A clinical observation of patients with hypertrophic cardiomyopathy and implantable cardioverter-defibrillators

Background and Objectives: Hypertrophic cardiomyopathy (HCM) is one of the most common heritable cardiac diseases. Patients with HCM are prone to ventricular tachyarrhythmias, and implantable cardioverter-defibrillator (ICD) implantation is recommended in high-risk patients to prevent sudden death. Clinical and tachycardial characteristics in patients with HCM have not been studied systematically. Subjects and Methods: Between April 1996 and February 2006, 23 patients with HCM underwent implantation of ICDs. ICDs were indicated for primary prevention in 9 patients and for secondary prevention in 14 patients. Clinical features, follow-up events and intracardiac electrograms were reviewed. Results: During a median follow-up period of 561 days (range 16 to 2,694 days), a total of 51 episodes of ventricular tachycardia (VT) occurred in 6 patients, while only one episode of ventricular fibrillation (VF) was recorded. There were 45 (64.2%) appropriate shocks [30 defibrillation shocks in 5 patients and 15 antitachycardia pacings (ATP) in 2 patients] in 6 patients, and 25 (35.7%) inappropriate shocks in 7 patients. The coupling intervals and VT cycle lengths were highly variable within individual patients. Over-drive acceleration in response to ATP was observed in 1 patient. Conclusion: As ventricular tachycardia is the main ventricular tachyarrhythmia in patients with HCM, an empirical ATP setting for VTs appears to be mandatory even in patients without previously documented VT. Based on the analyses of the intracardiac electrograms (presence of overdrive acceleration, variations in coupling intervals and cycle lengths), triggered activity may have an important role in the mechanism of a ventricular tachycardia.