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Ann Thorac Surg 2000;69:446-450
© 2000 The Society of Thoracic Surgeons

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Original Articles

Intraoperative map guided operation for atrial fibrillation due to mitral valve disease

^a Department of Cardiovascular Surgery, Ebina General Higashi Hospital, Kanagawa, Japan
^b Department of Cardiovascular Surgery, Yokohama Rosai Hospital, Kanagawa, Japan

Address reprint requests to Dr Harada, Department of Cardiovascular Surgery, Ebina General Higashi Hospital, 1519 Kawaraguchi, Ebina-City, Kanagawa 243-0433, Japan

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. This study was designed to determine if intraoperative atrial activation mapping facilitates operations for chronic atrial fibrillation associated with mitral valve disease.

Methods. Surgical treatment guided by intraoperative electrophysiologic mapping was performed in 12 patients with chronic atrial fibrillation associated with isolated mitral valve disease. In 10 of 12 patients, regular and repetitive activation (cycle length ranged from 118 to 210 msec) originated in the left atrial appendage and/or orifice of the left pulmonary vein. In the remaining 2 patients, dominant repetitive activation and sporadic complex activation were alternately observed in the left atrium. However, the activation sequence of the right atrium was extremely complex and chaotic.

Results. On the basis of intraoperative mapping, surgical procedures, including resection of the left atrial appendage and/or cryoablation of the orifice of the left pulmonary vein, were applied on the breakthrough site of the repetitive activation. No surgical procedure was performed on the right atrium in 11 patients. Ten of 12 patients (83%) have maintained sinus rhythm for 6 to 40 months (average 24.8 months) after operation.

Conclusions. In the majority of the patients with isolated mitral valve disease, the left atrium acts as an electrical driving chamber for chronic atrial fibrillation. Computerized intraoperative mapping should guide surgeons in determining the appropriate surgical procedure for chronic atrial fibrillation.

	Introduction

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During the past decade, operation has emerged as an increasingly important modality in the treatment of atrial fibrillation (AF) [1–9]. Selecting the appropriate surgical procedure to ablate AF should be related to the mechanism of AF, as verified by electrophysiologic mapping. Using a multipoint mapping system, Cox and colleagues [10] described atrial activation in experimental models and electrically induced AF in patients with Wolff-Parkinson-White syndrome. The study demonstrated the presence of macro reentrant circuits in the right atrium, and multiple wave fronts and conduction blocks in the left atrium. However, few detailed studies of atrial activation in chronic AF associated with mitral valve disease have been reported. Recently our electrophysiologic study [11] demonstrated that active repetitive activation sequences are perpetuated in the left atrium, and passive chaotic activation dominated in the right atrium, in the majority of patients with chronic AF associated with isolated mitral valve disease. Our study suggested that a simple procedure guided by intraoperative mapping rather than the complex Maze procedure without mapping is effective to treat AF. Therefore, assuming that the left atrium acts as an electrical driving chamber, we performed intraoperative map guided surgery for chronic AF.

	Material and methods

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Using a computerized atrial mapping system, intraoperative map guided surgery for chronic AF was performed in 12 patients with isolated mitral valve disease who were undergoing mitral valve operations. Age ranged from 33 to 77 years. There were 7 male and 5 female patients, 6 with mitral rheumatic mitral stenosis, 6 with mitral regurgitation, and 2 patients had left atrial thrombus. All patients had chronic atrial fibrillation for at least 2 years. Fentanyl citrate was used for the induction and maintenance of anesthesia, and median sternotomy followed by pericardiotomy was performed to expose the heart.

Before the institution of cardiopulmonary bypass, intraoperative mapping was performed. The card type electrode was attached to the right epicardial surface to record 30 unipolar local electrograms simultaneously. Then the electrode was switched and similarly attached to the left atrial epicardial electrograms. All unipolar electrograms were recorded at a frequency response of 100 to 1,000 Hz. A computer stored the digitalized unipolar data and displayed the wave forms. A computer program determined local activation times from unipolar tracings. The peak negative derivative of the major deflection of the unipolar complex was defined as the time of local activation. Within 30 seconds after acquisition of the atrial epicardial electrograms, atrial activation maps for a 100-millisecond window were automatically produced from the computer analysis and displayed sequentially. Total time spent atrial mapping was less than 20 minutes. The detailed methods for electrophysiologic mapping were reported previously [11]. We routinely used an intraoperative transesophageal echocardiography (TEE) to evaluate the thrombus of the left atrial appendage. In patients with mural thrombus, cardiac mapping was performed very carefully, using an electrode which makes only very superficial contact with the left atrium. However, in patients with pedunculated thrombus, cardiac mapping should not be performed to avoid a thromboembolic complication. In the present study there were no patients with pedunculated thrombus.

After the institution of cardiopulmonary bypass, the ascending aorta was cross-clamped and the heart was arrested with cold cardioplegic solution. Depending on surgeon preference, either superior-transseptal incision (10 patients) or standard left atriotomy (2 patients) was performed to expose the mitral valve. Mitral valve replacement in 6 patients, mitral valve plasty in 5 patients, and open mitral commissurotomy in 1 patient, were performed. After the mitral valve operations, procedures to ablate chronic AF were performed. According to the results of the atrial activation maps in each patient, different procedures including resection of the left atrial appendage and/or cryoablation were selected intraoperatively.

Both electrophysiologic mapping and operations were performed after informed consent had been obtained from each patient.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
The characteristics of atrial activation during chronic AF are summarized in Table 1. Regular and repetitive activation in the left atrium and chaotic activation in the right atrium were observed in the majority of patients. In 10 patients, repetitive activation sequences at cycle lengths of 118 to 210 milliseconds persisted in the left atrium. In 5 patients, two types of regular activation sequences were observed in the left atrium. These regular activation sequences emerged from the base of the left atrial appendage, lateral to the left pulmonary vein, or in the posterior wall adjacent to the atrioventricular groove.

Figures 1 and 2 demonstrate representative epicardial electrograms and sequential activation maps of the left atrium in patient 8. As shown in Figure 1, the left atrium was activated regularly at a cycle length of 148 millisec-onds. Atrial activation maps, constructed from the electrograms of Figure 1, demonstrated that there was a breakthrough of the regular activation in the middle portion of the posterior wall of the left atrial appendage (Fig 2). Activation spread coaxially from the site of the breakthrough to the body of the left atrium. On the basis of the activation pattern, the presence of either microreentry or automaticity was suspected. There was no evidence of macroreentry. The activation of the right atrium was complex and chaotic. No identical patterns of activation were observed and there were no evidence of macroreentry, microreentry, and automaticity in the right atrium. In this patient, we performed mitral valve replacement through standard left atriotomy. Then, using a cryoprobe, 3-mm in diameter, only 1 cryoablation (-60°C for 3 minutes) was applied on the breakthrough site of the repetitive activation. The patient has maintained normal sinus rhythm for 24 months after operation.

View larger version (55K): [in this window] [in a new window]   Fig 1. Electrocardiogram lead II and 30 epicardial electrograms recorded from the left atrium during atrial fibrillation. Electrocardiogram lead II (ECG) is drawn on the top of the tracings, and the lower 30 tracings are 30 unipolar electrograms recorded from the left atrium. E1, E2, ... and E30 indicate electrocardiograms recorded from electrode No. 1, electrode No. 2, ... and electrode No. 30 respectively. The numbers 200 to 1000 msec indicate milliseconds from the beginning of all tracings. This chart was directly copied from the computer display. Although these left atrial epicardial electrograms were recorded during chronic atrial fibrillation, regular and repetitive local activation at a cycle length of 148 msec was demonstrated in the left atrium.

View larger version (38K): [in this window] [in a new window]   Fig 2. Consecutive activation maps of the left atrium. Twelve activation maps directly copied from the computer display are presented. Maps A to L were constructed from epicardial electrograms in windows A to L divided by the vertical dotted lines shown in Figure 1. The same pattern of activation sequence emerged from the posterior portion of the left atrial appendage (LAA), indicated by a closed circle, and propagated in the direction of the body of the left atrium. The repetition of the same activation sequence is demonstrated in maps A, B, D, E, G, H, J, and K. Isochronous lines are drawn at intervals of 5 msec, and the black arrows indicate the direction of the spread of the activation. (PV = pulmonary vein.)

In patient 4, regular activation was mainly in the left atrial appendage but did not perpetuate. Existence of arrhythmogenecities in parts of the left atrium other than the left atrial appendage were suspected. Therefore, cryoablation on the orifice of the left pulmonary vein were added to the resection of the left atrial appendage.

In patients 5 and 6, the origin of the repetitive activation was identified in the orifice of the left pulmonary vein on which cryoablation was performed. However, additional resection of the left atrial appendage was performed due to the macroscopic finding that the left atrial appendage was remarkably dilated and the endocardium of it was thickened. There were no major complications including thromboembolism and postoperative bleeding.

Ten of 12 patients (83%) have maintained sinus rhythm, without any antiarrhythmic agent to control supraventricular arrhythmias, for 6 to 40 months (average 24.8 months) after the operation. However, AF was present even after operation in patient 3 and 4.

	Comment

Top Abstract Introduction Material and methods Results Comment References

 
Chronic AF associated with mitral valve disease may occur on the basis of either an automatic or a reentrant mechanism. As the selection of the appropriate type of surgical procedure to ablate AF should be pertinent to the mechanism, intraoperative mapping is essential for definitive surgical treatment. However, current surgical procedures to ablate AF have been exclusively performed without intraoperative atrial mapping, even though surgical treatment for other cardiac tachyarrhythmias requires intraoperative mapping. One of the reasons why intraoperative mapping is not performed for AF operation, may be that analysis of the activation sequence of AF requires a sophisticated and expensive mapping system, and an investigator with considerable experience. In order to overcome the problems of intraoperative mapping, we developed a special mapping system to analyze AF. Then, we reported the characteristics of atrial activation during chronic AF associated with mitral valve disease [11]. In our previous study of chronic AF, rapid repetitive activation originated in the left atrium, and complex activation was mainly in the left atrium in the majority of patients with mitral valve disease.

On the basis of this previous study, we hypothesized that chronic AF associated with isolated mitral valve disease, may be caused by electrical discharges in the left atrium in the majority of patients. Then, surgical procedures including exclusion and/or cryoablation were applied to the parts of the left atrium in which repetitive activations originated. As a result, chronic AF was successfully converted to sinus rhythm in 10 of 12 patients (83%). The results supported our hypothesis.

Graffigna and associates [4] reported the electrophysiologic effects of left atrial isolation for AF associated with mitral valve operations, in which the left atrium was electrically isolated from the remainder of the heart, and reentrant circuit and/or ectopic focus were confined to the left atrium [12]. They performed left atrial isolation in 100 patients with chronic AF complicated by mitral valve disease, and sinus rhythm was successfully restored in 79 (81.4%) of 97 survivors.

Sueda and colleagues [9] also devised a simple left atrial procedure to eliminate chronic AF during mitral valve operations. The procedure consisted of surgical incisions and cryolesion was performed only on the left atrium, while the right atrium was spared. The procedure was performed in 11 patients with chronic AF associated with mitral valve disease, and 10 patients continued to have a sinus rhythm (AF free rate, 91%).

The clinical reports of Graffigna, Sueda, and our study suggest that in more than 80% of chronic AF cases complicated by mitral valve disease, the left atrium plays an important role in maintaining AF but the right atrium does not.

AF recurred in patients 3 and 4, which is probably explained by the fact that the focus of AF could reach regions where mapping was unavailable. With current mapping systems, the electrode cannot be inserted into the posterior side of the left atrium or interatrial septum, so that no information is available from these areas. The right atrium may also play an important role in maintaining chronic AF in a few patients (those in whom the procedures failed to ablate AF), but detailed activation sequence of the right atrium has not been analyzed to present because of chaotic activation patterns. Therefore, we are making efforts to improve the mapping system and software in order to analyze the AF activation sequence.

A historical study of AF atrial activation has been reported by Cox and associates [10]. Based on the atrial activation sequence of electrically induced AF in experimental models and patients with WPW syndrome, they demonstrated the presence of macroreentrant circuits and the absence of both microreentrant circuits and evidence of atrial automaticity. Although various concepts of reentry and ectopic focus for the mechanism of AF have been proposed [10, 11, 13–16], the mechanism or activation sequence of chronic AF associated with mitral valve disease is still unknown.

Both our previous and present studies on atrial activation during chronic AF, in patients with isolated mitral valve disease, demonstrated regular and repetitive activation in the left atrium and intricate activation in the right atrium. Since our mapping system was limited to a 32-channel system, and simultaneous right and left atrial mapping was not performed, detailed mechanisms, whether ectopic or reentrant, were not determined. A more sophisticated mapping system, capable of simultaneous mapping of both right and left atria, is required to analyze the detailed mechanism of AF. Our electrophysiologic studies indicated the absence of macroreentry in both the right and left atria, and the presence of either microreentry or ectopic focus, mainly in the left atrium rather than the right atrium. As shown in Figure 2, regular and repetitive activation sequence spread coaxially from the sites of origin, and the presence of either microreentry or ectopic focus was strongly suspected from the activation pattern. The activation patterns of repetitive activation in the other patients were the same as in Figure 2. However, we do not think that all chronic AF occurs by the same mechanism, and intend to investigate chronic AF with other diseases as well.

The procedures, including surgical resection of the atrial tissue and/or cryoablation, were applied on the origins of repetitive activation. As shown in Table 1, depending on the activation pattern, a different procedure was performed for each patient. The advantage of intraoperative map guided operation is that it simplifies the procedure and does not require much time [17, 18]. All procedures to ablate chronic AF required less than 30 minutes (minimum 5 minutes in patient 8) and were acceptable as concomitant procedures for mitral valve operation.

Although AF is an extremely complex and intricate arrhythmia, we advocate performing intraoperative atrial mapping to investigate its detailed mechanism. We concluded that intraoperative mapping should guide surgeons in determining the appropriate surgical procedure, and facilitate operations to treat AF.

	References

Top Abstract Introduction Material and methods Results Comment 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): Kazuhiko Higuchi Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Harada, A. Articles by Sasaki, K. Search for Related Content PubMed PubMed Citation Articles by Harada, A. Articles by Sasaki, K. Related Collections Related Article