Atrial Fibrillation in a Patient With an Accessory Pathway.

A 24-year-old man with history of unspecified arrhythmia presented with palpitations and chest pain. Initial electrocardiogram (ECG) revealed irregular tachycardia with varying QRS width: 150 to 200 beats per minute for narrow complexes and 300 beats per minute for wide complexes. Following cardioversion, ECG revealed sinus tachycardia with a preexcitation pattern of positive delta waves in the anterolateral leads and negative delta waves in inferior leads. The patient remained in sinus rhythm and underwent successful ablation of a right posteroseptal accessory pathway. Subsequent ECG showed upright T waves in the leads I, aVL, and V2-6, large inverted T waves in leads III and aVF, and no delta waves. This case serves as an important reminder that atrial fibrillation (AF) in the presence of an accessory pathway may present with confounding ECG features, potentially leading to incorrect diagnoses and treatments that may be life threatening. Despite 10% to 30% prevalence of AF in the presence of an accessory pathway and the relative awareness of Wolff-Parkinson-White syndrome among general internal medicine providers, the clinical recognition of Wolff-Parkinson-White syndrome may be hindered in the presence of preexcited AF.