The effect of carotid artery stenting on capillary transit time heterogeneity in patients with carotid artery stenosis

Abstract

Introduction: Carotid revascularisation improves haemodynamic compromise in cerebral circulation as an additional benefit to the primary goal of reducing future thromboembolic risk. We determined the effect of carotid artery stenting on cerebral perfusion and oxygenation using a perfusion-weighted MRI algorithm that is based on assessment of capillary transit-time heterogeneity together with other perfusion and metabolism-related metrics.

Patients and methods: A consecutive series of 33 patients were evaluated by dynamic susceptibility contrast perfusion-weighted MRI prior to and within 24 h of the endovascular procedure. The level of relative change induced by stenting, and relationship of these changes with respect to baseline stenosis degree were analysed.

Results: Stenting led to significant increase in cerebral blood flow (p < 0.001), and decrease in cerebral blood volume (p = 0.001) and mean transit time (p < 0.001); this was accompanied by reduction in oxygen extraction fraction (p < 0.001) and capillary transit-time heterogeneity (p < 0.001), but an overall increase in relative capillary transit-time heterogeneity (RTH: CTH divided by MTT; p = 0.008). No significant change was observed with respect to cerebral metabolic rate of oxygen. The median volume of tissue with MTT > 2s decreased from 24 ml to 12 ml (p = 0.009), with CTH > 2s from 29 ml to 19 ml (p = 0.041), and with RTH < 0.9 from 61 ml to 39 ml (p = 0.037) following stenting. These changes were correlated with the baseline degree of stenosis.Discussion: Stenting improved the moderate stage of haemodynamic compromise at baseline in our cohort. The decreased relative transit-time heterogeneity, which increases following stenting, is probably a reflection of decreased functional capillary density secondary to chronic hypoperfusion induced by the proximal stenosis.Conclusion: Carotid artery stenting, is not only important for prophylaxis of future vascular events, but also is critical for restoration of microvascular function in the cerebral tissue.

Keywords: Atherosclerosis; capillary transit time; carotid artery stenting; flow heterogeneity; perfusion MRI.

Figure 1.

Illustration of images and annotations for four subjects with carotid stenosis undergoing stenting (Subject 1: Male, 52 years old, 51% right-sided stenosis; Subject 2: Female, 59 years old, 79% right-sided stenosis; Subject 3: Female, 61 years old, 63% left-sided stenosis; Subject 4: Female, 57 years old, 78% right-sided stenosis). The green, red, and blue annotations correspond to WM, GM, and WM hyperintensity regions, respectively, while the white contour denotes the MCA territory.

Figure 2.

Box-plots of haemodynamic markers prior to (white) and following (grey) carotid artery stenting. For better visualisation of the box-plots, outliers outside the visualisation area are not included in the plots, but are naturally included in the statistical analyses. The y-axes represent the relative values with respect to the contralateral hemisphere.

Figure 3.

Pre- and post-stent sample images of a patient undergoing left-sided carotid artery stenting.