The impact of arterial flow complexity on flow diverter outcomes in aneurysms

Abstract

The flow diverter is becoming a standard device for treating cerebral aneurysms. The aim of this in vitro study was to evaluate the impact of flow complexity on the effectiveness of flow diverter stents in a cerebral aneurysm model. The flow pattern of a carotid artery was decomposed into harmonics to generate four flow patterns with different pulsatility indexes ranging from 0.72 to 1.44. The effect of flow diverters on the aneurysm was investigated by injecting red dye or erythrocytes as markers. The recorded images were postprocessed to evaluate the maximum filling of the aneurysm cavity and the washout time. There were significant differences in the cutoff flows between the markers, linked to the flow complexity. Increasing the pulsatility index altered the performance of the flow diverter. The red dye was more sensitive to changes in flow than the red blood cell markers. The flow cutoff depended on the diverter design and the diverter deployment step was crucial for reproducibility of the results. These results strongly suggest that flow complexity should be considered when selecting a flow diverter. Flow diverters are common devices for treating large or complex intracranial aneurysms. As the mechanisms underlying aneurysm occlusion are still not fully understood, the choice of flow diverter is mainly empirical and based on the physician's own experience 1,2. Outcomes range from complete or partial occlusion after varying periods to lack of thrombosis or even haemorrhage 3,4. The factors responsible for occlusion following flow diverter placement are still under debate 3,5. Analysis of the flow inside large aneurysms reveals that, by contrast with small aneurysms where flow is similar to the parent vessel, the flow pattern can be markedly altered 6. Recent studies show that flow complexity is a key factor in flow diverter performance. Computational fluid dynamics (CFD) simulations showed that flow reduction following flow diverter treatment was more noticeable during diastole than systole and that flow diverter performance was related to the flow pattern 7,8. Although blood flow complexity can be fully described using a Fourier decomposition into harmonics, these values are not commonly used in the medical field 9. Instead, the pulsatility index, which can be directly assessed from Doppler or magnetic resonance imaging (MRI) examinations, is more widely used to describe the complexity of patient blood flows 10. The pulsatility index varies within the cerebral arterial tree and within the same artery in different patients, reflecting the diversity of flow patterns that can be encountered within the vessels altered by aneurysms 11,12. Different outcomes are therefore observed when the same flow diverter is used in situations of different flow patterns associated with vessel geometry and position in the cerebral arterial tree, and the physiological state and activity of the patient 13,14. In addition, flow diverter design, including the number of layers, porosity, number of holes, weave angle, wire diameter, a...

A heterogeneous model of endovascular devices for the treatment of intracranial aneurysms

“…In this view, several previous CFD studies 24–27 using a conformal approach showed on one hand that local device compaction, and thus struts placement and proximity, is strongly impacting downstream intra‐saccular velocities, and on the other hand that device wire density can be optimized to ease treatment decisions for a given case. This strong impact on intra‐saccular velocities has been recently confirmed in‐vitro by Chodzyǹski et al 28 who found that by deploying the same FD reference (length and diameter) inside a given idealized geometry three times with the same operator, local pore density changes occurred and caused significant differences in aneurysm filling over the cardiac cycle. One may also anticipate that representing the velocity gradient and associated shear stress at the struts is useful to better represent the platelet activation and thus the capability of the device to promote thrombosis, as described by Xiang et al 27 .…”

First Experience of Three Neurovascular Centers With the p64MW-HPC, a Low-Profile Flow Diverter Designed for Proximal Cerebral Vessels With Antithrombotic Coating

“…This dissonance is further contrasted by the fact that the hydrophilically coated p64MW, which is composed of a more densely woven and hemodynamically impactful mesh than the PED, achieved an inferior rate of early occlusions in our patient collective. The discrepant occlusion rates (65% vs. almost 80%) may simply reflect a greater hemodynamic complexity in the subset of aneurysms, which were treated with the p64MW-HPC ( 37 ). Aside from that, the anti-thrombogenic surface modifications either based on phosphorylcholine (Medtronic: Shield Technology) or hydrophilic glycan-containing polymers (Phenox: HPC) may interact differently with the circulating blood cells and the migratory cells from the vessel wall that are required for the formation of a neo-intima ( 9 , 10 ), and hence, influence its progress in a divergent way.…”

Effect of flow diverter stent malposition on intracranial aneurysm hemodynamics—An experimental framework using stereoscopic particle image velocimetry

“…Another pilot study comparing successful and unsuccessful treatments of aneurysms occurring at the internal carotid artery demonstrated the need to obtain a flow reduction below a critical absolute inflow value instead of simply a high relative reduction [ 28 ]. Recently, Chodzyǹski et al suggest that flow complexity should be considered when selecting a FD since increased pulsatility altered the performance of the device [ 29 ].…”