Over the past decade, the measurement of carotid artery intima-media thickness (IMT) using high-resolution B-mode ultrasonography has emerged as one noninvasive method of choice for determining the anatomic extent of atherosclerosis and its progression and for assessing cardiovascular and stroke risk (1–4).
In vitro and in vivo studies indicate that carotid artery IMT measurements obtained by ultrasonography correlate well with pathologic measurements, and numerous investigators (5) have demonstrated the reproducibility of this technique and the strong correlation between IMT and classic risk factors (male sex, aging, overweight, elevated blood pressure, high blood cholesterol, diabetes, and smoking). Many studies (6–8) have shown that the incidence of coronary artery disease (CAD) in diabetic patients is two or three times higher than that in nondiabetic control subjects. A few previous studies (9,10) have evaluated the association between IMT and CAD in diabetic patients. In all these studies, CAD was diagnosed from symptoms and clinical records rather than by coronary angiography. Yet it is not fully confirmed that IMT can be used as a predictor of CAD, even with its severly luminal coronary obstruction, in diabetic patients.
We investigated the association between carotid artery atherosclerosis, valued from the IMT and the presence of atherogenic plaques, and CAD (angiographic documentation: CAD was diagnosed by detection of >50% stenosis in one of the three major coronary arteries; evaluation with Gensini score: a scoring system for use in coronary artery angiography that can be used to determine the severity of coronary artery disease based on the degree of luminal obstruction ). From November 2002 to January 2003, high-resolution ultrasound examination (ATL-HDI 1500) was performed to check the carotid arteries (carotid bulb, internal, and external carotid arteries bilaterally), IMT (measured in millimeters), and for the presence of plaques (categories: homogeneous, heterogeneous, and ulcerative) in 21 patients with type 2 diabetes and CAD (group A) and 20 patients with type 2 diabetes and without CAD (group B). Demographic, biochemical, and clinical characteristics of the two groups were recorded [age, duration of diabetes, BMI, waist circumference, HbA1c, hypertension, drug treatment, diabetes complications, total serum cholesterol, LDL cholesterol, lipoprotein(a), apolipoprotein (apo)-B, serum homocysteine, and smoking].
Statistical analysis was performed using Student’s t test, Pearson χ2, and Pearson coefficient correlation.
The number of men and women in the two groups was identical. CAD diabetic patients had higher lipoprotein(a) (P = 0.018), serum total homocysteine (P = 0.026), and smoking (P = 0.008). In all patients of group A and in both carotid arteries, IMT was significantly higher. Mean IMT (mean ± SD) was 1.14 ± 0.286 vs. 0.875 ± 0.195 mm (P = 0.001). There were no significant differences between the two groups regarding BMI, waist circumference, duration and treatment of diabetes, HbA1c, hypertension, diabetes complications, serum total cholesterol, LDL cholesterol, HDL cholesterol, apo-B, triglycerides, or the number and constitution of the atherogenic plaques.
IMT was not associated with Gensini score (P = 0.728). In multivariate analysis, IMT was the only parameter that was found to be independent (P = 0.02). Using the receiver operating characteristic analysis, IMT values ≥0.925 mm were associated with a relative risk of 25 in regard to the presence of CAD.
In conclusion, our data demonstrate that 1) IMT measured by a simple, rapid, low-cost method for image processing, which can be performed directly during scanning of the carotid arteries, is a prognostic indicator for CAD in diabetic patients; and 2) there is no correlation between IMT and CAD regarding the coronary arteries luminal obstruction. However, it is possible to have severe CAD without coronary arteries luminal obstruction (unstable plaque). The lack of correlation of the extent of obstruction, judged angiographically on the basis of evident luminal obstruction, is consistent with the biological nature of plaque accumulation seen with type 2 diabetes (hence frequently negative stress tests despite abluminal disease that sets the stage for acute coronary syndromes).