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Ann Thorac Surg 2001;71:572-576
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Serial change in the atrial transport function after the radial incision approach

^a Department of Cardiothoracic Surgery, Nippon Medical School, Tokyo, Japan

Address reprint requests to Dr Nitta, Cardiothoracic Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan
e-mail: yosuke-i{at}jb3.so-net.ne.jp

Presented at the Poster Session of the Thirty-sixth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 31–Feb 2, 2000.

	Abstract

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Background. The left atrial transport function recovers slowly over several months after the maze procedure (Maze), but remains at a low level even during the long-term postoperative period. Because the Maze leaves an insufficient left atrial transport function, patients may still be prone to thromboembolism after the Maze. The radial incision approach (Radial) has been shown to preserve greater atrial transport function than does the Maze in the early postoperative period.

Methods. To examine the serial change in the atrial transport function after the Radial, out of 32 patients who underwent the Radial, 15 patients were assessed by transthoracic Doppler echocardiography 1, 3, 6, and 12 months after surgery. The atrial filling fraction and peak A/E velocity ratio were determined from the flow-velocity spectra across the mitral and tricuspid valves. The incidence of thromboembolic events was examined in 21 patients who were followed for more than 3 months after the Radial. The data were compared with data obtained from 13 patients after (41 ± 6 months) the Maze III procedure.

Results. The left atrial transport function after the Radial increased within 3 months to a significantly greater level than did that after the Maze in the long-term. The atrial filling fraction was 28.2% ± 7.9% at 3 months after the Radial and 15.1% ± 4.0% at 41 months after the Maze (p < 0.01). The peak A/E ratio was 0.52 ± 0.18 at 3 months after the Radial and 0.25 ± 0.07 at 41 months after the Maze (p < 0.01). This increased atrial transport function was maintained for an extended period after the Radial. There were no thromboembolic events in any of the patients after the Radial or Maze, irrespective of postoperative anticoagulant therapy.

Conclusions. The Radial approach prevents thromboembolism by restoring sufficient atrial transport function more effectively and faster than does the Maze.

	Introduction

Top Abstract Introduction Material and methods Results Comment References

 
Atrial fibrillation (AF) is the most common of the serious arrhythmias and is responsible for substantial morbidity and mortality in the general population [1]. The drawbacks of AF include an irregular heartbeat, risk of thromboembolism, and impaired hemodynamic function resulting from atrial transport dysfunction. Symptoms that cause discomfort related to the irregular heartbeat are palpitations, dizziness, and loss of consciousness [2]. Pharmacologic agents such as digitalis, ß-adrenergic blockers, and calcium antagonists have been used for the control of the ventricular rate. Sufficient control of the heart rate is not always achieved, and patients are prone to heart failure because of the negative inotropic effect of the drugs [3]. Thromboembolism is frequently caused by AF. From 6% to 24% of all ischemic stroke events are associated with AF [4]. In patients who have received prosthetic valve replacement, AF has been shown to increase the incidence of thromboembolic complications as high as 10% during a 10-year follow-up period after surgery despite anticoagulant therapy [5]. The atrial transport function is an important determinant of the hemodynamics in patients with diastolic dysfunction of the ventricles. Absence of the atrial contribution because of AF impairs diastolic filling of the ventricles and has been shown to decrease cardiac output and stroke volume up to 20% [6].

Surgery for AF is indicated with the aim of freeing patients from the above morbidities, which can be life threatening. The maze procedure (Maze) restores sinus rhythm in a majority of patients [7, 8]. However the left atrial transport function after the Maze is less than that in normal subjects. Although the left atrial transport function recovers slowly for several months postoperatively, it remains at a low level even in the long-term postoperative period [9]. Therefore, the Maze does not necessarily eliminate all of the above morbidities. The radial incision approach (Radial) is a new surgical procedure for AF in which the atrial incisions radiate from the sinus node toward the atrioventricular annular margins and parallel to the coronary arteries [10, 11]. The Radial has been shown to preserve greater atrial transport function than the Maze in the early postoperative period [12]. However, serial change in the postoperative atrial transport function has not been examined in detail. Furthermore, the impact of surgery for AF on the occurrence of thromboembolism has not been determined. We hypothesized that the Radial would provide more favorable hemodynamics and prevent thromboembolism more effectively than the Maze by restoring greater atrial transport function. This study was directed to examine the serial change in the atrial transport function and thromboembolic events after the Radial.

	Material and methods

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Patient characteristics
We examined the serial change in the atrial transport function and thromboembolic events in patients after the Radial and compared that with long-term data obtained from patients after the Maze. From November 1997 to July 1999, the Radial was performed in a total of 32 patients as surgical treatment for chronic AF. There were 15 men and 17 women ranging in age from 45 to 77 years. A total of 28 patients had heart failure due to valvular heart disease with a New York Heart Association (NYHA) functional class grade of II or III preoperatively. These patients received valvuloplasty or prosthetic valve replacement concomitantly. The remaining 4 patients were in NYHA class I; 3 patients had left atrial thrombosis and the other had an atrial septal defect. All 32 patients had chronic AF for at least 1 year (range, 1 to 20 years) preoperatively, but the accurate duration of the AF was not determined in all of the patients because of unclear patient memory. Sinus rhythm resumed in 90.6% of the patients after the Radial. Two patients required pacemaker implantation after the Radial for an insufficient sinus rate. Both of the patients were proved to have sick sinus syndrome by the postoperative electrophysiologic study. Two patients died in the early postoperative period from postoperative complications not related to the Radial. The causes of death were ischemic-reperfusion injury of the lower extremity and perioperative myocardial infarction. We performed transthoracic Doppler echocardiography in all 30 patients who survived the surgery and resumed sinus rhythm. Of the 30 patients, serial change in the atrial transport function was evaluated in 15 patients in whom more than 12 months had passed since their surgery. Postoperative thromboembolic events were examined in 21 patients who were followed for more than 3 months postoperatively.

The data were compared with data obtained from 13 patients who underwent the Maze III procedure from November 1993 to June 1995. Sinus rhythm resumed in 92.3% of the patients after the Maze. The preoperative patient characteristics of the two procedures are summarized in Table 1. The gender, age, cardiothoracic ratio, and left atrial dimension as determined by echocardiography did not differ significantly between the groups.

To compare the data with a reference value, the atrial transport function was examined in 5 age-matched lung cancer patients using the same method and technique as described above. There were 3 men and 2 women with an average age of 62.8 ± 6.6 years. They all had lung cancer (cT1N0 M0, cStage IA). None of them had any structural heart disease, hypertension, or history of AF. All the patients had normal ventricular function.

Thromboembolic events
The incidence of thromboembolic events was examined through the medical records of patients who resumed sinus rhythm and were followed for more than 3 months after the Radial (N = 21) and Maze (N = 12). All patients were followed at the outpatient clinic in our hospital or at the referring hospitals. Eleven patients in the Radial group received one or two mechanical valves concomitantly. They were placed on anticoagulant therapy postoperatively with warfarin sodium. Anticoagulants were discontinued 3 months after the Radial in 10 patients who underwent valvuloplasty (n = 3), bioprosthetic valve replacement (n = 3), or the Radial alone (n = 4).

In the Maze, 3 patients did not receive mechanical valve replacement. Also in these patients, anticoagulants were discontinued 3 months after the operation. The other patients, who received one or two mechanical valve replacements along with the Maze, were placed on anticoagulant therapy.

Statistical analysis
All values were expressed as mean ± 1 standard deviation (SD). The continuous variables were compared between the procedures by the analysis of variance. A value of p less than 0.05 was considered statistically significant.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
Serial change in the left atrial transport function
An A wave representing transmitral flow was clearly detected in all patients after the Radial. An A wave after the Maze was also detected in all patients. The serial change in the left atrial transport function after the Radial is shown in Figures 1 and 2. The AFF measured at 1 month after the Radial was larger than that at 41 months after the Maze (22.0% ± 9.2% vs 15.1% ± 4.0%) but did not reach a statistical significance. At 3 months after the Radial, the AFF was 28.2% ± 7.9% and was significantly larger than after the Maze (p < 0.01). The AFF at 6 and 12 months after the Radial (26.7% ± 0.7% and 29.4% ± 14.5%, respectively) was also significantly larger than after the Maze. The A/E ratio at 1 month after the Radial was also larger than that after the Maze (0.37 ± 0.20 vs 0.25 ± 0.07) but did not reach a statistical significance. The peak A/E ratio was significantly larger after the Radial than after the Maze at 3, 6, and 12 months (0.52 ± 0.18, 0.44 ± 0.11 and 0.52 ± 0.15, respectively).

View larger version (23K): [in this window] [in a new window]   Fig 1. Serial change in the left atrial transport function after the Radial procedure, compared with that in the long-term after the Maze. The atrial filling fraction (AFF) (A) and peak A/E ratio (B) measured at 1 month after the Radial are larger than those at 41 months after the Maze. The AFF and peak A/E ratio 3, 6, and 12 months after the Radial increased to a significantly greater level than those at 41 months after the Maze. In the reference patients the AFF was 27.5% ± 3.0% and the peak A/E ratio was 0.83 ± 0.14. Solid lines indicate the mean AFF (A) and peak A/E ratio (B) in the reference patients. Broken lines indicate 1 standard deviation of the AFF (A) and peak A/E ratio (B) in the reference patients.

View larger version (47K): [in this window] [in a new window]   Fig 2. Doppler flow-velocity spectra across the mitral valve recorded in a patient at 1, 6, and 12 months (M) after the Radial. The patient, a 66-year-old man, received the Radial and mitral valve replacement for chronic atrial fibrillation and mitral valve regurgitation. The atrial filling wave, which was small at 1 month after the Radial, became large at 6 and 12 months postoperatively. (E = early filling wave; A = atrial filling wave.)

	Comment

Top Abstract Introduction Material and methods Results Comment References

 
The present study showed that within 3 months after the Radial, the left atrial transport function increased to a significantly greater level than in the long-term after the Maze. This increased function was maintained for an extended period of time after the Radial. It has been reported that the left atrial transport function after the Maze recovers slowly, but remains at an unsatisfactory level even during the long-term postoperative period [9]. The rationale for serial change in the atrial contraction after surgery for AF is not well understood. It has been shown that the atrial contraction does not recover until 3 weeks after external defibrillation of AF even if patients have resumed sinus rhythm [15]. Atrial stunning due to the long-lasting tachycardia has been considered as a mechanism for the delayed recovery of the atrial contraction after defibrillation [16, 17]. Manning and colleagues [18] demonstrated that the atrial contraction did not return to normal until 4 weeks after defibrillation in patients with AF of more than 6 weeks duration, whereas atrial contraction recovered within 24 hours post defibrillation in the patients with AF of less than 2 weeks duration. In the present study most of the patients had AF for more than 1 year before the surgery. A similar mechanism could have delayed the recovery of the atrial contraction in the patients in this study as well. Furthermore multiple atrial incisions and subsequent scarring could affect postoperative atrial contraction [13]. We considered that all of the above mechanisms could delay the recovery of the postoperative atrial contraction after both the Radial and Maze. In the present study there were significant differences in the postoperative recovery of the left atrial transport function between the procedures. The Radial provides a more physiologic activation sequence and preserves a greater blood supply to most atrial segments. Although it took 3 months for the atrial contraction to recover, the Radial was able to restore a greater atrial transport function than the Maze.

None of the patients in the present study experienced any thromboembolic events even without anticoagulant therapy in the patients without mechanical valves after the Radial or Maze. Cox and colleagues [19] reported that there was only one late minor stroke among 215 post-Maze patients despite the lack of anticoagulants during a mean follow-up period of 44.4 months after surgery. Prevention of thromboembolism is the most important objective of surgery for AF. It is still not clear what magnitude of atrial contraction or what amount of the contractile atrial wall is required to prevent thrombus formation on the atrial endocardium. It has been revealed that a depressed left atrial contraction greatly increases the risk of thrombus formation and the incidence of stroke [20, 21]. The decreased blood flow velocity in the left atrium increases the incidence of atrial thrombus. Because the Radial provides a more physiologic atrial activation sequence with concordant atrial activation across the incisions than does the Maze, the subsequent organized contraction of the atrial walls across the incision may maintain a greater blood flow velocity. Moreover the Radial does not interrupt the atrial coronary arteries, and thus the blood supply to the atrial myocardium may be preserved. The above two mechanisms may maintain the magnitude of the atrial contraction in the Radial. The Maze isolates the posterior left atrium between the pulmonary vein orifices and decreases the amount of contractile atrial wall. Tsui and colleagues [22] showed that the isolated left atrial block represents 35% of the endocardial surface area of the entire left atrium. Atrial thrombus has been shown to occur on the isolated posterior left atrium in heart transplant recipients. Derumeaux and colleagues [23] stated that atrial thrombi were localized to the isolated posterior left atrium in 9% of the heart transplant recipients who were in sinus rhythm and placed on anticoagulant therapy. Because the Maze isolates the posterior left atrium, atrial thrombus may occur also in patients after the Maze. In contrast the Radial does not leave any noncontractile segments. Therefore the Radial would prevent intraatrial thrombus formation and subsequent thromboembolism more reliably than would the Maze.

The purpose of surgery for AF is the restoration of sinus rhythm, improvement of atrial transport function, and prevention of thromboembolism. Both the Radial and Maze resume sinus rhythm in the majority of patients. However the Maze leaves an insufficient left atrial transport function that can result in thromboembolic complications. The Radial preserves a greater atrial transport function than does the Maze throughout the early and late postoperative period. Therefore it is considered that the Radial provides more favorable hemodynamics and prevents thromboembolism more effectively than the Maze.

	References

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