Abstract
Background
The assessment of carotid plaque composition has attracted great interest as a tool to predict plaque vulnerability and subsequent risk of cardiovascular events. These vulnerable plaque lesions are characterized by the presence of intraplaque neovascularization (IPN). Previously, grayscale pixel ranges of ultrasound images have been correlated to various human tissue types. Thus, using these ranges, it is possible to assess the composition of atherosclerotic plaque non-invasively.
Purpose
This study sought to determine the relationship between carotid plaque composition and the degree of neovascularization in patients presenting with acute coronary syndrome (ACS), when compared to patients with stable angina.
Methods
A carotid focused vascular ultrasound was performed in 92 participants who had recently undergone coronary angiography due to stable angina or ACS. In 81 participants found to have atherosclerotic plaque in at least one carotid artery, plaque composition was assessed for tissue-like types by pixel distribution analysis: grayscale ranges 0–4 (blood), 8–26 (fat), 41–76 (muscle), 112–196 (fibrous), and 211–255 (calcium) (Figure 1). Participants also received microbubble contrast to assess IPN. IPN was graded based on the presence and location of microbubbles within each plaque (0, not visible; 1, peri-adventitial; 2, plaque core) and averaged to obtain an overall score. An independent t-test was used to compare continuous variables. Pearson pairwise correlations were used to assess associations between IPN and tissue composition.
Results
In the overall sample population, increased average IPN score correlated with increased plaque % blood tissue type (rho=0.28; p=0.01). Patients presenting with ACS (n=32) had increased neovascularization (IPN score of 1.47 vs 1.09; p=0.4), compared to patients with stable angina. In addition, ACS patients with an IPN score ≥1.25 had higher levels of plaque % blood (1.97% vs 0.75%; p=0.02).In ACS patients only, % blood increased with IPN score (r=0.34; p=0.06) and % fibrous tissue decreased with IPN score (r=−0.42; p=0.02).
Figure 1
Conclusion
The proportion of blood-like tissue in carotid plaque is associated with neovascularization and is increased in ACS patients. This may indicate hemorrhage within the plaque leading to rupture. Increased fibrous tissue may have a protective role, stabilizing the plaque when present. This data suggests that carotid plaque composition may be used as an imaging biomarker for cardiovascular risk, and its incorporation into routine screening practices may improve patient risk stratification.
Acknowledgement/Funding
CIHR CGS-Doctoral Award, Heart and Stroke Foundation of Canada, Canada Foundation for Innovation
TCT-195 Novel Quantitative Virtual Histology Parameters in the Asymptomatic and Symptomatic Carotid Atherosclerotic Plaque Imaging: Data from the First 222 Patients in CRACK-VH Study
