A combined endocardial and epicardial procedure for the treatment of atrial fibrillation is an objective and impartial way the cardiac surgeon and the electrophysiologist can explore as a team, an approach to achieve a superior long-term cure rate, achieved with a single-session procedure.
The basic concepts of cardiac surgery and electrophysiology in atrial fibrillation treatment are often obscured by different strategies that lead to conflicting trends and therefore misunderstandings. From the electrophysiologist’s viewpoint, ablation of the pulmonary veins with proof of an acute bidirectional electrical isolation is the cornerstone of most ablation strategies. On the surgical side, the foundation of a successful atrial fibrillation procedure is still a Cox maze procedure on the arrested heart, with no electrophysiological confirmation of the effect and quality of the lesion set. These distinctive characteristics of the two treatment platforms can only be changed if both the electrophysiologist and the cardiac surgeon are willing to accept their methodological limitations. If in each group we are able to confront this, then the necessity of a link between the two disciplines will become clear. In order to realize this multidisciplinary approach we must first understand the current limitations of energy delivery in the left and right atrium. The benefits of this multidisciplinary approach will enhance the controlled power delivery to targeted cardiac tissue and the accuracy of the visualization and mapping of the ablated tissue in both atria. Fundamental questions, like the necessity of a continuous and transmural lesion, will no longer be unanswered. We can map triggers and substrate at both the endocardium and epicardium, thus improving our understanding of the mechanisms of atrial fibrillation, and confirm lesion transmurality from both sides, with a single combined procedure.
Recent electrophysiology literature shows that long-lasting endocardial catheter isolation of the pulmonary veins, whether achieved with radiofrequency energy or cryo-thermia, remains challenging.1 Because of this limitation it is not clear whether complete circumferential antral ablation is necessary for successful pulmonary vein isolation in patients with paroxysmal atrial fibrillation, and it is accepted that non-circumferential antral ablation may achieve similar success rates with shorter procedure and ablation times than circumferential ablation. Therefore, attention could be focused on producing permanent lesions rather than on completing antral encirclement after isolation is achieved.2–4
This basic philosophy was the rationale of our initial experience with the minimally invasive surgical treatment of lone atrial fibrillation. In 2005 we developed a technique using a monolateral right thoracoscopic approach. The procedure consisted of the creation of a box lesion set to encircle all pulmonary veins with a catheter that used microwave energy to ablate left atrial tissue. At that time, this device was the only commercially available thoracoscopic minimally invasive surgical ablation tool.5,6 The concept and development of the box lesion as a minimal lesion set was based on several factors but, most importantly, a consequence of the absence of provocative electrophysiologic mapping and testing during the surgical procedure. The rationale was to maximize the number of excluded triggers by isolating the four pulmonary veins; try to obtain an important substrate modification by isolating the posterior wall of the left atrium; reduce the critical mass of the left atria; denervate the four major ganglionated plexi; and to ablate the ligament of Marshall. A major drawback for a monolateral right-sided approach was the lack of opportunity to exclude or occlude the left atrial appendage safely. Since the left atrial appendage is largely responsible for thrombo-embolic events in patients with atrial fibrillation, and can be part of the substrate responsible for atrial fibrillation, it could be preferable to occlude or exclude the left atrial appendage in a subgroup of atrial fibrillation patients. We therefore developed a technique with a monolateral left-sided approach for patients when isolation and exclusion of the left atrial appendage were deemed necessary. Freedom of atrial fibrillation at 1 year was 73% for the combined group of right- and left-sided interventions. A complementary endocardial approach was performed at 6 months in 18 patients.7 Since the success rate at 2-year follow-up was unsatisfactory,8 we changed the energy source from microwave to monopolar radiofrequency energy. Realizing that the concept of an epicardial box lesion had distinct limitations and was difficult to achieve on a beating heart (epicardial fat, heat-sink effect, power delivery of a monopolar ablation device), we combined the surgical procedure with a simultaneous endocardial electrophysiology procedure. A single-session hybrid atrial fibrillation procedure was born. For the first time, we could study the effect of an epicardial ablation on the endocardium in a human being as well as see the epicardial effects of an endocardial ablation, during the same procedure. Using this approach we could demonstrate that after epicardial creation of a box lesion with microwave or radiofrequency there was a conduction delay from the pulmonary veins and the posterior wall of the left atrium, but no exit or entrance block. This incomplete epicardial surgical ablation line necessitated a complementary endocardial isolation of one or more pulmonary veins and/or the roof and inferior line.
The importance of these findings was twofold: first, we proved that the concept of combining a percutaneous endocardial approach with a thoracoscopic epicardial approach was safe and technically feasible and, secondly, that creation of a continuous transmural box lesion from the epicardium with a monopolar energy source was not possible. Even with satisfactory clinical results, transmurality and continuity of epicardial lesions could not be assured. This could probably explain the relatively low success rate at long-term follow-up. Again we had to change our strategy. We decided to focus first on an antral epicardial isolation of the pulmonary veins. Our belief was that in order to be an alternative for an endocardial ablation, it was mandatory for the surgical portion of the hybrid approach to achieve a long-lasting antral isolation of the pulmonary veins. Since microwave and monopolar radiofrequency energy proved to be inconsistent, we had to search for an alternative. Prasad et al. showed in an animal model the potential of a bipolar radiofrequency clamp to isolate pulmonary veinselectrically.9 Damiano et al. studied the results of a Cox maze IV using a bipolar radiofrequency clamp and found that they were similar to the “cut and sew” Cox maze III.10 Thus it was assumed that a bipolar radiofrequency clamp could be able to isolate the pulmonary veins on the beating heart. However, endocardial redo procedures in patients with recurrence of atrial fibrillation who had had a thoracoscopic bipolar pulmonary vein isolation showed that in 50% there was failure to isolate one or more of the pulmonary veins.11 We demonstrated that mechanical clamping-induced ischemia could be responsible for these failures.12 Therefore, combining a bilateral thoracoscopic approach with antral isolation of the pulmonary veins, followed by an endocardial mapping and touch-up ablation, at least 30 minutes after the epicardial ablation, could avoid incomplete isolation of the pulmonary veins. Building upon this antral isolation of the pulmonary veins, we then could focus on the creation of linear lesions connecting the superior pulmonary veins and the inferior pulmonary veins using a bipolar unidirectional linear pen, thus achieving compartmentalization of the posterior left atrium.
The group of Damiano demonstrated in an animal model the potential risk of incomplete lesions using these devices.13 Our clinical experience confirmed their findings: in 23% of patients, the epicardial lines created with these linear ablation devices were not transmural and necessitated an endocardial touch-up ablation, demonstrating the importance of power application and mapping during the catheter treatment of atrial fibrillation.14 The possibility to perform such an endocardial touch-up to render epicardial lesions completely transmural is one of the major advantages of this dual epicardial–endocardial approach.
This hybrid procedure also appeared to be an advantage in performing a redo catheter ablation procedure by offering the possibility to map the patient endocardially first. An important percentage of patients that are sent for an epicardial treatment of atrial fibrillation will have had a previous endocardial procedure, mostly pulmonary vein isolation. Knowing which veins have been isolated, and which have not, can have important consequences for the treatment strategy. If all pulmonary veins have been electrically isolated, the epicardial procedure should be focused on linear lesions to compartmentalize the posterior left atrium and (mostly) exclusion of the left atrial appendage. In these cases the thoracoscopic procedure can be limited to the left-sided approach. If the pulmonary veins have been isolated on the left side, the thoracoscopic procedure could be limited to the right side.
Starting from a single-sided thoracoscopic procedure with a monopolar energy source on the beating heart, we were initially confronted with the surgical and technical limitations of the ablation devices and the procedure. A simultaneous endocardial approach seemed mandatory to understand the limitations of our minimally invasive approach. Initially setting up this collaboration with the electrophysiologist was challenging. Some of the obstacles we had to overcome were: trying to understand our common goals, organizing the availability of the different multidisciplinary teams, criteria for selection of patients, deciding where the procedure should be performed, and the sequence of the procedure. Evaluation of our findings acutely and over time has made necessary several changes to our approach and choice of ablation technologies and devices. This could only be achieved through a genuinely open-minded team approach that remained critical regarding the achieved success and also a willingness to take a retrospective view to compare this new approach to other more standard procedures.