Hypertrophic cardiomyopathy. An electrophysiological study.

Recordings of the transmembrane action potential of the cardiac myofibril from a patient with hypertrophic obstructive cardiomyopathy showed that the repolarization time was appreciably prolonged and that the maximum rate of follow was grossly reduced. This electrical abnormality is compatible with the late and irregular activation of the ventricular muscle in the disease. Propranolol was found to produce a similar "quinidine-like" effect on the transmembrane actionpotential in both cardiomyopathic and control tissue.