Effects of LBBB and slowed myocardial conduction on QRS-duration criteria efficacy across sexes

Determine how left bundle branch block and slowed myocardial conduction, individually and in combination, affect the diagnostic efficacy of conventional QRS duration thresholds and indexed QRS duration criteria (normalized by left ventricular end-diastolic volume, left ventricular mass, or height) for stratifying male versus female heart failure patients eligible for cardiac resynchronization therapy.

Background

Cardiac resynchronization therapy selection relies on QRS duration thresholds, yet women often have shorter QRS durations due to smaller heart size, contributing to sex differences in CRT response. Indexed QRS duration criteria, such as normalization by left ventricular end-diastolic volume, left ventricular mass, or height, have been proposed to mitigate these disparities.

Functional remodeling—including left bundle branch block and slowed myocardial conduction due to scarring or fibrosis—prolongs QRS duration and may confound CRT candidate selection. The interplay between these pathological substrates and sex-specific anatomy complicates the interpretation and performance of QRS duration–based criteria, motivating investigation into their diagnostic efficacy across sexes.