Abstract 11305: Isolated Left Anterior Fascicular Block is Associated With an Increased Risk of Atrial Fibrillation and Heart Failure

Abstract

Introduction: Isolated left anterior fascicular block (LAFB) can be caused by fibrosis of the conduction system. This ECG finding may therefore represent an early manifestation of diffuse myocardial fibrosis. We sought to test the hypothesis that LAFB in the absence of clinically manifest cardiovascular disease is associated with an increased risk of cardiovascular outcomes that can result from cardiac fibrosis: atrial fibrillation (AF), congestive heart failure (CHF), and death.

Methods: We studied individuals without prevalent cardiovascular disease from the Cardiovascular Health Study, a prospective community-based cohort established in 1989. LAFB was identified from the baseline 12-lead ECG. Incident events were obtained from clinic visits, participant report, the medical record, and hospital discharge diagnoses. Cox proportional hazards models were used to measure the association between baseline LAFB and incident AF, CHF, and all-cause mortality.

Results: Of 2,354 individuals without existing cardiovascular disease, the 54 (2.3%) with LAFB at baseline were older (median 73 vs. 71 years, p<0.001) and more likely male (69% vs. 38%, p<0.001). During 15.3 years of follow-up, 552 participants developed AF, 501 developed CHF, and 1,415 died. Prior to adjustment, LAFB was significantly associated with AF (HR 2.45, 95%CI 1.59-3.75), CHF (HR 3.04, 95%CI 2.00-4.63), and all-cause mortality (HR 1.86, 95%CI 1.38-2.51) (Figure). After adjusting for age, race, sex, body mass index, smoking, and alcohol consumption, LAFB remained statistically significantly associated with AF (HR 1.60, 95%CI 1.03-2.48) and CHF (HR 2.09, 95%CI 1.36-3.23) but not all-cause mortality (HR 1.28, 95%CI 0.94-1.74).

Discussion: In older individuals without clinical cardiovascular disease, LAFB is independently associated with the development of AF and CHF. LAFB may be a marker of diffuse cardiac fibrosis relevant to predicting adverse cardiovascular outcomes.