Effects of Chronic @i-Adrenergic Blockade on the Left Ventricular and Cardiocyte Abnormalities of Chronic Canine Mitral Regurgitation

The mechanism by which ft blockade improves left ventricular dysfunction in various cardiomyopathies has been ascribed to improved contractile function of the myocardium or to improved,8-adrenergic responsiveness. In this study we tested two hypotheses: (a) that chronic 13 blockade would improve the left ventricular dysfunction which develops in mitral regurgitation, and (b) that an important mechanism of this effect would be improved innate contractile function of the myocardium. Two groups of six dogs with chronic severe mitral regurgitation were studied. After 3 mo both groups had developed similar and significant left ventricular dysfunction. One group was then graduallyfl-blocked while the second group continued to be observed without further intervention. In the group that remained unblocked, contractile function remained depressed. However, in the group that received chronic,f blockade, contractil