Atrial Fibrillation Correction Surgery: Lessons From The Society of Thoracic Surgeons National Cardiac Database

Atrial Fibrillation Correction Surgery: Lessons From The Society of Thoracic Surgeons National Cardiac Database James S. Gammie, MD, Michel Haddad, MD, Sarah Milford-Beland, MS, Karl F. Welke, MD, T. Bruce Ferguson, Jr, MD, Sean M. O Brien, PhD, Bartley P. Griffith, MD, and Eric D. Peterson, MD, MPH Division of Cardiac Surgery, University of Maryland Medical Center, Baltimore, Maryland; Division of Cardiothoracic Surgery, Oregon Health and Science University, Portland, Oregon; East Carolina Heart Institute, Brody School of Medicine at East Carolina University, Greenville, and Duke Clinical Research Institute, Duke University, Durham, North Carolina CARDIOVASCULAR Background. We used The Society of Thoracic Surgeons 10,590) of those having aortic valve surgery, and 24% National Cardiac Database to document the utili- (5,438 of 22,388) of those having isolated coronary artery zation of surgical atrial fibrillation (AF) correction procedures bypass grafting. After adjusting for differences in preop- in North America. We also examined the subset oferative characteristics, mitral valve surgery patients with patients having mitral valve surgery to determine a surgical AF correction procedure did not have a significantly whether concurrent surgical AF correction procedures higher risk of mortality (adjusted odds ratio, 1.00; were associated with an increased risk of morbidity or95% confidence interval, 0.83 to 1.20) or major morbidity. mortality. Methods. Retrospective review of outcomes for 67,389 The risk for new permanent pacemaker implantation was higher (adjusted odds ratio, 1.26; 95% confidence interval, patients with AF having cardiac surgery between January 1.07 to 1.49) in the AF correction with mitral valve surgery 2004 and December 2006 was conducted. Multivariable group. logistic regression was performed to assess whether Conclusions. Although a growing number of patients concomitant AF correction procedures increased risk in with AF are treated with concurrent AF correction procedures the mitral valve surgery cohort. during cardiac surgery, nearly 60% of patients are Results. Overall, 38% (25,718 of 67,389) of patients with left untreated. Among patients with AF and mitral valve AF undergoing cardiac surgery had an AF correction disease, the addition of an AF correction procedure does procedure, increasing from 28.1% in 2004 to 40.2% innot increase perioperative morbidity or mortality. 2006. Surgical AF correction was performed in 52% (6,415 of 12,235) of mitral valve surgery patients, 28% (2,965 of (Ann Thorac Surg 2008;85:909 15) 2008 by The Society of Thoracic Surgeons The introduction of a variety of devices designed for atrial tissue ablation and atrial fibrillation (AF) correction has stimulated surgeons to consider treating patients with AF in the operating room. There is evidence that the addition of a Maze procedure at the time of cardiac surgery to a patient with AF is associated with improved quality of life and improved long-term freedom from stroke, bleeding, and mortality [1 4]. The purpose of this study was to answer the following questions: (1) what is the current utilization of surgical AF correction procedures in North America among all patients with preoperative AF undergoing cardiac surgery; (2) is utilization increasing with time; and (3) among mitral valve surgery patients with AF, does the performance of a surgical AF correction procedure add additional risk to that procedure? Accepted for publication Oct 30, 2007. Address correspondence to Dr Gammie, Division of Cardiac Surgery, University of Maryland Medical Center, N4W94, 22 S Greene St, Baltimore, MD 21201; e-mail: jgammie@smail.umaryland.edu. Material and Methods Data were extracted from The Society of Thoracic Surgeons National Cardiac Database. This is a voluntary cardiac surgery database that was established in 1989 to support national quality improvement efforts [5]. It contains detailed perioperative data on more than 3 million cardiothoracic surgical procedures and is estimated to include more than 75% of programs performing cardiac surgery in North America. Clinical sites enter data using uniform definitions (core data elements can be accessed at http://www.sts.org/doc/8428) and certified software systems. Data is warehoused and analyzed at the Duke Clinical Research Institute. Patient Population Patients undergoing cardiac surgery at all Society of Thoracic Surgeons National Cardiac Database participat- Dr Gammie discloses a financial relationship with CryoCath, Inc. 2008 by The Society of Thoracic Surgeons 0003-4975/08/$34.00 Published by Elsevier Inc doi:10.1016/j.athoracsur.2007.10.097

CARDIOVASCULAR 910 GAMMIE ET AL Ann Thorac Surg ATRIAL FIBRILLATION CORRECTION SURGERY 2008;85:909 15 Table 1. Prevalence of Preoperative Atrial Fibrillation and Likelihood of Receiving Concomitant Atrial Fibrillation Correction Surgery Among Patients Undergoing Cardiac Surgery Among Preoperative AF Operation Number of Patients (n) Preoperative AF (n) Preoperative AF (%) AF Correction Surgery (n) AF Correction Surgery (%) Mitral CABG 44,874 12,235 27.3 6,415 52.4 Aortic CABG 75,821 10,590 14.0 2,965 28.0 Isolated CABG 369,854 22,388 6.1 5,438 24.3 AF atrial fibrillation; CABG coronary artery bypass grafting. ing institutions between January 2004 and December 2006 were included in this analysis. Institutions with no reported AF correction procedures were excluded. For outcomes analyses, we focused on patients with AF undergoing mitral valve surgery alone or combined with coronary artery bypass grafting (CABG). We excluded high-risk patients including those considered salvage or emergent status, ongoing cardiopulmonary resuscitation, cardiogenic shock, dialysis, percutaneous coronary intervention within 6 hours, and myocardial infarction within 1 day of surgery. Outcomes The primary outcome was operative mortality, defined as the greater of 30-day or in-hospital mortality. Additional outcomes examined included reoperation for bleeding, deep sternal wound infection, stroke, prolonged ventilation, renal failure, dialysis, and need for permanent pacemaker implantation. Statistical Analysis Among patients from sites performing surgical AF correction procedures, frequencies of preoperative AF and AF correction procedures were evaluated across the following operative categories: isolated CABG, mitral valve surgery with or without concomitant CABG, and aortic valve surgery with or without concomitant CABG. Trends in utilization of AF correction procedures with time were measured using 6-month intervals among all cardiac surgery patients with preoperative AF, and significance was assessed using the Cochran-Armitage test for trend. Further analyses were restricted to mitral valve with or without CABG patients. Baseline demographic features, risk factors, operative characteristics, and outcomes of interest were compared according to whether patients received an AF correction procedure. Continuous variables were described as medians (with interquartile ranges), and categorical variables were described as frequencies. Continuous and ordinal categorical variables were compared using stratum-adjusted Wilcoxon rank-sum tests, and nominal categorical variables were compared using stratum-adjusted 2 tests when stratification is by hospital. In examining the relationship between AF correction status and outcomes, we initially performed unadjusted comparisons. Then, a multivariable logistic regression model was constructed to adjust for a broad range of potentially confounding patient preoperative and hospital characteristics (Appendix). To control for the clustering of patients within a hospital, all multivariable adjusted analyses were performed using generalized estimating equation models to account for withinhospital correlations. In addition, a stratified propensity analysis of surgical treatment of atrial fibrillation (STAF) on each outcome was performed. A logistic regression model predicting performance of STAF was created using the same set of covariates that were used in the multivariable analysis of operative outcomes. Patients were then divided into ten equally sized groups based on their propensity for receiving STAF. Standardized outcome rates were calculated across the ten propensity groups by applying direct adjustment with population total weights [6]. A Mantel- Haenszel test was used to test the hypothesis of no association between STAF use and outcome while stratifying on the propensity subclass. A probability value of less than 0.05 was established as the level of statistical significance for all tests. All analyses were performed using SAS software (version 8.2; SAS Institute, Cary, NC). Results All Surgical Atrial Fibrillation Correction Procedures Surgical AF correction procedures were performed in 92.7% (718 of 774) of centers reporting data to The Society of Thoracic Surgeons National Cardiac Database during the study. Among 587,479 patients undergoing cardiac surgery at these 718 centers during the study period, 67,389 (11.47%) had preoperative AF. The prevalence of AF and the likelihood of undergoing STAF varied by procedure (Table 1). Among all patients with preoperative AF, the overall likelihood of undergoing an AF correction procedure was 38% (25,718 of 67,389). Atrial fibrillation was most common, and most likely to be treated, among patients having mitral valve surgery, and least likely to be present and treated among patients having isolated CABG. The use of AF correction surgery among patients with preoperative AF increased significantly during the 3-year study period from 28.1% in the first 6 months to 40.2% in the last 6 months (Fig 1). During the study, only 1,184 of 25,718 (4.6%) of AF correction

Ann Thorac Surg GAMMIE ET AL 2008;85:909 15 ATRIAL FIBRILLATION CORRECTION SURGERY Fig 1. Prevalence of surgical atrial fibrillation (AF) correction procedures among patients with preoperative atrial fibrillation undergoing cardiac surgery. p 0.0001, test for trend. procedures were performed without concomitant cardiac surgery (ie, stand-alone procedure). Energy sources used for AF correction included bipolar radiofrequency (38.1%), cut-and-sew Maze (21.4%), cryothermy (12.4%), unipolar radiofrequency (6.1%), microwave energy (7.6%), and a combination (9.9%) of energy sources (Fig 2). Risks of Atrial Fibrillation Correction Procedures in Mitral Valve Surgery Cohort Among 44,874 patients undergoing mitral valve surgery with or without CABG during the 3-year period of this study, 12,235 (27.3%) had preoperative AF. After excluding high-risk patients (n 703) and patients with missing age, sex, or AF correction status (n 57), we found 11,475 patients who underwent mitral valve surgery with a diagnosis of preoperative AF. Surgical AF correction was performed in 54% (6,231 of 11,475) of these patients. Table 2 displays characteristics of mitral valve surgery patients as a function of whether they underwent surgical correction of AF. The group without AF surgery was more likely to have diabetes, renal failure, prior cardiac surgery, a history of myocardial infarction, and a previously implanted permanent pacemaker. Table 3 displays intraoperative and postoperative characteristics of the two groups. Patients having an AF correction procedure were somewhat less likely to undergo CABG. Median crossclamp time (9-minute difference) and cardiopulmonary bypass time (9-minute difference) were significantly longer in the AF correction surgery group. Unadjusted mortality was lower in the AF correction group (4.5% versus 6.6%; p 0.0001). Similarly, most postoperative complications were lower among those receiving an AF correction procedure. After adjusting for differences in preoperative characteristics, patients with a surgical AF correction procedure did not have a significantly higher risk of mortality (adjusted odds ratio, 1.00; 95% confidence interval, 0.83 to 1.20) or major morbidity (Table 3). In contrast, the risk of requiring a new postoperative pacemaker was slightly higher in the AF correction group versus not (6.8% versus 6.3%; p 0.0878) and became significantly higher after adjusting for preoperative clinical factors (adjusted odds ratio, 1.26; 95% confidence interval, 1.07 to 1.49; Table 4). We also performed a propensity analysis to assess the relationship between performance of STAF and outcome variables. A propensity score predicting the performance of STAF was created for each patient from the same set of covariates used in the multivariable analysis of operative outcomes. Patients were stratified into ten equally sized groups based on their propensity for receiving STAF, and standardized outcome rates were calculated across the ten propensity groups. This confirmed results of the multivariable analysis by demonstrating a lack of association between STAF use and morbidity and mortality, with the exception of the requirement for the insertion of a new postoperative pacemaker (Table 5). Comment This study used a national cardiac surgery database to describe contemporary utilization of AF correction surgery in North America and to assess the impact on perioperative mortality and morbidity of combining surgical AF correction with mitral valve surgery. We found increasing performance of surgical AF correction procedures during the course of this study, yet nearly two thirds of patients with preoperative AF were left untreated. In the mitral valve surgery cohort, our observational analyses also demonstrate that AF correction procedures appear safe with no measurable impact on procedural mortality or morbidity. Atrial fibrillation correction procedures were associated with an increased need for postoperative permanent pacemaker implantation. The prevalence of preoperative AF varied as a function of the primary cardiac surgical procedure being performed, from 6% among patients having isolated CABG to 27% among patients presenting for mitral valve surgery. Performance of AF correction surgery also varied by primary procedure, with half of mitral valve surgery patients with AF having a concomitant AF correction Fig 2. Energy sources used for surgical atrial fibrillation correction. (RF radio frequency.) 911 CARDIOVASCULAR

CARDIOVASCULAR 912 GAMMIE ET AL Ann Thorac Surg ATRIAL FIBRILLATION CORRECTION SURGERY 2008;85:909 15 Table 2. Preoperative Characteristics of Patients Having Mitral Valve Surgery With or Without Concomitant Surgical Treatment of Atrial Fibrillation Variable AF Correction Surgery (n 6,231) No AF Correction Surgery (n 5,244) p Value Age (median, y) 69.0 (60.0, 76.0) 72.0 (63.0, 78.0) 0.0001 Sex (male, %) 53.5 52.6 0.8608 Diabetes (%) 17.3 23.1 0.0001 Hypertension 65.9 69.2 0.0005 Smoker 47.4 49.5 0.0024 Renal failure 4.0 7.7 0.0001 Hx CVA 8.1 10.6 0.0001 Prior CABG or valve surgery 8.9 26.2 0.0001 MI 14.4 23.5 0.0001 EF (median) 0.520 (0.400, 0.600) 0.500 (0.400, 0.600) 0.0090 Previous pacemaker 5.8 12.1 0.0001 AF atrial fibrillation; CABG coronary artery bypass grafting; CVA cerebrovascular accident; EF ejection fraction; Hx history; MI myocardial infarction. procedure, whereas only 24% of isolated CABG patients with preoperative AF were treated with an AF correction procedure. Of interest, The Society of Thoracic Surgeons National Cardiac Database documents that there continue to be very few stand-alone AF correction procedures performed: during the 3-year study period only 4.6% (1,184 procedures) were performed in isolation. During the period studied, the most commonly used energy source was bipolar radiofrequency, followed by traditional cut and sew techniques and cryothermy. The widespread application of ablative technologies that facilitate rapid and safe performance of AF correction during concomitant cardiac surgical procedures is likely a key component of the trend toward increased performance of these procedures observed in this study. We also sought to understand whether performance of AF correction procedures added incremental risk to cardiac surgical cases. To study a more homologous group, we focused our analysis of outcomes on those patients having mitral valve surgery with or without CABG procedures. The likelihood of undergoing surgical AF correction was related to the amount of comorbidities and complexity of surgery, with sicker patients and those undergoing more complex operations less likely to have concomitant AF correction. We found that the performance of a surgical AF correction procedure appeared to only modestly prolong the duration of the procedure, adding, on average, 9 minutes to cross-clamp time and 9 minutes to cardiopulmonary bypass time. We also found that the addition of a surgical AF correction procedure did not appear to increase operative mortality or major morbidity risks, both before and after risk adjustment. These results are consistent with prior studies, including a retrospective case-matched study [1] and a prospective randomized study [2], both of which demonstrated that the addition of an AF correction procedure to mitral valve Table 3. Operative Characteristics of Patients Having Mitral Valve Surgery With or Without Concomitant Surgical Treatment of Atrial Fibrillation Variable AF Correction Surgery (n 6,231) No AF Correction Surgery (n 5,244) p Value Median CPB time (min) 138 (108, 176) 129 (99, 169) 0.0001 Median cross-clamp time (min) 102 (77, 131) 93 (70, 124) 0.0001 Concomitant CABG (%) 34.1 38.5 0.0001 Reoperation for bleeding 4.7 5.8 0.0008 DSWI 0.51 0.42 0.2207 Stroke 1.46 2.44 0.0020 Prolonged ventilation 14.8 20.5 0.0001 Renal failure a 6.5 8.1 0.0004 Permanent pacemaker b 6.8 6.3 0.0878 Operative mortality 4.5 6.6 0.0001 LOS (median, days) 7 (6, 10) 8 (6, 12) 0.0001 a Excluded patients with preoperative renal failure. b Excluded patients with preoperative pacemaker. AF atrial fibrillation; CABG coronary artery bypass grafting; CPB cardiopulmonary bypass; DSWI diastolic stroke work index; LOS length of stay.

Ann Thorac Surg GAMMIE ET AL 2008;85:909 15 ATRIAL FIBRILLATION CORRECTION SURGERY Table 4. Risk-Adjusted Mortality and Morbidities for Patients Having Mitral Valve Surgery With (Versus Without) Concomitant Surgical Treatment of Atrial Fibrillation, Adjusting for Participant Clustering and Other Potential Variables a Outcome Total N Adjusted OR Lower (95% CI for Adjusted OR) Upper (95% CI for Adjusted OR) 913 Adjusted p Value CARDIOVASCULAR Mortality Death 11,475 1.00 0.83 1.20 0.975 Complications Any reoperation 11,475 0.98 0.87 1.12 0.802 Renal failure/dialysis b 10,820 1.03 0.88 1.21 0.689 Prolonged ventilation 11,475 0.98 0.88 1.09 0.715 Need for permanent pacemaker c 10,475 1.26 1.07 1.49 0.007 Hospital stay Postprocedure LOS 14 days 11,475 1.00 0.88 1.13 0.949 a Variables in the model: age (linear spline with knots at 61, 70, 76, and 83 years), male, Caucasian race, body mass index (linear spline with knot at 35 kg/m 2 ), smoker, diabetes (insulin treated, non-insulin treated, and none), hypertension, cerebrovascular accident, immunosuppressive treatment, hypercholesterolemia, endocarditis, chronic lung disease (severe, moderate, mild, and none), peripheral vascular disease, cerebrovascular disease, two or more prior cardiac surgeries, prior intrapericardial or great vessel surgery, prior CABG, prior valve surgery, prior pacemaker, prior percutaneous coronary intervention (not within 6 hours) and no CABG, prior myocardial infarction (within 24 hours, 1 7 days ago, 1 3 weeks ago, 3 weeks ago, and none), congestive heart failure, New York Heart Association class IV, left main or triple-vessel disease, mitral stenosis, aortic stenosis, mitral insufficiency, tricuspid insufficiency, urgent status, concomitant CABG, mitral replacement surgery, ejection fraction (linear spline with knots at 0.30 and 0.40), dialysis or glomerular filtration rate (linear spline with knots at 60 and 90), surgery date (6-month intervals), participant residency status, participant annualized mitral valve procedure volume (1 35, 36 70, 71 140, and 141 ), and interactions between sex and body mass index. b Excluded patients with preoperative renal failure. c Excluded patients with preoperative pacemaker. surgery was not associated with increased morbidity or mortality. We did find an increased need for placement of a permanent pacemaker after AF correction surgery. Permanent pacemaker implantation is recognized as a potential adverse outcome of surgical AF correction procedures [7 9]. The Maze procedure, by abolishing AF, can unmask underlying sinus node dysfunction [10]. Not unexpectedly we found that the risk of new postoperative pacemaker insertion, after adjusting for preoperative patient characteristics, was higher in the surgical AF correction or mitral valve surgery group (adjusted odds ratio, 1.26; 95% confidence interval, 1.07 to 1.49; p 0.0007). Fewer patients in the group undergoing surgical AF correction had preexisting permanent pacemakers (5.8% versus 12.2%; p 0.0001). The unadjusted (actual) rate of new postoperative pacemaker insertion was similar in the two groups (6.8% in the surgical AF correction group versus 6.3% in the uncorrected group; p 0.088). The 6.8% rate of pacemaker implantation among patients undergoing surgical AF correction concomitant with mitral valve surgery is similar to what has been reported in the literature for isolated mitral valve surgery [11] and at the lower end of the spectrum among series reporting results of surgical AF correction [9]. Although this series contains information on the largest number of patients having AF correction surgery ever assembled, it is a retrospective review and therefore suffers from inherent treatment assignment bias by the operating surgeon. This bias is reflected in the fact that patients chosen for concomitant AF correction surgery were somewhat healthier than those in whom AF correction was not performed. It is possible that patients initially determined to be suitable for AF correction surgery were reassigned to the opposite group as a result of difficulties encountered intraoperatively. In speaking with surgeons who perform AF correction surgery, we have found that the vast majority perform the AF correction procedure in advance of the mitral valve operation. Although both the multivariable logistic regression analysis and the propensity analyses sought to remove bias and allow true comparison of outcomes, it is possible that unmeasured variables introduced important biases. Table 5. Standardized Outcome Rates Stratified Using Ten Propensity Subclasses Outcome Standardized Outcome Rate Among STAF Patients Standardized Outcome Rate Among Non-STAF Patients p Value for Mantel Haenszel Test Mortality 5.26% 5.34% 0.9955 Any reoperation 11.84% 11.84% 0.9542 Renal failure or dialysis 7.34% 6.92% 0.4363 Prolonged ventilation 18.84% 19.45% 0.4484 Need for permanent 7.10% 5.94% 0.0158 pacemaker Postprocedure LOS 14 days 14.68% 15.22% 0.5684 LOS length of stay; STAF surgical treatment of atrial fibrillation.

CARDIOVASCULAR 914 GAMMIE ET AL Ann Thorac Surg ATRIAL FIBRILLATION CORRECTION SURGERY 2008;85:909 15 The results of this study suggest that surgical AF correction procedures are increasingly being performed on patients with AF presenting for cardiac surgery, yet nearly two thirds of patients with preoperative AF are left untreated. Among patients with preoperative AF and mitral valve disease, the addition of an AF correction procedure does not appear to increase perioperative morbidity or mortality. As additional evidence accrues that supports the notion that it is of clinical value to treat AF in addition to the underlying cardiac surgical disease, we believe that this currently underutilized treatment option will be used in a larger number of patients. The relatively small number of patients receiving stand-alone or isolated Maze procedures suggests that patients and physicians are reluctant to consider surgical treatment for isolated AF, despite clear evidence of the superior efficacy of surgical Maze procedures compared with catheter-based ablation techniques [12 15]. This stands in contrast to the growing number of percutaneous AF ablations performed in the electrophysiology laboratory [16]. Given the present state of available evidence, cardiac surgeons should not hesitate to perform AF correction surgery concomitant with another cardiac surgical procedure. The Society of Thoracic Surgeons through the Adult National Cardiac Database and the Duke Clinical Research Institute supported this work. 7. Stulak JM, Sundt TM 3rd, Dearani JA, Daly RC, Orsulak TA, Schaff HV. Ten-year experience with the Cox-maze procedure for atrial fibrillation: how do we define success? Ann Thorac Surg 2007;83:1319 24. 8. Reston JT, Shuhaiber JH. Meta-analysis of clinical outcomes of maze-related surgical procedures for medically refractory atrial fibrillation. Eur J Cardiothorac Surg 2005;28:724 30. 9. Mack CA, Milla F, Ko W, et al. Surgical treatment of atrial fibrillation using argon-based cryoablation during concomitant cardiac procedures. Circulation 2005;112(9 Suppl):I-1 I-6. 10. Cox JL. Cardiac surgery for arrhythmias. J Cardiovasc Electrophysiol 2004;15:250 62. 11. Nienaber JJ, Glower DD. Minitransseptal versus left atrial approach to the mitral valve: a comparison of outcomes. Ann Thorac Surg 2006;82:834 9. 12. Cheema A, Vasamreddy CR, Dalal D, et al. Long-term single procedure efficacy of catheter ablation of atrial fibrillation. J Interv Card Electrophysiol 2006;15:145 55. 13. Calkins H, Brugada J, Packer DL, et al. HRS/EHRA/ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation: recommendations for personnel, policy, procedures and follow-up. A report of the Heart Rhythm Society (HRS) Task Force on catheter and surgical ablation of atrial fibrillation. Heart Rhythm 2007;4:816 61. 14. Damiano RJ Jr, Gaynor SL, Bailey M, et al. The long-term outcome of patients with coronary disease and atrial fibrillation undergoing the Cox maze procedure. J Thorac Cardiovasc Surg 2003;126:2016 21. 15. Cox JL, Ad N, Palazzo T. Impact of the maze procedure on the stroke rate in patients with atrial fibrillation. J Thorac Cardiovasc Surg 1999;118:833 40. 16. Cappato R, Calkins H, Chen SA, et al. Worldwide survey on the methods, efficacy, and safety of catheter ablation for human atrial fibrillation. Circulation 2005;111:1100 5. References 1. Raanani E, Albage A, David TE, Yau TM, Armstrong S. The efficacy of the Cox/maze procedure combined with mitral valve surgery: a matched control study. Eur J Cardiothorac Surg 2001;19:438 42. 2. Doukas G, Samani NJ, Alexiou C, et al. Left atrial radiofrequency ablation during mitral valve surgery for continuous atrial fibrillation: a randomized controlled trial. JAMA 2005; 294:2323 9. 3. Abreu Filho CA, Lisboa LA, Dallan LA, et al. Effectiveness of the maze procedure using cooled-tip radiofrequency ablation in patients with permanent atrial fibrillation and rheumatic mitral valve disease. Circulation 2005;112(9 Suppl):I-20 I-25. 4. Bando K, Kobayashi J, Kosakai Y, et al. Impact of Cox maze procedure on outcome in patients with atrial fibrillation and mitral valve disease. J Thorac Cardiovasc Surg 2002;124:575 83. 5. Ferguson TB Jr, Dziuban SW Jr, Edwards FH, et al. The STS National Database: current changes and challenges for the new millennium. Committee to Establish a National Database in Cardiothoracic Surgery, The Society of Thoracic Surgeons. Ann Thorac Surg 2000;69:680 91. 6. Rosenbaum PR, Rubin DB. The central role of the propensity score in observational studies for causal effects. 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Appendix Variables included in multivariable regression models (in addition to STAF status): age (linear spline with knots at 61, 70, 76, and 83 years), male, Caucasian race, body mass index (linear spline with knot at 35 kg/m 2 ), smoker, diabetes (insulin treated, non-insulin treated, and none), hypertension, cerebrovascular accident, immunosuppressive treatment, hypercholesterolemia, endocarditis, chronic lung disease (severe, moderate, mild, and none), peripheral vascular disease, cerebrovascular disease, two or more prior cardiac surgeries, prior intrapericardial or great vessel surgery, prior CABG, prior valve surgery, prior pacemaker, prior percutaneous coronary intervention (not within 6 hours) and no CABG, prior myocardial infarction (within 24 hours, 1 7 days ago, 1 3 weeks ago, 3 weeks ago, and none), congestive heart failure, New York Heart Association class IV, left main or triple-vessel disease, mitral stenosis, aortic stenosis, mitral insufficiency, tricuspid insufficiency, urgent status, concomitant CABG, mitral replacement surgery, ejection fraction (linear spline with knots at 0.30 and 0.40), glomerular filtration rate (linear spline with knots at 60 and 90), surgery date (6-month intervals), participant residency status, participant annualized mitral valve procedure volume (1 35, 36 70, 71 140, and 141 ), and interactions between sex and body mass index. INVITED COMMENTARY This article by Gammie and colleagues [1] reports the trend of surgical ablation for atrial fibrillation (AF) in modern times. The worldwide increase in popularity of surgical ablation started at the turn of the millennium, before any evidence from randomized trials or any official guideline encouraged concomitant ablation. Today, solid scientific evidence on the clinical benefits of AF surgery is available, and there is a growing consensus for concomitant ablation in patients affected by AF who are undergoing 2008 by The Society of Thoracic Surgeons 0003-4975/08/$34.00 Published by Elsevier Inc doi:10.1016/j.athoracsur.2007.12.025