Ultralow-Temperature Cryoablation Shows Promise for VT

CHICAGO, IL—Cryoablation delivered at temperatures as low as -120°C keeps most patients with monomorphic ventricular tachycardia (VT) free from recurrent episodes at 6 months, according to results from the single-arm FULCRUM-VT investigational device exemption (IDE) trial.

Overall, 59.0% of patients were free from sustained VT, appropriate implantable cardioverter-defibrillator (ICD) interventions, and escalation of antiarrhythmic drugs, with no difference in results between those with nonischemic versus ischemic cardiomyopathy, Atul Verma, MD (McGill University Health Centre, Montreal, Canada), reported here at Heart Rhythm 2026.

Rates of freedom from any ICD therapy and ICD shocks were 61.8% and 84.3%, respectively.

That was accompanied by a “very low” rate of protocol-defined major adverse events through the first 7 days (2.4%), the primary safety endpoint. There were five events, including two cardiac perforations/tamponade, a death, a cerebral infarct or systemic embolism, and a major bleeding requiring transfusion.

A broader endpoint encompassing procedure-related serious adverse events that were not considered device-related occurred in 8%, which Verma said he still considers very low. “These are sick patients, unlike our [atrial fibrillation] patients, and therefore many prior VT ablation trials have been dogged by the serious adverse event rate,” he noted.

Usha Tedrow, MD (Brigham and Women’s Hospital, Boston, MA), the discussant for the study, thought that rate, however, was “a little bit on the high side” based on what has been seen in prior trials, highlighting the four cases of cardiogenic shock, two pericardial effusions, and one cardiac perforation.

“What I don’t know is: are these related to the slightly bigger sheaths that had to be used for this catheter? Was the cardiogenic shock related to slightly longer procedures with longer ablation time? It’s possible,” Tedrow suggested.

She highlighted the positive findings as well, including the high rates of freedom from ICD shocks and acute success, the large reduction in use of amiodarone, and the similar results seen in nonischemic and ischemic cardiomyopathy.

Despite that, the effectiveness in terms of preventing recurrent VT remains around 60%, similar to prior trials.

“The big thing we all have to ask ourselves as we move forward with these larger-footprint devices for VT is: do we need to do some more basic work, go back to the drawing board, and find out mechanistically what’s going on that we’re not targeting the right substrate for our patients?” Tedrow said.

The FULCRUM-VT Trial

Verma noted that there have been challenges with VT ablation in terms of safely delivering energy deep enough “so that we can get to those midmyocardial and potentially epicardial substrates without the difficulty of epicardial access.”

The vCLAS system (Adagio Medical) evaluated in FULCRUM-VT was specifically designed for endocardial ventricular ablations. At temperatures of -120°C, greater ablation depth can be achieved with longer freezing times. Thirty seconds of freeze time penetrates less than 4 mm and 180 seconds of freezing creates lesions ≥ 10 mm deep, “which will cover you pretty much for anywhere in the left ventricle,” Verma said. Preclinical studies have shown that the system is unaffected by the presence of scarring.

The device has received CE Mark approval in Europe and was given a breakthrough device designation by the US Food and Drug Administration.

FULCRUM-VT, conducted at 19 sites, is the first IDE trial of a purpose-built VT ablation catheter, Verma said. The study enrolled 209 patients (mean age 68 years; 92.8% men) with monomorphic VT who had an LVEF of 20% to 50% (mean 35%) and no more than one prior VT ablation in the previous 2 years. Most patients (64.1%) had ischemic cardiomyopathy, with another 30.1% having nonischemic cardiomyopathy and 5.7% having both. About three-quarters of the participants had congestive heart failure, and nearly 70% were taking amiodarone at baseline.

The mean procedure duration was 209 minutes, incorporating a catheter dwell time of 109 minutes, an ablation time of 54 minutes, a freeze time of 47 minutes, a mapping time of 55 minutes, and a fluoroscopy time of 17 minutes.

The large-footprint catheter was used to deliver a mean of 12 lesions in patients with ischemic cardiomyopathy and 11 in those with nonischemic cardiomyopathy. The mean freeze time per lesion was 4 minutes. No cases of ablation-induced ventricular fibrillation occurred and there was no meaningful effect on ICD performance, Verma reported.

For acute success, 98% of VTs that were targeted for ablation were noninducible after the procedure.

There was also a reduction in VT burden, from a median of three episodes before ablation to zero afterward. ICD shocks fell by a little over 80%. Amiodarone use was reduced by a relative 60%, and 72% of patients were on a reduced dose or off the drug altogether at 6 months.

Rates of 30-day readmission for VT (1.9%), heart failure (1.9%), and all-cause mortality (8.4%) were lower compared with prior studies, Verma reported.

He noted that there is an ongoing expansion phase of the trial that is evaluating a second-generation form of the ablation catheter. It is smaller, deliverable through 8.5-Fr sheaths, has a softer and more curvable shaft, and requires 75% fewer freezes per lesion compared with the first-generation system.

‘A Significant Need’

Sana Al-Khatib, MD (Duke University Medical Center, Durham, NC), incoming president of the Heart Rhythm Society, said there is “a significant need” for additional therapeutic options for patients with VT because the source of the arrhythmia can be deep within the myocardium.

The approach studied in FULCRUM-VT sounds promising, she told TCTMD, noting the high rate of acute success, the low rate of complications, and the reduction in amiodarone use. Even so, additional studies are needed in order to evaluate how outcomes can be further optimized, Al-Khatib said.

“VT ablation can be a bit more challenging than let’s say A-fib ablation because the substrate in which VT occurs can be pretty complicated,” she said. “The focus can be pretty deep and also the disease evolves. And so even if you get rid of one clinical ventricular tachycardia, many times another clinical ventricular tachycardia emerges.”

Also, ejection fraction might decline, increasing the risk for other types of ventricular arrhythmias, Al-Khatib explained.

“It’s a challenging substrate,” she said. “But I feel like the technology is improving and I think we have certainly progressed in our understanding in terms of how to prepare for the procedure, how to select patients for the procedure, and how to do the procedure.”