Limitation of cardiac output by total isovolumic time during pharmacologic stress in patients with dilated cardiomyopathy: Activation-mediated effects of leftbundle branch block and coronary artery disease

Objectives We sought to separate the effects of associated left bundle branch block (LBBB) and coronary artery disease (CAD) on peak cardiac output (CO) during dobutamine stress in patients with dilated cardiomyopathy (DCM). Background The mechanisms limiting CO during stress in patients with DCM are unclear. Both LBBB and CAD may do so by prolonging the total isovolumic time (t-IVT). Methods A total of 59 patients with DCM—34 with CAD (20 normal activation [NA], 14 LBBB) and 25 without CAD (15 NA, 10 LBBB)—were studied. The total IVT (s/min; calculated as: 60 − [total ejection time + total filling time] ) and CO were measured by Doppler echocardiography. Results At rest, t-IVT was 8 s/min longer with LBBB (p < 0.001), was unaffected by CAD, and did not correlate with rest CO. During stress, CO correlated with t-IVT (r = −0.73, p < 0.001) in all four patient groups. In the absence of CAD, t-IVT became shortened (NA by 7 ± 3 s/min; LBBB by 9 ± 4 s/min) and correlated with a fall in the QRS duration (NA: R = 0.87; LBBB: R = 0.91), and CO increased with stress (NA by 4.7 ± 2.7 l/min; LBBB by 4.0 ± 2.3 l/min; all p < 0.001). With CAD, t-IVT did not shorten normally with stress. Instead, t-IVT was 5.6 s/min longer and CO was 3.3 l/min lower than in those without CAD (both p < 0.001), and t-IVT did not correlate with the QRS duration. Conclusions In patients with DCM, t-IVT during pharmacologic stress depends on changes in ventricular activation induced by LBBB or CAD and is, by itself, a major determinant of peak CO during stress.