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Ann Thorac Surg 2006;81:19-28
© 2006 The Society of Thoracic Surgeons
a Center for Atrial Fibrillation, The Cleveland Clinic Foundation, Cleveland, Ohio
b Departments 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 April 26, 2005.
* Address correspondence to Dr Gillinov, Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation/F24, 9500 Euclid Ave, Cleveland, OH 44195 (Email: gillinom{at}ccf.org).
Presented at the Forty-first Annual Meeting of The Society of Thoracic Surgeons, Tampa, FL, Jan 24–26, 2005. Winner of the J. Maxwell Chamberlain Memorial Award for Adult Cardiac Surgery.
| This article has been selected for the open discussion forum on the CTSNet Web Site: http://www.ctsnet.org/sections/newsandviews/discussions/index.html
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Abstract |
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 Top Abstract IntroductionPatients and MethodsResultsCommentOnline Discussion ForumDiscussionAcknowledgmentsReferences |
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METHODS: From July 1993 to January 2004, 152 patients underwent combined surgical treatment of paroxysmal atrial fibrillation and mitral valve disease. Ablation procedures included pulmonary vein isolation alone (n = 31, 20%), pulmonary vein isolation with left atrial connecting lesions (n = 80, 53%), and Cox-Maze (n = 41, 27%). The latter had longer durations of atrial fibrillation than the former (p < 0.0001). Rhythm documented on 1,225 postoperative electrocardiograms was used to estimate prevalence of, and risk factors for, atrial fibrillation across time. Ablation failure was defined as occurrence of atrial fibrillation any time beyond 6 months after operation.
RESULTS: Prevalence of postoperative atrial fibrillation peaked at 22% at 2 weeks and declined to 9% at 1 year. Risk factors included older age (p = 0.09), larger left atrium (p = 0.05), and rheumatic (p = 0.003) and degenerative etiologies (p = 0.03). Freedom from ablation failure was 84% at one year. Ablation procedure did not affect prevalence of atrial fibrillation or incidence of ablation failure.
CONCLUSIONS: Pulmonary vein isolation alone may be adequate treatment for patients with paroxysmal atrial fibrillation undergoing mitral valve surgery, particularly when it is of short duration. A randomized trial is necessary to examine this strategy, especially in patients with longer duration of paroxysmal atrial fibrillation.
Recent studies demonstrate that the pulmonary veins and posterior left atrium house triggers for paroxysmal atrial fibrillation (PAF) [1–3]. The data, recorded in patients without valvar heart disease, are the basis for catheter-based pulmonary vein isolation (PVI). In 60% to 90% of such patients, PVI is curative [1–3].
Armed with this knowledge and new surgical instrumentation, surgeons have more aggressively applied intraoperative ablation techniques to treat atrial fibrillation (AF), particularly in patients undergoing mitral valve surgery [4–7]. There is little information about the pathogenesis of PAF in patients with mitral valve disease, and the role of pulmonary vein triggers is unknown. These patients tend to have left atrial enlargement and may have a different electrophysiologic basis for PAF compared with isolated PAF patients [8]. Further, the optimum lesion set in these patients has not been determined. Some surgeons advocate a Cox-Maze procedure, while others favor simple PVI [6]. The objective of this study was to assess the effectiveness of three surgical treatments of PAF in patients undergoing mitral valve surgery.
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Patients and Methods |
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Ablation of AF
Approach
Ablation procedures included PVI alone (n = 31, 20%), PVI with left atrial connecting lesions (n = 80, 53%), and a Cox-Maze procedure (n = 41, 27%). All patients had excision or exclusion of the left atrial appendage in addition to ablation. Choice of lesion set was at the discretion of the surgeon and depended partly on the technology and ablation instrumentation available at the time. The Cox-Maze procedure has been employed since 1993, while other ablation strategies date from 2001. Patients having a Cox-Maze procedure had longer duration of AF and were more likely to have suffered a stroke. In contrast, patients receiving PVI alone had shorter duration of AF (median 3 months), more extensive coronary artery disease, and more left ventricular dysfunction (Table 2).
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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. A 2-minute application at –60°C was used, with transmurality confirmed by visualization of an ice ball on the epicardial surface of the heart.
PVI with connecting lesions
Pulmonary vein and antrum isolation was accomplished with bipolar RF. The most common connecting lesions were from left to right inferior pulmonary veins (created with bipolar RF) and from left inferior pulmonary vein to mitral annulus (created with cryothermy). In addition, 21 patients (26%) had a right atrial isthmus cryolesion.
Cox-Maze procedure
Six patients had a Cox-Maze II procedure, and 35 had a Cox-Maze III. These were performed as described by Cox and included cut-and-sew and cryothermy techniques [11].
Follow-Up
Assessment of AF
Postoperative electrocardiograms (ECGs) 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 month, 3 months, 6 months, 1 year, and annually thereafter. A total of 1,225 postoperative ECGs were retrieved, and every patient had at least one record available for analysis (range, 1 day–8.6 years). Thirteen patients died within 6 months of operation and thus did not have 6-month ECG follow-up. Among surviving patients, 103 (74%) had an ECG 6 months or more after operation and 61 (40%) had one 12 months or more after operation (Fig 1). For purposes of analysis, any one of the following three rhythms was considered postoperative AF: AF, atrial flutter, or a paced rhythm with underlying AF or atrial flutter.
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Data Analysis
Prevalence of AF and its risk factors
Because there is no practical method for continuous heart rhythm assessment and self-reported AF underestimates its occurrence [12], a novel statistical technique was developed to depict prevalence of AF versus time based on discrete ECG recordings [13]. Results of repeated ECG recordings for each patient were subjected to temporal decomposition (early and constant components in this instance) into which separate streams of modulating variables (Appendix) were incorporated for simultaneous analysis, using longitudinal binary logistic regression analysis for repeated measurements (PROC NLMIXED; SAS, Inc, Cary, NC).
Ablation failure and risk factors
Ablation failure was defined as any occurrence of AF or atrial flutter 6 months or more after ablation [4]. To be at risk of this, patients had to have an ECG obtained during this time frame. Patients were considered to have ablation failure even if late AF was transient. Data were considered interval censored, with the event assumed to occur between the time of an ECG showing AF and the time immediately preceding ECG not showing AF.
To identify risk factors for ablation failure, a parametric model was used to resolve the number of hazard phases and to estimate shaping parameters [13], with time zero set at 6 months. (For additional details, see http://www.clevelandclinic.org/heartcenter/hazard.) Variable selection was by bootstrap bagging using a retention criterion of p less than 0.05, with variables appearing in 50% or more of models considered reliably significant at this level [14, 15].
Presentation
Continuous variables are presented as mean ± standard deviation or equivalently as 15th, 50th (median), and 85th percentiles when the distribution of values was skewed. Non-time-related event data, time-related prevalences, and freedom from ablation failure are presented as percentages with asymmetric 68% confidence limits (CL), comparable with ±1 standard error. The CLs for prevalence of AF were obtained with the bootstrap percentile method [16]. Throughout, model coefficients are given with their standard errors rather than the odds ratio (logistic) or hazards ratio.
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Results |
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TopAbstractIntroductionPatients and MethodsResultsCommentOnline Discussion ForumDiscussionAcknowledgmentsReferences |
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Heart Rhythm
Prevalence of AF and its risk factors
Time-related predicted prevalence of AF or atrial flutter after operation is depicted in Figure 2. Early prevalence of AF peaked at 22% (CL 18% and 32%) at 2 weeks. By 6 months, prevalence fell to 10% (CL 8% and 12%), and at 1 year, it was 9% (CL 8% and 11%). At 6 months, 24% (CL 20% and 28%) of patients were taking antiarrhythmic medications, and 45% (CL 39% and 50%) were taking warfarin.
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Comment |
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TopAbstractIntroductionPatients and MethodsResultsCommentOnline Discussion ForumDiscussionAcknowledgmentsReferences |
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AF in Patients with Mitral Valve Disease
The rationale for restoring sinus rhythm in patients with mitral valve disease includes the following: (1) improving survival, (2) reducing risk of stroke and other systemic embolism, (3) avoiding anticoagulation, (4) reducing symptoms associated with tachycardia, and (5) improving cardiac output [6,17–20]. Successful intraoperative ablation of AF improves outcomes [19, 20], and thus the ideal operation would both correct mitral valve dysfunction and ablate AF. New, focused approaches to surgical AF ablation are based on improved understanding of the pathogenesis of AF and development of new ablation technologies.
Pathogenesis of AF
Most current information on pathogenesis of PAF is derived from studies of patients without valvar heart disease. Haissaguerre and colleagues' observation [1] that triggers of PAF usually reside in the pulmonary veins altered the approach to catheter- and surgical-based ablation of AF. It is now generally accepted that pulmonary vein triggers are responsible for initiation of PAF in most patients [1–3]. However, right atrial and other left atrial triggers initiate PAF in some patients [1].
Recent techniques for catheter ablation of AF are anatomically based and include wide, circumferential ablation of the left atrial cuff or antrum adjacent to each pulmonary vein, similar to our approach [2, 3, 21, 22]. In many instances, lesions overlap, producing ablation of most of the posterior left atrium. Results with wide circumferential PVI in patients with PAF are superior to those obtained with focal ablation, and the volume of left atrial tissue isolated affects results [2, 3, 21]. Although the pathogenesis of permanent AF is different from that of PAF, recent reports indicate that wide circumferential PVI is also effective in selected patients with permanent AF [2, 3].
Intraoperative mapping studies in patients with mitral valve dysfunction and permanent AF suggest that the left atrium is the electrical driving chamber in most instances [23–25]. Reports support this hypothesis by demonstrating that permanent AF in mitral valve patients can be cured by a left atrial procedure that includes PVI; addition of right atrial lesions appears unnecessary in most patients [26, 27]. Recent data demonstrate that catheter-based wide circumferential PVI successfully treats both paroxysmal and permanent AF in patients with moderate mitral valve disease [8]. Thus, although pulmonary vein triggers have not been identified in patients with mitral valve disease and PAF, mapping and clinical studies suggest the importance of the left atrium and pulmonary veins in initiating and maintaining AF in these patients.
Prevalence of AF and Ablation Failure
Early data (to 1 year) suggest equivalent effectiveness of PVI alone, PVI with left atrial connecting lesions (with or without a right atrial isthmus lesion), or a Cox-Maze procedure. With each approach, prevalence of AF and of ablation failure is similar, despite difference in duration of AF. Incidence of ablation failure is nearly constant over time, suggesting need for continued follow-up of these patients. Risk factors for postablation AF were patient-related, including rheumatic and degenerative etiologies, larger left atrial volume, and older age, all of which have been associated with late AF in previous studies [5]. Rheumatic etiology may be associated with pronounced atrial structural abnormalities that reduce ablation success [28].
Pulmonary vein isolation patients had a shorter duration of PAF than patients receiving other lesion sets. Therefore, results reported for PVI alone might not apply to patients with longer duration (> 3 months) of preoperative PAF. It is possible that a mitral valve procedure alone might have caused PAF to abate in some of these patients [29, 30]. Because PVI produced results equivalent to a Cox-Maze procedure, it is possible that the pulmonary veins play a role in initiating PAF in patients with mitral valve disease. However, none of these procedures cured all patients, suggesting the importance of other, unidentified factors in the pathogenesis of PAF. A more complete understanding of issues that lead to ablation failure, which may include incomplete lines of conduction block, triggers outside the pulmonary veins, alterations in autonomic tone, and presence of atrial scar tissue, is necessary to improve results.
Limitations
This series contains early follow-up of patients undergoing PVI alone or PVI with additional lesions. Choice of procedure was not randomized, introducing the possibility of surgeon bias. Patients with shorter duration of PAF were more likely to receive PVI alone, and this might have influenced the results.
Electrocardiograms used for analysis were obtained routinely in-hospital but opportunistically after hospital discharge. Attempts were made to contact each patient and cardiologist and to obtain both clinical and ECG follow-up. Although only 103 patients had ECGs beyond 6 months postoperatively, there were a sufficient number for analyses. Patients having late ECGs may have been selected because they had symptomatic AF, leading to overestimation of prevalence of AF and ablation failure. 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 might still fail to capture all AF episodes [12]. Our limited ability to document heart rhythm continuously over time led us to develop novel statistical methods that we believe provide the most accurate estimates of AF prevalence achieved to date. Although not perfect, this method represents an important improvement over analyses relying on rhythm at last follow-up or patient self-reporting [4, 5].
Results of AF ablation were assessed and presented in two fashions. We estimated prevalence of AF to depict the predicted prevalence of AF in the population at any given time after ablation. In such a depiction, a given patient might have AF on one ECG and sinus rhythm on the next, unlike a time-to-event analysis. We also estimated freedom from ablation failure, with ablation failure defined as any recurrence of AF beyond 6 months after operation.
Analyses of prevalence of AF and ablation failure do not account for antiarrhythmic medications patients may have been taking. Prevalence of antiarrhythmic use is reported separately. Although we recommend discontinuing antiarrhythmics 3 months after ablation, continued use is at the discretion of referring cardiologists, which hampered our ability to report prevalence of AF and freedom from ablation failure off medications.
We did not assess lesion integrity by pacing or other methods; it is therefore possible that operator error or other factors resulted in some patients receiving incomplete lesions, which may have contributed to ablation failures.
Clinical Inferences
Pulmonary vein isolation provides satisfactory early results in many patients with mitral valve disease and PAF, particularly if the PAF is of recent onset. Additional lesions do not appear to increase efficacy in such patients. A clinical trial with longer follow-up and more intense heart rhythm monitoring is necessary to confirm this strategy, especially in patients with longer duration of preoperative PAF.
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Online Discussion Forum |
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TopAbstractIntroductionPatients and MethodsResultsCommentOnline Discussion ForumDiscussionAcknowledgmentsReferences |
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Once the article selected for discussion is published in the online version of The Annals, we will post a notice on the CTSNet home page ( http://www.ctsnet.org ) with a FREE LINK to the full-text article. Readers wishing to comment can post their own commentary in the discussion forum for that article, which will be informally moderated by The Annals Internet Editor. We encourage all surgeons to participate in this interesting exchange and to avail themselves of the other valuable features of the CTSNet Discussion Forum and Web site.
For January, the article chosen for discussion under the Adult Cardiac Dilemma Section of the Discussion forum is:
Surgery for Paroxysmal Atrial Fibrillation in the Setting of Mitral Valve Disease: A Role for Pulmonary Vein Isolation?
A. Marc Gillinov, MD, Faisal Bakaeen, MD, Patrick M. McCarthy, MD, Eugene H. Blackstone, MD, Jeevanantham Rajeswaran, MSc, Gosta Pettersson, MD, PhD, Joseph F. Sabik III, MD, Farzad Najam, MD, Kathleen M. Hill, RN, Lars G. Svensson, MD, PhD, Delos M. Cosgrove, MD, Nassir Marrouche, MD, and Andrea Natale, MD
Tom R. Karl, MD
The Annals Internet Editor
UCSF Children's Hospital
Pediatric Cardiac Surgical Unit
505 Parnassus Ave, Room S-549
San Francisco, CA 94143-0118
Phone: (415) 476-3501
Fax: (212) 202-3622
e-mail: mailto:karlt{at}surgery.ucsf.edu
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Appendix |
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Discussion |
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TopAbstractIntroductionPatients and MethodsResultsCommentOnline Discussion ForumDiscussionAcknowledgmentsReferences |
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Importantly, hospital mortality was low. Prevalence of postoperative atrial fibrillation peaked at two weeks and declined to only 9% at one year. Freedom from ablation failure was 84% at one year, and the factors associated with recurrent atrial fibrillation were older age, larger atrium, and rheumatic or degenerative etiologies for mitral regurgitation. The key conclusion of the paper is that pulmonary vein isolation, pulmonary vein isolation with connecting lesions, and a formal Cox-Maze procedure all had similar ablation failure and success rates.
If one is to accept these conclusions, then I believe one can conclude that PVI (pulmonary vein isolation) is a simple and safe procedure to perform in combination with mitral valve repair or replacement, and that it provides similar relief of paroxysmal atrial fibrillation compared to these more complex procedures. I believe an extrapolation to clinical practice would be warranted, and one might conclude that, with rare exception, every patient in paroxysmal atrial fibrillation having another open cardiac surgical procedure should have PVI. That, however, is not exactly our clinical practice nationwide.
(Slide) These are blended industry and medical advisory board estimates for United States volumes. In red are patients who are going to the operating room for coronary bypass or valve repair or replacement and who have atrial fibrillation, either paroxysmal or permanent. In yellow are the total number of ablation procedures performed in the United States last year. You can see that we, as a Society looking for ways to reinvent ourselves and reinvigorate our specialty, are still missing an opportunity which represents about 30,000 cases of atrial fibrillation left untreated in the operating room.
As the invited discussant I am obliged to examine some concerns and pose some questions to Dr Gillinov. Marc, no other large studies have reported identical success rates for the Cox-Maze and pulmonary vein isolation. Why do you believe yours has? Clearly, follow-up in this retrospective study was a challenge after 10 years with an n of only 31 in the PVI group and with 40% EKG follow-up at one year. Are these data robust enough to guide changes in our clinical practice? Specifically, are spot EKGs to measure prevalence of atrial fibrillation (AF) in patients with paroxysmal AF adequate as a measure? Do you have data for patients who went to the operating room with PAF (paroxysmal atrial fibrillation) and who did not have the AF ablated? What would their recorded incidence of prevalence of A-fib be at one year as measured by spot EKGs? Marc, do you believe that these early success rates will remain high beyond the two to five-year interval? Do you have data from some of those earlier patients that you could share with us?
Switching gears slightly, is PVI alone adequate ablation for permanent atrial fibrillation in patients going to the operating room for other cardiac surgical procedures? And do you believe that every cardiac surgery patient with preoperative atrial fibrillation going to the OR for valvular or coronary bypass surgery should have an ablation? Specifically, how about patients who have a history of PAF but haven't had atrial fibrillation in some time and come to you in the operating room in sinus rhythm, do you ablate those?
Marc, congratulations on a wonderful paper, well deserving of the Chamberlain award.
DR TAKASHI NITTA (Tokyo, Japan): Congratulations on your excellent results and elegant data analysis. I have one question. The ablation failure could be the result of incomplete lines of conduction block, which is usually a procedure-related failure. Therefore, the more complex and extensive the lesion set, as in the Maze procedure, the more frequent the procedure-related failures that can occur.
Do you think the potential higher incidence of the procedure-related failures in the maze group may have increased the incidence of ablation failures and affected the results?
DR GILLINOV: Thank you for your questions. The question of the "best" lesion set for a given patient with atrial fibrillation is not yet answered. There are several studies that have examined different lesion sets in patients with atrial fibrillation. Some of them have demonstrated similar outcomes between a Maze procedure and lesion sets that are similar to a Maze, but I am not aware of one that has looked at pulmonary vein isolation, which is the simplest lesion set, versus a Maze, particularly in paroxysmal atrial fibrillation.
Dr Puskas asked about our follow-up, and that is an issue that we continue to work on. We do not yet have, and no one has, a robust, clinically applicable methodology for monitoring heart rhythm continuously. There is no question that with ECGs, or even Holter monitors or event recorders, we are going to miss asymptomatic atrial fibrillation. Up to 20% of postablation atrial fibrillation is asymptomatic and it will be missed in the absence of a reasonable means of continuous monitoring of heart rhythm; the harder you look, the more atrial fibrillation you find.
One of the questions was what will happen with long-term follow-up of pulmonary vein isolation? Well, our curve of ablation success is dropping off at a constant rate, and I suspect that the longer we follow these patients, the more atrial fibrillation we are going to see. Therefore, we do need continued long-term follow-up; at five years I doubt the results will be as good as they were at one or two years.
I can answer one of your questions, your second last, definitively. Pulmonary vein isolation is not as good as a Maze procedure for patients with permanent or continuous atrial fibrillation. In those patients a more extensive lesion set is necessary to guarantee cure. However, if you have an extremely high risk, complex patient, you may not want to do a full Maze procedure and you will get some efficacy with pulmonary vein isolation.
And finally, should every patient who has atrial fibrillation, even if it was ten years ago, have some sort of procedure in the operating room? Well, within reason, almost everyone should. If you have a very complex reoperative patient and the pulmonary veins are not accessible, you may consider skipping the ablation and concentrating on the primary operation.
Dr Nitta asked about the impact of incomplete lines of conduction block or an inadequate procedure on ablation failures. It is clear that if you have gaps in your ablation lines, you will create the substrate for failure. Now, with a Maze procedure we do not have gaps because we use a scissors and a knife. However, with the new ablation technologies, that is an important point; what we are lacking is a true on-line means of assessing our ablation at the time of the procedure. I think such a methodology will improve results by identifying those gaps before we leave the operating room. Thank you.
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Acknowledgments |
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