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Ann Thorac Surg 2007;84:1151-1157
© 2007 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Medical University of Vienna, Vienna, Austria
b Department of Cardiology, Medical University of Vienna, Vienna, Austria
c Department of Cardiothoracic and Vascular Anaesthesia & Intensive Care, Medical University of Vienna, Vienna, Austria
Accepted for publication May 11, 2007.
* Address correspondence to Dr Wisser, Department of Cardiothoracic Surgery, University of Vienna, Währinger Gürtel 18–20, Vienna, A-1090, Austria (Email: wilfried.wisser{at}meduniwien.ac.at).
Presented at the Forty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 29–31, 2007.
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Abstract |
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Methods: Retrospective data collection and analysis toward the outcome of 72 consecutive patients who underwent left atrial maze procedures between January 2003 and December 2005 was performed. Surgical ablation was performed concomitantly with valve and (or) coronary procedures. Group I (n = 29) received an endocardial left atrial ablation using unipolar saline irrigated radiofrequency (Medtronic Cardioblate surgical ablation pen; Medtronic Inc, Minneapolis, MN). Group II (n = 43) received epicardial isolation of the pulmonary veins using bipolar saline irrigated radiofrequency (Medtronic Cardioblate). Follow-up included 24h electrocardiogram and echocardiography 6 and 12 months postoperatively.
Results: Mean follow-up was 19.5 ± 1.0 months (17.7 ± 19.5 months group I vs 20.6 ± 1.1 months group II). Both groups were comparable with regard to duration of preoperative atrial fibrillation, European system for cardiac operative risk evaluation, left ventricular ejection fraction, aortic cross-clamp time, bypass time, intensive care unit and hospital stay (p > 0.05). No maze procedure-related mortality was observed. In group I, three patients required postoperative pacemaker implantation due to atrioventricular (AV) bloc, bradycardia, and sick sinus syndrome, respectively. In group II, five patients required postoperative pacemaker implantation (three AV bloc and two bradycardia). Freedom from atrial fibrillation at last follow-up was 85.7% and 58.5% in groups I and II, respectively (p = 0.016).
Conclusions: Pulmonary vein isolation alone seems to be insufficient in treating permanent chronic atrial fibrillation. In case of chronic permanent atrial fibrillation, left atrial endocardial maze, providing the connection lines to the mitral annulus and (or) between the pulmonary veins, seems to be mandatory.
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Introduction |
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Throughout the literature, the efficacy in respect to restoration of sinus rhythm is around 70% to 80% regardless the device, energy form, and lesion concept used. Recent reports revealed that left atrial endocardial maze seems to be nearly as efficient as biatrial endocardial maze in treating chronic permanent AF [11, 12] based on intraoperative mapping studies, suggesting that the left atrium is usually the electrical driving chamber [13].
Seeking strategies to minimizing surgical trauma, the lesion concept and approaches have been trimmed down gradually. On the one hand minimal invasive endoscopic approaches have been described for patients with lone AF [14, 15]; on the other hand epicardial [16, 17] and mixed epicardial and endocardial [18, 19] approaches have been developed. While good results have been described in the treatment of paroxysmal atrial fibrillation, it remains debatable whether pulmonary vein isolation (PVI) alone is a good option for the treatment of permanent AF. Sparse data exist about its application in conjunction with structural heart disease in surgical patients with complex double and triple valve diseases.
The aim of this study was to examine the efficacy of epicardial PVI in patients with chronic persistent AF and structural heart disease in respect to restoration of sinus rhythm, in comparison with a complete endocardial left atrial lesion set.
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Material and Methods |
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The indications for surgery in groups I and II are depicted in Table 1.
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All patients presented with chronic, permanent AF longer than six months despite antiarrhythmic therapy. The duration of AF was up to 20 years in group I and 10 years in group II. For demographic and preoperative data refer to Table 1. Patients were allowed to take their medication until the day before surgery.
Surgical Procedure
After median sternotomy, normothermic cardiopulmonary bypass was established in standard fashion. The venous drainage was accomplished by cannulating both vena cava in case of mitral, tricuspid valve procedures and left atrial endocardial maze procedures, or by cannulating the right atrium with a two-stage cannula in the remainder. The left atrial appendage was not resected or closed by any means.
Left Atrial Endocardial Maze
In group I the ablation lines were performed with a unipolar radiofrequency ablation tool. After onset of normothermic cardiopulmonary bypass, the venous inflow was occluded. Thereafter, the aorta was cross-clamped and the heart arrested. Myocardial protection was achieved with cold blood cardioplegia infused antegradely and retrogradely. The left atrium was entered through the interatrial groove and the left-sided maze was performed. In contrast to the original maze procedure, the left and right pulmonary veins were encircled separately, leading to two isolated isles, which were connected at the back of the left atrium creating a figure "H." Then the remaining lesions to the posterior mitral annulus and the left atrial appendage were carried out. After completion of the maze procedure, the necessary cardiac surgical procedures were performed and the left atrium closed by a double running suture.
Pulmonary Vein Isolation
In group II the pulmonary veins were isolated with a bipolar radiofrequency ablation tool. After onset of normothermic cardiopulmonary bypass, right and left pulmonary veins were dissected free on the beating heart. After encircling of the pulmonary venous cuffs, the jaws of the pliers were positioned on the atrial wall and closed. Care was taken to apply the ablation on the atrial myocardium rather than on the pulmonary vein itself. No further connecting lines to the mitral annulus or the left atrial appendage were drawn. The left atrial appendage was left untouched. Pacing or electrocardiogram recordings were not routinely used to verify a conduction block.
Ablation Tools
The unipolar radiofrequency system
The system used (Medtronic, Cardioblate surgical ablation pen; Minneapolis, MN) consists of a unipolar surgical ablation pen, which is saline irrigated (5 mL/minute) that cools the surface of the endocardium and provides a low impedance path allowing for the creating of deeper lesions [20]. The patient is earthed with an indifferent electrode, attached underneath the patient’s back. The power generator was set at 30 W. The tip was slowly oscillated about ten times over the same endocardial area, to create continuous transmural lesions.
The bipolar radiofrequency system
The bipolar ablation system (Cardioblate BP surgical ablation device; Medtronic, Minneapolis, MN) consists of a 5-cm-long pair of pliers. Both jaws are saline-irrigated (5 mL/minute) to cool the surface [21]. The generator delivers 30 W and continuously measures changes in tissue impedance as it is ablated. Heating the tissue results in reducing impedance. When impedance criteria are met energy delivery stops automatically, thus indicating a transmural burn. Due to the internal algorithm the application time varies but usually is around 15 seconds. On every site, the energy was delivered twice. In cases of large pulmonary venous cuffs, the jaws were placed from cranially and caudally creating overlapping linear lesions.
Postoperative Management
No antiarrhythmic therapy was given in patients with a regular rhythm. In case of AF amiodarone was administered, starting intraoperatively. Patients were loaded with 600 mg amiodarone intravenously over two hours, followed by 600 mg over 24 hours. Thereafter, 3 x 200 mg amiodarone were given perorally. After reaching therapeutic blood levels and still persisting AF, electrical cardioversion by DC shock (up to twice 360 joules) was performed. If AF occurred during the later follow-up period, cardioversion was tried twice.
All patients received anticoagulation therapy with Coumadin for a minimum of six months, targeting an international normalized ratio value between 2.2 and 2.5. Patients in stable sinus rhythm and no other reason for anticoagulation such as mechanical valve prosthesis, were weaned from Coumadin.
Follow-Up
Patients were evaluated 6 and 12 months after operation and then on a yearly basis. Rhythm was determined on the basis of 12-lead electrocardiogram and 24-hour Holter monitoring. Echocardiographic data were collected with emphasis on left and right atrial diameter.
Statistical Analysis
Data were analyzed using SPSS System software (SPSS Inc, Chicago, IL). Differences of preoperative data between the groups were analyzed by the 
2 test for categoric variables and analysis of variance for continuous variables. A p value less than 0.05 was chosen as significant. All values are expressed as mean ± standard error of the mean.
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Results |
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Hospital mortality was 7% (n = 3) in group II. The deaths are not related to the ablation procedure. One patient with poor left ventricular function preoperatively, died because of cardiac failure in hospital. One patient died due to intracerebral hemorrhage 15 months postoperatively. He was still on Coumadin because of persistent AF. One patient died 16 months postoperatively due to ventricular fibrillation. He underwent biological aortic valve replacement and aortocoronary bypass grafting and was in sinus rhythm without antiarrhythmic medication.
Postoperative complications included transient low cardiac output in 3.4% and 2.3% in groups I and II, respectively (one patient in each group). Postoperative bleeding occurred in 4.2% (one patient in group I and two patients in group II, respectively), which necessitated rethoracotomy. The patient in group I had perforation of the left pulmonary artery during positioning of a Swan-Ganz catheter. In both patients in group II bleeding sites were the right atrial suture line. Mean intensive care unit (ICU) stays were 4.26 ± and 2.4 ± 0.3 days in groups I and II, respectively (median, one and two days in groups I and II, respectively). One patient in group I experienced a severe systemic inflammatory response syndrome on the first postoperative day, which prolonged the intensive care to 47 days. The length of hospitalization was 14.2 ± 2.5 and 14.2 ± 1.5 days in groups I and II, respectively. Operative data are given in Table 3.
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All patients were either in sinus rhythm or electronically paced in DDD or AAI mode immediately after surgery at admission to the ICU. No patient had any cerebral thromboembolic complications postoperatively, but one patient died from intracerebral bleeding 15 months postoperatively.
In group I, three patients (10.3%) received a permanent pacemaker for atrioventricular block (one case; eight days postoperatively), sick sinus syndrome (one case; nine days postoperatively), and bradycardia (one case; two months postoperatively). At six months 18, 3, 3, and 4 patients were in sinus rhythm, on pacemaker, in atrial flutter, and in AF, respectively. At 12 months 20, 3, 1, and 4 patients were in sinus rhythm, on pacemaker, in atrial flutter, and in AF, respectively. At last follow-up 21, 3, 1, and 3 patients were in sinus rhythm, on pacemaker, in atrial flutter, and in AF, respectively.
In group II, five patients (11.6%) received a permanent pacemaker for AV bloc (two cases; seven and 14 days postoperatively) and bradycardia (three cases; nine days, six months, and 19 months postoperatively). Three patients had a pacemaker implanted preoperatively due to bradycardic AF. At six months 19, 5, and 17 patients were in sinus rhythm, on pacemaker, and in AF, respectively. At 12 months 18, 5, and 18 patients were in sinus rhythm, on pacemaker, and in AF, respectively. At last follow-up, 17, 7, and 17 patients were in sinus rhythm, on pacemaker, and in AF, respectively. Data are depicted in Figure 1. Freedom from atrial fibrillation at last follow-up was 85.7% and 58.6% in groups I and II, respectively (p = 0.016).
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Comment |
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In the cardiologic literature PVI is reported to be sufficient, with a success rate around 50%, depending upon the indication (permanent or paroxysmal AF, structural heart disease) and the follow-up examinations (single or serial electrocardiograms [ECGs], Holter-ECG). The underlying concept, reported by Haissaguerre and colleagues in 1998 [23], is the focal source of paroxysmal AF originating in the myocardial junction of the pulmonary veins. Pappone and colleagues [24] showed the catheter-based circumferential PVI to be an effective treatment for AF. Although somewhat inferior, even patients with permanent lone AF were free from AF (68%). Nevertheless, these patients represent a completely different entity than surgical patients with structural heart disease.
If the underlying theory that AF begins in most patients as a disorder of the left atrium with foci originating mainly around the pulmonary veins holds true, this lesion concept might be applied in surgical patients with chronic permanent AF as well. Sueda and colleagues [25] published a case report on a patient undergoing mitral valve replacement and successful pulmonary vein isolation. In a small series of 12 patients with chronic AF [26], this simple cut and sew technique was applied, isolating all four pulmonary veins as a box lesion. Freedom from AF during follow-up was 83%.
Deriving from these reports, a retrospective study was conducted to investigate the appealing concept of PVI. The study was designed to analyze the efficacy of epicardial PVI in comparison with a complete left atrial endocardial ablation concept in respect to restoration of sinus rhythm. It was decided to perform, in both groups, left-sided lesions only because several papers [11, 27] and one Australian metaanalysis [28] revealed a left atrial maze to be as effective as a bilateral approach. On the other hand, in a recent metaanalysis [29] biatrial ablation demonstrated superiority. Although this study comprises 69 studies with almost six thousand patients, one major limitation has to be mentioned. The left atrial approach group seems to be a mixture of similar but not identical lesion concepts. In a couple of included studies a PVI without any interconnecting lines has been used. In the paper these studies were defined as left atrial maze but do not represent a full left atrial lesion set. This may account for the reduced overall success rate in the so-called left atrial approach. Because the aim of our study was to evaluate the PVI the addition of a right-sided lesion would possibly have jeopardized the interpretation of results.
For the left atrial endocardial ablation group (group I) a complete lesion set with connection lines to the mitral annulus and the left atrial appendage was chosen. Unipolar saline irrigated radiofrequency, a widely used and proven [6, 7] energy form, was used as ablation device. Our observed AF-free rate in this group was 85.7%, which is consistent with data in the literature [5, 6, 30].
In group II the bipolar radiofrequency probe (Medtronic Cardioblate BP) was used; a pair of pliers with two 5-cm-long jaws, each of them being one electrode. The generator delivers 30 Watts thus heating the tissue between the jaws. The time of application is fast depending on the thickness of the atrial wall. An internal algorithm measuring the impedance controls the duration of radiofrequency deployment. Theoretically bipolar ablation should consistently create transmural lesions changing into isolating scar formations over time.
In spite of this we found the freedom from AF in group II significantly worse compared with group I. However, this might not be due to the different groups as the pattern of AF and the concomitant cardiac procedures do not appear to influence the results of the Cox-maze procedure. Only time of preoperative AF, older age, seems to be a predictor of unfavorable outcome as described recently [29].
However, a couple of possible reasons have to be discussed. The device used was the first generation device, which carries a couple of potential hurdles. The handle itself is curved like an S, but stiff. Therefore it is somewhat bulky to handle. Especially the ablation of the left pulmonary veins is sometimes hard to accomplish; the exact position may be difficult. For ease of access we always performed the ablation procedure on cardiopulmonary bypass. In addition, the effective ablating line ended in the first generation device about half a centimeter from the tip of the jaws. That is why one may leave gaps especially in cases of huge left atria, or large distances between the upper and lower pulmonary veins. We tried to overcome these situations by positioning the device from both sides, creating two overlapping linear lesions. Fortunately, the next generation of this device eliminated the gap on the tip. The effective ablating area begins at the very tip of the device. The next generation is now malleable as a whole and easier to use. The jaws can be bended as needed. Second, there is a potential risk for positioning the pair of pliers not far enough onto the left atrial wall. If the junction between the pulmonary vein orifices and the myocardial fibers (where the focal triggers arise) is not excluded, electrical bursts still reach the left atrium. Last, but most importantly, the lesion concept itself may be the reason for bad results. Our findings may suggest that pure PVI is not enough for patients with chronic permanent AF and structural heart disease. This is paralleled by the findings of Gillinov and colleagues [31] that PVI alone results in a higher postoperative AF prevalence. By adding connection lines to the mitral annulus the success rates were comparable with the cut and sew maze. This is supported by Jeanmart and colleagues [32]. They yielded an AF-free rate of 69.7% with an endocardial box lesion plus a connecting line to the mitral annulus. One could argue that the decisive connection line has to reach the mitral annulus. On the other hand, Maessen and colleagues [16] reported a conversion rate to sinus rhythm of 87% with epicardial microwave ablation of the pulmonary veins without connecting lines to the mitral annulus. One has to consider though, that in this series the circles around the pulmonary veins are connected at the posterior left atrium. It can be speculated that this connection cuts off reentries involving the posterior left atrial wall. A similar effect is achieved by the creation of a left atrial box lesion, which is reported to be equally effective by excluding the whole posterior aspect of the left atrium including the orifices of the pulmonary veins [33].
We can only speculate which additional connecting line is the most important. Nevertheless, it seems to be obvious that PVI alone is not enough. One still could argue that the catheter-based circumferential pulmonary vein isolation done by electrophysiologists leads to freedom from AF in 68% of patients, as shown by Pappone and colleagues [24]. However, the patient characteristics are completely different because none of the included patients suffered from structural heart disease. To our knowledge, mere PVI in a surgical setting was proven to be effective in patients with paroxysmal AF only. Suwalski and colleagues [34] reported excellent success rates in nonmitral valve patients with paroxysmal AF.
Interestingly all our patients, even those in group II, were either in sinus rhythm or electronically paced immediately after surgery. As with other studies [5] we observed early atrial arrhythmias within the first weeks postoperatively. The majority of these events in group I responded to antiarrhythmic therapy and seemed to diminish when the healing process was completed.
The complication rate between the two groups was similar. The maze procedure always is blamed for the production of AV bloc. The incidence in our series was 10.3% and 11.6% in groups I and II, respectively. It has to be taken into account that valve surgery itself carries a complication rate of 9% to 12% in terms of AV bloc.
Study Limitations
One limitation of our study is the significant difference in underlying indication. This study was a nonrandomized trial; the choice of the procedure was at the discretion of the surgeon. It therefore is explainable that in most cases of mitral valve procedures an endocardial maze approach was chosen because the left atrium has to be opened anyway. We are well aware of the relatively short follow-up period.
Regarding assessment of transmurality, there is the problem that some bipolar devices incorporate techniques to assess transmurality while unipolar cannot. Except for the optic verification by bulging the tissue or white lines, there are no specific techniques to verify transmurality in unipolar settings. However, as stated by Gillinov and colleagues recently [31], the importance of transmurality is still a matter of debate as it is unlikely that catheter-based techniques result in transmural lesions, but yield a high success rate. It is more important to debate about the right lesion set than which energy source should be used [28].
In conclusion, PVI alone seems to be insufficient in treating permanent chronic AF. In these cases, left atrial endocardial maze, providing the connection lines to the mitral annulus, seems to be mandatory. Nevertheless further investigations have to clarify the impact of the connecting lines in detail.
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Discussion |
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DR WISSER: The point is well taken. That is the major limitation of our study. It was not randomized and there definitely is a significant difference between the two groups in terms of indication, and we don’t know if mitrals behave the same like aortic valve patients. That is completely true. With regard to atrial size, they were comparable, as I showed on the slide. But of course, that is the limitation. On the other hand, we have no insights if pulmonary vein isolation really is beneficial in every patient, and therefore from an ethical point of view, we didn’t want to randomize these patients.
DR MICHAEL MACK (Dallas, TX): And what is the reason that you wouldn’t want to randomize from an ethical standpoint?
DR WISSER: Because results are poor.
DR MACK: But you didn’t know that ahead of time.
DR WISSER: There are a couple of papers out in literature which indicate that the results are worse, although they have some limitations as well. For instance, the Cleveland Clinic group reported their complete results and the problem with this paper, for instance, is that they only had availability of ECGs (electrocardiograms) in 80% of all these patients.
DR MACK: Now, in no patient in either group did you perform right atrial ablation, is that correct?
DR WISSER: That’s correct.
DR MACK: So is it a fair statement to say, and since atrial flutter was not a significant problem afterwards, that you don’t feel that a right atrial lesion set is necessary?
DR WISSER: I can only compare the results to our previous patients in whom we performed a biatrial lesion set, and the results between the biatrial historical control and the left atrial patients in this study were comparable.
DR MACK: Another question, there is evidence in the catheter-based literature that a box lesion set isolating the pulmonary veins may be better than separate pulmonary vein isolation due to the fact that you have larger exclusion of the antrum. Do you have any feelings one way or another about that?
DR WISSER: That is true. There are a couple of papers, even in the surgical literature out, showing that a box lesion has a much higher success rate than we found. The same is true for pulmonary vein isolation alone without interconnecting lines in between the pulmonary veins but the connection line to the mitral annulus. So I think the game is really open, if it is a box lesion, the most important one, or the connection line to the mitral annulus. They achieve approximately the same success rate. But to my knowledge, there is no paper out looking at mere pulmonary vein isolation without any interconnection line.
DR MACK: And one last question. There are now some intriguing ways of creating a full left-sided lesion set from the epicardial surface, of connecting the pulmonary veins from a line across the dome of the atrium as well as making the mitral connection line down to the fibrous trigone on the dome of the atrium rather than across the coronary sinus. My question is, do you think your results are due to the fact that it was a lesser lesion set or the fact it was performed endocardially or epicardially? Do you think that makes any difference?
DR WISSER: My personal opinion, although I can’t prove it, is that it is due to the lesser lesion set and not to the type of approach and (or) epicardially.
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