Left Superior Pulmonary Vein Rhythm Masquerading as Sinus Rhythm

A 55 year old male with a history of frequent symptomatic episodes of paroxysmal atrial fibrillation (AF) for four years was referred to us for catheter ablation. He had earlier tried flecainide and sotalol. However he was unresponsive to both of them. The echocardiogram was normal. Figure 1, left panel demonstrates his baseline electrocardiogram. The relatively slow rate and regularity of this rhythm was suggestive of sinus rhythm. However, notably the P wave morphology demonstrates positive P wave in V1, negative in aVL, isoelectric in lead I and notched and positive in inferior leads suggested that the rhythm was originating from the left atrium. The patient underwent catheter ablation during which mapping confirmed the origin of this slow rhythm (Figure 2, left panel) from the left superior pulmonary vein and that it competed with activity from the sinus node (Figure 2, right panel). Furthermore, fast tachycardia and atrial fibrillation was also noted to arise from this vein. Isolation of the left superior pulmonary vein eliminated all tachycardia and normalised the P wave on electrocardiogram (Figure 1, right panel). His procedure was completed with isolation of all four pulmonary veins by circumferential ablation.