Arrhythmia in hypertrophic cardiomyopathy: exercise and 48 hour ambulatory electrocardiographic assessment with and without beta adrenergic blocking therapy.

Submaximal treadmill exercise electrocardiography and 48 hour ambulatory electrocardiographic monitoring were performed in 30 patients with hypertrophic cardiomyopathy both with and without beta adrenergic blocking therapy. During ambulatory electrocardiographic monitoring 1 patient (3 percent) had no arrhythmia, 14 patients (46 percent) had supraventricular tachycardia or paroxysmal atrial fibrillation, 13 (43 percent) had multiform or paired ventricular extrasystoles and 8 (26 percent) had ventricular tachycardia. The frequency of these ventricular arrhythmias was almost identical with and without beta adrenergic blocking drugs (mean dose in "propranolol equivalents" 280 mg daily). With beta blocking therapy fewer patients had supraventricular tachycardia; however, the difference was not significant. During exercise testing 18 patients (60 percent) had ventricular extrasystoles and 3 patients (10 percent) had paired ventricular extrasystoles and the frequency was almost identical with and without beta adrenergic blocking therapy. No routine echocardiographic or hemodynamic measurement predicted the serious ventricular arrhythmias. It is concluded that asymptomatic ventricular arrhythmia is a common occurrence in patients with hypertrophic cardiomyopathy and its frequency is not reduced with beta adrenergic blocking therapy. Because occult arrhythmia may be the cause of sudden death it is important to detect it in these patients so that an effort can be made to improve prognosis with specific antiarrhythmic treatment.