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

Abstract

Purpose: We present the preliminary results of the STRA-MI-VT Study (NCT04066517), a spontaneous, phase Ib/II study, designed to prospectively test the safety and efficacy of stereotactic body radiotherapy (SBRT) in patientswith advanced cardiac disease and intractable ventricular tachycardia (VT).

Methods: Cardiac computed tomography (CT) integrated by electroanatomical mapping was used for substrate identification and merged with dedicated CT scans for treatment plan preparation. A single 25-Gy radioablation dose was delivered by a LINAC-based volumetric modulated arc therapy technique in a non-invasive matter. The primary safety endpoint was treatment-related adverse effects during acute and long-term follow-up (FU), obtained by regular in-hospital controls and implantable cardioverter defibrillator (ICD) remote monitoring. The primary efficacy endpoint was the reduction at 3 and 6 months of VT episodes and ICD shocks.

Results: Seven out of eight patients (men; age, 70 ± 7 years; ejection fraction, 27 ± 11%; 3 ischemic, 4 non-ischemic cardiomyopathies) underwent SBRT. At a median 8-month FU, no treatment-related serious adverse event occurred. Three patients died from non-SBRT-related causes. Four patients completed the 6-month FU: the number of VT decreased from 29 ± 33 to 11 ± 9 (p = .05) and 2 ± 2 (p = .08), at 3 and 6 months, respectively; shocks decreased from 11 to 0 and 2, respectively. At 6 months, all patients. showed a significant reduction of VT episodes and no electrical storm recurrence, with the complete regression of iterative VTs in 2/2 patients.

Conclusion: The STRA-MI-VT Study suggests that SBRT can be considered an alternative option for the treatment of VT in patients with structural heart disease and highlights the need for further clinical investigation addressing safety and efficacy.

Keywords: Catheter ablation; Multimodal imaging; Stereotactic body radiotherapy/radioablation; Structural heart disease/dilated cardiomyopathy; Ventricular tachycardia/ventricular arrhythmias.

Conflict of interest statement

The authors declare no competing interests.

© 2021. The Author(s).

Figures

Fig. 1

Interventional workflow. Step 1—cardiac CT data, integrated with endo-epicardial electroanatomical mapping, are merged with simulation “free-breathing” CT, acquired together with a “breathing-triggered” 4D-CT. Step 2—integrated “free-breathing” simulation-CT imaging is used as platform for the identification and contouring of the clinical target volume and of the organs at risk. The volumetric modulated arc therapy treatment plan is processed by the Eclipse RapidArc Planning System to deliver a single-fraction total dose of 25 Gy. Step 3—patient’s positioning setup is ensured by means of a vacuum immobilization cast on the treatment couch and is verified during the whole treatment process; two to three cone-beam CT scans are performed (image-guided radiotherapy), if necessary, for setup optimization. Step 4—the volumetric modulated arc therapy treatment is eventually delivered using the Varian Trilogy linear accelerator with the patient in the conscious state, lying down in a comfortable position in his/her immobilization cast. Abbreviation: CT, computed tomography

Fig. 2

CT imaging with myocardial fibrosis evaluation, integrated electroanatomical mapping, and SBRT-treatment plan in one patient undergoing SBRT are represented. Upper panels. CT myocardial fibrosis evaluation in the long-axis view is represented. CT scan was acquired 8 min after the injection of iodinated contrast medium, as per protocol indication. No hyperdense myocardial areas are evident with regard to the anterolateral wall (A, blue arrowheads). Areas of hyperdense myocardium are shown (B, C): red arrowheads point at a transmural (ischemic pattern) myocardial fibrosis in the inferior and posterolateral wall of the left ventricle. The left ventricular apex appears free from lesions (green arrowheads). Middle panel. High-density epicardial electroanatomical mapping combined with CT imaging (D). Mid- and basal segments of the inferior and posterior wall are covered by diseased electrograms, represented in red and yellow by the “color-coded” map, as expression of the underlying electrical scar (left). In the same location, CT shows a pattern of discrete transmural fibrosis, which perfectly matches with the lesion revealed by the electroanatomical map (right). The intracardiac echo fan acquired during the mapping procedure is visualized in the map with the corresponding view in the small box. Lower panels. The planning target volume in the axial (E), coronal (F), and sagittal (G) view, as delineated by the red contour line, is depicted. The colored area represents the dose coverage, from the 95% to the maximum of the prescription dose. Abbreviation: CT, computed tomography

Fig. 3

Follow-up summary. Months after SBRT for each patient are depicted, no patient was lost on follow-up and 4 patients completed the 6-month follow-up period. Red circles highlight the time for in-hospital check-ups; cross indicates patient’s death. Abbreviation: SBRT, stereotactic body radiotherapy

Fig. 4

Outcome of SBRT for the patients having completed the 6-month follow-up. From left to right, the number of VT episodes occurring during the 3 months preceding SBRT and during follow-up (up to 3 months from SBRT and in the following 3-month period) is depicted by bars. Blue bars refer to all VT episodes, red bars to VT causing ATP, green bars to VT causing shock. A Cumulative number of VT episodes, as average of events. B, C, D, and E Absolute number of VT episodes for each patient. Abbreviations: ATP, antitachycardia pacing; SBRT, stereotactic body radiotherapy; VT, ventricular tachycardia

Fig. 5

Outcome in patients with iterative slow VTs, not accounting for ICD interventions. The numbers of VT episodes during the 3 months preceding SBRT and during follow-up (up to 3 months from SBRT and in the following 3-month period) for pt. #1 (A) and for pt. #2 (B) are represented. Gray dots and lines refer to the overall number of VTs, orange to VT episodes lasting > 3 h, light blue to VT episodes lasting < 3 h. An early favorable trend is observed in these patients starting from the «blanking period». Abbreviations: SBRT, stereotactic body radiotherapy; VT, ventricular tachycardia