Scar burden, not intraventricular conduction delay pattern, is associated with outcomes in ischemic cardiomyopathy patients receiving cardiac resynchronization therapy

Background Patients with nonspecific intraventricular conduction delay (IVCD) benefit less from cardiac resynchronization therapy (CRT) than patients with left bundle branch block (LBBB). Objective The purpose of this study was to determine whether post-CRT outcome differences in patients with ischemic cardiomyopathy (ICM) relate to intrinsic QRS pattern and/or scar burden. Methods We analyzed 393 consecutive ICM patients with left ventricular ejection fraction (LVEF) ≤35%, QRS duration >120 ms, and LBBB or nonspecific IVCD who underwent single-photon emission computed tomography myocardial perfusion imaging and CRT-defibrillator implant. We compared scar burden; QRS duration; LVEF change; risk of death, transplant, or ventricular assist device; and risk of appropriate device shocks between LBBB and IVCD patients, using multivariable analyses to determine relative associations between QRS pattern vs scar burden and outcomes. Results Nonspecific IVCD is associated with greater scar burden and narrower baseline QRS duration than LBBB. IVCD patients demonstrated less QRS narrowing with CRT than LBBB patients, even when excluding IVCD patients with QRS duration Conclusion IVCD is associated with greater scar burden than LBBB in ICM CRT-defibrillator recipients. Scar burden, not QRS pattern, is independently associated with adverse clinical outcomes.