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Ann Thorac Surg 2006;82:1938-1947
© 2006 The Society of Thoracic Surgeons
a Mount Elizabeth Medical Centre, Singapore
b Gleneagles Medical Centre, Singapore
Accepted for publication May 18, 2006.
* Address correspondence to Dr Wong, Heart, Lung and Vascular Surgical Centre, 16-06 Mount Elizabeth Medical Centre, 3 Mount Elizabeth, Singapore 228510. (Email: javas{at}magix.com.sg).
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Abstract |
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 Top Abstract IntroductionMaterial and MethodsResultsCommentReferences |
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Introduction |
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However, there is a paucity of clinical data in the literature where a concurrent control arm (that is leaving the AF alone) is used as a comparison with concomitant AF maze in open heart surgery. A control is important to eliminate confounding variables that may inflate or deflate the efficacy of the maze procedure and the determination of clinical outcomes. Absence of a control arm also does not allow discernment of the absolute effect of the maze surgery because we cannot know how many of the patients would convert to sinus rhythm spontaneously.
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Material and Methods |
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The bibliographies of the published studies were also reviewed to identify additional references related to the topic.
Classification of the Maze Procedure
The maze pattern used in the studies must meet the criteria of the classical Cox maze III pattern or its modification and involve both atrias. Published papers that involve creating lines of block only in the left atrium are not included in this study. The surgical technique used can be of the cut and sew method or ablation using alternative energy sources.
Definition of Atrial Fibrillation
Chronic AF implies that the AF is present continuously in the atrium. Paroxysmal AF implies that the AF is intermittent.
Preoperative Baseline Characteristics Used for Comparison
The preoperative characteristics that were identified and used for matching were age, sex, New York Heart Association (NYHA) functional class III or IV, history of stroke or thromboembolism, AF duration, incidence of chronic AF, left ventricular ejection fraction, left atrial diameter, previous operation, mitral valve surgery and additional nonmitral valve surgeries. These are shown in Table 1
for the matched-controlled trials, and in Table 2
for the randomized trials.
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Results |
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In the matched-controlled studies, the long-term survival rate is 84% to 100% in the concomitant maze group versus versus 82% to 100% in the control (Fig 5A). In the four randomized studies, the long-term survival rate is 72%% to 100% in the concomitant maze group versus 92% to 100% in the control (Fig 6A). Although long-term survival was significantly better among patients receiving concomitant maze surgery in matched-controlled trials (OR, 2.27; 95% CI: 1.21 to 4.27), there was significant variability among the studies (Fig 5B). Conversely, there was little difference in survival after 1 to 1.5 years of follow-up among patients who received and did not receive concomitant maze surgery in randomized trials (Fig 6B)
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Comment |
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Maze and Stroke Risk Reduction
Intuitively, restoration of sinus rhythm is likely to reduce embolic complications. The first hint that the maze procedure can make a difference in stroke outcome in AF was reported by Cox and associates [7] in 1999, a 12-year study of 306 patients; 61% of the patients had paroxysmal AF, 39% of the patients had chronic AF, and 38% had concomitant open-heart procedures along with the maze. There were only 2 perioperative strokes (0.7%) in the whole series of 306 patients, and among the 265 patients followed up to 11.5 years, there was only 1 late stroke, which completely resolved. The result is outstanding, as 50% of this group of patients had an elevated risk of stroke. Fifty-eight patients had a history of stroke or transient ischemic attack, and 86 patients had one or more risk factors such as advanced age, hypertension, diabetes mellitus, congestive heart failure, and ischemic heart disease.
Matched-Controlled Trials of Maze and Concomitant Mitral Valve Surgery Versus Control
Of the seven matched-controlled studies, all [8–14] reported significant normal sinus rate conversion, with six of the studies [8–11, 13, 14] showing an associated benefit in stroke reduction.
Bando and colleagues [11, 14, 15] published three interesting papers supporting the use of the maze in concomitant mitral valve surgery on stroke reduction. Each paper supported a particular point. In their first paper [11], the patients were divided into three cohorts, namely, mitral valve replacement with the maze (MVR/maze), mitral valve repair with the maze (MV repair/maze), and mitral valve replacement alone (MVR). All the MVR patients received a mechanical valve. The freedom from AF and stroke at 5 years was significantly higher when the maze was added to the concomitant mitral valve surgery and was associated with a 20% stroke risk reduction. Importantly, this benefit was observed among patients who had received a mechanical prosthetic mitral valve and on anticoagulation. Despite anticoagulation therapy, the MVR alone group was at significant risk of stroke.
In their second paper [15], which was a retrospective analysis of 812 patients undergoing MVR with a mechanical valve from May 1977 to December 2001, a 24-year period in which the maze was added in 185 patients (23%), there was a late recurrence of AF in 25% of the patients who had the combined MVR/maze procedure. The incidence of stroke between patients who were in sinus rhythm after the concomitant MVR/maze was similar to those who were in native sinus rhythm. This finding would imply the restoration of sinus rhythm by the maze procedure seemed to eliminate the risk of late stroke and put the stroke risk on par with the patients who were in preoperative sinus rhythm going for MVR.
The third paper by Bando and colleagues [14], a series from 1991 to 2003, was a multi-institutional study that looked at 1,026 patients with nonischemic/noncardiomyopathy mitral valve regurgitation who underwent mitral valve plasty in three centers. In the subgroup that had AF, patients who had concomitant maze did better in stroke risk as compared with those whose AF was left alone (99.2% versus 82.6%; p < 0.001). Cardiac-related survival at 8 years was also better in the concomitant maze group than the AF left alone group (96.9% versus 81.6%; p < 0.01). However, the effect of the concomitant maze procedure was not significant when propensity score was used (p = 0.298). Only advanced age and left atrial diameter larger than 60 mm were significant.
Maze and Concomitant Mitral Valve Surgery Versus Percutaneous Mitral Commissurotomy in AF Patients
Mitral valve surgery with the addition of the maze (MVS/maze) appeared to be superior to percutaneous mitral commissurotomy . In a paper by Nakajima and associates [13], a series from April 1988 to March 2003, 114 patients who underwent MVS/maze were compared with 109 patients who had percutaneous mitral commissurotomy with the AF left alone. The MVS/maze group of patients were older, had longer duration of preoperative AF, larger left atrial diameter, and history of more previous left atrial thrombus. Despite being at higher risk for embolic events, those treated with MVS/maze were more likely to have a higher AF-free rate (85.7% versus 4.2%; p < 0.0001) and embolism-free rate including stroke (98.0% versus 84.8%; p = 0.01) at 5 years than percutaneous mitral commissurotomy alone, respectively. Atrial fibrillation would continue to be a source of embolism despite correction of the mitral stenosis by percutaneous mitral commissurotomy.
Randomized Trial Studies Comparing Stroke Rate Between Maze and Concomitant Mitral Valve Surgery Versus Control
None of the randomized control studies [16–19] were able to show any statistical difference in stroke rate. However, the numbers compared were small and the follow-up was short.
Stroke Rate, Atrial Contraction, and Resection of Left Atrial Appendage in the Maze Procedure
The reason for the reduced stroke rate may be related to the return of atrial contraction after the maze procedure which prevents blood stagnation in the left atria. Atrial transport function can be confirmed by Doppler echocardiography after the maze procedure, and the incidence of biatrial contraction is from 75% to 90% [20–23]. Only four studies in the present reported use of Doppler echocardiography to demonstrate atrial transport function [9, 13, 16, 17]. In general, atrial contraction was demonstrated in most of the patients with regular rhythm.
Another contributing factor to the reduced incidence of stroke may be related to the resection of the left atrial appendage as part of the Cox maze procedure. The source of 91% of nonrheumatic AF-related left atrial thromblism originates from the left atrial appendage [24]. Left atrial appendage resection has the potential to reduce stroke rate but not necessarily ligation [24–29]. In fact, Bando and colleagues [15], in looking at the subset of patient who had MVR only, found half of them had the left atrial appendage ligated and half had it left open. There were more strokes in the ligated group (43 strokes) than in the other group (26 strokes), of a total of 69 strokes.
Additional Benefits of Maze and Concomitant Mitral Valve Surgery on Reducing or Eliminating Antiarrhythmic Medications and Anticoagulation
Potential benefits of freedom of antiarrhythmic medications include absence of drug toxicity, side effects, proventricular arrhythmia effects, and cost savings. Four matched-controlled [8–11] and two randomized-controlled [17, 18] studies reported statistically significant complete freedom from or reduction in the usage of antiarrhythmic medication in the concomitant maze group versus control: 45% [8], 50% [9], 60% [10], 40% [11], 50% [17], and 80% [18] were using no or reduced antiarrhythmic medication in the concomitant maze group, versus 22%, 20%, 18%, 13%, 10%, 50% in the controls, respectively.
The risk of anticoagulation-related major bleeding episodes in patients with a heart valve prosthesis is 1% to 5% per patient-year [30]. The bleeding risk would potentially reach zero if anticoagulation therapy were not used in patients who have a successful sinus rhythm conversion maze procedure and concomitant valve repair or bioprosthetic valve replacement. Of the four matched-controlled studies that published figures for anticoagulant usage, 14% [8], 38% [10], 35% [11], and 10% [18] in the concomitant maze group were using anticoagulant, versus 50%, 69%, 100%, 10% in the control group, respectively. Anticoagulant usage may be affected by whether a mechanical valve was used or by other factors that a surgeon considered made a postsurgical patient still at risk for stroke. As for the valve factor, all the patients in the series by Handa and colleagues [8] had mitral valve repair. In the series by Raanani and colleagues [10] and Lima and associates [18], mitral valve replacement and repair were similar for the concomitant maze and control group. In the series by Bando and associates [11], all the mitral valve surgery in the control group was mitral valve replacement by a mechanical valve, and would require anticoagulation therapy anyway. In the concomitant maze group, 43% of the mitral valve surgery was mitral valve repair. This group forms 34% of the whole cohort, and only 35% were using anticoagulation therapy. Hence, the concomitant maze was able to eliminate the use of anticoagulation in almost two thirds of the AF patients going for mitral valve repair.
Long-Term Survival
The Framingham Study [2], in a 20-year biennial follow-up of 5,191 patients (30 to 62 years old), showed the mortality rate among those in whom AF developed to be twice that of those in whom it did not. The reduced survival with atrial fibrillation was probably related to the associated heart disease present in 80% of the patients as well as, in part, to the excess stroke risk resulting from the AF. The initial embolus is estimated to be to the brain in 65% of all cases of arterial embolization [31]. Among the survivors, more than half die of further cerebral emboli, often without clinical evidence of renal, mesenteric, splenic, or limb embolism [32]; 71% of cerebral emboli resulted in either death or severe neurologic deficit from the first emboli.
Preoperative AF Is an Independent Risk Factor for Operative Mortality or Decreased Survival After Open Heart Surgery
Kvidal and associates [33] analyzed survival among 2,359 patients undergoing their first aortic valve replacement from 1980 to 1995; 85% of the patients were in sinus rhythm and 15% of the patients were in AF. Their survival was compared with the expected survival of the general Swedish population stratified by age, sex, and 5-year calendar period that served as the control cohort. Multivariate analysis identified New York Heart Association functional class III and IV, age, concomitant CABG, aortic regurgitation, and AF to be significant in determining late survival. In particular, among patients who had preoperative AF, 40% and 18% were alive after 10 and 15 years, respectively. This corresponded to an excess mortality (observed mortality minus expected mortality) of 42% and 67%, respectively. Atrial fibrillation decreased relative survival substantially in patients with an aortic lesion and who had aortic valve replacement.
Verheul and colleagues [34] also observed similar findings in a multivariate analysis of long-term survival after aortic valve replacement. Atrial fibrillation has the highest hazard ratio for decreased survival compared with heart failure, coronary artery disease, age, and documented myocardial infarction in this paper.
Preexisting AF can be a incremental risk factor for time-related mortality in patients undergoing CABG [35]. Quader and colleagues [36] looked at the association of AF and reduced survival in 46,984 patients undergoing primary isolated CABG in the Cleveland Clinic. There were 451 patients (0.9% prevalence) with documented preoperative AF (n = 411) and atrial flutter (n = 40). The patients with preoperative AF were older and had more left ventricular dysfunction and hypertension, but less severe angina. Survival was significantly reduced among unmatched patients with AF compared with patients without AF. When propensity matched for age, comorbidities, left ventricular dysfunction, and left main disease to permit an apple-to-apple comparison, survival was again lower among patients with AF than among patients without AF.
Preoperative AF Is Not an Independent Factor of Operative Mortality and Long-Term Survival After Open Heart Surgery
Several studies [37–39] were not able to detect any statistical differences in operative mortality and long-term survival between the two groups of patients stratified by their preoperative atrial rythmn of sinus rythmn or atrial fibrillation undergoing mitral valve surgery. Atrial fibrillation was also not identified as important to operative mortality or decreased late survival in The Society of Thoracic Surgeons national cardiac surgery database [40].
Obadia and coworkers [41] found a similar conclusion. However, when the data were analyzed further according to their postoperative rhythm for the patients who had undergone mitral valve surgery, it was found that the postoperative return to sinus rhythm group was associated with improved survival compared with the group who continued to have persistent postoperative AF (94% versus 77%). Jessurun and colleagues [42] were also able to show persistent postoperative AF was associated with decreased survival (p = 0.05).
Impact of Maze and Concomitant Mitral Valve Surgery Versus Control on Operative Mortality and Long-Term Survival
Among the four randomized studies [16–19], there is no difference in perioperative mortality and long-term survival for patients treated with and without maze. Among the seven matched-controlled studies, only one [14] suggested improved survival if the maze was performed with concomitant mitral valve surgery. The 8-year freedom from cardiovascular-related death rate was significantly higher among those undergoing concomitant maze surgery compared with the control (96.9% versus 81.6%; p < 0.001). However, when propensity score was used, only advanced age and a preoperatively enlarged left atrial diameter greater than 60 mm were significant risk factors for late death.
Hence, the present data on the subject of whether late survival rate is improved by the conversion of sinus rhythm by the maze procedure is mixed. Data from the matched-controlled studies are retrospective and have important limitations, as not all the variables influencing long-term survival are equally matched. Among the randomized trials, the duration of follow-up is short, and the number of patients is small. These studies were a comparison between treatment strategies—concomitant maze versus no maze (control)—and it may not be appropriate to extrapolate that conversion to sinus rhythm offered no survival benefit. Similarly, the trials of rate control versus rhythm control strategies [43–45] did not show any mortality differences. However, about 10% to 30% of patients in the rate control strategy converted to sinus rhythm spontaneously. When the data were analyzed according to patient's actual rhythm, sinus rhythm versus AF, remaining in sinus rhythm was an independent predictor of survival after adjusting for clinical variables [46]. Correspondingly, survival benefit may be shown if we compared those who remained in sinus rhythm or in AF in this study. Nevertheless, it is difficult not to believe that the increased risk of major strokes that can be potentially lethal and that the potential major bleeding complications associated with anticoagulation use for patients remaining in AF will not affect the survival curve for those remaining in AF.
The patients enrolled in the matched-controlled and randomized trials also may not represent the full spectrum of AF. As frequency and severity of the symptoms relating to the AF was not mentioned, we were not certain whether there was any highly symptomatic AF subgroup included. This group would experience considerable morbidity and mortality from AF, such as exacerbation of heart failure, and would benefit most from sinus rythmn conversion in the long term. Chronic tachycardia associated with AF has also been shown to correlate with accelerating decline in left ventricular function and a lower survival rate a [47–50], and AF eradication improved hemodynamic status by optimizing ventricular filling. A small study by Schaff and colleagues [51] showed that the maze surgery improved left ventricular ejection fraction from 31% to 53% (p < 0.05) in 9 patients with AF. Hsu and associates [52] also showed that successful ablation of AF in 58 patients with associated congestive heart failure resulted in significant improvement in left ventricular function, compared with another 58 matched patients without congestive heart failure (increases in the ejection fraction and fractional shortening were 21% ± 13% and 11% ± 7%, respectively; p < 0.001). Exercise capacity, symptoms, and quality of life were also improved. The outcome from a controlled nonrandomized long-term study by Pappone and associates [53] of 1,171 patients from 1998 to 2001 showed that the 589 patients who were treated with ablation had lower rates of mortality and morbidity, including stroke and congestive heart failure, than a contemporary group of 582 patients with AF who were treated medically.
Conclusion
The ideal goal of AF surgery is a safe, simple, effective, and tailored approach to eradicate the most likely mechanism of the AF in a particular patient. New technologies in AF surgery have evolved in creating the lines of block faster, easier, safer, and transmurally. Correspondingly, different lesion patterns have been postulated based on further understanding of the mechanism of AF. The significance of these variations is still not entirely clear. The present discussion in the literature is usually on the techniques of AF surgery and whether the approach should be performed by the use of minimally invasive or conventional techniques, on pump or off pump, sternotomy or no sternotomy. The merits of various alternative energy sources used to create the lines of block of the maze are also the subject of debate. More important, AF surgery should be able to demonstrate improved clinical outcomes. This review by the use of pooled analysis showed that adding the maze procedure to concomitant mitral valve surgery is associated with a high incidence of sinus rhythm conversion and stroke rate reduction but not necessarily improvement in long-term survival. Properly conducted, larger, randomized trials or propensity-matched studies with adequate follow-up are needed to determine the true impact of concomitant maze surgery on clinical outcomes.
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