Abstract 16791: Conduction System Response to Cardiac Resynchronization Therapy

Abstract

Background: Cardiac resynchronization therapy (CRT) can be an effective treatment for cardiomyopathy patients with intraventricular conduction delay. However, significant controversy remains over the effect of QRS duration shortening on CRT outcomes. We hypothesize that reduction in QRS duration following CRT implantation is associated with echocardiographic outcomes. Methods: We included all adult patients with structural heart disease and CRT followed at UCLA. We reviewed all available electrocardiograms (ECG) and echocardiograms. We excluded patients with CRT for complete heart block, congenital heart disease, and those without intrinsic QRS ECGs prior to CRT. Patients were categorized as left bundle branch block (LBBB) if Strauss criteria were met prior to CRT implantation. Other patterns (including right bundle branch block with QRS duration ≥150ms) were classified as IVCD. We evaluated QRS duration before and immediately after CRT implantation. Changes in QRS duration post-CRT implant were calculated in percentage change. Echocardiograms were evaluated for changes in left ventricular end diastolic dimension (LVIDD) and ejection fraction (LVEF) following CRT implantation. Results: We included 108 patients (mean age of implant 66.1±12.8 years, 65% male, 63% nonischemic cardiomyopathy). Of these, 44 patients (41%) had LBBB. After CRT, patients with LBBB had significant decrease in QRS duration (-9.3±17.0% vs +16.9±30.9%, p < 0.001), improvement in LVEF (12.1±10.5% vs 1.85±10.7%, p < 0.001) and reduction in LVIDD (-0.6±0.7cm vs 0.1±0.7cm, p < 0.001) compared to patients with IVCD. Decrease in QRS duration was significantly correlated with both improvement in LVEF (Pearson r = 0.21, p = 0.037) and reduction in LVIDD (Pearson r = 0.28, p = 0.006). Conclusion: CRT resulted in significantly larger decrease in QRS duration amongst patients with LBBB compared to IVCD. QRS duration reduction was, in turn, significantly correlated with improvements in LVIDD and LVEF. This likely reflects the proximal nature of true LBBB, and the ability of CRT to utilize the remaining distal Purkinje system for impulse propagation. Further research on the electrical and mechanical response to CRT can help guide optimization of target populations.