The acute and chronic effects of verapamil on left ventricular function in patients with hypertrophic cardiomyopathy.

Verapamil therapy improves exercise tolerance and decreases symptoms in many patients with both obstructive and nonobstructive forms of hypertrophic cardiomyopathy. These salutory clinical effects result from favorable modification by verapamil of the pathophysiologic abnormalities in left ventricular function characteristic of this disease: impaired early diastolic relaxation and filling, reduced end-diastolic volume and stroke volume, hypercontractile systolic function, and, in many patients, subvalvular outflow tract obstruction. The acute administration of intravenous verapamil produces both significant negative inotropic effects and significant effects on left ventricular diastolic function, resulting in reduced contractile state, diminished outflow gradient, increased end-diastolic volume and stroke volume and improved relaxation and diastolic filling. In some patients, one effect may predominate over the other, and improved diastolic function may be masked by the profound changes in systolic function. During short-term oral therapy, enhanced diastolic function is the predominant effect, although negative inotropic mechanisms are evident in some patients. These effects on left ventricular systolic and diastolic function persist during chronic oral verapamil therapy, contributing to the long-term clinical improvement experienced by many patients.