Patients with life-threatening heart arrhythmias may soon have a noninvasive treatment option in the form of radiotherapy.

Physicians at Washington University School of Medicine in St. Louis have developed a new approach for treating ventricular tachycardia, an irregular heart rhythm condition that puts people at risk for sudden cardiac death, by applying stereotactic radiation directly to the heart. Their findings were compiled in a study published in The New England Journal of Medicine.

"Catheter ablation is the standard of care. While it can be quite effective in many patients, it has high rates of recurrence - 50 percent in some series - and the potential for death or severe short term toxicity, particularly in the sicker patients," first author Phillip S. Cuculich, an associate professor of medicine and cardiologist, told HCB News. "When patients have a recurrence after catheter ablation, or are too sick for catheter ablation, they have few options. Our totally noninvasive method of mapping the arrhythmia and delivering radiotherapy to the target in under 15 minutes has the chance to significantly improve short term safety for this patient population. We remain committed to monitoring for the long term effects of this treatment.

An estimated 300,000 deaths per year in the U.S. are credited to ventricular tachycardia, the leading cause of sudden cardiac death. Standard therapy consists of medication and invasive procedures that involve threading a catheter through a vein into the heart. While defibrillators can help save the lives of such patients, the shock applied can often be a traumatic experience.

The approach, the first entirely noninvasive process proposed for this condition, consists of imaging the heart using MR, CT or PET scans. Electrocardiographic imaging is then applied in which electrical mapping overlays scar mapping for pinpointing the location of arrhythmias and where they may progress. Radiation is then administered over a period of 10-15 minutes.

Researchers tested their approach on five participants who either were unable to undergo catheter ablation because of other high-risk conditions or did so only for their arrhythmias to return. Together, all five had experienced more than 6,500 episodes of ventricular tachycardia in the three months preceding radiation therapy with the average number per patient being 1,315 in a range of 5-4,312.

Radiation was applied using Varian TrueBeam, a linear accelerator with stereotactic radiation capabilities, administering a single dose on par with what might be provided to an early-stage lung tumor patient. The amount of doses applied ranged between one and five.

Six weeks following the procedure, patients experienced a decrease in episodes, with a total of 680 episodes together. The number then dropped to almost zero after the first six weeks, which doctors deemed the recovery period, to the point where patients were able to slowly come off medication for controlling their arrhythmias. A one year follow-up found patients had experienced a total of four such events in the course of that time with two not experiencing any at all.

One patient over the age of 80 died one month after treatment from unlikely related causes. Two of the remaining four, all in their 60s, now live unassisted without ventricular tachycardia. One, whose arrhythmia continues to be controlled, suffers from gradual heart failure and has received a left ventricular assist device. Another underwent a successful heart transplant but was on the waiting list for a new one prior to undergoing the procedure.

The authors caution that more research is required before the approach can be used on younger, healthier patients or be considered as a standard therapy for this condition or other heart arrhythmias.

"In theory, this could be used to treat a more common arrhythmia, atrial fibrillation. We are actively investigating that as a possibility," senior author Clifford G. Robinson, an associate professor of radiation oncology, told HCB News. "However, we felt it was key to focus our initial efforts on the patients who had the fewest available options, and with the most life-threatening disease. In contrast to ventricular tachycardia, there are many effective and safe options for atrial fibrillation."

“A lot of my work is focused on reducing toxicity of radiation therapy using modern technology,” Robinson said. “These patients have done quite well in the first 12 months after therapy, which is enough time to see the early toxicities. But we’re continuing to monitor patients for long-term side effects.”

Physicians continue to monitor the participants for long-term radiation side effects, such as lung scarring and further damage to the heart, and are currently enrolling patients in a clinical trial to further study this approach, which has been performed 23 times to date.