QRS morphology and electrical dyssynchrony in patients before and after cardiac resynchronization therapy and after device optimization

Introduction: QRS morphology and duration (QRS_d) impact electrical dyssynchrony and the likelihood of response to cardiac resynchronization therapy (CRT). Methods: Four groups of heart failure patients (n = 181) with CRT and left ventricular conduction delay were studied: Strauss left bundle branch block (Strauss LBBB; n = 73), LBBB not meeting Strauss criteria (non-Strauss LBBB; n = 29), interventricular conduction delay (IVCD; n = 54), and right ventricular pacing (RVp; n = 25). Electrical dyssynchrony was measured (using a novel proprietary technology) as systolic area under the curve (AUC) of multiple paired anterior and posterior electrocardiograms. LV electrical resynchronization was defined as the percent change in AUC during pacing, compared to native conduction (cardiac resynchronization index; CRI). Results: Native rhythm AUC was significantly (p < 0.01) more negative (greater dyssynchrony) in the Strauss LBBB and RVp groups than in the non-Strauss LBBB and IVCD groups. Native rhythm AUC (absolute value) increased significantly as QRS_d increased in all groups except RVp. Although native AUC differed between groups, no between-group differences were found in post-CRT baseline AUC (−35 ± 39 mV*ms), baseline CRI (57 ± 29 %), optimally programmed AUC (−3 ± 13 mV*ms) or optimally programmed CRI (90 ± 12 %). Electrical dyssynchrony maps plotting CRI at multiple different AVDs and VVDs showed similar patterns of wavefront fusion across all 4 patient groups. Conclusion: Electrical dyssynchrony varies significantly with QRS morphology during native conduction, but not during CRT pacing at baseline or optimal settings. Regardless of QRS duration or morphology, patients with LV activation delay demonstrate similar and large improvements in electrical synchrony with optimized CRT.