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Ann Thorac Surg 2005;79:2115-2118
© 2005 The Society of Thoracic Surgeons

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New technology

Midterm Clinical Experience With Microwave Surgical Ablation of Atrial Fibrillation

Legacy Health Systems, Good Samaritan Hospital, Portland, Oregon USA and Emanuel Hospital, Portland, Oregon, USA

Accepted for publication June 11, 2004.

^_* Address reprint requests to Dr Molloy, Legacy Health Systems, 2222 NW Lovejoy, Suite 315, Portland, OR 97210 (E-mail: tmolloy302{at}aol.com).

	Abstract

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PURPOSE: Multiple energy sources and lesion sets have been described as an alternative to the conventional cut-and-sew Maze procedure for atrial fibrillation (AF). Described are midterm results with microwave (MW) energy and a single left-sided lesion set so that surgeons can evaluate whether this approach may be appropriate for their patients.

DESCRIPTION: Twenty-nine consecutive patients with chronic (86%) or paroxysmal (14%) AF, undergoing surgery for coexisting heart disease, also underwent MW AF ablation by the use of a single lesion set. A single preoperative and postoperative management regimen was used.

EVALUATION: One hundred percent electrocardiogram follow-up was obtained. At minimum follow-up of 4 months (mean 315 days), 23 of 28 patients (86%) were in stable sinus rhythm.

CONCLUSIONS: The simplified lesion set performed with MW energy compares favorably with the cut-and-sew Maze procedure for patients presenting with AF and coexisting acquired cardiac disease. Connecting lesions to the mitral annulus and right-sided lesions may add potential morbidity without additional efficacy.

	Introduction

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Atrial fibrillation (AF) is a common arrhythmia associated with significantly increased risks of stroke and mortality [1]. Mechanisms of AF, including the ectopic foci theory and the multiple reentrant circuit theory, led to the development of the Cox Maze procedure for the treatment of AF. Two thirds of the patients had "lone" AF, and 98% were free of AF or atrial flutter at approximately 4 years [2]. Other larger series of patients undergoing Maze III concurrent with other cardiac surgical procedures have reported 75% sinus rhythm (SR) at midterm follow-up [3].

Since 1997, alternatives to the Maze procedure that use different lesion sets and energy sources have been described. Little midterm data are available on the efficacy of the use of specific energy sources for specific lesion sets. This study describes the clinical outcome of patients undergoing AF ablation surgery that used a single, left-sided lesion pattern created with a microwave (MW) energy source.

	Technology

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Patient Characteristics
Between September l, 2001, and June 30, 2003, 29 consecutive patients underwent ablation by the use of MW energy and the lesion set depicted in Figure 1. One patient died in the perioperative period. All patient outcomes were tracked with the Patient Analysis Tracking System database software program (Axis Clinical Software, Portland, OR). Additionally, electrocardiograms (ECGs) at discharge, 3 months, 6 months, and then annually were obtained in all Maze patients. Patient characteristics are summarized in Table 1.

View larger version (159K): [in this window] [in a new window]   Fig 1. Bilateral microwave Maze lesion set pattern in 29 patients. FLEX 4 Probe (AFx-Guidant, Santa Clara, CA) was used in 27 patients, and the FLEX 10 Probe was used in 2 patients. The ligament of Marshall was divided and cauterized. The left atrial appendage was excised. The procedure was performed on-pump in 16 patients and off-pump in 13 patients.

	Technique

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Median sternotomy was used in all patients. Lesions were performed from the epicardial side in all patients except for 2 patients undergoing reoperative surgery. In these patients the lesions were performed from the endocardial side.

The MW ablation system is depicted in Figure 2. The FLEX 4 Probe (AFx-Guidant, Santa Clara, CA) with a 4-cm antenna was used in 27 patients, and the FLEX 10 Probe with a 10-cm antenna was used in 2 patients. Modulated, unidirectional MW energy at 2.45 GHz was applied at 65 W for 90 seconds for all beating heart cases. The 2 reoperative patients underwent arrested heart endocardial ablation for 45 seconds at 65 W. The duration and power settings used have been shown to heat cardiac tissue within 4 mm of the MW antenna to 55°C, resulting in cellular death as determined by mitochondrial staining [4]. Electrical conduction across the lesion is blocked without disruption of connective tissues.

View larger version (18K): [in this window] [in a new window]   Fig 2. Microwave ablation system.

View larger version (94K): [in this window] [in a new window]   Fig 3. Transesophageal echo shows thrombus (arrow) in the left atrial appendage.

Based on the laboratory work of Hwang and colleagues identifying adrenergic fibers in the vein of Marshall, the ligament of Marshall was divided with electrocautery [5]. Left atrial appendage (LAA) excision was performed after the application of a partial occluding clamp in off-pump cases or with the left atrium open in on-pump ablation cases. The stump of the LAA was closed with simple running 3-0 Prolene (Ethicon, Somerville, NJ). No bleeding complications occurred at the LAA closure.

All mitral valve operations were approached with a Guiraudon transseptal incision. Of the 16 mitral valve procedures, 7 were mitral repairs and 9 were mitral valve replacements. The operative field was flooded with CO₂ at 6 L/min in all valve cases to facilitate the removal of air from the heart.

	Clinical Experience

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Two patients who received only coronary bypass grafting operations/Maze procedures were operated on without arresting the heart. The other patients underwent cold hyperkalemic cardiac arrest with alternating antegrade and retrograde blood cardioplegia to perform the associated cardiac procedure. No right-sided lesions or connecting lesions to the mitral valve annulus were performed.

All patients received an intravenous 150 mg/10 min loading dose of amiodarone immediately preoperatively, followed by 1 mg/min for 6 hours, then 0.5 mg/min until the patients were taking oral medications. Amiodarone was then given at 200 mg twice daily for 2 weeks, followed by 200 mg daily for 6 weeks beyond the last known episode of AF. Anticoagulation with warfarin sodium was also continued for a minimum of 2 months postoperatively or 6 weeks after the last known episode of AF. Additionally, prompt cardioversion for in-hospital AF and atrial pacing for bradyarrhythmias was used. Amiodarone was discontinued in 3 patients because of persistent bradyarrhythmias.

Follow-up is presented in Table 3. Nineteen of 28 patients (68%) were discharged in SR. At mean follow-up of 315 days, 23 patients were in stable SR with only 6 patients on antiarrhythmic medication (5 on amiodarone 1 on flecainide) other than β-blockers. Off-pump versus on-pump ablation was equally efficacious: 11 of 13 patients who underwent off-pump ablation (85%) compared with 13 of 15 (87%) who underwent ablation on cardiopulmonary bypass were in SR.

Failed Maze procedures are summarized in Table 2. Older age (81 vs 73) and lower preoperative ejection fraction (43% vs 55%) were associated with an increased risk of failure, but the differences were not statistically significant (p = 0.23 and 0.11, respectively). Left atrial size did not correlate with persistent AF after the Maze procedure. Only 1 patient had significant atrial flutter, but was subsequently converted to non-SR on flecainide.

	Comment

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The simplified lesion set described for the performance of the Maze procedure compares favorably with conventional cut-and-sew Maze techniques. Although Cox and colleagues reported a 98% success rate in 122 patients undergoing the Maze III procedure with follow-up greater than 3 months [2], over two thirds of these patients had lone AF. Kosakai reported on Maze III procedures in more than 2,500 patients in Japan, all of whom had concomitant procedures as in my series, and found 75% of the patients in SR at midterm [3].

The importance of a connecting lesion to the mitral valve annulus to prevent "left atrial flutter" is not supported by this series. This lesion was avoided because of concerns that the application of MW energy over the circumflex coronary artery might result in intimal damage.

I believe that the division of the ligament of Marshall may be an important adjunct to the simplified Maze procedure. As reported by Hwang and colleagues, the vein of Marshall was cannulated in 17 of 28 patients with paroxysmal AF. This site was then identified as the origin of AF in 6 patients, and radiofrequency (RF) ablation of only the vein of Marshall terminated AF in 4 of these patients [5].

Cardiac surgeons must choose between an array of devices and lesion patterns for the treatment of AF. The epicardial approach to cardiac tissue ablation on the beating heart with a unidirectional energy source represents a relatively safe approach to cardiac tissue ablation. Excess energy is absorbed by blood elements rather than by contiguous structures. Reports of esophageal perforation, though rare, argue against creating lesions from the endocardial surface with a unipolar RF energy source [6].

Bipolar RF devices such as the Medtronic device and AtriCure device (AtriCure, Inc, Cincinnati, OH) are expeditious and unlikely to damage contiguous structures. To avoid the rusk of subsequent pulmonary vein stenosis, care must be exercised (particularly in off-pump applications) not to ablate on the pulmonary veins. Furthermore, MW energy may provide deeper lesion penetration [7] than RF energy. The FLEX 4 MW ablation approach requires additional operating room time (usually 35 minutes) compared with only a few minutes for a simple pulmonary vein isolation with the bipolar RF devices. The clinical results with MW ablation have been acceptable despite the lack of transmurality feedback. I recently used a longer, flexible probe/antenna, the FLEX 10 device, off-pump in 10 procedures by using a box lesion set around the pulmonary veins (Fig 4). The probe is passed around the veins, then MW energy is delivered while the primary operation is continued, adding minimal operating time.

View larger version (88K): [in this window] [in a new window]   Fig 4. The FLEX 10 Probe (AFX-Guidant, Santa Clara, CA) device is a long flexible probe/antenna that can be used to create a box lesion set around the pulmonary veins.

Unfortunately, misinterpretation of the Atrial Fibrillation Follow-up Investigation in Rhythm Management (AFFIRM) trial has clouded the issue regarding the importance of rhythm control versus rate control in patients with AF [9]. It should be noted that 36% of the patients in this large multicenter trial had only a single episode of AF before entering the trial and therefore did not meet the definition of AF by American College of Cardiology or American Heart Association criteria. The rhythm control group gained very little rhythm control (54% were in SR at randomization and 63% had SR at 5 years). Fifteen percent of patients in the rate control/anticoagulation group were withdrawn from warfarin sodium because of complications. Death, stroke, and hemorrhage rates in both groups were alarming. Furthermore, quality of life for patients in AF on toxic medications was not assessed.

Alternatively surgical ablation as sole therapy for AF reported by Cox and colleagues [2] with cut-and-sew Maze and Mohr [10] with simplified RF Maze exceeds 90%. Over the next decade, AF ablation surgery, pioneered by Dr James Cox, may be seen as the most important contribution to cardiac surgery since valve replacement and coronary bypass surgery were developed in the 1960s and 1970s.

	Disclosures and Feedom of Investigation

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The microwave generator and ablation probes were purchased by Legacy Health Systems. I performed a free and independent evaluation of this new technology. I have no financial relationship with AFX-Guidant.

	Footnotes

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^Disclaimer The Society of Thoracic Surgeons, the Southern Thoracic Surgical Association, and The Annals of Thoracic Surgery neither endorse nor discourage use of the new technology described in this article.

	References

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1. Benjamin EJ, Wolf PA, D’Agostino RB, et al. Impact of atrial fibrillation on the risk of deaththe Framingham Heart Study. Circulation 1998;98:946-952.[Abstract/Free Full Text]
2. Cox JL, Schuessler RB, Boineau JP. The development of the Maze procedure for the treatment of atrial fibrillation Semin Thorac Cardiovasc Surg 2000;12:2-14.[Medline]
3. Kosakai Y. Treatment of atrial fibrillation using the Maze procedurethe Japanese experience. Semin Thorac Cardiovasc Surg 2000;12(1):44-52.[Medline]
4. Nath S, Lynch C, Whayne J, Haines D. Cellular electrophysiological effects of hyperthermia on isolated guinea pig papillary muscleImplications for catheter ablation. Circulation 1993;88:1826-1831.[Abstract/Free Full Text]
5. Hwang C, Wu TJ, Doshi RN, Peter CT, Chen PS. Vein of Marshall cannulation for the analysis of electrical activity in patients with focal atrial fibrillation Circulation 2000;101:1503-1505.[Abstract/Free Full Text]
6. Gillinov AM, McCarthy PM, Pettersson G, Lytle BW, Rice TW. Esophageal perforation during left atrial radiofrequency ablationis the risk too high?. J Thorac Cardiovasc Surg 2003;126(5):1661-1662.[Free Full Text]
7. Wonnell TL, Stauffer PR, Langberg JJ. Evaluation of microwave and radiofrequency catheter ablation in a myocardium-equivalent phantom model IEEE Trans Biomed Eng 1992;39(10):1086-1095.[Medline]
8. Saltman AE, Rosenthal LS, Francalancia NA, Lahey SJ. A completely endoscopic approach to microwave ablation for atrial fibrillation Heart Surg Forum 2003;6(3):E38-E41.[Medline]
9. Wyse DG, Waldo AL, DiMarco JP, et al. Affirm Triala comparison of rate control and rhythm control in patients with atrial fibrillation. N Engl J Med 2002;347:1825-1833.[Abstract/Free Full Text]
10. Mohr FW. Curative treatment of atrial fibrillation—acute and mid-term results of intraoperative radiofrequency ablation of atrial fibrillation in 150 patients Presented at the Annual Meeting of the American Association for Thoracic Surgery. 2001May.

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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): Thomas A. Molloy Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Molloy, T. A. Search for Related Content PubMed PubMed Citation Articles by Molloy, T. A.