Epicardial Conduction Between the Left Atrium and Left Superior Pulmonary Vein Through the Presumptive Marshall Bundle During a Single Ring Box Isolation

Abstract

A 65 year-old male with symptomatic persistent atrial fibrillation was referred for radiofrequency catheter ablation. He underwent a box isolation to simultaneously isolate all 4 pulmonary veins （PVs） and the left atrial （LA） posterior wall. During the box isolation with a double lasso catheter positioned in both the left superior and right superior PVs, the atrial fibrillation terminated spontaneously. After the box lesion set was created conduction was still observed between the LA and PVs. After an additional radiofrequency energy delivery to the bottom line of the box lesion, the activation sequence of the PVs became uniform during sinus rhythm and pacing from the coronary sinus （CS）, indicating that only one more conduction pathway was present. The 3-dimensional map revealed that the earliest activation site within the box lesion was located in the anterior aspect of the left superior PV during pacing from the CS, but that of the LA during pacing from the superior right PV within the box was on the postero-lateral LA wall below the left inferior PV. Since the activation in the Marshall vein during pacing from the superior left PV within the box was recorded earlier than that in the CS, we suspected that the LA-PV conduction was occurring via the Marshall bundle. A radiofrequency application at the anterior aspect of the left superior PV just inside the box lesion line isolated all the PVs.