Surgery for hypertrophic cardiomyopathy (HCM) is complex. Typically, the foundation of this procedure is septal myectomy, with the primary goal of alleviating left ventricular outflow tract (LVOT) obstruction. Over time, the mitral valve apparatus has been recognized as a key factor in this pathology. First, from a functional standpoint, as systolic anterior motion (SAM) of the AML in systole plays a crucial role in LVOT obstruction. Second, anatomically, since various mitral abnormalities associated with HCM have been documented, among which is a longer leaflet size in both leaflets compared to controls without the condition.

These findings have led many surgical teams to integrate techniques to reduce AML size (e.g., plication, resection) alongside septal myectomy to achieve greater and more effective LVOT obstruction relief. Although these techniques have been successfully reported in current literature, fewer studies describe surgical outcomes after extensive isolated septal myectomy without concomitant mitral procedures. Moreover, only a limited number analyze the direct relationship between mitral leaflet length and surgical outcomes following an isolated septal myectomy.

The primary aim of this study was to determine whether AML length influences surgical outcomes following extensive isolated septal myectomy for LVOT obstruction in HCM. The primary outcome measure was the reduction in LVOT gradient after isolated septal myectomy, while secondary outcomes included reductions in mitral regurgitation (MR) and the incidence of postoperative SAM. Additional relevant variables, such as posterior leaflet length and coaptation height, were also analyzed. To this end, a comparison of pre-procedural mitral leaflet lengths was conducted between the series of HCM patients undergoing septal myectomy and a control cohort undergoing surgery for other pathologies. A total of 564 HCM patients were treated with isolated septal myectomy, without any pre-planned mitral procedure. These patients were compared to controls undergoing coronary artery bypass grafting (CABG, n=90) and aortic valve replacement (AVR, n=92). Among the patients treated with septal myectomy, 74.5% (n=420) underwent isolated septal myectomy, while the remainder had CABG or AVR as concomitant procedures. Furthermore, 6.4% (n=36) and 1.4% (n=8) underwent concurrent mitral valve repair or replacement, respectively, for intrinsic pathology, and were excluded from the analysis.

A cut-off point for excessive AML length was set at 30 mm, categorizing patients into those with AML ≥30 mm (n=264) and those with AML <30 mm (n=300). Significant differences in patient distribution were observed between groups, as well as in pre- and intraoperative characteristics that could potentially impact outcomes. Bivariate analysis revealed an association between AML length, posterior leaflet length, and coaptation height with the development of postoperative SAM and the degree of residual MR, which was not significant in the multivariable model. HCM patients had an average AML length 5 mm longer than the control cohort.

Preoperative LVOT gradients were not correlated with leaflet lengths (AML <30 mm: median 49 mmHg vs. AML ≥30 mm: 50.5 mmHg; p = .76). Similarly, gradient reduction after myectomy did not correlate with leaflet length; patients with AML <30 mm had a median gradient reduction of 33 mmHg compared to 36.5 mmHg in patients with AML ≥30 mm (p = .36). The AML length was not associated with increased one-year mortality (p = .75). Differences between groups were observed only in the percentage of postoperative SAM: 65.5% in AML ≥30 mm vs. 47.6% in AML <30 mm.

COMMENTARY:

This article presents a high level of complexity with interesting findings. It is certainly a study open to multiple interpretations, from which we will highlight the most notable. Of particular interest is the single-center sample size of 564 HCM patients undergoing isolated septal myectomy within a three-year interval (2015-2018), which is a remarkable patient volume that is difficult to match. Thus, the techniques, experience, and resources used are likely challenging to replicate in other settings. Despite the debatable statistical methodology and interpretation, a series of this scale inevitably yields significant conclusions.

It is well-known that HCM patients have longer mitral leaflets. In this case, to validate this hypothesis, a comparative control cohort of patients operated for other pathologies at the same center was used. This cohort exhibited demographic differences in all variables except for BMI, making the groups difficult to compare. A propensity score analysis might have been more objective in assessing whether mitral leaflet length is associated with HCM, while recognizing the limitations of this method.

The HCM patient series was divided into two groups, with none undergoing mitral leaflet size reduction. Instead, only isolated septal myectomy was performed. Concomitant CABG or AVR procedures were deemed to have minimal impact on post-op LVOT hemodynamics concerning SAM, gradient variation, or residual MR (though in patients with AVR, this assumption might not hold, and they should perhaps have been excluded from the analysis). A 30 mm AML length threshold was used, a measure widely adopted in current literature to decide whether to include AML reduction techniques in surgery. Bivariate and multivariable analyses were conducted to define associations.

Although bivariate analysis suggested associations between mitral leaflet lengths or coaptation height, no associations were found in the multivariable analysis. While no significant association or differences in residual gradients between groups were observed, the proportion of residual SAM was higher in the AML ≥30 mm group. Hence, aside from the residual SAM percentage (not defined in detail or severity), no relationship between greater AML length and poorer surgical outcomes was found without applying techniques to the AML. These results must be interpreted cautiously, as patients with AML ≥30 mm had a higher body surface area, a greater proportion of males, and a younger age.

REFERENCE:

Lentz Carvalho J, Schaff HV, Nishimura RA, Ommen SR, Geske JB, Lahr BD, et al. Is anterior mitral valve leaflet length important in outcome of septal myectomy for obstructive hypertrophic cardiomyopathy? J Thorac Cardiovasc Surg. 2023 Jan;165(1):79-87.e1. doi: 10.1016/j.jtcvs.2020.12.143