Introduction: Equipoise remains regarding the utility of cardiac resynchronization therapy (CRT) in heart failure (HF) patients with right bundle branch block (RBBB) and reduced left ventricular ejection fraction (LVEF). Moreover, little is known regarding the acute hemodynamic changes with CRT in such patients.
Hypotheses: HF patients with a RBBB and reduced LVEF demonstrate a diminished LV hemodynamic response to biventricular pacing compared to LBBB patients. However, RBBB patients will demonstrate an improved RV hemodynamic response by correcting RV conduction delay.
Methods: Forty patients (9 with RBBB and 31 with LBBB) undergoing clinically-indicated CRT implantation underwent temporary pacing with varying configurations and AV delay. Acute hemodynamic response was assessed via invasive measurements of dP/dtmax in the LV as well as the RV in RBBB subjects.
Results: LBBB patients had a greater LV dP/dtmax response to CRT than the RBBB patients (11.3±11.1% vs 6.1±4.0%, p<0.05) during biventricular pacing. In RBBB patients, single or dual-site RV pacing configurations resulted in larger increases in RV dP/dtmax than biventricular pacing. Optimal AV delays that maximized RV dP/dtmax were significantly shorter than optimal AV delay for LV dP/dtmax for all the tested configurations (p<0.05, Figure). Furthermore, AV delays chosen to maximize improvement in RV dP/dtmax frequently resulted in negative effects on LV dP/dtmax (Figure).
Conclusions: These findings demonstrate a complex relationship between pacing configuration, AV delay and acute hemodynamic response to CRT. The biventricular hemodynamic response among HF patients with RBBB might be improved by optimizing pacing modalities and AV delays. This may be particularly important in such patients with diseases in which RV failure is associated with a poor prognosis, such as pulmonary hypertension and after left ventricular assist device.