Understanding Ventricular Remodeling after Correction of Mitral Regurgitation: Thinking Volumetrically

Abstract

Early after correction of mitral valve (MV) regurgitation, systolic function of the left ventricle (LV) declines, but the underlying mechanisms of this phenomenon are unknown. Most studies in this area have analyzed LV function at one week postoperatively or later. In a retrospective study from our Clinic, Enriquez-Sarano et al. reported a decline in LV ejection fraction (EF) from 62% to 52% ( P <0.001) in 217 patients with organic mitral regurgitation who were studied within the first year after MV replacement or repair. This decline was due to decreased left ventricular end-diastolic dimension (LVEDD) and minimal change in left ventricular end-systolic dimension (LVESD). Surgical investigators have compared the outcomes for different techniques of MV replacement and studies indicate that decline in EF may be mitigated by chordal preservation. It has been suggested that early postoperative measurements of cardiac geometry and function are confounded by the effects of global ischemia, reperfusion, and myocardial protection. Indeed, some clinicians have suggested that reduced EF early after MV repair results from myocardial dysfunction that, in turn, is related to poor myocardial protection. In addition, cardiac loading conditions change dramatically early after operation. We speculated that a postoperative decline in LV systolic indexes (eg, EF, FAC, and FS) may be interpreted as a volumetric adjustment of the heart to the correction of mitral regurgitation rather than as postoperative LV dysfunction due to impaired myocardial contractility, and clinical studies support this hypothesis. Soon after MV repair, the LV remodels gradually. Very early after correction of mitral regurgitation, the LVESD increases, preventing an acute increase in forward stroke volume. Within the next few postoperative days, the LVEDD begins to decrease and the LVESD changes accordingly to maintain a normal forward stroke volume; the remodeling occurs when neurohumoral mechanisms of the body adapt to the new hemodynamic milieu. This progression of remodeling may explain why some investigators have observed unchanged LV systolic and decreased diastolic size on the first postoperative echocardiogram about a week after MV repair.