Misinterpretation of the Determinants of Elevated Forward Wave Amplitude Inflates the Role of the Proximal Aorta

Abstract

BackgroundThe hemodynamic basis for increased pulse pressure (PP) with aging remains controversial. The classic paradigm attributes a predominant role to increased pulse wave velocity (PWV) and premature wave reflections (WRs). A controversial new paradigm proposes increased forward pressure wave amplitude (FWA), attributed to proximal aortic characteristic impedance (Zc), as the predominant factor, with minor contributions from WRs. Based on theoretical considerations, we hypothesized that (rectified) WRs drive the increase in FWA, and that the forward pressure wave does not depend solely on the interaction between flow and Zc (QZc product).Methods and ResultsWe performed 3 substudies: (1) open‐chest anesthetized dog experiments (n=5); (2) asymmetric T‐tube model‐based study; and (3) human study in a diverse clinical population (n=193). Animal experiments demonstrated that FWA corresponds to peak QZc only when WRs are minimal. As WRs increased, FWA was systematically greater than QZc and peaked well after peak flow, analogous to late‐systolic peaking of pressure attributable to WRs. T‐tube modeling confirmed that increased/premature WRs resulted in increased FWA. Magnitude and timing of WRs explained 80.8% and 74.3% of the variability in the difference between FWA and peak QZc in dog and human substudies, respectively.ConclusionsOnly in cases of minimal reflections does FWA primarily reveal the interaction between peak aortic flow and proximal aortic diameter/stiffness. FWA is strongly dependent on rectified reflections. If interpreted out of context with the hemodynamic principles of its derivation, the FWA paradigm inappropriately amplifies the role of the proximal aorta in elevation of FWA and PP.

Effects of organic and inorganic nitrate on aortic and carotid haemodynamics in heart failure with preserved ejection fraction

“…In addition, the ratio of backward/forward waves is confounded by rectified reflections (i.e., re-reflections in the heart), which substantially contribute to forward wave amplitude. (32) Despite the lack of change in reflection magnitude, detailed analyses in the time domain demonstrated favorable changes (delay in the onset of the reflected wave after ejection, and a trend towards improvement in the Buckberg index) with inorganic nitrate, but not with NTG.…”

Ventricular–Arterial Coupling in Chronic Heart Failure

“…44,45 Backward-travelling reflected waves can re-reflect at the left ventricle during systole, becoming part of the forward wave.…”

“…Forward pressure wave amplitude, therefore, cannot be interpreted purely as an index of mismatch flow needs and aortic root properties, because it also contains contributions from wave re-reflections. 44 The difference between measured pressure and the QZc product can be interpreted as the pulsatile pressure that is not primarily required to promote pulsatile systolic flow through the aortic root Zc, but is necessary to overcome the effect of wave reflection. An analogous concept was originally proposed by Hashimoto, Nichols and O'Rourke and called 'wasted LV effort', using pressure-only approaches.…”

Central systolic blood pressure and aortic stiffness response to dietary sodium in young and middle-aged adults

“…The forward wave amplitude has been shown to be an important predictor of incident cardiovascular disease and has been proposed to be due to a mismatch between aortic diameter and pulsatile flow [32]. However, Phan et al [33] more recently demonstrated that forward wave amplitude is also strongly influenced by wave reflections that are re-reflected/rectified at the heart, highlighting the importance of assessing both forward and reflected wave amplitudes.…”