REVIEW ARTICLE
Te rationale of surgifmcal pulmonary vemin isolation for treatment
of
atrial fibrillation
R.E. Accord, T.J. van Brakel, J.G. Maessen
With the development of less invasive surgical approaches and new ablation techniques, surgical treatment of atrial fibrillation has gained increasing interest over the past decade. Contrary to the complex Maze procedure, new less laborious approaches with pulmonary vein isolation as the main focus are within the reach of most cardiothoracic surgeons. However, although important new pathophysiological mechanisms have emerged in recent years due to extensive basic and clinical research, several uncertainties and hurdles concerning this treatment modality remain. This artide reviews the rationale of surgical pulmonary vein isolation, based on these increased insights. Furthermore, important technical aspects including the possible advantages of an epicardial approach, the optimal left-sided lesion set and the need for transmurality are discussed in depth. (Neth Heart J2005;13:181-5.)
Keywords: atrial fibrillation, pulmonary vein ablation, arrhythmia surgery n recent years, the observation of ectopic activity
Ioriginating from the pulmonary veins has focused interest on left-sided atrial lesions for the treatment of atrial fibrillation (AF), with the pulmonary veins as the main target.' The accepted golden standard for surgical AF treatment, the Cox-Maze operation, already consisted of a surgical lesion isolating the pulmonary veins, but additional lesions to the mitral valve annulus, the left and right atrial appendage, the tricuspid valve R.E. Accord TJ. van Brakel
J.Q.a Department of Cardiothoracic Surgery, Cardiovascular Research Institute Maastricht, Maastricht University Hospital, Maastricht Correspondence to: J.G. Maessen Department of Cardiothoracic Surgery, Maastricht University Hospital, PO Box 5800, 6202 AZ Maastricht E-mail: [email protected]
Netherlands Heart Journal, Volume 13, Number 5, May 2005
annulus, lesions between superior and inferior caval veins, and a lesion between right and left atrium made this lesion set complex. Simplification of the Maze lesion set in combination with recent developments in catheter technology, which have replaced the original cut and sew technique, made surgical AF treatment less invasive and therefore more accessible for general cardiothoracic practice. However, until recently, developments in surgical AF treatment seemed mainly driven by experience rather than by evidence. This article discusses the rationale of pulmonary vein isolation using surgical catheter ablation for the treatment of AF. Furthermore, advantages of this approach, as well as uncertainties concerning clinical outcome and hurdles still to overcome, are presented. Pulmonary veins more than a source of ectopic activity As early as in 1872, Brunton and Fayer observed pulsations in the pulmonary veins, which was suggestive of electrical activity.2 A century later, the presence of excitable myocardial tissue within the pulmonary veins was confirmed by Spach and co-workers, who demonstrated propagation of excitation from the atrium to the pulmonary veins in humans and in dogs.3 It was, however, only recently that Haissaguerre presented evidence that pulmonary veins are an important source ofectopic beats, initiating frequent paroxysms of atrial fibrillation.' Haissaguerre and co-workers demonstrated by endocardial mapping that the earliest electrical activity preceding the onset of atrial fibrillation was located within the pulmonary veins. Moreover, they showed that radiofrequency ablation of these pulmonary vein foci resulted in abrupt disappearance of this ectopic activity. The presumed role of the pulmonary veins was confined to AF initiation for almost a decade. However, there is now strong evidence that the pulmonary veins may also play a role in AF propagation and maintenance.4'5 The identification of the pulmonary veins as a source of ectopic triggers led to an increased interest in anatomic, electrophysiological and histological properties of the pulmonary veins and their surround181
The rationale of surgical pulmonary vein isolation for treatment of atrial fibrillation
ings in attempts to unravel the pathophysiological mechanisms involved. This led to the observation that atrial myocardial tissue continues beyond the venous orifice to the outside ofthe pulmonaryvein media.6 The extension towards the lung hila of these so-called myocardial sleeves differs among the various veins as well as between individuals, with a corresponding variation in electrophysiological properties.7 Several studies have shown that the upper left pulmonary vein has a longer sleeve with more ectopic activity." 7 A possible explanation for the presence of pulmonary vein foci is the existence of specialised conduction cells in human pulmonary veins as recently reported by Perez-Lugones et al.8 Blom et al. found that the myocardium around the common pulmonary vein of human embryos showed HNK- 1 expression, a generally accepted marker for atrioventricular conduction tissue.9 The distribution of left and right atrial pacemaker foci corresponded with these areas of HNK- 1 expression. The exact role of specialised conduction cells present in the pulmonary veins in the genesis of atrial fibrillation requires further investigation. The abolishment of AF after ablation of identified triggers served as important evidence supporting the hypothesis of the pulmonary veins as an important source oftrigger in some types ofAF. However, recent findings suggest that triggered activity only partly explains the results achieved with pulmonary vein isolation. Even after electrophysiologically incomplete isolation ofthe pulmonaryveins, clinical effetiveness is observed'0 and changed electrophysiological properties are found, which might decrease the susceptibility to AF." Todd et al. showed that within a surgically isolated pulmonary vein region, AF can easily be induced and maintained, while in the considerably larger remaining atrial region, AF was noninducible even after burst pacing.'2 This suggests that the pulmonary veins and their surroundings possess unique properties that provide the ability to maintain AF. The study by Todd et al. involved patients with lone AF without the typical fibrotic changes seen in patients with underlying cardiac disease. Recently, Nademanee's group showed that the electrophysiological substrate for AF, defined as complex fractionated electrograms, could be recorded within the pulmonary vein region in a majority of cases.'3 They showed that targeting the identified substrate by radiofrequency ablation resulted in AF abolishment. All of these findings implicate that the pulmonary veins and their surrounding area possess proarrhythmic properties, making these structures more than a source of ectopic activity.
Surgical lesion
s
The notion that the pulmonary veins play an important role in AF promoted the development of more attractive left-sided strategies with pulmonary vein isolation as a key element. Pulmonary vein isolation can be performed by ablating within the separate 182
pulmonary vein ostia'4'16 or by ablating around pulmonary vein ostia,'7-2' avoiding the risk of pulmonary vein stenosis. Several groups advocate a bilateral isolation of the pulmonary veins instead of one box lesion encircling all four pulmonary veins. It is thought that this minimises the amount ofvital tissue excluded from synchronic atrial contraction. However, extensive reduction of substrate mass under the critical level necessary to maintain AF might be necessary for AF abolishment, especially in enlarged atria. Since the pulmonary vein area appears to be involved in AF maintenance by additional mechanisms than ectopic triggers alone, a box lesion isolating all pulmonary veins might be even more effective than separate isolation. Several lesion concepts include an additional line between the isolated pulmonary veins and the mitral valve annulus."5"16"19-23 This line is thought to reduce the occurrence of postoperative atrial flutter. Especially after an incomplete pulmonary vein isolation there is the likelihood of such sustained macroreentrant arrhythmias around natural obstacles.24'25 The mitral valve line can, however, only be applied safely by an endocardial approach. Our own data revealed that in a group of 56 patients who underwent epicardial pulmonary vein isolation without additional lesions, only 3.6% showed atrial flutters within the 15 months of follow-up. In all cases the arrhythmias were selflimiting.26
Primary endpoints in evaluating various surgical approaches In the last decade, a large number ofreports have been published showing results ofseveral surgical variants for the treatment ofAF. Most reports focus on the ability to restore sinus rhythm, some on restoration of atrial transport function and others on clinical outcome parameters. A summary of recent reports focusing on left-sided surgical ablation techniques is presented in table 1 "4-16,19,2023,27-31 Conclusive evidence is lacking due to the retrospective nature of most studies. In addition, the published series involve antiarrhythmic interventions adjuvant to coronary and/or valvular surgery, making the interpretation of the results difficult. The effect of revascularisation and valve replacement or repair on AF substrate reduction in the course of time is often neglected. Although one ofthe main reasons for the renewed interest in the curative treatment ofAF was awareness that AF contributes to increased morbidity and mortality and thus increased healthcare consumption, little evidence about the effect of surgical AF treatment on these particular endpoints exists. Two publications describing the impact on heath-related quality of life (QOL) report improvement after the Maze III operation for lone AF.R2"' However, in both studies, patients with symptomatic drug-refractory AF who were highly motivated to undergo surgery were selected. Lonnerholm et al. indicated that a significant Netherlands Heart Journal, Volume 13, Number 5, May 2005
qic
The rationale of surgical pulmonary vein isolation for treatment of atrial fibrillation
vein isolation performed from the epicardial site can avoid an atriotomy and therefore does not contribute to prolonged cardiopulmonary bypass time. Furthermore, transmurality can be achieved without damage to the endocardium. This is important because extensive experience with endocardial catheter ablation has shown that endocardial tissue disruption can lead to thrombus formation and stroke, especially in leftsided ablation procedures.34 Another potentially life-threatening complication of endocardial application of heat-based energy is a burn injury of the oesophagus, which is located posterior to the LA posterior wall. The incidence reported by Doll et al. was 1%.35 When ablation is per-
placebo effect is unlikely because no decrease in QOL was noted after repeated measurement at one-year follow-up, compared with the QOL after six months.32 To the best of our knowledge, studies which concentrate on the impact on QOL and cost-effectiveness of other surgical treatment modalities as sole pulmonary vein isolation are lacking. This aspect of surgical AF treatment is an important subject for further investigation. The epicardlal approach In order to pursue a less invasive technique of surgical AF treatment, there is an increasing interest in epicardial instead of endocardial approaches. Pulmonary
Table 1. Overview of recent reports on left-sided surgical ablation techniques for treatment of AF in patients undergoing concomitant cardiac surgery.
Authors
Patients, follow-up
Mohr16 Sueda19
Manasse'5 Benussi22
234, 12 m 12, 6m 95, 36 m 132, 16.9 m
Pasic27
48, 4m Starck28 100, 7.3 m Mantovan29 103, 12.5m RuchatP0 40, 12.5m
Schuetz*'4 24, 12 m
Guden*23
57, 10.9 m
Deneke*31
21, 11 m
Application, energy source, lesion patron Endo, RF, linear PV connection, MV line Endo, C&S/ cryo, PV isolation Endo, cryo, linear PV connection, MV line Epi/Endo, RF, PV isolation with LAA connection, MV line Endo, RF, PV isolation, MV line Endo, RF, PV isolation, MV line Endo, RF, PV isolation
Epi/Endo, RF, PV isolation with LAA connection, MV line Endo, MW, PV isolation with LAA connection, MV lines Endo, RF, PV isolation with LAA connection, MV line, CS-line Endo, RF, PV isolation with LAA connection, MV line
Restoration Atrial transport Postoperative Thromboembolism function (% of AF patients In SR)
PM
Mortality
4.2% (IH) 6.4% (late) 0% (IH)
of SR
72.5%
nm
47.9%
nm
9.8%
75%
nm
nm
nm
nm
81.4%
80% biatrial
2.9%
4.2% CVA
6.3%
77% (3 yr)
100% biatrial
7.6%
1.5% (3 yr)
0%
3.2% (IH), 9.4% (late) 0.8% (IH)
92% (6 m)
100% biatrial
0%
11%
4% (IH)
80%
80%
nm
1 stroke death 0
0%
5% (IH)
81%
79.5%
11% AT or Afl
68%
26%
15%
3 thrombi LA,
Te rationale of surgifmcal pulmonary vemin isolation for treatment
of
atrial fibrillation
R.E. Accord, T.J. van Brakel, J.G. Maessen
With the development of less invasive surgical approaches and new ablation techniques, surgical treatment of atrial fibrillation has gained increasing interest over the past decade. Contrary to the complex Maze procedure, new less laborious approaches with pulmonary vein isolation as the main focus are within the reach of most cardiothoracic surgeons. However, although important new pathophysiological mechanisms have emerged in recent years due to extensive basic and clinical research, several uncertainties and hurdles concerning this treatment modality remain. This artide reviews the rationale of surgical pulmonary vein isolation, based on these increased insights. Furthermore, important technical aspects including the possible advantages of an epicardial approach, the optimal left-sided lesion set and the need for transmurality are discussed in depth. (Neth Heart J2005;13:181-5.)
Keywords: atrial fibrillation, pulmonary vein ablation, arrhythmia surgery n recent years, the observation of ectopic activity
Ioriginating from the pulmonary veins has focused interest on left-sided atrial lesions for the treatment of atrial fibrillation (AF), with the pulmonary veins as the main target.' The accepted golden standard for surgical AF treatment, the Cox-Maze operation, already consisted of a surgical lesion isolating the pulmonary veins, but additional lesions to the mitral valve annulus, the left and right atrial appendage, the tricuspid valve R.E. Accord TJ. van Brakel
J.Q.a Department of Cardiothoracic Surgery, Cardiovascular Research Institute Maastricht, Maastricht University Hospital, Maastricht Correspondence to: J.G. Maessen Department of Cardiothoracic Surgery, Maastricht University Hospital, PO Box 5800, 6202 AZ Maastricht E-mail: [email protected]
Netherlands Heart Journal, Volume 13, Number 5, May 2005
annulus, lesions between superior and inferior caval veins, and a lesion between right and left atrium made this lesion set complex. Simplification of the Maze lesion set in combination with recent developments in catheter technology, which have replaced the original cut and sew technique, made surgical AF treatment less invasive and therefore more accessible for general cardiothoracic practice. However, until recently, developments in surgical AF treatment seemed mainly driven by experience rather than by evidence. This article discusses the rationale of pulmonary vein isolation using surgical catheter ablation for the treatment of AF. Furthermore, advantages of this approach, as well as uncertainties concerning clinical outcome and hurdles still to overcome, are presented. Pulmonary veins more than a source of ectopic activity As early as in 1872, Brunton and Fayer observed pulsations in the pulmonary veins, which was suggestive of electrical activity.2 A century later, the presence of excitable myocardial tissue within the pulmonary veins was confirmed by Spach and co-workers, who demonstrated propagation of excitation from the atrium to the pulmonary veins in humans and in dogs.3 It was, however, only recently that Haissaguerre presented evidence that pulmonary veins are an important source ofectopic beats, initiating frequent paroxysms of atrial fibrillation.' Haissaguerre and co-workers demonstrated by endocardial mapping that the earliest electrical activity preceding the onset of atrial fibrillation was located within the pulmonary veins. Moreover, they showed that radiofrequency ablation of these pulmonary vein foci resulted in abrupt disappearance of this ectopic activity. The presumed role of the pulmonary veins was confined to AF initiation for almost a decade. However, there is now strong evidence that the pulmonary veins may also play a role in AF propagation and maintenance.4'5 The identification of the pulmonary veins as a source of ectopic triggers led to an increased interest in anatomic, electrophysiological and histological properties of the pulmonary veins and their surround181
The rationale of surgical pulmonary vein isolation for treatment of atrial fibrillation
ings in attempts to unravel the pathophysiological mechanisms involved. This led to the observation that atrial myocardial tissue continues beyond the venous orifice to the outside ofthe pulmonaryvein media.6 The extension towards the lung hila of these so-called myocardial sleeves differs among the various veins as well as between individuals, with a corresponding variation in electrophysiological properties.7 Several studies have shown that the upper left pulmonary vein has a longer sleeve with more ectopic activity." 7 A possible explanation for the presence of pulmonary vein foci is the existence of specialised conduction cells in human pulmonary veins as recently reported by Perez-Lugones et al.8 Blom et al. found that the myocardium around the common pulmonary vein of human embryos showed HNK- 1 expression, a generally accepted marker for atrioventricular conduction tissue.9 The distribution of left and right atrial pacemaker foci corresponded with these areas of HNK- 1 expression. The exact role of specialised conduction cells present in the pulmonary veins in the genesis of atrial fibrillation requires further investigation. The abolishment of AF after ablation of identified triggers served as important evidence supporting the hypothesis of the pulmonary veins as an important source oftrigger in some types ofAF. However, recent findings suggest that triggered activity only partly explains the results achieved with pulmonary vein isolation. Even after electrophysiologically incomplete isolation ofthe pulmonaryveins, clinical effetiveness is observed'0 and changed electrophysiological properties are found, which might decrease the susceptibility to AF." Todd et al. showed that within a surgically isolated pulmonary vein region, AF can easily be induced and maintained, while in the considerably larger remaining atrial region, AF was noninducible even after burst pacing.'2 This suggests that the pulmonary veins and their surroundings possess unique properties that provide the ability to maintain AF. The study by Todd et al. involved patients with lone AF without the typical fibrotic changes seen in patients with underlying cardiac disease. Recently, Nademanee's group showed that the electrophysiological substrate for AF, defined as complex fractionated electrograms, could be recorded within the pulmonary vein region in a majority of cases.'3 They showed that targeting the identified substrate by radiofrequency ablation resulted in AF abolishment. All of these findings implicate that the pulmonary veins and their surrounding area possess proarrhythmic properties, making these structures more than a source of ectopic activity.
Surgical lesion
s
The notion that the pulmonary veins play an important role in AF promoted the development of more attractive left-sided strategies with pulmonary vein isolation as a key element. Pulmonary vein isolation can be performed by ablating within the separate 182
pulmonary vein ostia'4'16 or by ablating around pulmonary vein ostia,'7-2' avoiding the risk of pulmonary vein stenosis. Several groups advocate a bilateral isolation of the pulmonary veins instead of one box lesion encircling all four pulmonary veins. It is thought that this minimises the amount ofvital tissue excluded from synchronic atrial contraction. However, extensive reduction of substrate mass under the critical level necessary to maintain AF might be necessary for AF abolishment, especially in enlarged atria. Since the pulmonary vein area appears to be involved in AF maintenance by additional mechanisms than ectopic triggers alone, a box lesion isolating all pulmonary veins might be even more effective than separate isolation. Several lesion concepts include an additional line between the isolated pulmonary veins and the mitral valve annulus."5"16"19-23 This line is thought to reduce the occurrence of postoperative atrial flutter. Especially after an incomplete pulmonary vein isolation there is the likelihood of such sustained macroreentrant arrhythmias around natural obstacles.24'25 The mitral valve line can, however, only be applied safely by an endocardial approach. Our own data revealed that in a group of 56 patients who underwent epicardial pulmonary vein isolation without additional lesions, only 3.6% showed atrial flutters within the 15 months of follow-up. In all cases the arrhythmias were selflimiting.26
Primary endpoints in evaluating various surgical approaches In the last decade, a large number ofreports have been published showing results ofseveral surgical variants for the treatment ofAF. Most reports focus on the ability to restore sinus rhythm, some on restoration of atrial transport function and others on clinical outcome parameters. A summary of recent reports focusing on left-sided surgical ablation techniques is presented in table 1 "4-16,19,2023,27-31 Conclusive evidence is lacking due to the retrospective nature of most studies. In addition, the published series involve antiarrhythmic interventions adjuvant to coronary and/or valvular surgery, making the interpretation of the results difficult. The effect of revascularisation and valve replacement or repair on AF substrate reduction in the course of time is often neglected. Although one ofthe main reasons for the renewed interest in the curative treatment ofAF was awareness that AF contributes to increased morbidity and mortality and thus increased healthcare consumption, little evidence about the effect of surgical AF treatment on these particular endpoints exists. Two publications describing the impact on heath-related quality of life (QOL) report improvement after the Maze III operation for lone AF.R2"' However, in both studies, patients with symptomatic drug-refractory AF who were highly motivated to undergo surgery were selected. Lonnerholm et al. indicated that a significant Netherlands Heart Journal, Volume 13, Number 5, May 2005
qic
The rationale of surgical pulmonary vein isolation for treatment of atrial fibrillation
vein isolation performed from the epicardial site can avoid an atriotomy and therefore does not contribute to prolonged cardiopulmonary bypass time. Furthermore, transmurality can be achieved without damage to the endocardium. This is important because extensive experience with endocardial catheter ablation has shown that endocardial tissue disruption can lead to thrombus formation and stroke, especially in leftsided ablation procedures.34 Another potentially life-threatening complication of endocardial application of heat-based energy is a burn injury of the oesophagus, which is located posterior to the LA posterior wall. The incidence reported by Doll et al. was 1%.35 When ablation is per-
placebo effect is unlikely because no decrease in QOL was noted after repeated measurement at one-year follow-up, compared with the QOL after six months.32 To the best of our knowledge, studies which concentrate on the impact on QOL and cost-effectiveness of other surgical treatment modalities as sole pulmonary vein isolation are lacking. This aspect of surgical AF treatment is an important subject for further investigation. The epicardlal approach In order to pursue a less invasive technique of surgical AF treatment, there is an increasing interest in epicardial instead of endocardial approaches. Pulmonary
Table 1. Overview of recent reports on left-sided surgical ablation techniques for treatment of AF in patients undergoing concomitant cardiac surgery.
Authors
Patients, follow-up
Mohr16 Sueda19
Manasse'5 Benussi22
234, 12 m 12, 6m 95, 36 m 132, 16.9 m
Pasic27
48, 4m Starck28 100, 7.3 m Mantovan29 103, 12.5m RuchatP0 40, 12.5m
Schuetz*'4 24, 12 m
Guden*23
57, 10.9 m
Deneke*31
21, 11 m
Application, energy source, lesion patron Endo, RF, linear PV connection, MV line Endo, C&S/ cryo, PV isolation Endo, cryo, linear PV connection, MV line Epi/Endo, RF, PV isolation with LAA connection, MV line Endo, RF, PV isolation, MV line Endo, RF, PV isolation, MV line Endo, RF, PV isolation
Epi/Endo, RF, PV isolation with LAA connection, MV line Endo, MW, PV isolation with LAA connection, MV lines Endo, RF, PV isolation with LAA connection, MV line, CS-line Endo, RF, PV isolation with LAA connection, MV line
Restoration Atrial transport Postoperative Thromboembolism function (% of AF patients In SR)
PM
Mortality
4.2% (IH) 6.4% (late) 0% (IH)
of SR
72.5%
nm
47.9%
nm
9.8%
75%
nm
nm
nm
nm
81.4%
80% biatrial
2.9%
4.2% CVA
6.3%
77% (3 yr)
100% biatrial
7.6%
1.5% (3 yr)
0%
3.2% (IH), 9.4% (late) 0.8% (IH)
92% (6 m)
100% biatrial
0%
11%
4% (IH)
80%
80%
nm
1 stroke death 0
0%
5% (IH)
81%
79.5%
11% AT or Afl
68%
26%
15%
3 thrombi LA,
