Variability of ventricular arrhythmias in hypertrophic cardiomyopathy and implications for treatment.

Asymptomatic ventricular arrhythmias are common in patients with hypertrophic cardiomyopathy (HC) and are associated with sudden death. The variability of ventricular extrasystoles and optimal duration of electrocardiographic (ECG) monitoring necessary to exclude ventricular tachycardia (VT) were assessed in 16 patients with HC in whom VT was detected during the first 48 hours of ECG monitoring. One hundred eight episodes of VT (range 0 to 10, mean 1.5 per day) were recorded (52% incidence) during 48 to 168 hours of ECG monitoring (median 72) without cardiac medication within a 1-year period. The likelihood of excluding VT on K days of ECG monitoring was determined. The probability of failing to detect VT in our selected group was 48% for 24 hours of ECG monitoring, 23% for 48 hours and 11% for 72 hours. Daily ventricular extrasystole rates were 2 to 17,693 (median 187). Analysis of variance, applied to 10 patients with enough ventricular extrasystoles for analysis, indicated that a 61% reduction of ventricular extrasystoles in consecutive 24-hour periods was necessary to attribute an effect to the intervention rather than to spontaneous variability with 95% confidence. A sine wave curve fitted to the ventricular extrasystole counts revealed a circadian rhythm with a night frequency peak in 5 patients and an afternoon peak in 5. Thus, 48- to 72-hour ECG monitoring represents a pragmatic compromise in assessing drug intervention once VT is detected;longer periods (5 to 6 days) of ECG monitoring are required to exclude VT at initial evaluation, although the prognostic significance of VT detected after the first 72 hours is uncertain.(ABSTRACT TRUNCATED AT 250 WORDS)