The ambulatory arterial stiffness index (AASI) has been proposed as a novel measure of arterial stiffness and has been prospectively shown to predict stroke and cardiovascular death, but not cardiac death. This index has prompted considerable controversy as to whether it is a true measure of arterial stiffness.

The aim was to examine three different measures of arterial stiffness, i.e., pulse wave velocity (PWV, Complior), wave reflection (augmentation index, AIx) and AASI in a large hypertensive population, comparing their determinants and inter-correlations, both unadjusted and adjusted for confounders and using Bland Altman analysis to determine 95% confidence intervals for the ability of the AASI to predict PWV, the proposed gold standard of arterial stiffness.

The AASI correlated univariately with both PWV and AIx in subjects overall (r= 0.28 for PWV and 0.24 for AIx; p<0.001 for both) and in those with untreated or treated hypertension. Adjustment for age in the current study negated entirely the positive correlation between AASI, PWV and AIx. Additional adjustment for confounders did not significantly alter these non-significant relationships. Furthermore, the 95% prediction limits for AASI to predict PWV were ± 4.18 meters/second and for AASI to predict AIx were +/−25.4%, suggesting that the methods would not be interchangeable in a clinical setting. Direct comparative studies would be required to establish the relative predictive strength of each measure and whether combining measures can provide additional risk prediction. Until such data become available, we propose that the measures should not be considered interchangeable.