Global EP Summit: AF Ablation

Podcast Transcript

Announcer:

Welcome to Cleveland Clinic Cardiac Consult, brought to you by the Sydell and Arnold Miller Family Heart, Vascular and Thoracic Institute at Cleveland Clinic.

Ayman Hussein, MD:

Good morning, everyone, and welcome to our Global EP Summit. In the coming 15 minutes, I will cover an important topic in Afib. That is the use of single-shot radiofrequency techniques for Afib ablation.

Despite technological advancement, radiofrequency catheter ablation for Afib ablation remains a challenging procedure, as maneuvering the catheter to targeted areas is technically complex and time-consuming. For this reason, a single-shot, primarily balloon-based ablation system has been developed in order to quickly and easily isolate the pulmonary veins. In clinical practice, single shot cryoballoon ablation has progressed at a fast pace and is currently widely used. On the other hand, single-shot radiofrequency techniques have lagged behind, and as of now, there are promising techniques in development, or early clinical stages. For the purpose of single-shot RF ablation, multiple tools have been developed over the past two decades, including circular RF ablation catheters, as well as radiofrequency balloons.

Starting with radiofrequency circular ablation catheters, we have here the pulmonary vein ablation catheter, PVAC, made by Medtronic. The PVAC is one member of the phased radiofrequency ablation catheters family. The phased RF system utilizes an anatomically designed multi-electrode catheters with tissue temperature monitoring. The generator itself uses radiofrequency energy, alternating between unipolar and bipolar currents. And to be noted here that during radiofrequency delivery, real-time electrogram signal monitoring is not feasible, and as such, signal assessment is made between applications. The system that I'm showing here is the second generation of the PVAC system. An observed high rate of silent cerebral infarcts on MRI with this technology led to initial withdrawal of the PVAC catheter. And then after technological improvement, it was reintroduced to clinical practice.

In this recent publication, Acute Outcomes and Safety of the Second Generation PVAC were reported in a large population of patients with paroxysmal and nonparoxysmal atrial fibrillation. Acute isolation of the pulmonary veins was achieved with very high success rates, and in addition, substrate modification targeting complex fractionated electrograms, CFAEs was performed in a significant proportion of patients with nonparoxysmal atrial fibrillation.

Using PVAC for Afib ablation in this population, procedure times were relatively short, especially with PV isolation only, and slightly longer in patients who underwent additional substrate modification which targeted CFAEs. The same applied fluoroscopy times and ablation. That eventually was possible without the added risk of complication with the additional substrate modification in patients with persistent Afib. That said, durable PVI and long-term arrhythmia free survival were not assessed in this paper, and further research is needed to address these topics, especially with the second generation PVAC system.

In terms of safety, in contrast to cryoballoon ablation, phrenic injury was found to be rare. And of note, stroke rates were at 0.3 percent, which is comparable to other published Afib ablation data. There were however some serious concerns about the rates of asymptomatic cerebral embolism, starting with the first generation of PVAC. These occurred in up to one third of patients in initial studies with the first generation, and many factors can actually contribute to that including electrode tissue contact and anticoagulation strategies including target ACT during procedures. That said, in order to reduce the risk of asymptomatic cerebral embolism the next generation PVAC gold catheter was redesigned to eliminate the potential for proximal and distal dipole interaction, and actually replaced the platinum electrodes with gold-plated electrodes to transfer resistive energy more efficiently. The precision gold study reported two percent, or 2.1 percent incidents of ACE legions, or asymptomatic cerebral embolism legions. But subsequent studies raise more concerns, including the study I'm showing here, with more than 20 percent cerebral embolism. That said, the definitions of asymptomatic cerebral embolism may vary, and incidents vary accordingly. But the bottom line is that the PVAC has been shown to have higher rates of asymptomatic cerebral embolism than the most widely used one shot ablation tool from the same manufacturer, Medtronic, referring here to cryoablation, with no clear added benefit. As such, this technology seems to be reaching a dead end.

An open irrigated circular ablation catheter, the nMARQ made by Biosense Webster was thought to potentially overcome with the PVAC system, and indeed showed initial good results with both safety and efficacy. However, due to observed fatal complications from inter esophageal fistulas, this catheter was recalled from the market in 2015. Attention has been since shifted to cryoablation catheter technology, and more recently, to electroporation.

Shifting gears to radiofrequency balloons, the Satake Hot Balloon ablation system is a radiofrequency system comprised of 13 french balloon catheter, 13 french deflectable transseptal sheath, and dedicated radiofrequency generator with a mixing pump. The balloon itself is made of polyurethane membrane, which is highly compliant and can be inflated to 20 to 35 millimeters in diameter with 10 to 20 milliliters of a mix of saline and contrast to allow fluoroscopic visualization. The balloon can be heated by delivering a radiofrequency current between a coil electrode mounted inside the balloon and four cutaneous patches positioned on the patient's back. And the mixing pump actually agitates the inner fluid to maintain a uniform heating pattern inside the balloon. Power up to 150 watts can be delivered in a temperature-controlled fashion to reach target balloon temperature of 65 to 75 degrees Celsius.

During the procedures the balloon can be manipulated within the left atrium via this steerable sheath and an over the wire technique. To be noted here, a separate circular mapping catheter is needed to assess the efficacy of pulmonary vein isolation. Once the balloon is positioned along one of the PV antral it is inflated, and PV occlusion can be confirmed with either ice or venography. The balloon is then heated for two to three minutes, and this can be repeated if residual PV potentials are observed. In addition to pulmonary vein isolation, posterior wall isolation is feasible using this balloon by dragging the balloon along the roof, and inferior aspects of pulmonary veins, and this has been shown in some studies.

Of note here, because of the temperature on the surface of the balloon being uniform, heating of surrounding structures like the esophagus or the phrenic nerve cannot be prevented. Therefore, cooling of the esophagus is performed via injection of ice saline, and phrenic nerve pacing is performed during ablation of the septal PVs. To be noted here, the rates of pulmonary vein stenosis with this balloon are not uncommon and were reported to be as high as five percent in some studies. Indeed, given its compliance profile, the balloon can be wedged too deep into the vein, as such increasing this risk. In terms of clinical outcomes, several clinical studies have been performed with the SATAKE Hot Balloon, which showed feasibility and safety and lead to its approval for clinical use in Japan. Legions with this balloon are typically less wide than those obtained with cryoballoon ablation, but outcomes have been found to be comparable and superior to medical rhythm control strategies. In fact, many studies using this balloon reported about 60 to 65 percent freedom from arrhythmia re-occurrences.

Another radiofrequency balloon is the Luminize Balloon, formerly known as Apama Balloon, which has an open irrigated ablation electrode, or multiple ablations electrodes, and the built in camera inside the balloon with LED lighting. The balloon is manipulated in the left atrium via steerable sheath and over the wire technique. Once the balloon is positioned along one of the PV antra tissue electrodes contacts is confirmed via direct visualization using the camera, and individual electrode impedance readings. In order to isolate the pulmonary veins, radiofrequency energy is delivered through the electrodes at the equator of the balloon, and in bipolar fashion at six to 10 watts for up to 60 seconds with irrigation of normal saline. If needed, radiofrequency delivery can be tailored at PV breakthrough sites, and can be limited to areas of esophageal or phrenic, never proximity.

In addition to pulmonary vein isolation with this balloon, it is possible to perform additional ablation using the forward-facing electrodes and both bipolar and unipolar ablation fashions, as such allowing ablation of non-PV targets. The clinical data with this balloon is still limited. More recently, the results of the AF-FICIENT trial were presented at the EHRA meeting last year and showed a high rate of acute PV isolation with no serious adverse events. But we note here that further studies planned to assess this technology, but the future is again unknown due to the wide use of cryoballoons with established safety and efficacy. But most importantly, with the rapid progress being made with electroporation.

The last radiofrequency ablation balloon that I will show here is the Heliostar RF Balloon from Biosense Webster. The system includes a 13.5 radiofrequency balloon catheter, a three french circular mapping catheter for mapping purposes, and a 13.5 french steerable sheath with a dedicated multichannel generator. The radiofrequency balloon itself is a 28-millimeter compliant balloon with 10 irrigated flexible gold-plated electrodes. The balloon's circular mapping catheters are equipped with sensors and visualized in CARTO. In addition, all electrodes can ablate, sense, and pace, but the circular mapping catheter is important here because it allows better assessment of time to isolation. Radiofrequency energy is delivered through each electrode independently in a unipolar and temperature-controlled fashion using a maximum power of 15 watts, and the maximum temperature of 55 degrees Celsius, which allows for quick single-shot circumferential as well as segmental ablation when needed.

In order to prevent esophageal injury here, radiofrequency energy is turned off after a maximum of 20 seconds in the posterior electrodes. In addition, phrenic nerve pacing from the superior vena cava is also performed while ablating the right PVs to prevent its injury. In addition to isolation of the pulmonary veins, extra-PV ablation is also possible with this balloon with dragging of the posterior wall and tailored RF application. With this technique there is still few clinical data available to date, but the feasibility study RADIANCE has shown an efficient and acute PV isolation in all patients enrolled with very good long-term results. That said, further and larger studies are still needed to prove the efficacy and safety of this technique, but the future also remains unclear for this technology as well.

In summary, many single-shot RF tools have been developed, and reproducibly found to be very efficient for acute PV isolation. There are safety concerns with circular radiofrequency ablation catheters, and better results with open irrigated radiofrequency balloons, especially the LUMINIZE and HELIOSTAR, however advantages over cryoballoon ablation techniques have yet to be established. On the other hand, the quick advancement in electroporation for A-fib ablation may eliminate the need for single-shot RF techniques, primarily due to cumulative about its safety and tissue selectivity. With this, I conclude my talk. Thank you very much for your attention.

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