Cardiac Resynchronization Therapy Response Assessment with Electromechanical Activation Mapping within 24 Hours of Device Implantation: A Pilot Study

Abstract

Background: Cardiac resynchronization therapy (CRT) response assessment relies on the QRS complex narrowing criterion. Yet one third of patients do not improve despite narrowed QRS after implantation. Electromechanical wave imaging (EWI) is a quantitative echocardiography-based technique capable of noninvasively mapping cardiac electromechanical activation in three dimensions. The aim of this exploratory study was to investigate the EWI technique, sensitive to ventricular dyssynchrony, for informing CRT response on the day of implantation.

Methods: Forty-four patients with heart failure with left bundle branch block or right ventricular (RV) paced rhythm and decreased left ventricular ejection fraction (LVEF; mean, 25.3 ± 9.6%) underwent EWI without and with CRT within 24 hours of device implantation. Of those, 16 were also scanned while in left ventricular (LV) pacing. Improvement in LVEF at 3-, 6-, or 9-month follow-up defined (1) super-responders (ΔLVEF ≥ 20%), (2) responders (10% ≤ ΔLVEF < 20%), and (3) nonresponders (ΔLVEF ≤ 5%). Three-dimensionally rendered electromechanical maps were obtained under RV, LV, and biventricular CRT pacing conditions. Mean RV free wall and LV lateral wall activation times were computed. The percentage of resynchronized myocardium was measured by quantifying the percentage of the left ventricle activated within 120 msec of QRS onset. Correlations between percentage of resynchronized myocardium and type of CRT response were assessed.

Results: LV lateral wall activation time was significantly different (P ≤ .05) among all three pacing conditions in the 16 patients: LV lateral wall activation time with CRT in biventricular pacing (73.1 ± 17.6 msec) was lower compared with LV pacing (89.5 ± 21.5 msec) and RV pacing (120.3 ± 17.8 msec). Retrospective analysis showed that the percentage of resynchronized myocardium with CRT was a reliable response predictor within 24 hours of implantation for significantly (P ≤ .05) identifying super-responders (n = 7; 97.7 ± 1.9%) from nonresponders (n = 17; 89.9 ± 9.9%).

Conclusion: Electromechanical activation mapping constitutes a valuable three-dimensional visualization tool within 24 hours of implantation and could potentially aid in the timely assessment of CRT response rates, including during implantation for adjustment of lead placement and pacing outcomes.

Keywords: Cardiac resynchronization therapy; Echocardiography; Electromechanical wave imaging; Heart failure; Response prediction; Ventricular resynchrony assessment.

Figure 1:. Study design.

Figure 2:. EWI-based evaluation metrics.

Mean left and right wall activation times (LWAT, RWAT) quantified on a) the 2D four-chamber and b) the 3D-rendered isochrone. c) Percentage of resynchronized myocardium (%RM).

Figure 3:. Distinguishing pacing conditions with the mean left/right wall activation times (LWAT/RWAT).

Isochrones of an 89-year-old male in a) RV pacing; b) LV pacing; and c) CRT setting in BiV pacing, d) 2D and 3D LWAT/RWAT in the different pacing conditions for cohort 1. Repeated measures one-way ANOVA followed by post-hoc analysis with Holm-Sidak’s multiple comparisons: * p≤0.05, ** p≤0.01, *** p≤0.001 and **** p≤0.0001.

Figure 4:. 3D-rendered ventricular isochrones for three males with CRT within 24 hours of their implant.

a) Patient 1 – non-responder: 65-year-old; b) Patient 2 – responder: 89-year-old; c) Patient 3 – super-responder: 64-year-old. LWAT were computed on the 3D-rendered isochrones.

Figure 5:. Clinical and EWI-based CRT metrics in the three response subgroups.

a) QRS durations at baseline; b) LWAT at baseline; c) %RM^LV at baseline; and d) Changes from baseline to post-CRT. The Δ values were computed by measuring the differences between post-CRT metrics and baseline metrics. One-way ANOVA followed by post-hoc analysis with Tukey’s multiple comparisons was performed across the response groups for each of the three metrics: * p≤0.05.

Figure 6:. Prediction metrics post-CRT within 24 hours of implantation in the three response subgroups:

a) QRS durations; b) LWAT; and c) %RM^LV. One-way ANOVA followed by post-hoc analysis with Tukey’s multiple comparisons for QRS and LWAT. Non-parametric Kruskal-Wallis followed by post-hoc analysis with Dunn’s multiple comparisons on %RM^LV: *p≤0.05.