Good Early Results for Conformable, ‘Single-Shot’ Pulsed-Field Ablation Catheter

BERLIN, Germany—A novel conformable pulsed-field ablation (PFA) catheter that contains both mapping and ablation capabilities can efficiently and safely isolate the pulmonary veins in patients with paroxysmal atrial fibrillation (AF), according to first-in-human results.

The “single-shot” Sphere-360 catheter (Medtronic) provided acute electrical isolation of all pulmonary veins, with durable results seen in patients who underwent remapping after the procedure, Vivek Reddy, MD (Icahn School of Medicine at Mount Sinai, New York, NY), reported last week at the European Heart Rhythm Association Congress 2024.

Moreover, there was a high rate of freedom from recurrent atrial arrhythmias through 1 year (81.8%) in the single-arm study, which was published simultaneously online in EP Europace. On the safety side, there were no device-related serious adverse events in the week after the procedure.

“In this first-in-human study, we conclude that this conformable PFA catheter was efficient, it was safe, and it was clinically effective in performing PV isolation,” Reddy said. “And it creates durable PV isolation lesions, at least with the final waveform.”

The Sphere-360 Study

The Sphere-360 catheter, which doesn’t have regulatory approval in the US or Europe, is an over-the-wire catheter with a conformable lattice tip that is delivered through an 8-Fr sheath; its maximum dimension is 34 mm. It has six sections that are independently and sequentially energized to deliver pulses to perform ablation, as well as six electrodes that provide mapping and stimulation. Because this is a single catheter, the ablation procedure can be performed through a single transseptal puncture, Reddy said.

The current study was a first-in-human series of 85 patients (mean age 58.3 years; 56% men) who underwent ablation with the Sphere-360 catheter at three European centers. All had symptomatic paroxysmal AF and either failure or intolerance to at least one class I-IV antiarrhythmic drug. Follow-up included weekly transmissions of arrhythmia recordings by telephone for the first 21 weeks, followed by monthly or symptom-driven transmissions after that; plus, 48-hour Holter monitoring was used at 6 months and 1 year.

The average procedure time was 56.5 minutes, which included a left atrial dwell time of 19.1 minutes and a fluoroscopy time of 5.7 minutes. The average number of lesions applied per pulmonary vein was 3.9.

Results using the first pulse waveform (PULSE1) in terms of lesion durability were not as good as the investigators wanted, so the waveform was modified over the course of the study. Ultimately, 30 patients were treated with PULSE1, 20 with PULSE2, and 35 with PULSE3, although only 12 of the patients in the last group had completed 1-year follow-up.

The primary efficacy endpoint was acute electrical isolation of all pulmonary veins using the Sphere-360 catheter, and this was achieved in 100% of cases. Freedom from atrial arrhythmia recurrences through 1 year (after a 3-month blanking period) was a secondary outcome, and this was achieved by 100% of patients treated using the most-optimized PULSE3 waveform.

A subset of patients underwent remapping about 75 days after the procedure, and this showed that most lesions were durable. Per pulmonary vein, 82% of lesions were durable using the initial PULSE1 waveform, 88% with PULSE2, and 99% with PULSE3.

The primary safety endpoint was study device-related serious adverse events within 7 days of the procedure, and no such events were observed. There was one serious adverse event related to the procedure, however—a patient had symptoms of diplopia and vertigo that resolved after 2 days, with MRI ruling out an embolic event. “We believe this was the sort of migraine-like phenomenon that we sometimes see after ablation procedures,” Reddy said.

Subsets of patients underwent esophageal assessments and brain MRIs. There were no cases of thermal injury to the esophagus. On brain MRI, 10% of patients had signs of acute ischemia with FLAIR hyperintensity and 8% had signs of acute ischemia without FLAIR hyperintensity. The rate of silent cerebral ischemic events and lesions is in line with what has been seen with other pulsed-field and thermal ablation technologies, the researchers say.

‘Need to Learn More’

Reddy acknowledged the limitations of the study, including the relatively small number of centers, operators, and patients who participated; the use of intermittent monitoring for recurrent arrhythmias, which likely overestimated success; and the uncertain impact of this catheter for other lesion sets or in patients with nonparoxysmal AF.

Nonetheless, “certainly the data look really impressive,” said Jonathan Kalman, MBBS, PhD (Royal Melbourne Hospital and the University of Melbourne, Australia), who served as the discussant following Reddy’s presentation. He noted that “we’re now in the era of PFA and this really dizzying array of new technologies.”

On the positive side, the Sphere-360 catheter showed good outcomes in terms of arrhythmia recurrence, solid durability of lesions, and excellent safety, Kalman said. In addition, procedure times were short for a first-in-human study, with the integrated 3D mapping allowing for a better understanding of what operators are doing and limited fluoroscopy time, he said. Plus, the sphere can adjust to the venous anatomy and sheath size is smaller than others that operators have been using.

But there are caveats in terms of efficacy, safety, and durability, Kalman said, pointing to the relatively small number of patients treated in the study. He also highlighted the possibility that the intermittent arrhythmia monitoring used during follow-up may have missed some AF episodes. The size of the sphere delivering the energy pulses may be an issue, too, he indicated.

“In careful hands, this is a very effective tool, but it could do a lot of damage very rapidly if you’re less careful, and one wonders with the deformability and the 34-mm size whether you might inadvertently isolate the appendage,” he said.

Overall, Kalman said, “I think this is a really exciting technology, . . . and I think we just await more accumulating data.”

Agreeing was K.R. Julian Chun, MD (CardioAngiologisches Centrum Bethanien, Frankfurt, Germany), who commented to TCTMD that “the big uncertainty is of course the translation of this very, very initial clinical experience into practice.”

The outcomes of this study are encouraging, Chun said, adding that the over-the-wire setup will help stabilize the device compared with other types of systems. “Still, however, we need to learn more,” he noted.

Additional data on safety will be key, too, he indicated. “Of course, safety is a very, very big thing. This is the promise of PFA, in my opinion, and therefore we need to learn also more about this on the safety side.”