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Ann Thorac Surg 2003;75:57-61
© 2003 The Society of Thoracic Surgeons

Original article: cardiovascular

Surgical outcome of the maze procedure for atrial fibrillation in mitral valve disease: rheumatic versus degenerative

Jae Won Lee, MDa*, Nam Hee Park, MDa, Suk Jung Choo, MDa, Min Seop Jo, MDa, Hyun Song, MDa, Meong Gun Song, MDa

a Thoracic and Cardiovascular Surgery, Asan Medical Center, University of Ulsan, Seoul, South Korea

* Address reprint requests to Dr Lee, Department of Thoracic and Cardiovascular Surgery, Asan Medical Center, University of Ulsan, 388-1 Pungnap-dong, Songpa-gu, Seoul 138-736, South Korea.
e-mail: jwlee{at}amc.seoul.kr

Presented at the Thirty-eighth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 28–30, 2002.


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Comment
 Acknowledgments
 Discussion
 References
 
BACKGROUND: The results of the maze procedure are known to be less satisfactory in rheumatic mitral disease than in nonrheumatic mitral valve disease. The aim of this study was to determine whether the etiology of mitral valve disease affected surgical outcome.

METHODS: From July 1997 to January 2001, 129 consecutive patients with chronic atrial fibrillation associated with mitral valve disease had mitral valve operations with the maze procedure. The underlying mitral pathology was rheumatic in 86 patients (group R) and degenerative in 43 (group D). Echocardiograms and electrocardiograms were performed immediately and then repeated 3 months and 6 months postoperatively.

RESULTS: The mean age, duration of atrial fibrillation, and preoperative left atrial size were similar between the groups. There was no operative mortality and no significant difference in cardiopulmonary bypass and aortic cross-clamp times. The sinus conversion rate at 7 days postoperatively was 86% in both groups, and at 6 months it was 95.3% in group R and 97.7% in group D (p > 0.05). The transmitral A wave detection rates in groups R and D at 7 days and 6 months postoperatively were, respectively, 63.1% versus 67.4% and 90.4% versus 91.9% (p > 0.05). The transmitral A wave velocity (cm/second) at the same times (7 days and 6 months postoperatively) was 41.9 ± 41.6 versus 45.5 ± 37.7 and 67.8 ± 38.2 versus 69.8 ± 35.8 in groups R and D, respectively (p > 0.05).

CONCLUSIONS: The maze procedure is equally effective in treating chronic atrial fibrillation in patients with either rheumatic or nonrheumatic mitral valve disease in terms of sinus conversion rate and left atrial transport function.


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Comment
 Acknowledgments
 Discussion
 References
 
Atrial fibrillation (AF) is commonly associated with mitral valve disease and is present in 30% to 50% of patients who have had mitral valve operations [1]. Because AF causes systemic thromboembolism and lowered cardiac output, persistence of AF after mitral valve operation increases the morbidity and mortality rates [2, 3]. Consequently, the termination of AF is strongly recommended to enhance long-term quality of life. However, surgical reduction of pressure or volume overload to atrial tissue had little effect on the elimination of AF, and electrical or medical cardioversion was not satisfactory [4, 5]. In 1991, Cox and colleagues [6] introduced the concept of surgical ablation of macro reentry circuits that induced AF by multiple atrial incision. Since then the success rate of the procedure has increased steadily, which is attributable in part to modifications designed to enhance the outcome. The Cox-maze III procedure is accepted now as an established and reliable method for termination of AF, even in the presence of other cardiac diseases [7].

In chronic AF associated with mitral valve disease, some authors demonstrated that the results of the maze procedure were less satisfactory in rheumatic disease than nonrheumatic disease [8]. They claimed that the major benefits of the maze procedure, ie, the restoration and maintenance of sinus rhythm and the recovery of left atrial transport function, were lower in rheumatic disease. The possible cause of these observations has not been clearly documented; however, no prospective studies have been done. A significant number of patients who had mitral valve operations have chronic AF, and rheumatic involvement is more common than other causes in Korea. We have performed the Cox-maze III procedure concomitantly with mitral valve operations since 1997, and we prospectively analyzed the clinical results to determine whether underlying mitral valve disease affected the results of the maze procedure.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Comment
 Acknowledgments
 Discussion
 References
 
Patients
From July 1997 to January 2001, 129 consecutive patients were operated on for chronic AF associated with mitral valve disease, defined as AF lasting longer than 1 year. Patients who had paroxysmal AF or atrial flutter were excluded from this study. The maze procedure and mitral valve operation were performed concomitantly with or without other cardiac procedures. The patients were divided into the following two groups on the basis of the underlying mitral valve pathology: group R (n = 86) had rheumatic disease and group D (n = 43) had degenerative disease. Other preoperative clinical characteristics are given in Table 1. There were no significant differences in mean age, AF duration, left atrial dimension, F-wave voltage, and cardiothoracic ratio between the two groups. Rheumatic mitral valve disease was determined by echocardiography and gross findings of valve morphology as follows: first, all stenotic lesions of the mitral valve combined with aortic valve stenosis were considered rheumatic. The patterns of calcium deposit, which began at the tips of the leaflets, were also considered rheumatic. In mitral regurgitation, the lesions combined with leaflet defect and motion limitation, commissural fusion, thickening of leaflet tip, and chordal fusioning were also defined as rheumatic. Heavy calcification in the leaflet tip combined with thickening and retraction deformation was considered rheumatic.


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  		Table 1. Preoperative Clinical Characteristics

 
Surgical procedure
Before January 1999, we performed operations for AF by means of the conventional maze procedure. All patients entered into the database from January 1999 received AF procedures according to a modification devised by Lee and associates [9], which was designed to enhance functional performance of the left atrium after the maze procedure. Our modification includes minimizing the area of the pulmonary isolation incision, minimizing the number of sharp incisions, employment of cryoablation instead of incision, resection of the trabeculated portion of the left atrial appendage only, and reduction of the left atrial dimension. The modifications were focused on preserving left atrial functional integrity, contiguity, and arterial blood supply to the left atrium and sinus node. We also modified the incision and cryoablation to the right atrium to prevent recurrence of atrial flutter. The isthmus was isolated completely with cryoablation. Of note, the duration of cryoablation varied according to the thickness of the atrial tissue for a more thorough cryoablation. The cryoprobe was applied for 2 minutes at -60°C only after transmural freezing was observed. Therefore, the beginning of the 2-minute cryoablation can conceivably vary according to the thickness of the left atrial wall. The operative data of the two patient groups are shown in Table 2. Mitral valve repair was performed more commonly in group D. Concomitant procedures were performed in 66 patients, and are listed in Table 3. Of those patients, 38 had tricuspid annuloplasty or valvuloplasty. Other procedures included aortic valve procedures, coronary artery bypass grafting, and correction of congenital anomaly (Table 3).


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  		Table 2. Operative Data

 

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  		Table 3. Number of Concomitant Procedures

 
Postoperative follow-up
The patients’ rhythms were checked daily during their postoperative hospitalization by using standard 12-channel surface electrocardiography, and follow-up electrocardiograms were performed at 3 and 6 months postoperatively in all patients. The basic rhythm was classified into sinus rhythm, nodal rhythm, AF, atrial tachycardia, or atrial flutter. If AF was noted during follow-up, the antiarrhythmic agent amiodarone was given orally starting at 1200 mg and then tapered within 1 or 2 weeks. To evaluate left atrial transport function, transthoracic echocardiography was done before discharge and at 3 and 6 months postoperatively. The presence of transmitral A wave was evaluated, and the transmitral A wave velocity (cm/second) was measured by echocardiography. All data were collected prospectively and stored for later assessment in a specially designed and regimented database for uniformity, accuracy, and objectivity of the generated data.

Statistics
All data were expressed as mean ± standard deviation. The SPSS software package (SPSS Inc, Chicago, IL) was used for statistical analysis. For categorical variables, the {chi}2 test was used, and for assessment of continuous variables, Student’s t test was used. For comparison of repeated data between two sets of data within a group, the paired t test was used. A p value of 0.05 or less was considered significant.


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Comment
 Acknowledgments
 Discussion
 References
 
Mortality and morbidity
There were no operative deaths or need for permanent pacemaker in either group. There were two cases of reoperation for bleeding in group R. No other complications related to the procedures were noticed.

Electrocardiography
The postoperative rhythm during the entire study period is summarized in Table 4. There was no atrial tachycardia or atrial flutter postoperatively. With regard to the sinus conversion rate postoperatively, there was a greater tendency to convert to sinus rhythm in the immediate postoperative period in group R compared with group D; however, the difference did not reach statistical significance. The proportion of patients in sinus rhythm gradually increased with time in all groups. Comparison of the sinus conversion rate between the two groups during the subsequent study period did not show any significant difference between the two groups. At 6 months postoperatively, the sinus conversion rate reached 95.3% in the rheumatic group and 97.7% in the degenerative group, but the difference was not statistically significant.


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  		Table 4. Postoperative Rhythm Change Over Timea

 
Echocardiography
The transmitral A wave detection rate in the immediate postoperative period was similar between the two groups (62.7% in group R and 67.4% in group D; p = 0.603). It also steadily increased with time, but there was no statistically significant difference between the two groups at the same time period postoperatively. At 6 months postoperatively, the transmitral A wave detection rates were 90.7% in the rheumatic group and 93% in the degenerative group. The transmitral A wave velocity at 7 days postoperatively was 41.9 ± 41.6 cm/second in the rheumatic group and 45.5 ± 37.7 cm/second in the degenerative group (p = 0.631). The velocity increased to 67.8 ± 38.2 cm/second in group R and 69.8 ± 35.8 cm/second in group D (p = 0.789) at 6 months postoperatively. Comparison of both variables at 7 days, 3 months, and 6 months postoperatively showed no statistically significant difference between the two groups (Table 5).


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  		Table 5. Postoperative Echocardiographic Data

 

   Comment
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
Acknowledgments
 Discussion
 References
 
We found that there were no statistically significant differences between the two groups in restoration of sinus rhythm and left atrial transport function after the maze procedure for chronic AF associated with mitral valve disease. The proportion of patients in sinus rhythm increased constantly with time up to 6 months postoperatively, and more than 95% of the patients in each group showed sinus rhythm. Furthermore, the left atrial transport function, which was assessed by the presence and velocity of transmitral A wave, also increased equally with time in both groups. The velocity of transmitral A wave in both groups was considered to be enough to generate atrial kick. These findings suggest that the cause of the underlying mitral valve disease did not affect the early results of the maze procedure in patients with chronic AF associated with mitral valve disease.

Although the exact mechanisms of onset of AF in association with mitral valve disease are not known, the pressure or volume overload on atrial tissue might play an important role in AF onset. The structural changes of the atrial myocardium were observed in the R and D groups, and these changes might generate the ectopic atrial beat and unidirectional conduction block and create macro-reentry circuits [10]. Fukada and colleagues [8] suggested that rheumatic activity produced the fibrosis of atrial muscle and might contribute to the poor results of the maze procedure in rheumatic mitral valve disease. We have no data on whether there are different mechanisms of AF onset or any additional effects on AF in rheumatic mitral valve disease. However, our results demonstrated that the rheumatic inflammation did not affect the early outcomes of the maze procedure. Rheumatic inflammation is a chronic process, therefore long-term follow-up is necessary to evaluate how rheumatic inflammation affects the results of the maze procedure.

The maze procedure originally was designed to ablate all possible macro-reentry circuits by multiple atrial incisions. The causes of failure to restore sinus rhythm after the maze procedure are the preoperative sinus node dysfunction itself, the presence of shorter atrial refractory time or micro-reentry circuits, and incomplete ablation of macro-reentry circuits [11]. Kosakai and coworkers [12] reported that the different success rates of the maze procedure were derived from underlying disease rather than modification in atriotomies or use of cryoablation. However, our results were different. Kamata and associates [13] reported that the atrial fibrillatory wave and left atrial diameter were independent predictors of restoration of sinus rhythm, and the success rate of sinus rhythm restoration was similar between patients with rheumatic or degenerative disease. Cox [14] noted that the maze procedure, when performed properly, cured AF in nearly 100% of patients with or without mitral valve disease. We agree that complete surgical ablation is most important factor to restore the sinus rhythm in the maze procedure, and the underlying disease is not the cause of failure of the maze procedure.

The proportion of patients in sinus rhythm increased equally with time in both groups. That finding might be due to progressive sinus conversion from atrioventricular nodal rhythm or AF. Atrioventricular nodal rhythm, which is related to transient sinus node dysfunction caused by surgical trauma, is encountered frequently in the immediate postoperative period; however, it is usually converted to sinus rhythm [15]. Atrial fibrillation in the immediate postoperative period could also be converted to sinus rhythm with decreasing tissue edema and a longer refractory period.

The restoration of left atrial transport function is another important goal of the maze procedure. Poor left atrial contraction can negatively affect the contribution of the atrial kick to cardiac output and can lessen the thromboembolic tendency. When the atrial contribution to ventricular filling is absent, a decrease in cardiac output of as much as 40% has been noted, with a rapid ventricular rate. However, sinus rhythm does not necessarily imply effective atrial transport, even in cases of severe mitral stenosis, before the era of the maze procedure [16]. The proposed mechanisms for this phenomenon were unilateral left atrial fibrillation, an interatrial conduction disturbance, absence of left atrial depolarization, or electromechanical dissociation. The possible mechanism of noncontractile left atrium after the maze procedure is similar to that in nonmaze cases. Feinberg and colleagues [17] suggested that too much trauma to the left atrial wall, including vascular damage and delayed interatrial and intraatrial conduction, and lack of contractile muscle by too much excision and exclusion of left atrium might be a mechanism. We previously reported that enhanced left atrial transport function had been observed after modification of our surgical technique [9]. The transmitral A wave velocity measured by transthoracic echocardiogram is reliable for assessing left atrial transport function. The velocity was not affected by the underlying cause of mitral valve disease and increased equally with time, which was enough to generate atrial kick in both groups. The increased left atrial transport function seemed to be related to the remodeling of the atrial wall, recovery from the ischemic condition of atrial myocardium due to fibrillation, and improvement of the contractile force after restoration of sinus rhythm.

The advanced age, duration of AF, increased cardiothoracic ratio, low F-wave voltage, and severely dilated left atrium were known risk factors for failure of restoration of sinus rhythm and left atrial transport function. We did not study those issues in the current study; however, we found that the preoperative condition of patients was similar, and the results of the maze procedure were similar. We had no information that those so-called risky conditions were more commonly represented in rheumatic disease when an operation was scheduled. According to our results, we conclude that rheumatic mitral valve disease itself is not related to a lower success rate of the maze procedure. The maze procedure was equally effective in treating chronic AF associated with either rheumatic or degenerative mitral valve disease in terms of sinus conversion rate and restoring of left atrial transport function. The underlying pathology of the mitral valve did not affect the early results of the maze procedure, but long-term follow-up is necessary.


   Acknowledgments
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 Acknowledgments
Discussion
 References
 
We would like to express our deep gratitude to Kyung Sun Kim, RN, clinical nurse specialist, for her efforts related to patient registry and data handling.


   Discussion
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 Acknowledgments
 Discussion
References
 
DR LISHAN AKLOG (New York, NY): What percentage of the patients remained on anticoagulants for an indication other than atrial fibrillation after the procedure?

DR LEE: We maintained the patients on anticoagulation for 3 to 6 months, depending on the patient’s rhythm. In patients whose rhythm returned to sinus, anticoagulation was discontinued. However, warfarin sodium was restarted in case of recurrence of atrial fibrillation. This number comprised only a small percentage of patients. Another group of patients who received warfarin sodium irrespective of rhythm, even sinus, were those with mechanical prosthetic valvular implants. These patients made up 36.4% (47 of 129) of the total.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 Acknowledgments
 Discussion
 References
 

  1. Brodell G.K., Cosgrove D., Schiavone W., Underwood D.A., Loop F.D. Cardiac rhythm and conduction disturbances in patients undergoing mitral valve surgery. Cleve Clin J Med 1991;58:397-399.[Medline]
  2. Resnekov L. Haemodynamic studies before and after electrical conversion of atrial fibrillation and flutter to sinus rhythm. Br Heart J 1967;29:700-708.[Free Full Text]
  3. Wolf P.A., Dawber T.R., Thomas H.E., Jr, Kannel W.B. Epidemiologic assessment of chronic atrial fibrillation and risk of stroke: the Framingham study. Neurology 1978;28:973-977.[Abstract/Free Full Text]
  4. Skoularigis J., Rothlisberger C., Skudicky D., Essop M.R., Wisenbaugh T., Sareli P. Effectiveness of amiodarone and electrical cardioversion for chronic rheumatic atrial fibrillationafter mitral valve surgery. Am J Cardiol 1993;72:423-427.[Medline]
  5. Obadia J.F., Farra M.E., Bastien O.H., Lièvre M., Martelloni Y., Chassignolle J.F. Outcome of atrial fibrillation after mitral valve repair. J Thorac Cardiovasc Surg 1997;114:179-185.[Abstract/Free Full Text]
  6. Cox J.L., Schuessler R.B., Boineau J.P. The surgical treatment of atrial fibrillation: I. Summary of the current concepts of the mechanisms of atrial flutter and atrial fibrillation. J Thorac Cardiovasc Surg 1991;101:402-405.[Abstract]
  7. Cox J.L., Ad N., Palazzo T., et al. The maze-III procedure combined with valve surgery. Semin Thorac Cardiovasc Surg 2000;12:53-55.[Medline]
  8. Fukada J., Morishita K., Komatsu K., et al. Is atrial fibrillation resulting from rheumatic mitral valve disease a proper indication for the maze procedure?. Ann Thorac Surg 1998;65:1566-1569.[Abstract/Free Full Text]
  9. Lee J., Choo S., Kim K., et al. Atrial fibrillation surgery simplified with cryoablation to improve left atrial function. Ann Thorac Surg 2001;72:1479-1483.[Abstract/Free Full Text]
  10. Boyden P.A., Tilley L.P., Pham T.D., Liu S.K., Fenoglio J.J., Jr, Wit A.K. Effects of left atrial enlargement on atrial transmembrane potentials and structure in dogs with mitral valve fibrosis. Am J Cardiol 1982;49:1896-1908.[Medline]
  11. Kobayashi J., Kosakai Y., Isobe F., et al. Rationale of the Cox maze procedure for atrial fibrillation during redo mitral valve operations. J Thorac Cardiovasc Surg 1996;112:1216-1222.[Abstract/Free Full Text]
  12. Kosakai Y., Kawaguchi A.T., Isobe F., et al. Cox maze procedure for chronic atrial fibrillation associated with mitral valve disease. J Thorac Cardiovasc Surg 1994;108:1049-1055.[Abstract/Free Full Text]
  13. Kamata J., Kawazoe K., Izumoto H., et al. Predictors of sinus rhythm restoration after Cox maze procedure concomitant with other cardiac operations. Ann Thorac Surg 1997;64:394-398.[Abstract/Free Full Text]
  14. Cox J.L. Intraoperative options for treating atrial fibrillation associated with mitral valve disease. J Thorac Cardiovasc Surg 2001;122:212-215.[Free Full Text]
  15. Miralem P., Michele P., Henryk P., Barbara P., Takeo P., Roland H. Transient sinus node dysfunction after the Cox-maze III procedure in patients with organic heart disease and chronic fixed atrial fibrillation. J Am Coll Cardiol 1988;32:1040-1047.
  16. Betriu A., Sanz G., Adelman A.G., Wigle E.D. Sinus rhythm with ineffective left atrial contraction in severe mitral stenosis. Chest 1974;66:441-444.[Abstract/Free Full Text]
  17. Feinberg MS, Waggoner AD, Later KM, Cox JR, Lindsay BD, Perez JE. Restroration of atrial function after the maze procedure for patients with atrial fibrillation. Circ Assess Doppler Echocardiogr 1994;90(5 Pt 2):II285–92



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