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Ann Thorac Surg 2002;74:1259-1261
© 2002 The Society of Thoracic Surgeons

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How to do it

Microwave ablation of atrial fibrillation during mitral valve operations

^a Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio, USA

Accepted for publication April 30, 2002.

* Address reprint requests to Dr Gillinov, Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, F24, 9500 Euclid Ave, Cleveland, OH 44195 USA
e-mail: gillinom{at}ccf.org

	Abstract

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Although the Cox-Maze III procedure cures atrial fibrillation in the majority of patients, it has not had widespread application. Development of new operations that use alternate energy sources and different lesion sets have caused resurgence in the surgical treatment of atrial fibrillation. Microwave creates lines of conduction block by thermal damage and subsequent scar formation. We describe a rapid and simple technique for microwave ablation of atrial fibrillation in patients having mitral valve operations.

	Introduction

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Development of new operative procedures that use alternate energy sources and different lesion sets have caused resurgence in the surgical treatment of atrial fibrillation (AF). Microwave, which creates lines of conduction block by thermal damage and subsequent scar formation, is distinctly different from radio frequency energy [1]. We describe a simple and rapid technique for microwave ablation of AF in patients having mitral valve operation.

	Technique

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After median sternotomy, the patient is placed on cardiopulmonary bypass (CPB) through cannulas in the ascending aorta, superior vena cava, and inferior vena cava. The heart is arrested with cold blood cardioplegia delivered antegrade and retrograde. Microwave ablation is performed before the mitral valve procedure.

Each set of pulmonary veins is isolated separately. The right pulmonary veins are mobilized by dissecting the pericardial reflection between the right superior pulmonary vein and the superior vena cava and by freeing the right inferior pulmonary vein from the inferior vena cava. Waterston’s groove is developed for about 1 cm, and a standard lateral left atriotomy is constructed. A flexible microwave ablation tool (AFx Inc, Fremont, CA) that is 4 cm long is placed on the left atrial epicardium posterior and medial to the right pulmonary veins (Fig 1). The shielded microwave catheter is positioned 5 to 10 mm from the pulmonary vein orifices and oriented so that the microwave energy will be transmitted from the epicardium to the endocardium. The energy is set at 65 W, and the application time is 45 seconds. The surgeon observes the developing lesion from the endocardial surface. The endocardium turns yellow at the completion of the lesion. Two microwave applications are generally required to complete isolation of the right pulmonary veins.

View larger version (33K): [in this window] [in a new window]   Fig 1. Ablation of the right pulmonary veins. (A) The microwave probe is placed on the left atrial epicardium posterior and medial to the right pulmonary veins. (B) The ablation line consists of the cut edge of the left atriotomy in conjunction with a microwave lesion created with two applications of the probe.

The left atrial appendage is then excised. A connecting lesion is created from the cut edge of the left atrial appendage to the ablation line around the left pulmonary veins. The stump of the left atrial appendage is closed with running 4-0 polypropylene suture.

A final lesion connecting the two pulmonary vein encircling lesions is created. The table is returned to the midline position, and the apex of the heart elevated. The microwave probe is placed on the epicardium of the posterior left atrium, and a lesion created from the right inferior pulmonary vein to the left inferior pulmonary vein (Fig 2). At no time is energy directed toward the esophagus or other adjacent structures.

View larger version (56K): [in this window] [in a new window]   Fig 2. Left atrial lesion set created with epicardial microwave ablation. Each set of pulmonary veins is encircled separately. An additional lesion connects the pulmonary vein encircling lesions. The left atrial appendage is excised, and a connecting lesion is carried from the cut edge to the left pulmonary veins.

Ten patients had mitral valve operations (repairs in 8 patients, replacements in 2 patients) and microwave ablation of the pulmonary veins. AF was chronic in 6 patients and paroxysmal in 4 patients. Ablation was performed before the mitral valve procedure and took 10 to 15 minutes. Additional procedures included tricuspid valve repair or replacement (4 patients), coronary artery bypass grafting (3 patients), and aortic valve replacement (2 patients). Eight patients had perioperative AF develop. Rhythm at discharge was normal sinus rhythm in 6 patients, atrial fibrillation in 3 patients, and paced in 1 patient for sinus bradycardia.

	Comment

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Although the Cox-Maze III procedure successfully ablates AF in 75% to 100% of patients [2, 3], the complexity of this operation has limited its application by surgeons. Substitution of alternate energy sources for the standard cut-and-sew technique coupled with simplified lesion sets that address the left atrium and pulmonary veins have resulted in surgical procedures that take only 10 to 20 minutes. These procedures are safe and restore sinus rhythm in 70% to 80% of patients [4].

Microwave creates lines of conduction block by thermal damage and subsequent scar formation [1]. High frequency electromagnetic emission causes oscillation of water molecules in tissue, converting electromagnetic energy into kinetic energy or heat. Microwave heating has a potential advantage over radio frequency heating in that the depth and volume of heated tissue are greater for the same tissue surface temperature. This may result in a higher probability of transmural lesions.

Although microwave may be used to perform epicardial ablation of AF on the beating heart [5], in the setting of mitral valve operations we prefer to create epicardial lesions on the arrested heart. This is a simple and rapid procedure, and direct observation of the endocardium during or after lesion creation allows the surgeon to confirm that lesions are continuous and transmural.

Initial results with microwave ablation of AF are promising [6]. Long-term follow-up is necessary to document the efficacy of this technique. Preliminary results with alternate energy sources have demonstrated that many patients who leave the hospital in AF return to sinus rhythm within a few months [4]. This may occur after microwave ablation as well.

Surgeons are embracing new technologies and operations to treat AF. The goal is development of simple, low-risk procedures for patients with lone AF. Flexible, shielded microwave probes will likely enable minimally invasive, off-pump approaches to AF ablation. Such procedures, which will have low morbidity, will offer the possibility of permanent restoration of sinus rhythm to the large number of patients afflicted with chronic AF.

	References

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1. Wonnell T.L., Stauffer P.R., Langberg J.J. Evaluation of microwave and radiofrequency catheter ablation in a myocardium-equivalent phantom model. IEEE Transactions on Biomedical Engineering 1992;39:1086-1095.[Medline]
2. Cox J.L., Ad N., Palazzo T., et al. Current status of the Maze procedure for the treatment of atrial fibrillation. Semin Thorac Cardiovasc Surg 2000;12:15-19.[Medline]
3. McCarthy P.M., Gillinov A.M., Castle L., Chung M., Cosgrove D., III The Cox-Maze procedure: the Cleveland Clinic experience. Semin Thorac Cardiovasc Surg 2000;12:25-29.[Medline]
4. Williams M.R., Stewart J.R., Bolling S.F., et al. Surgical treatment of atrial fibrillation using radiofrequency energy. Ann Thorac Surg 2001;71.
5. Mazzitelli D., Park C.H., Park K.-Y., Benetti F.J., Lange R. Epicardial ablation of atrial fibrillation on the beating heart without cardiopulmonary bypass. Ann Thorac Surg 2002;73:320-321.[Abstract/Free Full Text]
6. Knaut M., Spitzer S.G., Karolyi L., et al. Intraoperative microwave ablation for curative treatment of atrial fibrillation in open heart surgery—The MICRO-STAF and MICRO-PASS Pilot Trial. Thorac Cardiovasc Surg 1999;47(Suppl):379-384.[Medline]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Nicholas G. Smedira Delos M. Cosgrove, III Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gillinov, A. M. Articles by Cosgrove, D. M. Search for Related Content PubMed PubMed Citation Articles by Gillinov, A. M. Articles by Cosgrove, D. M., III Related Collections Electrophysiology - arrhythmias