Daily step count as a simple marker of disease severity in hypertrophic cardiomyopathy

BACKGROUND: Individuals with hypertrophic cardiomyopathy (HCM) may be asymptomatic or display activity-limiting symptoms. A common cause of symptoms is left ventricular outflow tract obstruction (LVOTO), which may impact the individuals' ability to undertake physical activity. This study sought to examine daily step count as a potential marker of exercise capacity, which may represent a proxy marker of disease severity in HCM. METHODS: A cross-sectional study of 63 HCM patients was conducted from March to November 2015. Participants wore an ActiGraph GT3X+ (Pensacola, Florida, USA) accelerometer for 7 days. Minutes per day of light, moderate and vigorous physical activity and step count were calculated, and those with LVOTO were compared to those without. Similarly, those with good functional capacity (New York Heart Association; NYHA class I) were compared to those with NYHA class II-IV. RESULTS: The majority of HCM patients were male (n=45, 71%) with mean age of 48.8±14.9years. Hypertrophic cardiomyopathy patients with history of LVOTO and those NYHA class II-IV took significantly fewer steps per day (LV obstruction: 5527±2370 versus 7027±2095, p=0.01 and NYHA: 5346±1898 versus 6801±2339, p=0.03). No differences were observed across the different intensities of physical activity. CONCLUSIONS: Measurement of daily step count may be a useful and simple tool to determine exercise capacity and provide an indicator of disease severity in individuals with HCM.