A Hybrid Ablation Strategy for the Management of Long-standing Persistent Atrial Fibrillation

A combination of advanced catheter navigation and mapping along with simultaneous minimally invasive epicardial and endocardial ablation techniques have led to the development of a novel hybrid approach for the treatment of long-standing persistent atrial fibrillation.

While novel keyhole approaches for epicardial access and ablation have been developed from the surgical standpoint, a complex 3D mapping system such as the EnSite Precision™ Cardiac Mapping System (Abbott) allows for real-time visualization of the ablative procedure. 

The first Canadian hybrid ablation program for the treatment of AF was recently established at Queen’s University and Kingston Health Sciences Centre.

The specific approach adopted is quite unique, and yields the potential to radically impact the treatment of this complex subset of patients.  

A NEW APPROACH TO CARDIAC ARRHYTHMIA

Medical treatment of atrial fibrillation with antiarrhythmic medications has often been regarded as a first-line strategy, albeit it yields significant limitations and, in many instances, may lead to relevant long-term side effects. 

Patients with paroxysmal atrial fibrillation seem to benefit significantly from a transcatheter approach. Evidence has previously suggested that catheter ablation may even represent the first-line strategy, as compared to pharmacological treatment, in select cases with paroxysmal atrial fibrillation. However, clinical outcomes following catheter ablation in patients with long-standing persistent atrial fibrillation have been less favorable. Indeed, restoration of sinus rhythm in the absence of antiarrhythmic medication has been observed in only about 50% of cases in this complex subset of patients. 

Due to the aforementioned reasons, the Maze procedure is still regarded as the gold standard for the surgical treatment of complex forms of atrial fibrillation, such as long-standing persistent. Yet, it is very invasive, requiring cardiopulmonary bypass and opening of the cardiac chambers. The procedure is usually performed concomitantly during open-heart surgery in AF patients with other valvular or coronary diseases through a median sternotomy or, in very limited instances, as a standalone procedure. Therefore, there has been significant interest in the development of novel surgical techniques over recent years aimed at minimally invasive approaches with an epicardial target, avoiding the use of cardiopulmonary bypass and opening of the cardiac chambers. Thoracoscopic epicardial ablation has recently gained popularity among the surgical community given its possibility to deliver a surgical ablation via a keyhole route. Nonetheless, there have been difficulties associated with the possibility to reproduce all the lesion sets of the classical Cox-Maze III procedure via an endoscopic surgical approach. Hybrid ablation offers a necessary solution to overcome this limitation and improve outcomes.

In recent years, the hybrid procedure has emerged as a promising therapy for its ability to combine the advantages of minimally invasive surgical ablation of AF with the endocardial transcatheter approach. However, since hybrid ablation is still in its premature stages, the long-term benefits have yet to be confirmed by a larger series of patients.

RATIONALE FOR HYBRID ABLATION  

In patients with atrial fibrillation, the majority of cardiac triggers are located within or close to the four pulmonary veins. However, as atrial fibrillation transitions from paroxysmal to persistent, the location of the atrial substrate gradually shifts away from the pulmonary veins, which may ultimately guide the ablation approach for each individual patient. Therefore, surgical ablation allows for extensive isolation of all pulmonary veins and the posterior aspect of the left atrium, which not only excludes the ectopic foci within the pulmonary veins (box lesion set), but also targets the macroreentrant circuits and the fragmented potentials usually located within this area.

The minimally invasive procedure may also provide extended benefits with respect to post-ablation outcomes. The delivery of epicardial radiofrequency (RF) energy, creating a “box” lesion set, may mitigate the likelihood of an aorto-esophageal fistula occurring after an endocardial ablation. This technique is also able to address potential gaps in surgical ablation thanks to the possibility of performing a simultaneous assessment by the electrophysiologist to create additional ablation lines, if required. 

Recent findings into the pathophysiological mechanisms of more chronic forms of atrial fibrillation have also provided evidence for the emerging use of the hybrid approach. It has been demonstrated that asynchronous propagation of fibrillatory waves can occur in a three-dimensional fashion, from the epicardium to the endocardium and vice versa (epicardial breakthrough). Notably, endo-epicardial electrical dissociation has been found to be largely responsible for a percentage of such sources of re-entrant tachycardia. 

THE PROCEDURE 

One of the cornerstones of any kind of ablation (either surgical or transcatheter) is represented by the possibility of delivering an effective transmural lesion. In this light, the hybrid approach offers a novel and unique perspective since it provides clinicians with the potential to perform mapping opposite to the side of ablation; thus, a real-time endocardial assessment is performed by the electrophysiologist while the surgeon is performing the box lesion set. 

When this approach is adopted, it can either be performed as a concomitant (simultaneous) or a sequential-staged (delayed) procedure. While a sequential-staged approach does not allow for a sophisticated testing of surgical ablation (at a minimum, the electrophysiologist is present in order to acutely validate surgical ablation lines, by testing entrance and exit block), we opted for the simultaneous presence of  both the surgeon and electrophysiologist, as to offer not only the most advanced mapping system and validation of surgical ablation, but also to provide the option of delivering additional lesions if required, in a patient-tailored approach. The adoption of this simultaneous strategy necessitates the use of a hybrid operating room as well. 

The main steps of the simultaneous hybrid procedure, as developed at Queen’s University, are as follows:

1. Keyhole epicardial access: Three 1-cm incisions are created on the right chest, and by virtue of an endoscopic camera and dedicated instruments, epicardial access is safely and rapidly obtained.
2. Pre-ablation baseline voltage mapping: A baseline voltage map is created using the EnSite Precision Cardiac Mapping System prior to commencing epicardial ablation. This is a breakthrough technology that allows for monitoring and validation of epicardial ablation in an unprecedented way. Thousands of electrical points are collected within the left atrium to obtain a baseline of general atrial conductance. A single transseptal puncture is performed following insertion of two catheters into the right ventricle and coronary sinus. All voltage mapping is completed using a circular mapping catheter for an accurate representation of voltage conductance throughout the left atrium. 
3. Epicardial ablation: A linear device is advanced around all four pulmonary veins in order to create a continuous linear ablation (box lesion set) aimed at excluding not only the four pulmonary veins “en bloc”, but also the posterior aspect of the left atrium. Surgical ablation is achieved by a novel device that is secured to the epicardial surface due to a suction mechanism, and is capable of delivering both unipolar and bipolar RF energy. (Figure 1)
4. Endocardial assessment of ablation transmurality during epicardial RF: The same circular diagnostic mapping catheter is used to monitor local changes in the left atrium during the delivery of epicardial ablation. Following epicardial ablation, the catheter is positioned in all pulmonary veins and along the posterior wall during atrial pacing. (Figure 2)
5. Targeted, tissue-specific endocardial ablation: The post-epicardial ablation voltage map indicates regions of local conduction within the pulmonary veins and posterior left atrial wall, providing targets for tissue-specific endocardial ablation, if required. Endocardial ablation is performed by delivering energy to the sites along the antrum of the veins, targeting entrance sites or gaps in the connecting lines where high-voltage regions are detected. Targeted focal ablation is performed until entrance and exit block into the posterior wall of the left atrium (box lesion set) is established. 
6. Confirmation of electrical isolation of pulmonary veins and posterior wall: Once the target sites are sufficiently ablated, the ablation catheter is exchanged with the circular mapping catheter to re-determine whether conduction is still present. Isolation on the posterior wall and within the pulmonary veins is confirmed by successful demonstration of bidirectional block. High-output pacing is performed subsequent to the creation of a bipolar voltage map with the circular mapping catheter. Successful isolation of the posterior wall and pulmonary veins is confirmed.
7. Epicardial exclusion of the left atrial appendage: Once the ablation has been completed, three additional keyhole incisions are created on the left side of the chest to allow for the epicardial delivery of a clip to mechanically and electrically exclude the left atrial appendage.

CONCLUSIONS 

From a collaborative standpoint, the multidisciplinary nature of this procedure allows for an unprecedented combination of the most advantageous components from both a surgical and transcatheter strategy. As further technological advances are made, this interdisciplinary collaboration will be strengthened in order to provide enhanced and individualized care to this complex subset of patients.

In recent reports, the hybrid concept has yielded increased clinical outcomes when compared to a transcatheter approach in patients with long-standing persistent atrial fibrillation. The use of an epicardial strategy (for both ablation and exclusion of the left atrial appendage) could potentially contribute to a reduction in stroke risk and air embolism, as often observed during complex endocardial ablations, while offering durable results even in the presence of advanced atrial remodeling.

Disclosures: The authors have no conflicts of interest to report regarding the content herein. Outside the submitted work, Dr. Bisleri reports personal fees from AtriCure, Inc.