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MMCTS
(November 29, 2005). doi:10.1510/mmcts.2005.001081 Copyright © 2005 European Association for Cardio-thoracic Surgery
Procedure Concomitant ablation of atrial fibrillation during mitral surgeryDivision of Cardiac Surgery, S Raffaele University Hospital, via Olgettina 60, 20132 Milan, Italy * Corresponding author: * Tel.: +39-02-2643 7127; fax: +39-02-2643 7125. E-mail: benussi.stefano{at}hsr.it
Left atrial ablation with bipolar radiofrequency using the epicardial approach is described. After dissection of the pericardial reflections and of the Marshall fold, electrical isolation of the right and left pulmonary veins and that of the left appendage are carried out through epicardial ablation. After aortic cross clamping, through standard atriotomy, the connecting lines are then performed. The possible options for the mitral connecting ablation are discussed. At completion of the ablation procedure the base of the left appendage is sutured from inside.
Key Words: Atrial fibrillation • Bipolar radiofrequency • Cardiac surgery • Mitral valve disease • Radiofrequency ablation
First reported in 1999 [1], epicardial ablation has been described by many groups for the concomitant treatment of atrial fibrillation (AF) [2,3,4,5] and also as a possible option for curing lone AF [3,6]. Diverse unipolar ablating systems have been used for epicardial ablation on the beating heart, with variable success rates [4,5,7]. The major limitation of unipolar devices is that, due to the convective cooling of blood flowing through the atria and depending on the composition of the diseased atrial wall, they do not predictably yield epicardial transmural lesions [4,8]. Bipolar devices seem a promising way to obviate such problems: the first experimental trials demonstrated that bipolar radiofrequency (RF) ablation can reliably produce continuous transmural linear scars [9,10]. We report our ablation technique and initial results with bipolar RF.
Perioperative management A continuous heparin drip is started after cessation of postoperative bleeding and is continued until effective anticoagulation is reached with oral medications.
In the absence of indications other than AF, patients with stable sinus rhythm (SR) at Antiarrhythmic prophylaxis is carried out on a routine basis. Amiodarone is used as the first-choice drug: an intravenous bolus of 300 mg, followed by a continuous infusion of 1200 mg/24 h until the first postoperative day is generally administered. In the absence of A-V block greater than 1 degree or of unstable SR, oral administration of 200 mg of amiodarone, every 8 h until discharge, followed by a maintenance regimen of 200 mg/day is then continued. Patients with contraindications to amiodarone are administered sotalol, propaphenon or do not receive any antiarrhythmic medication. After discharge such medications are continued for 3 to 6 months, and are then generally tapered off.
The ablations are performed using a bipolar RF ablation device (Cobra Bipolar – MMCTSLink 75). Two 64-mm long ablating inserts are mounted on the opposing faces of the jaws of a stainless steel clamp (Video 1). Each insert is made of two electrodes lodged in a polyester cover. Each electrode has a thermocouple mounted on both ends. RF current is delivered for 40–45 s at 35–40 W, with a preset temperature of 90 °C. In our initial experience with bipolar RF, the mitral line was omitted because of concern about injuring a major coronary artery branch in the A-V groove (Schematic 1).
The epicardial ablations are generally performed on cardiopulmonary bypass (CPB) at 37 °C. After dissection of pericardial reflections, the bipolar device is clamped around the atrial cuff containing the inflow of the right pulmonary veins. Then RF energy is deployed yielding an encircling lesion (Video 2).
The heart is then lifted, the Mashall fold interrupted (Video 3), and a similar encircling lesion is performed on the left pulmonary vein cuff (Video 4).
Based on recent evidence [11,12,13], to increase the chance of an effective isolation of the pulmonary veins, it is advisable to either validate the encircling lines with intraoperative conduction block assessment, or at least to double such ablation lines. The appendage is then ablated at its base and connected to the left encircling by means of an additional epicardial ablation (Video 5).
The left atrial appendage (LAA) is then ablated at its base. At this time the ablating piece must be kept away from the A-V groove (around the upper portion of the base of the appendage) thus is preventing injury to a major coronary artery. After aortic cross clamping through a standard left atriotomy, the bipolar device can be used in the endo/epicardial mode (one jaw inside the heart and the other outside) to perform a connecting line between the two encirclings (Video 6).
In order to reduce the chance of a reentry circuit around the mitral annulus to sustain left flutter, the described ablation procedure has been recently revised (Schematic 2) by reintroducing a left isthmus ablation line, performed with a unipolar linear catheter (Video 7). As previously described [14], the site of such line is chosen based on coronary anatomy (Photo 1). After the ablations the LAA is sutured, generally from inside.
Clinical experience Starting in February 1998, we performed concomitant AF ablation in 492 patients undergoing open heart surgery. We report our experience in the first 100 patients (from February 2003 onward), scheduled for mitral surgery, who had the ablation procedure performed with bipolar RF. The indications for concomitant ablation were continuous AF (lasting at least 6 months) in 83 patients, and symptomatic intermittent AF refractory to antiarrhythmic medications or to prior percutaneous ablation in 17 patients. Preoperative data are summarized in Table 1. All patients had mitral valve disease as the main indication to surgery.
Fifty-two patients had mitral valve replacement, 43 had mitral repair, 5 had commissurotomy. Sixty-two patients had other associated cardiac procedures: tricuspid repair in 53 cases, aortic valve replacement in 12, correction of an atrial septal defect in 8, CABG in 5, and other procedures in 3. The time spent ablating during aortic occlusion never exceeded 2 min. No complication related to bipolar ablation was recorded. Four patients required re-exploration for bleeding. Overall, intensive care unit stay was 3±3 days and postoperative hospital stay was 8±6 days. One elderly woman died due to rectus muscles hematoma, leading to acute renal failure and respiratory insufficiency. Fourty-four patients experienced some form of sustained supraventricular arrhythmia during hospital stay. At discharge 62/99 patients were in normal sinus rhythm. During follow-up no thromboembolic event was recorded. No patient died. Graph 1 depicts the trend of rhythm status. Two patients experienced typical counterclockwise right atrial flutter 3 months after surgery and they were successfully treated by percutaneous RF isthmus ablation. Seven patients developed left atrial flutter, all of them within 3 months of mitral surgery. Two of them underwent an electrophysiological study with transseptal approach at three months. Both studies showed an optimal isolation of the pulmonary veins encirclings. In both cases a re-entry circuit around the mitral valve annulus was documented and interrupted through a left isthmus RF ablation line. Both patients recovered SR during the procedure. Of the remaining patients with left flutter, 1 recovered SR with medications, 1 needed DC-shock, 3 are waiting for the electrophysiological assessment.
Two patients are presently waiting to be admitted for electrophysiological assessment. No perioperative variable was related to postoperative left atrial flutter. All transthoracic echo-Doppler controls carried out three months or more after surgery, in patients in SR, showed an effective contraction (A-wave 10 cm/s) of both atria.
Conduction block validation
The 90% efficacy of Cox's original cut and sew maze are still unequalled today [15,16]. Nevertheless, such a technique has never become popular in the context of concomitant AF ablation, since it adds significantly to surgical time and it increases operative risk [17]. Furthermore, a concomitant maze carries a  20% risk of postoperative pacemaker implantation [16]. In the search of the simplest ablation procedure to be combined with concomitant open heart surgery, PV isolation alone was first reported by Melo in 1997 [18]. But the AF cure rate of such procedure in this context is in the range of 60 to 70% at 1–2 years [18,19]. More recently, after the first report by Sueda in 1996 [20], most of the surgeons dealing with AF embraced the so-called ‘left ablation approaches’, generally sharing pulmonary vein isolation and the connecting lines proper of the left part of the maze procedure [2,21,22]. By granting a success rate of approximately 80–90% at 1 year and around 75% at 3 years after surgery [7,21,23], such approaches have emerged as a cost-effective option for concurrent intraoperative ablation of AF. Cox has recently defined some of the lines of the original maze III operation – including all the right-sided lines except the cavo-tricuspid isthmus connection – as superfluous in most cases [24]. The rate of SR maintenance 18 months after concomitant surgical treatment of AF through bipolar RF left atrial ablation was 81% in our experience. Such a figure is coherent with the very promising results recently reported by other groups with intraoperative bipolar RF ablation [11,12,25]. When considering only reports on left atrial ablation approaches (PV isolation + connecting lines), other author's and our results with bipolar RF are in line with the 79 to 92% success rate reported after unipolar ablation [7,20,21,22,23]. In a comparable earlier series of patients treated at our institution with unipolar RF, in which the same lesion set was completed by a mitral connecting line, freedom from AF at 18 months was 79% [7]. So, the replacement of unipolar RF ablation catheters with modern bipolar devices, in our experience, translated itself into similar mid-term AF cure rates despite the temporary adoption of a lesser lesion set. Although infrequent and quite easy to cure through percutaneous ablation, typical right atrial flutter can occur after left atrial ablation for AF. Therefore, the addition of a cavo-tricuspid line during surgery, should probably be considered based on the programmed open heart procedure (need for right atriotomy) and on the available technology and expertise.
Collateral damage Damage to the surrounding structures related to the use of physical means to ablate AF can be of two types:
The first types have only been reported after ablation with ‘heating’ unipolar devices, generally following endocardial ablation, since in this case the heat spreads from the endocardium outward. Keeping away from the posterior wall of the left atrium can help in preventing such problems [14]. With the advent of bipolar devices, however, this type of complication will become very unlikely, since bipolar ablation renders thermal spread negligible. Thermal damage to the coronary arteries has been described both after ablation with heating devices and following cryoablation. It can theoretically be reduced by keeping blood flow within the vessel while ablating (i.e. beating heart or cardioplegia administration). Therefore, a clamping device, which by definition would interrupt blood flow across the ablation line, does not seem to be the safest way to overcome the problem. One effective way to prevent coronary injury is to reach the A-V groove in a coronary-free area [14].
Transmurality
Mitral line Interestingly, in our earlier experience with unipolar RF the incidence of left flutter/tachycardia was around 1% [7]. A possible explanation is that the omission of the mitral line, in order not to injure a major coronary branch during bipolar ablation in the A-V groove, has left the substrate for a left isthmus reentry unaddressed. It is noteworthy that a reentry circuit around the mitral valve annulus was found in both patients with left atrial flutter undergoing electrophysiological study in this series. Even if such arrhythmia is generally dealt with in the electrophysiology laboratory, at present such ablation procedures require a considerable expertise with transseptal mapping and ablation. Therefore, especially if a specific electrophysiological expertise is not available, omitting the mitral line may not be the best option when using bipolar RF. Some authors support the feasibility and safety of the mitral connection by clamping the bipolar device right across the A-V groove. As a preferable alternative we suggest performing the mitral line with a different unipolar device such as a reusable cryoprobe when this is available.
Left atrial appendage exclusion A number of physiologic functions of the LAA have been ascertained: due to its major compliance, the LAA functions as a volume reservoir. Its exclusion in patients undergoing surgery for coronary disease and for mitral insufficiency has been found to increase transmitral and pulmonary flow velocities as well as left atrial pressure and size [26]. The LAA contractility and its contribution to ventricular filling has been related to a significant increase in cardiac output in the isolated guinea pig heart [27]. The LAA is then implicated in mediating the thirst reflex as a response to volume depletion in the sheep [28]. Finally, the LAA plays a role in mediating diuretic and natriuretic responses by releasing atrial natriuretic peptide under volume expansion [29]. But whatever the physiologic function played by the LAA in patients with stable SR, it is probably out-weighed by its role in enhancing thrombus formation in patients with AF. The LAA is in fact the apparent source of left atrial thrombi in 57% of patients with AF secondary to rheumatic disease and in 91% of patients with nonrheumatic AF [30]. Its exclusion during mitral surgery appears to reduce the rate of late embolism in high-risk patients [31]. Therefore, ligation of the LAA during mitral surgery seems a sound option in all patients with AF undergoing cardiac surgery. Even when AF ablation is combined, in fact, the significant rate of early and late rhythm disturbances and the frequent need of DC shock cardioversions make elimination of the LAA advisable. When excluding the LAA meticulous watertight closure must be attained. Incomplete surgical exclusion, in fact, can occur in as many as 10–36% [31,32] of the patients and it has been associated with an increased risk of thrombus formation and of systemic embolization.
Left atrial ablation with bipolar RF is highly effective in eliminating AF after open-heart surgery. Epicardial ablation with bipolar RF allows to predictably achieve acute electrical isolation. The safety profile and the negligible addition of time makes bipolar RF an extremely suitable option for the concomitant treatment of AF even in the most complex cases. Based on our experience a left atrial set of ablations, possibly including a connecting line to the mitral annulus, can be indicated in virtually all patients with AF undergoing cardiac surgery.
We are grateful to Lorenzo Arcobasso for his invaluable help with editing the video material.
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Summary
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