Catheter-Free Radiation Ablation of VT Still 'Safe, Effective' at Late Follow-up

May 18, 2020

A technique borrowed from radiation oncology that takes the catheter out of catheter ablation continued to put in an impressive performance, observers say, in the longest yet follow-up of patients with intractable ventricular tachycardia (VT) who underwent the procedure.

Of the 19 patients who received VT ablation by stereotactic body radiation therapy, a fairly sick group that had failed to respond to antiarrhythmic therapy and prior standard ablations, 78% had a reduced VT burden at the 24-month follow-up compared to the 6 months prior to their procedure.

The corresponding rate 6 months post procedure had been 94% in the study called ENCORE-VT, which was published in November 2018 and covered at the time by theheart.org | Medscape Cardiology.

There were three serious adverse events believed related to the radioablation procedure during the follow-up averaging 34 months, including two pericardial effusions that were managed medically.

"Importantly, very few patients were actually cured of their VT. Most people still had small amounts of VT, but cure was not the intent of the study given the advanced illness in this patient group," Phillip Cuculich, MD, Washington University, St. Louis, Missouri, said at media briefing on the study presented May 8 as part of the Heart Rhythm Society (HRS) 2020 Scientific Sessions virtual presentation.

The potential late adverse tissue effects of radiation therapy are well recognized, so long-term follow-up is considered especially important for these patients, some of the earliest to undergo VT radioablation within a prospective study.

"I was and always will be nervous about the long-term effects of radiation intentionally delivered into the heart," Cuculich told theheart.org | Medscape Cardiology, "but more than the than the efficacy of this, I'm actually impressed by the safety so far."

Only one of the 19 patients was hospitalized with heart failure during the first 6 months, he said, "so the procedure itself is extremely safe. It doesn't seem to drive a heart failure phenotype, and it doesn't seem to drive any new ventricular arrhythmias."

Cuculich also described the procedure as "quick and noninvasive." The median treatment time was 15 minutes. "Patients are treated as outpatients. They literally get up, walk out, and go home after therapy," he said. "In general this appears to be a very gentle ablation experience for patients."

The current analysis, "a longer-term follow up of ENCORE-VT, showed an impressive persistent antiarrhythmic effect of radiation therapy," agreed Usha B. Tedrow, MD, Brigham and Women's Hospital, Boston, "despite a patient population a bit sicker than typical catheter-ablation series."

Tedrow, speaking as an invited discussant after Cuculich's presentation of the study, also raised concerns about the procedure's potential for adverse effects from radiation.

"What are the risk factors for gastrointestinal toxicity with radiation delivery? It's difficult to say with the number of patients studied here," she said. "Future investigations should surely include improving on existing methods for avoiding gastric and esophageal exposure to radiation during treatment."

The procedure's efficacy in the current cohort "appears to be quite good, and it's fairly durable," Paul C. Zei, MD, PhD, Brigham and Women’s Hospital, Boston, Massachusetts, told theheart.org | Medscape Cardiology. The results are exciting, he said, in light of what could be expected from available therapies for such high-risk patients with intractable VT.

"They really don't really have a lot of good options, so in context this is head and shoulders above what we've seen in larger studies, if you look at the VT ablation literature with ablation catheters," Zei said. There was "almost a quantum leap in efficacy. When you pair that with the ease of doing the procedure itself, in terms of procedural risk, it becomes very appealing."

Still, "I would have a very tempered view of this. I think we're very hopeful, but I think we really are all clamoring for a lot more data to try to validate this across larger populations." And as the procedure matures, Zei said, "there is going to be a gradation of increasing risk" as it is potentially extended to patients who are less and less sick. "I think that's something we're all going to need to be cautious about."

To be eligible for ENCORE-VT, patients were required to have monomorphic VT or cardiomyopathy from premature ventricular contractions (PVCs) with an LVEF less than 50%; the median was 25%. They were to have experienced at least three VT episodes over the prior 6 months or have a greater than 20% PVC burden and to have been unresponsive to at least one antiarrhythmic agent and to have undergone at least one unsuccessful catheter ablation.

Three fourths were in NYHA class 3-4 heart failure at the time of their procedure.

There were three serious procedure-related adverse events observed later than 6 months after the ablation: two cases of pericardial effusion, both treated with colchicine, and one gastropericardial fistula that became apparent 2½ years after the procedure and was successfully treated with surgery, Cuculich reported.

"Much work needs to be done to refine the technique," he said at the briefing. "Right now, based on these results, we believe that cardiac radioablation is best suited for high-risk patients who have failed conventional VT treatments."

However, the technique has the potential to make VT ablation more universally available. "There are 10 times to 20 times more radiotherapy units worldwide than catheter mapping systems," he noted. "So cardiac radioablation really has the potential to extend access to VT treatment to parts of the world that never would have considered getting a VT ablation from a catheter."

Cuculich discloses consulting for Varian Medical Systems and Medtronic. Tedrow discloses receiving honoraria or speaking or consulting fees from Medtronic, Biosense Webster, St. Jude Medical, and Thermedical. Zei has previously disclosed research support from or consulting for Cyber Heart, Biosense Webster, and Abbott/St. Jude Medical.

Heart Rhythm Society (HRS) 2020 Scientific Sessions: Late Breaking Clinical Trials 2. Presented May 8, 2020.

Follow Steve Stiles on Twitter: @SteveStiles2. For more from theheart.org | Medscape Cardiology, follow us on Twitter and Facebook.

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