Hypertrophic Cardiomyopathy: Sudden Death After Exercise

Source: Weissler-Snir A, Allan K, Cunningham K, et al. Hypertrophic cardiomyopathy-related sudden cardiac death in young people in Ontario. Circulation. 2019; 140(21): 1706– 1716; doi: 10.1161/CIRCULATIONAHA.119.040271Investigators from the University of Toronto, Ontario, Canada, conducted a retrospective study to determine the incidence of sudden cardiac death (SCD) in young people with hypertrophic cardiomyopathy (HCM) and evaluate the role of exercise in HCM-SCD. For the study, they identified cases of HCM-SCD in Ontario, Canada, occurring between 2005 and 2011 among individuals 10–45 years old, as confirmed by means of autopsy at the Office of the Chief Coroner for Ontario (OCCO). OCCO maintains a centralized database and includes information about all sudden deaths attended by the coroner in the province. A diagnosis of HCM as the cause of SCD was considered definite when the autopsy findings included marked cardiomyocyte hypertrophy with pleomorphic to bizarre nuclei and myofiber disarray. Cases with other findings consistent with HCM, but no myofiber disarray, were classified as possible HCM-SCD. Sudden deaths in individuals with known HCM, but in whom no autopsy was performed, were categorized as probable HCM-SCD. The incidence of HCM-SCD among the at-risk population was estimated by using Ontario census data and assuming a prevalence of HCM of 1:500.1 To assess the role of exercise in HCM-SCD, the authors reviewed the death investigation review conducted by the coroner in each autopsied case and categorized the activity level at the time of death as being during sleep, at rest, during light activity, or during moderate or vigorous exercise.During the study period, 44 definite, 3 probable, and 6 possible cases of HCM-SCD were identified. Based on an estimate of the population at risk, the incidence of definite HCM-SCD was calculated as 0.31 per 1,000 HCM person years (95% CI, 0.24–0.44). Including probable and possible cases increased the estimated incidence to 0.38 per 1,000 HCM person years (95% CI, 0.28–0.49). The median age of individuals with HCM-SCD confirmed by means of autopsy was 35.5 years (interquartile range, 26–42 years), and 83% were male; 70% of cases occurred in individuals without prior diagnosed HCM. Overall, 34% of cases occurred at rest, 30% during sleep, 17% during light activity, and 17% during or immediately after moderate or vigorous activity. However, among those ≤20 years, 77.4% of cases of HCM-SCD were associated with moderate or vigorous activity versus 4.8% in older victims.The authors conclude that HCM-SCD is uncommon in the population at risk and infrequently related to exercise, at least in older individuals.Dr Chung has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.Every summer, general pediatric offices await the influx of sports physical examination forms that document the preparticipation physical examination (PPE) required by most states.2 The pediatrician who signs the bottom of a PPE form, even if only for a fleeting second, bears the burden of wondering whether this will be the rare child who experiences SCD from undiagnosed HCM while participating in sports.The current investigators sought to describe the incidence of HCM-SCD and its association with exercise in a large, unselected ethnically diverse “young” population, ranging from 10–45 years old. In comparison to HCM-SCD occurring in those >20 years, HCM-SCD occurring in those ≤20 years was much more likely to be associated with exercise (77.8% vs 4.8%; P <.001). Although the authors conclude that HCM-SCD was infrequently related to exercise in older patients, it was frequently related to exercise in young patients.The authors found that the annual HCM-SCD incidence for the study population was low. Pediatricians should take heart knowing that most deaths occurred in those with previously undiagnosed HCM, a diagnosis that is often difficult to make in the absence of a positive family history.3 Only 25.1% of those with HCM, a prevalent autosomal dominant disorder,1 have a known affected first- or second-degree relative, according to recent findings from an international registry.3 Promising advances in recent years, including cascade screening, make it increasingly easier to diagnose and treat HCM.4,5The overall incidence of HCM-SCD in individuals 10–45 years old is low. Although HCM-SCD is infrequently associated with exercise in patients >20 years, nearly 80% of HCM-related SCDs among those ≤20 years are associated with exercise.Previous studies, specifically in young athletes, also reveal a low incidence of SCD. (See AAP Grand Rounds. 2018;40[5]:58.6) Although HCM is the predominant cause, anomalous origin of the coronary arteries, myocarditis, and arrhythmogenic right ventricular cardiomyopathy have been reported.6