Experimental mitral regurgitation: effects on left ventricular function before and after elimination of chronic regurgitation in the dog.

Chronic left ventricular-atrial regurgitation (LVAR) was created in 8 dogs by means of an external conduit so that the effects of acute correction of regurgitation on the mechanics of left ventricular performance could be studied in detail. LVAR of 46 to 77 per cent of the total left ventricular (LV) output was associated with a depression of the LV inotropic state (downward displacement of the stress-velocity relationship, reduction in V max), reduced forward flow, and signs of cardiac failure. Acute occlusion of the shunt (analogous to return of mitral valvular competence) in the anesthetized, open-chest animal resulted in a statistically significant increase in the integrated LV systolic wall stress (afterload), which averaged 18 per cent. In the dog with greatest depression of the LV inotropic state, the increase in afterload was associated with a decrease in forward flow. Occlusion of the shunt had no significant effect on the inotropic state. This model of mitral regurgitation appears to be useful in assessing the effect of chronic LVAR on cardiac performance and may explain the hemodynamic deterioration observed in some patients with severe mitral regurgitation following valve replacement.