Ethnic differences in myocardial infarction in patients with hypertension: effects of diabetes mellitus

BACKGROUND: It has been reported that hypertension carries a greater risk of myocardial infarction (MI) in South Asians living in the UK than in the indigenous British population. This has been attributed to some specifically Asian susceptibility factor. DESIGN: Using a longitudinal approach, we investigated the relationship between coronary heart disease (CHD) risk factors amongst hypertension patients attending Sandwell and City Hospitals, and the onset of cardiovascular events over a 5-year follow-up period. RESULTS: A total of 350 Caucasian (83.7% male) and 104 South Asian (66.3% male) patients with hypertension [age 63.7 (7.6) years and 57.1 (11.1) years respectively, P < 0.001] were followed-up for a mean (SD) period of 64.7(12.1) months. There were 11 (6.4/1000 patient years) cases of MI in Caucasian patients vs. 11 (17.8/1000 patient years) in South Asians, with event-free survival times being significantly lower amongst South Asians (log-rank test P = 0.04). The prevalence of diabetes mellitus was 22.9% higher amongst South Asians (P < 0.001), whilst mean serum cholesterol and fasting triglyceride levels were higher amongst Caucasians (P = 0.001). There were no ethnic differences in HDL cholesterol concentrations, the use of tobacco, statin therapy or anti-platelet therapies (all P = NS), or in composite endpoint (MI, angina, peripheral vascular disease, stroke, revascularization or death; P = 0.74). On Cox regression analysis of all independent cardiovascular risk variables, associated treatments and ethnicity, MI risk was associated with diabetes mellitus (odds ratio 3.77, 95%CI 1.55-9.15, P = 0.003) but not ethnicity per se (P = 0.26). CONCLUSION: Increased risk of MI in hypertensive South Asians in the United Kingdom appears to be the result of a higher prevalence of diabetes mellitus. Further work is required to understand the pathophysiological basis with which diabetes increases CHD risk in this ethnic group.