Left anterior fascicular block is associated with non-ischemic myocardial scar and proportionately decreased ejection fraction

Abstract

Background: Left anterior fascicular block (LAFB) has been associated with increased mortality, but the underlying causes are unknown. We hypothesized that LAFB is associated with increased left ventricular (LV) scar burden and reduced LV ejection fraction (LVEF). Methods: Patients referred for cardiovascular magnetic resonance imaging (CMR) and electrocardiography (ECG) were retrospectively enrolled. Patients with LAFB (n=51) and matched control patients without LAFB (n=600) were compared regarding size and location of LV scar, LVEF, and a dysfunction index describing the difference between measured LVEF and expected LVEF where the expected LVEF is based on scar size. Results: Compared to matched controls, patients with LAFB had on average a larger LV scar (median [interquartile range] 0.7 [0.0-6.6] vs 0.0 [0.0-1.5] % LV mass, p<0.001). LAFB was associated with a higher prevalence of any scar (59% vs 33%, p<0.001). Patients with LAFB had similar prevalence of ischemic scar (29% vs 23%, p=0.40) but a higher prevalence of non-ischemic scar (29% vs 10%, p=0.001) which was most frequently located in the basal and mid inferoseptal segments and the anterior and lateral apical LV segments. LVEF was lower in patients with LAFB than matched controls (58 [43-60] vs 60 [55-60] %, p=0.02), but there was no difference in dysfunction index (24.0 [17.8-25.5] vs 24.0 [19.0-27.8] %-points of LVEF, p=0.32) Conclusions: In a matched hospital cohort, LAFB was associated with a small decrease in LVEF that was proportionate to the increased LV scar burden. This increased LV scar burden was more commonly due to non-ischemic etiology and not infarction, and not more commonly located near the expected course of the left anterior fascicle.