Relation of exercise capacity to left ventricular systolic function and diastolic filling in idiopathic or ischemic dilated cardiomyopathy

Abstract

Although exercise intolerance is a cardinal symptom of patients with dilated cardiomyopathy (DC) and heart failure, the factors that limit exercise capacity in these patients remain a matter of debate. To assess the contribution of left ventricular (LV) diastolic filling to the variable exercise capacity of patients with DC, we studied 47 patients (60 ± 12 years) with DC in stable mild-to-moderate heart failure with a mean LV ejection fraction of 28%. Exercise capacity was measured as total body peak oxygen consumption (V̇O 2) during symptom-limited bicycle (10 W/min) and treadmill (modified Bruce protocol) exercise. LV systolic function and diastolic filling were assessed at rest before each exercise by M-mode, Doppler echocardiography, and radionuclide ventriculography. As expected, treadmill exercise always yielded higher peak V̇O 2 than bicycle exercise (21 ± 6 vs 18 ± 5 ml/kg/min, range 12 to 35 and 7 to 30 ml/kg/min, respectively, p <0.001). Both of these V̇O 2 measurements were highly reproducible (R = 0.98). With univariate analysis, close correlations were found between peak V̇O 2 (with either exercise modalities) and Doppler indexes of LV diastolic filling, as well as with the radionuclide LV ejection fraction. Stepwise multiple regression analysis identified 3 nonexercise variables as independent correlates of peak V̇O 2, of which the most powerful was the E/A ratio (multiple r 2 = 0.38, p <0.0001), followed by peak A velocity (r 2 = 0.54, p <0.0001) and mitral regurgitation grade (r 2 = 0.58, p = 0.024). In conclusion, our data indicate that in patients with DC, peak V̇O 2 is better correlated to diastolic filling rather than systolic LV function.