Valve orifice area alone is an insufficient index of aortic stenosis severity: Effects of the proximal and distal geometry on transaortic energy loss

Background and aims of the study: Standard measures of hemodynamic severity of aortic valve stenosis vary widely among patients with and without clini cal symptoms. Our hypothesis is that valve orifice area alone is not the so le determinant of adverse clinical outcome. Stenotic orifice area ratio is ratio of the cross-sectional stenotic orifice area to the downstream, ascen ding aorta cross-sectional area. Determination of workload together with ao rtic valve orifice area ratio might improve risk stratification among asymp tomatic patients with critical aortic stenosis. Accordingly, application of both parameters together might be useful in guiding management decisions i n this condition. Methods: In this study the dependency of transaortic fluid mechanical energ y transfer (one component of left ventricular workload) on aortic valve ori fice area is shown using modeling and experimental techniques. Results: For a stroke volume of 62 ml at a heart rate of 60 beats/min, the piston work (analogous to left ventricular work) increased by 17% as the st enotic orifice area ratio decreased from 0.60 to 0.25, by 35% as the ratio fell from 0.25 to 0.20, and by 73% as the ratio fell from 0.20 to 0.10. Conclusions: As predicted by the fundamental fluid mechanical theory, simul ated left ventricular work and energy loss in aortic stenosis are influence d not only by the effective stenotic valve orifice area, but also by the ge ometry of the inflow and outflow conduits, proximal and distal to the valve . These findings might explain clinically observed discrepancies between va lve orifice area and the onset of the classical symptoms of severe aortic s tenosis that reflect the left ventricular workload. Consideration of the le ft ventricular work in addition to the effective valve orifice area should enhance clinical evaluation, prognostication and risk stratification among patients with severe aortic stenosis.