Stereotactic radioablation for the treatment of ventricular tachycardia: preliminary data and insights from the STRA‑MI‑VT phase Ib/II study

Radiofrequency catheter ablation can be effective for certain patients with ventricular arrhythmias. However, its use is limited and is associated with high procedural risk. Single-session high-dose stereotactic body radiotherapy (SBRT) is a novel, non-invasive procedure that overcomes many of these limitations. Initial small studies have reported excellent outcomes in patients with ventricular tachycardia (VT), but clinical experience is limited.

The aim of this study was to evaluate the efficacy and safety of SRBT in the treatment of refractory VT in patients with advanced cardiomyopathy.

This is the first European prospective study to evaluate the efficacy and safety of SRBT in the treatment of arrhythmias. Preliminary data showed a substantial reduction in patients with VT arrhythmic episodes and an improvement in quality of life, without significant side effects.

SBRT appears to be a potential treatment option for the treatment of VT in patients with structural heart disease and ineligible for conventional approaches.

The STereotactic RadioAblation by Multimodal Imaging for VT (STRA-MI-VT) trial (NCT04066517) is an open-label, single-centre prospective clinical trial that aims to enrol 15 patients. Electroanatomical mapping plus delayed enhancement (DE) cardiac computed tomography (CT) were used to characterise the arrhythmia and define the target area. A 12-lead electrocardiogram (ECG) analysis of VTs was performed. Treatment was delivered using the Varian Trilogy linear accelerator with the patient lying down in a comfortable position. After SBRT, all patients were continuously monitored for at least 5 days. Follow ups were performed at weekly intervals for the first month, and then at 3, 6- and 12-months post-procedure, and involved 12-lead ECG and implantable cardioverter defibrillator (ICD) interrogation, echocardiography examination, and SF-36 Health Questionnaire. A radiotherapy evaluation and a thorax CT were planned at 3 and 12 months.

• Safety of SBRT during the first month post-procedure and at 3-, 6-, and 12-month follow-up.
• Total number of VT episodes detected by the ICD at 3, 6, and 12 months, compared to the 3-month period before the procedure.

• Total mortality at 12 months
• Variations in quality of life (QoL) using the SF-36 Health questionnaire
• Changes in cardiac function assessed by left ventricular ejection fraction (LVEF) on echocardiograph

• Structural heart disease and relapsing VT (≥ 3 VT episodes) refractory to any therapy
• Not eligible for conventional catheter ablation
• LVEF ≥ 20%
• Age ≥ 50 years
• Presence of an ICD
• Signed an IRB approved written informed consent document

• Previous radiotherapy with cardiac involvement
• Active myocardial ischemia
• Acute revascularisation in the past 120 days
• Acute hemodynamic instability (cardiogenic shock/NYHA IV)

• Among 127 patients with structural heart disease admitted for VT ablation between September 2019 and October 2020, 8 were enrolled in the study, 7 of whom underwent SBRT
• No adverse events occurred during SBRT and in the first month following SBRT
• At a median 8 months, 3 patients died, 2 of whom did not experience arrhythmia recurrence and one whose cause of death was unconfirmed
• In the 4 who completed 6-month follow up, no treatment related SAEs occurred.
• Compared with the 3-month period before SBRT, the total mean number of VT episodes was 29 ± 33 vs. 11 ± 9 (p=0.05), and 2 ± 2 (p=0.08) at 3 and 6 months respectively
•  The number of VT episodes with antitachycardia pacing (ATP) was 27 ± 35 vs. 11 ± 9 (p=0.05) and 2 ± 2 (p 0.2), at 3 and 6 months, respectively
• The number of VT episodes with shock was 2 ± 3 vs 0 (p=n.s.) and 0 (p = 0.13), at 3 and 6 months, respectively
• The number of appropriate shocks was 11 vs. 0 and 2, at 3 and at 6 months, respectively
• In 2 patients, doses of antiarrhythmic drugs were reduced and, in another patient, an antiarrhythmic drug was withdrawn

These preliminary data show that SBRT was safe and highly effective in preventing VT in patients with severe cardiomyopathy who were not eligible for any other therapy. The procedure was cost effective, and larger studies are warranted.

• This is a small study therefore the findings have limited statistical power
• These preliminary data have a short follow up and the possibility of longer-term SAEs cannot be ruled out