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 After the probe was withdrawn,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.