Rest and latent obstruction in hypertrophic cardiomyopathy: impact on exercise tolerance

Most patients with hypertrophic cardiomyopathy (HCM) show a limited exercise capacity. A correlation between exercise tolerance and diastolic dysfunction has already been demonstrated. On the contrary, the role of rest-induced or exercise-induced obstruction as a determinant of exercise capacity is still open to debate. The aim of the present study was to analyse the exertional behaviour of patients with HCM presenting different left ventricle (LV) obstructive profiles.

Thirty-five consecutive patients with HCM (mean age 45 ± 14 years, 23 men) underwent echocardiography during cardiopulmonary exercise (CPX) testing. Non-invasive measurement of cardiac output was obtained with an inert gas rebreathing system at the beginning and at peak of exercise.

Fifteen patients (43%) had neither resting nor provocable obstruction (group A: non-obstructive profile), 12 patients (34%) showed provocable obstruction during exercise (group B: latent-obstructive profile) and eight patients (23%) presented obstruction at rest (group C: rest-obstructive profile). Group A and B patients showed higher peak oxygen consumption in comparison with group C patients (24 ± 6 and 23 ± 6 vs. 17 ± 3 ml/kg per min; P = 0.016) and a greater increment of cardiac index during exercise (6.6 ± 1.3 and 6.0 ± 1.4 vs. 4.6 ± 0.8 l/min per m; P = 0.004).

In comparison with the rest-obstructive profile, latent and non-obstructive HCM patients seem to share a similar exertional behaviour characterized by a greater increment of cardiac index during exercise and a minor impairment of exercise tolerance. Accordingly, in HCM patients not obstructive at rest, latent obstruction cannot be suspected based on exertional behaviour and functional capacity. Echocardiography performed during CPX test providing an important adjunct, may be valuable in guiding treatment in patients with substantial exercise limitation.