ST LOUIS, MO — Stereotactic delivery of external-beam radiation can potentially be used to ablate the source of ventricular tachycardia (VT) that has resisted other drug and device treatments, suggests a small case series published today in the New England Journal of Medicine[2]. Targeting of the radiation was guided by imaging and noninvasive electrophysiologic mapping.
In the five patients with a high burden of drug-refractory VT, who had been suffering through repeated implantable cardioverter defibrillator (ICD) activations, VT prevalence fell off sharply even in the first 6 weeks after the treatment, the predefined blanking period for analyzing outcomes in the study. And the risk reduction reached 99% in follow-up out to 1 year.
Three of the four patients alive at 12 months were not on antiarrhythmic agents, according to the report, with lead author Dr Phillip S Cuculich (Washington University School of Medicine, St Louis, MO).
“We’ve developed a way to complete a complex heart-ablation procedure and do it noninvasively in under 15 minutes,” Cuculich told theheart.org | Medscape Cardiology.
The five patients had been going into VT regularly despite multiple antiarrhythmic agents and, in some cases, catheter ablation, he said. “So it was a very sick population that was sent our way, a very end-stage population. And to see a positive effect on these patients over the course of the first year was quite amazing.”
If this technique for “noninvasive” myocardial ablation were to prove effective in larger clinical trials as well, “it could fundamentally replace how we approach heart-rhythm disorders. But much work needs to be done before we can make that statement definitively.”
Dr Francis E Marchlinski (University of Pennsylvania, Philadelphia), who wasn’t involved in the research, agrees with the authors’ cautious optimism. The study, he said when interviewed, “showed a clear-cut efficacy benefit. Even if it’s in small numbers, the results were promising.”
For now, stereotactic radiation VT ablation will probably be used in the “sickest of the sick,” but with research there ought to be way to expand the range of patients in which it’s used, said Marchlinski, a leading expert on electrophysiologic VT mapping and treatment.
But, “I’m more concerned about the safety issues, and [acquiring] more extensive experience to make sure it’s really going to be effective, and how much you have to ablate to make it work,” he said. “So, this is preliminary, but it’s pretty darned exciting.”
Axial CT scan showing the radiation target (red outline), expansion of the target to allow for heart and lung motion (cyan outline), the left ventricle (yellow outline), the right ventricle (blue outline), and the aorta (red circle). Source: Dr Clifford Robinson
The VT ablation technique borrows from advances in neurologic and cancer surgery using stereotactic body radiation therapy (SBRT), which is noninvasive delivery of focused ablative radiation—in this case, 25 Gy of X-rays in a single fraction—to a volume of tissue.
In the current series, according to the authors, target volumes encompassing the VT circuits were defined by noninvasive ECG mapping (the patients wore a 256-electrode vest) and CT imaging, followed by programmed stimulation studies using the patients’ ICDs. Borders of myocardial scar were defined by single-photon-emission computer tomography (SPECT) or MRI. No anesthesia or sedation was used.
Conducted this way, Cuculich said, the procedure has several advantages over other treatment options for VT. “It can reach where catheters cannot, it can map noninvasively the entire circuit, and it can treat the entirety of the scar where both today’s and perhaps tomorrow’s VTs might originate.”
After the procedure, patients were followed by remote monitoring, and their ICDs were interrogated at regular scheduled clinic visits, with attempts to wean them off antiarrhythmic therapy at each visit, the authors write.
During the 3 months before the procedure, collectively the five patients had 6577 documented VT episodes. All were in NYHA class 3–4 heart failure and taking at least two antiarrhythmics on procedure day. The ablation procedure itself took a mean of 14 minutes; the longest time was 18 minutes. Patients were discharged in 1 to 3 days.
There were 680 VT episodes in all during the 6-week postprocedure blanking period, a time of heightened vulnerability to arrhythmias due to postablation inflammation, according to the report. Only four such episodes were seen during the rest of the 1-year follow-up, a total of 46 patient-months, for a risk reduction of 99.9%, it notes.
The number of ICD shocks across all patients went from 55 before the procedures to only one afterward; deliveries of antitachycardia pacing declined from 6577 to three.
Even with those good results, it’s unlikely that such SBRT ablation, which has “downsides,” will replace other forms of VT ablation, according to Marchlinski. Radiation therapy, he said, “can come with the cost of significant collateral damage, pneumonitis, and potential for late sequelae that need to be worked out before we jump in enthusiastically.”
In contrast, he said, clinicians have decades of experience with RF ablation, and “rarely do we set the stage for new tumors or new scar-related arrhythmias or new scar-related [inflammation] of some sort that we know radiation can do.”
An editorial accompanying the published report agrees[2]. “Unintended damage to adjacent structures is an important concern. VT substrate can be in close proximity to normal contracting myocardium, as well as the conduction system, valves, coronary arteries, lungs, nerves, and esophagus. Respiratory and cardiac motion may increase off-target delivery,” according to Drs Roy M John and William G Stevenson (Brigham and Women’s Hospital, Boston, MA).
“Imaging changes that were consistent with pneumonitis were observed in the present series,” they write.
“The present data are nevertheless compelling and support further investigation,” John and Stevenson say. “Early and late toxic effects need to be defined, including the risk of late cancer, if this method is applied to patients with milder heart disease who can be expected to have long postprocedural survival.”
The study was supported by grants from the National Institutes of Health. Cuculich reports grants from Barnes-Jewish Hospital Foundation, during the conduct of the study; he has a patent electrocardiographic imaging and SBRT for cardiac arrhythmia pending. Disclosures for the authors and editorialists can be found on the journal website. John reports personal fees from Abbott outside the submitted work and performs ablations for ventricular tachycardia as part of his clinical responsibilities at the Vanderbilt University Medical Center. Stevenson reports other compensation from St Jude Medical/Abbott and personal fees from Boston Scientific outside the submitted work. In addition, he has a patent issued on a method for ablating with needle electrode and will be performing catheter ablation as part of clinical responsibilities at Vanderbilt University Medical Center. Marchlinski consults for Biosense Webster and St Jude Medical.
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