Long-term outcomes of rate-dependent left bundle branch block during exercise testing: a single-centre retrospective...

Rate-dependent left bundle branch block (LBBB) during exercise testing is traditionally considered a potential marker of coronary artery disease (CAD), yet the long-term prognosis remains uncertain. This study assessed the long-term outcomes of patients presenting with rate-dependent LBBB during exercise testing.

In this retrospective single-centre cohort study, all bicycle exercise tests performed between 2000 and 2022 were reviewed. Patients with transient LBBB developing during exercise and resolving during recovery were included. Baseline characteristics, diagnostic work-up, and long-term outcomes were collected. The primary endpoint was progression to permanent LBBB. Secondary endpoints included new-onset left ventricular systolic dysfunction, cardiac implantable electronic device (CIED) implantation, and all-cause mortality.

Among 46,089 patients undergoing 51,220 exercise tests, 68 patients (0.15%) exhibited rate-dependent LBBB. Median age was 59.7 years (54.6-68.4) and 59.4% were male. CAD was present in 29.4%, while baseline heart failure was present in 11.8%. Rate-dependent LBBB occurred at a median heart rate of 126 bpm. During a median follow-up of 12.8 years (8.7-20.2), permanent LBBB developed in 36 patients (52.9%), with cumulative incidence of 46.5% at 10 years. New-onset systolic dysfunction occurred in 12 patients (17.6%), most often after or concurrent with permanent LBBB. CIED implantation was required in 12 patients (17.6%). All-cause mortality was 29.4% (8.1% at 10 years), with age as only independent predictor.

Rate-dependent LBBB is uncommon but frequently progresses to permanent LBBB and is associated with subsequent systolic dysfunction. These findings suggest that rate-dependent LBBB may represent an early manifestation of intrinsic conduction system disease.