Right Ventricular Septal Pacing in Patients With Right Bundle Branch Block and Heart Failure (The SPARK Trial)

Inclusion Criteria: * Cardiomyopathy; ischemic or non-ischemic on optimal medical therapy per current heart failure treatment guidelines for at least 3 months. * LVEF \< 35% by trans-thoracic echocardiogram assessment * Prior implantation of pacemaker/defibrillator with at least an atrial and RV mid septal lead. Atrial lead can be waived if RV lead has atrial sensing capabilities\* * Normal sinus rhythm at enrollment * RBBB with QRS duration \>120 msec on 12 lead surface EKG. * PR interval \<250 msec on 12 lead surface EKG * Subjects with biventricular pacemaker/ICD will be eligible for enrollment if their LV lead pacing function has been turned off by the subject's primary cardiologist prior to study enrollment for at least 3 months (this could be due to lead malfunction or the decision to deactivate the LV pacing therapy for any reason per primary cardiologist discretion) Exclusion Criteria: * Age younger than 18 years old * Pregnancy * Acute Myocardial infarction within 6 months of entry into the study * Inotrope dependent heart failure condition * Left ventricular assist device or heart transplantation * Any other known conditions other than heart failure that could limit survival to \< 6 months. * Atrial fibrillation or flutter burden \>10% of the time within the last 6 months * Atrioventricular node disease that requires ventricular pacemaker support \>10% of the time