Hemodynamics and prognosis after primary cardiac resynchronization system implantation compared to "upgrade" procedures.

Introduction: Left bundle brunch block (LBBB) and right ventricular stimulation (RVS) may be associated with asynchrony and heart failure. Differences between these two entities and their response to cardiac resynchronization therapy (CRT) are not well defined.

Methods: Patients receiving CRT from 1999 to 2006 were analyzed for cardiac events and prognosis separated between primary implants for LBBB (n = 221) and upgrades from RVS (n = 107).