Atrial fibrillation (AF) is the most common type of

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1 Atrial Flutter After Surgical Radiofrequency Ablation of the Left Atrium for Atrial Fibrillation Gregory Golovchiner, MD, Alexander Mazur, MD, Alex Kogan, MD, Boris Strasberg, MD, Yaron Shapira, MD, Menachem Fridman, MD, Jairo Kuzniec, MD, Bernardo A. Vidne, MD, and Ehud Raanani, MD Departments of Cardiology and Cardiothoracic Surgery, Rabin Medical Center, Petah Tiqwa, Israel, affiliated with Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel Background. Left atrial radiofrequency ablation is the most common technique for the treatment of atrial fibrillation during mitral valve surgery. Reported failure rates range between 15% and 30%, with some patients remaining in atrial fibrillation and others experiencing atrial flutter. The incidence and nature of the postoperative atrial flutter is not yet well defined. Methods. The study group consisted of 50 patients with atrial fibrillation who underwent mitral valve surgery combined with left atrial radiofrequency ablation, and were followed for a mean period of 15 7 months. The majority of patients (39; 78%) had persistent or permanent atrial fibrillation. Placement of the ablation lines was as follows: encircling the pulmonary veins, isolating the base of the left atrial appendage, and bridging the lateral or posterior mitral annulus and the margin of the pulmonary vein or the appendage-encircling ablation lines. Atrial fibrillation (AF) is the most common type of sustained rhythm disturbance, with an estimated 2.2 million cases in the United States [1]. Despite extensive, decades-long research, AF remains a major cause of substantial morbidity and mortality [2, 3]. The low efficiency of medical treatment [4 7] has led to the development of a catheter-based and surgical approach [8, 9]. The Maze III procedure was introduced as the curative treatment for AF by Cox and colleagues [10] in 1991 and has since been proven to be effective in numerous studies [11 13]. Nevertheless, its widespread use is limited because of its complexity and prolonged operative time [14]. To overcome these problems and simplify the surgical approach, a variety of procedures were developed [14 21]. One of the most popular is radiofrequency ablation in the left atrium, which is considered effective and safe also for patients undergoing mitral valve surgery [22, 23]. Recent studies reported the appearance of supraventricular tachycardias other than AF in 3% to 11% of patients after different types of surgical AF ablation [11, 16, 20, 22 25], mostly atrial flutter. The nature of Accepted for publication June 16, Presented at the Poster Session of the Fortieth Annual Meeting of The Society for Thoracic Surgeons, San Antonio, TX, Jan 26 28, Address reprint requests to Dr Raanani, Department of Cardiac Surgery, Sheba Medical Center, Tel-Hashomer, Israel 52621; ehud. raanani@sheba.health.gov.il. Results. There were three hospital deaths (6%). Thirtyfour (72%) patients were free of any atrial tachyarrhythmia events, and 37 (79%) patients were in sinus rhythm by the end of the study s follow-up. During the follow-up, 6 patients (12.7%) experienced atrial flutter and 1 patient had atrial tachycardia. Electrophysiologic study was performed in 5 of 6 patients with postoperative atrial flutter. In 4 of them, the study findings were consistent with left atrial flutter. One patient with typical isthmus-dependent right atrial flutter underwent successful ablation. Conclusions. Left atrial surgical radiofrequency ablation is associated with a high rate of postoperative atrial flutters that appear to be predominantly of left-sided origin. (Ann Thorac Surg 2005;79:108 12) 2005 by The Society of Thoracic Surgeons postoperative atrial flutter is unclear, with some authors reporting mostly typical right atrial isthmus-dependent flutter [22] and others, atypical atrial flutter [24]. A better understanding of the mechanisms underlying postoperative atrial flutter may help clinicians develop a more efficient approach to the treatment of AF. The aim of the present study was to evaluate the incidence and mechanisms of atrial tachyarrhythmias other than AF that occur after mitral valve surgery combined with radiofrequency ablation of the left atrium. Patients and Methods Patients Sixty patients with a history of AF underwent left atrial radiofrequency ablation during mitral valve surgery in the 18 months from October 2001 to October 2003 in our center. Of them, 50 patients who completed the study protocol requirement of at least 6 months follow-up were included in the final analysis. Patients with coagulation disorder or severe calcified left atrium were excluded. Mean age at operation was years (range, 30 to 79 years). Thirty-six patients (72%) were female. In the majority of patients (72%), rheumatic heart disease was the underlying mitral valve disease; others included ischemic mitral insufficiency (8%), degenerative mitral valve (18%), and hypertrophic obstructive cardiomyopathy (2%). Thirtynine patients (78%) had preoperative persistent or perma by The Society of Thoracic Surgeons /05/$30.00 Published by Elsevier Inc doi: /j.athoracsur

2 Ann Thorac Surg GOLOVCHINER ET AL 2005;79: ATRIAL FLUTTER AFTER SURGICAL ABLATION Table 1. Type of Operation in 50 Patients With Atrial Fibrillation Type of operation Mitral valve replacement 45 (90%) Mitral valve repair 5 (10%) Additional procedures TV replacement 6 TV repair 8 CABG 9 TV repair and CABG 1 TV and aortic valve replacement 2 Aortic valve replacement CARDIOVASCULAR CABG coronary artery bypass grafting; TV tricuspid valve. nent AF. The mean duration of AF for the whole group was months (range, 3 to 180 months). Mitral valve replacement was performed in 90% of cases, and mitral valve repair, in 10%. In 20 patients (40%), the operation was a redo heart surgery. Fifty-eight percent of the patients also had additional procedures, such as tricuspid valve surgery, coronary artery bypass grafting, and aortic valve replacement (Table 1). Surgical Procedure All operations were performed by means of a median sternotomy using standard cardiopulmonary bypass. The heart was arrested by infusing a cold blood cardioplegic solution through the aortic root and, in some cases, through the coronary sinus. The mitral valve was approached through an incision in the right side of the left atrium or through the interatrial septum. The ablation was performed first, after the left atrium was entered. We used a Saline-Irrigated radiofrequency System (Cardioblate; Medtronic Inc, Minneapolis, MN) consisting of a power generator (20 to 30 W) and a handheld, unipolar, flexible tip pen. The electrode tip is irrigated with saline, which cools the tissue and provides a low-impedance path. In this manner, deeper lesions can be created with less damage to the surrounding tissues [26]. The lesion is not created by heat conduction from the tissue surface, but by direct resistive heating in the deeper tissue layers. The size of the lesion is determined by the amount of energy delivered through the catheter, according to four variables: power (watts), saline irrigation speed, electrode diameter, and delivery time. A higher power leads to higher tissue-surface temperature upstroke, impedance rise, and tissue carbonization. Once the surface is carbonized, the impedance is high, and ablation of the underlying tissue cannot be accomplished. We used power limits of 26 to 32 W and ablation time of 120 seconds; saline irrigation speed was 5 ml/s. The completeness of lesion was determined by observing tissue color change to white. Placement of the ablation lines was as follows: encircling of each pulmonary vein separately; connecting each ipsilateral pulmonary vein line along the roof of the left atrium, connecting the right and left pulmonary veins; isolating the base of the left atrial appendage; and two Fig 1. Dotted lines indicate the ablations performed using radiofrequency energy. For detailed description see text. (LPVs left pulmonary veins; MV mitral valve; RPVs right pulmonary veins.) more linear ablation lines bridging the left pulmonary vein to the base of the left atrial appendage, and the base of the left atrial appendage to the lateral mitral valve annulus (Fig 1). Postoperative Management All patients received prophylactic antiarrhythmic therapy starting 24 hours after the operation. Sotalol was started in all patients at a dosage of 40 mg twice daily and subsequently increased to 80 mg twice daily during hospitalization under QT interval, heart rate, and blood pressure control. Anticoagulation therapy was prescribed according to the indications for valve surgery. If a mechanical prosthesis was not implanted, warfarin was prescribed for a minimum of 3 months. Patients with postoperative sinus bradycardia or slow nodal rhythm were temporarily paced. For patients with postoperative AF, electrical cardioversion was attempted 6 to 12 weeks postoperatively. Data Collection and Management During Follow-Up During the stay in the intensive care unit and cardiac surgery ward, a daily 12-lead electrocardiogram was performed in addition to clinical examination until discharge. The data on postoperative complications and medications and the results of the electrocardiographic analysis were recorded on a special form. All patients were seen in an outpatient clinic 6 to 8 week after the operation and every 3 to 6 months thereafter. The patients were instructed to report any documented arrhythmia events as well as symptoms suggestive of AF. The patients who reported symptoms underwent 24-hour ambulatory electrocardiographic monitoring. All patients diagnosed with postoperative atrial tachycardia or flutter

3 110 GOLOVCHINER ET AL Ann Thorac Surg ATRIAL FLUTTER AFTER SURGICAL ABLATION 2005;79: were advised to undergo electrophysiologic study (EPS) with radiofrequency ablation option. Electrophysiologic Study Activation and entrainment mapping using multipolar electrode catheters was performed in the right atrium. Ablation of the cavotricuspid isthmus was performed during the same session in all patients. Typical right atrial isthmusdependent atrial flutter was diagnosed on the basis of (1) the characteristic activation pattern, (2) concealed entrainment with the postpacing interval in the cavotricuspid isthmus less than the flutter cycle length by 40 ms or less, and (3) termination of flutter after ablation of the cavotricuspid isthmus. Left atrial flutter was suspected if one or more of the following criteria were met: (1) right atrial activation time less than 50% of flutter cycle length at more than 10 simultaneous recording sites, including the cavotricuspid isthmus, septum, and right atrial posterior and free walls; (2) manifest entrainment with a postpacing interval greater than the flutter cycle length by at least 40 ms at more than three right atrial stimulation sites including the cavotricuspid isthmus and right atrial free wall, and excluding the septum and coronary sinus; and (3) spontaneous variation of the flutter cycle length in the right atrium of greater than 100 ms with concomitant variation of less than 20 ms in the left atrium [27]. Atypical right atrial flutter was considered on the basis of appropriate activation and entrainment mapping findings as well as no response to the cavotricuspid isthmus ablation with documented bidirectional block in the isthmus. The cavotricuspid isthmus ablation was performed using saline-irrigated tip catheter (Cordis Webster, Inc, Diamond Bar, CA) and a Stockert- Cordis generator. Radiofrequency energy was delivered for 45 seconds at each site with a target temperature of 50 C and a power limit of 45 W. Bidirectional block in the isthmus was confirmed by the presence of double potentials along the ablation line or analysis of activation in the isthmus during pacing from the lateral isthmus and the ostium of the coronary sinus. Data Analysis All continuous variables are expressed as mean standard deviation. Results Early The additional average cross-clamp time required for the radiofrequency ablation was 15 4 minutes (range, 10 to 22 minutes). There were 3 hospital deaths, for a total hospital mortality of 6%. All 3 were female patients. The first was a 69-year-old woman undergoing a redo operation for mitral valve replacement and tricuspid valve repair who died in the operating room from intractable left ventricular failure. The other 2 patients, 77 and 68 years old, underwent mitral replacement and tricuspid valve repair and died of sepsis and multiorgan failure 3 and 7 days postoperatively. The only other significant in-hospital postoperative complications were bleeding requiring reexploration in 2 patients and transient ischemic attacks in 2 patients. Median stay in the intensive care unit was 40 hours (mean, hours), and median hospital stay was 8 days (mean, days). Only 1 patient required permanent pacemaker implantation for sick sinus syndrome. Overall, 36 patients (77% of the 47 survivors) were in sinus rhythm before hospital discharge. Eight patients were discharged with AF and 3 with atrial flutter. Follow-Up During a mean follow-up period of 15 7 months (range, 6 to 24 months), no patient was lost to follow-up. Two of the patients who had been discharged from the hospital with AF underwent successful electrical cardioversion 6 and 8 weeks after surgery. The other 6 patients remained in AF, and 1 additional patient exhibited recurrent AF during follow-up. Three more patients had atrial flutter, for a total of 6 (12.7%). Two patients with atrial flutter underwent successful cardioversion, and 1 underwent successful cavotricuspid isthmus ablation. One additional patient experienced atrial tachycardia 12 weeks after the operation, which was successfully treated by electrical cardioversion. Overall, 34 patients (72%) were free of any atrial tachyarrhythmia events, and 37 patients (79%) were in sinus rhythm by the end of the study s follow-up. There was no difference in the procedure outcome among patients with different types of underlying disease. All patients were in New York Heart Association functional class I or II. There was no late mortality. Atrial Tachycardia or Flutter After Surgery Overall, 7 patients (14.9%) had atrial tachyarrhythmias other than fibrillation during the follow-up: 6 had atrial flutter and 1 had atrial tachycardia. In 5 of the 6 patients with atrial flutter, P-wave morphology in the surface electrocardiogram was consistent with an atypical flutter. In 1 patient, the surface electrocardiographic morphology was suggestive of the typical counterclockwise right atrial flutter. Mean flutter cycle length was ms (range, 210 to 280 ms). Five of the 6 patients with postoperative atrial flutter underwent EPS and cavotricuspid isthmus ablation 3 to 15 months (mean, months) after the surgery. In 1 patient, EPS showed right atrial isthmus-dependent flutter, and the cavotricuspid isthmus ablation resulted in the arrhythmia termination. In the remaining patients, the EPS findings were consistent with left atrial flutter. These included (1) right atrial activation time less than 50% of flutter cycle length at greater than 10 simultaneous recording sites, including the cavotricuspid isthmus, septum, and right atrial posterior and free walls in all 5 patients; (2) manifest entrainment with a postpacing interval greater than the flutter cycle length by at least 40 ms at more than three right atrial stimulation sites including the cavotricuspid isthmus and right atrial free wall, and excluding the septum and coronary sinus in all 5 patients; and (3) spontaneous variation of the flutter cycle length in the right atrium of more than 100 ms with concomitant variation of less than 20 ms in the left atrium in 2 patients. In all patients with suspected left atrial flutter, cavotricuspid isthmus ablation resulted in a change of the right atrial endocardial

4 Ann Thorac Surg GOLOVCHINER ET AL 2005;79: ATRIAL FLUTTER AFTER SURGICAL ABLATION activation sequence suggesting block in the isthmus but without arrhythmia termination or changes in flutter cycle length. Comment The main finding of the present study is that radiofrequency ablation of the left atrium during mitral valve surgery was associated with high incidence (7 of 50 patients, 14.9%) of postoperative atrial tachyarrhythmias other than AF: atrial flutter in 6 patients (12.7%) and atrial tachycardia in 1 patient (2.1%). In the majority of patients with atrial flutter who underwent EPS (4 of 5), the study findings were consistent with left-sided origin of the arrhythmia. The remaining patient had typical isthmusdependent atrial flutter successfully treated by the cavotricuspid isthmus ablation. Understanding the mechanisms of atrial flutter occurring after surgical treatment of AF may significantly improve the procedure results. These mechanisms may vary, and may or may not be related to the surgery itself [28 30]. It is well known that AF and typical isthmusdependent right atrial flutter are frequently present in the same patient [31]. In this regard, the question remains whether ablation of cavotricuspid isthmus should be routinely performed in all patients during AF surgery. In the series of Usui and colleagues [24], typical right atrial isthmus-dependent atrial flutter was found in 4 of 41 patients (9.8%) who underwent a left-sided AF surgery and only in 1 of 32 patients (3%) after a Maze III procedure. On the basis of this finding, the authors suggested that typical isthmus-dependent right atrial flutter could be the most common mechanism of postoperative atrial flutter and that routine ablation of the cavotricuspid isthmus during AF surgery might be necessary. In contrast with these data, postoperative atrial flutter has been commonly found in other surgical series involving both the right and left atrium, suggesting limited efficacy of the cavotricuspid isthmus ablation in preventing this arrhythmia complication [11, 20, 22, 24]. In the present study, most cases of postoperative atrial flutter appear to be a consequence of the operation itself. This assumption is supported by the fact that in none of the patients was the arrhythmia documented before the operation. Furthermore, the EPS findings strongly suggested left atrial origin of the arrhythmia in all but one of these patients. There are several potential mechanisms that can be involved in surgery-related atrial flutter. Although left atriotomy scar may serve as a central obstacle in left atrial flutter circuits [28], this mechanism seems to be rare in patients with postoperative atrial flutters after mitral valve surgery [30]. The role of left atriotomy scar in the pathogenesis of arrhythmia found in our patients is unknown because mapping in the left atrium was not performed. Incomplete ablation lines can create anatomic substrate for macro-reentrant arrhythmias. This is the most common mechanism of atrial flutters that occur after nonsurgical radiofrequency ablation involving deployment of linear lesions in the left atrium [32]. Data on the role of this mechanism in atrial flutters after AF surgery are significantly limited. Thomas and colleagues [33] reported a high incidence of EPS-confirmed atrial flutter after biatrial modified ( star ) radiofrequency ablation. In 38% of these patients, there was clear evidence of deficiency in the ablation lines. Although, theoretically, incomplete lines seem to be the most likely candidate mechanism for atrial flutters in our patients, this hypothesis could be confirmed only during direct left atrial mapping. However, the safety of left atrial mapping in patients with mechanical mitral prosthetic valves is unknown. The cooled tip radiofrequency probe, used in our study, has been previously shown to produce more transmural lesions than conventional probes [26]. The visual confirmation of lesion transmurality used in our study may be significantly limited. However, there is no currently viable alternative to this method to guide intraoperative lesion deployment. The use of stimulation for the control of lesion completeness may be useful, but it would prolong the operation time and may not be feasible in patients undergoing valve replacement. Furthermore, acute findings may not correlate with longterm results because of conduction recovery with time [34]. Recent animal studies showed that bipolar radiofrequency energy can produce complete transmural permanent lesions [35 37]. Initial clinical experience with bipolar delivery of radiofrequency energy during the surgery for AF is promising, although this technology needs further evaluation [38]. Another potential cause of postoperative atrial tachycardia may be the right atriotomy scar after cannulation. The right atriotomy scar can facilitate occurrence of typical isthmus-dependent right atrial flutter [39]. In none of our patients were EPS data consistent with the arrhythmia specifically related to the atriotomy scar, ie, with the arrhythmia caused by reentry around the atriotomy scar and a protected isthmus different from the cavotricuspid [40]. All our patients had underlying heart disease, especially rheumatic disease. Atrial flutter may be more frequent after surgery for AF in patients with organic heart disease. Mohr and coworkers [16], in a 6-month follow-up study, found that none of their patients operated on solely for AF experienced atrial flutter. By contrast, atrial flutter developed in 5.6% of the patients with concomitant mitral surgery and 3.3% of patients operated on for other reasons. The effects of the structural heart disease, fibrosis, and chronic atrial dilatation may serve as the foundation for flutter circuit formation. Atrial flutter is common after surgical unipolar radiofrequency ablation of the left atrium in patients undergoing mitral valve operations. Our findings suggest predominantly left-sided origin of postoperative atrial flutters. These findings argue against routine ablation of the cavotricuspid isthmus during the AF surgery. References Sra J, Dhala A, Blanck Z, Deshpande S, Cooley R, Akhtar M. Atrial fibrillation: epidemiology, mechanisms, and management. Curr Probl Cardiol 2000;25: CARDIOVASCULAR

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