Measurement of carotid artery intima-media thickness improves the power of traditional risk factors to predict cardiovascular events

The intima media thickness (IMT) of the carotid artery plays a key role in atherosclerosis assessment. We performed a longitudinal observational study to investigate whether carotid Max-IMT, measured in clinical practice, can be combined with the Framingham Risk Score (FRS) to improve the prediction of cardiovascular events in patients at low to intermediate risk for such events. 1969 patients attending our Lipid Clinic received ultrasonic measurement of Max-IMT and its distribution was presented in age- and gender-specific tables from which a Max-IMT percentile (IMTperc) was derived for each patient. 242 patients with low or intermediate risk (FRS <20%) were followed-up for about 5 years. Twenty four of the low/intermediate risk patients (FRS<20%) suffered a cardiovascular event in the next 5 years. Both FRS and IMTperc were independent outcome predictors (P<0.04, both; Cox model), with a hazard ratio of 6.7 (95% CI 1.43, 31.04; P=0.015) in patients in whom both IMTperc and FRS were above specified values. In Kaplan-Meier analyses, adding the IMTperc improved the predictive value of the FRS (2=8.13, p=0.04; log-rank test). Patients with elevated values (even though FRS<20%) had the same risk as patients with 20%<FRS<30%. The FRS underestimated the risk for patients with IMTperc above the specified value. An equation to adjust the FRS on the basis of a raised IMTperc is suggested. The combined use of conventional risk factors and ultrasonic measurements of carotid IMT significantly increases the ability to predict cardiovascular events in low or intermediate risk patients.