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Ann Thorac Surg 2006;82:502-514
© 2006 The Society of Thoracic Surgeons
a Atrial Fibrillation Innovation Center (AFIC), The Cleveland Clinic Foundation, Cleveland, Ohio
b Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio
c Department of Quantitative Health Sciences, The Cleveland Clinic Foundation, Cleveland, Ohio
d Department of Cardiovascular Medicine, The Cleveland Clinic Foundation, Cleveland, Ohio
Accepted for publication February 4, 2006.
* Address correspondence to Dr Gillinov, Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic/F24, 9500 Euclid Avenue, Cleveland, OH 44195 (Email: gillinom{at}ccf.org).
Presented at the Forty-second Annual Meeting of The Society of Thoracic Surgeons, Chicago, IL, Jan 30–Feb 1, 2006.
| Dr Gillinov states that he has a financial relationship with AtriCure, Inc and Afx/Guidant, Inc. Dr Navia states that he has a financial relationship with Afx/Guidant, Inc, and Dr McCarthy states that he has a financial relationship with AtriCure, Inc. All three also disclose that they have financial relationships with un-named competitors of the above companies.
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Abstract |
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 Top Abstract IntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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METHODS: From November 1991 to January 2004, 575 patients underwent surgical treatment of permanent atrial fibrillation (duration > 6 months); mitral valve disease was the primary indication for surgery in 74%. Procedures included pulmonary vein isolation alone (n = 68, 12%), pulmonary vein isolation with left atrial connecting lesions (n = 265, 46%), and Cox-maze (n = 242, 42%). Rhythm documented on 5,120 postoperative electrocardiograms was used to estimate time-related prevalence of, and risk factors for, atrial fibrillation.
RESULTS: Prevalence of postoperative atrial fibrillation peaked at 46% two weeks after operation, declining to 24% at one year. Patient-related risk factors for increased prevalence included older age (p < 0.0001), larger left atrium (p < 0.0001), and longer duration of preoperative atrial fibrillation (p = 0.0008). The Cox-maze procedure and lesion sets resembling it created with alternative energy sources had a similarly low prevalence of late postoperative atrial fibrillation; in contrast, pulmonary vein isolation and lesion sets that did not include a lesion to the mitral anulus were less effective.
CONCLUSIONS: This study suggests that in cardiac surgical patients with permanent atrial fibrillation the left atrial lesion set should include wide pulmonary vein isolation, at least one connection between right and left pulmonary veins, and a connection to the mitral anulus. Availability of alternative energy sources to create lesions sets has virtually eliminated the need for the cut-and-sew Cox-maze procedure.
Long-term follow-up confirms the effectiveness of the Cox-maze III procedure, which uses a cut-and-sew technique, and cryothermy to create an extensive biatrial lesion set for treating atrial fibrillation (AF) [1, 2]. Surgeons are reluctant to perform this complex operation routinely, however, and instead seek simpler, quicker, but still effective procedures. Recent studies suggest that the pulmonary veins and left atrium are responsible for initiating and maintaining AF in most patients [3–5]. This information, coupled with new surgical devices that simplify creating lines of conduction block, has produced new options for surgical treatment of AF; however, paucity of results has made the choice of energy source and lesion set controversial.
Likely, pathogenesis of AF is variable, suggesting that the ablation procedure should be tailored to individual patients [6, 7]. The pattern of AF (paroxysmal, persistent, permanent) may offer a clue about the appropriate lesion set, because pathogenesis of AF appears to be fundamentally different for paroxysmal versus permanent AF [6, 7]; those with permanent AF likely require a more extensive lesion set to achieve successful ablation [6]. Our objective was to assess the effectiveness of different lesion sets in cardiac surgical patients with permanent AF, focusing primarily on patients with mitral valve disease.
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Patients and Methods |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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Ablation Procedure
Approach
A cut-and sew Cox-maze procedure was performed in 242 patients (46%, Fig 1), pulmonary vein isolation (PVI) alone in 68 (12%), and PVI with left atrial connecting lesions (PVI+) in 265 (46%, Fig 2) (Table 2). All patients had excision or exclusion of the left atrial appendage. Choice of lesion set for a particular patient was at the surgeon's discretion and depended partly on available technology. The Cox-maze procedure has been employed since 1991; other strategies date from 2001. Median duration of permanent AF was longer in those receiving a Cox-maze procedure (60 months) than in those receiving PVI (42 months) or PVI+ (48 months; Appendix 1).
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When cryothermy was used, the left atrium was opened and a 15- or 25-mm circular cryoprobe was placed on the left atrial endocardium directly over the orifice of each pulmonary vein, also incorporating the pulmonary vein antrum. A 2-minute application at –60°C was used, with transmurality confirmed by visualizing an ice ball on the epicardial surface of the heart.
PVI+
Pulmonary vein and antrum isolation with left atrial connecting lesions was accomplished with bipolar RF in 218 of 265 patients (82%), cryothermy in 27 (10%), and microwave in 20 (8%). The most common left atrial lesion sets are depicted in Figure 2. In general, connecting lesions from left to right pulmonary veins were created with bipolar RF and that from left inferior pulmonary vein to mitral anulus by cryothermy. Additionally, 140 patients (53%) had a right atrial procedure, usually consisting of a right atrial isthmus cryolesion. Right atrial lesions were added in patients with a history of atrial flutter and, in other cases, at the discretion of the surgeon.
Cox-maze procedure
Six patients had a Cox-maze II procedure and 236 a Cox-maze III. These were performed as described by Cox and included cut-and-sew and cryothermy techniques and a biatrial lesion set [1].
Follow-Up
Assessment of AF
Postoperative electrocardiograms (ECG) were used to assess AF. They were performed routinely before discharge and at the discretion of referring physicians during follow-up. Recommended ECG follow-up intervals were 1, 3, and 6 months, 1 year, and annually thereafter. A total of 5,120 postoperative ECGs were retrieved, and every patient had at least one record available for analysis (range, 1 day to 13 years). Four hundred seventy-five of 504 patients (92%) for whom it was possible to have had an ECG 6 months or more after operation had one, and 372 of 464 patients (80%) for whom it was possible to have had an ECG 12 months or more after operation had one (Fig 3). For analysis, three rhythms were considered postoperative AF: AF, atrial flutter, or paced rhythm with underlying AF or atrial flutter.
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Data Analysis
Prevalance of AF and its risk factors
Because there is no practical method for continuous lifelong heart rhythm assessment, and self-reported AF underestimates its occurrence [10], a novel statistical technique was used to depict prevalence of AF versus time based on discrete ECG recordings, as previously described [11]. In brief, results of repeated ECG recordings for each patient were subjected to temporal decomposition (early and late components in this instance) into which separate but simultaneous streams of modulating variables (Appendix 2) were incorporated. Multivariable analysis was performed in the odds domain to identify risk factors for each component and overall [12, 13].
Analyses of prevalence of AF do not account for antiarrhythmic medications. Prevalence of antiarrhythmic medication use, estimated by mixed modeling based on medication use at each follow-up assessment, is reported separately (Fig 1 of Appendix 3). Although we recommend discontinuing antiarrhythmics 3 months after ablation if the patient appears to be AF free, continued use is at the discretion of referring cardiologists. Use of electrical cardioversion was analyzed as a repeated event and is presented as cumulative incidence (events per patient) (Appendix 3) [14].
Heterogeneity of patients
Because characteristics of patients for whom each technique was used differed (see Appendix 1), two simultaneous saturated logistic regression models were developed for PVI versus Cox-maze and PVI+ versus Cox-maze using preoperative, concomitant procedure, and support variables (Appendix 2). From these, three propensity scores were calculated for each patient [15, 16]; two were used, as appropriate, to provide additional risk adjustment of multivariable analyses described above.
Presentation
Continuous variables are presented as mean ± standard deviation or equivalently as 15th, 50th (median), and 85th percentiles for skewed distributions. Non-time-related event data and time-related prevalences are presented as percentages with asymmetric 68% confidence limits (CLs), comparable to ±1 standard error. The CLs for AF prevalence were obtained with the bootstrap percentile method [17].
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Results |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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Heart Rhythm
Time-related prevalence of postoperative AF peaked at 46% (CL 43% and 50%) at 2 weeks, fell to 23% (CL 21% and 26%) by 6 months, and was 24% (CL 22% and 26%) at 12 months and 25% (CL 22% and 27%) at 18 months (Fig 4). At 1 year, 18% (CL 17% and 20%) of patients were taking antiarrhythmic medications, and 52% (CL 50% and 54%) were on warfarin (Fig 2 of Appendix 3). Of those on warfarin, 10% required anticoagulation for a mechanical prosthesis. Electrical cardioversion was used 208 times in 123 patients after hospital discharge (Fig 3 of Appendix 3); the rate of cardioversion was highest during initial hospitalization and declined rapidly thereafter. No patient had repeat AF ablation.
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Comment |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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The Cox-Maze Procedure
The Cox-maze procedure is the predicate for most operations designed to treat AF. It includes a biatrial lesion set designed to interrupt macro-reentrant circuits that characterize AF, while allowing the atria to resume sinus rhythm. Based on the understanding of AF in the late 1980s, the Cox-maze procedure also completely isolated the pulmonary veins and posterior left atrium, anatomic sites that are now known to house most triggers of paroxysmal AF [1, 6]. With follow-up extending to 15 years, the Cox-maze procedure is effective in 74% to 98% of patients [1, 2, 23]. Differences in reported effectiveness likely relate to variable frequencies and methods for heart rhythm assessment, different statistical methods used to analyze results, and different definitions of "success" that cloud possible true differences in results. The pattern of AF (paroxysmal, persistent, permanent) and concomitant cardiac procedures (mitral valve operation, coronary revascularization) do not appear to influence results of the Cox-maze procedure; however, patient factors, including duration of preoperative AF, age, and left atrial size, do [2].
Alternatives to Cox-Maze
Newer operations for AF employ alternative energy sources. These technologies replicate the lesion set of the Cox-maze III; however, in many instances they are used to create simplified lesion sets [7, 22]. In the current series, patients were treated with bipolar RF, microwave, and cryothermy; bipolar RF was the predominant alternative energy source. In all cases, lesions to the mitral anulus were created with cryothermy.
There is considerable controversy concerning the optimal alternative energy source. Options include radiofrequency (unipolar, bipolar, transpolar, irrigated, or dry), microwave, laser, ultrasound, and cryothermy. Similar results have been reported with each, and direct comparisons suggest equivalence [18, 20, 22, 24]. Some devices incorporate techniques to assess transmurality, while others do not. Although we believe transmurality is desirable, importance of acute transmurality is a matter of debate [5]. It is unlikely that catheter-based techniques result in contiguous, uniform transmural lesions in every case, yet many patients appear to be cured of AF [4, 5, 21]. Documented effectiveness of available alternatives suggests that the key question for surgeons is not "Which energy source?" but, rather, "Which lesion set?" We believe the answer to the latter depends on the pathogenesis of AF.
Pathogenesis of AF and Relationship to Lesion Set
Ideally, the operation should be tailored to the pathogenesis of AF in each patient. Current understanding of AF and electroanatomic mapping tools do not enable this analysis in the operating room. The surgeon can discern the temporal pattern of AF, and this information can guide the choice of lesion set. However, the pathogenesis of permanent AF is not well understood. Some argue that its mechanism is established macro-reentry; others have demonstrated focal drivers in some patients [6, 25]. Intraoperative mapping studies in those patients suggest that the left atrium is usually the electrical driving chamber [25, 26]. Clinical reports support this by demonstrating that permanent AF is frequently treated successfully by left atrial lesion sets that include PVI and connecting lesions [19].
Employing lesion sets similar to the Cox-maze, and a variety of energy sources, many groups have achieved 70% to 98% freedom from AF at 6 months to 2 years [18–20, 22–24]. Our results in cardiac surgical patients with permanent AF suggest that the procedure should include wide PVI, a connection between the right and left pulmonary veins, and a connection to the mitral anulus. A single connection between the left and right pulmonary veins appears adequate, as completion of the pulmonary vein encircling lesion does not influence results [18]. The lesion to the mitral anulus enhanced results; reasons for this are not fully understood, but may include further remodeling of the left atrial substrate and block of common forms of left atrial macro-reentry [21]. An essential requirement for this lesion (and other lesions) is that it incorporate a contiguous line of conduction block; an incomplete lesion at this location may actually potentiate macro-reentry, leading to recurrent atrial arrhythmias [21, 27]. Addition of right atrial lesions conferred no additional benefit in these patients. Finally, we believe that the left atrial appendage should also be excised or excluded.
Limitations
Electrocardiograms used for analysis were obtained routinely in-hospital but opportunistically after discharge. Attempts were made to contact each patient and cardiologist and to obtain both clinical and ECG follow-up. Patients having late ECGs may have been selected because they had symptomatic AF, leading to overestimation of prevalence of AF. Alternatively, asymptomatic AF episodes without ECG verification may have been missed, leading to underestimation of events. Although periodic Holter monitoring and event recorders would have provided more data for analysis, these methodologies still fail to capture all AF episodes [10].
These data provide insight into choice of lesion set in patients with permanent AF. Because the majority of these patients had mitral valve disease or another indication for cardiac surgery, results might not apply to those with lone AF. The optimum lesion set for patients with lone AF is controversial.
In patients treated with alternative energy sources, we did not uniformly assess conduction block using pacing or other methods; it is therefore possible that some patients received incomplete lesions, which might have contributed to recurrent AF. However, there is currently debate concerning the importance of conduction block in AF ablation, with some suggesting that substrate modification is of primary importance [28]. We did not directly assess or compare different modalities for lesion creation. Focused analysis of alternative energy sources requires detailed bench-top testing followed by prospective clinical evaluation.
Clinical Inferences
This study suggests that in cardiac surgical patients with permanent AF, the left atrial lesion set should include wide PVI, at least one connection between the left and right pulmonary veins, and a connection to the mitral anulus. Failure to include the lesion to the mitral anulus jeopardizes results. Availability of alternative energy sources to create these lines of conduction block has virtually eliminated the need to perform a cut-and-sew Cox-maze procedure.
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Appendix 1 |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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Appendix 2 |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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Appendix 3 |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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Discussion |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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DR GILLINOV: One year after surgery, 20% of the patients were on antiarrhythmic agents, and this is a little bit beyond our control because the patients move to the care of their cardiologists. What we recommend is that at six months, if the patient is on an antiarrhythmic agent, it is stopped. But what we find in clinical practice is sometimes a patient leaves on an antiarrhythmic agent and the medication is continued indefinitely.
We use electrical cardioversion in the first six months if the patient returns to atrial fibrillation, and the cumulative incidence of cardioversions in these patients continues to increase over time. So what you are getting at is, how many patients can we say are cured by the surgical procedure alone? The answer is, we don't know.
DR PAUL KURLANSKY (Miami, FL): I just want to congratulate you on a superb paper, particularly the fact that you addressed head on the issue, which most people try to skirt, of exactly how do you assess success for this procedure. The question I have is when, if ever, do you recommend taking these patients off of anticoagulation?
DR GILLINOV: We take people off anticoagulation if at six months they appear to be free of atrial fibrillation. We do not have data to support that practice, and nobody has data to support this strategy. I think it is going to require a randomized trial to answer the question, when can you remove the patient from anticoagulation? The freedom from stroke in this population at one year is 98%, and again, these people have the appendage removed, which may help. But that is what we do. I can't tell you for sure that that is right.
DR A. W. ATKINSON (Raleigh, NC): I just commend you on getting some really, I think, good information out of a lot of, I don't want to use too much the word, crummy data. I mean, you have got a lot of different people doing a lot of different things over a long period of time, but I think you have distilled the key fact that how you do it is important. But one thing that wasn't clear to me, and maybe because there is not enough basic data, and you suggested that whatever you do in the right atrium isn't relevant, but do you still have that opinion, because I know this is old data, in a sense, of what you do today in fixed atrial fibrillation? I am under the impression that things do change in the right atrium with chronic or persistent atrial fibrillation and maybe we ought to do something there. Would you comment on that?
DR GILLINOV: It is clear from some mapping studies that atrial fibrillation can arise from the right atrium, although atrial flutter is a more common arrhythmia generated from the right atrium. Our data suggests that at least in these patients the right atrial lesions do not add anything, but it may be that we don't have sufficient power or length of follow-up or intensity of follow-up to detect that. In fact, I make a right atrial isthmus lesion in almost everyone.
DR RALPH J. DAMIANO (St. Louis, MO): Marc, congratulations on a beautiful paper and your group's continuing contribution to our understanding of the treatment of these patients and trying to help us define the right lesion set. The only area we probably would disagree on is whether or not this is definitive data which would suggest that right atrial lesions are not important. There is a recent metaanalysis that Niv Ad has done that suggests that biatrial lesions do have a slightly higher cure rate than the left atrial approach alone. Our mapping data of patients with permanent atrial fibrillation would suggest that about 30% of the patients that were referred over the years to us seem to have their atrial fibrillation driven out of the right atrium, and that has been confirmed by a group at Case Western Reserve, which found the incidence of drivers outside the left atrium to be just over 20%. However, your data does certainly suggest that you can get very good success rates with a complete left atrial maze. I had a couple of questions for you to help me sort through this.
In our series we found the biggest factor for recurrence was the duration of atrial fibrillation. You gave us the median duration of atrial fibrillation in your whole group, but what was the median duration of atrial fibrillation in each separate lesion set and could that have impacted your results?
My second question is, you considered atrial flutter to be atrial fibrillation, but in the left atrial lesion sets alone, one would expect to see a higher incidence of atrial flutter. Did you see a higher incidence over time of atrial flutter in the left atrial lesion set alone, albeit your follow-up was probably shorter on the limited lesion sets than with the full Cox-maze because that was done earlier in your experience?
And finally my last question is, is there any patient you would always do the right atrial lesion sets? When you say you do not perform right atrial lesion sets, do you do the isthmus lesion in everybody? Certainly our group and Hartzell Schaff's group in Mayo have had success in patients with isolated tricuspid regurgitation, where we just perform the right atrial lesions and none of the left atrial lesion sets. In this population, our cure rate approaches 100%. How do you explain that? In a patient who comes to you with mixed mitral and tricuspid disease, would that be a patient you would do a biatrial maze?
DR GILLINOV: I will answer those questions quickly given the limited time that we have. The duration of atrial fibrillation was slightly different between groups. Patients with a cut and sew maze procedure had, on average, about five years of atrial fibrillation. Other groups had, on average, about four years.
The second two questions I will try to address together; the issue of flutter and the right atrium. Our data do not show any difference in effectiveness; whether or not you add a right atrial lesion. But, because the risk of adding a right atrial lesion is very low, because it is easy to do, and because theoretically it might have a benefit, I still add it. Among patients who only have left atrial lesion sets, about 15% develop some flutter postoperatively, but it is generally transient.
So the message here is, add a lesion to the mitral anulus in permanent atrial fibrillation. I think I can state that answer with some confidence. The right atrium is not the primary focus of this study, but I think it is worth adding a right atrial isthmus lesion in most people.
DR MICHAEL MACRIS (Houston, TX): Have you seen any increase in morbidity and/or mortality attributable to the addition of the maze procedure to any other operation, such as MVR/maze or CABG/maze?
DR GILLINOV: The answer is adding an atrial fibrillation ablation with alternate energy sources, which takes somewhere between 15 and 20 minutes, has not resulted in an appreciable change in morbidity or mortality. Adding a cut and sew-based procedure almost certainly will add to morbidity.
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Acknowledgments |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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References |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2Appendix 3DiscussionAcknowledgmentsReferences |
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