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

We analyzed the relationship between flow (Q) and aortic valve opening area (AVA) using a sequence of echocardiographic stress tests of increasing strength. Low-dose dobutamine stress echocardiography (DSE) has been used to differentiate pseudo-severe from true severe aortic stenoses. Because the Q-response to DSE is so variable between individuals, AVA has been projected to a standardized flow (AVA(pro)j) using linear interpolation. A linear Q-to-AVA relation implies that AVA shows an unconstrained increase. We applied three stress maneuvers of increasing strength to investigate whether AVA shows signs of saturation. We performed an echocardiographic examination at rest, during the passive leg raise maneuver (PLR), maximal dobutamine infusion (Dmax), and their combination (Dmax + PLR) in 45 patients with severe low-flow, low-gradient aortic stenosis. We analyzed the effect of the stress maneuver on Q, AVA, valve compliance (VC), and AVA(pro)j. We also compared the proportion of patients with nonconclusive test (Delta Q < 20%) between stress maneuvers. We computed the Akaike information criterion (AIC) to compare a linear with a saturating function for the Q-AVA relation. Q gradually increased from PLR to Dmax to Dmax + PLR (P < 0.0001), whereas the number of nonconclusive tests concomitantly diminished from n = 35 to n = 3. The stress sequence increased AVA (P < 0.001) but decreased AVA(proj) (P = 0.006) and VC (P = 0.005). In the pooled Q-AVA data, the AIC value was lower for the saturating (sigmoidal) model compared with the linear model fitting (-1,593 vs. -1,504). Dmax + PLR is capable of reducing the number of nonconclusive DSE tests. With increasing stress strength, the Q-AVA relation progressively flattens, indicating saturation. NEW & NOTEWORTHY The relation between transaortic flow (Q) and aortic valve opening area (AVA) shows a saturation when three different stress maneuvers are used to increase Q as much as possible. This has implications for the assessment of aortic stenosis severity.

Automated summary

This study analyzed the relationship between flow and aortic valve opening area, finding that the aortic valve opening area reaches saturation as the stress tests increase in strength.