Wall Shear Stress and T1 Contrast Ratio Are Associated With Embolic Signals During Carotid Exposure in Endarterectomy

Abstract

Background and Purpose- The frictional force because of blood flow may dislodge masses present on the surface of a plaque. Such frictional force is calculated as wall shear stress (WSS) using computational fluid dynamics. The aims of the present study were to determine whether, in addition to carotid plaque intensity on T1-weighted magnetic resonance (MR) imaging, WSS calculated using computational fluid dynamics analysis for carotid arteries is associated with development of an embolism during exposure of carotid arteries during carotid endarterectomy. Methods- One hundred patients with internal carotid artery stenosis (≥70%) underwent carotid plaque imaging with MR, and 54 patients with a vulnerable plaque (intraplaque hemorrhage or lipid/necrotic core) displayed as a high-intensity lesion underwent additional cervical 3-dimensional MR angiography. The maximum value of WSS within the most severe stenotic segment of the internal carotid artery was calculated using MR angiography. Transcranial Doppler monitoring of microembolic signals (MES) in the ipsilateral middle cerebral artery was performed during carotid endarterectomy. Results- Although none of the 46 patients with a nonvulnerable carotid plaque had MES during exposure of carotid arteries, 24 of the 54 patients with a vulnerable carotid plaque (44%) had MES. Logistic regression analysis showed that higher plaque intensity ( P=0.0107) and higher WSS ( P=0.0029) were significantly associated with the development of MES. When both cutoff points of plaque intensity and WSS in the receiver operating characteristic curves for predicting development of MES were combined, specificity (from 63% to 93%) and positive predictive value (from 66% to 90%) became greater than those for plaque intensity alone. Conclusions- In addition to carotid plaque intensity on T1-weighted MR imaging, WSS calculated using computational fluid dynamics analysis for carotid arteries is associated with development of an embolism during exposure of carotid arteries during carotid endarterectomy.

Keywords: angiography; carotid arteries; embolism; endarterectomy; magnetic resonance imaging.

Figure 1.

Relationship among the contrast ratio (CR), wall shear stress (WSS), and development of microembolic signals (MES) during exposure of the carotid arteries in patients with a vulnerable carotid plaque. Closed and open circles denote patients with and without MES, respectively. Vertical and horizontal lines denote the cutoff points lying closest to the upper left corner of the receiver operating characteristic curves for the CR and WSS in predicting the development of MES, respectively.

Figure 2.

Receiver operating characteristic curves for the contrast ratio (CR) and wall shear stress (WSS) in predicting the development of microembolic signals during exposure of the carotid arteries in patients with a vulnerable carotid plaque.

Figure 3.

T1-weighted magnetic resonance plaque images at the location in which the stenosis is most severe in the affected internal carotid artery (ICA; upper) and wall shear stress (WSS) images in the affected carotid artery (lower) in a 74-year-old man with microembolic signals (MES) during exposure of the carotid arteries (left) and a 71-year-old man without MES (right). Although the signal intensity of the plaque is approximately equal between these 2 patients, WSS in the stenotic portion of the ICA is considerably higher in the former patient than in the latter patient.