Crit Care Nurs Q CONTINUING EDUCATION Vol. 30, No. 3, pp. 233–242 Copyright c 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Surgical Approaches for

Barbara Schouchoff, RN, MHSA, CNA,BC

The Cox Maze procedure, a cardiac intervention that was developed by James Cox, MD, was first performed in 1988 to surgically cure atrial fibrillation. Over the years, changes in techniques of the classic maze were made, culminating in the Cox Maze III procedure, the Gold Standard. Mod- ifications in the original procedure included simplifying the procedure to a minimally invasive approach. As a result of some of these modifications, the initial maze-like series of surgical atrial incisions has been reduced with the use of alternate energy sources that create hyperthermic le- sion lines of conduction block that isolate and interrupt the abnormal impulses. The minimaze, a minimally invasive thorascopic approach, can be performed off pump, thus avoiding a and and cardioplegic arrest intraoperatively and ensuring a shorter, less painful recovery. Key words: atrial fibrillation, maze, minimaze, pulmonary vein isolation

TRIAL FIBRILLATION, the most com- maze, known as advanced therapy or curative A mon cardiac arrhythmia, affects more procedures. than 2.2 million Americans, with more than Patients may undergo a surgical procedure 350,000 new cases diagnosed each year.1 Lit- for atrial fibrillation when a pharmacologi- erature review discloses that atrial fibrilla- cal intolerance exists; traditional medical man- tion causes a significant increase in mortality agement proves ineffective or does not cor- due to thromboembolic events, tachycardia- rect atrial fibrillation; an intolerance to antico- induced , and hemodynamic agulants exists; atrial fibrillation exists in spite compromise.1 Thus, several factors prevent of medical management; embolic events oc- the establishment of global recommendations cur; and patients undergo surgery for a coex- for standardizing treatment in all patients ex- isting condition.2,3 periencing atrial fibrillation.2 These factors include the pathogenesis of atrial fibrilla- ATRIAL FIBRILLATION tion, patient symptoms, and variability in pa- 2,3 tient profiles. Presently, multiple therapeu- Atrial fibrillation increases dramatically the tic and surgical interventions based on the risk and severity of and is associ- patient’s symptoms are available for the treat- ated with increased morbidity and mortal- ment of atrial fibrillation. Treatment options ity. Benussi4 reports that the prevalence of include the use of pharmacological agents, atrial fibrillation is 0.4% in the general popu- known as traditional medical management, lation and about 5% in people older than 60. or surgical interventions, such as surgical ab- As stated by Bennusi,4 lone atrial fibrillation lation, Cox Maze, modified maze, or mini- (LAF) accounts for about 30% of the cases. Bloom5 noted that the prevalence of atrial fib- rillation is as high as 9% in patients 80 years From West Penn Allegheny Health System, Allegheny or older. The projected incidence of atrial fib- General Hospital, Pittsburgh, Pa. rillation by 2050 is expected to be more than The author has no conflict of interest. 5.6 million patients (Fig 1). Common diseases that contribute to the Corresponding author: Barbara Schouchoff, RN, MHSA, CNA,BC, 9174 Foxhunt Rd, Pittsburgh, PA 15237 etiology of atrial fibrillation include, but are (e-mail: [email protected]). not limited to, hypertension, coronary artery 233 234 CRITICAL CARE NURSING QUARTERLY/JULY–SEPTEMBER 2007

clinical manifestations as noted by Cox.7 The choice of intervention, pharmacologi- cal or nonpharmacological, is determined by whether atrial fibrillation is continuous or in- termittent, depending on variable underlying .7 The treatment goals for atrial fibrillation are conversion to sinus rhythm, controlling the heart rate, reducing the risk of stroke, and re- ducing or preventing embolic events. This can be accomplished by pharmacologic interven- tion, rhythm or rhythm-control drugs, rate- control medications, or a combination of war- farin with either a rate-control medication or a rhythm-control medication. Rhythm-control drugs restore the sinus rhythm, eliminating the risk of atrial fibrillation, and include drugs such as procainamide, sotalol, or amiodarone. Rate-control medications include digoxin, beta blockers, and calcium channel blockers. These drugs are administered to control the ventricular rate, minimize symptoms, Figure 1. Heart in atrial fibrillation. and reduce the likelihood of complications. Another option recommended is either elec- trical or chemical . A patient disease, valvular disease, chronic lung dis- undergoing an electrical cardioversion expe- ease, heart failure, cardiomyopathy, congeni- riences an electrical shock synchronized with tal heart disease, pulmonary embolism, hyper- the intrinsic activity of the heart, whereas in thyroidism, pericarditis, and viral infection. a chemical cardioversion, medications are ad- Atrial fibrillation may also be related to alco- ministered either intravenously or orally in an hol consumption, excessive caffeine intake, attempt to convert the heart rhythm to sinus stress, and electrolytic or metabolic imbal- rhythm. ance. In 10% of the cases, there is no underly- Device therapy is another intervention used 2–4 ing heart disease. for treating atrial fibrillation. Patients may The 3 detrimental sequelae associated with have an implantable atrial defibrillator in- atrial fibrillation are loss of atrial transport serted to treat the symptoms. The defibrillator function, irregular rhythm, and risk of em- 3 6 can be preprogrammed to identify an episode bolic events. Gage and associates state that of atrial fibrillation. It may also be manu- the major morbidity of atrial fibrillation is at- ally controlled by the patient to turn the de- tributable to left atrial thrombus formation vice on when symptoms occur to treat atrial and subsequent thromboembolic events, es- fibrillation. A permanent pacemaker may be pecially embolic stroke. implanted to mange the arrhythmia and im- prove the heart function. TREATMENT OPTIONS FOR ATRIAL Another treatment option for atrial fibril- FIBRILLATION lation is catheter . began as an experimental attempt to recre- The optimal treatment for atrial fibrilla- ate the Cox Maze III procedure. The goal of tion depends upon the proper understand- ablation therapy in atrial fibrillation is either ing of the electrophysiological basis of its to improve symptoms or to decrease atrial Surgical Approaches for Atrial Fibrillation 235

Figure 2. Catheter ablation procedure. thrombus formation and subsequent embolic tion with pacemaker implantation is an effec- events (Fig 2). tive therapeutic approach that relieves car- However, since 1994, the catheter ablation diac symptoms associated with a rapid and procedure has undergone procedural changes irregular rhythm. This approach can also im- and techniques because of recent advances prove left ventricular function in patients in understanding of the pathophysiology of with tachycardia-induced cardiomyopathy.10 atrial fibrillation and the contributions of the Jordaens11 states that the constraints of the pulmonary veins to the initiation and main- atrioventricular junctional ablation with pace- tenance of atrial fibrillation.8 As a result, 3 maker implantation include the inevitable pulmonary vein ablation techniques—termed need for anticoagulation therapy, loss of atri- segmental pulmonary vein isolation, circum- oventricular synchrony, and lifelong pace- ferential pulmonary vein ablation, and circum- maker dependency. Possible complications of ferential pulmonary vein isolation9—are uti- catheter ablation for atrial fibrillation include lized for catheter ablation of atrial fibrillation. systemic thromboembolism, pulmonary vein Interventional procedures are required for pa- stenosis, pericardial effusion, cardiac tampon- tients with atrial fibrillation and for patients ade, and phrenic nerve paralysis.11 with a rapid ventricular response that can- Surgical treatment for atrial fibrillation in- not be controlled with drugs. Radiofrequency cludes the Cox Maze, the modified maze, and catheter ablation of the atrioventricular junc- “keyhole”and minimally invasive approaches. 236 CRITICAL CARE NURSING QUARTERLY/JULY–SEPTEMBER 2007

Surgical treatment is considered when tradi- tion block without the standard cut-and-sew tional medical management proves ineffec- techniques. Given this surgical technique, the tive, medication or anticoagulation tolerance procedure can be performed more rapidly and exists, embolic events occur, or coexisting by an increasing number of surgeons. heart conditions exist. As a result of positive outcomes from the Patients undergoing the Cox Maze pro- Cox Maze procedure, surgical ablation plays cedure, also known as the “cut and sew” a significant role in curing atrial fibrillation maze, experience a traditional surgical in- in patients undergoing concomitant cardiac cision, where the sternum is opened, and surgical procedures. This has been attributed are placed on the cardiopulmonary bypass to the simplification of the surgical interven- machine. During the procedure, a series of tion, which has resulted in a reduction of precise incisions are made in the right and operating time and complications. Gait and left atria to create lines of conduction block associates14 state that although various tech- to stop electrical impulses from forming. In niques have been proposed, it is noteworthy more than 90% of the patients, the classic Cox that the posterior part of the and the Maze cures atrial fibrillation7; however, the osteo of the pulmonary veins are involved in procedure takes 1 hour to complete. Since all approaches despite variations in energy 1996, technological and procedural modifi- sources (ie, radiofrequency or cryoenergy) cations of the Cox Maze procedure resulted and intended lesion designs. in other surgical approaches for the treat- However, this procedure is not without ment of atrial fibrillation. These approaches complications such as atrioesophagus fistula reduce the number of incisions that com- and coronary damage.14 It is recommended prise the Cox Maze procedure and create a that surgical ablation be more routinely per- more limited lesion set around the pulmonary formed in patients with permanent or inter- vein orifices with various alternate energy mittent atrial fibrillation undergoing cardiac sources that prevent the need to cut and sew surgery. However, procedural and technolog- the atrial wall. For patients who have atrial ical modifications have enabled minimally in- fibrillation and are undergoing open heart vasive surgical ablation in patients with LAF. surgery for valvular or bypass grafting surgery, many surgeons prefer to use a modified maze SURGICAL PROCEDURE: DIFFERENCE (Fig 3). BETWEEN MAZE AND MINIMAZE The modified maze is also called surgical pulmonary vein isolation. Under direct obser- The original Cox Maze procedure under- vation, an alternate energy probe of choice, went significant modifications that included a such as , laser, microwave, or ra- more extensive use of cryosurgery and avoid- diofrequency, is used to create the lesion lines ance of excision of the left atrial appendage.13 of conduction block and promote the normal As described by Ad and Cox,12 the origi- conduction of impulses through the proper nal Cox Maze III procedure included a 30- pathway. During this procedure, the left atrial to 40-cm median sternotomy and approxi- appendage is excised and the tissue is closed mately 12 incisions in the two atria, includ- with a stapler. The average surgical time is ing excision of the left and right atria ap- 15 to 20 minutes and it restores normal sinus pendages and the pulmonary veins surgically rhythm in 75% to 85% of patients.12–15 isolated. The surgical procedure is based on Thermal techniques, such as ultrasound, the principle of the development of a maze. laser, microwave, and radiofrequency, for Appropriately placed atrial incisions interrupt atrial ablation have been dominant in the the conduction routes of the most common resurgence of surgical procedures for the reentrant circuits and direct the electrical im- treatment of atrial fibrillation. These alter- pulses to the atrioventricular node.7 Modifica- nate energy sources create lines of conduc- tions to the original Cox Maze III procedure Surgical Approaches for Atrial Fibrillation 237

Figure 3. (a) Medial sternotomy for open heart. (b) Modified maze procedure. (c) One type of isolator used in modified maze. resulted in a new minimally invasive, cryosur- The development of minimally invasive gical approach with a smaller chest wall in- surgery has led to epicardial ablation of atrial cision, a 7-cm right minithoracotomy, lesser fibrillation and even removal of the left atrial and smaller atriotomies, left atrial appendage appendage without entering the heart.8,16 In not excised, and the remainder of the pro- this thorascopic approach, the surgeon views cedure performed with specifically designed the epicardial surface of the heart using an en- cryoprobes.7,12,13 doscope. Specialized instruments are used to 238 CRITICAL CARE NURSING QUARTERLY/JULY–SEPTEMBER 2007

Three small incisions are made on each side of the chest wall. Wolf uses an Isolator clamp, a bipolar radiofrequency clamp, to ablate and electrically isolate the pulmonary veins bilat- erally, where the triggers that initiate atrial fib- rillation are located. With the Isolator clamp, the average time an ablation can be performed is 8 seconds. The ablation part of the proce- dure is the endoscopic exclusion of the left atrial appendage. The left atrial appendage is a suspected major source of cardioem- bolic stroke in patients with atrial fibrillation (Figs 5 and 6). This procedure and technology are de- signed to treat patients who have long- standing or chronic intermittent atrial fib- rillation and are nonresponsive or experi- Figure 4. Thorascopic approach for minimally in- ence intolerance to pharmacologic treatment. vasive minimaze. The Wolf minimaze is specifically focused on treating atrial fibrillation as a stand-alone isolate the pulmonary veins and create lines condition, that is, LAF/atrial flutter with of conduction block. The benefit of this pro- no other heart problems. Some advantages cedure is that the patient is not placed on car- of the minimaze are avoidance of a ster- diopulmonary bypass12,13 (Fig 4). notomy, cardiopulmonary bypass, and cardio- Ronald K. Wolf, a cardiothoracic surgeon, plegic arrest intraoperatively, a shorter and developed the minimaze, a minimally inva- less painful recovery, and decrease in medica- , sive surgical procedure for the treatment of tion reactions.12 18 atrial fibrillation.17 The minimaze is a video- assisted bilateral pulmonary vein isolation and PATIENT SELECTION FOR SURGICAL left atrial appendage exclusion for atrial fib- TREATMENT rillation. The minimaze procedure combines an ablation method and the Cox Maze proce- Fuster and associates2 state that the ini- dure without performing open heart surgery. tial clinical evaluation of a patient with

Figure 5. An example of a radiofrequency clamp used in minimaze. Surgical Approaches for Atrial Fibrillation 239

and/or coexisting valvular or . For the minimally invasive surgical ablation, that is, “keyhole”and thorascopic ap- proach or the Cox Maze procedure, patients need to have a history of either isolated or in- termittent atrial fibrillation. In both the “key- hole” and thorascopic approaches, the surgi- cal technique includes isolation of the pul- monary veins and left atrial excision.13 For patients undergoing a Wolf minimaze procedure, patient selection criteria can in- clude the following: man or woman aged be- tween 18 and 80; have a drug refractory atrial fibrillation; experience an intolerance of an- tiarrhythmic drugs or Coumadin; have left ventricular ejection fraction of 30% to 35%, which is determined by performed within 60 days; a transesophageal electrocardiogram confirms lack of thrombus Figure 6. Minimally invasive minimaze bilateral in the left atrial appendage; a left atrial size scars. less than or equal to 6 cm; life expectancy of at least 2 years; compliance with returning for follow-up visits; tolerance to single lung venti- suspected or proved atrial fibrillation in- lation; and body mass index less than or equal cludes characterizing the pattern of the ar- to 28 to 32. rhythmia as paroxysmal or persistent, de- termining the etiology, and defining the as- sociated cardiac and extracardiac factors. POSTOPERATIVE AND FOLLOW-UP CARE This is accomplished by a thorough history and physical examination, review of current Postprocedure for the Cox Maze, modified problems, pulmonary function, electrocardio- minimaze, and/or minimaze, the patient is gram, echocardiogram, Test, transferred to the critical care unit for close chest x-ray, and other diagnostic testing as cardiac monitoring for 24 to 48 hours. Upon required. admission to the unit, the patient’s endotra- As noted by Nitta,15 indications for surgery cheal tube is connected to the ventilator, but include patients with atrial fibrillation usually the patient is able to be extubated 5 associated with structural heart disease to 6 hours postoperatively. Depending upon who undergo cardiac surgical procedures; the surgeon’s postoperative orders, the pa- high-risk patients susceptible to systemic tient may be required to lie in supine position thromboembolic complications related to for 4 to 6 hours. left atrial thrombi; patients with failure or Chest tubes, which are inserted in stab recurrence following one or more catheter wounds distant from the primary surgical in- ablation procedures; and patients with intol- cision to reduce the risk of infection, are erable symptoms or an impaired quality of monitored by the nurse. Thoracic cavity man- life due to atrial fibrillation. agement consists of assessing and evaluating Candidates considered for the Cox Maze are the chest drainage system for the type and patients with isolated atrial fibrillation espe- amount of drainage from the chest tubes. The cially after failed percutaneous ablation, con- nurse performs respiratory assessments and tinual atrial fibrillation and/or enlarged atria, observes for complications such as tension 240 CRITICAL CARE NURSING QUARTERLY/JULY–SEPTEMBER 2007 pneumothorax, redness around the insertion failure, reoperation for bleeding, mediastini- site, or hemorrhagic shock. tis, stroke, and balloon pump insertion. The In providing wound management, initially, a Cox Maze III has equivalent operative risks surgically sutured wound is not disturbed un- and long-term efficacy for patients undergo- less there is drainage present. However, the ing both LAF operations and concomitant nurse must assess the appearance of the inci- procedures.19 However, the Cox Maze proce- sion and observe for inflammation, drainage, dure remains the standard against which alter- and/or swelling and notify the surgeon if any native procedures for atrial fibrillation must of these signs are present. When the pri- be judged.13 Postoperatively, an early com- mary dressing is removed, the wound is kept plication of the Cox Maze is fluid retention, cleaned and assessed each shift for any com- which is treated by fluid management and plications. diuretics. Other complications are bleeding, While in the unit, the patient is monitored wound infection, stoke, and pneumonia. for excessive pain, fluid retention, hemody- Throughout the hospitalization, the patient namic changes, blood loss, arrhythmias, signs is initially followed by the cardiac surgeon. of pericarditis, infection, elevated tempera- Upon discharge, patient instructions include, ture, and changes in neurological status. Any but are not limited to, notifying the referring changes in the clinical parameters are re- physician or cardiologist immediately if symp- ported to the cardiac surgeon immediately. tomatic from atrial fibrillation; a temperature When hemodynamically stable, the patient is of more than 100 degrees Fahrenheit; and transferred to a telemetry unit for further ob- redness, swelling, or drainage at the incision servation. site. Typical medications include antiarrhyth- Posthospitalization, the patient is followed mic drugs, anticoagulant therapy, diuretics, up by the cardiac surgeon and the patient’s re- steroids, and pain medication. Postopera- ferring physician or cardiologist. The patient tively, the patient may experience short is seen by the cardiac surgeon in 1 to 3 weeks, episodes of atrial fibrillation or skipped heart- postdischarge, to inspect the incision sites. beats. This is common due to the inflamma- The referring physician or cardiologist follows tion of the atrial tissue and is treated with an- the patient to monitor his/her heart rhythm. tiarrhythmic medication. In some cases, the By 3 months, the patient is weaned off an- treating surgeon and/or cardiologist may rec- tiarrhythmic and anticoagulant medications ommend cardioversion to control the persis- depending on the efficacy of treatment. It is tent atrial fibrillation if the patient does not re- recommended that an electrocardiogram be spond to pharmacological intervention, prior performed at 3, 6, and 12 months after surgery to discharge. However, after the incisions on and then annually. At 3- and 12-month periods, the heart have healed, the atrial fibrillation posthospitalization, Szaley and colleagues20 should subside. Approximately 6% of patients state that additional diagnostic studies and may require a pacemaker because of an un- evaluations may be requested, such as a stress derlying rhythm such as sinus sick syndrome electrocardiogram and a 24-hour electrocar- or heart block.13 diogram to detect bradycardic episodes and to Depending upon the surgeon’s preferences assess the effect of exercise on the patient’s and the patient’s response to therapy, the pa- heart rate and a electrophysiological evalua- tient may be discharged within 2 to 3 days tion to measure sinus node recovery and to postprocedure for the minimaze and 5 to provoke atrial fibrillation or atrial flutter. As 7 days depending on the surgical approach, noted by Szaley and associates,20 echocardio- such as a Cox Maze with open heart surgery, graphy and magnetic resonance imaging may and the patient’s response to treatment. be ordered to classify atrial transport function Major complications for LAF operations or and determine whether anticoagulation could as a concomitant procedure include renal be discontinued. Surgical Approaches for Atrial Fibrillation 241

Successful results of the maze procedure the presence of preoperative are long-term cure from atrial fibrillation; stenosis. decreased symptoms such as fatigue and dyspnea; decreased incidence of embolic CONCLUSION events; decreased atrial size in patients with an enlarged atria preoperatively, particu- There are many treatment options for atrial larly those who undergo the maze with a fibrillation, but when traditional medical man- mitral ; improved cardiac agement fails, surgical interventions, such as ejection fraction; and the discontinuation the Cox Maze and Wolf minimaze, provide al- of Coumadin. In reviewing the long-term ternatives for these patients that previously effectiveness of the Cox Maze III procedure did not exist.12 The underlying etiology that for lone versus concomitant procedures for promotes and sustains atrial fibrillation is an atrial fibrillation, a study performed by Prasad important factor in selection of the appropri- and associates1 noted the following: only 4 ate arrhythmic intervention. The understand- (4.1%) of 98 patients in the lone group were ing of the pathophysiology of atrial fibrilla- in atrial fibrillation at follow-up and 2 (2.5%) tion has led to continual improvements in the of 79 patients were in atrial fibrillation in the treatment of this arrhythmia.7 Given the tech- concomitant group. Szaley and colleagues20 nological improvements and procedural mod- stated that the following preoperative predi- ifications to the original Cox Maze procedure, cators for failure of a concomitant minimaze patients are experiencing faster, simpler, and operation for symptomatic chronic atrial minimally invasive approaches.18,19 As these fibrillation were longer duration of preop- procedural and technological changes con- erative atrial fibrillation; increased left atrial tinue to be developed, these new approaches diameter; increased right atrial diameter; will be assessed and evaluated on their ability reduced left ventricular function; increased to continue to reduce morbidity and mortality left ventricular end-diastolic diameter; and and effectively treat atrial fibrillation.

REFERENCES

1. Prasad SM, Maniar HS, Camillo CJ, et al. The Cox maze 7. Cox JL. Surgical treatment of atrial fibrillation: a re- procedure for atrial fibrillation: long-term efficacy in view. Europace. 2004;5(suppl 1):S20–S29. patients undergoing lone versus concomitant proce- 8. Marine JE, Dong J, Calkins H. Catheter ablation dures. J Thorac Cardiovasc Surg. 2003;126(6):1822– therapy for atrial fibrillation. Prog Cardiovasc Dis. 1828. 2005;48(3):178–192. 2. Fuster V, Ryden LE, Asinger RW, et al. ACC/AMA/ESC 9. Dong J, Calkins H. Technology insight: catheter ab- guidelines for the management of patients with lation of the pulmonary veins in the treatment of atrial fibrillation. J Am Coll Cardiol. 2001;38:1231– atrial fibrillation. Nat Clin Pract Cardiovasc Med. 1265. 2005;2(3):159–166. 3. Go AS, Hylek EM, Phillips KA, et al. Prevalence 10. Gonzalez MD. Rate control versus pulmonary vein of diagnosed atrial fibrillation in adults. JAMA. isolation. Am J Geriatr Cardiol. 2005;14(10):26–30. 2001;285:2370–2375. 11. Jordaens L. Treatment of atrial fibrillation by catheter- 4. Benussi S. Treatment of atrial fibrillation. Eur J Car- based procedures. Europace. 2004;5(suppl 1):S30– diothorac Surg. 2004;26S1:S39–S41. S35. 5. Bloom HL. Concise review of atrial fibrillation: 12. Ad N, Cox J. The Maze procedure for the treatment treatment update consideration in light of AF- of atrial fibrillation: a minimally invasive approach. J FIRM and RACE. Clin Cardiol. 2004;27(9):495– Cardiac Surg. 2004;19:196–200. 500. 13. Cox JL. The minimally invasive Maze III procedure. J 6. Gage BF, Cardinalli AB, Alberts GW, et al. Cost effec- Thorac Cardiovasc Surg. 2000;5:79–92. tiveness of warfarin and aspirin for prophylaxis of 14. Gaita F, Riccardi R, Gollotti R. Surgical approaches stroke in patients with non-vascular atrial fibrillation. to atrial fibrillation. Cardiac Electrophysiol Rev. JAMA. 1995;274:1839. 2002;6(4):401–405. 242 CRITICAL CARE NURSING QUARTERLY/JULY–SEPTEMBER 2007

15. Nitta T.Surgery for atrial fibrillation. Ann Thorac Car- 18. Gillinov AM, Wolf RK. Surgical ablation of atrial fib- diovasc Surg. 2005;11(3):154–158. rillation. Prog Cardiovasc Dis. 2005;3:169–177. 16. Lemery R, Guiraudon G. Catheter and surgical ab- 19. Gillinov AM, McCarthy PM. Advances in the sur- lation strategies in atrial fibrillation: what have we gical treatment of atrial fibrillation. Cardiol Clin. learned? Cardiology. 2005;20(1):26–30. 2004;22(1):47–57. 17. Wolf RF. Lecture: Demonstration at West Penn Al- 20. Szalay ZA, Skwara W, Klovekorn WP, et al. Predictors legheny Health System/Allegheny General Hospital. of failure to cure atrial fibrillation with the mini-maze Pittsburgh, Pa; 2005. operation. J Cardiac Surg. 2004;19:1–6.