Limitation of exercise tolerance in chronic heart failure: distinct effects of left Bundle-Branch block and coronary artery disease Original Research Article

Objectives The aim of this study was to identify resting measurements of left ventricular (LV) function that predict exercise capacity in dilated cardiomyopathy (DCM); in particular, the effects of left bundle branch block (LBBB), coronary artery disease (CAD), and total isovolumic time (t-IVT). Background The t-IVT is a major determinant of cardiac output during dobutamine stress in DCM, and is itself determined by the presence or absence of LBBB and CAD. Methods A total of 111 patients with DCM, 51 with CAD (29 LBBB), and 60 without CAD (30 LBBB) were studied with echocardiography and cardiopulmonary exercise testing. The t-IVT (in s/min) was measured by Doppler echocardiography, and maximal oxygen consumption (peak Vo2) and percentage of the normal predicted peak Vo2 (%predicted peak Vo2) were obtained from exercise testing. Results Left bundle branch block reduced peak Vo2 (by 10.5 ml·kg−1min−1) and %predicted peak Vo2 (by 33%, both p < 0.001) compared with patients without LBBB. Coronary artery disease reduced peak Vo2 (by 5.5 ml·kg−1min−1, p < 0.001) and %predicted peak Vo2 (by 14%, p < 0.01) compared with those without CAD (p < 0.01). The t-IVT, CAD, LBBB, and QRS duration were univariate predictors of exercise tolerance, but only t-IVT and CAD were independent predictors. The t-IVT at rest correlated with peak Vo2 (r = −0.68) and %predicted peak Vo2 (r = −0.74, both p < 0.001). The combination of t-IVT and CAD explained 57% (r = 0.75, p < 0.001) of the total variance in exercise capacity. Conclusions Resting t-IVT and less prominently, CAD, are major determinants of exercise tolerance in DCM. Left bundle branch block significantly determines resting t-IVT and thus peak Vo2. Prediction of maximum exercise capacity in DCM is therefore possible from time-domain analysis of LV function at rest.