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Updated: Feb 9, 2026

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
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Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing

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Scar burden, not intraventricular conduction delay pattern, is associated with outcomes in ischemic cardiomyopathy

Evan C Adelstein1, Andrew D Althouse1, David Schwartzman1

  • 1Heart and Vascular Institute, University of Pittsburgh, Pittsburgh, Pennsylvania.

Heart Rhythm
|June 1, 2018
PubMed

Insights

Patients with nonspecific intraventricular conduction delay (IVCD) show less benefit from cardiac resynchronization therapy (CRT) compared to those with left bundle branch block (LBBB). Scar burden, not QRS pattern, independently predicts adverse outcomes in ischemic cardiomyopathy patients receiving CRT-defibrillators.

Area of Science:

  • Cardiology
  • Medical Devices
  • Electrophysiology

Background:

  • Nonspecific intraventricular conduction delay (IVCD) is associated with poorer outcomes following cardiac resynchronization therapy (CRT) compared to left bundle branch block (LBBB).
  • Understanding the factors contributing to these outcome disparities is crucial for optimizing CRT in ischemic cardiomyopathy (ICM).

Purpose of the Study:

  • To investigate whether differences in post-CRT outcomes between ICM patients with LBBB and IVCD are linked to intrinsic QRS patterns or myocardial scar burden.
  • To identify the independent predictors of CRT response and clinical outcomes in ICM patients with varying QRS morphologies.

Main Methods:

  • Analysis of 393 consecutive ICM patients with LVEF ≤35% and QRS duration >120 ms, categorized by LBBB or IVCD.
  • Assessment of myocardial scar burden using single-photon emission computed tomography (SPECT) and comparison of QRS duration, LVEF changes, and clinical outcomes (death, transplant, VAD, appropriate shocks).
  • Multivariable analyses were employed to determine the relative contributions of QRS pattern and scar burden to patient outcomes.

Main Results:

  • Patients with IVCD exhibited greater scar burden and narrower baseline QRS duration than LBBB patients.
  • IVCD patients showed less QRS narrowing post-CRT and less LVEF improvement compared to LBBB patients.
  • Myocardial scar burden, not QRS morphology or duration, was independently associated with LVEF increase and improved long-term clinical outcomes (survival, reduced need for VAD/transplant, fewer appropriate shocks).

Conclusions:

  • In ICM patients receiving CRT-defibrillators, IVCD is linked to higher myocardial scar burden compared to LBBB.
  • Myocardial scar burden, rather than the specific QRS pattern (LBBB vs. IVCD), is the independent predictor of adverse clinical outcomes.
Abstract

Keywords:
Cardiac resynchronizationIntraventricular conduction delayIschemic cardiomyopathyLeft bundle-branch blockScar burden

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