Pacing Affects Cardiovascular Endpoints in Patients With Right Bundle-Branch Block (The PACE-RBBB Trial)

Heart failure (HF) affects 5 million Americans and is responsible for more health-care
expenditure than any other medical diagnosis. Approximately half of all HF patients have
electrocardiographic prolongation of the QRS interval and ventricular dyssynchrony, a
perturbation of the normal pattern of ventricular contraction that reduces the efficiency of
ventricular work. Ventricular dyssynchrony is directly responsible for worsening HF
symptomatology in this subset of patients. Resynchronization of ventricular contraction is
usually achieved through simultaneous pacing of the left and right ventricles using a
biventricular (BiV) pacemaker or implantable cardioverter-defibrillator. Clinical trial
evidence supporting the use of BiV pacing in patients with prolonged QRS duration was
obtained almost exclusively in patients with a left bundle-branch block (LBBB)
electrocardiographic pattern. Recent evidence suggests that resynchronization of ventricular
contraction in patients with LBBB can be obtained by univentricular left ventricular pacing
with equal or superior clinical benefits compared to BiV pacing. Animal studies suggest that
ventricular resynchronization can be obtained in subjects with right bundle-branch block
(RBBB) through univentricular right ventricular pacing. No clinical trial evidence exists to
support the use of BiV pacing in patients with RBBB. Thousands of patients with symptomatic
HF and RBBB currently have univentricular ICDs in place for the prevention of sudden cardiac
death. Most of these devices are currently programmed to avoid RV pacing. We aim to
determine if ventricular resynchronization delivered through univentricular RV pacing
improves symptoms in patients with RBBB and moderate to severe HF who have previously
undergone BiV ICD implantation for symptomatic heart failure. We further aim to determine if
ventricular resynchronization improves myocardial performance and ventricular geometry as
detected by echocardiographic measures and quality of life for patients with HF and RBBB. We
hypothesize that RV univentricular pacing delivered with an atrio-ventricular interval that
maximizes ventricular synchrony is equivalent to BiV pacing for improvement in cardiac
performance, HF symptoms, and positive ventricular remodeling in patients with HF and RBBB.