Stent retrievers more harmful to arterial wall than ADAPT in animal model

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A new study comparing acute damage to the arterial wall caused by ADAPT (a direct aspiration first pass technique) or stent retrievers during thrombectomy procedures has found that while both techniques caused acute damage to the vessel walls, thrombectomy with a stent retriever appeared to be more harmful to all layers of the arterial wall, particularly the endothelium.

The aims of the study, conducted by Simone Peschillo (University of Rome, Italy) and others and published in the Journal of NeuroInterventional Surgery, were to assess the histological and ultrastructural changes occurring in the arterial wall in the acute phase following endovascular treatment with ADAPT or a stent retriever, and compare the findings in order to determine which is the least harmful technique.

According to the study authors, the normal histological characteristics of porcine extracranial arteries are well-known and offer the possibility of evaluating pathological lesions. Against this background, Peschillo and colleagues designed a protocol for use of swine to assess the histological and ultrastructural damage to vessels treated with mechanical thrombectomy, comparing the two most widely used techniques, stent retrievers and ADAPT. The protocol was principally designed to assess the degree and type of vascular damage. Recanalisation rate, vasospasm, arterial perforation, and distal embolism were also reported.

The procedures were performed after injecting thrombi into the selected arteries (arteries with diameters similar to those of the human internal carotid artery and first segment of the middle cerebral artery). After the procedures, the animal was euthanised and 12 arterial samples were obtained for analysis by optical and electronic microscopy.

“It was seen that both techniques cause alterations to the structure of the vessel wall; in detail, there was almost total denudation of the endothelium together with thickening of the internal elastic lamina in the vessels treated with stent retriever; on electron microscopy only a few endothelial cells could be seen incorporated in a fibrin matrix and associated with degeneration of the elastic fibres of the bordering tunica media/adventitia. In contrast, in the vessels treated with ADAPT, optical microscopy revealed a clear undamaged elastic lamina in both samples and a continuous endothelium lining the vessels, although the cell alignment of the M1 segment was altered. There was some degeneration of the elastic fibres between the tunica media and the adventitia, albeit to a lesser extent than that found following stent retriever treatment. Scanning electron microscopy of ICA treated with ADAPT revealed the presence of ‘scratches’: these tissue lacerations seem to be due to the aspiration system or, more probably, weakening of the tissue during handling,” they explain.

The investigators state that several factors may explain these lesions. Not least, unlike the aspiration technique which applies an aspiration force to the proximal base of the thrombus, the stent retrievers used in thrombectomy capture the clot by exerting a continuous radial force against the vessel wall, which may injure the endothelium.

“The differences in histological and ultrastructural damage are probably due to the different mechanisms of clot removal. In detail, ADAPT, unlike stent retriever, acts on the clot, explaining the lesser damage to the vessel wall. However, it is precisely this mechanism of action that could account for the slight increase in embolisation to new territories that has been found with ADAPT. Given these results, ADAPT seems to be less traumatic to the vessel wall, and in particular to the endothelial layer. However, in this study, we only analysed the acute damage to the vessel wall after a single attempt at clot removal. Further studies should clarify whether the vascular damage is directly proportional to the number of passages with the stent retrievers or ADAPT,” Peschillo and colleagues write.

In terms of future research, the investigators point out that this study only evaluated acute damage to the vessel wall. In the future, they say, it would be interesting to evaluate both the evolution of the parietal lesions in the subacute phase and in the long term, and whether the damage influences patients’ outcomes in any way. Additionally, the authors acknowledge that given that a single swine model was used, it was not possible to obtain a sufficiently large number of samples to be able to perform a statistical analysis in this study and further research is therefore needed to confirm these findings.