Outcomes for Surgical Treatment of Atrial Fibrillation Using Cryoablation During Concomitant Cardiac Procedures

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1 Outcomes for Surgical Treatment of Atrial Fibrillation Using Cryoablation During Concomitant Cardiac Procedures Naima M. Rahman, Richard B. Chard, FRACS, FCSANZ, and Stuart P. Thomas, PhD, FRACP Department of Cardiology and Cardiothoracic Surgery, Westmead Hospital, Westmead, New South Wales, Australia Background. Surgical treatment of atrial fibrillation (AF) with heat-based therapies has been associated with a high rate of arrhythmia recurrence. We studied the short-term to medium-term outcomes with a unique biatrial linear ablation procedure for AF treatment using an argon-based cryoablation device during concomitant cardiac operations. Methods. Between March 2005 and July 2008, 57 patients (47% men) with problematic AF underwent a linear endocardial ablation procedure (Star pattern) using the flexible argon-based cryoablation probe during concomitant cardiac operations. Procedures were performed with valve or coronary operations, including mitral valve replacement (25%), mitral valve repair (16%), coronary artery bypass grafts (21%), and congenital heart surgery (8%). Atrial fibrillation was persistent or long-standing persistent in 50.9% of patients. Results. Kaplan-Meier survival curves (with the standard error) demonstrated 91% (3.9%) of patients were still free of their first recurrence at 6 months, 81% (5.6%) at 12 months, and 70% (6.8%) at 24 months. Time to first recurrence was not significantly associated with age (p 0.47), gender (p 0.52), or type of AF (p 0.69). There were no complications attributed to the cryoablation procedure. There was one in-hospital death and one death after discharge. Twelve patients (21%) required permanent pacemaker implantation postoperatively. There were no early or late thromboembolic events. Conclusions. This study demonstrated the mediumterm efficacy of cryoablation with a unique biatrial pattern of linear lesions for the treatment of AF during a concomitant cardiac operation. Short-term to mediumterm outcomes were at least equivalent to those reported for other energy modalities. (Ann Thorac Surg 2010;90:1523 8) 2010 by The Society of Thoracic Surgeons Atrial fibrillation (AF) is the most common clinically significant cardiac arrhythmia [1]. It is present in 1% of the general population and its incidence sharply increases with age [2]. AF is associated with an elevated risk of stroke in untreated patients [3, 4], with the risk of stroke increasing to 23.5% in AF patients aged 80 to 89 years [5].It is also responsible for disabling symptoms, decreased cardiac output, palpitations, and congestive heart failure [6]. AF is an independent predictor of death [7]. The gold standard for the surgical treatment of AF remains the cut-and-sew Cox-Maze III procedure, and in the largest documented series, Cox and colleagues [8, 9] reported 95% freedom from AF in 308 patients at a median follow up of 3.7 years. Although the Cox-Maze procedure has produced excellent long-term results in a large percentage of patients, widespread use of this surgical technique has been limited by concerns about increased cardiopulmonary bypass and cross-clamp times, complexity of lesions, and bleeding complications [10, 11]. Further understanding of the pathogenesis of AF, particularly the role of pulmonary veins in paroxysmal AF initiation, has led to the development of different approaches to the surgical treatment of AF [10, 12]. A number of energy sources are now used to create transmural lesions that can both effectively block atrial conduction and reduce or eliminate the amount of cut-andsew required. In this article, we report our results for a unique biatrial pattern of lesions, which we refer to the Star pattern, using argon-based cryoablation on patients undergoing concomitant cardiac operations. The aim of the Star pattern is to reduce isolated regions of myocardium, maintain craniocaudal atrial activation, and minimize disruption to the normal pattern of atrial activation. Material and Methods This study was approved by the Human Research Ethics Committee of Sydney West Area Health Service. Accepted for publication May 10, Address correspondence to Dr Thomas, Department of Cardiology, Westmead Hospital, Westmead, NSW 2145, Australia; stuartpt@ yahoo.com. Dr Thomas discloses that he has financial relationships with St. Jude Medical and Johnson & Johnson by The Society of Thoracic Surgeons /$36.00 Published by Elsevier Inc doi: /j.athoracsur

2 1524 RAHMAN ET AL Ann Thorac Surg STAR PROCEDURE USING CRYOABLATION FOR AF 2010;90: Patients All patients were considered for the Star procedure using cryoablation if they were undergoing a cardiac operation and had clinically important AF that had been resistant to medical therapy. Patients were included in this study if they had a complete Star pattern of lesions (both left and right side) and were aged older than 18 years. All procedures were performed at The Westmead Hospital, The Westmead Private Hospital, or The Sydney Adventist Hospital. Patients were categorized as having paroxysmal or persistent/long-standing persistent AF using international guidelines [13]. Demographics and perioperative and follow-up data were retrospectively analyzed. Cryoablation The Cryocath cryoablation device (SurgiFrost 7, Life Systems Medical Pty Ltd, Victoria, Australia) uses argon gas to achieve rapid cooling to temperatures as cold as 160 C. The flexible metal probe conforms to the cardiac contours around the heart structures. The device also has an adjustable insulation sheath that can cover the cryoablation segment. This offers an ablation zone between 0 and 60 mm. Surgical Procedure All operations were performed through a median sternotomy. The Star procedure was performed using the Cryocath to create linear lesions (ablation time of 60 seconds at each lesion site, as specified by the manufacturer at that time). Lesions were created from the posterior inferior mitral annulus opposite the left pulmonary veins and around the left pulmonary veins, from the posterior and inferior mitral annulus opposite the right pulmonary vein, and around the right pulmonary veins using the atrial access incision as part of the isolation. The left atrial appendage was oversewn from within the left atrium. The right-sided cryocatheter freezes were performed from the superior vena cava to the inferior vena cava posteriorly, from the posterior inferior tricuspid annulus (isthmus lesion) to the coronary sinus, down the coronary sinus for 2 cm, and then from the coronary sinus to the inferior vena cava. This completes the Star lesions (Fig 1). It takes approximately 15 minutes to complete all the freezes. These lesions are used to prevent macroreentry while maintaining a physiologic activation sequence. Further, the lesions interrupt known common pathways of macroreentry in the left and right atria. The Star procedure was not performed as a lone procedure on any of the patients. The concomitant procedures are listed in Table 1. Postoperative Management Unless there were contraindications, patients received anticoagulation therapy on discharge for a minimum of 3 months. Long-term warfarin was recommended for patients with mechanical valves or a CHADS 2 (Congestive heart failure, Hypertension 140/90 mm Hg or treated with medication, Age 75 years, Diabetes mellitus, Stroke or transient ischemic attack) score exceeding 1. Fig 1. The Star pattern of lesions is designed to allow normal activation to radiate out from the sinus node with as little disruption as possible to normal activation. (Solid line cryoablation; dashed line surgical incision; CS coronary sinus; IVC inferior vena cava; LI left inferior; LS left superior; RI right inferior; RS right superior; SVC superior vena cava.) Antiarrhythmic medication, amiodarone or sotalol, was prescribed to patients if postoperative AF developed. Antiarrhythmic medications were discontinued within the first 3 to 6 months postoperatively at the discretion of the treating cardiologist. Follow-Up After discharge from the hospital, patients were reviewed by the treating surgeon. They were also examined by their treating cardiologist after discharge, again at intervals of 3, 6, and 12 months, and then as required according to symptoms. Patients were evaluated using electrocardiograms, direct physical examination, and 24-hour Holter monitoring if paroxysmal AF was suspected but not identified on the electrocardiogram. Patient rhythms were recorded from discharge and over periods of 1 to 3 months, 3 to 6 months, 6 to 12 months, 1 to 2 years, and 2 to 3 years. Medical records were examined and telephone interviews were conducted to complete the data. Any documented episode of AF or atrial tachycardia lasting longer than 30 seconds was considered an arrhythmia recurrence. Results From March 2005 to July 2008, 57 patients (53% women) underwent the Star procedure using cryoablation for AF treatment during a concomitant cardiac operation, which is detailed in Table 1. The patients were a mean age of years (range, 21 to 83 years). Twenty-eight patients (49%) had paroxysmal AF, and 29 (51%) had persistent or long-standing AF. The mean duration of AF was months. The mean left atrial size was mm and calculated from 48 patients (84%) for whom we could retrieve this data (Table 2). Complete Star lesion sets were performed endocardially. The mean cardiopulmonary bypass time was minutes, and mean cross-clamp time was minutes.

3 Ann Thorac Surg RAHMAN ET AL 2010;90: STAR PROCEDURE USING CRYOABLATION FOR AF Table 1. Operative Data Procedure No. (%) Patients, total 57 Star Cryoablations 57 Concomitant procedures, total 87 Lone MVR 7 (8) MVR concomitant procedures 15 (17) Lone MV repair 9 (10) MV repair concomitant procedures 5 (6) Aortic valve replacement 12 (14) Coronary artery bypass grafting 18 (21) Tricuspid valve replacement 2 (2) Tricuspid valve repair 10 (11) Pulmonary valve repair 2 (2) Atrial septal defect repair 6 (7) Ventricular septal defect repair 1 (1) 1525 MV mitral valve; MVR mitral valve replacement Kaplan-Meier analysis was used to determine survival without AF recurrence after 3 months postoperatively. Kaplan-Meier survival curves demonstrated that 91% (standard error [SE], 3.9%) of patients were free of any AF recurrence at 6 months, 81% (SE, 5.6%) at 12 months, and 70% (SE, 6.8%) at 24 months of follow-up (Fig 2). At their last follow-up, 28% of patients in sinus rhythm were still Table 2. Underlying Heart Disease Underlying Disease No. % Underlying heart disease Valvular Mitral regurgitation, total Mild 7 12 Moderate 6 11 Severe Aortic regurgitation, total 7 13 Mild 2 4 Moderate 3 5 Severe 2 4 Tricuspid regurgitation, total Mild 1 2 Moderate 4 7 Severe 7 12 Coronary artery disease Rheumatic Atrial septal defect 6 11 Ventricular septal defect 1 2 Left ventricular ejection fraction Normal 58 Mild dysfunction 19 Moderate dysfunction 9 Severe dysfunction 4 Previous percutaneous ablation 7 Preoperative pacemaker 2 Previous heart operation 1 Fig 2. Kaplan-Meier estimates of arrhythmia recurrence showed an 81% freedom from atrial fibrillation or flutter at 12 months. taking antiarrhythmic drugs. Postoperative atrial arrhythmias were not identified as recurrences if they occurred in the first 3 months after the operation. Time to first AF recurrence was not significantly associated with age (p 0.47), gender (p 0.52), type of AF (p 0.69), left atrium size (p 0.77), or left ventricular function (p 0.85). At the 3- to 6-month review, 45 of the 56 patients (80%) were in sinus rhythm, and 8 (14%) were in AF. Figure 3 demonstrates rhythm at various postoperative intervals. In the immediate postoperative period, 39 patients were given antiarrhythmic medications (sotalol or amiodarone), 26 patients received antiarrhythmic drugs at some time after the first 3 months, and 16 were still using antiarrhythmic medications at the last follow-up. At their last follow-up, 28% of patients in sinus rhythm were still taking antiarrhythmic drugs. Twelve patients (21%) required permanent pacemaker implantation in postoperative the period ( months). Indications were second-degree heart block in 4, complete heart block in 1, sick sinus syndrome in 1, persisting bradycardia in 3. The remaining patients re- Fig 3. Cross-sectional outcomes for sinus rhythm (black bars), atrial fibrillation (AF, white bars), and atrial flutter (Aflutter, striped pattern).

4 1526 RAHMAN ET AL Ann Thorac Surg STAR PROCEDURE USING CRYOABLATION FOR AF 2010;90: ceived permanent pacemakers for combined sinoatrial and atrioventricular nodal dysfunction that limited antiarrhythmic therapy. One patient, an 80-year-old woman with valvular and coronary artery heart disease, died of sepsis and multisystem organ failure 4 days after a concomitant mitral valve replacement, coronary artery bypass graft, and cryoablation Star procedure. Another 83-year-old patient with congestive heart failure, diabetes, and unstable chronic renal failure underwent mitral valve repair combined with cryoablation died after 2 years from renal failure. Neither death was attributed to the cryoablation procedure. No complications were associated with the use of cryoablation. One patient required reoperation in the immediate postoperative period for mediastinal bleeding. There have been no episodes of thromboembolic stroke or transient ischemic attacks (TIA) after the operation to date. No instances of pulmonary venous stenosis or esophageal injuries were documented. Continuation or cessation of warfarin was at the discretion of the referring physician. Fifty-one patients used warfarin in the postoperative period. Our advice was to continue warfarin for all patients with recurrence of arrhythmia and a CHADS 2 score greater than 1, and all patients with mechanical valves. At their last follow-up, 71% of patients were using warfarin. Comment The results from this study support the hypothesis that the Star procedure using cryoablation produces shortterm to medium-term outcomes that are at least equivalent to those reported for other ablation strategies using cryoablation or radiofrequency (RF) energy [1, 5, 6, 11, 14, 15]. Using cryoablation, we were able to perform the complete Star lesion set in approximately 15 minutes in combination with other cardiac procedures. A diverse range of devices (microwave, laser, ultrasound, RF, RF bipolar, RF irrigated) and lesions sets (including modified Maze, left-sided Maze, pulmonary vein isolation, left atrial lesions) have been used in surgical treatment of AF. Rates of 70% to 95% of patients free of arrhythmia at 12 months or longer have been reported with commonly used procedures [9, 16 18]. Hyperthermal energy sources have been associated with a number of complications, including cardiac perforation, thromboembolic events, pulmonary vein stenosis, esophageal injury, phrenic nerve paralysis, and atypical atrial flutter [19 21]. Cryothermal energy has been used in cardiac operations for decades. We chose argonbased cryoablation for its theoretic advantages over hyperthermal modalities. These advantages include the preservation of underlying tissue architecture, possibly decreasing the risk of thrombus formation, strong adherence of the probe to tissue surface during freezing, which helps positioning, and the ability to create long lesions relatively quickly [22 25]. When the cryoprobe is applied to the myocardial surface, an ice ball forms that causes the probe to adhere to the tissue. This acts as a heat sink, extracting heat from the tissue and causing intracellular ice crystal formation [9, 26]. The initial freeze is followed by a thaw period where microcirculatory failure contributes to cell damage [27]. After the freeze/thaw phase, the myocardial tissue develops hemorrhage, edema, and inflammation (coagulation necrosis) [26]. Cell death (necrosis and apoptosis) can continue for weeks after ablation, followed by replacement fibrin and collagen. The resulting lesions are small, well demarcated, and densely fibrotic [22]. Rahmanian and colleagues [28] recently reported the results of a prospective study of 141 patients where a similar argon-based cryoablation device was used to correct AF during concomitant mitral valve operations. They reported 87% of patients were not in AF at a mean follow up of days. We achieved similar results, with 81% (SE, 5.6%) of patients free from any AF recurrence at 12 months and 77% (41 of 53) in sinus rhythm at 6 to 12 months of follow-up. They also reported higher rates of AF recurrence in later follow-up, with freedom from AF decreasing from 89% at 12 months to 71% at 24 months. Our results at 2 years demonstrated 70% (SE, 6.8%) of patients were still free of their first AF recurrence, and 83.9% were in stable sinus rhythm. The current study demonstrated that similar results could be achieved with a different lesion set. Thomas and colleagues [29] reported the results of 25 patients in whom the Star procedure was used to treat AF using an endocardial surgical RF ablation approach. At a mean follow up of months, 91% were free from AF; however, there was a high incidence of atrial flutter in follow-up. Clinical electrophysiology studies on the patients with atrial flutter demonstrated the main mechanism was gaps in the lines of ablation. We used cryoablation in the current study to perform a similar lesions set. The results of the present study are similarly favorable for freedom from AF postoperatively; however, episodes of atrial flutter are lower in the present study, with 91% (SE, 3.9%) of patients free from any episodes of atrial fibrillation/flutter at 6 months and 81% (SE 5.6%) at 12 months. The procedure times were also significantly lower, with a mean bypass time of minutes compared with minutes. Left atrial size and type of AF were identified in previous studies as predictors of AF recurrence [18, 28, 30]. In our study, corresponding with the findings of Gaynor and colleagues [31], left atrial size (p 0.77) and type of AF (p 0.69), among others such as age (p 0.47), gender (p 0.52), and left ventricular function (p 0.85), were not predictive of AF recurrence. Patient selection, sample size variation, and differences in lesion pattern are among other factors that may have contributed to the difference in results observed. There was a high incidence of pacemaker implantation in this study. The investigators had a low threshold for pacemaker implantation. The patients had previously had difficulty with control of AF before operations; therefore, pacemakers were frequently used to help control arrhythmias after procedures. This strategy allowed the use of antitachycardia pacing algorithms and more ag-

5 Ann Thorac Surg RAHMAN ET AL 2010;90: STAR PROCEDURE USING CRYOABLATION FOR AF gressive dosing of antiarrhythmic medications. None of the lesions were close to the atrioventricular or sinus node and therefore it is unlikely that the lesions damaged the conducting system. The main limitation of our study is the relatively small sample size and the absence of routine long-term monitoring techniques to confirm rhythm in follow-up. The small sample size reduced our capacity to detect predictors of success. In conclusion, this study demonstrates that the Star procedure using cryoablation can offer safe and effective surgical treatment of AF. Further investigation of the long-term outcomes is required, however. We acknowledge contributions of Karen Byth, Statistician, Westmead Millennium Institute, Mervat Halaka, Cardiothoracic Data Manager, and Dr Toon Wei Lim, The Cardiology Department, Westmead Hospital, Westmead, New South Wales, Australia. References 1. 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J Thorac Cardiovasc Surg 2005;129: INVITED COMMENTARY The article by Rahman and colleagues [1] summarizes the results of a medium-size series following bi-atrial cryoablation using the most advanced cryothermal surgical platform (ie, the argon-based cryothermal system). The study uses an ablation concept that is different from the Cox-Maze III procedure. The lesion pattern described here is designed to address typical right atrial flutter and to isolate the pulmonary veins with significant 2010 by The Society of Thoracic Surgeons /$36.00 Published by Elsevier Inc doi: /j.athoracsur