Acute biventricular hemodynamic effects of cardiac resynchronization therapy in right bundle branch block

Abstract

Controversy remains regarding the use of cardiac resynchronization therapy (CRT) in patients with heart failure with right bundle branch block (RBBB) and reduced left ventricular (LV) ejection fraction. Moreover, little is known about acute hemodynamic changes with CRT in this subgroup as compared with patients with left bundle branch block (LBBB). The purpose of this study was to evaluate the acute biventricular hemodynamic response of CRT and other pacing configurations, including the effects of atrioventricular (AV) delay and atrial pacing, to understand the effects of CRT in RBBB. Forty patients (9 with RBBB and 31 with LBBB) undergoing CRT implantation underwent temporary pacing with varying configurations and AV delay. The acute hemodynamic response was assessed via invasive measurements of dP/dtmax (maximal rate of change in pressure) in the left ventricle (LV) as well as the right ventricle (RV) in patients with RBBB. Patients with LBBB had a greater LV dP/dtmax response to CRT than did patients with RBBB. In patients with RBBB, single- or dual-site RV pacing configurations resulted in greater increases in RV dP/dtmax than did biventricular pacing. Optimal AV delays that maximized RV dP/dtmax were shorter than optimal AV delays for LV dP/dtmax. Furthermore, AV delays chosen to maximize improvement in RV dP/dtmax frequently resulted in negative effects on LV dP/dtmax. These findings demonstrate a complex relationship between pacing configuration, AV delay, and hemodynamic responses. The biventricular hemodynamic response in patients with heart failure with RBBB might be improved by optimizing pacing modalities and AV delays. This may be particularly important in patients with diseases in whom RV failure predominates, such as patients with pulmonary hypertension and LV assist device.