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  • Computed tomography (CT) assessment of the membranous septal anatomy prior to transcatheter aortic valve replacement (TAVR) with the balloon-expandable SAPIEN 3 valve

    • Posted: 09/12/2018
    • Author:

      Brett A. Oestreich, Mackenzie Mbai, Sergey Gurevich, Prabhjot S. Nijjar, Selcuk Adabag, Stefan Bertog, Rosemary Kelly and Santiago Garcia

    • CRM2018

    Abstract

    Objectives

    The lower limit of the membranous septum (MS) is considered an anatomic landmark for the emergence of the Bundle of His into the left ventricle. Computed tomography (CT) assessment of MS anatomy may provide useful information about the risk of conduction abnormalities following transcatheter aortic valve replacement (TAVR).

    Methods and results

    The study included 102 consecutive patients undergoing TAVR with the Edwards Sapien 3 (S3) valve. Using pre-TAVR CT and post-procedure angiography we evaluated for the presence of calcium in the left ventricular outflow tract (LVOT), calcium depth (CD), implantation depth (ID) and MS length. The MS length minus the prosthesis ID was calculated (Delta MSID). Outcomes included new left bundle branch block (LBBB) or permanent pacemaker (PPM) within 30 days. Seventeen patients (17%) received a PPM and 28 (27%) developed new LBBB following TAVR. Mean (± SD) MS length and delta MSID were 7.5 mm (2) and 0.9 mm (4.5), respectively. Twenty-one patients (20%) had calcium in the device landing zone and the mean (SD) CD was 6.8 mm (± 4). Calcium in the device landing zone (37% versus 16%, p = 0.02) and implantation depth (6 mm (4–8) versus 4 mm (4–5), p = 0.02) predicted new conduction abnormalities after TAVR.

    Conclusions

    The presence of calcium in the device landing zone is associated with increased risk of conduction abnormalities after TAVR with S3. In such cases, a more aortic deployment of the prosthesis may be warranted.

    Highlights

     

    • • 

      Pre-procedure CT assessment of the interventricular septum may aid in procedural planning prior to TAVR.

    • • 

      Calcium at the membranous septum landing zone is associated with increased risk of conduction abnormalities after TAVR.

    • • 

      Membranous septum length did not predict conduction abnormalities which may be due to a more aortic implantation depth in our cohort.

     

    1

    Introduction

    Conduction abnormalities and the need for permanent pacemaker (PPM) implantation remain a significant problem following transcatheter aortic valve replacement (TAVR), and the only complication that appears to be increasing in incidence  . Conceptually, the development of conduction abnormalities after TAVR results from the interplay of patient, valve, and procedural characteristics  .

    Contrast-enhanced multidetector computed tomography (CT) is the preferred method for assessing the aortic valvular complex anatomy prior to TAVR  . More recently, CT assessment of the membranous septum (MS) and left ventricular outflow tract (LVOT) anatomy has been shown to provide useful information about the risk of atrioventricular (AV) block  . The lower limit of the MS is considered an anatomic landmark for the emergence of the Bundle of His into the left ventricle  . Damage to this structure during deployment of the transcatheter heart valve, principally due to its high radial force, is thought to be the main reason for AV conduction abnormalities during TAVR  .

    The objective of this study was to identify CT predictors of AV conduction abnormalities and PPM requirement after TAVR with the balloon-expandable Edwards SAPIEN 3 prosthesis (S3, Edwards Lifesciences, Irvine, CA). We hypothesized that the presence of calcium in the LVOT in addition to shorter membranous septal length, as detected on contrast-enhanced multidetector CT, will predict conduction abnormalities and need for PPM implantation following TAVR with S3 valve.

    2

    Methods

    2.1

    Study population

    One hundred thirty-five consecutive patients with symptomatic severe aortic stenosis undergoing TAVR with the S3 prosthesis between August 2015 and November 2016 at 2 academic hospitals were studied. After excluding 17 patients with prior pacemaker or implantable cardioverter-defibrillator, 5 patients undergoing valve-in-valve procedure, 3 patients with baseline left bundle branch block on resting electrocardiogram, and 8 patients who did not undergo CT prior to TAVR, there were 102 patients included in the study.

    Baseline demographic and clinical information was recorded along with procedural outcomes. Information relating to new conduction abnormalities or need for PPM insertion within the first 30 days following TAVR was also recorded. The study was approved by the institutional review board at each hospital.

    2.2

    CT acquisition protocol

    CT scan protocols were standardized as defined by the Society for Cardiac Computed Tomography  . Thin section, electrocardiogram (ECG)-gated contrast enhanced, multidetector CT of the heart, aortic root, aorta, and iliofemoral vessels was performed on one of two CT imaging platforms: Siemens Dual Source Flash CT scanner, Siemens Medical Solutions, Malvern, PA, and 320-detector row volume CT scanner, Aquilion One; Toshiba Medical Systems, Otawara, Japan. When appropriate, beta blockade was administered to achieve optimal heart rate control (target heart rate < 60 beats per minute). Real-time bolus tracking was utilized to trigger image acquisition and biphasic iodinated contrast injection of 100–140 ml was given at an infusion rate of 5–6 cm 3 /s. Scanning protocols incorporated tube voltage and current adaptations for body mass index to minimize radiation exposure. For the dual source CT scanner, a contrast-enhanced prospectively, ECG-triggered axial scan with a wide acquisition window was performed for heart rates < 60 bpm. For higher heart rates, a retrospective, ECG-gated spiral acquisition CT angiogram of the heart was performed. This was immediately followed by a high pitch spiral CT angiogram of the chest, abdomen, and pelvis to evaluate the thoracoabdominal aorta and iliac vasculature. For the volume CT scanner, a prospectively ECG-triggered volume CT of the heart was performed immediately followed by a helical CT angiogram of the chest, abdomen, and pelvis to evaluate the thoracoabdominal aorta and iliac vasculature. CT images were reconstructed as appropriate for each scanner with limited field of view for the heart, minimum slice thickness, and slice increments of 50% of the slice width used .

    2.3

    CT data analysis

    The reconstructed CT datasets were transferred to one of two dedicated workstations (Aquarius iNtuition 4.4, TeraRecon, Foster City, CA, USA, or Vitrea 6.0; Vital Images, Minnetonka, MN) to allow for post-processing. The reconstructed CT datasets in the best systolic phase (usually 30 or 40% of the R-R interval) were used for data analysis. 

    Fig. 1
    A. Basal septal calcification identified on computed tomography.
    Contrast-enhanced multidetector computed tomography of the aortic root and left ventricular outflow tract demonstrating basal septal calcification (blue arrow). The calcium is measured from the annular plane (red dashed line) to the most inferior portion of the calcium (green dashed line) giving a calcium depth of 4.2 mm.
    B. Membranous septum measurement on computed tomography.
    Contrast-enhanced multidetector computed tomography of the aortic root in the double-oblique view demonstrating the junction between the membranous and the muscular interventricular septum (blue arrow). Membranous septal length is measured from this junction of the annular plane (red dashed arrow) to the most inferior edge of the membranous septum (green dashed line) and measures 7.3 mm.

     

    Measurements of the virtual aortic basal ring were obtained using double-oblique images created from standard coronal, sagittal and transverse views as previously described by Achenbach et al. and others  . To confirm the plane was at the level of the basal leaflet attachments, the leaflet nadirs had to disappear or appear simultaneously when the transverse plane was moved inferior or superiorly. The LVOT was examined for the presence of calcium in the basal ventricular septum within the possible device landing zone defined as the interventricular septum below the right and non-coronary cusps and extending from the virtual aortic basal plane to a depth of 10 mm within the LVOT. If calcium was identified, its depth was measured from the virtual aortic annular plane to the most inferior portion of the calcification in the oblique coronal view ( Fig. 1 A). Using this same view, the membranous septal length was measured as the distance from the aortic annular plane to the most superior portion of the muscular interventricular septum ( Fig. 1 B). A detailed, step-by-step description of how MS length was measured in our study is presented in the supplementary appendix ( Supplemental Fig. 1 ).

    2.4

    Transcatheter aortic valve replacement

    All patients underwent careful evaluation prior to TAVR by a dedicated heart team consisting of cardiologists, interventional cardiologists and cardiothoracic surgeons. Procedures were performed in a hybrid operating room under general anesthesia or conscious sedation. All patients received the Edwards SAPIEN 3 prosthesis in the sizes 20 mm, 23 mm, 26 mm, or 29 mm. Valve sizing was based on CT-derived area of the aortic annulus with additional information from echocardiographic and angiographic studies when necessary. Implantation depth (ID) was determined by reviewing cineangiograms after valve deployment. It was defined as the distance from the native aortic annulus to the lowest edge of the S3 prosthesis in the LVOT ( Fig. 2 ). We measured ID for the non-coronary and left-coronary cusps. The MS length minus the prosthesis ID (delta MSID) was calculated. The primary outcome was new left bundle branch block and/or new PPM within 30 days of the TAVR procedure. The decision to implant a PPM following TAVR was left up to the discretion of the heart team in consultation with cardiac electrophysiologists. 

    Fig. 2
    Cineangiogram of the TAVR prosthesis performed in the implant angle. Implant height is measured from the aortic annulus (red dashed line) to the inferior border of the stent frame (green dashed line) on the non-coronary cusp side. Implant height in this patient is 9.2 mm.

     

    2.5

    Statistical analysis

    Continuous variables are presented as mean ± SD or as median with interquartile range. Categorical variables are reported as frequencies and percentages. Continuous variables were compared using the unpaired Student t- test or Mann-Whitney U test as appropriate. Discrete variables were compared with the chi-square test or Fisher exact test as appropriate. Delta MSID was analyzed as a continuous variable and as a dichotomous variable using 0 mm as a cutoff. A delta MSID < 0 mm would indicate complete overlap of the membranous septum by the TAVR prosthesis. A 2-sided p value < 0.05 was considered to be statistically significant. Medcalc® version 17.2 statistical software was used.

    3

    Results

    The mean age (± SD) of patients was 79 (8) years and 88% were male. The median Society of Thoracic Surgeons (STS-PROM) score was 5.6 (IQR 3-8).Baseline patient characteristics were similar among groups ( Table 1 ). Eighty percent of patients underwent transfemoral access and no difference in conduction abnormality or PPM implantation was seen based on access site ( Table 2 ). The 29 mm valve size was most frequently used (42%) followed by 26 mm (41%). In total, 17 patients (17%) received a PPM and 28 (27%) developed a new left bundle branch block (LBBB) following TAVR ( Table 3 ). Indications for PPM implantation included complete heart block (n = 13), LBBB with abnormal electrophysiology study ( n = 2), and tachy-brady syndrome ( n = 2). 

    Table 1
    Baseline characteristics.
     All ( n = 102)PPMI or LBBB ( n= 40)No PPMI or LBBB (n = 62)PvaluePPMI ( n = 17)No PPMI ( n= 85)Pvalue
    Age (mean) years (± SD) 79 (8) 79 (9) 80 (7) 0.80 78 (9) 80 (8) 0.32
    Male (%) 90 (88%) 34 (85%) 56 (90%) 0.41 16 (94%) 74 (87%) 0.41
    STS score (median-IQR) 5.6 (3–8) 6.4 (4–9) 5.2 (3–8) 0.16 5.6 (2–9) 5.6 (3–8) 0.79
    HTN (%) 74 (72%) 33 (82%) 41 (66%) 0.07 13 (76.5%) 61 (71%) 0.69
    Diabetes (%) 38 (37%) 17 (43%) 21 (34%) 0.48 6 (35%) 32 (37%) 0.64
    Previous CABG (%) 29 (28%) 14 (35%) 15 (24%) 0.23 6 (35%) 23 (27%) 0.49
    Previous stroke (%) 15 (14%) 6 (15%) 9 (14.5%) 0.94 3 (17%) 12 (14%) 0.70
    COPD (%) 44 (43%) 15 (38%) 29 (47%) 0.81 9 (53%) 35 (41%) 0.80
    Home O2 (%) 12 (11%) 4 (10%) 8 (13%) 0.65 3 (17%) 9 (10%) 0.41
    Baseline ECG              
    Atrial fibrillation 38 (37%) 18 (45%) 20 (32%) 0.19 10 (58%) 28 (32%) 0.04
    1st degree AV block 12 (12%) 5 (12.5%) 7 (11%) 0.22 3 (17) 9 (10%) 0.41
    RBBB 13 (12%) 6 (15%) 7 (11%) 0.58 6 (35%) 7 (8%) 0.002
    LAFB 5 (5%) 2 (5%) 1 (1.6%) 0.22 1 (5%) 5 (5%) 0.90
    PPMI: permanent pacemaker implantation, LBBB: left bundle branch block, STS: Society of Thoracic Surgeons, IQR: interquartile range, HTN: hypertension, CABG: coronary artery bypass graft, COPD: chronic obstructive pulmonary disease, O2: oxygen, ECG: electrocardiogram, AV: atrioventricular, RBBB: right bundle branch block, LAFB: left anterior fascicular block.
    Table 2
    Procedural characteristics.
     All ( n = 102)PPMI or LBBB (n = 40)No PPMI or LBBB (n = 62)PvaluePPMI ( n= 17)No PPMI ( n= 85)Pvalue
    Access site
    Transfemoral n-% 81 (80%) 30 (75%) 51 (82%) 0.37 13 (76%) 68 (80%) 0.74
    Transapical n-% 10 (9.8%) 5 (12%) 5 (8%) 0.46 3 (17%) 7 (8%) 0.23
    Transaortic/subclavian n-% 11 (10.2%) 5 (12%) 6 (8%) 0.65 1 (6%) 10 (11%) 0.47
     
    Valve size (mm)
    20 mm n-% 1 (1%) 0 1 (1%) 1.00 0 (0%) 1 (1%) 1.00
    23 mm n-% 16 (16%) 6 (15%) 10 (16%) 0.87 1 (6%) 15 (17%) 0.22
    26 mm n-% 42 (41%) 13 (32%) 29 (47%) 0.15 6 (35%) 36 (42%) 0.59
    29 mm n-% 29 (42%) 21 (52%) 22 (35%) 0.09 10 (59%) 33 (38%) 0.12
    Area oversizing (%) 
    Mean (± SD) a    		 6 (± 13) 6 (± 12) 5 (± 14) 0.82 9 (± 9) 5 (± 14) 0.29
    PPMI: permanent pacemaker implantation, LBBB, left bundle branch block.

    a Percentage oversizing = (THV nominal area/MCT annular area-1) × 100. (may be positive or negative percentage).

    Table 3
    CT characteristics of patients according to whether they required a permanent pacemaker (PPM) implantation or developed a new LBBB following TAVR.
     All ( n = 102)PPMI or LBBB ( n = 40)No PPMI or LBBB ( n = 62)PvaluePPMI (n = 17)No PPMI ( n= 85)Pvalue
    Minimal diameter (mm) - mean (± SD) 22 (± 2) 22 (± 2) 23 (± 2) 0.58 23 (± 1) 22(± 2) 0.53
    Maximal diameter (mm) - mean (± SD) 28 (± 2) 28 (± 2) 28 (± 2) 0.64 29 (± 2) 28 (± 2) 0.20
    Area (mm2) - mean (± SD) 514 (92) 523 (± 80) 508 (± 100) 0.44 528 (± 63) 511 (± 97) 0.50
    Membranous septum length (mm) - mean (± SD) 7.5 (± 2) 7.9 (± 2) 7.2 (± 2) 0.20 7.9 (± 2) 7.3 (± 2) 0.40
    Membranous septal length – Implantation depth (MSID) (mm) - mean (± SD) a 0.9 (± 4.5) 0.5 (± 4) 1.1 (± 4) 0.48 1 (± 4) 0.8 (± 4) 0.91
    Calcium in basal septum/LVOT(%) 21 (20%) 11 (29%) 10 (17%) 0.19 4 (25%) 17 (21%) 0.76
    LVOT calcium length (mm) - mean (± SD) 6.8 (4) 8 (± 3) 5 (± 4) 0.24 8 (± 3) 6.5 (± 4) 0.45
    Implantation depth (mm) NCC 
    Median–IQR    		 4.9 (3.9–7.6) 5 (4–9) 4 (3–6) 0.03 5 (4–9) 4 (3–7) 0.21
    Implantation depth (mm) LCC 
    Median–IQR    		 4.80 (3.60–6.80) 5 (3–8) 4 (3–6) 0.28 5 (3–8) 4 (3–6) 0.83
    PPMI: permanent pacemaker implantation, LBBB: left bundle branch block, LVOT: left ventricular outflow tract, NCC: non-coronary cusp, LCC: left coronary cusp.

    a MSID: Membranous septal length – implantation depth (NCC).

     

    3.1

    Baseline electrocardiogram

    Patients were more likely to require PPM implantation if they had baseline atrial fibrillation (58% vs 32%, p = 0.04) or right bundle branch block (35% vs 8%, p = 0.002) ( Table 1 ). There were no significant differences in the rate of PPM implantation or the composite of LBBB or PPM implantation in patients with first-degree atrioventricular block ( p = 0.41 and 0.22, respectively) or left anterior fascicular block ( p = 0.90 and 0.22, respectively).

    3.2

    CT characteristics

    The mean (± SD) dimensions (minor and major) and area of the native aortic valve annulus were 22 mm (± 2), 28 mm (± 2), and 514 mm2 (± 92), respectively.

    Twenty-one (20%) patients had calcium in the LVOT. Among patients with LVOT calcification, the mean extension from the aortic annulus into the LVOT or calcium depth was 6.8 mm (± 4). Patients with calcium in the basal ventricular septum were more likely to develop LBBB following TAVR (37% vs 16%, p = 0.02). However, the depth of such calcium in the LVOT did not predict LBBB (7 ± 3 vs 6 ± 4 mm, p = 0.49) ( Table 3 and Table 4 ). There was no difference in the rate of PPM implantation with basal ventricular septal calcium ( p = 0.76). 

    Table 4
    CT characteristic of patients according to the presence of new LBBB following TAVR.
     LBBB (28)No LBBB (74)P value
    Minimal diameter (mm) - mean (± SD) 22 (2) 23 (2) 0.39
    Maximal Diameter (mm) - mean (± SD) 29 (6) 28 (2) 0.18
    Area (mm2) - mean (± SD) 526 (86) 509 (95) 0.42
    Membranous Septum length (mm) - mean (± SD) 7.8 (3) 7.3 (2) 0.47
    Membranous septal length – Implantation Depth (MSID) (mm) - mean (± SD) a 0.05 (5) 1.24 (4.2) 0.24
    Calcium in basal septum/LVOT (%) 10 (37%) 11 (16%) 0.02
    LVOT calcium depth (mm) mean (± SD) 7 (3) 6 (4) 0.49
    Area Oversizing (%) 
    Mean (± SD) b    		 4 (14) 6 (13) 0.57
    Implantation depth (mm) NCC 
    Median–IQR    		 6 (4–8) 4 (4–5) 0.02
    Implantation depth (mm) LCC 
    Median–IQR    		 5 (4–8) 4 (3–7) 0.44
    LBBB: left bundle branch block, LVOT: left ventricular outflow tract, NCC: non-coronary cusp, LCC: left coronary cusp.

    a MSID: Membranous septal length – implantation depth.

    b Percentage oversizing = (THV nominal area/MCT annular area-1) × 100. (may be positive or negative percentage).

     

    The mean (± SD) MS length in the cohort was 7.5 mm (2). No differences were noted in MS length among patients who developed a new LBBB or PPM versus those who did not (7.9 mm (± 2) versus 7.2 mm (± 2), p = 0.20) (Tables 3,4 ). The incidence of LBBB or PPM among different quartiles of MS is presented in Fig. 3 ( p = NS). 

    Fig. 3
    Incidence of new LBBB or PPM according to quartiles of MS length (black) and MSID (grey).

     

    3.3

    Procedural characteristics

    Greater implantation depth into the LVOT was more likely to cause LBBB (6 mm (IQR:4–8) vs 4 mm (IQR:4–5),p = 0.02) and the composite of LBBB and PPM (5 mm (IQR:4–9) vs 4 mm (IQR:3–6), p = 0.03) ( Table 3 andTable 4 ). The incidence of LBBB or PPM among different quartiles of ID is presented in Fig. 4 . The highest quartile of ID had an incidence of new LBBB or PPM of 62% ( p = 0.04). Among patients with calcium in the basal ventricular septum, the incidence of new LBBB or PPM was 72% in the highest quartile of ID and < 10% for the other ID quartiles ( Fig. 5 ). 

    Fig. 4
    Incidence of new LBBB or PPM according to quartiles of implantation depth.
    Fig. 5
    Incidence of new LBBB or PPM according to quartiles of implantation depth among patients with LVOT calcium below NCC.

     

    The mean (± SD) delta MSID was 0.9 mm (4.5). There was significant overlap in delta MSID among patients that developed a new LBBB or required a PPM after TAVR and those who did not (0.5 mm (4) versus 1.1 mm (4) ( p = 0.48) ( Table 3 and Fig. 5 ). When delta MSID was dichotomized, we found a non-significant trend toward more PPM and LBBB among patients with a negative delta MSID (57% versus 42%, p = 0.17). The mean (± SD) amount of prosthesis oversizing relative to the aortic annulus area was 6% (12). There was no statistical difference in area oversizing among patients that required PPM implantation (9 ± 9 vs 5 ± 14 mm, p = 0.29), developed a new LBBB (4 ± 14 vs 6 ± 13 mm, p = 0.57), or the composite of PPM or LBBB (6 ± 12 vs 5 ± 14 mm,p = 0.82) ( Table 3 ).

    4

    Discussion

    The aim of this study was to investigate whether anatomical characteristics of the membranous septum seen on pre-TAVR CT would predict conduction abnormalities and the need for PPM implantation following TAVR. Specifically, we examined calcium in the basal ventricular septum and the length of the membranous interventricular septum. We found that calcium in the basal septum is present in 1 out of 5 patients undergoing TAVR and is predictive of new conduction abnormalities. In such cases, a more aortic deployment of the prosthesis may be warranted since 3 out of 4 patients who developed a new LBBB or required a PPM in this group were in the highest ID quartile (ID > 7.6 mm). Conversely, the risk of new conduction abnormalities was < 10% with ID < 7.6 mm (quartiles 1–3). Therefore, anatomical characteristics seen on pre TAVR CT may result in procedural modifications that can mitigate the risk of conduction abnormalities.

    We found a 15% absolute difference in rates of PPM and LBBB with negative (< 0 mm) delta MSID values, but these differences did not reach statistical significance for the association of MS length or delta MSID with conduction abnormalities or the need for PPM implantation. We believe there are several possible explanations for this finding which may be at variance with previously published literature  . First, while manually obtaining double oblique views as described has the advantage of demonstrating the true long axis of the LVOT, measuring the MS like we did in our study, from the virtual aortic basal ring to the inferior edge of the membranous septum, has the disadvantage that it may underestimate the true length of the membranous septum. Second, due to a small sample size the study might have lacked statistical power to demonstrate a true association between MS length and conduction abnormalities. Finally, prior studies have shown that the risk of PPM implantation with the Edwards SAPIEN 3 valve can be reduced by utilizing a higher, or more aortic, implant height  . One small study suggested implanting the S3 valve no deeper than 8 mm into the LVOT while a larger study suggested maintaining an aortic percentage > 70%  . The median implant depth in our study was more aortic than in previous studies (76% aortic or 4.9 mm of stent frame in the LVOT with an interquartile range of 3.9–7.6 mm). Thus, the higher implant height in our study may have decreased the interaction between the valve and conduction system and reduced the effects of short MS length and delta MSID on the risk of PPM implantation. It should be noted that the interaction of ID and the outcome of PPM or LBBB was significant for the non-coronary cusp but not the left coronary cusp. This further suggests importance of the LVOT anatomy below the non-coronary cusp (i.e. the membranous septum) in the role of conduction abnormalities following TAVR.

    Conduction disturbances following TAVR are thought to occur from direct compression of the conduction system by the TAVR prosthesis  . While such compression may occur anywhere along the interface of the prosthesis and conduction system, it is most likely to occur where the bundle of His emerges into the left ventricular outflow tract which has been demonstrated to be where the interventricular membranous septum meets the muscular septum  . Several factors including baseline conduction abnormalities, LVOT anatomy, and procedural outcomes such as valve size and implant depth combine to varying degrees to affect the interaction between the valve and conduction system  . Thus being able to balance all of these variables becomes crucial in minimizing the risk of conduction abnormalities.

    In a prior study of primarily self-expanding TAVR prostheses (Medtronic CoreValve, Medtronic, Minneapolis, MN, USA) Hamdan et al. found that shorter membranous septal length was associated with increased need for PPM implantation  . In the study by Hamdan et al., there was a statistically significant between MS and implantation depth (delta MSID) between patients who did and did not receive PPM following TAVR (− 1.2 ± 4.2 mm vs 3.7 ± 4.3 mm, p < 0.001)  . Implant depth is accepted to be an important risk factor for PPM following CoreValve  .

    Maeno et al. recently showed that shorter MS length predicted PPM implantation following TAVR with the SAPIEN 3 valve  . One possible explanation for the observed differences in outcomes from our study could be differences in procedural factors including ID and the degree of prosthesis oversizing  . While it is difficult to definitively prove this theory without analyzing patient-level data it does appear that the ID was, in general, more ventricular in the group of patients from Maeno (mean ID 7 ± 2.3 mm in PPM group vs 5.2 ± 1.3 mm in the no PPM group) compared to our study (5 mm (IQR: 4–9) in the PPM group versus 4 mm (IQR: 3–7) in the no PPM group, p = 0.21). While the study by Maeno et al. emphasizes the importance of MS length in regards to PPM implantation, our study finds that this factor may be modifiable with a more aortic deployment.

    4.1

    Limitations

    Our study highlights several key issues regarding conduction abnormalities following TAVR with several limitations. While our principal finding of an increased rate of LBBB in patients with calcium in the basal interventricular septum undergoing TAVR with the S3 valve is notable, we showed a numerical but not statistically significant association of the interaction between membranous interventricular septum length and conduction abnormalities. The reasons for these differences may be multifactorial and include different measurements techniques of the MS length, TAVR implantation practices, and small sample size (type II error). We chose the oblique coronal view because it shows the true long axis of the LVOT, but it also may underestimate the MS length when measured from the virtual basal ring to the inferior border of the membranous septum. It should be noted that the membranous septum is a three dimensional (3D) structure and none of the measurements truly captures the 3-D essence of the MS anatomy.

    5

    Conclusions

    Assessment of the membranous septal anatomy prior to transcatheter aortic valve replacement with a balloon expandable valve provides information about the risk of AV conduction abnormalities after TAVR. The presence of calcium in the device landing zone increases the risk of AV conduction abnormalities. In such cases, a more aortic deployment of the prosthesis may be warranted.

    The following is the supplementary data related to this article. Supplemental Fig. 1

    Detailed description of membranous septum measurement by computed tomography.

    Author bio

    Cardiovascular Revascularization Medicine, 2018-07-01, Volume 19, Issue 5, Pages 626-631, Copyright © 2017

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