Paradoxical response to exercise in asymptomatic hypertrophic cardiomyopathy: a new description of outflow tract obstruction dynamics

The purpose of this study was to analyze left ventricular obstruction in patients with hypertrophic cardiomyopathy (HCM) during exercise echocardiography.Despite the association of symptoms with left ventricular outflow tract obstruction in HCM, there exist paradoxical situations in which significant intraventricular gradients (50 mm Hg) at rest occur in conjunction with excellent exercise tolerance.To examine this phenomenon, we performed exercise echocardiography and analyzed the clinical status of 107 HCM patients with and without resting obstruction.At rest, 69 patients had no obstruction and 38 exhibited an intraventricular gradient, 9 of whom exhibited a decrease in gradient of at least 30 mm Hg (99.4 ± 35.5 mm Hg to 30.2 ± 14.3 mm Hg, p0.001) during exercise (paradoxical response to exercise [PRE]). The PRE patients presented with a significantly lower New York Heart Association clinical class and higher left ventricular volumes and arterial pressure both at rest and during exercise than HCM patients in whom the gradient increased or did not change during stress echocardiography. Finally, PRE patients exhibited a trend toward a reduced rate of cardiac events.Our study reports a subgroup of HCM patients, designated PRE based on a decreased intraventricular gradient during exercise. The reduced exertional obstruction may account for the better functional class and trend toward fewer clinical events in PRE patients.