Embolus Trajectory Through a Physical Replica of the Major Cerebral Arteries

Abstract

Background and Purpose-The observed distribution of cerebral infarcts varies markedly from expectations based on blood-flow volume or Doppler embolus detection. In this study, we used an in vitro model of the cerebral arteries to test whether embolus microspheres encountering the circle of Willis are carried proportionally to volume flow or express a preferred trajectory related to arterial morphology or embolus size. Methods-Our model consisted of a patient-specific silicone replica of the cerebral macrocirculation featuring physiologically realistic pulsatile flow of a blood-mimicking fluid at approximately 1000 mL/min and an input pressure of approximately 150/70 mm Hg. Particles of 200, 500, and 1000 m diameter with equivalent density to thrombus were introduced to the carotid arteries and counted on exiting the model outlets. Results-The middle cerebral arteries (MCAs) of the replica attracted a disproportionate number of emboli compared with the anterior cerebral arteries; 98%Ϯ3% of 1000 m and 93%Ϯ2% of 500 m emboli entered the MCA compared with 82%Ϯ5% of the flow. The observed distribution of large emboli was consistent with the ratio of MCA:anterior cerebral artery infarcts, approximately 95% of which occur in territories supplied by the MCA. With decreasing embolus size, the distribution of emboli approaches that of the flow (approximately 89% of 200 m emboli took the MCA). Key Words: cerebral hemodynamics Ⅲ embolic stroke Ⅲ experimental Ⅲ transcranial Doppler E pidemiological evidence, 1,2 autopsy studies, 3,4 and the trajectories of "balloon emboli" in patients undergoing cerebral angiography 5 suggest that emboli incident from the common carotid artery (CCA) are more than 20 times as likely to come to rest in territories supplied by the middle cerebral artery (MCA) than the anterior cerebral artery (ACA). However, in vivo transcranial Doppler ultrasound insonation of the MCA-ACA junction performed by Wijman et al found emboli to be only 2 to 3 times more likely to enter the MCA 6 suggesting that emboli are carried roughly proportionally to flow volume. Wijman et al concluded that "cerebral embolism is unlikely to be the only cause of ACA and MCA infarcts." In this study, we clarify the relationship among blood flow, arterial topology, and embolization by implementing a physiologically realistic 3-dimensional phantom of the major cerebral arteries to investigate embolus trajectory. We hope that a better understanding of the relationship among arterial topology, blood flow, and embolus trajectory will assist in the development of patient-specific computer simulations for monitoring patients at high risk of stroke. 7 Although previous models of the circle of Willis have been developed to investigate blood flow, 8 -11 ours is the first to use a 3-dimensional in vitro model of the cerebral arteries to study embolization. Conclusions-Embolus Materials and Methods Replica AnatomyA physical model of the cerebral arteries was purchased from a company specializing in vascular replicas (Elastrat, Geneva, Switz...

Selective Vulnerability of Cortical Border Zone to Microembolic Infarct

“…Selective involvement of the perforating vessels feeding the cortex when compared with perforating vessels feeding the white matter or basal ganglia is explained by the relatively greater flow reaching the cortex. 21 Supratentorial lesions clustered in the CBZ between main branches of anterior cerebral artery, MCA, and posterior cerebral artery, whereas infratentorial lesions clustered in the distal territories of posterior inferior cerebellar artery, possibly matching border zone between major cerebellar arteries. 22 This selective vulnerability of CBZ to SCI after atrial fibrillation transcatheter ablation has not been directly demonstrated to date and may be explained in different ways, mainly related to the particular features of its vascularization.…”

“…Pial vessel branches are frequently asymmetrical, with one dominant and one secondary branch; trajectory of the emboli in an experimental replica of brain vessels bifurcation depended on the relative size of the embolus and on the relative flow. 21 Roughly, emboli sized more than one quarter of the vessel diameter preferentially get the bigger branch, whereas smaller emboli distribute proportionally to the relative flow. If this applies to all bifurcations of brain arteries, emboli from 50 to 100 µm would distribute proportionally to the flow in large Willisian bifurcations.…”

Larger A1/M1 Diameter Ratio Predicts Embolic Anterior Cerebral Artery Territorial Stroke

“…In vitro experimental models have highlighted the additional importance of the particle-tobranch diameter ratio in preferentially guiding the trajectory of larger emboli into wider bifurcation branches. [8][9][10] This notion could possibly explain the higher prevalence of atrial fibrillation, which is known to cause large emboli, observed in cases of territorial infarction of the MCA, which typically has the larger terminal ICA bifurcation branch diameter.…”

Preclinical Investigations for Thrombectomy Devices—Does it Translate to Humans?

“…The experimental setup allows for determination of the trajectory of the microemboli into the circle of Willis. 18 By collecting and analyzing the effluent, the size and number of the disrupted microemboli generated during the thrombectomy procedure can be studied. It should be noted that these microemboli are invisible on follow-up imaging; however, their existence could predispose patients to poor clinical outcomes.…”