Recurrences of ventricular tachycardia after stereotactic arrhythmia radioablation arise outside the treated volume: analysis of the Swiss cohort

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: Public grant(s) – EU funding. Main funding source(s): The project is part of the STOPSTORM.eu consortium and has partially received funding from the European Union’s horizon 2020 research and innovation program BACKGROUND: Stereotactic arrhythmia radioablation (STAR) has been recently introduced for the management of ventricular tachycardia (VT) refractory to antiarrhythmic drugs and catheter ablation (CA). VT recurrences have been reported after STAR but the mechanisms remain largely unknown. PURPOSE: We analyzed recurrences in the Swiss Cohort after STAR for refractory VT in order to assess their location related to the irradiated volume. METHODS: From 09.2017 to 01.2020, 20 patients (68±8y, LVEF 37±15%) suffering from refractory VT were enrolled. The underlying cardiopathy was ischemic in 6, inflammatory in 4, neoplastic in 1 and idiopathic in 9 patients. Sixteen out of 20 patients had a history of at least 1 electrical storm. Before STAR, an invasive electro-anatomical mapping (Carto3) of the VT substrate was performed. A mean dose of 23±2Gy was delivered to the planning target volume (PTV). RESULTS: The median ablation volume was 26 ml (range 14-115) and involved the interventricular septum (IVS) in 75% of patients. During the first 6 months after STAR, VT burden decreased by 92% (median value, from 108 to 10 VT/semester, p<0.005). After a median follow-up of 25 months, 12/20 (60%) developed a recurrence with 14 sustained VTs and underwent a redo CA. VT recurrence was located in proximity of the treated arrhythmogenic substrate in 9 cases, occurred remote from the PTV in 3 cases and involved a larger substrate over ≥3 LV segments in 2 cases. No recurrences occurred inside the PTV. The estimated dose delivered at sites of VT recurrence was very heterogeneous, ranging from 0.11 to 28.37 Gy, and less than 15 Gy in 12/14 cases. Voltage measurements showed a significant decrease in both bipolar and unipolar signal amplitude. CONCLUSION: STAR is a precious new tool available for the treatment of therapy-refractory VT, allowing for a significant reduction of VT burden. VT recurrences are common during follow-up, but no recurrences were observed inside the PTV. Local efficacy was supported by a significant decrease in both bipolar and unipolar signal amplitude. [Figure: see text]