Evidence for a sigmoidal flow-to-valve opening relation in low-flow low-gradient aortic stenosis

Area of Science:

• Cardiology
• Echocardiography
• Hemodynamics

Background:

• Low-dose dobutamine stress echocardiography (DSE) is used to differentiate true severe aortic stenosis from pseudo-severe cases.
• The flow (Q) response to DSE is highly variable, necessitating projection of aortic valve opening area (AVA) to a standardized flow (AVAproj) using linear interpolation.
• A linear Q-AVA relationship assumes unconstrained AVA increase, which may not reflect physiological saturation.

Purpose of the Study:

• To investigate if AVA exhibits saturation under increasing stress.
• To compare linear versus saturating models for the Q-AVA relationship.
• To evaluate the impact of sequential stress maneuvers on Q, AVA, and test conclusiveness in severe low-flow, low-gradient aortic stenosis.

Main Methods:

• Echocardiography was performed at rest, during passive leg raise (PLR), maximal dobutamine infusion (Dmax), and combined Dmax + PLR in 45 patients.
• Analyzed changes in Q, AVA, valve compliance (VC), and AVAproj across stress levels.
• Compared the proportion of nonconclusive tests (ΔQ < 20%) between maneuvers.
• Used Akaike Information Criterion (AIC) to compare linear and saturating Q-AVA models.

Main Results:

• Flow (Q) increased progressively with stress (PLR to Dmax to Dmax + PLR; P < 0.0001).
• The number of nonconclusive tests significantly decreased from 35 to 3 with increasing stress.
• AVA increased (P < 0.001), while AVAproj (P = 0.006) and VC (P = 0.005) decreased.
• A saturating (sigmoidal) model provided a better fit to the pooled Q-AVA data (AIC: -1,593) than a linear model (AIC: -1,504).

Conclusions:

• The combination of Dmax + PLR effectively reduces nonconclusive DSE tests.
• The Q-AVA relationship demonstrates saturation with increasing stress, flattening as flow increases.
• This saturation phenomenon has significant implications for accurately assessing aortic stenosis severity.