One Year Follow-up and Toxicity Review in a Series of 6 Patients Receiving Stereotactic Arrhythmia Radioablation for Ventricular Tachycardia

Abstract

Stereotactic body radiation therapy (SBRT) to arrhythmogenic scar regions defined by noninvasive cardiac mapping has recently been described for patients with treatment refractory ventricular tachycardia (VT). Long-term outcomes and both intra- and extra-cardiac toxicities are not well described in this patient population. We report the outcomes following at least 1-year post-treatment along with toxicity for 6 patients treated with this technique in our institution. A total of 6 patients treated between 2019 and 2022 with refractory VT with previously failed ablations and at least one anti-arrhythmic drug was treated at our institution. All were treated with 25 Gy in a single fraction to the suspected arrhythmogenic scar. Cardiac microstructure contouring was done following the atlas by Duane et al. 2017. Implantable cardioverter defibrillator (ICD) interrogation was performed regularly by the treating cardiologist to assess the number of VT and ICD events, and, patients were seen immediately following SBRT, and at 3, 6, and 12 months respectively. Computed tomography of the chest was done at 3 months to assess for radiation induced pneumonitis and transthoracic echocardiograms were done as per the cardiologist's discretion. Radiation toxicity was evaluated using CTCAE v5.0. The median follow-up time for the 6 evaluated patients is 24 months. Three patients (50%) remained VT free during the one-year period post SBRT. Two of these patients remain VT free and are either on reduced or discontinued anti-arrhythmic drugs, while another failed at 24 months in an area of the arrhythmogenic substrate that was intentionally not irradiated due to organ at risk safety concerns. Among those that failed, the median time to failure was 4 months (range 3-5 months). All 6 patients tolerated treatment with no immediate acute side effects. Three (50%) of patients had no acute clinical or radiographic side effects. Grade 1 esophagitis, grade 1 fatigue, and grade 1 cough was reported in 1 (17%) patient each (all different patients), and 1 patient required hospitalization 4 months after SBRT for a heart failure exacerbation (potentially SBRT related). One patient (17%) died within 3 months following treatment but their death was not attributed to radiation treatment. No cardiac microstructure toxicity has been reported to date. Despite increasing reports in the literature, there are no established criteria to predict success for SBRT in the context of treatment-refractory VT, or the optimal treatment dose for success, making it difficult to identify optimal patients. Current limited evidence suggests that this technique may be a relatively safe approach to provide an acute reduction in VT burden for those refractory to standard of care and has an acceptable acute toxicity profile however longer term follow-up is required. Long term toxicity, specifically to cardiac microstructures, and dose optimization is currently are the focus of ongoing study.