A small study by Phillip S Cuculich (Washington University School of Medicine, St Louis, USA) et al has shown that radiation therapy, commonly used to treat cancer, can be used as a noninvasive radioablation approach to treat patients with ventricular tachycardia (VT). The study is based on the treatment of five VT patients, and was published in The New England Journal of Medicine.
From an aggregate 6,577 VT episodes in the five patients during the 15 patient-months before the procedure, the number dropped to 4 episodes of VT during the 46 patient-months following a post-procedure blanking period of six weeks. The number was a relative reduction of 99.9% from baseline.
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The patients had not responded to standard treatments and collectively experienced more than 6,500 episodes of VTin the three months before they were treated with noninvasive radioablation therapy. When delivered directly to arrhythmogenic scar regions in the myocardium, the radiation therapy resulted in a dramatic reduction in the number of VT events in these patients, as measured by their implanted cardioverter-defibrillators (ICDs).
An analysis of the patients’ experiences is reported in the paper. There have been two previous cases reported of treating VT with radiation therapy, but this is the first to do so in an entirely noninvasive process, from imaging to treatment.
“As a radiation oncologist who specialises in treating lung cancer, I have spent most of my career trying to avoid irradiating the heart,” said senior author Clifford G Robinson (Washington University School of Medicine, St Louis, USA), an associate professor of radiation oncology. “But I also have been exploring new uses for stereotactic body radiation therapy that we use almost exclusively for cancer.”
At the same time, Cuculich was looking for new ways to treat VT in patients who did not respond to conventional treatments. Cuculich acknowledges the “life-saving” importance of ICDs, but also points out their potentially detrimental effects on patients’ quality of life: “The shock can be a traumatic event. Patients understand that they have just avoided death. And when this happens repetitively, often without warning, it can be devastating for patients.”
VT commonly develops following myocardial infarction and scarring. While traditional catheter ablation is often an appropriate treatment, the procedure can be risky for patients with comorbidities, and VT recurrence is common even after ablation.
The five patients in the study had either undergone catheter ablation procedures with subsequent VT recurrence, or were unable to undergo the procedure because of other high-risk clinical conditions. One patient was on the waiting list for a heart transplant. Four of the patients were in their 60s, while one patient was over age 80.
In the three months before treatment with noninvasive radiation therapy, the five patients together experienced more than 6,500 VT events. The average number of events per patient during this time was 1,315, with a range of five to 4,312. During the first six weeks following radiation therapy, as the patients were recovering, they experienced a total of 680 episodes. In the one year of continued follow-up, the patients collectively experienced four events. Two patients did not experience any episodes at all.
Unknown long-term effects of noninvasive radioablation therapy
The investigators are cautious, saying they are still monitoring for long-term side effects of radiation therapy, such as lung scarring and further damage to the heart itself. They emphasised that their use of noninvasive radioablation only included very ill patients in end-stage disease who had run out of options. More research is required before doctors might consider this approach for younger, healthier patients or as a possible addition to standard therapies.
“A lot of my work is focused on reducing toxicity of radiation therapy using modern technology,” Robinson says. “These patients have done quite well in the first 12 months after therapy, which is enough time to see the early toxicities. But we are continuing to monitor patients for long-term side effects.”
The single dose of radiation these patients received is comparable to what might be given to a patient with an early-stage lung tumor. Doctors can target such tumors with a large dose of radiation given once or up to five times.
Noninvasive radioablation: a 10-15 minute procedure
The preparation and mapping of the anatomy and electrical circuits of the heart is time-intensive, but the treatment itself takes 10-15 minutes, the researchers said.
“A traditional catheter ablation procedure can take six hours or more and requires general anesthesia,” Cuculich says. “This new process is entirely noninvasive. We take pictures of the heart with various imaging methods—MRI, CT, PET scans. But the unique piece is the noninvasive electrical mapping called electrocardiographic imaging. This allows us to pinpoint where the arrhythmias are coming from. When we overlay the scar mapping with the electrical mapping, we get a beautiful model of heart function that lets us see not only where the arrhythmia comes from, but where it might progress.”
“Based on these maps, Robinson is then able to deliver the energy entirely noninvasively,” Cuculich added. “It is simply amazing to see a ventricular tachycardia patient get an ablation therapy for a few minutes and then get up off the table and walk out the door.”
Electrocardiographic imaging (ECGI) was developed by co-author and Washington University biomedical engineer Yoram Rudy (Washington University School of Medicine, St Louis, USA).
The radiation therapy does not take effect immediately. The number of arrhythmia events went down but did not disappear in the first six weeks after treatment, which the doctors characterise as a recovery period. After that six-week period, however, the number of events dropped to almost zero. Patients were able to slowly come off antiarrhythmic medication therapy.
Of the five patients, one patient died in the first month after treatment of causes unlikely to be related to treatment. This patient, who was over age 80, had other heart conditions in addition to VT. The remaining four, who are all in their 60s, are alive two years after radiation therapy. The patient on the transplant list went on to receive a new heart. One whose arrhythmia continues to be controlled also is dealing with gradual heart failure, and has received a left ventricular assist device. Two patients continue to live unassisted without VT.
The researchers are currently enrolling patients in a clinical trial to further evaluate the approach and, to date, have performed the procedure on 23 patients.