941-22 Role of Dynamic Changes in Left Ventricular Function in Determining Exercise Capacity in Patients with Nonobstructive Hypertrophic Cardiomyopathy

Measurements of LV morphology and function at rest predict weakly exercise capacity in hypertrophic cardiomyopathy (HC). Aim of this study was to verify whether dynamic changes in LV function relate to exercise duration in HC. Accordingly, we studied 25 patients, off-drugs, with nonobstructive HC (15 males, aged 43±13 yrs). who undervvent baseline Doppler echocardiography, cardiac catheterization, and symptom-limited supine bicycle exercise (25watt/2mins) with postexercise Doppler echocardiography. Exercise capacity ranged from 50 to 125 (mean: 79±27) watts. No relation was found between exercise time and indices of LV morphology (i.e. maximal wall thickness, wall thickness index, end-diastolic and end-systolic dimensions). or function at rest (i.e. LV ejection fraction, stroke volume index, right- and left-sided intracavitary pressures, Doppler indices of LV diastolic filling). In contrast, exercise capacity correlated significantly (p<0.01) with the magnitude of changes recorded at peak exercise in ejection fraction (r=0.65). LV end-diastolic volume (r=0.67), and Doppler peak early filling velocity (r=0.60). Change in ejection fraction related significantly (p<0.01) to change from baseline in both LV end-diastolic volume (r=0.71) and peak early filling velocity(r=0.55). Multiple regression analysis revealed that the response of ejection fraction to exercise was the strongest predictor of exercise capacity (p=0.001). Noteworthy, 10/25 patients exhibited the lack of stress-induced increase in ejection fraction. We conclude that in nonobstructive HC: (1) dynamic changes in LV function correlate with exercise duration; (2) indices of LV morphology and function at rest do not predict exercise capacity; (3) exercise intolerance seems to be caused by worsening in diastolic filling, leading to the inability to increase LV volume with exercise to maintain systolic function