Pre-excited atrial fibrillation: A lower threshold for electrical cardioversion

Wolff-Parkinson-White syndrome is characterized by the presence of ventricular pre-excitation on the electrocardiogram (ECG) and associated tachycardia symptoms.The characteristic electrocardiographic pattern is present in 0.1---0.2% of the general population and in most cases is an incidental finding.Pre-excitation may, however, not be detected as it appears only intermittently or is very subtle and goes unnoticed on the ECG (such as in left lateral pathways, far from the atrioventricular [AV] node).The most frequent arrhythmia in patients with this syndrome is AV reentry tachycardia (about 80%) followed by atrial fibrillation (AF), which occurs in 20---30%.Most patients with asymptomatic pre-excitation have a good prognosis, but sudden death occurs in 1.25 per 1000 person-years 1 and may be the first manifestation of the disease.Sudden death has been attributed to the coexistence of AF and accessory pathways with a short antegrade refractory period leading to a very fast ventricular response and subsequent degeneration into ventricular fibrillation (VF).The case report presented by Nunes et al. in this issue of the Journal 2 describes a patient admitted with irregular