Syncope Associated With Alternating Fascicular Block in an Elderly Woman: A Case Report.

Alternating fascicular block (AFB) is defined by intermittent left anterior fascicular block and left posterior fascicular block on serial electrocardiograms. Although alternating bundle branch block is well recognized as a high‑risk conduction abnormality warranting permanent pacing, evidence and guideline clarity for AFB remain limited. This case describes an 81‑year‑old woman with recurrent syncope. AFB was found on EKG, and a permanent pacemaker was introduced. AFBs are a supporting marker of advanced infra‑Hisian conduction disease and can be associated with syncope and clinically significant bradyarrhythmias. In symptomatic patients, early consideration of permanent pacing is reasonable despite the absence of explicit guideline recommendations. This case highlights key diagnostic features and management considerations while underscoring the need for clearer evidence-based guidance regarding AFB.