Catecholamine response to exercise in patients with non-obstructive hypertrophic cardiomyopathy

Intense physical activity, a potent stimulus for sympathetic nervous system activation, is thought to increase the risk of malignant ventricular arrhythmias among patients with hypertrophic cardiomyopathy (HCM). However, the impact of exercise intensity on plasma catecholamine levels among HCM patients has not been rigorously defined. We conducted a prospective observational case-control study of men with non-obstructive HCM and age-matched controls. Laboratory-based cardiopulmonary exercise testing coupled with serial phlebotomy was used to define the relationship between exercise intensity and plasma catecholamine levels. Compared to controls (C, n=5), HCM participants (H, n=9) demonstrated higher left ventricular mass index (11520 vs. 9016g/m(2), P=0.03) and maximal left ventricular wall thickness (161 vs. 81mm, P<0.001) but similar body mass index, resting heart rate, peak oxygen consumption (H=4013 vs. C=42 +/- 7ml/kg/min, P=0.81) and heart rate at the ventilatory threshold (H=78 +/- 6 vs. C=78 +/- 4% peak heart rate, P=0.92). During incremental effort exercise in both groups, concentrations of adrenaline and noradrenaline were unchanged through low- and moderate-exercise intensity until reaching a catecholamine threshold (H=82 +/- 4 vs. C=85 +/- 3% peak heart rate, P=0.86) after which levels of both molecules rose rapidly. In patients with mild non-obstructive HCM, plasma catecholamine levels remain stably low at exercise intensities below the ventilatory threshold but rise rapidly at higher intensities of exercise. Routine cardiopulmonary exercise testing may be a useful tool to provide an individualized moderate-intensity exercise prescription for patients with HCM.