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New AF ablation techniques on horizon to address current challenges
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Catheter ablation for the treatment of atrial fibrillation has historically been a challenging procedure, with many patients ultimately experiencing recurrence of atrial fibrillation within months. This often results in the need to repeat the ablation procedure.
Multiple procedures can be associated with risks as well as increased costs to the health care system. Even with this strategy of multiple ablations, the success rates for maintenance of sinus rhythm in patients with paroxysmal AF approaches only 70%. Although this approach achieves the desired result in many patients, some continue to have symptomatic arrhythmias.
Available treatment options
The cornerstone of ablation therapy for the treatment of AF is pulmonary vein isolation.
Tom McElderry
Takuma Yamada
During the procedure, the electrophysiologist attempts to encircle the pulmonary vein with an ablation lesion set that serves to isolate the vein from the atrial tissue. For patients who undergo recurrent procedures to treat AF, return of the pulmonary vein to left atrial conduction is a ubiquitous finding.
In the United States, there are two FDA-approved ablation therapies for the treatment of AF: radiofrequency and cryoablation. Each of these systems has shortcomings that contribute to their current suboptimal success rates.
With radiofrequency ablation, a 3.5-mm open-irrigated ablation catheter is used in conjunction with a 3-D mapping system (Biosense Webster) to create a circumferential lesion set in a point-by-point fashion. The size of each individual point radiofrequency ablation lesion is often very different, even if the same power and duration are administered by the operator. Radiofrequency energy preferentially flows to the lower impedance blood pool in such a way that the majority of applied energy often does not contribute to lesion formation. Factors such as contact force and tissue geometry, which vary from location to location, influence the relative distribution of radiofrequency energy. This lesion heterogeneity renders it challenging to create a contiguous lesion set around the vein.
Cryoballoon ablation has arisen as an alternative approach, but this technique is not without its own shortcomings. The warming effect of blood flow over the balloon often prevents regions from achieving necessary temperatures to create durable ablations. Occlusion of blood flow in each vein is critical to achieving the desired temperature. Since the cryoballon is noncompliant, the balloon location to achieve occlusion can vary. If unable to achieve occlusion, differential cooling of the balloon can yield inconsistent lesions, resulting in lack of circumferential pulmonary vein isolation. The inability to titrate energy and balloon size may contribute to complications such as phrenic nerve paralysis.
Technologies designed to address challenges
In the United States, there are new technologies on the horizon designed to address procedural challenges associated with the currently available techniques. The University of Alabama at Birmingham, along with several leading US cardiac centers, have recently completed enrollment and treatment phases, including more than 350 patients, in the FDA pivotal trial of the HeartLight endoscopic ablation system (CardioFocus). This device features unique intraoperative visualization capabilities and laser energy delivery. The pivotal trial was designed to investigate its safety and efficacy as a potential new treatment for AF.
The HeartLight laser balloon, unlike cryo, is completely compliant and allows adjustability to accommodate for variations in pulmonary vein anatomy. This permits consistent placement of the system at the pulmonary vein ostia. Once the balloon is positioned at the ostia of the vein, a live endoscopic view is rendered. This endoscopic view is used to plan the lesion path. A 30-degree arc of focused laser energy is used to create the ablation lesions. Laser applications are typically 20 to 30 seconds at each location. The operator is able to titrate energy delivery to adjust to differences in tissue thickness. Because the laser energy directly heats the tissue while the balloon displaces intervening blood, there is very little energy loss. This results in more consistent lesion creation. Additionally, because the operator can directly visualize the location of energy delivery, sufficient lesion overlap and contiguity can be assured.
Currently, the system is in clinical use throughout Europe, with multicenter data showing comparable, if not better, acute and durable isolation rates compared with alternative available systems. Some European investigators, such as Boris Schmidt, MD, of the Cardioangiologisches Centrum Bethanien in Frankfurt, Germany, have also recently reported positive initial experiences in using the HeartLight system in the treatment of persistent AF.
Future of ablation
In summary, our center’s experience with the endoscopic ablation system has been very positive and we look forward to the results that will be coming forward this year. The visually guided laser balloon system has shown to be safe and effective in initial studies, and has become commercially successful in Europe and Australia in effectively providing durable lesions and decreasing the need for repeat ablation procedures.
Disclosure: McElderry reports financial ties with Boston Scientific, Biosense Webster, St. Jude Medical, Vytron US and Voyage Medical. Yamada reports no relevant financial disclosures.