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J Thorac Cardiovasc Surg 2007;133:1022-1027
© 2007 The American Association for Thoracic Surgery
Surgery for Acquired Cardiovascular Disease |
Division of Cardiovascular Surgery, Mayo Clinic and Foundation, Rochester, Minn.
Read at the Eighty-sixth Annual Meeting of The American Association for Thoracic Surgery, Philadelphia, Pa, April 29-May 3, 2006.
Received for publication May 3, 2006; revisions received August 21, 2006; accepted for publication September 8, 2006. * Address for reprints: Hartzell V. Schaff, MD, Division of Cardiovascular Surgery, Mayo Clinic College of Medicine, 200 First St SW, Rochester, MN 55905. (Email: schaff{at}mayo.edu).
| Abstract |
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Methods: Radiofrequency ablation was used to create full Cox maze lesions in 56 patients between January 2002 and February 2005; these patients were matched with those who underwent the standard cut-and-sew method. Matched variables were gender (33 male, 23 female, both), age (67.5 vs 67.2 years), New York Heart Association class (mean 2.28 vs 1.96), atrial fibrillation type (37 paroxysmal, 19 continuous, both), and concomitant mitral valve surgery (37 in both). Hypertension, preoperative left atrial size, and preoperative duration of atrial fibrillation were similar between groups.
Results: When compared with matched controls, fewer patients undergoing radiofrequency ablation were free from atrial fibrillation at dismissal (63% vs 88%; P = .0039) and at last follow-up (62% vs 92%; P = .016). According to logistic regression for matched pairs, patients undergoing radiofrequency ablation were 4.5 times more likely to be in atrial fibrillation at dismissal (95% confidence intervals [CI], 1.8, 10.9) and 5 times more likely to be in atrial fibrillation at follow-up (95% CI, 1.4, 17.3). No other covariate was associated with atrial fibrillation status at hospital dismissal or follow-up.
Conclusion: Creating Cox maze lesions with radiofrequency ablation is associated with less freedom from atrial fibrillation both early and late postoperatively. Because transmurality can be assured, the standard cut-and-sew Cox maze procedure remains the gold standard for the surgical treatment of atrial fibrillation.
| Introduction |
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The largest clinical experience using alternate energy sources is with radiofrequency (RF) ablation, which uses alternating current to transfer energy to atrial tissue. Success of this technology in the catheterization laboratory has led surgeons to apply RF directly to the heart during cardiac surgery.7-9
Several instruments have been developed to create atrial lesions, including rigid unipolar probes with cooled tips,10,11
flexible unipolar probes,12
and bipolar clamps with13
and without irrigation.14
Despite reports of successful ablation of AF with these new instruments and techniques, the effectiveness of RF compared with the standard CS maze procedure has not been clearly demonstrated. Analysis of results is further complicated by variable definitions of success. We sought to more precisely evaluate the impact of one ablation technology by direct comparison with the CS technique using a case-matched study design holding the lesion set constant and evaluating cure by several clearly defined criteria.
| Patients and Methods |
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These patients were strictly matched with 56 patients from a database of 335 patients who underwent the classic CS Cox maze procedure at our institution between March 1993 and December 2002. Medical records were reviewed for patient demographics, past cardiac medical and surgical history, operative procedure, preoperative and postoperative cardiac rhythm, early and late morbidity, and survival.
Matched variables were gender, age, New York Heart Association (NYHA) class, AF type, and concomitant mitral valve as shown in Table 1. Additional variables potentially affecting outcome, including hypertension (RF vs CS) (23 vs 22 patients; P = .85), left atrial size (67.5 vs 66.7 mm; P = .799), and preoperative duration of AF (52 ± 10 vs 67 ± 4 months; P = .69), were similar between groups.
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| Statistical Analysis |
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| Results |
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Freedom from AF at dismissal was significantly lower in the RF group than in the CS group (64% vs 88%; P = .0039). According to a multivariable model, patients in the RF group were 4.5 times more likely to be in AF at hospital dismissal. The use of RF ablation was the only significant predictor of AF status at dismissal (RF, P = .011; tricuspid valve surgery, P = .6031; aortic valve surgery, P = .4643; septal myectomy, P = .8184).
New permanent pacemaker implantation was required in significantly more patients in the RF group than in the CS group (25% vs 5%; P = .004). In the RF group, indications for permanent pacemaker implantation were sinus node dysfunction in 12 patients, long QT syndrome in 1, and complete heart block in 1. In the CS group, permanent pacemaker implantation was required for sinus node dysfunction in all 3 patients. According to a multivariable model, patients in the RF group were 4 times more likely to be dismissed with a new permanent pacemaker (P = .02).
Of the 56 early survivors, 8 were lost to follow-up in the RF group and 2 in the CS group. Late follow-up extended up to 33 months (mean 8.4 months, median 8 months). Follow-up results of these 48 patients were then compared with their respective 48 matched controls from the CS group. The CS control matches for the 8 RF patients lost to follow-up were excluded from comparison. Although the CS maze patients had a longer follow-up period, "rhythm at last follow-up" was defined as last follow-up for the RF maze patients and their respective matches from the CS group at the same period in time postoperatively. In addition, when RF patients ceased follow-up, their respective CS matches were excluded from analysis from that point onward. Patients available for follow-up in the RF group included 48 at 3 months, 26 at 6 months, 18 at 9 months, 12 at 12 months, and 12 at 15 months. There were 2 late deaths in the RF group resulting from noncardiac causes (malignancy in 1 and pneumonia in 1). Both patients were in AF before death. There were no late deaths in the CS group.
Antiarrhythmic medications at last follow-up were required in 36 (75%) patients in the RF ablation group and 12 (25%) patients in the CS control group (P < .05). Forty-one (85%) patients in the RF ablation group were still receiving warfarin anticoagulation at last follow-up compared with 12 (25%) patients in the CS control group (P < 0.05).
Success of the procedure in treating AF was evaluated as rhythm at last follow-up, by actuarial methods, and by rhythm at interval contact (Table 3). Freedom from AF at last follow-up was significantly lower in the RF ablation group than in the CS control group (62% vs 92%; P = .0157). According to a multivariable model, RF ablation patients were 5 times more likely to be in AF at follow-up (95% confidence intervals [CI]: 1.447, 17.267), and no covariate other than use of RF ablation was associated with presence of AF at last follow-up. Similarly, sinus rhythm at last follow-up was significantly less common in the RF ablation group than in the CS control group (43% vs 85%; P = .00002). According to a multivariable model, CS ablation patients were 10.5 times more likely to be in normal sinus rhythm at follow-up (95% CI: 2.46, 45.45), and no covariate other than the use of RF ablation was associated with a decreased rate of sinus rhythm at last follow-up.
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| Conclusions |
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A surprising finding of this study was that new permanent pacemaker implantation was required in significantly more patients in the RF group than in the CS group. Although the RF group underwent more tricuspid valve operations, as well as aortic valve replacements and septal myectomies, by multivariate analysis these were not significant predictors of new pacemaker implantation. Complete heart block would have been the expected indication for permanent pacemaker implantation if increased tricuspid valve surgery, aortic valve surgery, or septal myectomy placed the patient at higher risk for permanent pacemaker need. However, in these patients, the major indication for permanent pacemaker implantation was sick sinus syndrome. Perhaps the patients in the RF group represented a group with greater underlying cardiac disease (as evidenced by more concomitant procedures performed), and thus a higher incidence of sick sinus syndrome when AF was ablated.
Prior studies have documented that AF can be surgically ablated by RF energy.17-20
The comparative effectiveness with conventional surgical lesions, however, has not been previously subjected to case-matched comparison. There are theoretical reasons why these new RF ablation technologies may be less effective. Achieving and ensuring transmurality of lesions may be complicated by differences in atrial tissue characteristics (thickness, fibrosis, fat) as well as operative techniques (normothermia vs hypothermia, beating heart vs arrested heart). The unpredictability of conditions at the time of ablation will undoubtedly affect the quality of the lesions regardless of the energy source used. It is impossible to apply uniform energy and uniform techniques to atria that offer considerable variability. We continue to use cryolesions at the mitral and tricuspid valve annuli and to create the transseptal lesion, similar to our approach in the standard CS procedure. A different algorithm was used with the AtriCure device using two ablations to satisfactorily achieve a transmural lesion. We do not routinely evaluate transmurality by measuring electrophysiologic isolation of the pulmonary veins at the time of ablation, and there remains a question as to whether this equates with transmurality. Conversely, ablation procedures have been reported to convey high rates of success despite a demonstrably or even intentionally incomplete pulmonary vein encircling lesion.21
The literature on surgical treatment options for AF is complicated by multiple criteria for defining success. In our study, we report rhythm at last follow-up, actuarial freedom from AF, and rhythm at interval contact. In all instances, the results with CS were superior to RF, but the apparent "cure" rate differed among methods. These data highlight some of the difficulties in comparing reports of series of patients undergoing the Cox maze procedure or any other treatment for AF. It is therefore critical that criteria be clearly defined and that results be reported and analyzed in a uniform manner.
The retrospective, nonrandomized nature of this study is a major limitation. Although the groups were matched for demographics and clinical characteristics, there were differences in concomitant procedures performed that may have affected outcome. Additionally, although we report success in three ways, only electrocardiograms were analyzed and Holter monitoring was not performed. A significant percentage of AF may be entirely asymptomatic.22
In addition, although follow-up was also case-matched (matched controls were censored when RF patients ceased follow-up), there were a significant number of patients who lacked long-term follow-up. To account for this, we also reported success in a KaplanMeier analysis. The RF group represents the institutions first 56 patients in whom RF was used to create the maze lesion set. Individual surgeon learning curve, as well as a potential institutional learning curve, may have influenced our results when compared with other surgical series using RF. However, analysis of individual surgeon outcome, as well as analyzing the first group of 28 procedures and the second group of 28 procedures performed, did not yield any significant differences in outcome. Despite these shortcomings, the principal strength of this study is the consistency in the lesion set, leaving only lesion creation source as a variable.
The underlying mechanism for the observed difference in results may or may not be completely attributable to a lack of transmurality, but comparative studies such as this one raises important issues for consideration for future studies. Most important, the discrepancy in reported results for ablation tools is most likely multifactorial (differing techniques, differing methods of assessment and reporting success) and the ultimate clinical impact of transmurality and selection of lesion set is not completely understood.* More comparative studies are required to compare not only the efficacy of products from different companies, but also different alternate energy sources used. The ultimate goal in addressing these issues is to develop more successful ablation procedures.
If the indication for operation is medically refractory AF, the CS Cox maze operation offers the patient the highest chance at freedom from AF. However, the use of RF while performing concomitant operations may simplify the procedure significantly but at the expense of a potentially lower chance of ablation of AF.
| Footnotes |
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* Accord RD, Khargi K, Maessen JG. The issue of transmurality in surgical ablation for atrial fibrillation. Article in Cardiothoracic Surgery Network. 2006. ![]()
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