Longer inter-lead electrical delay is associated with response to cardiac resynchronization therapy in patients with presumed optimal left ventricular lead position.

Aims: In a randomized trial of cardiac resynchronization therapy (CRT), a presumed optimal left ventricular (LV) lead position close to the latest mechanically activated non-scarred myocardium was achieved in 98% of patients by standard implantation. We evaluated whether inter-lead electrical delay (IED) was associated with response to CRT in these patients. Methods and results: We prospectively included 160 consecutive patients undergoing CRT. Pre-implant speckle-tracking echocardiography radial strain and 99mTc myocardial perfusion imaging determined the latest mechanically activated non-scarred myocardial segment. We measured procedural IED as the time interval between sensed signals in right ventricular and LV lead electrograms. All patients had LV pacing site concordant or adjacent to the latest mechanically activated non-scarred segment verified by cardiac computed tomography. Response to CRT was defined as ≥15% reduction in LV end-systolic volume at 6 months follow-up. Selecting a practical IED cut-off value of 100 ms, more patients with long IED than patients with short IED responded to CRT (87 vs. 68%; P = 0.004). In multivariate logistic regression analysis, IED ≥100 ms remained associated with CRT response after adjusting for baseline characteristics, including QRS duration and scar burden [odds ratio 3.19 (1.24-8.17); P = 0.01]. Categorizing IED by tertiles, CRT response improved with longer IED (P = 0.03). Comparable response rates were observed in patients with a concordant and adjacent LV lead position. Conclusion: A longer IED was associated with more pronounced LV reverse remodelling response in CRT recipients with a presumed optimal LV lead position concordant or adjacent to the latest mechanically activated non-scarred segment.