Background: Hypertrophic cardiomyopathy (HCM) is characterized by inappropriate left ventricular (LV) wall thickness. Adaptations to exercise can occasionally mimic the HCM phenotype. However, it is unclear whether physical activity (PA) affects HCM genotype expression and disease characteristics.
Purpose: We aimed to 1) evaluate the effect of physical activity on genotype to phenotype transition and therefore we compared physical activity volumes between HCM gene carriers (G+) with a positive (P+) and negative (P-) HCM phenotype (G+/P+ versus G+/P-), and 2) we compared disease appearance and characteristics across tertiles of lifelong physical activity among HCM patients (G+/P+ and G-/P+).
Methods: HCM genotype positive individuals who were either HCM phenotype positive (G+/P+) or negative (G+/P-), as well as genotype negative HCM patients (G-/P+) were included. PA volumes were calculated as lifelong and pre-diagnosis average Metabolic Equivalent of Task (MET)-hrs/week. PA volumes were compared between G+/P+ and G+/P-participants. Secondly, clinical parameters of cardiac magnetic resonance imaging, echocardiography and Holter monitoring were compared across tertiles of PA volumes among all P+ participants.
Results: We included n=109 subjects (51±15 years, 51% male), including 44 G+/P+ HCM patients, 22 G+/P- HCM gene carriers, and 43 G-/P+ HCM patients without a (known) genetic mutation. PA volumes were not different (p=.33) between G+/P+ and G+/P- subjects. Secondly, there was no difference in LV function, LV morphology, LV wall thickness, LV mass, LGE, HighT2 presence and troponin levels across physical activity tertiles (all p>.05), but the most active HCM patients were younger at the time of diagnosis (tertile 1: 51±15 vs. tertile 2: 50±15 vs. tertile 3: 41±17 years, p=.045) and more often experienced non-sustained ventricular tachycardia on Holter monitoring (tertile 1: 4% vs. tertile 2: 31% vs. tertile 3: 28%, p=.03).
Conclusion: We found no differences in physical activity characteristics between HCM gene carriers with and without HCM phenotype. We also found no evidence of increased LV wall thickness, LV mass, HighT2 presence or elevated cardiac troponin levels among the most active HCM patients. However, the most active HCM patients were younger at the time of diagnosis and had a higher arrhythmic burden. These observations warrant further exploration of the role of exercise in HCM disease development.