Objectives: The aim of the study was to assess inducibility of left ventricular outflow tract (LVOT) gradient by change of position from supine to upright and by treadmill exercise in treated patients with hypertrophic cardiomyopathy (HCM) without obstruction at rest.
Methods: We studied 37 treated HCM patients (21 men and 16 women, mean age 44 +/- 12 years) with LVOT gradient <30 mmHg at rest in supine position. The patients were then placed in upright position and the gradient was reexamined. The patients who developed LVOT gradient >or= 30 mmHg during this maneuver were not exercised, whereas the remaining patients (nonobstructive in orthostatic position) performed moderate-intensity exercise on a treadmill, with continuous monitoring of the LVOT gradient. For comparison with resting measurements, gradients at peak exercise (in upright position) and at recovery (in supine position) were used. The resting minimal distance between the mitral valve and ventricular septum at systole was used to assess the degree of narrowing of LVOT.
Results: The orthostatic position provoked LVOT gradient >or= 30 mmHg in 8 of 37 patients. At peak exercise, 10 of the remaining 29 patients developed significant LVOT gradient. At recovery in supine position, this significant gradient disappeared in 6 of 10 patients, despite only a short delay in measurement. Of resting echocardiographic parameters, only systolic mitral-septal distance differentiated between the provocable and nonprovocable subgroups. Patients with provocable gradient (either by changing position or by exercise) presented with lower values of this parameter than the nonprovocable subgroup.
Conclusions: In nonobstructive HCM patients under treatment, the LVOT gradient was inducible by upright position in 21.6% and by upright moderate exercise in 34.5%. The minimal septal-mitral distance may be useful to identify patients with provocable obstruction.