[Correlation of left ventricular outflow obstruction with mitral regurgitation]

Our previous study of mitral regurgitation in obstructive hypertrophic cardiomyopathy suggested that left ventricular outflow obstruction due to systolic anterior motion of the distal residual anterior mitral leaflet may hydrodynamically induce mid-systolic mitral regurgitation. To test this hypothesis, we examined whether drug-induced left ventricular outflow obstruction in dogs might cause mitral regurgitation. Dobutamine, 20-60 micrograms/kg/min, induced the obstruction due to mitral systolic anterior motion with mitral-septal contact in 11 of 18 dogs. Pulsed Doppler and contrast echocardiography demonstrated that mitral regurgitation was concomitantly induced in the 11 dogs. The regurgitation was prominent during mid-systole from the onset to the end of mitral-septal contact. Two-dimensional echocardiography showed reduction of the mitral annular dimension and anterior shifts of the mitral valve coaptation during drug infusion in the 11 dogs. Accordingly, the distal portion of the mitral valve, especially of its anterior leaflet, became residual, and moved anteriorly in early systole and protruded into the outflow tract during mid-systole. Catheter-tip pressure recordings simultaneous with two-dimensional echocardiographic observation revealed that the outflow pressure gradient occurred across the protruding distal residual mitral valve. The onset and the end of the pressure gradient were nearly simultaneous with those of the mitral-septal contact. After cessation of the infusion, the mid-systolic mitral regurgitation disappeared together with the obstruction. These results indicate a close relationship between left ventricular outflow obstruction and mid-systolic mitral regurgitation, and strongly support the hypothesis that the obstruction due to systolic anterior motion of the distal residual anterior mitral leaflet is responsible for mitral regurgitation.