Site of latest activation in patients eligible for cardiac resynchronization therapy: patterns of dyssynchrony among different QRS configurations and impact of heart failure etiology.

Introduction: Cardiac resynchronization therapy (CRT) has emerged as a treatment option for patients with end-stage heart failure and a QRS duration ≥120 ms. Nonetheless, many patients with a prolonged QRS do not demonstrate left ventricular (LV) mechanical dyssynchrony, and discrepancies between electrical and mechanical dyssynchrony have been observed. In addition, several studies demonstrated that superior benefits after CRT could be achieved when the LV pacing lead was positioned at the most delayed myocardial segment.

Methods: A total of 248 heart failure patients scheduled for CRT were included. In all patients, a 12-lead electrocardiogram and 2-dimensional echocardiogram were obtained. Patients were divided into 5 QRS configuration subgroups: narrow, left bundle-branch block, right bundle-branch block, intraventricular conduction delay, and right ventricular pacing. With speckle-tracking radial strain analysis, we evaluated time to peak radial strain. Next, the segments with the least and with the most mechanical activation delay were identified, and LV dyssynchrony was defined as the time delay between the two.

Results: Mean QRS duration was 164 ± 31 ms. Mean LV dyssynchrony in all patients was 186 ± 122 ms. Site of latest activation was predominantly located in the lateral (27%), posterior (26%), and inferior (20%) segments. Furthermore, extent of LV dyssynchrony was comparable between QRS configuration subgroups. An unequal distribution of LV segments with the most mechanical delay was observed in the left bundle-branch block and right ventricular pacing subgroups (P < .001 for both), whereas in the narrow, right bundle-branch block, and intraventricular conduction delay subgroups, a more homogeneous distribution was noted. No differences in distribution pattern or in extent of LV dyssynchrony were observed between ischemic and nonischemic heart failure patients.

Conclusion: The lateral, posterior, and inferior segments take up 73% of the total latest activated segments in heart failure patients eligible for CRT. Presence of LV dyssynchrony can be observed in all QRS configurations. The site of latest activation may be outside the lateral or posterior segment, making echocardiographic assessment of LV dyssynchrony and site of latest activation a valuable technique to optimize patient outcome after CRT.