Epicardial approach
All patients were required to be on oral anticoagulant therapy for at least four weeks before the scheduled surgery and were asked to withdraw oral anticoagulation therapy 3 days before the procedure. Enoxaparin sodium (100 IU/kg twice daily) was administered until the evening before surgery. Oral anticoagulant therapy was recommenced the day following surgery.
a) Surgical box lesion:
A circumferential lesion set was delivered anterior to the PVs in an attempt to isolate the PVs and posterior left atrium (Box lesion set) according to a previously described approach(4). Briefly, after general anesthesia, transesophageal echocardiography was performed to rule out an atrial thrombus before surgery. A 3-4 cm right minithoracotomy was performed at the 3rd intercostal space level and a soft-tissue retractor was applied. Thoracoscopic camera was used in all the cases, and the pericardium was opened above the right phrenic nerve. The oblique sinus was entered through blunt dissection. The Estech COBRA Fusion™ 150 Surgical Ablation System (Estech, San Ramon, Calif) was used in all the patients.
The introducer with the magnetic tip was pushed into the transverse sinus until the left atrial appendage was passed. The second introducer was then advanced into the oblique sinus until its tip hinged the first introducer. Care was taken to avoid lesion of the atrial appendage and pulmonary veins were encircled with the ablation probe. The device used suction to stabilize the contact with the epicardium and achieve uniform energy delivery. A circular box lesion was created with bipolar and unipolar radiofrequency energy. Different patterns of energy delivery are available with the device used; in our series, ablation was performed by 2 energy applications lasting 150 seconds each. These were followed by a 60-second application after the probe was moved circumferentially, to achieve complete closure of the box lesion. All the cases were performed off-pump. After the probe was withdrawn, efficacy assessment was usually done by measurement of conduction across the lesion. Conduction block was routinely tested for by recording signals from the posterior wall of the left atrium; if conduction block was not present, additional lesions were delivered. Chest was closed after hemostasis and insertion of a drain.
b) Bachmann’s bundle ablation
An adjunctive BB ablation was performed in the BB group. Bachmann bundle was ablated by introducing the magnetic tip below the ascending aorta and above the roof of the left atrium, and then advanced until the base left atrial appendage. No further dissection was required. The ablation line goes from the left to the right atrial appendage behind the non-coronary aortic sinus and efficacy assessment was done by measurement of conduction across the line (Figure 1).
As for the box lesion, the second introducer was advanced into the oblique sinus until its tip hinged the first introducer. Ablation was performed with 2 energy bipolar and unipolar applications, each lasting 150 seconds.