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Eur J Cardiothorac Surg 2005;27:243-249
© 2005 Elsevier Science NL

Three years experience with monopolar and bipolar radiofrequency ablation surgery in patients with permanent atrial fibrillation

^a Department of Cardiac Surgery, AK St. Georg, Lohmuehlenstrasse 5, 20099 Hamburg, Germany
^b Department of Cardiology, AK St. Georg, Hamburg, Germany

Received 31 August 2004; received in revised form 15 October 2004; accepted 18 October 2004.

^* Corresponding author. Tel.: +49 40 2890 4150/4151; fax: +49 40 2890 4184. (E-mail: stephan.geidel{at}ak-stgeorg.lbk-hh.de).

	Abstract

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion 5. Limitations Appendix A. Conference... References

 
Objective: In our population permanent atrial fibrillation (pAF) is a frequent concomitant problem in patients undergoing open heart surgery. A 3-year experience with a treatment strategy using mono- and bipolar radiofrequency (RF) ablation procedures in a heterogeneous group of patients is reported. Methods: In a prospective analysis the incidence of pAF among all patients undergoing open heart surgery in our department between February 2001 and July 2004 was evaluated. In a second step a selective group of 106 patients with pAF (primary mitral: n=63; aortic: n=24; CABG: n=16; aortic+mitral: n=3) underwent either monopolar (n=86) or bipolar (n=20) RF ablation procedures creating two encircling isolation lesions around the left and the right pulmonary veins (PVs) and a connection line between both. In addition amiodarone was given for 3 months after surgery. Regular follow-ups were performed 3, 6, 9, 12, 18, 24 and 36 months after surgery. Results: The incidence of pAF in the total group of 4.110 patients was 3.6%. While the rate was low in cases without severe heart valve disease (1.1%), a significantly higher presence of pAF in patients scheduled for heart valve surgery (10.3%) was observed (P<0.0001). The incidence was 30–39% in patients with degenerative and rheumatic mitral valve (MV) disease, and further particularly high in the older aged compared to younger patients (4.2–8.3% at 70–99 years; P<0.001). Hospital mortality after combined open heart and RF ablation surgery was 1.9%. Whereas patients with small left atrial size (LA-diameters <56mm; n=59) had SR in almost 90% at follow-up, LA enlargement (LA-diameter 56mm; n=47) was associated with a significant risk of persisting pAF after surgery (P=0.033, 0.002 and 0.006 at 3, 6 and 9 months follow-up). Conclusion: The use of RF ablation procedures in combination with amiodarone therapy represents a safe and efficient option to cure pAF during open heart surgery in a selective group of patients. The preoperative LA size was of significant importance for the outcome in this investigation.

Key Words: Atrial fibrillation • Atrial fibrillation surgery • Radiofrequency ablation • Arrhythmia surgery • Heart valve surgery • Bipolar radiofrequency ablation

	1. Introduction

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion 5. Limitations Appendix A. Conference... References

 
Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia treated in clinical practice. In cardiac surgery permanent atrial fibrillation (pAF) is exceptionally important because it is a common concomitant problem in patients scheduled for open heart surgery [1]. Further its associated morbidity causes significantly poorer survival rates compared to patients with stable sinus rhythm (SR) [2]. Since Cox has demonstrated that AF can be definitely eradicated [3], efforts were made to achieve less invasive and time consuming methods than the Maze procedure [4,5]. But even if many different concepts of AF ablation surgery have been presented recently, it is still an open debate, how to achieve most satisfactory results. And even if the Maze procedure still represents the standard against which the effectiveness of these ablation techniques is measured, the goal of stable SR is not always assured [6–8]. In regard of this background, we report our 3-year experience with a (compared to many other techniques) simplified surgical approach, which includes a reduced ablation lesion pattern in a heterogeneous group of patients.

	2. Patients and methods

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion 5. Limitations Appendix A. Conference... References

 
In a prospective analysis the relative frequencies of pAF (following the classification of the ACC/AHA/ESC Practice Guidelines [9]) which had been documented to persist for a period of at least 6 months among all patients undergoing open heart surgery in our department between February 2001 and July 2004 was evaluated. Since February 2001 a selective group of patients hospitalized for open heart surgery in our institution and concomitant pAF (6 months) was treated intraoperatively with RF ablation procedures. Exclusion criteria for ablation surgery were: any other form of AF (intermittent or permanent lasting less than 6 months), emergency operation, severe reduced left ventricular function (EF25%), acute endocarditis or myocardial infarction (7 days), considerable cachexia (body mass index (BMI) 18), severe intracardiac thrombosis or extreme left atrial size (LA-diameters of 72mm were assessed to be our limit for the procedure). Patients with primary heart valve surgery and pAF underwent monopolar RF ablation, since March 2003 also a bipolar RF ablation procedure was performed in CABG cases and since October 2003 in aortic valve (AV) cases. Etiology of heart valve disease was assessed by clinical history, intraoperative valve examination and histological analysis.

2.1. Surgical procedure
2.1.1. Monopolar RF ablation
The surgical procedure has been described as detailed before [10]. To create endocardial RF ablation lesions two almost identical systems (either the Thermaline^® device or since January 2002 the Cobra^® device (both Boston Scientific Corporation, San Jose, USA) were used (Fig. 1). Monopolar RF ablation was performed using 100W RF power for 120s, the local temperature was set at 70°C. The first lesion line completed the isolation of the right pulmonary veins (RPVs) from the inferior to the superior RPV using the left atriotomy (Fig. 2). Isolation of the left pulmonary veins (LPVs) was performed with a semicircular ablation line close to the inferior, and another one around the superior LPV. These were connected by a transverse lesion across the posterior wall of the LA. The left atrial appendage (LAA) was sutured from the endocardial side in cases with LA enlargement (LA-diameters 56mm; since July 2003). Arrangements to avoid thermic esophageal injury were: (1) monopolar RF ablation was performed precisely under direct view during conventional open heart valve surgery only, (2) the transesophageal echocardiogram (TEE) probe was removed during the ablation procedure, (3) a dry compress was passed behind the LA before delivery of RF energy, (4) a flexible ablation probe was used and adapted to the tissue without pressure, (5) local temperature was set at only 70°C and (6) cachectic patients were excluded.

View larger version (73K): [in this window] [in a new window]   Fig. 1. RF ablation procedures using the monopolar Cobra®/Thermaline® device (above) or the bipolar Atricure® device (below).

View larger version (20K): [in this window] [in a new window]   Fig. 2. Ablation scheme. LAA, left atrial appendage; LPVs, left pulmonary veins; RPVs, right pulmonary veins; MV, mitral valve.

2.2. Perioperative management, follow-up and statistical analysis
Standard 12-lead electrocardiogram (ECG) and transthoracic echocardiogram (TTE) were routinely performed on admission and before discharge. TTE was performed by an experienced cardiologist of our hospital, assessment of the left atrial size was done by evaluating the LA-diameter (antero-posterior diameter on parasternal axis view at end systole). An LA with a diameter of larger than or equal to 56mm (mean value of all patients with pAF between February 2001 and July 2004) was termed as large (<56mm, small). Administration of amiodarone was started with an intravenous bolus of 300mg before end of cardiopulmonary bypass followed by an infusion of 900mg/day for 3 days. After that oral administration of 5x200mg up to 7–10g dependent of body weight was begun, 1x200mg/day followed for 3 months. In cases of thyroid disease, amiodarone imcompatibility or other contraindication for amiodarone administration, sotalol was given alternatively (first intravenous bolus of 10mg, then 1mg/kg for 24h; oral administration of 2–3x40–80mg dependent of body weight for 3 months). Persisting bradycardia for more than 10 days lead to a termination of amiodarone/sotalol. An indication for permanent pacemaker implantation was persisting bradycardia for 2 weeks. Early recurrence of AF was DC cardioverted after saturation with amiodarone/sotalol and after exclusion of intracardiac thrombosis by TEE. During initial antiarrhythmic drug saturation, in cases of AF recurrence or bradycardia, patients were observed with continuous monitoring, first on the intensive, then on an intermediate care unit. Heparin was given after resolution of postoperative bleeding. Patients with CABG, MV repair or bioprosthesis got cumarine for 3 months, patients with mechanical valves lifelong anticoagulation. All patients were restudied 3, 6, 9, 12, 18, 24 and 36 months after surgery by standard 12-lead ECG and clinical examination.

Quantitative preoperative and operative data were normally distributed and described by arithmetic mean±standard deviation; qualitative distributed data were presented as absolute frequencies. For pAF and sinus rhythm (SR) the relative frequency among all patients and some subgroups were calculated. Qualitative characteristics were compared using the exact Fisher ²-test. All P-values were two-tailed and interpreted nominal that is not adjusted for multiple comparisons. P-values <0.05 were considered to be statistically significant. Analysis was performed with SPSS for Windows 11.5.1.

	3. Results

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion 5. Limitations Appendix A. Conference... References

 
3.1. Relative frequencies of pAF
The incidence of pAF in the total group was 3.6% (148 of 4.110; male/female: 70/78; age: 70.7±8.8 years; pAF duration 69.8±67.4 months; LA-diameter: 56.4±7.6mm). While the rate was low in cases without severe heart valve disease (1.1%; 34 of 3.001), a significantly higher presence of pAF in patients scheduled for heart valve surgery (10.3%; 114 of 1.109) was observed (P<0.0001) (Table 1). The occurrence was particularly high in patients with degenerative (30.0%; 33 of 111) and rheumatic (39.0%; 39 of 100) MV disease. The incidence increased with age and was 1.5, 2.3, 3.3, 4.2, 5.1 and 8.3% at 15–49, 50–59, 60–69, 70–79, 80–89 and 90–99 years. In patients with an age of older than or equal to 70 years the incidence was 4.5% (88 of 1.968) compared to 2.8% (60 of 2.142) among younger patients (P<0.001).

View this table: [in this window] [in a new window]   Table 1. Incidence of pAF (6 months) among 4.110 open heart cases (according to primary etiology of heart disease)

View larger version (13K): [in this window] [in a new window]   Fig. 3. Relation of preoperative LA-diameter, AF duration and etiology of heart disease in 106 patients with pAF.

All patients were regularly restudied (mean follow-up: 16.6±11.5 months), follow-up of mono- and bipolar treated patients differed substantially (19.2±11.0 months in the monopolar and 5.3±4.3 months in the bipolar group). Administration of amiodarone/sotalol was stopped after 3 months in all cases. Late mortality occurred in 7 cases and was related to 2 cardiac (sudden cardiac death at almost 4 and 14 postoperative months; both patients were without amiodarone/sotalol; no autopsy) and 5 non-cardiac deaths (cancer disease: n=2; pulmonary disease: n=2; stroke syndrome as a consequence of severe stenosis of both internal carotid arteries: n=1).

At late follow-up approximately 75% of all patients and almost 90% of those without LA enlargement were in stable SR (Table 3): The rate of SR was significantly higher in patients with small preoperative LAs compared to those with LA enlargement (P=0.033, 0.002 and 0.006 at 3, 6 and 9 months follow-up). After bipolar RF ablation procedures at 3, 6, 9 and 12 months 12 of 15, 7 of 8, 5 of 5 and 3 of 3 patients were in stable SR. In primary CABG and AV patients (n=40) a longterm success-rate of almost 80% was observed (Table 4). After ablation surgery in CABG and AV cases there were no severe complications at all.

	4. Discussion

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion 5. Limitations Appendix A. Conference... References

Already in 1962 Moe presented a remarkable concept to explain the pathophysiology of AF [12]. His most widely accepted ‘multiple wavelet hypothesis’ still represents the basis for almost all efforts to cure AF: He proposed that AF is a consequence of multiple independent re-entrant wavelets which spread through the atrium. Allessie indicated that only six wavelets are necessary to sustain AF [13]. The Maze procedure and many of its modifications were based on this concept and demonstrated efficiency to abolish AF [3]. The principles of Maze surgery are: PV isolation, block of re-entrant wavelets by complex incisions and (more or less) reduction of atrial size. But even if high success rates have been described in the early 1990s, the method is avoided by many surgeons because of its complexity. Besides, some investigations indicate that the goal of stable SR is not always assured [6–8]. Notably Cox recently reported, that the preclusion of all theoretical macro-reentrant circuits (as in the Maze procedure) is possibly unnecessary and most patients with AF could be cured with simplified procedures and less lesions [14].

In 1998 Haissaguerre described that the initiation of AF originates from rapidly firing foci predominantly located inside the PVs [15]. According to that the concept was developed that isolation of the PVs should be a sufficient ‘basis’ for a surgical ablation procedure. To save LA function, to bar potential generation of foci and to keep the ablation procedure as short as possible, the Maze pattern of multiple incisions was reduced to encircling isolation lesions of the left and the right PVs and a short connection line between both: In contrast to classical Maze surgery [3] and in congruity with the ‘Mini-Maze procedure’ [14], a septal lesion and a lesion to the LAA were abandoned; moreover neither a lesion to the MV annulus, nor any right atrial lesions were performed. An electrophysiological isolation or resection of the LAA was also abandoned. Many other groups, who used various AF ablation techniques in the past, followed more or less closely the ‘complex’ Maze-principles to block re-entrant circuits as completely as possible. However, as the mechanisms of AF initiation and maintenance and the individual electrophysiological and pathological atrial tissue changes in cases with pAF [17–19] obviously vary, it is still an open debate, which lesions appart from PV isolation are definitely obligatory to restore SR in most of the patients, and which not.

As in MV surgery the LA has to be opened anyway, an endocardial ablation technique was performed in our series. However, with the application of monopolar RF energy two theoretical deficiencies remain: (1) transmurality of the created lesions is not definitely guaranteed; and (2) rare but fatal complications because of too deep lesions (e.g. esophageal injury) have been described [16]. However, this serious complication did not occur in our series, presumably because of the described arrangements (as outlined above) to avoid this problem. Because of these theoretical deficiencies of the monopolar technique since March 2003 a bipolar RF approach was used in all non-MV patients, with the additional advantage of less invasiveness and a shorter aortic cross clamping time (by avoiding a left atriotomy). Notably preparation before using the bipolar device was more prolonged than in monopolar technique, even if the ablation time was shorter. However, both procedures were normally terminated within only 15min.

Our data of the relative frequencies of pAF (high incidence in MV cases, increase with age) are in congruity with the literature: the relationship of pAF, chronic heart valve disease and advanced age could be interpreted by the long-standing processes of structural and electrophysiological changes as a consequence of persistent LA pressure, volume overload (both predominantly in chronic MV disease) and/or myocardial damage with necrosis of cardiac myocites and interstitial fibrosis [17–19]. Even if the precise mechanisms of these electrophysiological effects are still incompletely understood, it can be anticipated that inhomogeneous local activity on the basis of structural changes, or rather deteriorations, may produce re-entrant circuits leading to the maintenance of cardiac arrhythmias, particularly pAF.

We interpret our clinical results of ablation surgery particularly on the basis researches of others [12,14,15]: AF wavelets sustained by foci located inside the PVs were blocked by the created lesions, the described antiarrhythmic drug protection with amiodarone or sotalol supported SR during the unstable initial stage, which was approximately 3 months. Amiodarone was given as first choice antiarrhythmic drug to reduce postoperative recurrence of AF according to the data of Roy et al. [20] and the clinical experience of others [5]. AF recurred soon after surgery in more than half of the patients because the refractory period of the atrium was still shortened. In the case of AF recurrence DC cardioversion was recommended, so the influence on the longterm results must be further evaluated. Notably, despite continuous anticoagulation two patients with AF recurrence had developed a small atrial thrombus after surgery. Compared with the literature, which reveals almost only ablation data concomitant to MV surgery, our investigation indicates (1) that pAF ablation surgery in non-MV cases is also effective; (2) further the preoperative LA size was of significant concern for the success of the described method. LAA closure in the large LA cases was a consequence of poorer results in that group to prevent thromboembolism. However, LA enlargement as a consequence of persistent LA pressure and volume overload is particularly found in chronic MV disease. Notably almost all cases in this study with large LAs belonged to the group of MV patients. According to the research of Melo et al. [4], which termed LA size to be a prognostic factor for longterm results after RF ablation, almost 90% of patients with small LA diameter had SR at follow-up. In contrast to these cases, large LAs were associated with a significant risk of AF recurrence. Reviewing literature, the presence of LA enlargement has also been described as a strong independent risk factor for Maze procedure failure, with the consequence of a tendency to perform Maze surgery selectively [6–8]. Isobe et al. suggested a higher risk of persistent AF after Maze surgery in patients with LA-diameters greater than 80mm [7]. In contrast to that Choo et al. recently reported a success-rate of Maze surgery of 95% in MV patients with LA-diameters greater than or equal to 60mm [21]. These authors and other groups recommend a policy of aggressive LA size reduction in pAF patients with dilated LA [22,23]. However, it remains uncertain whether the LA size itself is the critical issue. It can be expected instead that cellular, structural morphologic and in parallel electrophysiological changes of the atrial tissues are more marked in cases with progressive enlargement and hypertrophy of the atria [18–20,24,25]: ‘Atrial remodeling’ seems to be a time-dependent process that develops as an adaptive regulation of atrial myocites against external ‘stressors’, which are predominantly tachycardia and volume/pressure overload as a consequence of a heart failure syndrome. Either in atrial tachycardia-dependent or in heart failure-dependent remodeling, both reversible and irreversible changes (interstitial fibrosis and necrosis/apoptosis) occur. This ‘structural remodeling’ adds the abnormalities of refractoriness to a deterioration of conduction velocity and may explain the reduced efficiency of pAF surgery in patients with enlargement and hypertrophy of the atria. However, we suppose that the described strategies, which include a reduced ablation lesion pattern, are effective and seem to simplify the treatment of pAF in a selective group of patients, particularly in cases without severe LA enlargement.

	5. Limitations

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion 5. Limitations Appendix A. Conference... References

 
This study consists of a heterogeneous patients group regarding the type of pathology and the type of RF ablation technique that limits the evidence. The data were not evaluated under randomized conditions, further the groups were not matched. Patients with an LA-diameter of 72mm were excluded and no regression statistical analysis to assess the effect of the LA size on SR conversion rate was performed. Besides two different cardioplegic strategies were used (Bretschneider solution in valve surgery and intermittent cross clamping in CABG) that is a confounding factor of the study. For rhythm evaluation only 12-lead ECG was used, to assess the possibility of non-permanent AF or atrial flutter the follow-up data should be completed by performing a 24-h-ECG registry. Further the number of procedures in the bipolar group was too small for final judgement.

	Appendix A. Conference discussion

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion 5. Limitations Appendix A. Conference... References

 
Dr S. Redzepagic (Melbourne, Australia): I would like to make a couple of comments. From our experience and also from some very recent publications, in regards to achieving sinus rhythm and really have the biatrial transport function, it has been actually documented that although we may achieve 80% to 90% of the sinus rhythm on ECG, the real transport function is only achievable, and it depends on which research group you follow, in only 35% to 55%. So what is your mean on following up the patients postoperatively, especially 6 to 12 months? And what method do you use to actually identify if there is a real transport function? We may have an ECG pattern of sinus but not the real transport function.

Dr Geidel: The routine follow-up included only standard electrocardiogram and clinical examination, but at least at one time in all cases one Holter-monitoring and transthoracic echo was performed in addition.

Dr T. Mesana (Ottawa, Ont., Canada): I have two questions. Maybe I missed it in your slides. What percentage of the mitral valve patients were discharged in normal sinus with or without conversion before discharge?

Dr Geidel: It was the same in the mitral valve and non-mitral valve groups, about 63%. There was no difference between these two groups.

Dr Mesana: How could you achieve a higher rate? You converted them like at 2 months or just spontaneous cardioversion with amiodarone? You have a higher number at 3 months, right?

Dr Geidel: We had a higher number in the non-mitral valve cases, yes.

Dr Mesana: So did they convert themselves?

Dr Geidel: Obviously, yes.

Dr Mesana: So my question, then, is why do you cardiovert the patients before discharge and not 2 or 3 months later?

Dr Geidel: It's an open debate if early cardioversion should be done in these cases. So we started with this concept even if other groups stopped and waited for the patients to cardiovert themselves.

Dr Mesana: And my final question, if I may, what is your hypothesis for these failures? You only have the hypothesis of the size and not technical issues? You have a wide series, so you should have some hypothesis for us.

Dr Geidel: LA enlargement is obviously the consequence of LA pressure overload following a heart failure syndrome, predominantly in mitral valve disease. So it's still the question if the LA size itself is the critical issue, but I would say that rather the morphological and electrophysiological changes in diseased atria are more marked in these cases. So what we're talking about is atrial remodeling, and we know from the basic research of atrial remodeling that there are a lot of reversible, but also many irreversible changes in these atria.

	Footnotes

 
Presented at the joint 18th Annual meeting of the European Association for Cardio-thoracic Surgery and the 12th Annual Meeting of the European Society of Thoracic Surgeons, Leipzig, Germany, September 12–15, 2004.

	References

Top Abstract 1. Introduction 2. Patients and methods 3. Results 4. Discussion 5. Limitations Appendix A. Conference... References

 

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				M. Lamotte, L. Annemans, B. Bridgewater, S. Kendall, and M. Siebert A health economic evaluation of concomitant surgical ablation for atrial fibrillation Eur. J. Cardiothorac. Surg., November 1, 2007; 32(5): 702 - 710. [Abstract] [Full Text] [PDF]

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