Valve orifice area alone is an insufficient index of aortic stenosis severity: effects of the proximal and distal geometry on transaortic energy loss.
OBJECTIVE
Standard measures of hemodynamic severity of aortic valve stenosis vary widely among patients with and without clinical symptoms. Our hypothesis is that valve orifice area alone is not the sole determinant of adverse clinical outcome. Stenotic orifice area ratio is ratio of the cross-sectional stenotic orifice area to the down-stream, ascending aorta cross-sectional area. Determination of workload together with aortic valve orifice area ratio might improve risk stratification among asymptomatic patients with critical aortic stenosis. Accordingly, application of both parameters together might be useful in guiding management decisions in this condition.


METHODS
In this study the dependency of transaortic fluid mechanical energy transfer (one component of left ventricular workload) on aortic valve orifice 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 stenotic 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, simulated left ventricular work and energy loss in aortic stenosis are influenced not only by the effective stenotic valve orifice area, but also by the geometry of the inflow and outflow conduits, proximal and distal to the valve. These findings might explain clinically observed discrepancies between valve orifice area and the onset of the classical symptoms of severe aortic stenosis that reflect the left ventricular workload. Consideration of the left ventricular work in addition to the effective valve orifice area should enhance clinical evaluation, prognostication and risk stratification among patients with severe aortic stenosis.
Heinrich
R S
RS
Institute for Bioengineering and Bioscience and the School of Biomedical Engineering, Georgia Institute of Technology, Atlanta 30332, USA.
Marcus
R H
RH
Ensley
A E
AE
Gibson
D E
DE
Yoganathan
A P
AP
D001011:Aorta / Q000473:pathology*; D001021:Aortic Valve / Q000473:pathology* / Q000503:physiopathology; D001024:Aortic Valve Stenosis / Q000473:pathology / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D004735:Energy Transfer; D006339:Heart Rate; D006801:Humans; D008955:Models, Cardiovascular; D008961:Models, Structural; D013318:Stroke Volume; D016277:Ventricular Function, Left / Q000502:physiology