For patients living with refractory ventricular tachycardia, the clinical path can become increasingly complex. When medical therapies fail and repeated catheter ablations cannot stabilize the heart’s rhythm, the available options for managing these life-threatening arrhythmias are often limited. New data presented this week at Heart Rhythm 2026 introduces a noninvasive approach that leverages the physics of charged particles to target the heart’s electrical substrates with high precision.
The research, reported by Konstantinos C. Siontis, MD, of the Mayo Clinic and colleagues in Heart Rhythm, details the first-in-human application of proton beam therapy for VT. The study focused on a small group of patients with advanced cardiomyopathy and recurrent arrhythmias, aiming to determine if this modality could deliver therapeutic energy to the heart without damaging the surrounding anatomy.
The physics of the sparing effect
The primary distinction between this approach and previous attempts at radioablation lies in the nature of the radiation itself. While photon beam radioablation has been investigated for refractory VT, proton beam therapy utilizes a different modality to achieve its goal.
“The radiation modality is a charged particle which is emitted into the heart tissue, or whatever the target might be, with a higher accuracy compared to the photons,” Konstantinos C. Siontis, MD, Mayo Clinic
From a clinical perspective, the advantage is found in the sparing effect
. Unlike photons, which can scatter and affect unintended areas, protons possess biophysical properties that allow clinicians to concentrate the energy on the specific VT substrate. This precision is intended to protect the nontargeted myocardium, the coronary arteries, and other noncardiac structures from collateral radiation damage.
Siontis noted that this mechanism is already well-established in oncology. According to the researcher, the medical community knows from cancer care that protons offer more of a sparing effect than conventional radiation, such as photons. By applying this principle to the heart, the goal is to ablate the problematic tissue while leaving the healthy heart muscle and adjacent organs intact.
Patient selection and clinical baseline
The feasibility study involved seven patients with a mean age of 68 years. The cohort was predominantly male, with six men and one woman completing the treatment. These individuals represented a high-risk population with significant cardiac dysfunction; the median left ventricular ejection fraction (LVEF) at baseline was 26%.
The group’s medical history underscored the refractory nature of their condition. Five patients had undergone two or more catheter ablations in the past, and all seven experienced breakthrough VT following their most recent ablation procedure, despite ongoing drug therapy. In the weeks leading up to the proton beam therapy, six patients were treated with amiodarone, with or without mexiletine.
The patient profiles varied by disease type: four patients had nonischemic cardiomyopathy, one had ischemic cardiomyopathy, and two presented with mixed disease. Additionally, three patients had biventricular implantable cardioverter-defibrillator (ICD) devices, and two of those patients had high-grade atrioventricular block at baseline.
Evaluating safety and toxicity
Because this was an early feasibility study, the primary metric of success was safety rather than a definitive cure. The transition from preclinical work to human subjects required rigorous planning to ensure the charged particles did not cause unintended harm to the heart or other vital organs.
“We were able to enroll patients and successfully plan and deliver treatment in seven humans, building upon the extensive preclinical work that has been done here at the Mayo Clinic,” Konstantinos C. Siontis, MD, Mayo Clinic
The results indicated that the procedure was well-tolerated. Researchers reported no signs of toxicity and no evidence of harm to the heart or other organs.
“We did not observe any probable or definite treatment-related toxicities that could be related to the proton beam therapy. Certainly, we’re quite happy with that.” Konstantinos C. Siontis, MD, Mayo Clinic
What to watch in future trials
While these early results clear the way for future studies, the small sample size means that the long-term efficacy and the optimal dosing of proton radiation for VT remain unknown. The current data establishes that the therapy can be delivered safely, but it does not yet provide a comprehensive map of how many patients will achieve lasting arrhythmia suppression.
Future research may involve expanding the patient cohort to further evaluate the sparing effect
and its impact on cardiac function. Researchers will likely continue to monitor the durability of the treatment and the frequency of breakthrough VT events following the targeting of the electrical substrate.
As the medical community moves from this feasibility stage toward larger trials, the focus will remain on evaluating the clinical utility of proton beam therapy for those who have exhausted other available treatment options.