Evidence for a Sigmoidal Flow-to-Valve Opening Relation in Low-Flow Low-Gradient Aortic Stenosis

Introduction: 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 (AVAproj) 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. Methods: We performed an echocardiographic exam 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 AVAproj. We also compared the proportion of patients with non-conclusive test (ΔQ<20%) between stress maneuvers. We computed the Akaike Information Criterion (AIC) to compare a linear with a saturating function for the Q-AVA-relation. Results: Q gradually increased from "PLR" to "Dmax" to "Dmax+PLR" (p<0.0001), while the number of non-conclusive tests concomitantly diminished from n=35 to n=3. The stress sequence increased AVA (p<0.001), but decreased AVAproj (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 to the linear model fitting (-1593 versus -1504). Conclusion: "Dmax+PLR" is capable of reducing the number of non-conclusive DSE tests. With increasing stress strength, the Q-AVA-relation progressively flattens, indicating saturation.