Abstract
Purpose:
Although the maze procedure using a radiofrequency ablation device is a prevalent treatment for atrial fibrillation, a bipolar radiofrequency device is generally not used on the mitral and tricuspid annulus owing to the risk of coronary artery injury. We report the performance of the maze procedure using only a bipolar radiofrequency ablation device in our institute since 2009.
Methods:
We performed the maze procedure using only a bipolar device in 35 patients (bipolar group) and compared their operative outcomes with 56 patients who underwent standard radiofrequency ablation using bipolar and unipolar devices (standard group) for atrial fibrillation.
Results:
Preoperative characteristics were similar in the two groups. Operative data were also similar in the two groups except for a higher number of concomitant tricuspid valve repairs in the bipolar group (p = 0.007). There were no significant differences in mortality and morbidity between the two groups. Sinus rhythm was restored in a significantly higher number of patients in the bipolar group (71.4%) than in the standard group (39.3%; p = 0.002) at the first postdischarge follow-up.
Conclusion:
The maze procedure using only a bipolar radiofrequency device can be safely performed and results in a satisfactory sinus rhythm restoration.
Introduction
Since its introduction, 1 the maze procedure has been established as the gold standard technique for surgical treatment of atrial fibrillation (AF). In spite of excellent results with greater than 90% of patients being free from AF,2,3 the procedure was not commonly implemented at first because of its complexity and associated morbidity. 4 However, in the last decade, the maze procedure is widely performed using ablation device since various ablative energy sources have become available.5,6
When electrical isolation lines are made using a radiofrequency ablation (RFA) device, a unipolar device is preferred for mitral and tricuspid annulus lesion sets to avoid coronary artery injury. However, a unipolar device can cause spreading thermal damage, 7 take more time, and most importantly, result in incomplete transmurality, 8 compared to a bipolar ablation device.
Since 2009, we have performed the maze procedure for AF using only a bipolar device, and herein report the impact of this technique on patient outcomes.
Patients and methods
Patients
AF treatment by RFA was performed in 91 patients between September 2004 and December 2013. The standard maze procedure using a unipolar device for the mitral and tricuspid annulus was performed in the first 56 cases (standard group) and the technique was performed using a bipolar device in the remaining 35 cases (bipolar group). To evaluate the efficacy of this technique, we compared operative outcomes such as mortality, morbidity, and restored sinus rhythm (SR) rate between the two groups. Maze operations for paradoxical AF and cases of pulmonary vein (PV) isolation alone for chronic AF were excluded from the study. Maze operations concomitant with cardiac surgery via a right intercostal incision were also excluded because left PV isolation was carried out using a unipolar device. The study was reviewed and approved by the Institutional Review Board of the Kouseikai Hospital.
Surgical techniques
When bipolar RFA was planned, a preoperative coronary angiogram was conducted to confirm the absence of extreme variant coronary arteries.
Bilateral PV isolations were performed epicardially on beating hearts under cardiopulmonary bypass (CPB). After the aorta was cross-clamped, a connecting line was established by clamping the left atrial wall from the right-sided left atriotomy to the mitral annulus with the jaw clearly grasping the posterior mitral annulus (Figure 1). In the first several cases, a 20G needle was inserted in the posterior left atrial wall from the exterior to mark the coronary-free area of the atrioventricular (AV) groove, identifying it preliminarily, as reported by Benussi et al. 9 However, after the safety of ablating the mitral annulus using a bipolar device was empirically recognized, a clamp was used to mark the cleft between the middle and medial scallop of the posterior mitral leaflet.
The posterior left atrial wall is ablated with the proximal part of the clamp intersecting the atriotomy and the tip of the inner jaw biting the posterior mitral annulus.
Subsequently, bilateral PV isolation lines were connected by sliding the jaws cranially. The left atrial roof was then ablated as connecting the bilateral PV isolation lines to complete a “box isolation.” A connecting line between the left appendage and the left upper PV was also provided by clamping the left atrial wall from inside by inserting one jaw of the bipolar device in the orifice of the left upper PV and another in the left appendage. The left appendage was ligated externally after the entire cardiac procedure.
The right atrium ablation lines were also created based on Cox-maze lesion set. When ablating from an atriotomy to the tricuspid annulus, the groove is entered by separating the sulcus fat and the right coronary artery, which is clearly identified by inspection with scissors and is left on the ventricular side of the dissection. The right atrial wall and tricuspid annulus were then clamped and ablated (Figure 2). The same dissection was performed when ablating between the right appendage and the anterior tricuspid annulus.
The bipolar device is inserted after dissecting the atrioventricular groove. The tip of the jaw is clearly biting the tricuspid annulus.
In the standard group, all the ablations were carried out with a bipolar device except for the mitral and tricuspid annulus, in which a unipolar ablation device was applied.
Epicardial PV ablation was performed twice, while the other ablations were ordinarily performed once.
Statistical analysis
Continuous variables were reported as mean ± standard deviation and compared using Student’s t test. Categorical variables were reported as counts with percentages and compared by the χ2 test or Fisher’s exact test as appropriate. A probability value of <0.05 was considered to be statistically significant. The data were analyzed using the Dr SPSS II software (SPSS Inc., Chicago, IL, USA).
Results
In the standard group, 27 and 29 patients underwent the maze procedure by AtriCure (AtriCure, Inc., Cincinnati, OH, USA) and Cardioblate (Medtronic, Inc., Minneapolis, MN, USA), respectively. In the bipolar group, the procedures were performed using Cobra (Estech Inc., Camino Ramon, CA, USA) in all patients.
Preoperative characteristics and surgical data are listed in Table 1. There was no significant difference between the two groups in preoperative characteristics or comorbidities. In addition, no significant differences were observed in the preoperative cardiac data. AF duration could not be investigated from our database. There was no case omitted the maze procedure on the ground of extreme variant coronary arteries.
Patients’ characteristics.
EF: ejection fraction.
Operative data are listed in Table 2. All maze operations were performed concomitantly with other cardiac surgeries. In most cases, the maze technique was performed together with mitral valve surgery, and there was no statistically significant difference between the groups (p = 0.676). The tricuspid valve surgery ratio was significantly higher in the bipolar group (p = 0.007). The operative and CPB times were similar in the bipolar and standard group (p = 0.208 for operative time and p = 0.186 for CPB).
Operative data.
LA: left atrium; MVP: mitral valvuloplasty; MVR: mitral valve replacement; AVR: aortic valve replacement; TAP: tricuspid annuloplasty; CABG: coronary artery bypass grafting.
Clinical outcomes are shown in Table 3. There were two hospital deaths in the standard group and none in the bipolar group. Pacemaker implantation was required for two patients in the standard group and one in the bipolar group. No cases of perioperative myocardial infarction were observed, and the ejection fraction was maintained in both groups.
Operative results.
EF: ejection fraction.
Sinus rhythm was restored in 71.4% of patients in the bipolar group, as 39.3% of standard group (p = 0.002) at the first follow-up after discharge.
Discussion
In this study, we report the impacts of complete bipolar RFA. The SR restoration rate was higher in bipolar group compared to standard procedure.
The maze operation, first described by Cox, 1 divides atrium using a series of cuts and sews to block the triggered activity transmitted to the atrium and to eliminate macro-reentry. In the last decade, several ablation devices have been developed as less invasive alternative to create electrical obstacles rather than using original cut and sew procedure. RFA devices have resulted in widespread adoption of the maze operation and a significant increase in the number of operations that are performed annually for AF. 8
In general, when the maze operation is performed by RFA, a unipolar device is preferred to ablate the area near mitral annulus or tricuspid annulus to avoid coronary injury. Unipolar ablations have proven effective for transmurality on the arrested heart. 10 However, cases have been described when use of unipolar devices results in less transmurality on the beating heart 11 or inferior success rates of PV isolation compared with use of bipolar device. 12 Moreover, incomplete transmural ablation may lead to postoperative atrial tachycardia.13,14 Against this background, we referred to Benussi et al., 9 who reported the efficacy and safety of RFA involving the mitral line using a bipolar radiofrequency device. They recommend inserting a small hypodermic needle in the posterior left atrial wall externally to mark the coronary-free area to avoid coronary injury. Although we initially performed the same technique, we were able to subsequently create the ablation line between the atriotomy and the mitral annulus without using the needle after recognizing the safety of clamping the mitral annulus. There is a concern that clamping the mitral annulus may injure the coronary artery, but we believe that clamping the mitral and tricuspid annulus is safe since there were no cases of myocardial infarction or decreased ejection fraction in our study.
Preoperative left atrium size and AF duration are well-known predictive factors of SR restoration after the maze operation. 15 Therefore, in some cases where SR was difficult to restore, we omitted the maze operation concomitant with cardiac surgery in a nod to risk-to-benefit ratio. Omission of cases may affect the increased success rate of the maze procedure and influence our results. We emphasize, however, that the performance rate of the maze operation was nearly equivalent between the bipolar and standard groups.
Although we had used AtriCure or Cardioblate RFA devices, we began using the Cobra at the time of initiating the bipolar RFA. This positively influenced the improvement of SR restoration rate. There are few studies about how the different RFA devices influence the results of the maze procedure, although each device may be distinct in transmurality ability. The Cobra system possesses temperature-controlled radiofrequency energy which continuously monitors and maintains tissue temperature at target levels throughout the procedure, as opposed to the energy of AtriCure or Cardioblate which are controlled by electrical resistance of the ablating tissue. We think that this simple temperature-controlled ablation is superior in terms of transmural ablation ability.
This study has some limitations. It is a retrospective study, includes a relatively small number of patients, and there is no long-time follow-up of the patients. Since standard ablation and bipolar ablation procedures were not performed simultaneously, operator proficiency may have influenced the SR restoration rate. Although the percentage of chronic AF patients in the bipolar groups was equivalent between the two groups, the selection bias was not negligible. It is also the limitation, because different devices are used between two groups. There is no study about the difference of performance between devices, so it is one of the future issues.
Conclusion
The maze procedure using only a bipolar radiofrequency device can be safely performed with satisfactory restoration of SR. In our experience, there were no complications related to ablation of annulus, including myocardial infarction or bleeding. This technique also seems to be less expensive and take less time than the standard RFA using both bipolar and unipolar devices.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.