Adult: Mitral Valve
Undersizing mitral annuloplasty alters left ventricular mechanics in a swine model of ischemic mitral regurgitation

Read at the 99th Annual Meeting of The American Association for Thoracic Surgery, Toronto, Ontario, Canada, May 4-7, 2019.
https://doi.org/10.1016/j.jtcvs.2020.09.141Get rights and content

Abstract

Objective

Undersizing mitral annuloplasty (UMA) is a frequently used surgical repair technique to correct ischemic mitral regurgitation in patients with heart failure. In this study, we sought to test the hypothesis that downsizing the mitral annulus can adversely affect the shape and mechanics of the left ventricle inhibiting its functional recovery.

Methods

Eighteen farm swine that underwent an inferolateral myocardial infarction and developed ischemic mitral regurgitation of >2+ severity after 2 months were assigned as follows: 9 swine received an undersized mitral annuloplasty, 6 received papillary muscle approximation (PMA), and 3 animals did not receive any other intervention. Animals lived another 3 months and cardiac magnetic resonance imaging was performed before termination to assess ventricle mechanics and function.

Results

Ejection fraction was comparable between the 2 repair groups before surgery, but was significantly lower in UMA at 38.89% ± 7.91% versus 50.83% ± 9.04% in the PMA group (P = .0397). Animals receiving UMA had lower regional peak fractional shortening and reduced systolic and diastolic radial velocities compared with PMA and in some regions were lower than sham. Animals that underwent UMA had higher circumferential strain than sham, but lower than PMA. UMA animals have lower longitudinal strain compared to sham group and lower LV torsion than PMA.

Conclusions

Undersizing the mitral annulus with an annuloplasty ring can restore valvular competence, but unphysiologically impair ventricle mechanics. Mitral valve repair strategies should focus not only on restoring valve competence, but preserving ventricle mechanics.

Graphical abstract

Top row, Schematic representation of experimental design of this study. Bottom row, Key findings from this study that demonstrate the deleterious effect of undersizing mitral annuloplasty on left ventricle mechanics compared with papillary muscle approximation alone.

  1. Download : Download high-res image (248KB)
  2. Download : Download full-size image

Section snippets

Experimental Design and Animal Use

The experimental design is summarized in Figure 2. Use of animals in this research was necessary, and the surgical procedures and medications to manage postoperative pain were reviewed and approved by the designated Institutional Animal Care and Use Committee at Emory University. The studies were performed in accordance to the National Institutes of Health guidelines for use of animals in research. Yorkshire farm swine (female or castrated male) were acquired from US Department of

Procedural Parameters and Outcomes

Of 29 animals that underwent a myocardial infarction, 18 were used in this study. Details of animal exclusion, deaths, and those lost during follow-up are included in Appendix E1 and Figure E3.

Valve and Ventricle Function

MR fraction was 24.5% ± 0.4% in the study population before surgery. At 3 months after surgery when cardiac magnetic resonance imaging was performed, neither of the repaired groups had any MR, whereas MR severity persisted in the sham group. In the UMA group, the mitral annular septal–lateral diameter was

Discussion

Data from this chronic heart failure model12 demonstrate that both UMA and PMA are effective in correcting IMR acutely and there is no recurrence of IMR within the 3-month follow-up duration. The unexpected finding is that despite correcting IMR completely in both repairs, LV function was significantly better in the animals that received PMA than those that received an annuloplasty ring. In the PMA group, ejection fraction was not only improved at 3 months compared with the preoperative

Conclusions

Undersizing the mitral annulus with an annuloplasty ring can restore valvular competence, but unphysiologically impair ventricular mechanics and torsion. Such perturbations to ventricular mechanics may inhibit reverse remodeling achieved after MR correction. Subannular repair with PMA, which did not perturb ventricular mechanics, yielded equal reduction in valvular competence and significant improvement in ventricular function after the repair. Altogether, mitral valve repair strategies may

References (25)

  • R.E. Michler et al.

    Two-year outcomes of surgical treatment of moderate ischemic mitral regurgitation

    N Engl J Med

    (2016)
  • G.W. Stone et al.

    Transcatheter mitral-valve repair in patients with heart failure

    N Engl J Med

    (2018)
  • Partially supported by grants 1R01HL135145, 1R01HL133667, and 1R01HL140325 from the National Institutes of Health, grant 14SDG20380081 from the American Heart Association, and infrastructure funding from the Carlyle Fraser Heart Center at Emory University Hospital Midtown to Dr Padala.

    View full text