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

Background: 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 suffered 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 classified as responders in case of an increase in EF > or = 25% in combination with an increase in NYHA class > or = 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 classified as responders. Whereas a significant 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 significant influence of response or underlying heart disease (ICM/DCM) on delta QRS duration (P = 0.7).

Conclusions: CRT results in an electrical remodelling with a reduction of the intrinsic QRS duration.