Exploring the relationship between embolic acute stroke distribution and supra-aortic vessel patency: key findings from an in vitro model study

Abstract

Background: We investigated differences in intracranial embolus distribution through communicating arteries in relation to supra-aortic vessel (SAV) patency.

Methods: For this experimental analysis, we created a silicone model of the extracranial and intracranial circulations using a blood-mimicking fluid under physiological pulsatile flow. We examined the sequence of embolus lodgment on injecting 104 frangible clot analogues (406 emboli) through the right internal carotid artery (CA) as SAV patency changed: (a) all SAV patent (baseline), (b) emboli from a CA occlusion, (c) emboli contralateral to a CA occlusion and (d) occlusion of the posterior circulation. The statistical analysis included a descriptive analysis of thrombi location after occlusion (absolute and relative frequencies). Sequences of occlusions were displayed in Sankey flow charts for the four SAV conditions. Associations between SAV conditions and occlusion location were tested by Fisher's exact test. Two-sided p values were compared with a significance level of 0.05.

Results: The total number of emboli was 406 (median fragments/clot: 4 (IQR: 3-5)). Embolus lodgment was dependent on SAV patency (p<0.0001). In all scenarios, embolism lodging in the anterior cerebral artery (ACA) occurred after a previous middle cerebral artery (MCA) embolism (MCA first lodge: 96%, 100/104). The rate of ipsilateral ACA embolism was 28.9% (28/97) at baseline, decreasing significantly when emboli originated from an occluded CA (16%, 14/88). There were more bihemispheric embolisations in cases of contralateral CA occlusion (37%, 45/122), with bilateral ACA embolisms preceding contralateral MCA embolism in 56% of cases (14/25 opposite MCA and ACA embolism).

Conclusions: All emboli in the ACA occurred after a previous ipsilateral MCA embolism. Bihemispheric embolisms were rare, except when there was a coexisting occlusion in either CA, particularly in cases of a contralateral CA occlusion.

Keywords: Carotid Stenosis; Cerebrovascular Circulation; Embolism; Stroke; Thromboembolism.

Figure 1. Sequential lodges by the 406 total emboli for the four anatomical conditions of the supra-aortic vessels tested. After fragmentation, the median number of lodgments per clot was four, with a minimum of 1 and a maximum of 8. The number indicated over each graphic (ranging from 1 to 8) is the sequential number of lodgments referred to in that chart. See the online supplemental table S1 for a more detailed description. ACA, anterior cerebral artery; ICA, internal carotid artery; MCA, middle cerebral artery; PCA, posterior cerebral artery.

Figure 2. Sankey flow diagrams of sequential embolic lodgments by anatomical condition of the supra-aortic vessels. The diagram shows the flows and their relative quantities in proportion to each other. Vertical coloured lines represent each lodgment (first, second, third, etc). Horizontal flow lines represent the relative quantity of fragments anchored at a particular intracranial location after a specific prior clot allocation. Emboli that migrated to the opposite hemisphere are shown in blue. Emboli that travelled to the ipsilateral ACA are shown in green. (A) Baseline: supra-aortic vessels without occlusion (97 emboli from 29 injected clots); (B) Emboli from an occluded right CA (88/25); (C) Emboli through the right CA with occlusion of the left CA (122/24); (D) Emboli through the right CA with concomitant occlusion of both vertebral arteries (99/26). ACA, anterior cerebral artery; CA, carotid artery; ICA-T, terminal internal CA; MCA, middle cerebral artery; PCA, posterior cerebral artery.