Carotid plaque, intima media thickness, cardiovascular risk factors, and prevalent cardiovascular disease in men and women: the British Regional Heart Study.

BACKGROUND AND PURPOSE

B-mode ultrasound is a noninvasive method of examining the walls of peripheral arteries and provides measures of the intima-media thickness (IMT) at various sites (common carotid artery, bifurcation, internal carotid artery) and of plaques that may indicate early presymptomatic disease. The reported associations between cardiovascular risk factors, clinical disease, IMT, and plaques are inconsistent. We sought to clarify these relationships in a large, representative sample of men and women living in 2 British towns.

METHODS

The study was performed during 1996 in 2 towns (Dewsbury and Maidstone) of the British Regional Heart Study that have an approximately 2-fold difference in coronary heart disease risk. The male participants were drawn from the British Regional Heart Study and were recruited in 1978-1980 and form part of a national cohort study of 7735 men. A random sample of women of similar age to the men (55 to 77 years) was also selected from the age-sex register of the general practices used in the original survey. A wide range of data on social, lifestyle, and physiological factors, cardiovascular disease symptoms, and diagnoses was collected. Measures of right and left common carotid IMT (IMTcca) and bifurcation IMT (IMTbif) were made, and the arteries were examined for plaques 1.5 cm above and below the flow divider.

RESULTS

Totals of 425 men and 375 women were surveyed (mean age, 66 years; range, 56 to 77 years). The mean (SD) IMTcca observed were 0. 84 (0.21) and 0.75 (0.16) mm for men and women, respectively. The mean (SD) IMTbif were 1.69 (0.61) and 1.50 (0.77) mm for men and women, respectively. The correlation between IMTcca and IMTbif was similar in men (r=0.36) and women (r=0.38). There were no differences in mean IMTcca or IMTbif between the 2 towns. Carotid plaques were very common, affecting 57% (n=239) of men and 58% (n=211) of women. Severe carotid plaques with flow disturbance were rare, affecting 9 men (2%) and 6 women (1.6%). Plaques increased in prevalence with age, affecting 49% men and 39% of women aged <60 years and 65% and 75% of men and women, respectively, aged >70 years. Plaques were most common among men in Dewsbury (79% affected) and least common among men in Maidstone (34% affected). IMTcca showed a different pattern of association with cardiovascular risk factors from IMTbif and was associated with age, SBP, and FEV1 but not with social, lifestyle, or other physiological risk factors. IMTbif and carotid plaques were associated with smoking, manual social class, and plasma fibrinogen. IMTbif and carotid plaques were associated with symptoms and diagnoses of cardiovascular diseases. IMTbif associations with cardiovascular risk factors and prevalent cardiovascular disease appeared to be explained by the presence of plaques in regression models and in analyses stratified by plaque status.

CONCLUSIONS

IMTcca, IMTbif, and plaque are correlated with each other but show differing patterns of association with risk factors and prevalent disease. IMTcca is strongly associated with risk factors for stroke and with prevalent stroke, whereas IMTbif and plaque are more directly associated with ischemic heart disease risk factors and prevalent ischemic heart disease. Our analyses suggest that presence of plaque, rather than the thickness of IMTbif, appears to be the major criterion of high risk of disease, but confirmation of these findings in other populations and in prospective studies is required. The association of fibrinogen with plaque appears to be similar to its association with incident cardiovascular disease. Further work elucidating the composition of plaques using ultrasound imaging would be helpful, and more data, analyzed to distinguish plaque from IMTbif and IMTcca, are required to understand the significance of thicker IMT in the absence of plaque.