Mitral annuloplasty as a ventricular restoration method for the failing left ventricle: a pilot study

BACKGROUND AND AIM OF THE STUDY: Undersized mitral annuloplasty (MAP) is effective in patients with dilated cardiomyopathy and functional mitral regurgitation (MR) since, as well as addressing the MR, the MAP may also reshape the dilated left ventricular (LV) base. However, the direct benefits of this possible reshaping on LV function in the absence of underlying MR remain incompletely understood. The study aim was to identify these benefits in a canine model of acute heart failure. METHODS: Six dogs underwent MAP with a prosthetic band on the posterior mitral annulus, using four mattress sutures. The sutures were passed individually through four tourniquets and exteriorized untied via the left atriotomy. Sonomicrometry crystals were implanted around the mitral annulus and left ventricle to measure geometry and regional function. Acute heart failure was induced by propranolol and volume loading after weaning from cardiopulmonary bypass; an absence of MR was confirmed by echocardiography. MAP was accomplished by cinching the tourniquets. Data were acquired at baseline, after induction of acute heart failure, and after MAP. RESULTS: MAP decreased mitral annular dimensions in both commissure-commissure and septal-lateral directions. Concomitantly, the diastolic diameter of the LV base and LV sphericity decreased (i.e., improved) from 37.4 +/- 9.3 to 35.9 +/- 10 mm (p = 0.063), and from 67.9 +/- 18.6% to 65.3 +/- 18.9% (p = 0.016), respectively. Decreases were evident in both LV end-diastolic pressure (from 17 +/- 7 to 15 +/- 6 mmHg, p = 0.0480 and Tau (from 48 +/- 8 to 45 +/- 8 ms, p <0.01), while fractional shortening at the LV base increased from 7.7 +/- 4.5% to 9.4 +/- 4.5% (p = 0.045). After MAP, increases were identified in both cardiac output (from 1.54 +/- 0.57 to 1.65 +/- 0.57 1/min) and Emax (from 1.86 +/- 0.9 to 2.41 +/- 1.31 mmHg/ml). CONCLUSION: The data acquired suggest that isolated MAP may have certain benefits on LV dimension/function in acute heart failure, even in the absence of MR. However, further investigations are warranted in a model of chronic heart failure.