Electrical remodelling in cardiac resynchronization therapy: decrease in intrinsic QRS duration

Introduction Cardiac resynchronization therapy (CRT) provides a therapeutic option for patients with congestive heart failure (CHF) and left bundle-branch block. Structural myocardial remodelling due to CRT has been described extensively. We hypothesized that CRT might also induce electrical remodelling, thus decreasing the intrinsic QRS duration. Methods: In 38 patients with CHF (ejection fraction (EF): 26 ± 7%) a CRT device was implanted. 18 patients suff ered from ischaemic cardiomyopathy (ICM) and 20 from dilated cardiomyopathy (DCM). Echocardiography and 12-lead ECGs without pacing were obtained prior to implantation and after 6 and 12 months. Patients were classifi ed as responders in case of an increase in EF ≥ 25% in combination with an increase in NYHA class ≥ 1. Variance analysis was performed to determine the impact of response or underlying heart disease (ICM/DCM) on the extent of change in QRS duration (delta QRS duration). Results: The EF increased to 36 ± 10% (P < 0.0001) after 6 months and 40 ± 12% (P < 0.0001) after 12 months of CRT. Intrinsic QRS duration decreased from 171 ± 18 ms before CRT to 164 ± 23 ms (P= 0.027) after 6 months and 161 ± 25 ms (P= 0.002) after 12 months of CRT. 22 patients (58%) were classifi ed as responders. Whereas a signifi cant decrease in intrinsic QRS duration was observed in responders, only a slight decrease was seen in non-responders. However, two-factorial variance analyses did not show a signifi cant infl uence of response or underlying heart disease (ICM/DCM) on delta QRS duration (P= 0.7). Conclusion: CRT results in an electrical remodelling with a reduction of the intrinsic QRS duration.