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Original Articles: Cardiovascular

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

^a Division of Cardiac Surgery, University of Maryland Medical Center, Baltimore, Maryland
^b Division of Cardiothoracic Surgery, Oregon Health and Science University, Portland, Oregon
^c East Carolina Heart Institute, Brody School of Medicine at East Carolina University, Greenville
^d Duke Clinical Research Institute, Duke University, Durham, North Carolina

Accepted for publication October 30, 2007.

^_* Address correspondence to Dr Gammie, Division of Cardiac Surgery, University of Maryland Medical Center, N4W94, 22 S Greene St, Baltimore, MD 21201 (Email: jgammie{at}smail.umaryland.edu).

Dr Gammie discloses a financial relationship with CryoCath, Inc.

 

	Abstract

Top Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
Background: We used The Society of Thoracic Surgeons National Cardiac Database to document the utilization of surgical atrial fibrillation (AF) correction procedures in North America. We also examined the subset of patients having mitral valve surgery to determine whether concurrent surgical AF correction procedures were associated with an increased risk of morbidity or mortality.

Methods: Retrospective review of outcomes for 67,389 patients with AF having cardiac surgery between January 2004 and December 2006 was conducted. Multivariable logistic regression was performed to assess whether concomitant AF correction procedures increased risk in the mitral valve surgery cohort.

Results: Overall, 38% (25,718 of 67,389) of patients with AF undergoing cardiac surgery had an AF correction procedure, increasing from 28.1% in 2004 to 40.2% in 2006. Surgical AF correction was performed in 52% (6,415 of 12,235) of mitral valve surgery patients, 28% (2,965 of 10,590) of those having aortic valve surgery, and 24% (5,438 of 22,388) of those having isolated coronary artery bypass grafting. After adjusting for differences in preoperative characteristics, mitral valve surgery 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. The risk for new permanent pacemaker implantation was higher (adjusted odds ratio, 1.26; 95% confidence interval, 1.07 to 1.49) in the AF correction with mitral valve surgery group.

Conclusions: Although a growing number of patients with AF are treated with concurrent AF correction procedures during cardiac surgery, nearly 60% of patients are left untreated. Among patients with AF and mitral valve disease, the addition of an AF correction procedure does not increase perioperative morbidity or mortality.

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?

	Material and Methods

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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 participating 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 within-hospital 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

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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 procedures were performed without concomitant cardiac surgery (ie, stand-alone procedure).

View larger version (12K): [in this window] [in a new window]   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.

View larger version (19K): [in this window] [in a new window]   Fig 2. Energy sources used for surgical atrial fibrillation correction. (RF = radio frequency.)

	Comment

Top Abstract Introduction Material and Methods Results Comment Acknowledgments References

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 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 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.

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.

	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/m²), 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.

	Acknowledgments

Top Abstract Introduction Material and Methods Results Comment Acknowledgments References

 
The Society of Thoracic Surgeons through the Adult National Cardiac Database and the Duke Clinical Research Institute supported this work.

	References

Top Abstract Introduction Material and Methods Results Comment Acknowledgments References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): James S. Gammie Michel Haddad Karl F. Welke T. Bruce Ferguson, Jr Bartley P. Griffith Eric D. Peterson Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gammie, J. S. Articles by Peterson, E. D. Search for Related Content PubMed PubMed Citation Articles by Gammie, J. S. Articles by Peterson, E. D. Related Collections Electrophysiology - arrhythmias Related Article