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Background: Elevated plasma B-type natriuretic peptide (BNP) is a predictor of outcome and helpful for risk stratification in aortic stenosis (AS). However, left ventricular (LV) diastolic dysfunction progresses with aging and may also influence plasma BNP levels in elderly patients. We hypothesized that plasma BNP levels may be influenced by age in severe AS, and that factors that affect the elevation of plasma BNP levels may be different between elderly and younger patients with AS. Methods: We performed echocardiography in 341 patients with severe AS (aortic valve area (AVA)< 1.0cm²] and classified them into two groups by age (elderly ≥75 years old, n = 201 ; younger patients <75 years old, n = 140). We used multivariate linear regression analysis to assess the factors that determine plasma BNP levels in both groups. Results: Age was found to be one of the independent determinants of plasma BNP levels in all patients (>3 = 0.135, p = 0.005). Although AVA was similar in the two groups, plasma BNP levels and E¡e' were significantly higher in elderly than younger patients [133.0 (IQR, 73.3-329.7) pg/dl vs 92.8 (IQR, 40.6-171.8) pg/dl, p < 0.01 ; 20 ± 8 vs 16 ± 6, p < 0.01, respectively). In multivariate stepwise linear regression analysis, AVA index, LV ejection fraction, mass index, £/e', estimated systolic pulmonary artery pressure (eSPAS), and the presence of atrial fibrillation were independent determinants of plasma BNP levels in younger patients. In contrast, the independent determinants of plasma BNP levels in elderly patients were LV ejection fraction, mass index, E/e', eSPAS, the presence of atrial fibrillation, age, and hemoglobin levels, but not AVA index. Conclusions: There may be differences in the factors that influence plasma BNP levels between elderly and younger patients with severe AS. In elderly patients, plasma BNP levels may be influenced more by these factors than AS severity compared with younger patients. [ABSTRACT FROM AUTHOR]