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Description
Calcific Aortic Stenosis (CAS) involves narrowed aortic valve (AoV) orifice, fibrotic thickening and is clinically presented with a high transvalvular gradient and jet velocity. by Echocardiography (EC) derived opening area (EOA) estimation is used as an index for accurate assessment of stenotic severity. However, there are often discrepancies between EC derived EOA and invasive indices of CAS, thus leading to incorrect assessment of CAS severity and clinical decisions. There exists a need for an alternative non-invasive quantification method for analyzing the AoV dysfunction which serves as a predictor of CAS onset and progression of AoV. It is generally agreed upon that CAS progression is influenced by alterations in the valve hemodynamics, wherein it is continually subjected to cyclic stretches, bending, pressures, and shear stresses. The objective of this study is to measure the effect of leaflet fusion and stiffening on geometric opening area (GOA), hemodynamics (pressure and flow) and mechanical strain response in the AoV using a cardiac simulator. Seven bioprosthetic porcine AoVs were tested under controlled matched conditions. Fusion was simulated by suturing the leaflet edges together along one (F1) or two of the commissures (F2) and fibrosis by applying a thin layer of cyanoacrylate adhesive on the aortic face of one of the valve leaflets (F1S, F2S). The cardiac simulator is a mock circulatory loop that has preprogrammed settings of cardiac contractility (Off, Low, Medium) at a heart rate of 72 bpm. Pressure and flow are measured at several points in the system and a single CCD camera mounted under the simulator records images of the valve as it opens and closes in response to biomechanical changes. Images are analyzed to obtain the GOA values during the cycle. The mean GOA decreases due to commissural fusion and stiffening. Statistical analysis has confirmed that level of cardiac support and fusion (P < 0.01) are the most significant contributors to GOA reductions, which are indicators of stenosis. Fibrotic stiffening alongwith commissural fusion of the AoV contributes to reduced distensibility as seen by the strain response; this in turn is believed to lead to an increase in the internal stress. Additional studies are required to confirm this finding.
