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J Thorac Cardiovasc Surg 2007;134:1519-1525
© 2007 The American Association for Thoracic Surgery

Evolving Technology

Successful low-energy cardioversion using a novel biodegradable gel pad: Feasibility of treating postoperative atrial fibrillation in animals

^a Department of General and Cardiothoracic Surgery, Kanazawa University School of Medicine, Kanazawa, Japan
^b The School of Materials Science and the 21st Century COE Program, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa, Japan.

Received for publication October 27, 2006; revisions received February 25, 2007; accepted for publication April 26, 2007.

^_* Address for reprints: Kenji Iino, MD, Department of General and Cardiothoracic Surgery, Kanazawa University of Medicine, 13-1 Takaramachi, Kanazawa 920-8641, Japan. (Email: k-iino{at}m8.dion.ne.jp).

Objective: Postoperative atrial fibrillation is one of the most frequent complications of cardiac surgery. We developed a novel biodegradable gel pad consisting of biopolymers that directly attach to the myocardium by electrostatic interaction. The present study examines the feasibility and effectiveness of low-energy internal cardioversion using these pads.

Methods: The hearts of 6 pigs were exposed through a median sternotomy under general anesthesia, and 2 monopolar pacing wires were placed on the left pulmonary veins (chest open group). Two biodegradable cardioversion gel pads were placed on the right appendage and the left atria without suturing. All wires were extruded through the skin and secured with a suture. Sustained atrial fibrillation was induced by burst-pacing from the pulmonary veins in continuous 20-ms cycles. Shock intensity started at 0.5 J, and the energy level was increased in 0.5-J increments until cardioversion occurred. This protocol was repeated 5 times per pig. In a second group of 6 pigs (chest closed group), the epicardial cardioversion electrode gel pads and pacing wire electrodes were positioned as described above. Shock intensity was started at 0.5 J. If the shock was unsuccessful, the energy level was increased in 0.5-J increments until 2 consecutive cardioversions were achieved at a single energy level. At postoperative days 1, 3, 5, and 7, the defibrillation threshold was determined with the chest closed. At postoperative day 10, the cardioversion wires were removed. At predetermined time intervals, the heart was reexposed and the extent of degradation in vivo was visually evaluated and histologically assessed after sacrifice.

Results: All pigs with induced atrial fibrillation were cardioverted to sinus rhythm on the determined postoperative day. The mean energy and lead impedance in the chest open group were 0.65 ± 0.23 J and 97.6 ± 5.52 , respectively, and the overall values of mean energy and lead impedance in the chest closed group were 1.67 ± 1.00 J and 75.9 ± 13.3, respectively. No complications were observed after wire removal. The gel pads became degraded and decreased in thickness, and signs of mild inflammation were evident on the gel pad. However, the gel pads did not elicit significant severe inflammatory reactions according to both gross and histologic assessments at 1 month after the surgery.

Conclusion: Atrial cardioversion using novel biodegradable gel pads that are easily affixed may afford a straightforward and effective treatment for atrial fibrillation after cardiac surgery.