Which Patients with AV Block Should Receive CRT Pacing?

OPINION STATEMENT: The benefits of cardiac resynchronization therapy (CRT) are well-established, with the majority of large clinical trials focused on individuals with advanced systolic heart failure and patients with prolonged QRS duration. The favorable outcomes from CRT have been expanded from initial investigations in patients with severe heart failure to those with milder degrees of heart failure. More recently, studies have evaluated whether there is benefit from CRT in individuals requiring ventricular pacing but with asymptomatic left ventricular dysfunction. Recent studies have demonstrated that biventricular pacing may be superior to right ventricular (RV) pacing in patients requiring pacing who have normal to mildly depressed left ventricular function. However, pacing-induced cardiomyopathy does not occur in all RV-paced patients. CRT non-responders account for about one-third of patients receiving this therapy. Moreover, the complexity of the procedure carries with it higher complication risks than conventional pacemaker implants, and hence routine CRT implantation may not be justified in the entire population. In this paper, we provide a comprehensive review of the physiology and consequences of RV pacing, the pathophysiology of pacing-induced cardiomyopathy, the benefits of CRT, and the factors that should be considered for CRT implantation in this population.