FROM THE NEW ENGLAND JOURNAL OF MEDICINE
A one-time dose of radiation to arrhythmogenic scars eliminated or at least greatly reduced ventricular tachycardia in five patients who had failed to respond to medical management and, in some cases, catheter ablation, according to a report in the New England Journal of Medicine.
The procedure, carried out at Washington University in St. Louis, was completely noninvasive and appeared safe. Treatment targets were identified by MRI, CT, and electrocardiographic imaging to map the ventricular tachycardia (VT) circuit during a run of VT induced through the patients’ implantable cardioverter defibrillators; a single fraction of 25 Gy of radiation was then delivered to the target by stereotactic body radiation therapy – a common technique in oncology – while patients were awake but immobilized. Treatment took about 15 minutes.
During the 3 months before the procedure, the five subjects had 6,577 episodes of VT, ranging from 5 to 4,312 per patient. In addition to failing to respond to medications, three had failed catheter ablation; that procedure was contraindicated in the other two.
During the 6-week postablation blanking period, when inflammation can trigger arrhythmias, there were 680 VT episodes. After the first 6 weeks, there were four episodes over 46 patient-months, for a reduction from baseline of 99.9%.
The oldest subject, an 83-year-old woman who had had 4,312 pretreatment episodes, had a fatal stroke 3 weeks after the procedure, with no clear relationship to treatment on autopsy. In the 3 weeks before she died, her VT burden was reduced 82%.
Among the rest – all men aged 60-65 years, with pretreatment episodes numbering from 5 to 2,210 – there was no decline in left-ventricular ejection fraction during the 12-month follow-up; mild adjacent lung inflammatory changes noted at 3 months resolved during that follow-up period.
The investigators have launched a phase 1-2 trial called ENCORE-VT to further evaluate the technique.
“Although catheter ablation is the current state-of-the-art treatment for drug-refractory ventricular arrhythmias in patients with structural heart disease, it is not curative for many patients” because of inadequate ablation and other problems. Radiation ablation “has the potential to overcome these challenges. … If a noninvasive approach to ablation of ventricular tachycardia is shown to be safe and effective, it would be a potentially important therapeutic advance,” said investigators led by Washington University cardiologist Phillip Cuculich, MD . However, “because of the novelty of noninvasive radioablation, its potential for harm, and the limited number of patients who were included in this analysis, this procedure should not be considered to be suitable for clinical use, pending the results of further research studies,” they said.
The long-term effects of high-dose radiation to previously injured heart tissue is unknown. “The volumes of myocardium that are subjected to radiotherapy in these patients (from 17 to 81 mL) are large enough that effects on specialized cardiac structures (papillary muscles, coronary arteries, conduction system, and valves) are of potential concern, as is the risk of overall effects on ventricular function, although no such effects were seen during the 12-month follow-up,” they said.
Of the four patients who were alive at 12 months, three were no longer on antiarrhythmic medications. One restarted amiodarone at 9 months after the first posttreatment episode of antitachycardia pacing. One patient had catheter ablation 4 weeks after treatment because of incomplete VT cessation, with no further episodes during follow-up.
In the 3 months before treatment, patients had an aggregate number of 55 implantable cardioverter defibrillator shocks and 6,577 episodes of antitachycardia pacing. Over the following 12 months, there was just one shock and three pacing episodes. After the blanking period, one patient had three VT episodes, one had one, and two didn’t have any, including a man who had 2,210 in the 3 months before treatment; he was the subject who had the secondary catheter ablation.
The work was funded by the Barnes-Jewish Hospital Foundation, Washington University, and the National Institutes of Health. Dr. Cuculich and another author have a patent pending on electrocardiographic imaging and stereotactic body radiation therapy for cardiac arrhythmia. Several authors reported receiving personal fees from and other involvement with a number of companies, including ViewRay, Varian, Elekta, and Medtronic.
aotto@frontlinemedcom.com
SOURCE: Cuculich P et al. N Engl J Med. 2017 Dec 13. doi: 10.1056/NEJMoa1613773.
