In patients with severe chronic mitral regurgitation, predominant early symptoms frequently include lassitude, fatigue, generalized weakness, and exercise-induced dyspnea, which are felt to reflect a low cardiac output as a result of a large regurgitant volume of blood ejected into an enlarged left atrium. In contrast to the data available for aortic regurgitation, there are few data on left ventricular volume or forward and regurgitant flow at rest and during exercise in patients with severe mitral regurgitation.
The patients in our study all had severe mitral regurgitation, without other valvular heart disease or suspected coronary artery disease. In addition, patients in the present study had “normal” resting systolic function, as determined by resting ejection fraction measurements. Due to favorable loading conditions in MR, however, patients with a normal resting ejection fraction may have significantly reduced overall contractility, when measured by a preload independent indicator such as the end-systolic stress/end-systolic volume index. Despite a resting regurgitant fraction that averaged 63 percent, resting forward cardiac index was reasonably maintained (mean of 2.9 L/min/m2) via marked left ventricular dilatation (mean EDVI of 155 ml/m2 with 65 ± 13 ml/m2 being the mean value in our laboratory) and hyperdynamic resting left ventricular function (mean resting ejection fraction of 0.69). Although there was considerable variability in ejection fraction changes with exercise, mean resting and exercise ejection fraction did not differ significantly in our patients, which is in agreement with a prior large study.
In normal individuals, systemic vascular resistance (SVR) usually falls markedly by 60-80 percent during maximal dynamic exercise. A significant fall in SVR during exercise in patients with severe mitral regurgitation could be expected to produce an effect similar to that produced by vasodilators—a fall in SVR should result in a decrease in regurgitant fraction with an associated increase in forward cardiac flow. A prior small study demonstrated that regurgitant fraction declined with exercise in patients with MR. Unlike our study, this prior report included patients with low resting ejection fraction (three of seven patients) and other cardiac diseases (two of seven had mitral stenosis with uncertain coronary status). Our study did not demonstrate any significant change in regurgitant fraction with exercise.