Cardiac resynchronization therapy improves myocardial conduction

BACKGROUND Cardiac resynchronization therapy (CRT) reverses left ventricular remodeling and improves left ventricular systolic function. However, little is known about whether CRT improves ventricular conduction. OBJECTIVE To determine the relationship between CRT response and QRS narrowing. METHODS The study included consecutive patients who underwent CRT with defibrillator (CRT-D) implantation between January 2002 and December 2012 and had subsequent generator replacement (GR). At the time of GR, super-responder was defined as those who had left ventricular ejection fraction (LVEF) of 50% or more; patients who had an LVEF of 36-49% with an increase of more than 5% were considered responders, and the others were nonresponders. All patients were assessed 6 months after CRT-D implantation and at the time of GR. RESULTS Of 114 study patients, 58 (50.9%) were nonresponders, 29 (25.4%) responders, and 27 (23.7%) super-responders. QRS narrowing at 6 months was significant in super-responders (175.4 ± 21.4 to 159.7 ± 20.7 ms, P = 0.001) and responders (169.0 ± 21.3 to 157.7 ± 17.6 ms, P = 0.008). At time of GR, only super-responders had further QRS narrowing (159.7 ± 20.7 to 146.3 ± 19.2 ms, P