Stereotactic body radiotherapy for cardiac arrhythmias: Current evidence and clinical boundaries

Stereotactic arrhythmia radioablation (STAR), also known as cardiac stereotactic body radiotherapy, is an emerging noninvasive strategy for arrhythmia substrate modification. It translates electrophysiological and anatomic information into a radiotherapy target, but it should not be treated as catheter ablation delivered from outside the body. Its biology remains unsettled: early electrical reprogramming may precede delayed fibrosis, dose-response relationships are poorly defined, and atrial and ventricular substrates may not respond in the same way. The most developed clinical experience is in refractory ventricular tachycardia (VT), where prospective studies and pooled analyses show large reductions in VT burden and implantable cardioverter-defibrillator therapies, although recurrence, competing mortality, and delayed toxicity keep VT-STAR in a salvage role. Atrial fibrillation (AF) remains experimental. Preclinical studies support radiation-induced atrial lesion formation, and small human series demonstrate that AF-STAR can be technically delivered in selected elderly patients with paroxysmal AF; however, these findings do not establish durable rhythm control or clinical suitability. In particular, the current 25-Gy regimen cannot be assumed safe for the thin left atrial posterior wall or other large atrial targets, whereas substantially lower doses may not achieve durable electrical isolation, leaving no validated therapeutic window. AF-STAR therefore still lacks acute verification of isolation, reproducible target standards, disease-specific dosing, and mature esophageal and coronary safety data. This review follows STAR from mechanistic uncertainty through the VT evidence to the experimental AF field, emphasizing disease-specific target design, motion-aware planning, and long-term safety surveillance.