Ambulatory arterial stiffness index and its role in assessing arterial stiffness in dialysis patients

OBJECTIVE: Ambulatory arterial stiffness index (AASI) is a parameter derived from ambulatory blood pressure (ABP) readings. It is calculated as 1 minus the linear slope of DBP on SBP. We tested its value in assessing arterial stiffness in dialysis patients. METHODS: We performed a cross-sectional analysis of the baseline data from a cohort study. A total of 344 patients on maintenance hemodialysis from six tertiary hospitals were included. All patients underwent ABP monitoring and carotid-femoral pulse wave velocity (cfPWV) measurement. Clinical determinants of AASI were analyzed, and the ability of AASI for assessing arterial stiffness was compared with ambulatory pulse pressure (PP). RESULTS: Multiple regression analysis revealed that ambulatory PP (β = 0.003), current smoker (β = -0.069), age (β = 0.003) and ambulatory SBP (β = 0.001) were independent determinants of AASI. Ambulatory PP correlates better with cfPWV than AASI (r = 0.28 for AASI and 0.59 for PP; P for difference: <0.001). When cfPWV was treated as a categorical variable, receiver operating characteristic curve analysis also showed a more potent predictive value of PP over AASI (area under the curve: 0.64 for AASI, 0.80 for PP; P for difference: <0.001). Net reclassification improvement and integrated discrimination improvement analysis demonstrated no added predictive value of AASI to PP (net reclassification improvement = -2.2%, P = 0.26; integrated discrimination improvement = 0.001, P = 0.51). Sensitivity analysis in patients with more ABP readings (≥49) yielded similar results. CONCLUSION: For dialysis patients, AASI has very limited value in assessing arterial stiffness, whether used alone or added to PP. Our results suggest that this index should not be used as a surrogate marker of arterial stiffness for dialysis patients in future practice and studies.