Impaired Microvascular and Endothelial Function Among African-Americans With Coronary Artery Disease

Background: African-Americans have disproportionately higher burden of mortality from coronary artery disease (CAD) compared to Caucasians even after adjusting for socioeconomic and cardiovascular risk factors. Racial differences in arterial stiffness have been described, but data on microcirculatory and endothelial vascular function are more limited and it is unknown whether they differ by race in CAD patients. Methods: We studied 313 patients with a recent history of myocardial infarction (MI). Microvascular function was assessed by digital pulse amplitude tonometry (EndoPAT) to determine reactive hyperemia index (RHI), and endothelial function as brachial artery flow mediated dilation (FMD) using ultrasound. Arterial stiffness was assessed using applanation tonometry (Sphygmocor) to determine pulse-wave velocity (PWV) and central augmentation index (C-AIx). Data on sociodemographics, cardiovascular risk factors, medication use, and CAD severity were collected. Multivariate linear regression models were used to assess the relationship between race and various vascular function measures with adjustment for risk factors. Measures of arterial stiffness were included as control factors in the adjusted model for FMD and RHI. Results: The mean age of this post-MI sample was 51 years (± 6.7 SD); 50% were African-Americans and 49% were female. Compared to Caucasians, African-Americans had worse microvascular function as indicated by lower mean (± SD) RHI (1.7±0.5 vs 2.0±0.6, p<0.0001) and worse endothelial function [FMD mean (3.4±2.4 vs 4.7±3.1, p=0.0002)]. African-Americans also had greater arterial stiffness, including a higher mean C-AIx (26.5±9.0 vs 23.0±9.3, p=0.0019) and PWV (7.7±2.0 vs 7.1±1.8, p<0.0267). After adjustment for cardiovascular risk factors, medications, CAD severity, and arterial stiffness (C-AIx and PWV), black race remained significantly associated with lower RHI (β=-0.30, p<0.001) and FMD (β=-1.06, p=0.004). Conclusion: African-Americans with CAD have impaired microvascular and endothelial vasodilatory function compared to Caucasians, independent of CAD risk factors and arterial stiffness. Racial differences in microcirculatory and endothelial function may contribute to worse outcomes among African-Americans with CAD.