The Evolving Role of Electrocardiography in Cardiac Resynchronization Therapy

This study aims to summarize the literature on the role of electrocardiography (ECG) in (i) patient selection for cardiac resynchronization therapy (CRT), (ii) predicting clinical response after CRT system is implanted, and (iii) optimizing CRT programming.

Progress has been made in interpreting ECG beyond QRS duration and left bundle branch (LBBB) morphology to select patients for CRT. We now understand a higher chance of response to CRT in patients with atypical right bundle branch block and lower response rates in subgroups with atypical LBBB. QRS area has emerged as a novel marker to quantify baseline electrical dyssynchrony to improve patient selection. After CRT, the resultant QRS narrowing remains the most validated predictor of long-term favorable outcome. There is increasing awareness of prolonged left ventricular pacing latency hindering the desired response to CRT. There is active interest in using ECG beyond minimizing QRS duration to optimize CRT programming for maximal resynchronization. Novel strategies include fusion of paced and/or conducted wavefronts and minimization of paced QRS area. ECG remains the ubiquitous method for ventricular electrical mapping in context of CRT. The role of ECG in elucidating baseline electrical dyssynchrony to aptly select patients for this treatment continues to evolve, and ECG is increasingly being evaluated as a reliable endpoint for optimal CRT programming.