The treatment of long-standing persistent atrial fibrillation (AF) still represents a major clinical challenge, with the most appropriate treatment strategy being a matter of vivid debate. Pharmacological therapy has very limited efficacy in persistent AF patients, with the most effective drugs available maintaining fewer than 20% of long-standing persistent AF patients in normal sinus rhythm during the first 6 months of treatment.1–4 Although better than pharmacological therapy, percutaneous catheter-based approaches also yield poor success rates in this specific subset of patients.5–7
From the surgical standpoint, the most effective treatment described to date has been the Maze IV operation, albeit still implying the use of cardiopulmonary bypass.8 Recently, novel approaches for minimally invasive surgical treatment of AF have been adopted in clinical practice, with results often comparable to or better than those of catheter-based approaches.9 Nevertheless, these endoscopic techniques allow for a limited set of lesions and could therefore offer less than optimal treatment especially in patients with persistent AF, in whom an extensive lesion set may often be required.
We therefore combined a surgical and catheter-based approach in a staged fashion to treat patients with persistent AF, with thoracoscopic ablation being performed first then followed by an electrophysiological (EP) transcatheter approach.
Twenty-four consecutive patients meeting study requirements were prospectively enrolled. Qualifying patients were refractory to drug therapy, did not require concomitant cardiac surgery, and were in persistent AF. Both persistent (three patients, 12.5%) and long-standing persistent (21 patients, 87.5%) isolated AF patients were enrolled. In the study population, the mean age was 63.2 ± 9.3 years, the mean left atrial dimension was 50.5 ± 8 mm, and the mean AF duration was 82.7 months (range, 7–240 months). Additional data are summarized in Table 1.
We sought to use a staged hybrid approach in this subset of patients, that is, patients were initially scheduled to undergo thoracoscopic ablation with intraoperative testing of the lesion set, which is then followed at 30 days by an EP evaluation to assess the efficacy of the thoracoscopic ablation and to complete the lesion set if required.
Before the thoracoscopic treatment, a 6F decapolar electrode catheter (P-SUPRA CS; Webster, Diamond Bar, CA USA) was positioned in the coronary sinus of all patients to assess the thoracoscopic lesions afterward. The patients were then immediately transferred to the surgical theater for endoscopic epicardial ablation.
The surgical procedure consisted of a thoracoscopic, monolateral, right-sided, closed-chest approach to deliver a continuous lesion encircling the origin of all pulmonary veins (“box” lesion set) as previously described.10 Before ablation, an extensive removal of the epicardial fat at the level of the Waterston groove was performed. The ablation device used to create the box lesions was a temperature-controlled, internally cooled, radiofrequency monopolar device with suction adherence (Cobra Adhere XL; Estech, San Ramon, CA USA). The device settings used were a 150-watt maximum power limit with a temperature control setting of 80°C and a 120-second ablation time; a negative suction pressure of at least 500 mm Hg was reached before ablation had been started. The Cobra Adhere XL probe has 10 electrodes, five proximal and five distal. Briefly, the proximal electrodes are positioned at the level of the transverse sinus down to the left atrial appendage, and the distal ones were positioned at the level of the oblique sinus (Fig. 1). Multiple ablations (at least twice) were delivered from both the proximal or distal electrodes of the probe on the epicardial surface. Extensive overlapping ablations between the proximal and distal electrodes is performed at the level of the Waterston groove.
Once the surgical ablation had been completed, testing was performed according to EP guidelines to validate the entrance and exit blocks. A tetrapolar catheter (AVAIL electrophysiology catheter, Josephson Curve, type A; Webster, Diamond Bar, CA USA) was introduced through the lower port and advanced first onto the right atrium to test pacing thresholds. The same catheter was then positioned within the box lesion (at the level of the right pulmonary veins and the posterior aspect of the left atrium) and used as a pacing probe, with the catheter in the coronary sinus sensing potential captures (exit block); in particular, the tetrapolar catheter allowed for an assessment and confirmation of local capture. Finally, the entrance block was assessed by stimulating the catheter in the coronary sinus and sensing with the tetrapolar catheter positioned on the posterior wall of the epicardium within the box (Table 2).
In all patients, a staged catheter procedure was performed 30 to 45 days after surgery to assess the durability of conduction block achieved by the surgical lesions and to deliver additional ablation lesions as deemed appropriate by the electrophysiologist. As a minimum, the treatment protocol required that any gaps in the box lesion be closed by endocardial ablation. Inducibility of AF and atrial flutter was elicited by means of rapid atrial pacing.
At the time of the surgical ablation procedure, an implantable loop recorder (Reveal XT; Medtronic, Inc, Minneapolis, MN USA) was implanted in each study subject. The device was interrogated every month postoperatively so as to obtain an accurate assessment of rhythm status for each patient. Recurrence of AF was defined as the presence of AF episodes with a duration longer than 5 minutes11 or an overall monthly burden of AF less than 0.5% of the time.12
Successful completion of the procedure was achieved in all cases, with a mean ablation time of 29 ± 9 minutes and an overall procedural time of 84 ± 16 minutes. During surgical ablation, exit block was documented in all cases, whereas bidirectional (entrance-exit) block was achieved in 87.5% (21 of 24 patients). All patients were extubated in the operating room, no intensive care unit stay was required, and no complications occurred postoperatively. Hospital mortality was 0%. Postoperative hospital stay was 3.1 ± 1.2 days.
Staged EP Evaluation
At a mean interval of 33 ± 2 days after surgery, an EP study was performed: bidirectional block was confirmed in 79.1% (19 of 24 patients), whereas gaps at the level of the box lesion were observed in 20.8% of the patients (5 of 24 patients). Gaps in the box lesion were closed using EP ablation catheters in these five patients; additional catheter endocardial right- and left-sided lesions were performed, with lesions applied to sites of focal triggers initiating AF and sites of fragmented potentials and to complete the cavo-tricuspid isthmus line in patients with a history of right atrial flutter. Ablation was performed in 62.5% of cases (15 of 24 patients), as shown in Figure 2. A breakdown of the different sites of EP ablation during the second step is depicted in Figure 3. Of note, no patient required lesions at the level of the mitral isthmus.
At a mean follow-up of 28 months (range, 1–55 months), 87.5% of the patients (21 of 24 patients) were in stable sinus rhythm, as confirmed by the analysis of implantable loop recorders: patients off antiarrhythmic drugs and anticoagulation were 75% (18 of 24 patients) and 91.6% (22 of 24 patients), respectively. The incidence of left atrial flutter was 0% in the current series, even in patients with the longer follow-up period. The trends in rhythm outcome as well as withdrawal of antiarrhythmic drugs and anticoagulation therapy are depicted in Figure 4.
The Cox-Maze operation represented the gold standard so far for the treatment of persistent AF. Although the superior long-term results of this approach, Cox-Maze has been hampered by the technical complexity, associated morbidity, and degree of invasiveness. Refinements in surgical techniques and technologies have nowadays allowed for a significantly less invasive approach for the treatment of AF either via thoracoscopic or mini-thoracotomy approaches.9
Nevertheless, a minimally invasive approach is often associated with a limited number of lesions created, thus reducing procedure efficacy. To overcome such a drawback, we applied the box lesion set combining surgical and EP techniques in a hybrid fashion.13
A hybrid approach could be performed as either a concomitant14 or a staged procedure. The staged procedure with surgery first provides significant advantages: first, it allows for further “evolution” of the ablative lesions (requiring usually a few weeks) to avoid false-positives in early inducible arrhythmias15; second, false-negatives are minimized because acute demonstration of a bidirectional block could only be transient and not confirmed by delayed testing at 1 month after surgery. For the aforementioned reasons, our treatment algorithm consisted of an initial thoracoscopic ablation followed by a transcatheter procedure at 1 month. Despite still requiring multiple procedures (two in our series), we believe that this approach yields important advantages because both sides of the atrial wall (ie, epicardial and endocardial) are treated; moreover, the surgical procedure in particular can target most of the ganglionated plexi on the epicardial surface, which are also associated with potential recurrences if untreated. In our study, procedural endpoints were strictly adherent to EP guidelines for AF ablation. As per Heart Rhythm Society guidelines, the endpoint for successful ablation should be at least the presence of unidirectional block; in our series, we tested for a bidirectional block but maintained as endpoint for success the presence of at least a unidirectional block. The staged protocol proved to be effective in depicting those instances in which transient blocks (ie, confirmed during the surgical ablation) then underwent reconnection but were then successfully targeted during the delayed EP evaluation.
The surgical ablation lesion set always performed was the box lesion, which is also the “core” lesion in the Maze technique. The box lesion can be complemented with additional ablative lines by EP colleagues at a later stage, if required. The unipolar radiofrequency probe used for the surgical ablation proved to be effective both in the acute setting (with a bidirectional and exit-only block in 87.5% and 100% of cases, respectively) and at a later stage during the EP evaluation where durable lesions were proven in 80% of patients. Finally, this approach allows for a true minimally invasive approach, by means of a right-sided thoracoscopic technique to perform epicardial ablation, avoiding the need for a cardiopulmonary bypass.
Of note, no lesion to the mitral annulus was required in the current series because of the lack of either iatrogenic or inducible left atrial flutter. Lesion to the mitral annulus has been considered a cornerstone to prevent the occurrence of such arrhythmia, albeit especially in the epicardial setting, it could be cumbersome to perform a fully transmural lesion that instead could lead, if incomplete, to a substrate prone to develop atypical flutter, as previously demonstrated.15
The use of unipolar RF in epicardial beating heart setting may raise concern with respect to the effectiveness of the ablation itself. Nevertheless, we believe that the consistent results we obtained in our preliminary series are caused in part by the effectiveness of the ablation probe itself, in particular, thanks to the presence of suction (allowing for maximal adherence with the tissue) and internal cooling (which reduced the risk of overheating at the delivery site and thereby allowing for better penetration of the RF energy within the tissue). Finally, from the technical standpoint, we adopted the current delivery protocols as described in the “Methods” section after an extensive experience and collaboration with EPs, which allowed for intraoperative validation of lesion effectiveness.
From the EP standpoint, the presence of an extensive ablative pattern such as the box lesion permitted a faster transcatheter procedure mainly targeted at the cavo-tricuspid isthmus (in patients with a history of right atrial flutter), additional pulmonary veins antral isolation (to reduce the risk of potential late PV electrical reconnection), or gaps in the box lesion itself (Fig. 3). As nearly 40% of patients did not require any additional touch-up from the EP standpoint, it may be inferred that this subgroup of patients underwent unnecessary EP procedures after the surgical ablation. We believe that it was important to validate the results of the surgical ablation in this initial series of hybrid ablations, albeit the protocol may be modified accordingly in the future, especially in the presence of a continuously stable sinus rhythm after the surgical ablation, which could avoid the need for an additional EP evaluation.
As outlined in Figure 4, the benefits of the sequential hybrid ablation were consistent throughout the study period, up to a mean follow-up of 28 months, with 87.5% of patients in sinus rhythm and with 75% of patients free of class I and III antiarrhythmic drugs. The use of implantable loop recorders permitted continuous monitoring of the rhythm outcome, establishing a new standard in patient evaluation after AF ablation. In conclusion, the combination of a full thoracoscopic and transcatheter approach in a staged hybrid fashion proved to be a safe procedure, providing excellent results at mid-term in patients with long-standing isolated AF.
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This is a case series from Dr. Muneretto and his colleagues from Brescia, Italy, describing a novel staged hybrid approach combining surgical thoracoscopic and catheter ablation in patients with lone atrial fibrillation (AF). Twenty-four patients were prospectively enrolled. All the patients had either persistent or long-standing persistent AF. This is a group of patients in which catheter-based pulmonary vein isolation has not been as successful as in patients with paroxysmal AF. This series is unique in that all patients had a continuous monitoring rhythm device implanted at the time of surgery. First, all patients underwent thoracoscopic isolation of the posterior left atrium using a temperature-controlled, internally cooled unipolar radiofrequency device with suction. A month later, patients underwent an electrophysiological study. Bidirectional block was confirmed in 79% at the time of the study. Additional endocardial right- and left-sided lesions were performed in 63% of the patients. The authors reported excellent preliminary results and no late atrial flutter.
This group has been a pioneer in hybrid approaches to AF. The authors are to be congratulated for their excellent results. Readers are to be cautioned that this is still a small experience, and greater numbers and longer follow-up will be needed to fully evaluate this new approach. The advantages of a hybrid staged approach over either catheter or surgical ablation alone will need to be evaluated in a prospective randomized fashion. Although their early results are good, it is notable that the authors did not follow the present Heart Rhythm Society guidelines (Calkins H, Kuck KH, Cappato R, et al. HRS/EHRA/ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation: recommendations for patient selection, procedural techniques, patient management and follow-up, definitions, endpoints, and research trial design. Heart Rhythm. 2012;9:632–696) and defined “failure” as the presence of AF episodes with a duration of more than 5 minutes or an overall monthly burden of AF of greater than 0.5%. The accepted definition is any AF episode longer than 30 seconds.
Despite these shortcomings, this group is to be congratulated on their pioneering work, and we will look forward to continued follow-up of this unique cohort of patients.
Keywords:Copyright © 2012 by the International Society for Minimally Invasive Cardiothoracic Surgery. Unauthorized reproduction of this article is prohibited.
Persistent atrial fibrillation; Hybrid AF ablation; Thoracoscopic ablation; Percutaneous ablation