Influence of Stenotic Valve Geometry on Measured Pressure Gradients and Ventricular Work: the Relationship Between Morphology and Flow

The physiologic impact of aortic valve stenosis is most directly reflected by an increased workload placed on the ventricle. In the pediatric population the morphology of aortic stenosis varies considerably. Fluid dynamic principles suggest that different morphologies may require the ventricle to accelerate blood to different maximal velocities for constant cardiac outputs and valve areas, resulting in different ventricular workloads. This study examined this important concept in in vitro models designed to isolate the effect of valve geometry on distal velocity, pressure gradients, and proximal work. Four stenotic valve morphologies were examined using a variable-voltage pump system. For constant orifice areas and flows, markedly different workloads were required by the pump, and this difference was reflected in direct measurements of pressure gradient and Doppler predictions of gradient. These fundamental fluid dynamic studies isolate the relationship between flow, work, and stenotic valve morphology. Different orifice geometries affect the value of the coefficient of contraction, which is reflected in different maximum velocity values for stenosis with constant anatomic areas and flows. The proximal pumping chamber must generate different levels of force to achieve these different velocities, and this variability is reflected in the clinically measured pressure gradient.