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The effect of aortic valve replacement on three-dimensional (3D) mitral annular geometry has not been well-described. Emerging transcatheter approaches for aortic valve replacement employ fundamentally different mechanical techniques for achieving fixation and seal of the prosthetic valve than standard surgical aortic valve replacement. This study compares the immediate impact of transcatheter aortic valve replacement (TAVR) and standard surgical aortic valve replacement (AVR) on mitral annular anatomy.
Real-time 3D echocardiography was performed in patients undergoing TAVR using the Edwards Sapien® valve (n=10) or AVR (n=10) for severe aortic stenosis. Mitral annular geometric indexes were measured using Tomtec EchoView to assess regional and global annular geometry.
Mixed between-within ANOVA showed no differences between TAVR and AVR groups in any of the mitral annular geometric indices pre-operatively. However, post-operative analysis did demonstrate an effect of AVR on geometry. Patients undergoing open AVR had significant decrease in annular height, septolateral diameter, mitral valve transverse diameter and mitral annular area after valve replacement (P≤.006). Similar changes were not noted in the TAVR group.
TAVR preserves mitral annular geometry better than AVR. Thus, TAVR may be a more physiological approach to aortic replacement.
Surgical aortic valve replacement (AVR) is the established therapy for symptomatic aortic stenosis; however, transcatheter aortic valve implantation (TAVR) has recently been shown to demonstrate acceptable early and intermediate outcomes in high risk patients with symptomatic severe aortic stenosis. [1–3] The effect of either technique for aortic valve replacement on mitral valve three-dimensional (3D) anatomy has not been described.
TAVR and AVR are anatomically and physiologically divergent procedures. Surgical AVR requires resection of the leaflet tissue with the valve anchored by sutures that draw aortic annular tissue inwards toward the valve prosthesis. In contrast, the TAVR device is placed without leaflet resection and imposes outwardly directed radial anchoring forces on adjacent structures to achieve fixation of the prosthetic valve. Given these differences in technique, we hypothesized that TAVR and AVR would have distinct immediate effects on mitral annular anatomy. In this study, using real-time three-dimensional echocardiography, we compared mitral annular geometry in patients undergoing TAVR and AVR.
Patients undergoing surgical treatment for severe or critical aortic stenosis were selected for inclusion in this study. Patients received a TAVR (N=10) (Sapien, Edwards Lifesciences, Irvine, CA) or standard open aortic valve replacement (N=10). TAVR valve sizing was determined by the discretion of the surgeon based on 2D echocardiographic annular diameter measurements at the time of surgery. For surgical AVR, selection of the valve type was done at the discretion of the surgeon at the time of cardiac surgery. Valve sizes were determined using conventional valve sizers.
All patients underwent intraoperative imaging of the mitral valve at the time of cardiac surgery, before and after aortic valve implantation. Real-time 3D transesophageal echocardiography data sets were acquired in addition to standard 2D echocardiographic exams, including color Doppler images of the mitral valve. Pre implantation imaging data sets were carried out in the operating room after induction of general anesthesia and before sternotomy. Post implantation imaging data sets were carried out after sternal closure and prior to leaving the operating room. Images were acquired through a mid-esophageal view with a Philips ie33 (Andover, MA, USA) ultrasound system equipped with a 2 to 7 MHz X7-2t TEE matrix transducer. For the rt-3DE data sets, electrocardiographically gated full-volume images were acquired over 4 cardiac cycles at a frame rate of 17–30 frames/s. For the 2D data sets, color Doppler images were used to determine the degree of MR.
This study was approved by the University of Pennsylvania Institutional Review Board.
Each full-volume data set was then exported to an Echo-View 5.4 (Tomtec Imaging Systems, Munich, Germany) software workstation for image analysis. The highest-quality data set was selected for each subject. Analysis was performed at midsystole. The plane of the mitral valve orifice was rotated into a short-axis view. The geometric center was then translated to the intersection of the 2 corresponding long-axis planes, which then corresponded to the intercommissural and septolateral axes of the mitral valve orifice. A rotational template consisting of 18 long-axis cross-sectional planes separated by 10 degree increments was superimposed on the 3D echocardiogram. Two annular points intersecting each of the 18 long-axis rotational planes were then identified by means of orthogonal visualization of each plane; the 2 points were marked interactively (Figure 1). The anterior and posterior commissures were defined as annular points at the junction between the anterior and posterior leaflets. Once the annular geometry was established, annular planes were marked at fixed 1-mm intervals along the entire length of the intercommissural axis. Free-hand curves for each 2D annular plane were traced along atrial surface delineating the anterior and posterior leaflets as well as the coaptation zone. 600–1200-point data sets were created for each valve (Figure 1). The Cartesian coordinates of each assigned point were then exported to MatLab (The Mathworks, Inc, Natick, MA).
Eight MV geometric indices were defined for comparison between groups. (Table 1). Using custom MatLab algorithms and orthogonal distance regression, the least squares plane of the data point cloud for the annulus was aligned to the x-y plane. Under these geometric conditions, the annular height for each point (zn) was plotted as a function of rotational position on the annulus. A number of anatomic landmarks were identified. The septum (S) was identified as the anterior horn of the annulus at the aortic valve. The lateral annulus (L) was identified as the middle of the posterior annulus circumference. The septolateral (SL) diameter was defined as the distance between these two points. With the annular model rotated such that the commissures were aligned along the y-axis, the maximum and minimum y-values of the annulus were identified as the anterolateral (AL) and posteromedial (PM) annular points. Annular height was defined as the zmax-zmin. Commissural width (CW) was defined as the 3D distance between the two commissures. Mitral annular area (MAA) was defined as the area enclosed by the 2D projection of a given annular data set onto its least squares plane. Mitral valve transverse diameter (MTD) was defined as the 3D distance separating the anterolateral annulus and the posteromedial annulus (Figure 2).
Continuous variables are presented as mean ± standard deviation. Categorical variables are presented as percentages and compared using Chi-square or Fisher’s Exact tests where appropriate. Mixed between-within ANOVA was used to compare the eight MV annular outcome variables among patients undergoing TAVR and AVR, before and after intervention. To minimize the likelihood of inflating type I error and to account for the eight dependent variables, P≤.006 (≈.05÷8) was taken to be statistically significant. If indicated, post hoc paired T-tests were performed between pre- and post-procedure groups and unpaired T-tests performed between TAVR and AVR groups. All statistical analysis was performed using SPSS software (SPSS Inc., Chicago, IL).
Baseline patient characteristics are presented in Table 2. Four patients in the TAVR cohort underwent transapical aortic valve implantation whereas six patients underwent transfemoral aortic valve implantation. Eight patients received a 23 mm Edwards-Sapien® valve and two received a 26 mm Edwards-Sapien® valve. All patients undergoing AVR received a bioprosthetic valve (CE Magna pericardial valve, N=7, Sorin MitroFlow, N=2 and St. Jude Trifecta, N=1). Of these, four patients received a 21 mm valve, three received a 23 mm valve and three received a 25 mm valve.
In the TAVR cohort, 50% of patients had mild MR, 40% had moderate MR, and 10% had severe MR prior to valve implantation. In comparison, 20% of patients in the AVR group had no MR, 40% had mild MR, and 40% had moderate MR. The degree of MR remained unchanged for 50% of TAVR patients and improved in 50%. In the AVR group, 60% had unchanged MR whereas 40% had an improvement in MR (Figure 3).
Prior to aortic valve implantation, there were no differences in annular geometry between patients undergoing TAVR versus patients undergoing AVR based on between groups ANOVA (all P values NS), as summarized in Table 3.
Results of the within group ANOVA showed significant differences as a result of the operative effect for a variety of parameters, also summarized in Table 3. Post hoc analysis confirmed that patients undergoing surgical AVR had significant decreases in annular height, septolateral diameter, mitral valve transverse diameter and mitral annular area (P≤.006), as depicted in Figures 4 and and5.5. For patients undergoing TAVR, there was no statistically significant change in annular geometry after valve placement.
Three-dimensional modeling of the mitral valve was used to evaluate eight discrete mitral annular geometric indices. These indices were compared between groups to evaluate for differences in baseline and post-procedure MV annular geometry between the TAVR and AVR cohorts. Interestingly, patients undergoing TAVR have preserved mitral annular geometry compared to patients undergoing standard AVR.
The Edwards SAPIEN heart valve consists of a bovine pericardial valve which is mounted on a stent and deployed by balloon expansion. The expandable device flattens the native aortic valve leaflets against the aortic wall and remains anchored in a sutureless fashion by virtue of the direct outward radial forces of the stent on the aortic valve annulus and leaflets. Given the bulk of the stent and relationship to the left ventricular outflow tract, we had hypothesized that distortions of the mitral annulus might occur with the Sapien device. Despite these concerns, the 3D geometry of the annulus remained unchanged after TAVR. In comparison, the patients undergoing AVR demonstrated significant deformation of the mitral annulus. The etiology of this deformation is likely the valve-anchoring sutures in the mitral-aortic continuity. The AVR group showed a decrease in annular height, narrowing in the anterior-posterior direction, and an overall reduction in size.
There was a trend towards an attenuation of relative saddle shape in patients undergoing AVR likely as result of the tethering effect of the sutures. Previous work has shown that the natural mitral annular saddle shape aids in reducing mitral annular strain [4–5], optimizing leaflet curvature profiles, reducing leaflet stress,  and improving leaflet coaptation.  Similarly, functionally impaired valves such as those in ischemic MR, have been shown to have severe alterations in 3D annular geometry with loss of the relative annular saddle shape.  Optimization of annular geometry and improving coaptation is, likely, important for promoting valve competence.
Functional MR (FMR) secondary to LV remodeling and elevated LV pressures in the setting of aortic stenosis has routinely been documented and frequently improves after AVR. [9–12] Nevertheless, despite previous attempts to characterize the long term durability of standard AVR in resolving concomitant FMR, a substantial degree of uncertainty still exists as to which patients warrant mitral valve interventions at the time AVR. Over the past decade, authors have sought to understand both the degree to which FMR improves after valve replacement and the clinical significance of residual MR. For example, Ruel and colleagues  described the natural history of patients undergoing surgical AVR with concomitant FMR and found that postoperative FMR ≥ 2+ was occurred in 10.7% of patients with preoperative FMR ≤ 1 and in 31.6% of patients with preoperative FMR ≥ 2+. At 18 months after surgery, FMR ≥ 2+ increased to 36.5% with 1 preoperative CHF risk factor and to 55.6% with 2 preoperative CHF risk factors. As illustrated by this study, there is a higher degree of improvement in MR when patients have less preoperative MR. As such, it could be hypothesized that TAVR might provide a more durable option for improving FMR in the setting of AS since it preserves the natural annular saddle shape and geometric dimensions to a greater degree than AVR. Further studies will be needed to fully investigate the long-term functional impact of TAVR on the degree of MR; however, early reports on transcatheter interventions are beginning to show promising data. For example, Webb and colleagues reported on patients who received the Edwards-Sapien valve for AS.  53% of patients in their study had moderate to severe MR at baseline and the median grade of MR decreased from 2 to 1 at discharge. Moreover, the percentage of patients with moderate to severe MR continuously decreased at 1, 6 and 12 month follow-up. They observed that there was a trend towards ongoing improvement in MR especially in patients with moderate to severe MR. Hekimian and colleagues reported similar results for patients having TAVR.  In the current study, MR was improved in 50% of patients undergoing TAVR and 40% of patients undergoing surgical AVR; however, the majority of patients had only mild to moderate MR. Although this work is limited by its small sample size and is not designed to specifically answer questions about the long term durability of TAVR, it does report a novel approach to looking at the functional consequences of aortic devices and may prove to be a more physiologic approach to aortic valve replacement, with respect to MV annular geometry.
This work was supported in part by grants from the National Heart, Lung and Blood Institute of the National Institutes of Health, Bethesda, MD, HL63954, HL73021, HL103723 and HL108330. R. Gorman and J. Gorman were supported by individual Established Investigator Awards from the American Heart Association, Dallas, TX. M. Vergnat was supported by a French Federation of Cardiology Research Award.
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