Impact of Effective Management Strategies on Patients With the Most Extreme Phenotypic Expression of Hypertrophic Cardiomyopathy

Advances in treatment options for hypertrophic cardiomyopathy (HC)have proven effective in many patients for promoting favorable long-term outcomes. Whether this expectation is similar for patients with the most extreme expression of massive left ventricular (LV)hypertrophy, a particularly aggressive form of the disease is unresolved. Of 1,766 consecutive HC patients presenting to Tufts HC Institute (2004 to 2015), 92 were identified with extreme LV wall thickness (30 to 48 mm), and compared with 1,674 HC patients with less marked hypertrophy (13 to 29 mm). Follow-up assessment was over 5.3 ± 3.4 years. Patients with massive LV hypertrophy (n = 92)had higher sudden death event rates (3.0%/year)than did patients with lesser hypertrophy (0.8%/year; p <0.001). In 16 of the 92 patients (17%), potentially lethal ventricular tachyarrhythmia were successfully aborted by primary prevention implantable cardioverter defibrillator (ICD)therapy at 30 ± 13 years (n = 11), or by resuscitated cardiac arrest with external defibrillation (n = 5)and later by secondary prevention interventions (n = 3); no patient experienced arrhythmic sudden death. Aborted sudden death events (3.0%/year)exceeded HC-related mortality by 7-fold (n = 2; 0.4%/year; p <0.001). European Society of Cardiology risk score would have failed to identify 60% of patients with arrhythmic sudden death events, leaving them exposed to sudden death without ICDs. In addition, 35 patients required surgical myectomy for progressive heart failure due to LV outflow obstruction (improved to NYHA I/II in 30). Eighty-eight (96%)of the 92 patients have survived to age 38 ± 14 years (23% ≥ 50 years). All-cause mortality did not differ from an age and gender-matched general population (p = 0.62). In conclusion, in this referral-based population, patients with the most extreme expression of HC are at increased arrhythmic sudden death risk reliably prevented with prophylactic ICDs. Progressive heart failure secondary to outflow obstruction was reversible with surgical myectomy. Despite extreme phenotypic expression, with contemporary treatment interventions young HC patients have an opportunity to achieve extended survival with good quality of life.