Could the sonographic characterization of carotid plaque improve the surrogacy of intima-media thickness for vascular outcomes?

Abstract

Hiukka's recent negative trial of fenofibrate in type 2 diabetics should not have come as a surprise to those experienced in the acquisition and measurement of intima-media thickness (IMT). Although her study was apparently well designed and carefully conducted, the key issues of plaque quality and vulnerability were not addressed. In order to improve the clinical relevance of conventional cardiovascular risk factors, we translated some of the most robust into age equivalents and used their combined average to compute CardioMetablic Age (CMA), the age equivalent of pooled cardiovascular risk. Five clinical parameters determine CMA-non-HDL cholesterol, HDL cholesterol, fasting glycemia, supine pulse pressure, and a Framingham risk-adjusted nearest decade. Using high resolution B-mode carotid ultrasound, we also developed a similar image-based carotid index called Intima-Media Age (IMA), the apparent sonographic age of carotid arteries. Five ultrasound characteristics determine IMA-the average of common carotid far wall IMT (CIMT), maximum observed carotid lumen narrowing, maximum observed common carotid elasticity and recoil, plaque layers and components, and plaque layout and architecture. After reviewing the charts of 42 consecutive patients who had carotid sonograms, our 2008 quality audit of CIMT found that IMA was a better predictor of vascular outcomes than CIMT, which was not better than the vascular age predicted by 1/2 (CMA+age). In conclusion, we believe that multifactor plaque analysis-looking for structural, compositional, and hemodynamic signs of plaque vulnerability-could strengthen the surrogacy of CIMT and significantly change the outcomes of some intima-media studies such as Hiukka's trial.