Racial difference in atrial size and extracellular matrix homeostatic response to hypertension: Is this a potential mechanism of reduced atrial fibrillation in African Americans?

BACKGROUND: Atrial fibrillation (AF) is less common in African Americans (AA) than Caucasians (C) despite a higher prevalence of risk factors such as hypertension (HTN). OBJECTIVE: Test the hypothesis that differences in extracellular matrix (ECM) between AA and C in response to HTN might attenuate atrial enlargement and alter myocardial fibrosis. METHODS: ECM-related plasma biomarkers and echo data were collected from 326 C and 129 AA subjects with no history of AF, stratified by the presence of HTN, HTN with left ventricular hypertrophy (LVH), or HTN with LVH and heart failure with preserved ejection fraction (HFpEF). RESULTS: Left atrial size was significantly smaller and the extent of enlargement in the presence of HTN was less in AA despite similar ventricular relative wall thickness, echocardiographic measures of diastolic function, and 6 minute-walk-test. AA had significantly lower levels of collagen I telopeptide and higher levels of collagen I propeptide among all strata, suggesting unique collagen homeostasis. Matrix metalloproteinases (MMP) and tissue inhibitors of matrix metalloproteinase (TIMP) showed a distinctive response to HTN in AA, with significantly lower levels of MMP-2, MMP-3, and MMP-8 in AA with HTN and significantly lower levels of TIMP-1 and TIMP-3 in AA with HTN and AA with LVH. AA had significantly lower levels of NT-pro-BNP in all strata. CONCLUSION: This cross-sectional study demonstrates a racial disparity in ECM blood biomarkers and atrial remodeling in response to HTN and in the development of LVH and HFpEF that may partly help explain the decreased risk of AF in AA.