Long-term survival after cardiac arrest in hypertrophic cardiomyopathy

Background: Patients with hypertrophic cardiomyopathy (HCM) and aborted cardiac arrest are generally regarded as a high-risk subgroup susceptible to future major cardiac events and an unfavorable prognosis. However, outcome over extended time periods after major arrhythmic events is unresolved in such HCM patients. Objective: This study sought to more completely define the natural history of HCM. Methods: Of 916 HCM patients in the Minneapolis Heart Institute registry, 39 experienced either cardiac arrest (n = 21) or an appropriate shock from a prophylactically implanted cardioverter-defibrillator (ICD) (n = 18), and were assessed prospectively. Results: Age at initial arrhythmic event was 34 ± 17 years (range 8 to 68; 67% <40 years). Of the 39 study patients, 32 (82%) survived after their initial cardiac event (for 9.4 ± 7.6 years; up to 30 years), including 14 patients for ≥10 years (36%) and 4 patients ≥20 years (10%). Of the 32 survivors, 15 (47%) have not experienced subsequent events, and 17 (53%) had ≥1 additional cardiac arrest or appropriate ICD intervention. Annual HCM-related mortality was 1.4%, similar to general HCM populations, and 88% of patients were free of HCM-related death over the follow-up period. Survival from potentially lethal arrhythmias was associated with no or only mild heart failure symptoms in 29 of 32 patients (91%) at most recent evaluation. Conclusion: In HCM, long-term survival up to 30 years may follow cardiac arrest with or without ICD intervention. Disabling heart failure symptoms were uncommon after these arrhythmic events, at last follow-up. These novel observations regarding the natural history of HCM underscore the unpredictability of the arrhythmogenic substrate, which may remain dormant over extended periods of time.