Should the Augmentation Index be Normalized to Heart Rate?

Abstract

Pulse wave analysis (PWA) is widely used to investigate systemic arterial stiffness. The augmentation index (AIx), the primary outcome derived from PWA, is influenced by the mean arterial pressure (MAP), age, gender and heart rate (HR). Gender-and age-specific reference values have been devised, and it is recommended that the MAP be used as a statistical covariate. The AIx is also commonly statistically adjusted to a HR of 75 b·min; however, this approach may be physiologically and statistically inappropriate. First, there appears to be an important physiological chronic interaction between HR and arterial stiffness. Second, the method used to correct to HR assumes that the relationship with AIx is uniform across populations. A more appropriate practice may be to include HR as an independent predictor or covariate; this approach is particularly recommended for longitudinal studies, in which changes in HR may help to explain changes in arterial stiffness.

Increased aortic blood pressure augmentation in patients with congenital heart defects — A cross-sectional study in 1125 patients and 322 controls

“…Finally, AIx also decreased with higher heart rate during the measurement. As recommended in a recent paper [26] heart rate was therefore added as a covariate in the regression model. Those correlations of AIx to height, age, gender and heart rate are in good agreement to other report [13,25,27] aiming on AIx.…”

Reliability of pulse waveform separation analysis

“…The transit time is affected by the reflected wave timing, amplitude, and ventricular function, which in turn are known to be influenced by a number of factors, including heart rate. [8,9] For example, in the current study, heart rate was 4.3 (CI: 1.9, 6.7) bpm higher in the non-fasted state and may have acted as an additional source of variability. Thus, the decreased AIx and RM in the non-fasted state may have not fully resulted from decreased wave reflection.…”

“…The non-standardization of caffeine consumption likely added an additional source of error variance to AIx and RM, as both of these parameters are known to be influenced by heart rate. [8,9] The known relationship between these parameters and heart rate further indicates the need to standardize testing conditions.…”

“…[4,7] The AIx, which is calculated by dividing the central augmentation pressure by the corresponding pulse pressure, is affected by the reflected wave transit time. [8,9] Alternatively, by assuming a triangular or a physiologic flow waveform, [10] the aortic wave can be separated into its forward (Pf) component and timing-independent reflected component (Pb). Two large prospective studies [4,5] suggest that wave separation analysis may be superior to AIx as a subclinical marker of cardiovascular disease, one reporting that Pb better predicts 15-year cardiovascular mortality than AIx, [5] the other that reflection magnitude (RM, Pb/Pf) better predicts cardiovascular events than AIx.…”

Serum osteoprotegerin levels associated with the aortic augmentation index in renal transplant recipients

“…The European Society of Cardiology Working Group described the importance of peripheral noninvasive vascular biomarkers for primary and secondary CV disease prevention [2]. Among them, noninvasive methods to assess central hemodynamics/wave reflections such as the aortic augmentation index (AIx) of central blood pressure have been widely used as clinical indices of arterial stiffness [23]. The AIx (augmentation pressure-to-pulse pressure ratio) is a measure of the contribution that wave reflection makes to the central pressure wave: it is defined as the difference between the second and first peaks corresponding to the systolic blood pressure (SBP) and expressed as a percentage of the pulse pressure.…”