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Ann Thorac Surg 2001;72:1251-1255
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Predictors for atrial transport function after mini-maze operation

^a Department of Cardiothoracic Surgery, Kerckhoff-Clinic Foundation, Bad Nauheim, Germany
^b Department of Cardiology, Kerckhoff-Clinic Foundation, Bad Nauheim, Germany
^c Department of Radiology, Kerckhoff-Clinic Foundation, Bad Nauheim, Germany
^d Department of Cardiology, University Hospital, Zürich, Switzerland

Address reprint requests to Dr Bauer, Department of Cardiothoracic Surgery, Kerckhoff-Clinic Foundation, Benekestrasse 2-8, D-61231 Bad Nauheim, Germany
e-mail: epb53{at}yahoo.com

Presented at the Thirty-seventh Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 29–31, 2001.

	Abstract

Top Abstract Introduction Material and methods Results Comment Discussion References

 
Background. Restoration of atrial transport function (ATF) is a major goal of the maze procedure. This prospective study was undertaken to evaluate predictors of left atrial transport function in patients undergoing a mini-variant of the maze III procedure 3 and 12 months postoperatively.

Methods. Mini-maze operation was performed in 72 patients with a mean age of 64 ± 8.7 years during a 5-year period. Seventy of 72 (97%) had combined procedures. Clinical and electrophysiologic examination was carried out before surgery, and 3 and 12 months postoperatively.

Results. Early mortality was 1.4% (1 of 72 patients) and late death occurred in 5.6% (4 of 71 patients). After 3 months, 54 of 68 (80%) patients showed sinus rhythm, and 48 of 60 (80%) after 12 months. ATF was restored in 87% (echocardiography) and 82% (magnetic resonance imaging) after 3 months, and in 86% (echocardiography) and 78% (magnetic resonance imaging) after 12 months. Independent predictors for ATF restoration after 12 months were better preoperative left ventricular function (p = 0.02), and smaller preoperative left atrial diameter (p = 0.005). Correlation between echocardiography and magnetic resonance imaging was 80% after 12 months.

Conclusions. Restoration of ATF after mini-maze procedure is achieved in over 80%. Independent predictors for ATF restoration are smaller preoperative left atrial diameter and better preoperative left ventricular ejection fraction.

	Introduction

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The maze procedure was designed with three specific goals in mind: (1) The permanent ablation of atrial fibrillation (AF); (2) the restoration of atrioventricular synchrony, and (3) the preservation of atrial transport function [1]. The hemodynamic function of the atria and their significance have been debated for a long time. Meanwhile, it seems clear that the atrium makes a definite contribution to the general adaptability of cardiac output. Especially in hearts with marked depressed ventricular function, atrial activity may be important as a compensatory mechanism [2]. However, the magnitude of these effects are quiet variable among patients [3]. It is well known that atrial transport function (ATF) may recover after cardioversion for atrial fibrillation within weeks [4]. The same is true after the maze procedure and its modifications [5–8]. However, predictors for restoration of atrial transport function are not well known, especially in patients undergoing maze modifications combined with other cardiac procedures. This prospective study was undertaken to evaluate left atrial transport function after a mini-variant of the maze III procedure, 3 and 12 months postoperatively.

	Material and methods

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Between November 1995 and October 2000, a mini-maze procedure was performed in 72 patients with chronic symptomatic atrial fibrillation. There were 37 men and 35 women with a mean age of 64 ± 8.7 years (range 40 to 83 years). Mean duration of AF was 7 ± 6.3 years (range 1 to 35 years). Seventy of 72 (97%) patients had concomittant procedures (Table 1). The technique of mini-maze procedure is described elsewhere [9]. In brief, incisions to mitral and tricuspid annulus as well as atrial septal incision were not carried out as described by Cox and colleagues [1]. However, amputation of left and right atrial appendages, circumcision of pulmonary veins, division of the tissue bridge between the appendage amputation site to the pulmonary vein isolation incision, longitudinal incision of right atrium, and V-incision from the top of the inferior vena cava (IVC) cannula across the lower right atrial free wall to the right atrioventricular (AV) groove were carried out as described for maze III procedure [1].

Echocardiography
Two-dimensional and Doppler transthoracic echocardiography was performed using a Hewlett-Packard Sonos 4500 or 5500 (Hewlett-Packard, Andover, MA) machine. Standard parasternal and apical images were obtained, and left ventricular function was assessed visually. Atrial mechanical function was assessed by pulsed Doppler examination of the mitral inflow, using the apical four-chamber view. The Doppler sample volume was positioned between the tips of the mitral leaflets. All measurements were made during quiet respirations with the patient in the left lateral position. Peak velocities of the early filling (E) wave and atrial filling (A) wave were measured, as well as their velocity-time integrals and percent A filling. Atrial mechanical activity was considered present if an atrial filling (A) wave was detected in late diastole after the electrocardiogram (ECG) P wave [10].

Magnetic resonance imaging
MRI-examination was carried out with a 1.5 T unit (Vision or Sonata; Siemens Corp, Erlangen, Germany). Flow measurement was performed with an ECG-triggered segmented velocity encoded (venc) gradient echo (GE) sequence in breath-hold (fast low angle shot [FLASH], repetition time [TR] 28 ms, echo time [TE] 5.5 ms, venc 150 cm). The slice for flow measurement was placed across mitral valve area. Acquisition was repeated three times to calculate a velocity-time curve on 18 points during the entire cardiac cycle. The E and A wave was identified, and quotation of A max to E max was assessed.

The patients were divided into 2 groups: Group 1 (with atrial transport function) showed left atrial contraction in either echocardiography or MRI; group 2 (without atrial transport function) did not.

Statistical analysis
Statistical analysis was performed with SPSS 9.0 for windows (SPSS Inc, Chicago, IL). The distribution of continuous variables is expressed as mean ± standard deviation, and comparison was tested by two-tailed t test (Mann-Whitney U test). Categorical variables were compared by ² test and Fisher’s exact test, as appropriate. Multivariate analysis was performed by logistic regression. p values less that 0.05 were considered significant.

	Results

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Early mortality was 1.4% (1 of 72 patients) and late death occurred in 5.6% (4 of 71 patients). Cause of late death was cardiac related (sudden death) in 3 patients and noncardiac related (subphrenic abscess with sepsis) in another patient. Two were in sinus rhythm and 2 in atrial fibrillation prior to death. After 3 months, 54 of 68 (80%) patients showed sinus rhythm (or atrial pacing) in electrocardiography, whereas there were 48 of 60 (80%) after 12 months. In patients with sinus rhythm, echocardiography revealed ATF in 45 of 52 (87%) patients after 3 months, and in 37 of 43 (86%) patients after 12 months. MRI showed ATF in 27 of 33 (82%) patients with sinus rhythm after 3 months, and in 21 of 27 (78%) patients after 12 months.

Twelve of 72 (17%) patients needed pacemaker implantation: Seven were implanted in patients with persistent atrial fibrillation due to brady-tachycardia, and 5 in patients due to sick sinus syndrome. All patients with atrial pacing showed atrial transport function after 3 and 12 months. Comparison of group 1 (patients with atrial contraction) and group 2 (patients without atrial contraction) are depicted in Tables 2 through 5. Univariate analysis shows that the smaller the diameter of the left atrium before the maze operation, the greater the chance of atrial contraction restoration. The presence of mitral stenosis negatively influenced restoration of atrial transport function after 3 months in echocardiography and MRI (p = 0.012 and p = 0.024). After 1 year, better left ventricular ejection fraction was a predictor for restoration of atrial contraction (p = 0.02). Multivariate logistic regression analysis revealed that an independent factor for restoration of atrial transport function after 3 months and 12 months was a smaller preoperative left atrial diameter (p = 0.004 and p = 0.005). Furthermore, better preoperative left ventricular function was a predictor for restoration of atrial transport function 1 year after operation (p = 0.02). Five of 54 (9.3%) patients, who did not show atrial contraction in echocardiography after 3 months, had transport function after 12 months. However, 4 of 54 (7.4%) patients who showed left atrial transport function after 3 months had loss of contraction after 12 months. Estimation of atrial transport function after 3 months correlated well between echocardiography and MRI in 34 of 39 (87%) cases. However, atrial contraction was observed in echocardiography but not in MRI in 3 cases, and in MRI but not in echocardiography in 2 cases. After 1 year, echocardiography and MRI correlated in 24 of 30 (80%) cases. Five of 25 (20%) patients with atrial contraction in echocardiography did not show transport function in MRI.

	Comment

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Restoration of atrial transport function after the maze procedure has already been studied by numerous authors [8, 13–17]. Cox and colleagues recognized both right and left atrial transport function recovery immediately after the maze procedure [6]. After 6 months, they could show that left atrial transport function and contribution to cardiac output was present in 94% after maze III [6]. We found left atrial contraction in 87% patients with sinus rhythm after 3 months, and in 86% after 12 months in echocardiography, which concurs with the results of Cox and associates. However, our patient population was different, compared with Cox and coworkers’ group, in that we performed concomitant procedures in 97%. Others who performed combined procedures in up to 100% confirmed left atrial contraction in 63% to 90% [8, 14, 16, 17]. Yet, authors who measured magnitude of contractile function reported restored function to be one-half to one-third less than in control subjects [14, 15, 17]. Severe injury to left atrial myocardium or mechanical stress as the result of mitral valve lesion might contribute to the reduction of left atrial contractility [17]. This could also be the reason why our patients with mitral stenosis showed significantly less atrial contraction after 3 months. Feinberg and associates showed in an echocardiographic study that left and right atrial contraction could be restored in 83% and 93%, respectively [7]. Others also showed better restoration of right atrial function compared with left atrial function [13, 15–17, 18]. In theory, one could assume that atrial transport function is more effective after a mini-maze operation compared with the "classic" maze operation, since less atrial incisions are carried out during this procedure [9]. Nitta and colleagues found superior left atrial transport function after radial incision approach compared with atrial contraction after the classic maze operation [19]. Cutting lines for radial incision approach are shorter and the direction is different. Furthermore, the number of incisions is smaller compared with maze III.

Yuda and associates found that patients with giant left atrium had less left atrial contraction compared with patients without giant left atrium [20]. Others also think that left atrial dimension prior to maze procedure may be useful in predicting atrial contractile function postoperatively [18]. We also found that the smaller diameter of the left atrium preoperatively, the greater the chance of atrial transport function restoration. Furthermore, better preoperative left ventricular ejection fraction was an independent predictor for postoperative left atrial contraction. Structural abnormalities of both left ventricle and left atrium could be the reason for this interesting result. In contrast to others, we did not find duration of AF adversely affecting restoration of left atrial mechanical function [16, 17]. However, we also observed that patients without atrial transport function had longer duration of atrial fibrillation.

Correlation between echocardiography and MRI was excellent in our study. Unfortunately, there are no other studies comparing these two methods. Some patients showed left atrial contraction after 3 months but not after 12 months, and vice versa. To fully understand this observation, longer follow-up periods might be necessary.

We found that 7.4% of patients lost atrial contraction between 3 months and 12 months. A possible explanation for this phenomenon could be an increase of adhesions around the atria. However, MRI did not reveal any tissue growth around the hearts in these patients. Furthermore, there were no interval problems such as increasing valve incompetence or new myocardial infarction.

It is questionable whether anticoagulation can be discontinued if atrial contraction restores. Cox and coworkers found that risk of stroke is decreased dramatically after restoration of sinus rhythm [21]. This is the reason why he proposes not to anticoagulate patients after a maze procedure except in patients with mechanical heart valves. He states that anticoagulation can be discontinued even in patients with no demonstrable atrial transport function.

	Discussion

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DR PATRICK M. McCARTHY (Cleveland, OH): The past decade has seen the development of numerous variations on the theme of the maze procedure originally set forth by Dr Jim Cox. Today, some surgeons use radiofrequency ablation instead of suture lines, some use extensive cryoablation, others do not use any cryoablation, and Dr Klövekorn and his colleagues avoided cryoablation and omitted some of the classic incisions from the maze III operation. When I read the title of the paper, I thought that this would be a minimally invasive procedure, but it is more appropriately a partial maze operation.

The authors should be congratulated for demonstrating a very low perioperative mortality in patients undergoing very complicated cardiac operations. The 80% return of sinus rhythm is good, better than usually achieved with limited radiofrequency ablation that just isolates the pulmonary veins, but it is not as good as many other reports using a more complete maze III procedure.

My first question has to do with the atrial dimensions. Like others, the authors had less success in patients with large atria. So do you attempt to remove atrial tissue and reduce atrial size, and if so, do you think that that would help avoid atrial fibrillation recurrence?

Second, you noted a 78% to 87% return of left atrial contraction in patients with sinus rhythm. Did you measure also right atrial systole? Our theory is that the posterior left atrial wall and pulmonary veins are electrically isolated and therefore do not contract. This accounts for the reduced left atrial contraction compared to normal patients and also why other studies have documented more frequent right atrial than left atrial contraction. There are no electrically inert areas in the right atrium after the maze operation. New approaches therefore that isolate the pulmonary veins separate from the posterior left atrium should be beneficial in that the posterior wall can then contract.

Finally, in our estimation, the most important data now emerging has been the prevention of late embolic events and strokes after the maze. Dr Cox found about a 1% risk of late stroke in his patients, and we published on no late embolic events in our first 100 maze patients. This remarkable long-term effectiveness, along with minimally invasive surgical techniques, has stimulated us to perform almost 100 maze operations last year, up from about 15 per year average during the 1990s. So, Dr Klövekorn, have you also observed few late embolic events?

DR KLÖVEKORN: Doctor McCarthy, thank you very much for your comments. Referring to your first question concerning the dimension of the left atrium and trying to reduce the dimension, we tried this. Before we started with our mini-maze version, we used the classical Cox III version. One of the reasons we stopped it was that there was too much aortic cross-clamping time. But in our experience, reducing the size of the left atrium did not help much, mainly because we had patients with giant left atria in the beginning, and some of them with calcified walls, so it was pretty difficult to do this.

We measured the left atrial contraction. It was more or less out of methodological reasons because it is easier to judge this with the measuring of the E and A wave with the echo and the MRI. But we also assessed the right atrial contraction, and it is just about similar because the main contraction does not come from the posterior side of the left atrium but it is the side walls and mainly the septum, and if it contracts, it is the same contraction on the left and right side. But one of the problems, of course, if you have seen our patient data, was that there were a lot of patients with tricuspid valve problems and with enlarged right atria. It is very difficult if you have an enlarged right atrium, because of tricuspid regurgitation, to differentiate between the effect of reduced size of the right atrium, if there is a remaining problem from the tricuspid valve disease.

And, of course, as for the last question, we did not observe strokes in our patients. We terminated the Coumadin therapy in all the patients where we could prove atrial transport function and those who had sinus rhythm, as well as in those 5 patients who had atrial pacemakers. And I think, as you mentioned too, this is one of the main advantages, that these patients really can be relieved from the Coumadin therapy, which has quite a considerable morbidity, and I think we are increasing our number of procedures. This was more or less a preliminary study because we still do not know if we should use cryoablation or if we should use radiofrequency, but we may stick to the normal surgical cutting of the atrium.

Thank you.

	References

Top Abstract Introduction Material and methods Results Comment Discussion 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): Erwin P. Bauer Zoltan A. Szalay Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bauer, E. P. Articles by Klövekorn, W. P. Search for Related Content PubMed PubMed Citation Articles by Bauer, E. P. Articles by Klövekorn, W. P. Related Collections Electrophysiology - arrhythmias