Ultrasound evaluation of the carotid artery in a population at high risk of type 2 diabetes mellitus

Abstract

BACKGROUND: Diabetic patients are at increased risk of cardiovascular events and stroke, and its prevention is therefore the desired goal. In the arsenal of available techniques, ultrasound plays a vital role in primary healthcare. It is reliable, cost-effective and a noninvasive diagnostic tool that may prove beneficial for screening individuals at risk of cardiovascular disease (CVD) and stroke in SA. OBJECTIVE: To determine the interrelationships between carotid ultrasound findings with glycaemia status and contributing risk factors of atherosclerosis in the selected population. METHODS: Initially blinded by the glycaemia status, blood results, contributing risks and patient demographics, both carotid arteries were evaluated with duplex ultrasound (DUS), during July 2010 – July 2011. Using graphs, figures, frequency tables, means and standard deviations for the selected study population, univariate, multivariate and stepwise regression analysis was done to determine the association between ultrasound findings and risk factors for atherosclerosis. The hypothesis tested in this study was to determine if there is an increased incidence of carotid artery intima-media thickening (CIMT), plaque formation and stenosis in patients diagnosed with T2DM and hyperglycaemia in a very specific sub-population of mixedancestory, residing in Bellville South Africa (BSA). RESULTS: Of 534 subjects, 375 were of mixed ancestry and ≥35yrs of age, which met the inclusion criteria for the carotid ultrasound substudy. The glycaemic status for each individual was established, and 44% (165/375) were diagnosed hyperglycaemic, of which 66.7% (110/165) were diabetic (T2DM) and 33.3% (55/165) were pre-diabetic (Pre-DM). Majority (56%:265/375) had a normal glycaemic status. The ultrasound measurement of the carotid wall thicknesses (Mean Rt. and Lt. CIMT) revealed a statistically significant rise from normal glycaemia status to DM status for both the males (p = 0.0115*; p = 0.0259*) and females (p < 0.0001**; p < 0.0001**) respectively. In terms of plaques and internal carotid artery (ICA) stenosis (124/375), when grouped into normal and hyperglycaemic sub-groups, indicated plaque presence and some form of narrowing. A <50% stenotic ratio noted in 61% (76/124) of the hyperglycaemic group, that was 1.6 times higher than those with normal glycaemia (48/124). Predisposing factors demonstrated significantly higher levels in the females than in the males. The univariate multiple regression analysis after adjusted R² of 0.3247 for all independent variables (predisposing /contributing risk factor markers) of age (yrs.), SBP (mmHg), hs-CRP (mg/L), S-Cotinine (ng/mL) and LDL (mmol/L) showed statistically significant positive associations with dependent variable of the mean carotid wall thickness (p < 0.0001**, p< 0.0001**, p = 0.0033*, p = 0.0409* and p = 0.0044)* respectively. Statistically significant positive differences and standard error (SE), for every unit of change (1yr.) of age (yrs.), as a contributing factor for herosclerosis, there was a change in the mean carotid wall thickness as predicted according to this model. The total contribution of independent risk factors to CIMT ultrasound measurements were calculated as 34.5% (Adjusted R² = 0.3247). In the multivariate stepwise regression analysis, the independent variables of age (p< 0.0001) ** and systolic blood pressure (p < 0.0001) ** showed the strongest positive association with carotid wall thickeness changes. The hs-CRP (mg/L) inflammatory markers (p = 0.0014)* and LDL (mmol/L) (p = 0.0208)* were the 2nd and 3rd highest positive associated contributory risk factors for carotid artery wall thickening. The hip circumference (p = 0.0008)* and waist circumference (p = 0.0 555) + risk factors related to obesity was significant and approached significance, respectively, with the predicted increase of carotid artery wall thickening. CONCLUSION: Subjects diagnosed with T2DM and hyperglycaemia had increased levels of CIMT, plaques and carotid artery stenosis, compared to those subjects without T2DM. Age and systolic blood pressure, inflammatory (raised hs-CRP) and LDL cholesterol changes, and central (truncal) waist circumference adiposity, were positively associated with increased carotid intima media thickness. Smoking (S-Cotinine) and gender also reflected a direct relationship with CIMT changes. The hip circumference adiposity and diastolic blood pressure measurements were not directly associated with an increase in CIMT, which are in keeping with hypertension and obesity formulas. These findings confirm the association of thickened CIMT, plaques and stenosis with ‘unhealthy’ T2DM subjects at higher risk of CVD and stroke. The total contribution of independent risk factors to CIMT measurements were calculated as 34.5% (Adjusted R² =0.3247). The gathered information, discussion of results, and concluding statements thereby supports the recommendation of carotid artery ultrasound evaluation, for screening and diagnosis in primary health care, for ‘flagging’ high risk individuals at risk of stroke, so that lifestyle changes and appropriate management is early adopted.