HOW TO SELECT THE APPROPRIATE CANDIDATES FOR CARDIAC RESYNCHRONIZATION THERAPY
M. Haghjoo
Department of Pacemaker and Electrophysiology, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran

A central issue in cardiac resynchronization therapy (CRT) is the identification of patients most likely to respond that is patients with significant atrioventricular (AV) and/or inter- and/or intraventricular mechanical dys-synchrony (DYS) who would most likely benefit from CRT. Almost all prospective, controlled studies on CRT have been conducted on patients with severe congestive heart failure (CHF) presenting with a wide QRS complex. In the original hypothesis of CRT, a wide QRS complex, a marker of electrical DYS, was correlated with mechanical ventricular DYS. While this may generally be correct, it is worth mentioning that some patients with a wide QRS do not have marked mechanical ventricular DYS and, conversely, that some patients with a narrow QRS may be candidates for CRT due to significant mechanical DYS. On the other hand, although short-term experimental studies have shown that patients with wider QRS complexes have a greater immediate mechanical response to CRT, most long-term studies have shown that QRS duration does not predict a response to CRT; and QRS narrowing does not predict a functional improvement following CRT, although the opposite has been observed in some studies in which the right ventricular (RV) lead was positioned at the RV septum. This may explain the relatively high percentage of nonresponder (NR) patients who have been selected for CRT based on QRS duration as a surrogate for mechanical ventricular DYS. We review recent studies on the predictors of long-term response, and their impact on patient selection for CRT.