First experience with radiofrequency catheter ablation in horses with recurrent, persistent naturally occurring atrial fibrillation

BACKGROUND: Myocardial sleeves in the caudal vena cava and pulmonary veins are a potential trigger for initiation and perpetuation of atrial fibrillation (AF) in horses. OBJECTIVES: Isolation of myocardial sleeves in the caudal vena cava or pulmonary veins might reduce the risk for AF recurrence. STUDY DESIGN: Case series. METHODS: Records from seven horses with persistent, recurrent, naturally-occurring AF that were treated with three-dimensional electro-anatomical mapping and radiofrequency catheter ablation (RFCA) in order to reduce recurrence risk were reviewed. Mapping of the caudal vena cava was performed in all horses, while the pulmonary vein ostia I and IV were mapped in two horses and pulmonary vein ostia II and III in one horse. Arrhythmogenic substrate was subsequently isolated by point-by-point RFCA. RESULTS: Mapping identified arrhythmogenic substrates in the caudal vena cava (n = 6), ostium II (n = 1) and ostium IV (n = 2), which were isolated as confirmed by entrance and/or exit block. Five cases recurred (after 2 days, and 6, 11, 11 and 30 months). The horse that relapsed after 6 months underwent a second procedure to isolate ostium III, but the arrhythmia recurred 4 months later. To date, two of seven horses remain in sinus rhythm with a follow-up of 14 and 47 months. MAIN LIMITATIONS: Small number of horses and limited follow-up. CONCLUSIONS: Arrhythmogenic substrate was identified in the caudal vena cava and pulmonary veins in horses with recurrent AF. Two of seven horses remain in sinus rhythm 14-47 months after RFCA. This study does not allow to demonstrate the benefit of ablation. Catheter ablation in horses to reduce AF recurrence risk remains challenging at this point and more research is needed to identify AF triggers and improve ablation technique.