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Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Bern Center for Precision Medicine (BCPM) Introduction The echocardiographic diagnosis of aortic stenosis (AS) is established by assessing its maximal opening area (OA). The behavior of OA is dependent on transvalvular flow which can be low in case of low-flow, low-gradient AS. However, the complicated decision tree of the current guidelines for the assessment of AS does not consider flow but rather a stroke volume and does not take into account the size of the valve. This experiment was designed to create a graphical representation of the OA versus flow for various valve stiffness values to eventually build a model with iso-stiffness lines and simplify the assessment of aortic stenosis Methods We filmed a harvested porcine aortic valve mounted in a pulsatile flow loop during the ejection time with a high speed camera (2000Hz), measured for each time point OA and the instantaneous flow through the aortic valve at 10 different mean flow rates (ranging from 0.5 to 5.0 liters/min). We stiffened the valve by treating it with a protein cross-linking agent (formaldehyde) to yield a total of three stiffness grades (a, b, c) and repeated the procedure for each of those grades. We divided both OA and flow, by the area of left ventricular outflow tract (LVOT) in order to account for different valve sizes. We plotted each OA against its corresponding flow after correcting for the intersignal delay. In order to analyze the cycle portion corresponding to the most steady flow, we only included the 5% highest instantaneous flow rates (for each of the 10 mean flow rates). We then measured the relative stiffness by measuring the relative pump work between stiffness grades, 1 being defined as the native stiffness grade. We predicted relative stiffness grade of each valve in a k-fold validation algorithm (each valve being sequentially taken as the test set and all the other remaining valves in the training set), taking a sigmoid function model. Finally we performed a linear regression of each measured and predicted stiffness grade of each valve to assess the accuracy of the model. Results We could analyze 11 valves and performed an 11-fold cross validation. We could predict the relative stiffness of each of the valve with a good slope value (slope = 0.898) and a modest accuracy (r = 0.639). Conclusions We could predict with modest accuracy the inherent stiffness of the valve only with valve size, flow and opening area, all information available with echocardiography. This will allow to create iso-stiffness line to better classify valve stenosis and compare any patient on one single graph at any flow or valve" size, potentially simplifying the grading system of aortic stenosis, especially for patient with low-flow, low-gradient AS. Abstract Figure. Combination of Flow and OA  Abstract Figure. 3 stiffness stages and Cross-validation

An in-vitro model of stiffened aortic valves to develop an iso-stiffness-lines graph for aortic stenosis classification