Atrial tachyarrhythmias, especially atrial fibrillation

Right-Sided Maze Procedure for Right Atrial Arrhythmias in Congenital Heart Disease David A. Theodoro, MD, Gordon K. Danielson, MD, Co-burn J. Porter, MD, and Carole A. Warnes, MD Division of Cardiovascular and Thoracic Surgery, Section of Pediatric Cardiology, and Division of Cardiovascular Diseases, Mayo Clinic and Mayo Foundation, Rochester, Minnesota Background. Atrial fibrillation and flutter, commonly associated with congenital heart anomalies that cause right atrial dilatation, may cause significant morbidity and reduction of quality of life, even after surgical repair of the anomalies. Methods. In an effort to reduce the incidence of atrial tachyarrhythmias after repair of right-sided congenital heart disease, we performed a concomitant right-sided maze procedure. Results. Eighteen patients with paroxysmal atrial fibrillation or flutter (n 12) or chronic atrial fibrillation or flutter (n 6) aged 10.9 to 68.4 years (mean 34.9 years) underwent a right-sided maze in association with repair of Ebstein s anomaly (n 15), congenital tricuspid insufficiency (n 2), and isolated atrial septal defect (n 1). There were no early deaths, reoperations, or complete heart block. Discharge rhythm was sinus (n 16) or junctional (n 2). Follow-up was complete in all 18 patients and ranged from 3.1 to 17.2 months (mean 8.1 months); all are in New York Heart Association class I. Early postoperative arrhythmias developed in 3 patients (all were converted to sinus rhythm by antiarrhythmic drugs). There were no late deaths or reoperations. Conclusions. The inclusion of a right-sided maze procedure with cardiac repair in patients having congenital heart anomalies that cause right atrial dilatation and associated atrial tachyarrhythmias is effective in eliminating or reducing the incidence of those arrhythmias. (Ann Thorac Surg 1998;65:149 54) 1998 by The Society of Thoracic Surgeons Atrial tachyarrhythmias, especially atrial fibrillation and atrial flutter, are commonly associated with congenital heart anomalies that cause right atrial dilatation [1 4]. We report our results in a group of patients undergoing surgical treatment of right-sided congenital heart disease in which a concomitant right-sided maze procedure, a modification of the Cox maze III operation [5], was performed for the correction of atrial fibrillation or flutter. Patients and Methods Patients Between February 21, 1995, and February 1, 1997, 22 patients with right-sided congenital heart disease associated with atrial fibrillation or flutter underwent a concomitant right-sided maze procedure at the time of cardiac repair. For reasons of length of follow-up, the first 18 patients (9 men, 9 women) were selected for this review; ages at operation ranged from 10.9 to 68.4 years (mean, 34.9 years). The right-sided maze procedure was combined with correction of Ebstein s anomaly (n 15), congenital tricuspid insufficiency (n 2), and isolated atrial septal defect (n 1). Diagnoses were based on clinical evaluation and echocardiography. All patients Presented at the Thirty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Feb 3 5, 1997. Address reprint requests to Dr Danielson, Section of Cardiovascular Surgery, Mayo Clinic, 200 First St, SW, Rochester, MN 55905. had severe right atrial enlargement demonstrated on preoperative chest radiography and echocardiography. Indications for operation included New York Heart Association functional class III or IV, progressive cyanosis, and progressive exercise intolerance. Associated cardiac defects included atrial septal defect (n 12), accessory conduction pathway(s) (n 2), and pulmonary artery stenosis (n 2). Previous cardiovascular operations included tricuspid valve surgery (n 2), pulmonary valvotomy (n 2), closure of ventricular septal defect (n 2), surgical ablation of accessory conduction pathway(s) (n 2), and coronary artery bypass grafting, Blalock-Taussig shunt, and ligation of aneurysm of right coronary artery (n 1). Three patients had undergone catheter ablation of accessory conduction pathways elsewhere. Documented atrial tachyarrhythmias included paroxysmal atrial fibrillation or flutter (n 12) and chronic atrial fibrillation or flutter (n 6). Fourteen patients were receiving antiarrhythmic drugs preoperatively, including digoxin, -receptor antagonists, calcium-channel antagonists, quinidine, propafenone, procainamide, and amiodarone, and 7 had required multiple electrocardioversions. Preoperative electrocardiography showed sinus rhythm in 12, atrial flutter in 4, and atrial fibrillation in 2 patients. The duration of documented atrial fibrillation or flutter ranged from 6 months to 54 years (mean, 14.2 years). Follow-up information was obtained from correspondence with the patients and referring physicians and from telephone interviews conducted with all of the patients. 1998 by The Society of Thoracic Surgeons 0003-4975/98/$19.00 Published by Elsevier Science Inc PII S0003-4975(97)01193-4

150 THEODORO ET AL Ann Thorac Surg RIGHT-SIDED MAZE PROCEDURE 1998;65:149 54 Fig 1. A surgeon s view of the right atrium and right atrial appendage (RAA), superior vena cava (SVC), inferior vena cava (IVC), and the location of the sinus node (SN). (Reprinted with permission of the Mayo Clinic.) Surgical Technique Cardiopulmonary bypass is instituted with standard cannulation of the ascending aorta for arterial inflow and direct cannulation of the superior and inferior venae cavae for venous drainage. The perfusate temperature is lowered to 25 to 30 C depending on the anticipated length of the procedure. A left ventricular vent is inserted through the right superior pulmonary vein and an aortic tack vent is placed. Atrial septal defects are closed by direct suture or pericardial patch, and congenital tricuspid insufficiency is treated by valve repair, when feasible, or valve replacement. Our operative management of patients with Ebstein s anomaly is described in detail in previous reports from our institution [1] and consists of (1) electrophysiologic mapping for localization of accessory conduction pathways in those patients having ventricular preexcitation, (2) excision of any attenuated atrial septum and pericardial patch closure of the septal defect for patients having an atrial septal defect or patent foramen ovale, (3) selective plication of the atrialized right ventricle, (4) reconstruction of the tricuspid valve, when feasible, or valve replacement, (5) correction of associated anomalies such as relief of pulmonary stenosis and division of accessory conduction pathways, and (6) excision of redundant right atrial wall (right reduction atrioplasty). Our modification of the Cox maze III procedure [5] is illustrated in Figures 1 through 6. The right atrial appendage is excised and the first maze incision is made from the base of the resected appendage inferolaterally to within 3 to 4 cm of the inferior vena cava (Figs 1, 2). The second maze incision is made anteriorly full thickness through the atrial myocardium to the anterior aspect of the tricuspid annulus. The area at the annulus is cryoablated or, more recently, lightly electrocoagulated to ensure all remaining muscle fibers are ablated, and the incision is closed (Fig 3). The third incision is made from the superior vena cava to the inferior vena cava parallel to the plane of the atrial septum (Fig 3). The inferior end Fig 2. Initial steps in the right-sided maze procedure. The right atrial appendage is excised and the first maze incision is made from the base of the resected appendage inferolaterally to within 3 to 4 cm of the inferior vena cava. (Reprinted with permission of the Mayo Clinic.) of this incision is repaired for approximately 2 cm. A fourth incision is made perpendicularly from the caudal portion of incision number 3 and carried to the posterolateral aspect of the tricuspid valve annulus (Fig 4). The area at the annulus is lightly electrocoagulated and the incision is partially repaired. If not required earlier to facilitate exposure, the aorta is then cross-clamped and the heart is arrested with cold blood cardioplegia and topical hypothermia. A fifth incision is made from the midportion of incision number 3 across the atrial septum and fossa ovalis, down to the tendon of Todaro near the coronary sinus; this incision is extended into the left atrium laterally for 1 to 2 cm and then closed (Fig 5). Procedures for the tricuspid valve and thin portions of the atrialized right ventricle are then performed as indicated. The remaining right atrial maze incisions are then Fig 3. The second maze incision is made anteriorly full thickness through the atrial myocardium to the anterior aspect of the tricuspid annulus. The area at the annulus is lightly electrocoagulated to ablate all remaining muscle fibers and the incision is closed. The third incision is made from the superior vena cava to the inferior vena cava parallel to the plane of the atrial septum. (Reprinted with permission of the Mayo Clinic.)

Ann Thorac Surg THEODORO ET AL 1998;65:149 54 RIGHT-SIDED MAZE PROCEDURE 151 Fig 4. The inferior end of incision 3 is repaired for approximately 2 cm. A fourth incision is made perpendicularly from the caudal portion of incision No. 3 and carried to the posterolateral aspect of the tricuspid valve annulus. The area at the annulus is lightly electrocoagulated and the incision is partially closed. (CS coronary sinus; FO fossa ovalis; TV tricuspid valve.) (Reprinted with permission of the Mayo Clinic.) closed (Fig 6). We prefer to close all atrial incisions with a double row of continuous nonabsorbable monofilament suture. Temporary pacing wires are attached to the right atrium and right ventricle and cardiopulmonary bypass is terminated after removal of air, reperfusion, rewarming, and establishment of sinus or atrial-paced rhythm. Fig 5. A fifth incision is made from the midportion of incision 3 across the atrial septum and fossa ovalis down to the tendon of Todaro near the coronary sinus; this incision is extended into the left atrium laterally for 1 to 2 cm and then closed. (Reprinted with permission of the Mayo Clinic.) Fig 6. After concomitant cardiac procedures, the remaining right atrial maze incisions are closed. (SN sinus node.) (Reprinted with permission of the Mayo Clinic.) The immediate postoperative results are assessed by pressure measurements and intraoperative transesophageal echocardiography. Results A right-sided maze procedure was performed in all 18 patients. Concomitant cardiac procedures included tricuspid valve replacement (n 16), closure of an atrial septal defect (n 12), repair of pulmonary stenosis (n 2), division of accessory conduction pathway (n 2), and repair of tricuspid valve (n 1). Cardiopulmonary bypass times ranged from 119 minutes to 307 minutes (median, 152 minutes) and aortic cross-clamp times ranged from 33 minutes to 100 minutes (median, 78 minutes). The patient with the longest bypass time had Ebstein s anomaly and a previous procedure elsewhere for pulmonary valvotomy and closure of atrial septal defect and ventricular septal defect. She required tricuspid valve replacement, pulmonary valve replacement, pericardial patch enlargement of the main pulmonary artery, patch closure of recurrent ventricular septal defect, and the right-sided maze procedure. This patient also had the longest duration of chronic atrial fibrillation (8 years); she has been in normal sinus rhythm since the operation. Most patients were paced atrially during weaning from cardiopulmonary bypass. There were no early deaths. No patient required intraaortic balloon pumping for hemodynamic support, and no patient had development of complete heart block or required early reoperation. Early postoperative complications included ventricular arrhythmia in 3 patients (multiple premature ventricular beats [n 2]) and one run of nonsustained ventricular tachycardia) and prolonged (5 days) mechanical ventilation in 1 patient. An electrocardiogram at the time of

152 THEODORO ET AL Ann Thorac Surg RIGHT-SIDED MAZE PROCEDURE 1998;65:149 54 hospital discharge showed sinus rhythm in 16 patients and junctional rhythm in 2 patients. The postoperative hospital stay ranged from 5 to 18 days (median, 7 days). No late deaths have occurred in follow-up times ranging from 5.3 to 24 months (mean, 13 months). All patients are in functional class I and no patients have required late reoperation. One patient required placement of a dual-chamber rate-responsive pacemaker for chronotropic insufficiency with exercise. Late atrial arrhythmias developed in 3 patients at 3.0, 3.5, and 8.0 months postoperatively, respectively (mean 4.6 months). The rhythm was paroxysmal atrial flutter in 2 patients and paroxysmal atrial fibrillation in 1 patient. All three arrhythmias were converted to sinus rhythm by antiarrhythmic drugs with or without electrocardioversion. At last contact, 10 patients were receiving medications, including digoxin (n 5), amiodarone (n 2), -receptor antagonist (n 2), and propafenone (n 1). Late follow-up electrocardiograms ranging from 2.5 to 16 months (mean 9.3 months) showed 16 patients were in sinus rhythm (1 with intermittent pacemaker function) and 2 patients were in junctional rhythm. Comment Congenital heart anomalies in which right atrial dilatation occurs are frequently associated with atrial tachyarrhythmias, especially atrial fibrillation or flutter [1 4]. Acquired cardiac lesions that produce isolated right atrial dilatation, such as traumatic tricuspid insufficiency, are also frequently associated with atrial fibrillation or flutter [6]. Ebstein s anomaly was the most frequent diagnosis in the present series. In this anomaly, deformity and displacement of the tricuspid valve cause severe tricuspid valve insufficiency and right atrial dilatation. There is also an attenuation and dilatation of the atrialized right ventricle and hypertrophy and dilatation of the functioning right ventricle. The pathology of this disorder provides an anatomic substrate that increases susceptibility to conduction abnormalities and both atrial and ventricular tachyarrhythmias [1, 7]. An additional source of tachyarrhythmias in Ebstein s anomaly is the presence of atrioventricular accessory conduction pathways, which were present in 14% to 15% of our surgical series [1, 8]. Of 306 patients who underwent operation for Ebstein s anomaly, 44 had concomitant surgical ablation of one or more accessory conduction pathways. The pathways were successfully ablated in all patients and survival was 100% at 10 years [8]. None of the atrial tachyarrhythmias in this review were related to accessory conduction pathways. The frequency of atrial arrhythmias in patients with Ebstein s anomaly varies among reported series, in part because of the ages of the patients in the series. The incidence of arrhythmias increases with age [7, 9]. The mean duration of paroxysmal or chronic atrial fibrillation or flutter in the present series was 14.2 years. The mean age for patients in the present review (34.9 years) is considerably older than the mean age for our entire series of patients undergoing operation for Ebstein s anomaly (19.1 years) [1]. In a report from our institution, Oh and associates [2] reviewed 52 consecutive patients who underwent operation for Ebstein s anomaly. In this group, 18 patients (34.6%) had documented paroxysmal supraventricular tachycardia and 10 patients (19%) had paroxysmal atrial fibrillation or flutter preoperatively. Of the 10 patients with paroxysmal atrial fibrillation or flutter, one-third continued to have symptomatic atrial tachycardia when followed up for an average of 36 months after operation. A subsequent review at our institution [3, unpublished data] compared the incidence of preoperative and postoperative arrhythmias in 188 patients who underwent operation for Ebstein s anomaly. When patients with accessory conduction pathways were excluded, supraventricular tachycardia was present in 40% of the patients preoperatively and in 28% postoperatively during an average follow-up of 6 years. In a subgroup of 81 patients followed up for more than 6 years, there was no significant difference in the incidence of preoperative and postoperative atrial arrhythmias (42% versus 37%, respectively). These results included both persistence of preoperative atrial fibrillation or flutter and the development of new atrial fibrillation or flutter during the follow-up period. Atrial tachyarrhythmias are poorly tolerated by patients with unrepaired congenital heart disease, and they may be a source of considerable morbidity and even mortality after successful cardiac repair [2, 7]. The mechanism of death is presumably atrial fibrillation or flutter with rapid ventricular conduction or degeneration into ventricular fibrillation [7]. Treatment may require one or more antiarrhythmic drugs, most of which have a negative inotropic effect that may further depress myocardial function in patients with congenital heart disease. A pacemaker may also be required in combination with antiarrhythmic drugs for complete control of atrial tachyarrhythmias. For these reasons, although the incidence of postoperative atrial tachyarrhythmias is decreased by the standard repairs for the Ebstein and other congenital cardiac anomalies, we planned to institute a policy of performing a concomitant antiarrhythmia procedure in patients undergoing repair of congenital heart disease in whom atrial fibrillation or flutter was present on the basis of right atrial dilatation. The Cox maze III operation is currently the surgical procedure of choice for management of medically refractory atrial fibrillation [5, 10]. In addition to being used in patients with atrial fibrillation or flutter and no underlying structural disease, the maze procedure has been added to the operation for patients requiring mitral valve repair, closure of atrial septal defect, septal myectomy for hypertrophic obstructive cardiomyopathy, and coronary artery bypass grafting [11 13]. There have been two recent reports in which atrial incisions in the maze procedure have been applied to the left atrium only, with some beneficial reduction in late atrial fibrillation [14, 15]. We modified the standard Cox maze III procedure by limiting the incisions to the right atrium and atrial septum. If effective, the right-sided maze would have several advantages over the standard maze operation including shorter operating time, minimizing the dissec-

Ann Thorac Surg THEODORO ET AL 1998;65:149 54 RIGHT-SIDED MAZE PROCEDURE 153 tion necessary when dense adhesions are present, limiting the number of atrial suture lines, eliminating suture lines behind the heart where control of bleeding can be difficult, avoiding a possible postoperative noncontractile left atrium, and possibly decreasing the risk of systemic embolization. In addition, the decreased number of suture lines appears to decrease the tendency for postoperative fluid retention caused by a decrease in atrial natriuretic peptide. In this small series, the operation did not add to the operative or late mortality (both were zero), and there was a gratifying decrease in the incidence of atrial fibrillation or flutter from 100% to 17% (83% decrease). This decrease in preoperative supraventricular tachyarrhythmias, excluding those as a result of accessory conduction pathways, is greater than the reduction from 40% to 28% (30% decrease) that has been noted with the standard repair for Ebstein s anomaly [3] and other congenital lesions with right atrial enlargement in our experience. For the standard maze procedure, early ( 3 months) arrhythmias are common, ranging from 40% to 50% [10]. With the passage of time and further resolution of postoperative changes, this incidence decreases. Because all three of the arrhythmia occurrences in our review were early (mean of 4.6 months), this incidence may decrease in the months ahead. It remains to be seen how much improvement the patients in this review will experience and what the incidence of late arrhythmias will be. In the meantime, this experience has been encouraging enough that we plan to continue with concomitant right-sided maze procedures in patients with atrial fibrillation or flutter associated with a large right atrium and structural heart disease. We thank Merrilee S. Rogotzke and Susan L. Burns for excellent secretarial support and Betty J. Anderson for outstanding data management support in the preparation of the manuscript. References 1. Danielson GK, Driscoll DJ, Mair DD, Warnes CA, Oliver WC. Operative treatment of Ebstein s anomaly. J Thorac Cardiovasc Surg 1992;104:1195 202. 2. Oh JK, Holmes DR, Hayes DL, Porter CJ, Danielson GK. Cardiac arrhythmias in patients with surgical repair of Ebstein s anomaly. J Am Coll Cardiol 1985;6:1351 7. 3. Cordes TM, Porter CJ, Danielson GK. Ebstein s and arrhythmias: the outcome after surgical repair. J Am Coll Cardiol 1994;23:104A. 4. Driscoll DJ, Offord KP, Feldt RH, Schaff HV, Puga FJ, Danielson GK. Five- to fifteen-year follow-up after Fontan operation. Circulation 1992;85:469 96. 5. Cox JL, Jaquiss RDB, Schuessler RB, Boineau JP. Modification of the maze procedure for atrial flutter and atrial fibrillation. II. Surgical technique of the maze III procedure. J Thorac Cardiovasc Surg 1995;110:485 95. 6. Van Son JAM, Danielson GK, Schaff HV, Miller FA. Traumatic tricuspid valve insufficiency: experience in thirteen patients. J Thorac Cardiovasc Surg 1994;108:893 8. 7. Olson TM, Porter CJ. Electrocardiographic and electrophysiologic findings in Ebstein s anomaly. Pathophysiology, diagnosis, and management. Prog Pediatr Cardiol 1993;2:38 50. 8. Theodoro DA, Danielson GK, Warnes CA, Porter CJ. Ebstein s anomaly with associated Wolff-Parkinson-White syndrome: operative treatment [abstract]. Circulation 1996; 94(Suppl 1):I-120 I-121. 9. Celermajer DS, Bull C, Till JA. Ebstein s anomaly: presentation and outcome from fetus to adult. J Am Coll Cardiol 1994; 23:170 6. 10. Cox JL, Boineau JP, Schuessler RB, Jaquiss RDB, Lappas DG. Modification of the maze procedure for atrial flutter and atrial fibrillation. I. Rationale and surgical results. J Thorac Cardiovasc Surg 1995;110:473 84. 11. Sandoval N, Velasco VM, Orjuela H, et al. Concomitant mitral valve or atrial septal defect surgery and the modified Cox-maze procedure. Am J Cardiol 1996;77:591 6. 12. Kosakai Y, Kawaguchi AT, Isobe F, et al. Modified maze procedure for patients with atrial fibrillation undergoing simultaneous open heart surgery. Circulation 1995;92(Suppl 2):II359 II-364. 13. McCarthy PM, Cosgrove DM, Castle LW, White RD, Klein AL. Combined treatment of mitral regurgitation and atrial fibrillation with valvuloplasty and the maze procedure. Am J Cardiol 1993;71:483 6. 14. Brodman RF, Frame R, Fisher JD, Kim SG, Roth JA, Ferrick KJ. Combined treatment of mitral stenosis and atrial fibrillation with valvuloplasty and a left atrial maze procedure [Letter]. J Thorac Cardiovasc Surg 1994;107:622 4. 15. Sueda T, Shikata H, Orihashi K, et al. Efficacy of left atrial only procedure for the treatment of chronic atrial fibrillation associated with mitral valve disease. J Jpn Assoc Thorac Surg 1996;44:785 9. DISCUSSION DR PEDRO J. DEL NIDO (Boston, MA): First I would like to comment that our technique of doing the Fontan connection is most commonly a lateral tunnel technique, which has been blamed for creating a suture line and scarring that is a substrate for atrial flutter. It is interesting to note that in your technique, which I believe is quite different than this, atrial flutter also occurs. So clearly, there is more to this pathology than simply suture lines. The question I have, though, is that the real control group for this type of procedure is cardiac catheterization and ablation in the catheterization laboratory. In other words, most of our Fontan patients with atrial flutter are ablated in the catheterization laboratory. Could you tell us what your experience is with that approach and how the two techniques compare? Most of these macroreentrant pathways follow a circle around your suture line, and you may interrupt them by incising from the inferior vena caval suture line to the right atrioventricular valve, in essence cutting off the reentrant circuit. This may be a much simpler addition to the Fontan connection in an effort to try to prevent the problem with atrial flutter. DR THEODORO: Thank you for your comments. With regard to arrhythmias related to the modified Fontan procedure, a recent study from our institution identified several risk factors for early and late atrial flutter or fibrillation, including factors on both the right and left sides of the heart. One of the risk factors was found to be location of the suture line when six different types of modifications were compared (Durongpisitkul et al, unpublished data).

154 THEODORO ET AL Ann Thorac Surg RIGHT-SIDED MAZE PROCEDURE 1998;65:149 54 With regard to catheter radiofrequency ablation of atrial flutter not related to cardiac surgery, our electrophysiology laboratory has had experience with more than 50 patients. For those patients with classic atrial flutter in whom the isthmus between the inferior vena cava and the tricuspid valve participates in the reentry circuit and in whom an isthmus block can be created, the early success rate is 95% and the late success rate is 85%. It should be recognized that many cases of atrial flutter after cardiac surgery have reentry around a scar or suture line and are therefore not the classic kind of atrial flutter that uses the isthmus for the reentry circuit, so a surgical incision or catheter burn in the isthmus might not be expected to be effective. Experience with treatment of atrial fibrillation using catheter techniques only in the right atrium is early and much less successful. Increasing sophistication in preoperative and intraoperative mapping should improve understanding of the mechanisms of various atrial flutter and fibrillation arrhythmias and thereby increase the success rate for their ablation. In addition, it is likely that fewer incisions or catheter burns will be required to interrupt a given reentry pathway once its mechanism is known. The patients in this report were operated on for correction of congenital cardiac anomalies, and the right-sided maze incisions were added to the other operative procedures in an attempt to additionally treat their atrial tachyarrhythmias. The addition of the right-sided maze procedure does appear to be effective in reducing the incidence of atrial arrhythmias over and above the reduction achieved in our previous series of patients who underwent repair of the congenital lesions alone. DR BRADLEY S. ALLEN (Chicago, IL): Although the pathophysiology of atrial fibrillation may be different in pediatric compared with adult hearts, one reason that the Cox maze procedure was first developed as a biatrial procedure was to ensure a 100% success rate. If you perform biopsy of the atrium in an adult patient immediately after atrial fibrillation develops secondary to a reversible problem, such as mitral regurgitation, you either find normal muscle or only the left atrium is altered. However, if you repeat the biopsy after the patient has been in atrial fibrillation for several months, not only is the left atrium abnormal, but now the right atrium is affected. Consequently, both sides have become a substrate for atrial fibrillation. Therefore, if you only do a left-sided maze procedure at the time you repair the mitral valve in a patient in chronic fibrillation, atrial fibrillation usually develops postoperatively. Therefore, my concern would be that just doing a right-sided maze procedure in patients who have been in chronic atrial fibrillation would be inadequate, as their left atrium may now also be abnormal. Therefore, I am wondering whether the patients in whom postoperative arrhythmias developed in your series were in atrial fibrillation for a longer period of time before operation than the patients who stayed in sinus rhythm. DR THEODORO: The possibility that the left atrium may have contributed to the atrial flutter or fibrillation in our patients was certainly a concern of ours. To minimize this concern, we selected our patients on the basis of right atrial dilatation in the presence of normal left atrial size. Because of the greater simplicity of the right-sided maze as opposed to a biatrial maze, particularly in the setting of adhesions from previous operations, we thought it was reasonable to explore the merits of adding a right-sided maze only. We realize that Cox s original data have shown that both atria can be substrates for atrial fibrillation, at least for chronic atrial fibrillation arising from mitral insufficiency. However, there have been a few recent reports in which a left-sided maze only was performed for left-sided cardiac lesions, one of the largest being from Japan. Further experience and longer follow-up will be required to provide the data necessary to evaluate the comparative incidences of recurrence of atrial arrhythmias after the left-sided or right-sided maze versus the biatrial maze. The patient who had the longest duration of chronic atrial fibrillation in our series (8 years) has actually not had a recurrence of atrial fibrillation. For the 3 patients who had recurrence of their arrhythmia (paroxysmal atrial fibrillation or flutter), the preoperative duration of their arrhythmia ranged from 2 years to a little shy of 10 years, and was not different from the duration of arrhythmias in the patients who had no recurrence. We looked specifically at the presence of left atrial dilatation on the preoperative echocardiogram of the 3 patients who had a recurrence, and there was no difference from the left atrial sizes of the patients who did not have a recurrence. Actually, the recurrences occurred at 3 months, 3 1 2 months, and 8 months postoperatively, respectively. Even in Cox s series, there is an early recurrence rate of up to 45% to 50% when the biatrial maze is performed, but many of these arrhythmias subside with further duration of follow-up. DR ALLEN: But, were the 3 patients in whom you saw a recurrence of arrhythmias in atrial fibrillation for a longer period of time than those patients who remained in sinus rhythm? DR THEODORO: No, absolutely not. They had been within the same range of duration as for patients with no recurrences. Perhaps, as this series increases in number, such a difference will become apparent. DR HIROSHI WATANABE (St. Louis, MO): I congratulate you on your excellent results. I have one question. Do you have electrophysiologic data before and after operation, especially provocation tests for atrial fibrillation or flutter? DR THEODORO: Five of these patients had inducible atrial fibrillation or flutter on preoperative electrophysiologic testing. We have not yet performed follow-up electrophysiologic testing on this series of patients.