A new technique that uses a targeted high dose of radiation seems to prevent recurrence of a potentially deadly heartbeat for at least two years, researchers from Washington University School of Medicine in St. Louis report.
This irregular rhythm, called ventricular tachycardia (VT), occurs when the heart's lower chambers start to beat uncontrollably fast. Once it starts, it can kill within minutes.
"Patients with VT who have already failed traditional therapies have limited treatment options," said lead researcher Dr. Clifford Robinson, an associate professor of radiation oncology and cardiology.
"This new therapy opens up the potential for a large number of patients with few options to experience reduced VT and improved quality of life, all with a single outpatient treatment," he said.
Most people who die from sudden cardiac death experience VT in the moments before the heart stops. Those lucky enough to survive often continue to have episodes of this life-threatening arrhythmia and need a defibrillator-pacemaker implanted to restore the heartbeat to normal.
But the devices have a downside: The shock they deliver can be painful and affect a patient's quality of life.
With radiation therapy, the defibrillator remains in place, Robinson said, but the hope is that patients will experience fewer shocks.
The 19 patients in this trial had run out of available treatment options, including more drugs and catheter ablation, which is used to scar parts of the heart where the abnormal rhythm begins.
Catheter ablation is invasive and can take hours under general anesthesia. Moreover, the treatment doesn't work for about half the patients who receive it, Robinson said.
Radiation is not invasive, takes under 10 minutes, and patients can go home the same day. As with cancer treatment, doctors use electrical maps to pinpoint spots where radiation is needed.
Researchers assumed radiation would work the same way as ablation, by scarring areas where the arrhythmia occurred. But Robinson said patients began having fewer bouts of VT even before scarring developed.
Exactly how radiation stops VT remains a mystery, he said. On the plus side, any hospital that does radiation therapy for cancer has the equipment and the know-how to provide this treatment, he noted.
Robinson's team previously reported a 90% reduction in VT episodes among the 19 patients, and their survival improved in the six months after treatment.
In this second phase of the study, 80% of the patients had fewer VT episodes over two years after a one-time treatment.
In the year after radiation, 72% of patients survived, and after two years, 52% were still alive, Robinson said.
Nine patients died. Of those, six died of heart-related causes, including heart failure and VT. Three died from other causes, including an accident, a reaction to the heart drug amiodarone and pancreatic cancer.
The researchers said two of the surviving patients had side effects of radiation, including inflammation of the heart lining and an opening between the heart and stomach called a fistula, which required an operation to fix.
Dr. Byron Lee, director of electrophysiology laboratories and clinics at the University of California, San Francisco, welcomed the findings.
"These are exciting findings that may eventually revolutionize how we treat abnormal heart rhythms," he said.
Someday, Lee added, all arrhythmias may be treated non-invasively with radiation, rather than with drugs or invasive procedures.
"This technology is still just emerging and the long-term risks have yet to be clarified," Lee said. "Therefore, this approach should only be used now for patients with severe life-threatening arrhythmias, like ventricular tachycardia."
The findings were presented Sunday at a meeting of the American Society for Radiation Oncology, in Chicago. Research presented at meetings is typically considered preliminary until published in a peer-reviewed journal.
The study was funded in part by a grant from the U.S. National Institutes of Health.