Radiation therapy shows promise as safer alternative for severe heart rhythm disorder

Radiation therapy may offer a comparable and potentially safer alternative to repeat catheter ablation for patients with severe abnormal heart rhythms that can no longer be controlled with medication.

In the first study to directly compare cardiac radiation with standard catheter ablation for ventricular tachycardia, patients treated with cardiac radiation experienced fewer complications with similar effectiveness at controlling disease than those treated with cardiac ablation. Findings of the retrospective analysis will be presented today at the American Society for Radiation Oncology (ASTRO) Annual Meeting and published in the International Journal of Radiation Oncology • Biology • Physics (Red Journal).

Several large, single-arm trials have confirmed that stereotactic radiation therapy is a safe and effective option for patients with recurrent ventricular tachycardia, but our study is the first to measure outcomes from cardiac radiation directly against those from standard catheter ablation. For patients who do not respond to traditional therapies and are at high risk of complications, noninvasive radiation may be a safer alternative to repeating an invasive catheter ablation procedure."

Shannon Jiang, MD, lead author of the study and radiation oncology resident physician at Washington University School of Medicine in St. Louis

Ventricular tachycardia (VT) is a dangerous disturbance of the heart's rhythm that is associated with substantial morbidity and mortality. Patients with advanced VT often live with a heavy disease burden, frequently requiring high doses of rhythm-controlling drugs that cause difficult side effects, implantable defibrillators that deliver powerful shocks when the heart slips into arrythmia, and hospital stays that add further physical and psychological strain.

Management becomes especially challenging when VT no longer responds to medication or initial ablation procedures. Patients in this stage, known as refractory or end-stage VT, are often medically fragile and at high risk for complications from further invasive procedures. Catheter ablation, the standard treatment for VT that is not responsive to medication, requires anesthesia and threading a small tube into the heart through a vein in the leg to destroy abnormal heart tissue. While effective for some, repeat procedures carry increasing risks.

In recent years, stereotactic arrhythmia radiation therapy (also known as STAR) has emerged as a novel, noninvasive alternative. By precisely delivering pinpoint beams of radiation to the scarred tissue that drives the abnormal heart rhythm, it aims to achieve the same goal as ablation – bringing the heart back into normal rhythm – without invasive catheters or anesthesia.

In the landmark ENCORE-VT trial previously published by the Washington University team, cardiac radiation reduced VT episodes and anti-arrhythmic drug use with modest short-term effects, and improved quality of life. Dr. Jiang and colleagues designed the new analysis to add comparative evidence on radiation versus ablation, as well as to report on longer-term results.

For the new study, they retrospectively analyzed records from 43 patients with high-risk refractory VT at a single high-volume center between 2015 and 2018. All patients had end-stage VT that was not responsive to anti-arrhythmic drugs. Most (90%) had previously undergone at least one catheter ablation procedure, and the remaining patients were deemed too high-risk to safely undergo an invasive catheter ablation.

Patients were treated with either stereotactic radiation (n=22) or standard repeat catheter ablation (n=21). Those on the radiation arm received a single fraction/dose of radiation therapy, with treatment delivered through close collaboration between radiation oncology and cardiology teams.

Patients treated with stereotactic radiation experienced substantially fewer serious side effects than those treated with catheter ablation. Within a year of treatment, eight patients (38%) in the ablation group experienced serious adverse events requiring hospitalization, compared with two patients (9%) in the radiation group. Complications also occurred sooner after ablation (median 6 days) than after radiation (10 months).

Four patients on the ablation arm died within a month of treatment, all shortly after experiencing treatment-related adverse events, and one did not survive the procedure. By comparison, no deaths on the radiation arm within the three-year follow-up period were attributed to treatment-related side effects.

"From our study, it looks like radiation might be safer especially within that early time window," said Dr. Jiang. "There wasn't the same early peak in adverse events, and that seems to drive the benefit. Many of the early serious adverse events after ablation were closely followed, unfortunately, by patient deaths."

"Going under anesthesia for an invasive procedure can involve outsized risk for a person who's already very sick," she explained. "With radiation, we don't have to use anesthesia. I think this study highlights that radiation being a noninvasive procedure helps us avoid a great deal of risk."

Both treatments were similarly effective at controlling arrhythmia. The time before patients experienced a new persistent VT episode or defibrillator shock was a median of 8.2 months with radiation versus 9.7 months with ablation (p=0.95).

Median overall survival favored radiation (28.2 vs. 12.2 months), though the difference was not statistically significant due to small sample sizes. Dr. Jiang said, "our interpretation is that many patients lived longer after radiation because they avoided the early complications that can follow ablation." One year after treatment, overall survival was 73% for the radiation arm and 58% for ablation; at three years, it was 45% in both groups.

Dr. Jiang emphasized that the study, while encouraging, is limited by its small size and retrospective design. She said the results of RADIATE-VT (NCT 05765175), which is currently accruing patients for the first international, multi-center, randomized controlled trial to evaluate the safety and efficacy of these treatment approaches, will be important to confirm these findings and identify which patients may benefit most.

They also hope the results will spur interest in expanding patient access. Few centers currently offer stereotactic radiation for VT, she said, "but I think our research adds legitimacy to the approach and underscores its potential as an option for patients, especially those at high risk for complications from anesthesia or ablation."