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Ann Thorac Surg 2001;72:1479-1483
© 2001 The Society of Thoracic Surgeons

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Original article: cardiovascular

Atrial fibrillation surgery simplified with cryoablation to improve left atrial function

^a Department of Thoracic and Cardiovascular Surgery, Asan Medical Center, University of Ulsan, Seoul, South Korea
^b Division of Cardiology, Asan Medical Center, University of Ulsan, Seoul, South Korea

Accepted for publication July 30, 2001.

* 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}www.amc.seoul.kr

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. The Maze procedure restores atrial fibrillation to normal sinus rhythm. However, concurrent left atrial functional recovery is not always achieved. To address this limitation, a modification using linear cryo-ablation is described.

Methods. Between July 1997 and December 1999, 83 patients received atrial fibrillation surgery in association with mitral valve surgery with or without additional concurrent procedures by either the conventional technique, group I (n = 30) or the modified technique, group II (n = 53). Onset of sinus conversion and echocardiographic assessment of postoperative left ventricular function, left atrial size, and mitral A-wave velocity were compared in the early postoperative period and 6 months after surgery.

Results. Sinus conversion occurred significantly earlier in group II, 2.4 ± 5 days versus group I, 7.0 ± 10 days. The mean transmitral A-wave velocity and the incidence of A-wave appearance in the early postoperative period and 6 months postoperatively were greater in group II than group I.

Conclusions. With the current modification, restoration of sinus rhythm and superior left atrial contractile function occurred earlier than with the standard Maze III technique.

	Introduction

Top Abstract Introduction Material and methods Results Comment References

 
The Maze procedure is an established method of surgically treating atrial fibrillation [1]. Although effective in restoring atrial fibrillation to normal sinus rhythm, it has not always resulted in concomitant restoration of left atrial (LA) transport and contractile function. Echocardiography studies by Feinberg and colleagues [1] showed restoration of left atrial contraction in only 61% of patients who underwent the Maze procedure at around 8 months versus restoration of right atrial contraction in 83%. Shapiro and associates [2] hypothesized that there is a slow but gradual improvement in atrial transport function after the conversion to normal sinus rhythm due to ischemia of the atrial myocardium. In any event, persistence of transient atrial dysfunction regardless of electrophysiological normalcy of rhythm predisposes the patient to increased risk of thromboembolic complications [3]. To achieve the goals of atrial fibrillation surgery, namely, prevention of systemic thromboembolism and optimization of cardiac output, not only is restoration of normal sinus rhythm important, but also that of LA transport function. In the present study, a modification on the Maze III procedure is introduced in which excellent early postoperative recovery of rhythm and LA function were observed.

	Material and methods

Top Abstract Introduction Material and methods Results Comment References

 
Patients
Between July 1997 and December 1999, 83 patients received surgery for atrial fibrillation. The patients were divided into 2 groups: in group I (n = 30), atrial fibrillation surgery was performed by the "conventional" Maze III procedure [4]; in group II (n = 53), a modification devised by the authors’ institute was used. All of the patients in group I received surgery prior to January 1999, and those in group II received surgery after January 1999. The preoperative characteristics of the 2 patient groups are shown in Table 1. With regards to the type of valvular pathology, fibrillation wave type or atrial fibrillation duration and preoperative ejection fraction, there were no differences. Giant left atrium was defined as the maximum anteroposterior left atrial diameter exceeding 60 mm by transthoracic echocardiography on two-dimensional mode. There were significantly more patients meeting this criteria in group II than in group I. Thus the 2 groups differed only in the preoperative LA dimension and sex distribution, where more females were present in group II. All of the patients in the current series received either a mitral valve replacement or mitral valvuloplasty with or without further procedures (Table 2).

The technical details of the "standard" Maze III procedure are described elsewhere [4]. The schema of the current modification is shown in Figures 1 and 2B. The procedure was initiated with a 5-cm incision in the right atrial auricle, through which direct retrograde coronary sinus cardioplegic cannulation was performed. Upon commencing cardiopulmonary bypass, a longitudinal left atriotomy was made through the inter-atrial groove. With this incision, pulmonary venous isolation (pulmonary isolation) was initiated. The cephalad end of this incision was directed in a sharp postero-inferior direction towards the right inferior pulmonary vein (Fig 1, a–b). The incision was continued variably towards the left inferior pulmonary vein, (Fig 1, b–c). At this point, some of the thin LA roof was resected in excessively redundant and enlarged left atria as shown in the shaded area in Figure 1. Next, the caudal end of the inter-atrial groove incision was extended leftward, short of actually reaching the left inferior pulmonary vein (Fig 1, d–e). If a large portion of the LA roof was resected as a result of an excessively dilated LA, the upper and lower parts of the pulmonary isolation converged near the mid-point between the left and right inferior pulmonary veins (Fig 2). However, if the amount of resected left atrial tissue was minimal, the upper and lower pulmonary isolation incisions did not join and ran parallel to each other as shown in Figure 1. At this stage, the isolation of the right pulmonary veins was completed. Next, the rough trabeculated tip of the left auricle was resected. As shown in Figures 1 and 2, the left atrial tissue between the auricular resection margin and the left upper pulmonary vein was cryoablated at -60°C with a 15-degree angled 30 mm long freeze tip having a diameter of 9 mm (Frigitronics Cardiac Cryosurgical System 200; Frigitronics, Inc, Coopersurgical, Shelton, CT) (Fig 1, f). On the left atria, the probe was usually applied for 2 minutes, while on the right it was applied for 1 minute. However, the duration of freezing sometimes varied at the surgeon’s discretion depending on the myocardial thickness. The left auricular resection margin was then closed carefully ensuring removal of all trabeculated portions. The smooth portion of the left auricle was mostly preserved. To complete the pulmonary isolation, a cryoprobe was passed through a 1-cm linear incision over the left upper pulmonary vein. Through this opening, the left pulmonary veins were isolated with cryothermia by joining the cryolesions with the previously created pulmonary isolation incisions from the right side, (Fig 1, g and h). Thereby, the pulmonary isolation was completed. A vertical incision in the posterior left atrial wall extending from the inferior pulmonary isolation incision to the left atrioventricular groove was made (Fig 1, i). At the distal end of this incision, the coronary sinus was cryoablated (Fig 1, j). Prior to repair of the LA wall, some of the LA as shown in the shaded area in Figure 1 between the lower margin of the pulmonary isolation and the mitral valve annulus was resected depending on the degree of LA redundancy. The appropriate mitral valve procedure was then performed and the rest of the left atrial incisions were closed with running sutures (Fig 2B). The Maze procedure on the right side was continued with an incision created near the inferior vena cava (Fig 1, k). The right atrial free wall between this incision and the tricuspid annulus was cryoablated (Fig 1, l). The counter-incision to the right auricular incision, mentioned in the Maze III procedure, which reaches the tricuspid annulus, the incision connecting the two vena cava, and the atrial septal incision were all cryoablated (Fig 1, m, n, and o, respectively). The heart, while still cross-clamped, was perfused retrogradely with warm blood at this point. This usually induced spontaneous cardiac contractions. Just prior to releasing the cross-clamp, the patient was placed in steep reverse Trendelenberg position. The electrocardiogram frequently showed normal sinus rhythm with prominent P waves.

View larger version (31K): [in this window] [in a new window]   Fig 1. Schematic illustration of the current Cox Maze III modification. Cryolesions are represented by the shaded lines and the portions of muscles to be resected are in stripes. Sharp incisions are represented by stitch marks. Procedures a–n are detailed in the text. (CS = coronary sinus; IVC = inferior vena cava; LAA = left atrial auricle; LSA = left sinus node artery; PSA = posterior sinus node artery; RSA = right sinus node artery; SN = sinus node; TV = tricuspid valve annulus.)

View larger version (23K): [in this window] [in a new window]   Fig 2. Technical illustration of the current modification of the Maze procedure. (A) The anterior view of the posterior left atrial wall; sites of the sharp incisions and cryolesions. (B) The posterior view of the left and right heart; the completed modified Maze procedure. Sharp incisions repaired with sutures are represented by the stitch marks, whereas the cryoablated areas are indicated by the dotted lines. (CS = coronary sinus; IVC = inferior vena cava; LAA = left atrial auricle; LIPV = left inferior pulmonary vein; LSPV = left superior pulmonary vein; MV = mitral valve; RIPV = right inferior pulmonary vein; RSPV = right superior pulmonary vein; SVC = superior vena cava.)

Statistics
The results were expressed as the mean ± the standard deviation. The SPSS software package (SPSS Inc, Chicago, IL) was used for statistical analysis. For categorical variables, the ² test was used, and for assessment of continuous variables, the 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 Material and methods Results Comment References

 
There was no perioperative mortality or need for permanent pacing in either group. The aortic cross-clamp and total cardiopulmonary bypass times were shorter in group II, but only the disparity in cardiopulmonary bypass time was statistically significant. The intraoperative sinus conversion rate between the 2 groups showed little disparity, while conversion of the postoperative sinus rhythm occurred significantly earlier in group II (Table 3). At 6 months, no patient was in either atrial fibrillation or flutter. However, 1 patient in group I was in regular junctional rhythm with neither tachycardia nor bradycardia. The patient showed stable vital signs. The transmitral A wave appeared more frequently in group II than in group I in both the early and 6-month postoperative periods, although the difference was statistically significant only at 6-months postoperatively. Similarly, the left atrial transmitral A-wave velocity in both postoperative periods were greater in group II, but the mean A-wave velocity was statistically significantly larger only in the early postoperative period (Table 4). Regardless of technique used, the transmitral A-wave velocity within each group, however, increased significantly with time (Fig 3). The mean LA dimension was reduced from 57 ± 9 mm and 62.8 ± 9 mm in groups I and II, respectively, to a mean of 46 mm in both groups.

View larger version (21K): [in this window] [in a new window]   Fig 3. Evaluation of left atrial transmitral A-wave velocity after the Maze procedure. Within each group, there was a significant increase in the A-wave velocity over time. Although the larger value of the A-wave velocity noted in group II was statistically significant only in the early postoperative period, a definite trend showing a larger A-wave velocity in group II was present.

	Comment

Top Abstract Introduction Material and methods Results Comment References

An earlier onset of sinus rhythm and a greater transmitral A-wave velocity was observed in the early postoperative period in group II. This improvement in left atrial function persisted for up to at least 6 months into the postoperative period. Furthermore, there was a tendency for the A wave to be present more frequently in group II than in group I. With a larger patient group, a more definite distinction would probably be evident. With regards to the preoperative mean left atrial dimension, it was significantly larger in group II than group I, but postoperative LA functional recovery was better in group II.

With the current modification, only a minimal amount of left atrial tissue adjacent to the right pulmonary veins was physically incorporated into the margins of the pulmonary isolation. One advantage of selectively performing pulmonary isolation may be in minimizing the unnecessary entrapment of LA muscle, as this may result in inter-atrial conduction delay [1]. Haissaguerre and coworkers [7] reported successful management of spontaneously initiating atrial fibrillation due to ectopic beats from the pulmonary veins with radiofrequency ablation at the focal sources. Based on the hypothesis that ectopic foci from the pulmonary veins could act as drivers for maintaining chronic atrial fibrillation, Sueda and associates [8] proposed a method of selective pulmonary vein isolation through a single circular incision in the left atrium, between the left and right pulmonary veins, utilizing a combination of sharp incisions and cryoablation. An excellent atrial fibrillation disappearance rate of 83% over a 3-month follow-up period was noted. Thus, these articles showed no evidence to support additional benefit of unnecessarily including adjacent left atrial tissue within the margins of the pulmonary vein isolation in the treatment of chronic atrial fibrillation.

Any abnormal excess in tissue from an enlarged LA was resected to minimize the risk of atrial fibrillation recurrence [4, 5]. The determination to undergo LA reduction was based on several criteria. The most important was LA size greater than 60 mm. We experienced earlier on a poorer atrial fibrillation cure rate in giant LA patients in whom size reduction was not performed versus those who did receive size reduction. Gross appearance of an excessively thin and dilated left atrium was also an indication for partial left atrial resection. We observed no additional risk of postoperative morbidity in those who had LA size reduction compared to those who had normal LA. The method of LA size reduction as described in the current article was very effective.

With regards to fluid retention after right atrial appendage resection, pulmonary congestion and edema were noted in some of the patients in group I in the early phase of our series. However, after implementing the modified technique in which the right atrial appendage was in the most part preserved, we no longer experienced postoperative pulmonary congestion or edema in patients undergoing the Maze procedure. Continued administration of minimal amounts of diuretics for 6 months seemed sufficient, which is actually not much different from the standard regimen used for patients undergoing valvular heart disease without the Maze procedure.

Although cryoablation is widely used clinically in the treatment of cardiac arrhythmia [4, 9] there is no evidence to support the absolute safety of deep freezing on the coronary arteries. However, animal experiments on the safety of cryoablation showed mixed results with regards to the injury incurred on the coronary arteries. Bakker and associates [10] showed coronary occlusion to be induced by transmural cryogenic injury by 6 months after the injury due to thrombosis and intimal hyperplasia. Other investigators have demonstrated a more selective injury on the myocardium with the coronary arteries being relatively spared [11, 12]. In a study by Fujino and colleagues [13], the histologic changes to the atrioventricular junction after cryothermia in pigs 8 weeks after the insult to the central conducting tissue were investigated. Microscopically, the ablated sites became fibrotic and scarred while the coronary patency was relatively preserved apart from some mild intimal proliferation. Studies as these suggest that cryoablation may induce the desired injurious effect on the myocardium while preserving patency of the coronary vasculature. Clinically, the use of cryoablation in the surgical treatment of atrial fibrillation to simplify the procedure has already been used in a large series [9]. In the current series, sharp incisions were limited to those necessary for resecting and removing excess tissue, for allowing passage of the cryothermia probe, and to secure a minimum operative field of vision to perform concomitant mitral valve procedures. Through the widespread use of cryoablation, not only was the operative time reduced but the potential risk of damaging arteries to the sinus node and the left atrium were also lessened. If the left atrium was thin and dilated, the right pulmonary veins were isolated posteriorly via an incision rather than by cryoablation to resect the excess redundant tissue. Later on in our series, these incisions were replaced by cryoablation, provided that the left atrial size was normal.

In conclusion, the current modification was effective in inducing early restoration of postoperative left atrial contractility and normal sinus rhythm. An important clinical implication may lie in the earlier obviation of anticoagulation with reduced risk of perioperative stroke and other complications arising from systemic embolization.

	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): Jae Won Lee Suk Jung Choo Kun Il Kim Hyun Song Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lee, J. W. Articles by Song, M. G. Search for Related Content PubMed PubMed Citation Articles by Lee, J. W. Articles by Song, M. G. Related Collections Electrophysiology - arrhythmias