Early Antiarrhythmic Efficacy of Noninvasive Cardiac Radioablation for Ventricular Tachycardia

Abstract

<h3>Purpose/Objective(s)</h3> Noninvasive cardiac radioablation has been reported to be effective and relatively safe for ventricular tachycardia (VT) in preclinical and clinical studies. However, previous studies implementing cardiac radioablation set a 6-12 weeks of "blanking period" and focused on long-term effects rather than reporting the early changes. In this prospective trial, we focused on the early antiarrhythmic effects within one month after cardiac radioablation. Especially, we tried to seek the differences in response according to the cause of VT. <h3>Materials/Methods</h3> From September 2019 to December 2020, 6 patients (3 ischemic VTs and 3 non-ischemic VTs) were included in this trial and treated with stereotactic body radiotherapy (SBRT) with a single fraction of 25 Gy for intractable VT. A synthesis of imaging studies, 12-lead ECG, and electrophysiological mapping were used to localize the treatment target. The internal target volume was delineated on either maximal intensity projection of 4D-CT or deep inspiration breath hold CT. A 24-hour Holter monitoring was performed for all patients one month before and after SBRT and except for one patient, it was performed from 24 hours before SBRT to 48 hours after SBRT to measure the early response after SBRT. <h3>Results</h3> The number of total ventricular beats decreased by 58% and 60% within 24 hours and 48 hours after SBRT, respectively. It further decreased to 29% of pre-SBRT number of total ventricular beats at one month after SBRT. The decrease of total ventricular beats could be attributed to the decrease of VT burden rather than that of premature ventricular contractions (PVCs) because the burden of VT decreased earlier and more dramatically than that of PVC. After cardiac radioablation, the duration of the longest VT run was shortened. This indicated that cardiac radioablation decreases the VT burden by shortening the durations of VTs. Notably, the cardiac radioablation was more effective for ischemic VTs than non-ischemic VTs in that the VT burden decreased more markedly after SBRT. The electrophysiologic characteristics of VT/PVC were changed after treatment. During one month after SBRT, there was no severe acute toxicity. <h3>Conclusion</h3> In six patients with intractable VT, the noninvasive cardiac radioablation with a dose of 25 Gy was effective even in 1-month follow-up. The decrease of VT burden through shortening of VTs already began within 24 hours after the procedure and continued to decrease until one month after the radioablation. The treatment effect was more remarkable in ischemic than non-ischemic VT patients.