Population Burden of Sudden Death Associated With Hypertrophic Cardiomyopathy

ypertrophic cardiomyopathy (HCM) is a genetically transmitted cardiac disease, characterized by increased left ventricular (LV) wall thickness in the absence of abnormal loading conditions. 1 The estimated prevalence of HCM is ≈1 per 500 in the general population, 2 with a diverse clinical course including heart failure and sudden cardiac arrest (SCA), but also asymptomatic survival to normal life expectancy.3 SCA attributable to ventricular arrhythmias is a major cause of mortality in young and middle-aged patients with HCM. 4 With modern management strategies, including implantable cardioverter-defibrillator therapy for high-risk individuals, contemporary disease-related mortality has been reported to be ≈0.5% annually.4 These estimates are derived from several HCM patient registries, representing a somewhat selected patient population.However, the absence of symptoms causes HCM to remain undetected in a large proportion of patients.Because few data exist on the burden of HCMrelated SCA in the community, in the present study we assessed the incidence and characteristics of HCM-related SCA in the young and middle-aged general population from the ongoing Oregon SUDS (Oregon Sudden Unexpected Death Study).This study was approved by the institutional review boards of Cedars-Sinai Medical Center, Oregon Health and Science University, and all participating hospitals.The Oregon SUDS uses multiple-source ascertainment to prospectively identify all cases of out-of-hospital SCA occurring in the Portland, Oregon, metropolitan area (catchment population ≈1 million).5 All existing medical information, including emergency medical services reports, patient's lifetime clinical records, death certificates, and autopsy reports, were obtained for each case.Subjects included in the present study were 5 to 59 years of age.Because of the likely low burden of HCM-related SCA in the elderly, 3 and increasing difficulties in differentiating HCM from secondary LV hypertrophy, our study did not include patients ≥60 years of age.Diagnosis of HCM was based on echocardiography or autopsy reports.As recommended in the current guidelines, 1 echocardiographic LV wall thickness ≥15 mm without a secondary cause such as aortic stenosis or hypertension was used to diagnose HCM.In autopsied patients, significant unexplained LV hypertrophy ≥17 mm with histological evidence of HCM or characteristic asymmetrical LV hypertrophy was required for HCM diagnosis.For comparisons between clinical and demographic characteristics of HCM and other SCA cases, the independent samples t test and the Pearson χ 2 test were used.For calculation of SCA incidence rates, the analysis was limited to data collected from Portland's Multnomah County (average 5-to 59-year-old population, 547 570).For the subgroup of patients experiencing SCA without significant SCA comorbidities diagnosed before the arrest, and no autopsy or lifetime echocardiography data available, the incidence of HCM was imputed based on the prevalence of HCM detected by echocardiography and autopsy (Figure ).