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The detailed physiological consequences of aerobic training, in patients with hypertrophic cardiomyopathy (HCM) are not well understood. In athletes and non-athletes with HCM, there are two hypothetical concerns with respect to exercise: exercise-related worsening of the phenotype (e.g. promoting hypertrophy, fibrosis), and/or triggering of arrhythmia. The former concern is unproven and animal studies suggest an opposite effect, where exercise has been shown to be protective. The main reason for exercise restriction in HCM is fear of exercise-induced arrhythmia. Whilst the safety of sports in HCM has been reviewed, even more recent data suggest a substantially lower risk for sudden cardiac death (SCD) in HCM than previously thought, and there is an ongoing debate about restrictions of exercise imposed on individuals with HCM. This review outlines the pathophysiology of HCM, the impact of acute and chronic exercise (and variations of exercise intensity, modality, and athletic phenotype) in HCM including changes in autonomic function, blood pressure, cardiac dimensions and function, and cardiac output, and the underlying mechanisms that may trigger exercise-induced lethal arrhythmias. It provides a critical evaluation of the evidence regarding risk of SCD in athletes and the potential benefits of targeted exercise prescription in adults with HCM. Finally, it provides considerations for personalized recommendations for sports participation based on the available data.

Introduction: Strategies for reliable selection of high-risk hypertrophic cardiomyopathy (HCM) patients for prevention of sudden cardiac death (SCD) with implantable cardioverter-defibrillators (ICDs) continue to be debated. Objective: Assess the sensitivity of sudden death risk strategies in predicting SCD events (appropriate ICD shocks, sudden death or out of hospital cardiac arrest) among a large multicenter cohort of high-risk HCM patients. Methods: Observational longitudinal study from 6-HCM centers in North America and Europe to determine outcomes in consecutive HCM patients considered high risk for sudden death based on an enhanced ACC/AHA (U.S./Canada) guidelines-based risk factor algorithm with primary prevention ICD placement. ESC risk score was retrospectively calculated in this cohort and compared to ACC/AHA risk factor method for predicting SCD events. Results: Of 1185 patients with primary prevention ICDs implanted based on ≥ 1 major risk marker, 162 (14%) experienced device therapy terminating VT/VF episodes at 49 ± 18 years of age and 4.6 ± 4.2 years after device implant. Within the 6 HCM centers, only 28 other patients not implanted with ICD died suddenly or had resuscitated cardiac arrests, including 19 (68%) with risk-markers who declined ICDs. Of these 190 high risk patients with SCD or SCD events, 67 (35%) had ESC risk-scores scores ≥6%/5-years, considered sufficient to recommend a prophylactic ICD, while 83 (44%) had low risk scores (<4%/5-years) that likely would have excluded an ICD recommendation. Compared to enhanced ACC/AHA risk factors, the ESC risk-score was less sensitive than ACC/AHA (35% vs. 95%, p<0.01), consistent with identifying fewer high-risk patients with events. Conclusion: In this large multicenter study of high-risk HCM patients, an enhanced ACC/AHA risk factor strategy was superior to the ESC risk score in identifying patients at greatest risk for SCD events.