Insights into left ventricular dyssynchrony: Consequences for myocardial function and response to cardiac resynchronization therapy

Abstract

In hearts with left bundle branch block (LBBB), there is typically reduced function in the early-activated interventricular septum and compensatory increased function in the late-activated left ventricular (LV) lateral wall. In heart failure patients with LBBB, cardiac resynchronization therapy (CRT) may improve LV function, but about one third of patients do not benefit from the therapy. The aim of the thesis was to study the effect of LBBB on LV function during increased blood pressure and ischemia, and to find a better method to select CRT candidates. First, we found that patients with LBBB were hypersensitive to a moderate blood pressure increase as this caused a substantial reduction in LV function. The underlying mechanism was septal dysfunction. Second, we found that during LBBB, lateral wall ischemia led to markedly improved septal function. Third, in a prospective multicenter study, we demonstrated how the presence of marked septal dysfunction with compensatory lateral wall hyperfunction identified patients who responded to CRT with added value to current guidelines. The mechanism of CRT response was increased septal function and consequently patients with septal scar responded poorly.