Exercise limitation in hypertrophic cardiomyopathy: combined stress echocardiography and cardiopulmonary exercise test.

Abstract

The study aims to investigate exercise-limiting factors in hypertrophic cardiomyopathy (HCM) using combined stress echocardiography and cardiopulmonary exercise test. A symptom-limited ramp bicycle exercise test was performed in the semi-supine position on a tilting dedicated ergometer. Echocardiographic images were obtained concurrently with gas exchange measurements along predefined stages of exercise. Oxygen extraction was calculated using the Fick equation at each activity level. Thirty-six HCM patients (mean age 67±6years, 72% men, 18 obstructive HCM) were compared with age and sex-matched 29 controls. At rest, compared with controls, E/E' ratio (6.26±2.3 vs. 14±2.5, P<0.001) and systolic pulmonary artery pressures (SPAP) (22.6±3.4 vs. 34±6.2mmHg, P=0.023) were increased. Along with the stages of exercise (unloaded; anaerobic threshold; peak), diastolic function worsened (E/e' 8.9±2.6 vs. 13.8±3.6 P=0.011; 9.4±2.3 vs. 18.6±3.3 P=0.001; 8.7±1.9 vs. 21.5±4, P<0.001), SPAP increased (23±2.7 vs. 33±4.4, P=0.013; 26±3.2 vs. 40±2.9, P<0.001; 26±3.5 vs. 45±7mmHg, P<0.001), and oxygen consumption (6.6±1.7 vs. 6.8±1.6, P=0.86; 18.1±2.2 vs. 14.6±1.5, P=0.008; 20.3±3 vs. 15.1±2.1mL/kg/min, P=0.01) was reduced. Oxygen pulse was blunted (6.3±1.8 vs. 6.2±1.9, P=0.79; 10±2.1 vs. 8.8±1.6, P=0.063; 12.2±2 vs. 8.2±2.3mL/beat, P=0.002) due to an insufficient increase in both stroke volume (92.3±17 vs. 77.3±14.5 P=0.021; 101±19.1 vs. 87.3±15.7 P=0.06; 96.5±12.2 vs. 83.6±16.1mL, P=0.034) and oxygen extraction (0.07±0.03 vs. 0.07±0.02, P=0.47; 0.13±0.02 vs. 0.10±0.03, P=0.013; 0.13±0.03 vs. 0.11±0.03, P=0.03). Diastolic dysfunction, elevated SPAP, and the presence of atrial fibrillation were associated with reduced exercise capacity. Both central and peripheral cardiovascular limitations are involved in exercise intolerance in HCM. Diastolic dysfunction seems to be the main driver for this limitation.