Atrial fibrillation in partial anomalous pulmonary venous return: right atrial drainage from one vein and epicardial conduction from another vein

A 72-year-old man with a history of patch closure of sinus venosus atrial septal defect (ASD) and uncorrected partial anomalous pulmonary venous return (PAPVR) of the right superior pulmonary vein (RSPV) draining to right superior vena cava (Figure 1A) presented for atrial fibrillation (AF) ablation. In addition to the PAPVR of the RSPV, computed tomography angiography showed four veins draining into the left atrium (LA): a right middle pulmonary vein (RMPV), a right inferior pulmonary vein, and two left-sided pulmonary veins. Mapping showed the RSPV was electrically silent but pulmonary vein potentials were present in all other pulmonary veins. An irrigated radiofrequency ablation catheter was used to perform wide antral circumferential ablation of the pulmonary veins in the LA. After completion of the line as well as a carinal line, an entrance block was seen in all pulmonary veins except the RMPV. Mapping while pacing the posterior LA showed earliest activation was deep within the RMPV 1 cm from the antrum. Pacing within the pulmonary vein at the low output (ensuring absence of direct RA capture) showed earliest activation in the posterior right atrium (RA) even prior to LA activation (Figure 1B). These findings were consistent with bidirectional conduction across an epicardial electrical connection between RMPV and RA. The site of earliest RA activation was directly adjacent to the phrenic nerve as delineated by high output pacing. As such, ablation was not undertaken to isolate this vein out of concern for phrenic nerve injury. Recurrence of AF has not been seen at a 6-month follow-up.