COMMENTARY

ENCORE-VT: Noninvasive Ablation of VT Could Disrupt EP

John M. Mandrola, MD

Disclosures

November 13, 2018

This year's American Heart Association (AHA) meeting may be remembered as the moment electrophysiology began a new era:  The video at the beginning of the ENCORE-VT presentation commanded your attention:

A man with severe heart disease and refractory ventricular arrhythmia casually walks into the electrophysiology lab in street clothes, gets on the table, undergoes minutes of painless stereotactic ablation of an arrhythmogenic spot in his ventricle, gets off the table, smiles, and shakes the hands of his doctors as he walks out.

There were no hospital gowns, no intravenous lines, no catheters, and no anesthesia. But that's not the best part of noninvasive ventricular tachycardia (VT) ablation. The best part is that it worked.

The ENCORE-VT study,[1] presented in Chicago and published simultaneously in Circulation, describes the results of noninvasive ablation using stereotactic radiation in 19 patients with refractory VT. It extends work from a smaller case series.[2]

The Washington University (St. Louis) authors began with safety outcomes: The single dose of 25 Gy did not cause any acute toxicity or dysfunction of implantable cardioverter defibrillators (ICDs); one patient had pericarditis and another, mild pneumonitis (both treated without incident). Contrast this safety record to published reports of complications in 6% to 7% of standard catheter-based ablation cases.[3,4]

Efficacy was impressive. Ablation reduced the median number of VT episodes from 119 (range, 4 to 292) to 3 (range, 0 to 31; P<.001). VT episodes or premature ventricular contraction burden was reduced in 17 of 18 patients. Crucially, ICD shocks went from a preablation median of 4 (range, 0 to 30) to 0 (range,  0 to 7). Although VT burden decreased in most patients, 69% (11 of 16) had some late recurrence VT in the 6 weeks to 6 months after ablation. At 6 months, 89% of the patients were alive and at 12 months, 72% were alive.

The authors made cautious conclusions: "this was a single-center, nonrandomized study in a limited number of patients, which prohibits generalization to a larger population" and "this technique remains investigational." 

Comments

I sat down with first author, Clifford Robinson, MD, a radiation oncologist; senior author, Phillip Cuculich, MD, an electrophysiologist; and study coordinator Kaitlin Moore here in Chicago.  

Here are the take-home messages I learned about this novel technique:

The energy source is basic x-rays, the type used in radiating solid tumors for years. The radiation dose in this study was within the spectrum used to treat most cancers. Robinson described the stereotactic delivery as akin to spokes on a wheel: the focal point of the radiation, the scar in the ventricle, is the hub and the small doses of radiation delivered by a device rotating around the patient are the spokes.

Stereotactic ablation requires intense collaboration between electrophysiologists and radiation oncologists. My initial impression of radioablation, that it simply homogenized an entire area of scar, may be wrong: Cuculich explained that successful ablation can be achieved with more focal targeting than that. And more focused ablation should improve safety. X-rays, it turns out, keep going after they affect the myocardium. Reducing scatter is key.

VT disappeared much faster than expected from the radiation effects alone. Robinson told me that radiation takes weeks to months to cause fibrosis, but in this study, VT went away almost immediately. The authors could not explain this. There is more to learn about the way radiation therapy works, they added. Cuculich was excited that patients were informing the science, which is different from the normal frame in which preclinical science informs patient care.

The ease of the 15-minute ablation belies the complexity of the entire procedure. To prepare patients, the authors use CT, MRI, and/or positron emission tomography to define the anatomy. Then they induce VT noninvasively with the ICD while the patient is wearing a 250-electrode electrocardiogram vest. A software algorithm combines the electrical and anatomic information into a three-dimensional map of the VT circuits. This is called the ECGI procedure,[5] which was developed at Washington University by ENCORE-VT coauthor Yoram Rudy, PhD.[6] Cuculich told me the electrical mapping data from the vest was helpful in most patients because it allowed more focused ablation in those with large ventricular scars.  

Both Cuculich and Robinson emphasized the need to have other centers replicate their success. They are close to launching a multicenter trial, and multiple groups have expressed interest in participating.

 When I asked Cuculich if they are doing this procedure now, he answered, "No" because they want to stay true to the science. They will do this novel procedure only in the setting of a clinical trial.

Conclusion

The authors' caution is refreshing and laudable. Indeed, this work is early, but it fulfills both definitions of elegant: It's stylish in appearance and pleasingly ingenious.

I see two reasons to be excited. One is that if this technique is confirmed and scalable to other centers, noninvasive ablation will fill an unmet need in the care of patients with treatment-resistant VT. These patients suffer, and help getting rid of VT would be big,

The more provocative reason to be excited about this approach is that it could redefine what it means to do ablation, or be an electrophysiologist. Might the next generation look back on the days of catheter-based ablation as archaic?

Stay tuned.

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