The CardioFocus HeartLight® Ablation System: Clinical Trial and Initial Experience

Introduction

Pulmonary vein isolation (PVI) for the treatment of paroxysmal atrial fibrillation (PAF) has historically been a challenging procedure, with a large percentage of patients ultimately experiencing recurrence of PAF within the first 1-2 years. The majority of these recurrences are a result of recurrent electrical conduction that occurs relatively acutely or subacutely following PVI. Many studies have shown that the recurrence rates for PV conduction post ablation are as high as 50-80%.1,2 Moreover, follow-up electrophysiology studies in patients who did not have clinical AF recurrence following PVI have shown that a significant percentage of this population have recurrent PV conduction in one or more veins. These data suggests that durable PVI is a difficult goal to achieve.

The CardioFocus HeartLight Endoscopic Ablation System features unique capabilities, including intraoperative direct visualization of the PVs and laser energy delivery, which may lead to a more durable ablation procedure, based on recent clinical experience.^2,3  At our center, we recently completed enrollment in the HeartLight clinical trial, which is examining the efficacy and safety of this system for PAF in a pivotal study. In this article, we will review our experiences applying the technology to clinical practice and honing our technique in terms of energy delivery and device positioning.

About the System

The HeartLight system uses a variable diameter, compliant balloon with a flexible tip to avoid trauma in the PV (Figure 1). This catheter is inserted via a steerable 12 Fr sheath and positioned in the ostia of the PV to occlude blood flow and allow for antral/ostial tissue visualization. The balloon is inflated and cooled with sterile D20 and can be sized to fit a large range of orifices. In the center lumen of the balloon there is an endoscopic camera that allows for direct visualization of the PV tissue when the balloon is properly positioned and occluding PV ostium. Additionally, the central lumen contains a maneuverable optical fiber that generates a 30° arc of both visible and near-infrared ablative light (laser) energy. This arc of laser energy is focused at the desired location on the PV antrum and then can be moved distally or proximally and also rotated around the perimeter of the balloon, (using a knob on the catheter handle), to allow for a circumferential ablation. The HeartLight catheter is attached to a freestanding console where inflation size is controlled, images obtained by the endoscope are shown in real time, and ablation power can be selected and delivered. The console also has the ability to store and reference images of each ablation lesion location so these can be reviewed by the operator to ensure circumferential ablation has been completed. 

Clinical Practice

Twenty-one clinical investigators (including the Medical University of South Carolina) have now completed enrollment and treatment phases in the pivotal HeartLight trial comparing this system to traditional open-irrigated ablation in more than 350 patients with paroxysmal atrial fibrillation. The results of this trial should be available in the next year. Prior to this study, the first 200-patient experience was previously reported and the system demonstrated acute PVI success rates of 99%, with high rates of durable PV isolation.³ This translated into a 60% AF-free survival at one year, which is comparable to RF ablation. Additionally, the HeartLight system was shown to be reasonably safe with no incidences of stroke, atrioesophageal fistula or PV stenosis; however, there is a low rate of phrenic nerve injury (but lower than other approved balloon-based ablation systems) and pericardial tamponade (due to the large, potentially traumatic delivery sheath). Procedural, ablation and fluoroscopic times with this system can initially be long, but decreases with operator experience. 

The HeartLight system is currently under FDA evaluation in the U.S., but has received CE Mark in Europe and is in commercial use across the EU. Some European investigators have reported their initial experiences using the HeartLight system in persistent AF, which have been positive.⁴

Experience at MUSC

In our clinical experience, there are several key advantages of the HeartLight system over traditional ablation and other balloon systems. The HeartLight system allows for directly guided visualization of the lesions that are made. While lesions are often difficult to see in vivo on the PV tissue, the console is able to store each ablation location for each vein and ensure that the operator has achieved satisfactory lesion “overlap” with complete circumferential coverage. In our experience, this “forces” the operator to complete a full circle of lesions prior to electrogram mapping to check for isolation. Often, during RF ablation operators can see isolation before complete anatomic circumferential ablation is completed; if ablation is terminated at this time, it provides a substrate for inadequate lesion formation and PV reconnections. Acute success rates for PV isolation are excellent (at 99%), and our experience is similar. We have seen that after a few cases, we have been able to get “first pass” isolation in the vast majority of PVs. Higher power titration in areas of thicker tissue, such as the left atrial appendage (LAA) ridge, may also expedite isolation and reduce rates of PV reconnection, while decreasing power in thinner areas of tissue that are adjacent to ancillary structures (e.g., esophagus, phrenic nerve) may avoid potential complications.^3,5 Also, as shown in initial clinical studies, the durability of isolation with the HeartLight system is very high. We have noted that it is rare for veins to reconnect intraprocedurally even after long wait times and pharmacologic challenges. Finally, our clinical success in patients undergoing a single HeartLight procedure is very promising.

Compared to a cryoablation balloon, the HeartLight balloon is compliant and its size is variable, allowing a single catheter to treat a broad range of vein sizes. As previously noted, the HeartLight catheter also allows for lesions to be delivered at specific locations at varying power levels along the balloon surface, thus potentially increasing lesion depth in regions of thick atrial tissue and avoiding damage to adjacent structures; on the contrary, the cryoballoon system does not allow this flexibility as the same level of ablation energy is applied over the entire balloon surface area. Additionally, one recently published article suggested that clinical outcomes may be improved with HeartLight over cryoballoon ablation.⁶

Challenges and Limitations  

The HeartLight system is robust, user friendly, and has a relatively rapid learning curve for most operators, but like any new technology, there are a few limitations with its use. First, the delivery sheath is large, and requires a low and anterior transseptal puncture in order to facilitate easy cannulation of the right inferior pulmonary vein (RIPV), which can often be difficult with large ablation catheter systems due to its proximity to the interatrial septum. In our experience, we have used a combination of ICE imaging, pulmonary venography and left atrial angiography to ensure that we have a low and anterior transseptal access that will allow sufficient room between the puncture site and the ostium of the RIPV to facilitate access to this vein. Also, the original prototype of the transseptal sheath used for the HeartLight catheter was stiff and there were cases of tamponade due to LA perforation/laceration with the sheath. The newly designed catheter (which was used in the pivotal trial) has a much softer tip design and tamponade rates are now much lower and comparable to RF ablation. As with any larger steerable sheath, management of the sheath is critical to avoid complications. We have employed the technique of “safe parking” to avoid sheath-related trauma, which ensures the sheath edge is never exposed in the LA without the soft-tipped balloon catheter located out of the sheath into a pulmonary vein.

Limitations of many balloon catheter systems, including HeartLight, include cases where there are very large common veins that cannot be occluded even at the largest inflation sizes, or very small ancillary veins that cannot be cannulated and occluded without “watermelon seeding.” These relatively rare anatomic variants may limit an operator’s ability to use the HeartLight system alone in a given patient; however, pre-ablation imaging using CT angiography can predict these cases ahead of time and, in fact, no patients needed to be excluded in the pivotal clinical trial based on PV size due to wide protocol criteria. Another common limitation of balloon ablation catheters includes the “ostial” level of isolation achieved compared to a more antral isolation using traditional RF catheters.⁷ We have found that careful balloon positioning using varying balloon sizes and proper sheath positioning and torque will allow for complete PV occlusion which provides good tissue visualization at a more antral level. Finally, similar to cryoballoon ablation, there is a small risk of phrenic nerve injury (2-3%) with the HeartLight system, which is considerably lower than the >10% rate reported with cryoballoon in the STOP AF trial.^3,8 We have noted that high-output pacing from the SVC allows us to monitor phrenic function during ablation (particularly of the right superior PV), and titrate our power at different locations in the vein antrum to avoid permanent injury.

The HeartLight system also can include longer procedure and ablation times compared to traditional RFA. While there is no doubt that delivering complete circumferential ablation takes time and may be longer than RFA or cryoballoon, both procedure and ablation times do dramatically decrease with only limited operator experience (i.e., 10-15 cases).³ Techniques that facilitate more time-efficient procedures include proper balloon and catheter positioning, allowing for total PV occlusion and avoiding the need for repositioning during circumferential ablation. Also, titrating up power delivery in thicker regions of tissue can reduce procedure times by achieving “first pass” isolation after a single series of circumferential applications. In our lab, we always try to use at least 8.5W of power wherever we have good contact, and increase the power to 10-12W in the anterior segments of the PV antra, especially at the LAA ridge. 

Finally, there are small risks of thrombus formation with the HeartLight system, especially if ablation is performed in a stagnant blood pool where contact is poor. We avoid this using preventive measures, such as ensuring maximal PV tissue contact prior to ablation, and when perfect contact cannot be achieved, titrating to lower powers (5.5W) and ablating only in regions where blood flow is active and passive cooling may occur. We always stop ablation when energy is delivered into stagnant blood, as this can result in balloon perforation (which is not dangerous but requires new catheter insertion) and more importantly could cause embolism and stroke.

Conclusions

In summary, achieving good long-term outcomes following AF ablation remains challenging due to difficulty obtaining complete and durable PVI. A novel technology using the HeartLight visually-guided laser balloon system may allow for better lesion formation and outcomes in patients with PAF. This technology has been shown to be safe and effective in initial clinical trials, and is already in commercial use in Europe with good success. Our center’s experience in the pivotal HeartLight trial has been very promising, and we look forward to the results that will be coming forward in the next year.

Disclosures: Dr. Cuoco reports travel/accomodations expenses covered or reimbursed by CardioFocus for off-site training. Ms. Adams has no conflicts of interest to report. Dr. Gold reports grants/grants pending to his institution for the clinical trial. 

References

1. Cappato R, Negroni S, Pecora D, et al. Prospective assessment of late conduction recurrence across radiofrequency lesions producing electrical disconnection at the pulmonary vein ostium in patients with atrial fibrillation. Circulation. 2003;108(13):1599-604.
2. Dukkipati SR, Kuck KH, Neuzil P, et al. Pulmonary vein isolation using a visually guided laser balloon catheter: the first 200-patient multicenter clinical experience. Arrhythm Electrophysiol. 2013;6(3):467-72.
3. Dukkipati SR, Neuzil P, Kautzner J, et al. The durability of pulmonary vein isolation using the visually guided laser balloon catheter: multicenter results of pulmonary vein remapping studies. Heart Rhythm. 2012;9(6):919-25.
4. Schmidt B, Böhmer MC, Perrotta L, Bordignon S, Fürnkranz A, Dugo D, Chun KRJ. Is there a role for Balloon Catheter Ablation in Persistent Atrial Fibrillation? The Laser versus RF Study. Abstract submitted October 2013.
5. Metzner A, Wissner E, Schoonderwoerd B, et al. The influence of varying energy settings on efficacy and safety of endoscopic pulmonary vein isolation. Heart Rhythm. 2012;9(9):1380-5.
6. Bordignon S, Chun KR, Gunawardene M, et al. Comparison of balloon catheter ablation technologies for pulmonary vein isolation: the laser versus cryo study. J Cardiovasc Electrophysiol. 2013;24(9):987-94. 
7. Reddy VY, Neuzil P, d’Avila A, et al. Balloon catheter ablation to treat paroxysmal atrial fibrillation: What is the level of pulmonary venous isolation? Heart Rhythm. 2008;5:353-360.
8. Packer DL, Kowal RC, Wheelan KR, et al; STOP AF Cryoablation Investigators. Cryoballoon ablation of pulmonary veins for paroxysmal atrial fibrillation: first results of the North American Arctic Front (STOP AF) pivotal trial. J Am Coll Cardiol. 2013;61(16):1713-23.