Pulsed Field Ablation Measures Up in Head-to-Head Trial

AMSTERDAM -- Pulsed field ablation appeared as safe and effective as thermal ablation in treating paroxysmal atrial fibrillation (Afib) in the first randomized head-to-head trial for the novel technology.

Efficacy failure of the procedure -- initial procedural failure, documented atrial tachyarrhythmia after a 3-month blanking period, antiarrhythmic drug use, cardioversion, or repeat ablation -- at 1 year met the Bayesian noninferiority criterion, with an estimated probability of 73.3% compared with 71.3% among patients randomized to cryoablation or radiofrequency ablation.

Serious adverse events related to the Farawave device or procedure likewise occurred at a similar rate in the two groups (six of 305 vs four of 302, estimated incidence 2.1% vs 1.5%, posterior probability of noninferiority >0.999), reported Vivek Y. Reddy, MD, of the Icahn School of Medicine at Mount Sinai in New York City, at the European Society of Cardiology (ESC) congress. The findings also were published in the New England Journal of Medicine (NEJM).

Expectations for this technology were high to potentially increase efficacy and safety, so the fact that the trial met non-inferiority but not the secondary aim of superiority for efficacy might have been a little disappointing, suggested ESC session study discussant Samuel Kiil Sorensen, MD, of Gentofte University Hospital in Copenhagen, Denmark. Although "compared to decades of developments in thermal ablation, this was the first generation pulsed field ablation catheter," he added to MedPage Today.

While not directly comparable, he pointed to efficacy rates in earlier trials closer to 80%.

The findings follow the positive pivotal results of the PULSED AF trial with another pulsed field ablation catheter this spring. In that single-arm trial, 66.2% of paroxysmal Afib patients achieved 12-month freedom from abnormal rhythms, as did 55.1% of those with persistent Afib at baseline.

However, even the same efficacy with greater safety and speed is likely worthwhile, Reddy said at the hotline session.

"There are reasons to be excited," he said, pointing to shorter procedure times as one way to look at performance and the lack of any esophageal or phrenic nerve injury -- despite taking no precautions to prevent it with the pulsed field procedure -- whereas there were two cases of persistent phrenic nerve injury in the thermal ablation group.

Pulsed field ablation catheters, which are not yet approved in the U.S., use microsecond-scale, high-voltage electrical fields to damage cell membranes and thus induce tissue necrosis, without relying on very high or very low temperatures to do so. It is delivered over a guidewire to each pulmonary vein with a deflectable sheath.

The promise of this non-thermal ablative approach was that it would increase safety by not transmitting damaging thermal energy to adjacent phrenic nerve and esophageal structures.

Indeed, the trial included pulmonary vein area as a secondary safety endpoint to get at the advantage for phrenic nerve safety in a trial not large enough to reliably catch rare events. It declined by −0.18 cm² (0.9%) with pulsed field ablation and −1.18 cm² (12.0%) with thermal ablation, which met the criterion for superiority.

The ADVENT trial randomly assigned 607 patients with drug-refractory paroxysmal Afib to undergo single-blind pulsed field ablation with the Boston Scientific/Farapulse catheter or thermal ablation, with roughly half of centers assigned conventional radiofrequency and the rest assigned cryoballoon ablation.

Pulsed field ablation procedures were shorter by nearly 20 minutes (total procedure time 105.8 vs 123.1 minutes), although their mean fluoroscopy time was longer (21.1 vs 13.9 minutes). Reddy called this notable given that most operators had never used the pulsed field catheter before the trial but had done thousands of prior thermal ablation procedures. The protocol called for one to three roll-in patients per center for the sake of familiarity with the catheter.

In terms of efficacy and safety, Reddy said, "I look at this as the floor."

Even so, there were no cases of esophageal or phrenic nerve injury despite use of no specific strategies to avoid them. In fact, esophageal-management strategies, like temperature monitoring, cooling, or deviation, were discouraged for pulsed field ablation but allowed for thermal ablation.

Two patients who underwent pulsed field ablation had pericardial tamponade. One who had mechanical injury from the catheter died 10 days later; the other case of tamponade was also felt to be mechanical.

While there was no data from this trial to answer whether tamponade risk was specific to pulsed field ablation, Reddy laid out the case that it was a "spurious" finding.

"This complication occurred as a result of catheter manipulation and was not related to the delivery of pulsed field energy," the researchers wrote in NEJM, adding that "[s]uch complications may become less frequent with greater operator familiarity with the technology. Indeed, in the initial postapproval European experience in the observational MANIFEST-PF study of the pulsed field ablation catheter, the incidence of pericardial tamponade seemed to decrease with increasing operator experience, and death occurred in 1 of 1758 patients (0.06%)."

"A fatality is always concerning," acknowledged Soerensen.

However, he agreed that the risk didn't look worrisome. "In the large registries, we have safety data of more than 1,500 patients with only one death. In these large, real-world registries we get a better estimate about the mortality rate than we do in this trial."

Questions of durability would be best answered by large, potentially post-marketing, randomized trials with mandatory remapping of the pulmonary veins longer term after the procedure comparing pulsed field with thermal ablation, he suggested.

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