Implantable defibrillators and prevention of sudden death in hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is the most common cause of sudden cardiac death in young people, including trained athletes. The implantable cardioverter-defibrillator (ICD), although initially designed as a treatment for older patients with coronary artery disease, has more recently proved to be a safe and effective therapeutic intervention in young patients with HCM, both for primary or secondary prevention of sudden death. The largest such report of >500 patients showed that the ICD intervened appropriately to abort ventricular tachycardia/fibrillation (VT/VF) in 20% of patients over an average follow-up period of only 3.7 years, at a rate of about 4% per year in those patients implanted prophylactically, and often with considerable delays of up to 10 years. Extensive experience with high-risk HCM patients showed that appropriate device discharges for VT/VF occur with similar frequency in patients with 1, 2, or > or = 3 noninvasive risk markers. Despite the extreme morphology characteristic of HCM, often with massive degrees of left ventricular (LV) hypertrophy and/or LV outflow tract obstruction, ICDs performed in a highly effective fashion, with failure to convert life-threatening arrhythmias extraordinarily rare. In conclusion, in a large high-risk HCM cohort, ICD interventions for life-threatening ventricular tachyarrhythmias were frequent and highly effective in restoring normal rhythm. An important proportion of ICD discharges occurred in primary prevention patients with only one risk factor. Therefore, a single marker of high risk may represent sufficient evidence to justify the recommendation for a prophylactic ICD in selected patients with HCM.