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The significance of atrial fibrillation ablation in patients undergoing mitral valve surgery
The Significance of Atrial Fibrillation Ablation in Patients Undergoing Mitral Valve Surgery Niv Ad and James L. Cox Atrial fibrillation is present in close to 50% of all patients undergoing surgery for mitral valve disease.1-3 However, surgical correction of atrial fibrillation in patients with other cardiac pathology that requires surgical intervention such as mitral valve disease was never considered as a standard approach. The Maze procedure for the treatment of atrial fibrillation was introduced in 1987 and was performed safely in hundreds of patients with excellent outcomes.4-7 As a result, several centers have begun to combine the Maze procedure with other cardiac procedures, especially mitral valve surgery, without adding undue operative risk to patients.8 When properly performed, the results with this combined approach have been excellent.9,10 Copyright 2002, Elsevier Science (USA). All rights reserved.
A
trial fibrillation is the most common sustained arrhythmia with an incidence of 1% of the general population and 4% of those above the age of 60 years. Atrial fibrillation has been identified as one of the most powerful independent risk factors predisposing for stroke. It also has a significant impact on longevity, approximately doubling all causes of cardiovascular mortality.11-16 It is clear today that there is also a direct impact on the quality of life of patients who have paroxysmal or chronic atrial fibrillation.17 Thus, atrial fibrillation should be treated aggressively when possible and the Maze procedure should be applied when ever indicated and safe.
Mitral Valve Surgery Since the first successful prosthetic mitral valve replacement in 1959,18 mitral valve surgery has become a common cardiac procedure and probably one of the single most important developments in the care of cardiac patients. Since then, different types of prosthetic valves have been used, including both biological and mechanical. Although a tremendous amount of research and development have been invested in finding the From Hadassah University Hospital, Jerusalem, Israel, and The World Heart Foundation, Washington, DC. Address reprint requests to Niv Ad, MD, Thoracic and Cardiovascular Surgery, Hadassah University Hospital, Jerusalem 91120, Israel. Copyright 2002, Elsevier Science (USA). All rights reserved. 1043-0679/02/1403-$35.00/0 doi:10.1053/stcs.2002.35290
perfect prosthetic valve, one with long durability, low thrombogenicity, and very good hemodynamic properties is yet to be found. Today the prosthetic valves that are most commonly used are the bileaflet mechanical valves and the Hancock and the Carpentier-Edwards heterografts.19 In 1971, Carpentier et al introduced an advanced technique of valve repair20 with a physiologic classification of mitral insufficiency that serves as the basis of our current understanding of the pathophysiology of mitral insufficiency and of contemporary repairative techniques. Early in the 20th century, various operative techniques for mitral stenosis were used until the mid-40s when Harken et al and Baily reintroduce the closed mitral commissurotomy that was suggested first in 1925 by Soutar.21,22 This technique was further improved through its evolution into an open commissurotomy using the heart lung machine, and finally, the balloon mitral valvuloplasty, which is usually possible for early mitral stenosis.23
Indications for Mitral Valve Surgery During the last decade, the indications for surgical intervention in patients with mitral insufficiency have been evolved owing to a better understanding of the pathophysiology and the advancement in mitral valve repair.24 Currently, asymptomatic patients are considered operative candidates when the left ventricular function begins to deteriorate. Waiting for a patient to progress to functinal class III often prolongs left ventricular overload and causes permanent left
Seminars in Thoracic and Cardiovascular Surgery, Vol 14, No 3 ( July), 2002: pp 193-197
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ventricular dysfunction. This causes an increased operative morbidity and mortality when surgery is then performed.25 Clearly, surgical intervention should precede irreversible left ventricular dysfunction.26 The indications for surgical intervention in mitral stenosis are based on the severity of the stenosis and the symptoms of the patients.27 During the past few years, cardiac rhythm combined with left atrial size has been recognized to be an important factor in determining the optimal timing for mitral valve surgery, and, as a result, surgical intervention is taking place at earlier stages in the disease. This earlier intervention has also been accompanied by the recognition that the quality of life and the prognosis of the patients are much better if sinus rhythm can be maintained postoperatively. Thus, paroxysmal atrial fibrillation now serves as a relative indication for earlier surgical intervention for mitral valve disease, especially in young patients.28,29
Complications After Mitral Valve Surgery Despite advances in design and material selection, none of the currently available prosthetic or bioprosthetic heart valves approaches the normal human valve in either hemodynamic characteristics, longevity, or freedom from valve-related complications. Among the most significant valverelated complications are thromboembolism and bleeding events secondary to anticoagulation. Thromboembolism and hemorrhage are the most frequent mechanical valve complications and constitute nearly 75% of all valve-related complications.30 Valve thrombsis secondary to left atrial thrombus formation may be a fatal complication if detected late. During the last few years, many studies have been conducted to assess the incidence of such a complication and the risk factors for its occurrence. Patients who present to surgery with an enlarged left atrium and a history of paroxysmal or chronic atrial fibrillation have a higher risk for left atrial thrombus formation and an associated systemic thromboembolic event.31 Independent predictors of left atrial thrombus formation in patients after mitral valve replacement include atrial fibrillation, postoperative left atrial spontaneous echo contrast, preoperative thrombus, and mitral valve prosthesis. Furthermore, a high prevalence
of postoperative left atrial spontaneous echo contrast and thrombi has been documented in patients with a mechanical valve prosthesis and atrial fibrillation. Patients with a mitral valve prosthesis may be asymptomatic, and anticoagulation intensity is unrelated to the occurrence of postoperative left atrial spontaneous echo contrast and thrombi.31,32 Exclusion of the left atrial appendage may reduce the risk of left atrial thrombus formation but does not eliminate it in patients with an enlarged left atrium and chronic atrial fibrillation.33,34 Anticoagulation-related bleeding after prosthetic valve replacement with a mechanical valve occurs at a rate of 0.3 to 4.9 events per patient year and is unrelated to the valve position, although there are some differences between the different mechanical valve used.35 Patients who have a bioprosthetic prosthesis in the mitral position have fewer thromboembolic events (1.4 to 1.9 per patient year) and bleeding episodes (0.6 to 2.1 per patient year).31 Unlike the mechanical valves, the incidence of bleeding in patients with a bioprosthesis in the mitral position is higher than for the aortic position. This is probably owing to the fact that many patients in the mitral group require life-long anticoagulation for chronic atrial fibrillation.36
How Should We Approach Patients With Combined Mitral Valve Disease and Atrial Fibrillation? The existence of operative tools to treat atrial fibrillation make it possible to offer a better surgical solution for patients who have combined atrial fibrillation and mitral valve disease. However, there are a few unresolved issues: Should the Maze procedure be performed in patients undergoing mitral valve replacement? Which ablation protocol should be used? Which energy source is the safest and most effective in achieving reliable ablation lines? What, if any, are the contraindications for a combined procedure?
Should the Maze Procedure be Performed in Patients Undergoing Mitral Valve Replacement? Atrial fibrillation, atrial size, and flow pattern in the atria are all interrelated and have a negative
Atrial Fibrillation Ablation
impact on the long-term morbidity and mortality of patients after mitral valve replacement.30-32 Moreover, the basic design of prosthetic valves, especially the modern mechanical valves, is based on the prosthetic’s performance during sinus rhythm and the fact that the leaflets and their hinge mechanisms are being washed with every cardiac cycle. Unfortunately, these valves are not “washed” properly on every cardiac cycle when the patient is in atrial fibrillation and as a result, they are more prone to thrombosis than when the patient is in normal sinus rhythm. Using this logic, it seems obvious that all patients with atrial fibrillation who require a mitral valve replacement should have the Maze procedure performed concomitantly unless otherwise contraindicated.
Which Ablation Protocol Should Be Used? During the past several years, at least 2 major observations regarding atrial fibrillation have had a direct impact on the intraoperative techniques that have been used to treat atrial fibrillation. The first is that when the Maze procedure is properly performed, it cures atrial fibrillation in nearly 100% of patients with or without mitral valve disease.9,10 The second is that the majority of paroxysmal atrial fibrillation originates within the orifices of 1 or more of the pulmonary veins.37 Thus, to our knowledge, all of the techniques now being used to treat atrial fibrillation during mitral valve surgery incorporate some combination of the linear lesions of the Maze procedure with isolation of 1 or more of the pulmonary vein orifices. Unfortunately, the scientific basis of these various approaches is somewhat less than completely sound, and the success rate of the different modifications of the Maze procedure is less than optimal, especially in patients with large atria and chronic atrial fibrillation. The attempts at ablating atrial fibrillation during mitral valve surgery should be encouraged. However, surgeons should make every effort to ensure that the lesions they create are transmural in every instance and that they follow the known electrophysiologic principles relating to atrial fibrillation. Otherwise, the operation is doomed to a high rate of failure.38,47
195
Which Energy Source Is the Safest and Most Effective in Achieving Reliable Ablation Lines? The basic principle of arrhythmia surgery is that fibrocytes will not conduct electrically.39 Indeed, if the operative goal is to create a complete permanent block in the atrium, such a line should be continuous and transmural or else electrical activity can traverse the line of the lesion.38 When the Maze procedure was originally developed, it was based on the use of a “cut-and-sew technique.” With such a technique, the surgeon could be absolutely certain that each and every atrial lesion was transmural. However, it is clear that the classical surgical Maze III procedure is too complex to be applied on a routine basis. As a result, we attempted to find a surgical approach that would not violate the basic principles of the Maze procedure but would be much simpler to perform. This evolved into our use of cryosurgery rather than the cut-and-sew technique because we could accurately reproduce the atrial lesion pattern of the Maze procedure with 100% certainty that each and every lesion was transmural. Moreover, cryosurgery was known to be very safe (it is the only ablative energy source that preserves collagen tissue) and very fast.40-42 The major drawback to using other energy sources such as radiofrequency, microwave, and laser is that there is no way to document at the time of lesion application that the lesions are transmural. Studies have been performed to relate the depth of a lesion to the energy expended, time of application, and the temperature at the probe tip,43-45 but the fact remains that there is simply no real time method of being certain that a given lesion is transmural using these energy sources.
Are There Any Contraindications for a Combined Procedure? There are no absolute contraindications to performance of the Maze procedure, although our experience showed that the following patients are at a higher risk for the procedure. Patients who are at high risk for the use of cardiopulmonary bypass in general, such as patients with renal failure or pulmonary hypertension, are also at a higher risk for postoperative complications after the Maze procedure. Al-
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though much more quickly performed with the newer technologies, the Maze procedure is still time-consuming, and its application in combination with other cardiac procedures will result in a longer operation. There are a few reports that the Maze procedure is ineffective in patients with large atria.46 We find this statement puzzling because the solution is so intuitive if one understands the basis of the Maze procedure. The same lesion pattern is used in all patients regardless of atrial size. In normal or moderately enlarged atria, the lesions are close enough together that all potential macro-reentrant circuits in the atria are abolished, thereby making it impossible for the atria to fibrillate. However, in grossly enlarged atria, this same lesion pattern will result in lesions that are so far apart that macro-reentrant circuits can form between them and the operation simply does not work. In such enlarged atria, it is essential to resect strips of atrial wall before closing the atriotomies so that on completion, the atria are relatively normal in size. The Maze pattern is then just as effective in these patients as in those with normal-sized atria.
Summary The attempts at ablating atrial fibrillation during mitral valve surgery using multiple energy sources that are easy to handle and quick to apply are to be strongly encouraged. However, surgeons should make every effort to ensure that the lesions they create are transmural in every instance, or else the operation is doomed to a high rate of failure.38 Further, until less complex patterns of atrial lesions have been shown to be as effective as the Maze procedure, we believe that the design of the lesions applied during surgery should conform as closely as possible to the pattern of the Maze procedure. With minor modifications, the Maze procedure can now be performed with the use of linear cryoprobes to ensure transmurality without substantially increasing the complexity or the duration of mitral valve surgery and with expectation that more than 95% of the atrial fibrillation associated with the mitral valve disease will be cured. That should be the goal of any other energy source and of any other pattern of atrial lesions.
References 1. Chua YL, Orszulak TA, Moris JJ: Out come of mitral valve repair in patients with preoperative atrial fibrillation: Should the maze procedure be combined with mitral valvuloplasty? J Thorac Cardiovasc Surg 107:408-415, 1994 2. Obadia JF, el Ferra M, Bastien OH, et al: Outcome of atrial fibrillation after mitral valve repair. J Thorac Cardiovasc Surg 114:179-185, 1997 3. Jessurun ER, van Hemel NM, Kelder JC, et al: Mitral valve surgery and atrial fibrillation: Is atrial fibrillation surgery also needed? Eur J Cardiothorac Surg 17:530-7.: 628-35. 2000 4. Cox JL, Boineau JP, Schuessler RB, et al: Five-year experience with Maze procedure for atrial fibrillation. Ann Thorac Surg 55:578-580, 1993 5. Arcidi JM, Doty DB, Millar RC: The Maze Procedure: The LDS hospital experience. Semin Thorac Cardiovasc Surg 12:38-43, 2000 6. Schaff HV, Dearani JA, Daly RC, et al:Cox Maze procedure for atrial fibrillation: Mayo Clinic Experience. Semin Thorac Cardiovasc Surg 12:30-37, 2000 7. McCarthy PM, Gillinov AM, Castle L, et al: The Cox maze procedure: The Cleveland Clinic Experience. Semin Thorac Cardiovasc Surg 12:25-29, 2000 8. Izumoto H, Kawazoe K, Kitahara H, et al: Can the Maze procedure be combined safely with mitral valve repair? J Heart Valve Dis 6:166-170, 1997 9. Hanada N, Schaff HV, Morris JJ, et al: Outcome of valve repair and the Cox maze procedure for mitral regurgitation and associated atrial fibrillation. J Thorac Cardiovasc Surg 118-124, 1999 10. Cox JL, Ad N, Palazzo T, et al: The Maze III procedure combined with valve surgery. Semin Thorac Cardiovasc Surg 12:53-55, 2000 11. Wolf PA, Abott RD, Kannel WB. Atrial fibrillation as an independent risk factor for stroke: The Framingham Study. Stroke 22:983-988, 1991 12. Risk factors for stroke and efficacy of antithrombotic therapy in atrial fibrillation. Aanlysis of pooled data from five randomized controlled trials. Arch Intern Med 154: 1449-1457, 1998 13. Hart RG, Sherman DG, Easton JD, et al: Prevention of stroke in patients with nonvalvular atrial fibrillation. Neurology 51:674-681, 1998 14. Benjamin EJ, Wolf PA, D’Agostino BD, et al: Impact of atrial fibrillation on the risk of death: The Framingham Study. Circulation 98:946-952, 1998 15. Kannel WB, Abbort RD, Savage DD, et al: Epidemiologic features of chronic atrial fibrillation: The Framingham Study. N Engl J Med 306:1018-1022, 1982 16. Gajewski J, Singer RB: Mortality in an insured population with atrial fibrillation. JAMA 245:1540-1544, 1981 17. Bubien RS, Sanchez JE: Atrial fibrillation: Treatment rationale and clinical utility of nonpharmacological therapies. AACN Clin Issues 12:140-155, 2001 18. Braunwald NS, Cooper T, Morrow AG: Complete replacement of the mitral valve. J Thorac Surg 40:1-3, 1960 19. Muehrcke DD, Cosgrove DM: Mitral valvuloplasty, in Edmunds HL Jr (ed): Cardiac Surgery in the Adult. New York, McGraw-Hill, 1997, p 992
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20. Carpantier A, Deloche A, Dauptain J: A new reconstructive operation for correction of mitral and tricuspid insufficiency. J Thorac Cardiovasc Surg 61:1-8, 1971 21. Harken DE, Ellis LB, Ware PF, et al: The surgical treatment of mitral stenosis:Valvuloplasty. N Engl J Med 239: 801, 1948 22. Baily CP: The surgical treatment of mitral stenosis (mitral commissurotomy). Dis Chest 15:377, 1949 23. Smith WM, Neutze JM, Barrat-Boyes BG, et al: Open mitral valvolotomy: Effect of reoperative factors on results. J Thorac Cardiovasc Surg 82:738-751, 1981 24. Mudge GH Jr: Asymptomatic mitral regurgitation: When to operate. J Cardiac Surg 9:248-251, 1994 (suppl) 25. Schuler G, Peterson KL, Johnson A, et al: Temporal response of left ventricular performance to mitral valve surgery.Circulation 59: 1218-1231, 1979 26. Zile MR: Chronic aortic and mitral regurgitation: Choosing the optimal time for surgical correction. Cardiol Clin 9:239-253, 1991 27. Carabello BA: Timing of surgery in mitral and aortic stenosis. Cardiol Clin 9:229-228, 1991 28. Mudge GH Jr: Asymptomatic mitral regurgitation: when to operate. J Cardiac Surg 9:248-251, 1994 (suppl) 29. Cosgrove DM, Stewart WJ: Mitral valvuloplasty. Curr Probl Cardiol 14:359-415, 1989 30. Edmunds LH Jr: Thrombotic and bleeding complication of prosthetic heart valves. Ann Thorac Surg 44:430-455, 1987 31. Butchart C: Thrombosis, embolism and bleeding, in Bohnar E, Frater R (eds): Replacement of Cardiac Valves. New York, McGraw Hill, 1992, p 77 32. Lee TM, Chou NK, Su SF, et al: Left atrial spontaneous echo contrast in asymptomatic patients with a mechanical valve prosthesis. Ann Thorac Surg 62:1790-1795, 1996 33. Johnson WD, Ganjoo AK, Stone CD, et al: The left atrial appendage: Our most lethal human attachment! Surgical implications. Eur J Cardiothorac Surg 17:718-722, 2000 34. Blackshear JL, Odell JA: Appendage obliteration to reduce stroke in cardiac surgical patients with atrial fibrillation. Ann Thorac Surg 61:755-759, 1996 35. Cohn LH, Lipson W: Selection of complications of cardiac valvular prostheses, in Baue AE, Geha AS, Hammond GL, et al (eds): Glenn’s Thoracic and Cardiovascular Surgery (ed 6). Stamford, CT, Appelton and Lange,1996, pp 20462047
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36. Burdon TA, Miller DG, Oyer PE, et al: Durability of porcine valves at fifteen years in a representative North American patient population. J Thorac Cardiovasc Surg 103:738-743, 1992 37. Haissagurerre M, Jais P, Shah DC, et al: Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. N Engl J Med 339:659-666, 1998 38. Thomas SP, Wallace EM, Ross DL: The effect of residual isthmus of surviving tissue on conduction after linear ablation in atrial myocardium. J Intervent Cardiol Electrophysiol 4:273-281, 2000 39. Cobb FR, Blumenschein SD, Sealy WC, et al: Successful surgical interruption of the bundle of Kent in patients with Wolf-Parkinson-White syndrome. Circulation 38: 1018-1029, 1968 40. WL Holman, Ikeshita M, Lease JG, et al: Alteration of antegrade atrioventricular conduction by cryoablation of peri-atrioventricular nodal tissue. J Thorac Cardiovasc Surg 88:67-75,1984 41. GM Guiraudon: Cryoablation, a versatile tool in arrhythmia surgery. Ann Thorac Surg 43:129-130,1987 42. Holman WL, Ikeshita M, Douglas JM Jr, et al: Cardiac cryosurgery: Effects of myocardial temperature on cryolesion size. Surgery 93:268-272, 1983 43. Erdogan A, Grubrecht S, Carlsson J, et al: Homogenicity and diameter of linear lesions induced with multipolar ablation catheters: in vitro and in vivo comparison of pulsed versus continuous radiofrequency energy delivery. J Intervent Cardiol Electrophysiol 4:655-661, 2000 44. Ndrepepa G, Schneider MA, Vallaint A, et al: Acute electrophysiologic effects and antifibrillatory actions of the long linear lesions the right atrium in a sheep model. J Intervent Cardiol Electrophysiol 4:529-536, 2000 45. Von Oppell UO, Rauch T, Hindricks G, et al: Effectiveness of two radiofrequency ablation system in atrial tissue. Euro J Cardiothorac Surg 20:956-960, 2001 46. Thomas SP, Nicholson IA, Nunn GR, et al: Radiofrequency lesions produced by handheld temperature controlled probes for use in atrial fibrillation surgery. Euro J Cardiothorac Surg 20:1188-1193, 2001 47. Kosakai Y: Treatment of atrial fibrillation using the Maze procedure: The Japanese experience. Semin Thorac Cardovasc Surg 12:44-52, 2000
A
trial fibrillation is the most common sustained arrhythmia with an incidence of 1% of the general population and 4% of those above the age of 60 years. Atrial fibrillation has been identified as one of the most powerful independent risk factors predisposing for stroke. It also has a significant impact on longevity, approximately doubling all causes of cardiovascular mortality.11-16 It is clear today that there is also a direct impact on the quality of life of patients who have paroxysmal or chronic atrial fibrillation.17 Thus, atrial fibrillation should be treated aggressively when possible and the Maze procedure should be applied when ever indicated and safe.
Mitral Valve Surgery Since the first successful prosthetic mitral valve replacement in 1959,18 mitral valve surgery has become a common cardiac procedure and probably one of the single most important developments in the care of cardiac patients. Since then, different types of prosthetic valves have been used, including both biological and mechanical. Although a tremendous amount of research and development have been invested in finding the From Hadassah University Hospital, Jerusalem, Israel, and The World Heart Foundation, Washington, DC. Address reprint requests to Niv Ad, MD, Thoracic and Cardiovascular Surgery, Hadassah University Hospital, Jerusalem 91120, Israel. Copyright 2002, Elsevier Science (USA). All rights reserved. 1043-0679/02/1403-$35.00/0 doi:10.1053/stcs.2002.35290
perfect prosthetic valve, one with long durability, low thrombogenicity, and very good hemodynamic properties is yet to be found. Today the prosthetic valves that are most commonly used are the bileaflet mechanical valves and the Hancock and the Carpentier-Edwards heterografts.19 In 1971, Carpentier et al introduced an advanced technique of valve repair20 with a physiologic classification of mitral insufficiency that serves as the basis of our current understanding of the pathophysiology of mitral insufficiency and of contemporary repairative techniques. Early in the 20th century, various operative techniques for mitral stenosis were used until the mid-40s when Harken et al and Baily reintroduce the closed mitral commissurotomy that was suggested first in 1925 by Soutar.21,22 This technique was further improved through its evolution into an open commissurotomy using the heart lung machine, and finally, the balloon mitral valvuloplasty, which is usually possible for early mitral stenosis.23
Indications for Mitral Valve Surgery During the last decade, the indications for surgical intervention in patients with mitral insufficiency have been evolved owing to a better understanding of the pathophysiology and the advancement in mitral valve repair.24 Currently, asymptomatic patients are considered operative candidates when the left ventricular function begins to deteriorate. Waiting for a patient to progress to functinal class III often prolongs left ventricular overload and causes permanent left
Seminars in Thoracic and Cardiovascular Surgery, Vol 14, No 3 ( July), 2002: pp 193-197
193
194
Ad and Cox
ventricular dysfunction. This causes an increased operative morbidity and mortality when surgery is then performed.25 Clearly, surgical intervention should precede irreversible left ventricular dysfunction.26 The indications for surgical intervention in mitral stenosis are based on the severity of the stenosis and the symptoms of the patients.27 During the past few years, cardiac rhythm combined with left atrial size has been recognized to be an important factor in determining the optimal timing for mitral valve surgery, and, as a result, surgical intervention is taking place at earlier stages in the disease. This earlier intervention has also been accompanied by the recognition that the quality of life and the prognosis of the patients are much better if sinus rhythm can be maintained postoperatively. Thus, paroxysmal atrial fibrillation now serves as a relative indication for earlier surgical intervention for mitral valve disease, especially in young patients.28,29
Complications After Mitral Valve Surgery Despite advances in design and material selection, none of the currently available prosthetic or bioprosthetic heart valves approaches the normal human valve in either hemodynamic characteristics, longevity, or freedom from valve-related complications. Among the most significant valverelated complications are thromboembolism and bleeding events secondary to anticoagulation. Thromboembolism and hemorrhage are the most frequent mechanical valve complications and constitute nearly 75% of all valve-related complications.30 Valve thrombsis secondary to left atrial thrombus formation may be a fatal complication if detected late. During the last few years, many studies have been conducted to assess the incidence of such a complication and the risk factors for its occurrence. Patients who present to surgery with an enlarged left atrium and a history of paroxysmal or chronic atrial fibrillation have a higher risk for left atrial thrombus formation and an associated systemic thromboembolic event.31 Independent predictors of left atrial thrombus formation in patients after mitral valve replacement include atrial fibrillation, postoperative left atrial spontaneous echo contrast, preoperative thrombus, and mitral valve prosthesis. Furthermore, a high prevalence
of postoperative left atrial spontaneous echo contrast and thrombi has been documented in patients with a mechanical valve prosthesis and atrial fibrillation. Patients with a mitral valve prosthesis may be asymptomatic, and anticoagulation intensity is unrelated to the occurrence of postoperative left atrial spontaneous echo contrast and thrombi.31,32 Exclusion of the left atrial appendage may reduce the risk of left atrial thrombus formation but does not eliminate it in patients with an enlarged left atrium and chronic atrial fibrillation.33,34 Anticoagulation-related bleeding after prosthetic valve replacement with a mechanical valve occurs at a rate of 0.3 to 4.9 events per patient year and is unrelated to the valve position, although there are some differences between the different mechanical valve used.35 Patients who have a bioprosthetic prosthesis in the mitral position have fewer thromboembolic events (1.4 to 1.9 per patient year) and bleeding episodes (0.6 to 2.1 per patient year).31 Unlike the mechanical valves, the incidence of bleeding in patients with a bioprosthesis in the mitral position is higher than for the aortic position. This is probably owing to the fact that many patients in the mitral group require life-long anticoagulation for chronic atrial fibrillation.36
How Should We Approach Patients With Combined Mitral Valve Disease and Atrial Fibrillation? The existence of operative tools to treat atrial fibrillation make it possible to offer a better surgical solution for patients who have combined atrial fibrillation and mitral valve disease. However, there are a few unresolved issues: Should the Maze procedure be performed in patients undergoing mitral valve replacement? Which ablation protocol should be used? Which energy source is the safest and most effective in achieving reliable ablation lines? What, if any, are the contraindications for a combined procedure?
Should the Maze Procedure be Performed in Patients Undergoing Mitral Valve Replacement? Atrial fibrillation, atrial size, and flow pattern in the atria are all interrelated and have a negative
Atrial Fibrillation Ablation
impact on the long-term morbidity and mortality of patients after mitral valve replacement.30-32 Moreover, the basic design of prosthetic valves, especially the modern mechanical valves, is based on the prosthetic’s performance during sinus rhythm and the fact that the leaflets and their hinge mechanisms are being washed with every cardiac cycle. Unfortunately, these valves are not “washed” properly on every cardiac cycle when the patient is in atrial fibrillation and as a result, they are more prone to thrombosis than when the patient is in normal sinus rhythm. Using this logic, it seems obvious that all patients with atrial fibrillation who require a mitral valve replacement should have the Maze procedure performed concomitantly unless otherwise contraindicated.
Which Ablation Protocol Should Be Used? During the past several years, at least 2 major observations regarding atrial fibrillation have had a direct impact on the intraoperative techniques that have been used to treat atrial fibrillation. The first is that when the Maze procedure is properly performed, it cures atrial fibrillation in nearly 100% of patients with or without mitral valve disease.9,10 The second is that the majority of paroxysmal atrial fibrillation originates within the orifices of 1 or more of the pulmonary veins.37 Thus, to our knowledge, all of the techniques now being used to treat atrial fibrillation during mitral valve surgery incorporate some combination of the linear lesions of the Maze procedure with isolation of 1 or more of the pulmonary vein orifices. Unfortunately, the scientific basis of these various approaches is somewhat less than completely sound, and the success rate of the different modifications of the Maze procedure is less than optimal, especially in patients with large atria and chronic atrial fibrillation. The attempts at ablating atrial fibrillation during mitral valve surgery should be encouraged. However, surgeons should make every effort to ensure that the lesions they create are transmural in every instance and that they follow the known electrophysiologic principles relating to atrial fibrillation. Otherwise, the operation is doomed to a high rate of failure.38,47
195
Which Energy Source Is the Safest and Most Effective in Achieving Reliable Ablation Lines? The basic principle of arrhythmia surgery is that fibrocytes will not conduct electrically.39 Indeed, if the operative goal is to create a complete permanent block in the atrium, such a line should be continuous and transmural or else electrical activity can traverse the line of the lesion.38 When the Maze procedure was originally developed, it was based on the use of a “cut-and-sew technique.” With such a technique, the surgeon could be absolutely certain that each and every atrial lesion was transmural. However, it is clear that the classical surgical Maze III procedure is too complex to be applied on a routine basis. As a result, we attempted to find a surgical approach that would not violate the basic principles of the Maze procedure but would be much simpler to perform. This evolved into our use of cryosurgery rather than the cut-and-sew technique because we could accurately reproduce the atrial lesion pattern of the Maze procedure with 100% certainty that each and every lesion was transmural. Moreover, cryosurgery was known to be very safe (it is the only ablative energy source that preserves collagen tissue) and very fast.40-42 The major drawback to using other energy sources such as radiofrequency, microwave, and laser is that there is no way to document at the time of lesion application that the lesions are transmural. Studies have been performed to relate the depth of a lesion to the energy expended, time of application, and the temperature at the probe tip,43-45 but the fact remains that there is simply no real time method of being certain that a given lesion is transmural using these energy sources.
Are There Any Contraindications for a Combined Procedure? There are no absolute contraindications to performance of the Maze procedure, although our experience showed that the following patients are at a higher risk for the procedure. Patients who are at high risk for the use of cardiopulmonary bypass in general, such as patients with renal failure or pulmonary hypertension, are also at a higher risk for postoperative complications after the Maze procedure. Al-
196
Ad and Cox
though much more quickly performed with the newer technologies, the Maze procedure is still time-consuming, and its application in combination with other cardiac procedures will result in a longer operation. There are a few reports that the Maze procedure is ineffective in patients with large atria.46 We find this statement puzzling because the solution is so intuitive if one understands the basis of the Maze procedure. The same lesion pattern is used in all patients regardless of atrial size. In normal or moderately enlarged atria, the lesions are close enough together that all potential macro-reentrant circuits in the atria are abolished, thereby making it impossible for the atria to fibrillate. However, in grossly enlarged atria, this same lesion pattern will result in lesions that are so far apart that macro-reentrant circuits can form between them and the operation simply does not work. In such enlarged atria, it is essential to resect strips of atrial wall before closing the atriotomies so that on completion, the atria are relatively normal in size. The Maze pattern is then just as effective in these patients as in those with normal-sized atria.
Summary The attempts at ablating atrial fibrillation during mitral valve surgery using multiple energy sources that are easy to handle and quick to apply are to be strongly encouraged. However, surgeons should make every effort to ensure that the lesions they create are transmural in every instance, or else the operation is doomed to a high rate of failure.38 Further, until less complex patterns of atrial lesions have been shown to be as effective as the Maze procedure, we believe that the design of the lesions applied during surgery should conform as closely as possible to the pattern of the Maze procedure. With minor modifications, the Maze procedure can now be performed with the use of linear cryoprobes to ensure transmurality without substantially increasing the complexity or the duration of mitral valve surgery and with expectation that more than 95% of the atrial fibrillation associated with the mitral valve disease will be cured. That should be the goal of any other energy source and of any other pattern of atrial lesions.
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