Experimental use of stereotactic radiosurgery in non-invasive interventions in arrhythmology

Funding Acknowledgements Type of funding sources: None. Background Non-invasive stereotactic treatment with particle beam may be considered as a promising alternative to catheter ablation in patients with different types of tachyarrhythmias. Purpose the purpose of the experimental study was to develop a technique for stereotactic radioablation in order to create a stable functional and morphological damage in heart tissue with subsequent analysis of precision, efficiency and safety of the exposure in the long-term observation period. Materials and methods The research was carried out on four domestic pigs. The animals were 10-12 weeks old, the average weight was 30 ± 2.7 kg. Beam delivering linear accelerator was used during the experiment. Animals were divided into groups according to the zones of planned radiation exposure: 1st animal – atrioventricular (AV) node (dose 35 Gy), 2nd animal - AV node and the apex of the left ventricle (LV) (dose 40/35 Gy, respectively), 3rd animal - pulmonary veins muscle sleeves and left atrium (dose 30 Gy), 4th - AV node and free wall of the LV (dose 45/40 Gy, respectively). Under intravenous sedation with hemodynamic monitoring, contrast-based CT scan of the heart was performed to assess the degree of displacement of the heart chambers in one respiratory and cardiac cycle- and to assess the anatomy of the chambers of the heart and adjacent organs. The allocation and the contouring of the target zones were carried out in three projections: axial, frontal and sagittal. For electrophysiological control, loop recorders were implanted in each animal. The average exposure time was 11 ± 7 minutes. The long-term follow-up period was six months, followed by morphological examination of autopsy material. The study followed the "Principles of laboratory animal care". Results The average follow-up period after the experiment was 134.75 ± 77.34 days. The electrophysiological effect of the ablation was considered to be achieved in cases of complete AV-block development. This effect was developed in two out of three animals, whose AV-node was exposed: 2nd animal - 40 Gy on 108th day of observation and 4th animal - 45 Gy on 21st day of observation. No cardiac arrhythmias were recorded in all cases. The results of macro- and microscopic examination showed significant changes in the target zones. These areas had precise but uneven damage boundaries, which were within the planned ones (conformal exposure with a high degree of precision). The transmural nature of the changes was noted as well (pic. 1 A, B, C). Massive fields of fibrous tissue of various degrees of maturity (with a predominance of subepicardial localization) with focal hemorrhages of various ages and granulations were detected, which were surrounded by cardiomyocytes with coagulated and vacuolated cytoplasm (pic. 1 D, E, F). Conclusion The use of non-invasive stereotactic treatment of tachyarrhythmias has high potential in modern arrhythmology as an alternative ablation method. Abstract Figure. Macro- and microscopic results