control group (p=0.03) (Table 2). Similarly, the GA at first IUT was postponed by a median of 22 [+11; +49] days in the IVIG group while it occurred in average 2 days earlier [-17 ;

Table 1 :

 1 Baseline characteristics of the 2 groups treated or not with intravenous immunoglobulins (IVIG)

			No IVIG for index				IVIG for index
	Gestational age at first IUT	(weeks of gestation)	15 20 25 30 35	pregnancy	Gestational age at first transfusion	(weeks of gestation)	15 20 25 30 35	pregnancy
			10					10
				GA at previous	GA at index				GA at previous	GA or postnatal
				pregnancy	pregnancy				pregnancy	corrected age at
									index pregnancy

* Titrations were performed for all types of antibodies ** Quantitations were performed only for anti-D (RH1) and anti-c (RH4).

Table 2 :

 2 Comparison of the severity of the hemolytic disease of the fetus and newborn and outcomes in both groups

	* without considering the 2 patients whose fetus did not receive intrauterine
	transfusion during the index pregnancy treated with IVIG.
	** considering the 2 patients whose fetus did not receive intrauterine transfusion
	during the index pregnancy treated with IVIG, but whose children received neonatal
	transfusion
	*** Morbidity related to preterm birth include: intraventricular hemorrhage III-IV and/or
	periventricular leukomalacia, bronchopulmonar dysplasia and necrotizing
	enterocolitis.
	† DAT: Direct Antiglobulin Test (Coombs

GA: gestational age ; IUFD: intrauterine fetal death ; IUT: intrauterine transfusion ; IQR : interquartile range ; MCA-PSV : Middle Cerebral Artery -Peak Systolic Velocity ; WG weeks of gestation ; IVIG : intravenous immunoglobulins Data are expressed in median [Interquartile Range].

Table 3 :

 3 Description of first intrauterine tranfsusions at previous and index pregnancies according to IVIG treatment Fetuses were tested by non-invasive fetal RHD, KEL1 or RHc genotyping in case of anti-D (RH1), anti-Kell (KEL1) or anti-c immunization respectively. At first intravascular IUT, they were also tested for ABO, Rh and Kell blood groups in order to confirm fetomaternal incompatibility. In addition, a direct antiglobulin test was performed on fetal blood. In cases 18, 31 and 32, the fetuses were incompatible concerning D, C and S. In case 36, incompatibility could be confirmed only for RHD.Legend: C/S: cesarean section; DOL: days of life; IPT: intraperitoneal fetal transfusion; IUFD: intrauterine fetal death; IUT: intrauterine transfusion; IUT †: intrauterine transfusion followed by intrauterine fetal death; IVIG: Intravenous immunoglobulins; NA: nonavailable; TOP: termination of pregnancy; WG: weeks of gestation

			Previous pregnancy		Index pregnancy
	Patient	Anti-bodies	Event	Gestationnal age at event	Number of IgIV infusions	Gestationnal age at first IUT	Hemo-globin (g/dL)
	1	D	Neonatal death	NA	No	21 WG + 2	8.7
	2	D	IUT	21 WG + 2	No	20 WG + 0	5.6
	3	Kell	IUT and TOP	21 WG + 0	No	17 WG + 5	9.6
	4	D+C	IUT	21 WG + 3	No	25 WG + 0	6.4
	5	D	IUFD	NA	No	17 WG + 0	IPT
	6	D	Neonatal death	24 WG + 0	No	22 WG + 3	4.3
	7	Kell	Neonatal death	NA	No	18 WG + 5	1.3 (IPT)
	8	Kell	IUT †	18 WG + 5	No	15 WG + 5	IPT
	9	D	IUT	22 WG + 6	No	18 WG + 0	4.8
	10	D+E	IUT	18 WG + 0	No	19 WG + 3	2.3
	11	D	IUT	24 WG + 0	No	30 WG + 0	7.0
	12	D	IUT	22 WG + 0	No	22 WG + 6	4.8
	13	D	Neonatal death	NA	No	28 WG + 0	6.4
	14	Kell	IUFD	NA	No	24 WG + 0	7.5
	15	c	Neonatal death	NA	No	24 WG + 5	2.2
	16	D	IUFD	NA	No	27 WG + 2	3.5
	17	D	IUFD	NA	No	28 WG + 3	3.4
	18	D+C+S	IUT †	20 WG + 0	No	21 WG + 5	3.4
	19	D	IUT †	23 WG + 2	No	25 WG + 1	2.6
	20	D+C	Neonatal death	C/S at 34 WG	No	21 WG + 5	3.8
	21	Kell	IUT	25 WG + 4	No	23 WG + 2	5.0
			Neonatal death	C/S at 26 WG
	22	Kell	IUFD	17 WG	8	24 WG + 4	3.9
	23	D+C+G	IUT	18 WG + 0	5	17 WG + 0	IPT
	24	D	Neonatal death	C/S at 34 WG	8	24 WG + 0	5.0
	25	D	IUT †	24 WG + 0	9	26 WG + 0	9.0
	26	D+C	IUT	21 WG + 5	9	20 WG + 0	3.5
	27	D+G	IUT †	19 WG + 6	10	21 WG + 4	3.3
	28	D+C	IUT	21 WG + 0	11	23 WG + 6	6.0
	29	Kell	IUFD	27 WG + 0	18	29 WG + 5	9.9
	30	c	IUT †	21 WG + 1	25	No IUT / transfusion at DOL 14
	31	D+C+S	IUT	21 WG + 5	16	29 WG + 3	9.1
	32	D+C+S	IUT	21 WG + 5	6	18 WG + 2	2.6 (IPT)
	33	D	IUT	20 WG + 0	11	21 WG + 4	3.8 (IPT)
	34	D	IUT	20 WG + 0	13	24 WG + 4	3.8
	35	D	IUT	18 WG + 1	8	20 WG + 1	IPT
	36	D+s	IUT †	18 WG + 0	8	21 WG + 3	3.2
	37	D	IUT	23 WG + 0	24	No IUT / transfusion at DOL 24
	38	D+C+E	Neonatal death	C/S at 32 WG	8	20 WG + 4	7.3
	39	Kell	IUT †	17 WG + 0	9	20 WG + 3	2.6
	40	D+C	IUT	24 WG	15	30 WG + 5	9.0
	41	D+C	IUT	24 WG	21	32 WG + 0	9.0

Ethics

Subjects gave their informed consent and the study protocol was approved by the national committee in obstetrics and gynecology research (CEROG 2019-OBS-1205).

Results

Among the 24 patients treated with IVIG for RBC alloimmunization, 20 patients fulfilled the inclusion criteria. All these pregnancies were D, K or c maternal-fetal incompatible. We excluded 4 patients from the analysis : one patient had a history of IUFD with signs of fetal anemia and hydrops at 38 WG related to severe anti-D alloimmunization, but her previous follow-up was inappropriate (no weekly Doppler examination) ; one patient started IVIG at 11 WG and had a miscarriage at 13 WG ; one intrauterine fetal death occurred at 16 WG, without sign of fetal anemia at ultrasound and without etiology found after thorough evaluation including placental and fetal pathology, extensive biological and bacteriological tests and Kleihauer-Betke test ; one patient had a first IUT at 21 WG (hemoglobin increased from 5.2 to 11.2 g/dL) and then she asked for a termination of pregnancy for Down syndrome diagnosed on fetal blood sampling. The 20 patients treated with IVIG were compared with 21 controls (Figure 1). All the baseline obstetrical and immuno-hematological characteristics were comparable in both groups (Table 1). The fathers were the same in pregnancies in both groups. Only antibodies' quantitation at the beginning of the index pregnancy tended to be higher in the IVIG group: 100 [72 -128] IU/mL and 48 [26 -70] in the control group (p=0.09). Among all the patients presenting with very severe RBC alloimmunization, 33/41 pregnancies resulted in a live birth (80%). Concerning the primary outcome,


MD, PhD Eric Durand
email: eric.durand@chu-rouen.fr

MD Maryline Penso

MD Thibault Hemery

MSc Thomas Levesque

MD a ; Gustavo Moles

MD Christophe Tron

MD a ; Najime Bouhzam

MD Nicolas Bettinger

MD b ; Stephanie Wong

MD, PhD b ; Jean-Nicolas Nicolas Dacher

MD Hélène Eltchaninoff

Standardized Measurement of Femoral Artery Depth by Computed Tomography to Predict Vascular Complications after Transcather Aortic Valve Implantation

Keywords: Aortic valve stenosis, Transcatheter Aortic Valve Implantation, Vascular injuries, Multidetector computed tomography

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INTRODUCTION

Transcatheter aortic valve implantation (TAVI) is currently recommended in patients who are not suitable for surgical aortic valve replacement (SAVR) and in patients who are at increased surgical risk, particularly if patients are suitable for a transfemoral (TF) approach [START_REF] Baumgartner | ESC/EACTS Guidelines for the management of valvular heart disease[END_REF][START_REF] Nishimura | AHA/ACC Focused Update of the 2014 AHA/ACC Guideline for the Management of Patients With Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines[END_REF][START_REF] Popma | Transcatheter Aortic-Valve Replacement with a Self-Expanding Valve in Low-Risk Patients[END_REF][START_REF] Mack | Transcatheter Aortic-Valve Replacement with a Balloon-Expandable Valve in Low-Risk Patients[END_REF]. Major vascular complications (VCs) are feared after TF TAVI given their prognostic impact although they have considerably decreased in recent years with improved patient selection and size reduction of introducers [START_REF] Popma | Transcatheter Aortic-Valve Replacement with a Self-Expanding Valve in Low-Risk Patients[END_REF][START_REF] Mack | Transcatheter Aortic-Valve Replacement with a Balloon-Expandable Valve in Low-Risk Patients[END_REF][START_REF] Généreux | Vascular complications after transcatheter aortic valve replacement: insights from the PARTNER (Placement of AoRTic TraNscathetER Valve) trial[END_REF][START_REF] Steinvil | Vascular complications after transcatheter aortic valve implantation and their association with mortality reevaluated by the valve academic research consortium definitions[END_REF]. Multidetector computed tomography (MDCT) of the ilio-femoral access is currently the gold standard technique to determine the feasibility of a TF approach [START_REF] Blanke | Computed Tomography Imaging in the Context of Transcatheter Aortic Valve Implantation (TAVI)/Transcatheter Aortic Valve Replacement (TAVR): An Expert Consensus Document of the Society of Cardiovascular Computed Tomography[END_REF]. MDCT traditionally evaluates the degree of arterial tortuosity, the extent and localization of calcification (particularly at the puncture site), and the minimal diameter to compute the sheath-to-femoral-artery ratio (SFAR) [START_REF] Francone | CT and MR imaging prior to transcatheter aortic valve implantation: standardisation of scanning protocols, measurements and reporting-a consensus document by the European Society of Cardiovascular Radiology (ESCR)[END_REF]. Among these parameters, it SFAR is considered as the strongest predictive factor of major VCs [START_REF] Hayashida | Transfemoral aortic valve implantation new criteria to predict vascular complications[END_REF][START_REF] Okuyama | Transfemoral access assessment for transcatheter aortic valve replacement: evidence-based application of computed tomography over invasive angiography[END_REF][START_REF] Van Kesteren | Incidence, Predictors, and Impact of Vascular Complications After Transfemoral Transcatheter Aortic Valve Implantation With the SAPIEN 3 Prosthesis[END_REF]. On the other hand, it has been frequently observed that puncture of the femoral artery in obese patients, especially when the artery is deep, is more difficult and increases the risk of VCs [START_REF] Cox | Comparison of the Risk of Vascular Complications Associated With Femoral and Radial Access Coronary Catheterization Procedures in Obese Versus Nonobese Patients[END_REF]. However, to our knowledge, the impact of femoral artery depth (FAD) to predict VCs after TF TAVI has been poorly evaluated. The aim of our study was therefore to assess the impact of FAD on VCs after TF TAVI using a new standardized protocol to measure FAD using MDCT.

METHODS

Between January 2013 and December 2018, 1,411 consecutive patients were prospectively included in our TAVI database. All patients selected by our multidisciplinary team had severe symptomatic aortic stenosis (AS) and gave written informed consent. Patients who had TAVI via a non-femoral route and who did not have CT in our center or when CT was not archived were excluded. The study was approved by our local ethics committee with a waiver for retrospective analysis.

Pre-procedural MDCT examinations were performed either with a 64-slice Discovery 350 HD ® or with a 256-slice Revolution ® CT scanner (both from General Electric Healthcare, Milwaukee, WI, USA). Acquisition protocol was homogeneous and conformed to the recommendations of the Society of Cardiovascular Computed Tomography and the European Society of Cardiovascular Radiology [START_REF] Francone | CT and MR imaging prior to transcatheter aortic valve implantation: standardisation of scanning protocols, measurements and reporting-a consensus document by the European Society of Cardiovascular Radiology (ESCR)[END_REF].

Tube voltage was set at 100 kVp when patient's body mass index (BMI) was less than 25 kg.m -2 and 120 kVp when BMI exceeded 25 kg.m -2 . Sixty milliliters of 350 mgI/mL contrast agent (iohexol or iobitridol) were injected at a flow rate of 4 mL/s pulsed by 20 mL of saline at the same flow rate. Bolus tracking was used. CT scanning of the thorax and abdomen was performed on breath-hold in a craniocaudal direction. Chest scanning was prospectively ECG-gated. ECG was automatically switched off during acquisition for scanning the abdomen and pelvis down to the common femoral artery bifurcation. Cardiac images were not considered in the present study. Sub-millimetric abdominal-pelvic images were reconstructed and transferred to a workstation (ADW Server ® , General Electric Healthcare, Milwaukee, WI, USA) Measurements were performed with the Reformat® tool of the workstation and standardized as follows. To measure FAD, the axial view passing through the center of the femoral heads was first selected (Figure 1). A horizontal line was drawn between the ischial spines. An orthogonal vertical line was drawn from this bi ischiatic line and directed anteriorly. Another orthogonal horizontal line connected the vertical line to the geometric center of the common femoral artery that was used as vascular access for TAVI. Finally, a second vertical line was traced from the center point of the common femoral artery to the skin surface. An experienced examiner processed all measurements retrospectively on the side of the arterial puncture used for TAVI. The same operator reproduced blindly the same measures a second time in 30 random patients to evaluate intra-observer variability. A second experienced examiner performed independently the measures in the same 30 patients to evaluate inter-observer variability. MDCT reports were also reviewed for calcification and tortuosity, and scored, as previously described [START_REF] Francone | CT and MR imaging prior to transcatheter aortic valve implantation: standardisation of scanning protocols, measurements and reporting-a consensus document by the European Society of Cardiovascular Radiology (ESCR)[END_REF]. Briefly, calcification at the puncture site were quantified as follows: 0) absent; 1) < 30% of the circumference of the vessel; 2) 30-50% of the circumference of the vessel; 3) > 50% of the circumference of the vessel; and 4) 100% of the circumference of the vessel or the totality of the anterior wall. The tortuosity of the ilio-femoral axis was also analyzed using a semi quantitative score as follows: 0) no tortuosity; 1) mild tortuosity (30° to 60°); 2) moderate tortuosity (60° to 90°); and 3) severe tortuosity (> 90°). Finally, Iliac and femoral artery diameters were measured. SFAR was obtained by dividing the sheath size (outer diameter) by the minimum ilio-femoral diameter on the access side.

In our center, TAVI procedures have been performed since 2002 [START_REF] Cribier | Percutaneous transcatheter implantation of an aortic valve prosthesis for calcific aortic stenosis: first human case description[END_REF]. The operating team for TF TAVI consists of 5 experienced operators. Prior to the procedure, the decision to perform TAVI was made by a multidisciplinary team. Only if small ilio-femoral vessel diameters and/or vascular abnormalities preclude a transfemoral approach did patients have TAVI via non-femoral access. Oral anticoagulants were stopped 3 to 4 days before the procedure and we did not use a loading dose of clopidogrel. Balloon and self-expandable prostheses were used during this study: SAPIEN XT prosthesis from January 2013 to September 2014 and SAPIEN 3 prosthesis thereafter. For the SAPIEN XT prosthesis, we used a 16-F sheath for the 23-mm valve, an 18-F sheath for the 26-mm valve, and a 20-F sheath for the 29-mm valve. For the SAPIEN 3 prosthesis, we used a 14-F sheath for the 23 and 26 mm valves and a 16-F sheath for the 29-mm valve. During the studied period, first generation Corevalve was used in 2013 with an 18-F sheath. From 2014 to 2017, we used the Corevalve Evolut R with a 14-F sheath, and since 2018, the Corevalve Evolut Pro is preferred with a 16-F sheath.

All the procedures were performed using exclusively local anesthesia ± conscious sedation with access site closure using a single Prostar device (Abbott Vascular, Santa Clara, California, USA) [START_REF] Durand | Transfemoral aortic valve replacement with the Edwards SAPIEN and Edwards SAPIEN XT prosthesis using exclusively local anesthesia and fluoroscopic guidance: feasibility and 30-day outcomes[END_REF]. Angiographic guidance was used for puncture of the common femoral artery. Heparin (70 UI/kg) was administered after sheath insertion. Anticoagulation was measured by activated clotting time with, if necessary, repetitive administration of heparin to achieve a clotting time of 250-300 seconds. Protamine was systematically administered at the end of the procedure before vascular closure. Final angiography was obtained to verify the absence of VCs. Dual antiplatelet therapy was prescribed for one month in patients without indication for anticoagulant. In patients at high risk of bleeding, a single antiplatelet therapy was preferred. In patients with an indication for anticoagulant, vitamin K antagonist or direct oral anticoagulant were used without antiplatelet therapy [START_REF] Durand | Comparison of two antiplatelet therapy strategies in patients undergoing transcatheter aortic valve implantation[END_REF][START_REF] Altisent | Warfarin and Antiplatelet Therapy Versus Warfarin Alone for Treating Patients With Atrial Fibrillation Undergoing Transcatheter Aortic Valve Replacement[END_REF].

VCs were defined according to the updated standardized endpoint definitions for TAVI according to the Valve Academic Research Consortium (VARC-2 criteria) and classified as minor or major [START_REF] Kappetein | Updated standardized endpoint definitions for transcatheter aortic valve implantation: the Valve Academic Research Consortium-2 consensus document[END_REF]. Thirty-day mortality was also recorded.

Quantitative variables were expressed as mean ± SD or median (25th to 75th interquartile range) and compared with the Student t test or Wilcoxon rank-sum test, depending on variable distribution. Correlations were assessed using Spearman's rank correlation coefficient. Qualitative variables were presented as number with percentage and compared with chi-square test or Fisher's exact test. A logistic regression multivariable analysis was used to assess independent correlates of major VCs and the need for a stent-graft. Receiver operator characteristic curves were also used to predict major VCs and the need for a stent-graft. To analyze the SFAR and FAD thresholds that best predicted major VCs and the need for a stentgraft, the intersection of sensitivity and specificity curves was determined with their accompanying positive and negative predictive values. Inter-and intra-observer variabilities were evaluated using Bland-Altman plot and linear logistic regression analysis.

Differences were considered statistically significant at a P value of ≤0.05. All data were analyzed using SPSS software (version 23.0, IBM, Chicago, IL, USA).

RESULTS

The flowchart of the studied population is presented in Figure 2. From January 2013 to December 2018, 1411 patients had TAVI in our center. Among them, 182 (12.9%) patients were excluded because they were implanted via a non-femoral route. An additional 540 (38.3%) TF TAVI patients were excluded because MDCT was performed in another center or was not archived in the picture archiving computerized system (PACS) currently used in our center (Carestream ® , Rochester, NY, USA). Thus, 689 (55.7%) TF TAVI patients were included and represented the studied population.

Baseline characteristics of the studied population are shown in Table 1. The mean age was 83.9 ± 6.0 years and 45.8% of patients were male. The mean logistic EuroSCORE was 15.4 ± 8.9% and all patients had severe symptomatic AS.

MDCT analysis of the ilio-femoral axis is represented in Table 2. The median of FAD was 49.0 (36.2-66.7) mm. Intra-and inter-observer variability of the measurement of the FAD site was evaluated using Bland-Altman analysis (supplemental figure 1). Using linear regression, we observed a good agreement for both analyses. There was a significant correlation between FAD and weight (p<0.0001), BMI (p<0.0001), and body area (p<0.0001) but not with height (p=0.4) (Figure 3). In the studied population, 154 (22.3%) patients had a BMI > 30 Kg/m 2 .

FAD was significantly higher in obese patients than in non-obese patients [73.4 (55.9-93.8) vs. 43.8 (33.7-57.2) mm, p<0.0001].

Moderate or severe tortuosity of the ilio-femoral axis selected for the implantation was observed in 44.6%. No or less than 30% of anterior calcification was observed at the puncture site in the majority of cases (80.7%). The median of the minimal femoral diameter at the puncture site and SFAR were 6.8 (5.9-7.6) mm and 0.95 (0.81-1.18), respectively. The severity of tortuosity and calcification were not significantly different in obese and non-obese patients. In contrast, SFAR was significantly lower in obese than in non-obese patients [0.91 (0.79-1.08) vs. 0.95 (0.82-1.20) mm, p=0.02].

A balloon-expandable valve was used in 88.8%. A 14-F, 16-F, and 20-F sheath was used in 446 (65.1%), 204 (29.8%), and 35 (5.1%) patients, respectively.

During in-hospital follow-up, 105 (15.2%) patients had a VC classified as minor in 68 (9.9%) patients and major in 37 (5.4%) patients. Of note, the incidence of major VC in patients excluded of our study was closely similar (5.5% vs. 5.4%, p=0.92).

The distribution types of vascular complications of the studied population are shown in Figure 4. Most of the VCs were access-related. The most frequent complication was hematoma and 4 patients had a non-access related major VC all related to annulus rupture. A stent-graft was used in 49 (7.1%). In 48 cases, the stent-graft was used for failure of vascular closure device (VCD) and in one case due to iliac rupture. Among patients who need a stent-graft, 25 had a minor VC and 24 had a major VC. Five (0.7%) patients required vascular surgery and all had major VC. Vascular surgery was indicated in 2 cases for persistent bleeding after stent-graft implantation, in 2 cases for evacuation of large hematoma, and in 1 case for acute lower limb ischemia. Obese patients (BMI > 30 kg/m 2 ) required more frequently a stent-graft as compared to those with a BMI < 30 kg/m 2 (13.6% vs. 5.4%, p<0.0001) and the incidence of major VCs was increased, but not significantly different, in obese patients as compared to non-obese patients (7.8% vs. 4.8%, p=0.15). FAD was significantly greater in patients requiring a stent-graft for a VC (P=0.007, Figure 5A). In contrast, minimal femoral diameter and SFAR were not significantly different in patients requiring or not a stent-graft (Figure 5B and5C). The degree of the tortuosity and the extent of calcification at the puncture site were not significantly different in patients requiring or not a stent-graft (P=0.82 and P=0.51, respectively). The incidence of stent-graft increased according to the size of the sheath (P=0.04).

FAD was not significantly different in patients with or without major VCs (Figure 6A). The minimal femoral diameter was not significantly different in patients with or without major VCs (Figure 6B). In contrast, SFAR was significantly higher in patients with than without major VCs (p<0.0001, Figure 6C). The degree of the tortuosity was not significantly different in patients with or without major VCs (P=0.81) but the extent of calcification at the puncture site was significantly greater in patients with than in those without major VCs (P=0.02). The incidence of major VCs increased according to the size of the sheath (P<0.0001).

Predictors of major VCs and the need for a stent-graft were evaluated using multivariate and ROC curve analysis.

After multivariate analysis, FAD was the only predictor of the need for a stentgraft (Table 3) whereas SFAR was the only predictor of major VCs (Table 4) ROC curve analysis for predictors of the need for a stent-graft is shown in Figure 7. The area under the ROC curve for FAD was 0.61 (0.51-0.70, p=0.04) indicating poor accuracy to predict the need for a stent-graft. Other parameters were not significant.

ROC curve analysis for predictors of major VCs is shown in Figure 8. The area under the ROC curve for SFAR was 0.70 (0.58-0.81, p=0.001) and for sheath diameter was 0.66 (0-54-0.78, p=0.006) indicating fair and poor accuracy to predict major VCs, respectively. Other parameters were not significant.

To analyze the FAD that best predicted the need for a stent-graft, sensitivity and specificity curves were composed. The identified intersection point of the 2 curves provided a threshold of 54 mm. The accompanying sensitivity for the threshold was 63.3% with a specificity of 40.9%, a positive predictive value of 4.9%, and negative predictive value of 89.4%.

To analyze the SFAR that best predicted major VCs, sensitivity and specificity curves were also composed. The identified intersection point of the 2 curves provided a threshold of 1.03. The accompanying sensitivity for the threshold was 67.6% with a specificity of 65.2%, a positive predictive value of 9.5%, and negative predictive value of 97.4%.

Interestingly, major VCs were significantly higher in patients who combined a SFAR >1.03 and a FAD >54 mm than in those with a SFAR < 1.03 and a FAD <54 mm (12% vs. 2.1%, p<0.0001). Two examples of low-risk and high-risk patients of VCs according to MDCT analysis of the ilio-femoral access are shown in supplemental figure 2.

The 30-day mortality rate was 8.6% for patients with major VCs and 2.3% for patients without major VCs (P=0.06). The 30-day mortality rate for patients requiring a stent-graft was 4.3% and 2.5% for patients not requiring a stent-graft (P=0.45).

DISCUSSION

We aimed to evaluate a new MDCT parameter (i.e., measurement of FAD), in addition to usual parameters, to predict major VCs and the need for a stent-graft after TF TAVI. The main results can be summarized as follows: 1) FAD measurement using standardized MDCT is easy and reproducible and was significantly increased in patients requiring a stent-graft; 2) FAD was the only predictor of the need for a stent-graft although ROC curve analysis indicated poor accuracy with a threshold value of 54-mm; 3) Among the other usual parameters, SFAR was the only factor with a fair accuracy to predict major VCs.

For a long time now, it has been known that femoral arterial puncture in obese patients, particularly when the artery is deep, is more difficult and the risk of VCs and bleeding is increased [START_REF] Cox | Comparison of the Risk of Vascular Complications Associated With Femoral and Radial Access Coronary Catheterization Procedures in Obese Versus Nonobese Patients[END_REF][START_REF] Benamer | A multicentre comparison of transradial and transfemoral approaches for coronary angiography and PTCA in obese patients: the TROP registry[END_REF]. Surprisingly, it has been reported that major VCs are not significantly increased in obese patients after TF TAVI [START_REF] Généreux | Vascular complications after transcatheter aortic valve replacement: insights from the PARTNER (Placement of AoRTic TraNscathetER Valve) trial[END_REF][START_REF] Hayashida | Transfemoral aortic valve implantation new criteria to predict vascular complications[END_REF][START_REF] Van Kesteren | Incidence, Predictors, and Impact of Vascular Complications After Transfemoral Transcatheter Aortic Valve Implantation With the SAPIEN 3 Prosthesis[END_REF][START_REF] Sannino | Meta-Analysis of Effect of Body Mass Index on Outcomes After Transcatheter Aortic Valve Implantation[END_REF]. We hypothesized that the measurement of FAD, rather than BMI, would be more appropriate to evaluate the risk of major VCs and in particular the risk of failure of VCD, requiring a stent-graft. In our study, we first showed that FAD can be easily and reproducibly measured using CT. Interestingly, FAD was not significantly different in patients with or without major VCs and FAD was not predictive of major VCs. These results are in accordance with those showing that obesity does not increase the risk of major VCs after TF TAVI [START_REF] Généreux | Vascular complications after transcatheter aortic valve replacement: insights from the PARTNER (Placement of AoRTic TraNscathetER Valve) trial[END_REF][START_REF] Hayashida | Transfemoral aortic valve implantation new criteria to predict vascular complications[END_REF][START_REF] Van Kesteren | Incidence, Predictors, and Impact of Vascular Complications After Transfemoral Transcatheter Aortic Valve Implantation With the SAPIEN 3 Prosthesis[END_REF][START_REF] Sannino | Meta-Analysis of Effect of Body Mass Index on Outcomes After Transcatheter Aortic Valve Implantation[END_REF]. However, we observed that FAD was increased in patients requiring a stent-graft and was the only predictive factor of the need for a stent-graft. Of note, most of the stent-grafts were related to the failure of VCD in our study. We therefore hypothesized that the deeper the femoral artery, the greater the risk of failure of VCD. Predictive factors of failure of VCD for coronary angiography and/or PCI using a femoral approach have been reported. Interestingly, obesity was an independent predictors of failure of VCD [START_REF] Vidi | Vascular closure device failure in contemporary practice[END_REF]. Predictive factors of failure of VCD have been evaluated in patients with large arteriotomy for aneurysm repair or TAVI [START_REF] Chen | Factors in ProGlide Vascular Closure Failure in Sheath Arteriotomies Greater than 16 French[END_REF]. In accordance with our studies, the distance between skin and common femoral artery (i.e., FAD) was a strong predictor of failure of VCD [START_REF] Urbach | Computed tomographic angiography-derived risk factors for vascular complications in percutaneous transfemoral transcatheter aortic valve implantation[END_REF]. In order to reduce the risk of failure of VCD requiring a stent-graft in patients with a deep femoral artery, several options are possible. First, the shallowest femoral artery should be selected because FAD is commonly asymmetrical. Second, the lower belly should be pushed upwards and the puncture should be performed in a straight direction, otherwise the insertion of the sheath or preclosure device may become difficult. Third, a preventive crossover balloon occlusion technique may be also used to reduce bleeding in case of failure of VCD in patients presenting with very deep femoral artery [START_REF] Genereux | Clinical outcomes using a new crossover balloon occlusion technique for percutaneous closure after transfemoral aortic valve implantation[END_REF]. On the other hand, a surgical cut down can be also discussed in obese patients but it has been reported that the incidence of major VCs is similar between percutaneous and surgical femoral approaches [START_REF] Bernardi | Surgical cutdown versus percutaneous access in transfemoral transcatheter aortic valve implantation: insights from the Brazilian TAVI registry[END_REF]. Finally, alternative accesses (e.g. trans-carotid, trans-subclavian, trans-apical) should be privileged in patients with multiple elements unfavorable for femoral approach.

We also assessed the impact of other MDCT parameters to predict VCs after TAVI. In our study, the degree of ilio-femoral tortuosity and the extent of calcification at the puncture site were neither predictive of major VCs nor the need for a stentgraft. In all the studies, the degree of ilio-femoral tortuosity was not an independent predictor of major VCs after TAVI [START_REF] Hayashida | Transfemoral aortic valve implantation new criteria to predict vascular complications[END_REF][START_REF] Van Kesteren | Incidence, Predictors, and Impact of Vascular Complications After Transfemoral Transcatheter Aortic Valve Implantation With the SAPIEN 3 Prosthesis[END_REF]. On the other hand, conflicting results were obtained for the extent of calcification at the puncture site [START_REF] Hayashida | Transfemoral aortic valve implantation new criteria to predict vascular complications[END_REF][START_REF] Van Kesteren | Incidence, Predictors, and Impact of Vascular Complications After Transfemoral Transcatheter Aortic Valve Implantation With the SAPIEN 3 Prosthesis[END_REF]. We believe that calcification was not predictive in our study since patients with circumferential or anterior calcification at the puncture site had systematic TAVI via a non-femoral approach.

Our study confirmed that SFAR remains the strongest predictor of major VCs after TF TAVI although the area under the ROC curve is variable among the studies and its positive value is low to predict VCs [START_REF] Hayashida | Transfemoral aortic valve implantation new criteria to predict vascular complications[END_REF][START_REF] Okuyama | Transfemoral access assessment for transcatheter aortic valve replacement: evidence-based application of computed tomography over invasive angiography[END_REF][START_REF] Van Kesteren | Incidence, Predictors, and Impact of Vascular Complications After Transfemoral Transcatheter Aortic Valve Implantation With the SAPIEN 3 Prosthesis[END_REF]. However, to our knowledge, we are the first to evaluate the impact of SFAR on the need for a stent-graft. SFAR was not significantly different in patients with or without a stent-graft and FAD was the only predictive factor. We therefore believe that SFAR and FAD provide additional information and that FAD could be systematically and easily assessed during MDCT in order to evaluate the feasibility of a TF approach before TAVI. This analysis was retrospectively conducted in a prospectively acquired singlecenter, nonrandomized cohort with inherent limitations related to its design. Therefore, we were only able to identify correlations and not prove any causality.

Additionally, although it represents a real-world situation with inclusion of approximately 700 patients, the number of major VCs was relatively low (7.5%) and the results should be confirmed in a larger population. Furthermore, we excluded about 40% of the patients for whom MDCT was not archived in the PACS currently used in our center. It is therefore possible that this could have resulted in a selection bias. Finally, our results were obtained using preclosing with Prostar device and could not be extrapolated with other VCD.

In conclusion, the results of our study show that FAD measurement is easy and reproducible and can be performed during MDCT assessment of ilio-femoral vessels, before TAVI. Based on our findings, we suggest that FAD is an independent predictor of the need for a stent-graft for VC after TF TAVI. Further studies are needed to confirm our results prospectively and in a larger population. First, a horizontal line was drawn between the ischial spines (green line). An orthogonal vertical line (green line) was drawn from this bi-ischiatic line and directed anteriorly. Another orthogonal horizontal line (pink) connected the vertical line to the geometric center of the common femoral artery that was used as a vascular access (the right one in the present case). Finally, a second vertical line (blue) was traced from the center point of the common femoral artery to the skin surface.

Figure 1 .

 1 Figure 1. Axial CT slice passing through the geometric center of the femoral heads.

Figure 2 .Figure 3 .

 23 Figure 2. Study flow chart

Figure 4 .

 4 Figure 4. Distribution types of vascular complications. The rates of all vascular

Figure 5 .

 5 Figure 5. Scatter box plot of femoral artery depth (A), minimal femoral diameter (B),

Figure 6 .Figure 7 .

 67 Figure 6. Scatter box plot of femoral artery depth (A), minimal femoral diameter (B),

Figure 8 .

 8 Figure 8. ROC curve analysis of SFAR (blue), femoral artery depth (green),

Table 1 .

 1 Baseline characteristics

	Characteristics

Table 2 .

 2 Computed Tomography analysis of the ilio-femoral axis.

	Characteristics	Overall Population
		(N=689)
	Tortuosity
	-Absent or mild	381 (55.3%)
	-Moderate	247 (35.8%)
	-Severe	61 (8.8%)
	Calcium
	-Absent	184 (26.7%)
	-< 30%	372 (54.0%)
	-30-50%	110 (16.0%)
	-> 50%	23 (3.3%)
	Minimal femoral diameter (mm)	6.8 (5.9-7.6)
	Femoral artery depth (mm)	49.0 (36.2-66.7)
	SFAR	0.95 (0.81-1.18)
	Abbreviations. SFAR: sheath-to-femoral-artery ratio

Table 3 . Predictors of the need for a stent graft

 3

	Variables	HR	CI 95%	P
	SFAR	0.77	0.14-4.34	0.77
	Tortuosity	1.01	0.60-1.71	0.97
	Calcification	0.81	0.50-.32	0.40
	Sheath diameter	1.23	0.93-.64	0.15
	Minimal femoral diameter	0.96	0.65-1.41	0.83
	Femoral artery depth	1.02	1.00-1.04	0.048
	Abbreviations. SFAR: sheath femoral artery ratio

Table 4 . Predictors of major vascular complications

 4

	Variables	HR	CI95%	P
	SFAR	8.86	1.42-55.24	0.02
	Tortuosity	0.64	0.32-1.28	0.21
	Calcification	1.00	0.58-1.73	0.99
	Sheath diameter	1.09	0.80-1.49	0.58
	Minimal femoral diameter	1.32	0.81-2.14	0.26
	Femoral artery depth	1.00	0.98-1.02	0.86

Abbreviations. SFAR: sheath femoral artery ratio

ACKNOWLEDGMENTS

The authors are grateful to Nikki Sabourin-Gibbs for her help in editing the manuscript.

SOURCES OF FUNDING

None

DISCLOSURES

Hélène Eltchaninoff has received lecture fees and is proctor for Edwards Lifesciences. Eric Durand has received lecture fees from Edwards Lifesciences. Helène Eltchaninoff and Eric Durand have received a grant by the French Government, managed by the National Research Agency (ANR) under the program "Investissements d'avenir" with the reference ANR-16-RHUS-0003"