Impact of dyslipidaemia on arterial structure and function in urban Indigenous Australians

Abstract

Background

Premature cardiovascular disease (CDV) is highly prevalent in urban Indigenous Australians. We studied arterial structure and function in 144 volunteers aged 15–66 years to assess the role of dyslipidaemia and other traditional vascular risk factors on cardiovascular risk in young and older urban Indigenous Australians.

Methods

We assessed carotid intima-media thickness (CIMT) by high-resolution B-mode ultrasound imaging of the common carotid artery and peripheral wave reflection using applanation tonometry to obtain the aortic augmentation index (AI) in Indigenous Australian participants of the Darwin Region Urban Indigenous Diabetes (DRUID) study.

Results

Participants aged 15–24 years demonstrated fewer cardiovascular risk factors than the older group (25–66 years) and predictors of CIMT and AI differed between younger and older groups. CIMT was higher in the older group (0.67 mm vs. 0.61 mm, p = 0.004) and in those with diabetes (0.81 mm vs. 0.67 mm, p < 0.001). AI was higher in the older group (24% vs. 0%, p < 0.001), but was not affected by diabetes status. On multivariate regression analysis, low HDL-cholesterol was the only independent predictor of CIMT in the younger group; triglycerides, heart rate (inverse) and height (inverse) were independent predictors of AI in the same group.

Conclusion

Dyslipidaemia (low HDL-cholesterol or elevated triglycerides) is independently associated with non-invasive measures of cardiovascular disease in a relatively healthy and young subgroup of this high-risk population. We propose that triglycerides and low HDL-cholesterol may represent the most useful commonly measured clinical indicators of cardiovascular risk in young, urban Indigenous Australians.

Introduction

Rates of cardiovascular mortality amongst Indigenous Australians aged 25–64 years are 7–10 times higher than for non-Indigenous Australians [1]. This may be attributed, at least in part, to the 10-fold higher prevalence of diabetes amongst Indigenous Australians aged 20–50 years [2].

As in other populations, a high prevalence of components of the metabolic syndrome precedes the onset of type 2 diabetes in Indigenous Australians [3]. Dyslipidaemia (low high-density lipoprotein (HDL)-cholesterol and high triglycerides) is a hallmark of the metabolic syndrome, and hypertriglyceridaemia and low HDL-cholesterol levels are the most striking abnormalities of the lipid profile in Indigenous Australians. They are also strongly associated with other features of the metabolic syndrome in this high-risk population [2]. Compared to the general Australian population (as reported in the AusDiab study), Torres Strait Islanders have a lower prevalence of hypercholesterolaemia but a higher prevalence of dyslipidaemia [4]. Aboriginal populations appear to have more extreme dyslipidaemia than Torres Strait Islanders [5].

Dyslipidaemia contributes to early increased cardiovascular risk [6]. Techniques of non-invasive assessment of cardiovascular disease (CVD) in the Indigenous Australian setting must be practical for remote and field-based data collection. Two techniques were employed in this study: carotid intima-media thickness (CIMT) and pulse wave analysis (PWA), measures of arterial structure and function, respectively. CIMT, measured by external vascular ultrasound, is a reliable and reproducible method for predicting coronary disease and stroke [7]. CIMT is increased in those with known type 2 diabetes and correlates with components of the metabolic syndrome [8]. We have recently reported a graded increase in CIMT from urban Australians of European ancestry (lowest) to urban Indigenous Australians to remote Indigenous Australians (highest) and attributed higher CIMT to variables associated with the metabolic syndrome as well as cigarette smoking, elevated C-reactive protein (CRP) and albuminuria [9].

Aortic augmentation index (AI) derived using PWA is independently predictive of all-cause mortality and cardiovascular events in coronary disease and end-stage renal disease [10], [11]. AI correlates with cardiovascular risk factors and angiographically assessed coronary artery disease [11], [12] and has been shown to correlate with CIMT [13].

We aimed to evaluate the impact of type 2 diabetes and components of the metabolic syndrome on cardiovascular risk in this high-risk population by comparing non-invasive measures of cardiovascular disease (CIMT and AI) and their predictors in young and older urban Indigenous Australians.