Cardiovascular disease, type 2 diabetes and carotid ultrasound
Robertson, Christine Mary
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Cardiovascular disease contributes significantly to global morbidity and mortality and is particularly prevalent among individuals with Type 2 diabetes, which is thought to in part be due to the association between diabetes and the metabolic syndrome. Traditional cardiovascular risk prediction scores perform well in the general population but their use in people with Type 2 diabetes is limited as they are thought to underperform in high risk groups. Indeed, the use of any risk prediction in people with Type 2 diabetes is a point of discussion among clinicians as people with diabetes are thought by some to be at immediate high risk of CVD, whereas others view them as having a degree of modifiable risk which can be addressed using risk prediction. In the general population, novel markers such as cIMT and carotid plaque, as well as other potential biomarkers of cardiovascular risk, have been explored as possible adjuncts to risk scores in the prediction of cardiovascular disease. The evidence for their use in general populations has been established, although there have been no firm conclusions with regard to recommendations for their use, which is partly due to the high degree of variability in cIMT measurement. However, the evidence for their use in people with Type 2 diabetes is sparse, despite the use of such markers as surrogate CV endpoints in clinical trials. This thesis aimed to describe the frequency, distribution and change of cIMT and carotid plaque, as well as to explore the relationship of cIMT and carotid plaque with cardiovascular risk factors, prevalent cardiovascular disease and future cardiovascular events in older people with Type 2 diabetes. The association between cIMT, carotid plaque and other novel risk markers was also explored. The analysis was performed using data from the Edinburgh Type 2 Diabetes Study (ET2DS). This study is a large, prospective cohort study of 1066 men and women with Type 2 diabetes, aged 60-75 years at recruitment, living in Edinburgh and the Lothians. cIMT and carotid plaque were measured at year 1 follow up of the study. Variables concerning cardiovascular risk factors used in this thesis were obtained from the data collection performed at baseline and year 1. A mean of 3.5 years of follow up was available for analysis and is complete for the baseline cohort as data linkage was performed. Mean values of cIMT in the ET2DS were comparable with other studies of cIMT in people with Type 2 diabetes and may indeed be higher than cIMT in the general population. Measurement of cIMT by the sonographer was comparable with computer aided measurements. Increasing cIMT was independently associated (although only modestly) with increasing age, male sex and raised systolic blood pressure. Mean cIMT was associated with prevalent vascular disease and was predictive of incident global cardiovascular events and coronary artery events (but not stroke) over and above UKPDS risk factors, although the clinical impact of this on the reclassification of vascular risk (as demonstrated by net reclassification index (NRI)) was limited. There was a high prevalence of carotid plaque, and in particular “high risk” plaque, in the ET2DS. Different measures of carotid plaque were independently associated with several cardiovascular risk factors. Carotid plaque thickness was independently associated, albeit modestly, with increasing age, male sex, duration of diabetes and hypertension, plaque score with increasing age, hypertension, smoking and low BMI, and high risk plaque with hypertension and low BMI. All measures of carotid plaque were associated with prevalent vascular disease. However, despite these associations, carotid plaque did not have any additional predictive value for incident cardiovascular events over and above UKPDS risk factors. Finally, measures of cIMT and carotid plaque in the ET2DS were associated with the biomarkers ankle brachial index (ABI) and NTproBNP. In addition these markers were significantly higher in those individuals with prevalent vascular disease, suggesting a more extensive exploration of the association of these markers in relation to cardiovascular disease in the ET2DS may be warranted. cIMT and carotid plaque are modestly associated with traditional cardiovascular risk factors and prevalent cardiovascular disease in older adults with Type 2 diabetes. cIMT has been shown to be predictive of incident events while carotid plaque was not, in people with Type 2 diabetes, over and above traditional cardiovascular risk factors, although its impact on risk reclassification may only be small. Further evidence is required from the longer follow up of the ET2DS before firm conclusions can be drawn on the usefulness of cIMT and carotid plaque as risk markers in people with Type 2 diabetes. In addition, large collaborative studies could be used to further explore the relationship of carotid plaque, and change in cIMT with incident cardiovascular events, as well as exploring the additive effect of cIMT and plaque on risk prediction.