VT Reduced With Single Radiation Treatment

Pam Harrison

September 16, 2019

CHICAGO — A noninvasive cardiac radioablative approach that treats ventricular tachycardia (VT) the same way many cancers are now treated dramatically reduces VT occurrence in the majority of patients and allows many to reduce or eliminate antiarrhythmic drug therapy, a small phase I/II study is showing.

"This could democratize VT ablation," Clifford Robinson, MD, associate professor of radiation oncology, Washington University School of Medicine in St. Louis, Missouri told Medscape Medical News.

"Many centers don't have a catheter lab or a hospital that can handle complex ablations, but modern radiation delivery devices are being put in all over the world and we've helped almost three dozen sites to do this — they send us their information, we help them target and plan [the procedure], and then they deliver the radiation. So it's very promising and pretty exciting," he added.

Findings were presented here at the 61st annual meeting of the American Society for Radiation Oncology (ASTRO).

The study involved 19 patients with refractory VT, all of whom had failed to respond or who were too sick to withstand other conventional treatments for VT, including an implantable cardioverter-defibrillator (ICD) and catheter ablation.

"All patients had significant cardiac impairment with an average heart function [ejection fraction] of less than half of normal," Robinson noted.

They also had a heavy baseline VT burden and were heavily medicated, with 58% of them on two or more drugs and most on large doses of amiodarone. As Robinson noted, amiodarone has significant toxicities that are cumulative and, in some patients, lethal.

Patients were then treated with an electrophysiology (EP)-guided noninvasive cardiac radioablation technique called ENCORE.

This approach involves noninvasive cardiac mapping of a patient's heart to pinpoint the damaged tissue giving rise to VT.

Once the damaged portion of the heart has been mapped, clinicians then target it with a single dose of stereotactic body radiation (SBRT) that, on average, takes about 14 minutes to deliver, Robinson noted.

In the first report of their ENCORE results, Robinson and colleague Phillip Cuculich, MD, an EP expert and associate professor of cardiology and radiation oncology at Washington University, found that 94% of patients had a significant reduction in VT episodes in the first 6 months following the intervention compared with the 6 months prior to being treated.

Now, long-term follow-up out to approximately 2 years showed that 78% of patients continued to have reduced VT burden.

"Quality of life is an important goal in this patient population, and it is important to try and reduce the use of toxic antiarrhythmic medications," Robinson observed.

For the 12 patients still alive at 12 months postprocedure, "we saw a significant reduction in the use of these drugs and in the use of amiodarone in particular," he noted.

Safety Profile

After 90 days following the ENCORE procedure, researchers observed only one case of pericarditis, which resolved with steroids.

Now, with almost 2 years of follow-up, "we had three additional serious adverse events (AEs) — two pericardial effusions and one unusual case of gastropericardial fistula," Robinson reported.

It's important to note, Robinson stressed, that these late serious AEs occurred at around the 2-year follow-up mark, indicating that long-term follow-up of these patients is necessary to reveal late toxicities.

As expected in patients with refractory VT, 9 patients had died by the end of the 2 years, 6 from cardiac causes; nevertheless, 52% of treated patients were still alive at study endpoint.

The most concerning potential issue with ENCORE is the fact that radiation delivered directly to the heart might cause significant heart damage.

As Robinson cautioned, there has been a "long storied" history detailing the toxic effects radiation can have on the heart — certainly a concern in breast cancer patients, for example, where late toxicities could negatively influence survival odds.

"However, VT patients are much sicker, and sometimes they do not have any or very good treatment options," he noted.

Researchers are also targeting only the diseased portion of the heart, just as they would when treating lung cancer with SBRT, where they clearly try to avoid healthy lung tissue, he added.

"ENCORE is a great salvage option if patients have failed other treatment options, but the procedure is still best suited for high-risk patients who have failed conventional treatments for VT," he stressed.

Commenting on the findings, Joost Verhoeff, MD, PhD, University Medical Center, Utrecht, the Netherlands, observed that this is a "new frontier" for patients with refractory VT, but the findings are still very preliminary.

"VT is a really debilitating disease, so I think every new treatment option should be tested carefully," he said.

And while he cautioned that very few patients have been treated with this novel therapeutic option to date, a larger study with longer-term results will help put into perspective the risk of late toxicities from the ENCORE approach vs the benefit of improved quality of life for these patients.

Robinson declares he has received research grants from Varian, Elektra, and Merck and has served as a consultant for Varian, AstraZeneca, EMD Serrano, and Radialogica. He has also received a speakers' fee from Varian and ViewRay and owns stock options in Radialogica. Verhoeff has disclosed no relevant financial relationships.

American Society for Radiation Oncology (ASTRO) 2019 Annual Meeting: Abstract LBA4 Presented September 17, 2019.

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