Characteristics of recurrent ventricular tachycardias after stereotactic body radiotherapy

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Public grant(s) – EU funding. Main funding source(s): Grant project AZV NU20-02-00244 from the Ministry of Health of the Czech Republic and European Union's Horizon 2020 research and innovation program under grant agreement No 945119. INTRODUCTION: Stereotactic body radiotherapy (SBRT) is a novel treatment for otherwise resistant ventricular tachycardias (VTs). Different mechanisms of SBRT for VT suppression were proposed that include radiation-induced fibrosis but also SBRT-triggered increase in myocardial conduction velocities without significant fibrotic changes. PURPOSE: The study compared the morphologies and cycle lengths (CLs) of inducible VTs during re-do catheter ablation after SBRT with VTs before SBRT. METHODS: We investigated patients that underwent SBRT (a single session of 25 Gy) for refractory VT and subsequent electrophysiology study / reablation for recurrences of VTs. All inducible VTs were analysed concerning morphology and CL. RESULTS: A total of 9 patients (2 women, aged 60 ± 13 years) were included. Two patients had ischemic heart disease, six patients had nonischemic cardiomyopathy, and one had a cardiac fibroma. All patients were on chronic amiodarone treatment. The mean ejection fraction of the left ventricle was 35 ± 12%. The mean planning target volume for SBRT was 39 ± 21 ml. Electrophysiology study/reablation was performed at a mean interval of 8 months (interquartile range: 2-10months) after SBRT. A total of 23 and 27 distinct VT morphologies were inducible before and after SBRT, respectively. Twelve pairs of VTs (44%) were identified that had identical morphology before and after SBRT. The mean CL of these VT pairs decreased from 399 ± 98 ms to 472 ± 74 ms (P = 0.01) after SBRT. Overall, 15/27 of all VT morphologies induced after SBRT originated from the irradiated region. CONCLUSIONS: Recurrent VTs after SBRT had commonly origin in the irradiated region. In pairwise comparison, the CL of VTs has prolonged after the SBRT. This suggests that SBRT results in radiation-induced fibrosis rather than an increase in conduction velocity. [Figure: see text]