Variation of longitudinal strain along the arterial wall adjacent to the asymptomatic carotid plaque

Abstract

The motion, and resulting strain, of the arterial wall nearby an atheromatous plaque is believed to be affected by the plaque and therefore may carry important information about disease status. Strain of the arterial wall in the longitudinal direction, i.e. along its length, has recently gained attention as determinant of cardiovascular risk. In this work, longitudinal strain (LS) was estimated along the wall proximal to asymptomatic carotid plaque, in an attempt to highlight the significance of arterial wall kinematics in atherosclerotic subjects without cerebrovascular events. Twenty five atheromatous carotid arteries of elderly male adults (59-81 y.o., 50-100% stenosis) were imaged in longitudinal sections, and videos of Bmode images were analysed using a previously developed method based on optical flow. The analysis consisted in the estimation of the longitudinal positions of three regions of interest (ROIs) on the posterior wall. LS was subsequently defined as the normalised difference of the longitudinal positions between two ROIs, and was assessed at two locations along the wall. A longitudinal strain index (LSI) was then calculated as the average of the amplitudes of the LS curves over 2-3 cardiac cycles. LSIs at location 1 (closer to the plaque) were significantly higher than at location 2 (4.74±1.66 vs. 2.54±1.08, p-value=1.25E-06). This indicates that the wall closer to the plaque undergoes higher strain than the wall farther from it, which may be due to the effect of the presence and motion of the nearby lesion; an effect, which seems to be extended to the area around it. These findings show promise toward better understanding the complex mechanical phenomena taking place not only within the plaque but also in the neighbouring tissues.