Objectives: Implantable cardioverter-defibrillators have become standard of care to prevent sudden cardiac death in patients following an episode of ventricular tachycardia (VT). Several strategies are used to reduce painful shocks and improve quality of life. There is a rising interest in using radiosurgery to modify arrhythmogenic substrate in patients with recurrent VT. However, data on the safety are still inadequate. This is toxicity evaluation based on the compilation from pilot case series and clinical trial NIRA-VT (NCT03601832).

Methods: Between 2014 and January 2019, 25 patients (24 male, 1 female; mean age 64 ± 9 years) with structural heart disease (20 ischemic cardiopathy, 4 dilated cardiopathy, 1 fibroma) from two electrophysiology centers in the Czech Republic (Trinec, Prague) underwent radiosurgery for recurrent VT, 19 of them were included in case series (first group) whereas 6 patients were treated under the clinical trial NIRA-VT (second group). In first group, radiosurgery was performed after at least one failed catheter ablation for VT. The critical part of the VT substrate was identified by electroanatomic mapping using a combination of voltage mapping, pace mapping, and activation mapping; and it was marked on a contrast-enhanced computer tomography study as a CTV. In second group CTV included scar based on PET/CT. In both groups CTV-PTV margins were 3 mm, however in first patients no CTV-PTV margins were added to decrease probability of unknown toxicity. Radiosurgery system with real-time motion tracking using the tip of the electrode of an indwelling defibrillator as a fiducial marker was used. A total radiation dose of 25 Gy was delivered to the ablation target in a single session during free breathing. Radiation-induced toxicity was evaluated according to the Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. 

Results: The mean CTV and PTV were 29 ± 10 ml and 44 ± 24 ml respectively, and the mean duration of the therapy was 78 ± 16 minutes. No patient exhibited acute (up to 3 months) elevation of troponin, pericardial effusion, or a decrease in left ventricular ejection fraction from baseline. Four patients developed acute mild nausea, which waned after antiemetic drugs. Two patients gradually developed significant progression of mitral regurgitation after SBRT. both had to undergo mitral valve replacement (grade 4 toxicity). One radiation toxicity related death (grade 5 toxicity) due to the unresectable esophagi-pericardial fistula was seen. No other cardiac or pulmonary radiation related toxicity was observed during a median follow-up of 25 months. Three deaths at 6, 3.5 and 3 months were related to electrical storm. Three more patients died during long follow-up at 54, 43 and 18 month after radiosurgery, no deaths were related to VT recurrence or complication of radiosurgery.

Conclusions: This is the compilation of case series and clinical trial data of patients who underwent electroanatomical mapping - guided and scar based radiosurgery respectively. Our data indicate the feasibility of both procedures, majority of patients presented no radiation related toxicity and decrease of VT burden. However, we have seen three cases of severe toxicity including one death. To further investigate long-term safety and efficacy of SBRT for VT, we initiated a prospective multicentric study (NCT03819504).