Aim The aims of this in vitro experimental study were to examine perfusate flow during aspiration thrombectomy in a closed in-vitro system in more detail to further investigate the reasons for decreased favorable outcomes from suction thrombectomy when compared to stentrievers as shown in clinical trials.
Methods A mathematical model of blood flow in an open and obstructed cerebral blood vessel was developed. A physical flow model was then set up to visualize flow patterns in vitro.
The mathematical model
A computational fluid dynamics (CFD) model was used to simulate the fluid flow characteristics of a typical catheter used for our experiments.
The physical flow model
The model was set up containing a glass model of the MCA, with a downstream pinch point at which the thrombus is applied.
Results Mathematical model of suction thrombectomy
Results of the modeling showed that in an open system (cerebral artery not obstructed by a thrombus) flow is drawn from upstream of the tip of a device when suction is applied. In a closed system (cerebral artery obstructed by a thrombus) the mathematical model showed that flow came from behind the tip of the device when suction was applied, and that there was no traction effect on flow distal of the tip.
More than 30 clot extraction experiments were performed. Suction at 5kPa produced no successful recanalizations. At 10 kPa, 2/6 attempts were successful with average time to remove clot of 9s. At suction pressures above 10 kPa clot engagement was immediate (<1s) and 100% recanalization (6/6 attempts) was observed.
At all flow rates and separation distances, fluid was clearly drawn from behind the catheter and not from in front when a clot was present. As the flow became steady an area of turbulence was observed in front of the catheter tip and this area of turbulence increased with increasing flow rates. The turbulence had no effect on clot removal at any distance from the catheter, the catheter needed to be touching the clot before suction had any effect. At further separation distances, no clot movement or engagement with the suction catheter was observed in any of the experiments.
Conclusion We have shown that suction in an occluded vessel when the catheter is not fully engaged with the thrombus leads to aspiration of blood from more proximal patent vessels. This could result in reversal of flow and reduction of perfusion pressure in collateral vessels. As the ischemic penumbra is dependent on perfusion though collaterals, reduction in collateral pressure is likely to have an adverse effect on outcome.
Use of aspiration only results in vessel patency if or when full clot capture is attained and therefore in patients where there are prolonged procedures before clot capture this may become significant. The use of aspiration catheters not engaged fully with the clot, and in which suction is routinely applied at some distance from the clot may result in collapse of the collateral vessels with changes to the already poor perfusion pressure to the salvageable ischemic penumbra.
Disclosures S. Nayak: None. F. Lally: None. M. Soorani: None. C. Jadun: None. Y. Yang: None. J. McCrudden: None. S. Naire: None. C. Roffe: None.
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