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 < 0.001). QRS duration change after 6 months was independently associated with super-response (hazard ratio: 1.20 for every 5 ms QRS duration narrowing; 95% confidence interval, 1.06–1.38; P = 0.005), and QRS narrowing of 10 ms or more was associated with lower risk of all-cause mortality after GR. Conclusion: Continuous QRS narrowing after CRT, as an electrical marker, is associated with a super-response to CRT. Further QRS narrowing 6 months after CRT implantation was associated with lower risk of mortality after GR.