The prevalence of arrhythmias in hypertrophic cardiomyopathy: role of ambulatory monitoring and signal-averaged electrocardiography.

Hypertrophic cardiomyopathy (HCM) is associated with a high incidence of supraventricular and ventricular arrhythmias. The presence of ventricular tachycardia (VT) in patients with HCM has been associated with a high risk of sudden death. Forty-seven patients with HCM (31 male, 16 female, mean age 47 years) underwent continuous 24-hour ambulatory electrocardiographic (ECG) monitoring. High grade ventricular arrhythmias (modified Lown class 3, 4a, 4b) were found in 20 patients (43%) with VT in 11 (24%). In each case the arrhythmia was asymptomatic. Supraventricular arrhythmias were detected in 16 patients (34%). Signal-averaged electrocardiography in 27 patients showed late potentials in three of 11 patients with repetitive ventricular arrhythmias and was negative in 15 of 16 patients without these arrhythmias. In conclusion, asymptomatic high grade ventricular and supraventricular arrhythmias are common in HCM and are readily detected with continuous electrocardiographic monitoring. Signal-averaged ECG has low sensitivity for the detection of subclinical VT in patients with HCM.