Mechanics of Left Ventricular Contraction in Chronic Severe Mitral Regurgitation

Abstract

The mechanics of left ventricular contraction were studied during diagnostic cardiac catheterization using high-speed cineangiography in 11 patients with severe chronic mitral regurgitation. Compared with a group of previously studied normal subjects, most of the patients with mitral regurgitation demonstrated a reduced velocity of shortening (V_cf) during ejection at maximum wall stress, average = 1.01 circumferences/sec (circ/sec) (range 0.64-1.47 circ/sec). Maximum and mean V_cf values also were reduced in these patients, averaging 1.40 and 0.94 circ/sec, respectively. These findings are in contrast to those in acute experimental mitral regurgitation, and to observations of normal shortening velocities in chronic experimental volume overloading, in which left ventricular contraction velocity is augmented. Compared with normal subjects, patients with mitral regurgitation had significantly larger left ventricular end-diastolic circumferences and volumes, and higher total left ventricular stroke volumes. The mean regurgitant volume was 41% of the total stroke volume, of which an average of 46% was ejected into the left atrium prior to aortic valve opening. The ejection fraction and extent of fiber shortening were normal in all but two patients despite depressed shortening velocities in most. It is concluded that analysis of velocity in the ejecting phase of left ventricular contraction is useful in detecting apparent alterations in inotropic state in the face of the altered loading conditions accompanying chronic mitral regurgitation. Further, favorable unloading conditions early during systole in patients with mitral regurgitation appear to mask the effects of a depressed inotropic state on the pumping function of the heart.