Potentially lethal arrhythmias and their management in hypertrophic cardiomyopathy

The prevalence of potentially lethal arrhythmias (PLA) in groups of patients with hypertrophic cardiomyopathy has been assessed, but the rate at which they develop (their incidence) during long-term follow-up has not been reported. Therefore, conduction system disease (CSD) (sick sinus syndrome and His-ventricular disease), ventricular couplets and ventricular tachycardia (VT) detected by routine electrocardiograms, periodic 24-hour Holter monitoring and periodic exercise stress testing were studied in 50 patients treated with large doses of β-adrenergic blocking drugs who were followed for 2 to 14 years (mean 5.9). Sixteen PLAs detected at the beginning of observation were excluded from actuarial analysis for new PLAs. Twenty-one patients had 24 new PLAs (7 with CSD, 1 patient with sustained supraventricular tachycardia, 6 with ventricular couplets and 10 with VT); only 43% of these PLAs were heralded by new symptoms. In 6 patients, the arrhythmia caused symptoms and was identified by a routine electrocardiogram. The 3 patients with His-ventricular disease presented with syncope and required electrophysiologic confirmation of this diagnosis. In only 1 patient was a PLA (ventricular couplets) detected only by exercise testing. All other ventricular arrhythmias were detected by Holter monitoring. The incidence of CSD in 47 patients free of this condition at entry was 5% at 5 years and 33% at 10 years. The incidence of ventricular couplets or VT in 39 patients free of these at entry was 26% at 5 years and 75% at 10 years, and the incidence of VT only was 18% at 5 years and 40% at 10 years. The incidence of all categories of new PLAs in the 50 patients was 32% at 5 years and 81% at 10 years. Because new PLAs are frequent during long-term follow-up and most cannot be detected adequately without surveillance, periodic Holter monitoring—at least on an annual basis—is recommended.