A histological study of vessel wall reaction after endovenous ultrasound ablation in an animal model

Abstract

Introduction. Along with the generally accepted thermal methods of saphenous varicose veins ablation, the use of non-thermal and combined methods becomes attractive. Due to the variety of mechanisms of action, low-frequency ultrasound is a promising technology for performing a wide range of minimally invasive intravascular operations, including the treatment of varicose veins. Aim. To elucidate the mechanism of action of a novel endovenous ultrasound ablation method and evaluate its effect on vein wall injury and lumen occlusion in an animal model. Materials and methods. A total of 34 central ear vein (CEV) medial ramus were treated in 17 rabbits according to the follow-up protocol. Six femoral veins from three rabbits enrolled into the acute experiment were harvested 45 min after the procedure. All treated CEV medial ramus in the follow-up experiment were divided into four treatment groups with an observation time of: (0) 30 days, control procedure; (1) 60 days, ultrasound ablation; (2) 95 days, ultrasound ablation; (3) 138 days, ultrasound ablation. Results. Occlusion was achieved in all but one CEV medial ramus (29/30; 97%) treated with ultrasound. Histologic examination of treated veins showed heat- and mechanical-induced changes in the vein wall, such as abrasion of the endothelium and fibrotic lesions in the tunica media and tunica adventitia. The occluded segments consisted mainly of cellular fibrotic material. In the acute group, histological evidence of damage to all vessel wall layers was found. Discussion. Ultrasound ablation results in homogeneous and uniform damage to the venous wall. The results of this study suggest that the ultrasound treatment leads to venous occlusion by the additive thermomechanical mechanism of damage to the vessel wall. Conclusions. Endovenous ultrasound ablation showed a similar pattern of thermal damage as endovenous laser (EVLA) and radiofrequency ablation (RFA) and damage to the endothelium as mechanochemical ablation (MOCA). Four months after ultrasound ablation, the occlusion rate was 90%.