Influence of Stenotic Valve Geometry on Measured Pressure Gradients and Ventricular Work: The Relationship Between Morphology and Flow E.G. Cape, D.L. Kelly, J.A. Ettedgui, S.C. Park Cardiac Dynamics Laboratory, Division of Pediatric Cardiology, Children’s Hospital of Pittsburgh, University of Pittsburgh, 3705 Fifth Avenue, Pittsburgh, PA 15213, USA Abstract. The physiologic impact of aortic valve steno- sis 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 predic- tions of gradient. These fundamental fluid dynamic stud- ies isolate the relationship between flow, work, and ste- notic valve morphology. Different orifice geometries af- fect the value of the coefficient of contraction, which is reflected in different maximum velocity values for ste- nosis with constant anatomic areas and flows. The proxi- mal pumping chamber must generate different levels of force to achieve these different velocities, and this vari- ability is reflected in the clinically measured pressure gradient. Key words: Aortic valve — Stenosis — Congenital heart disease — Hemodynamics The physiologic impact of aortic valve stenosis is most directly reflected by an increased workload placed on the ventricular chamber that drives flow [3]. The clinical assessment of the severity of stenosis is based on the pressure gradient across the valve, obtained by direct measurement during cardiac catheterization or predicted by Doppler ultrasonography [1, 6, 9, 10, 13, 16, 18]. The relationship between pressure gradient and the severity of obstruction is based on the physical principle that volumetric flows driven through decreasing cross- sectional areas must produce increased pressure drops (and these elevated pressure drops are associated with increased velocities in the stenotic jet). Thus regardless of whether gradients are measured directly by catheter- ization or predicted by Doppler studies, the implicit as- sumption in all pressure gradient-based methods is that the magnitude of the gradient reflects the area available for flow [8]. Fluid dynamic principles suggest that significantly different maximal velocities may be obtained for equiva- lent stenotic valve areas depending on the geometry, or morphology, of the obstruction (see Theory, below) [2, 17]. Because flow must be accelerated from a relatively stagnant ventricular velocity to the maximum distal ve- locity, this variability in distal velocities imposes differ- ent left ventricular force requirements, which are re- flected in different pressure gradients. Although two valves may appear to be equally obstructed when viewed during or after surgery, they may have produced different levels of physiologic impact on the ventricle. Therefore it is reasonable to postulate that the different acceleration requirements for different valve morphologies could po- tentially be related to quantities that more directly reflect the physiologic impact of stenosis, such as force, work, and power requirements placed on the ventricle [14]. In the pediatric population the morphology of aortic valve stenosis varies considerably [7], depending on the etiology (congenital versus acquired), the long-term evo- lution, and the age of the patient (Fig. 1, top). In view of the above fluid dynamic principles, this study addressed the hypothesis that valve morphology influences mea- sured pressure gradients and ventricular work while ana- tomic valve area and cardiac output are held constant. In view of the rapid development of three-dimensional echocardiographic techniques [11], the use of valve mor- Correspondence to: E.G. Cape Pediatr Cardiol 17:155–162, 1996 Pediatric Cardiology © Springer-Verlag New York Inc. 1996