Assessment of Aortic Valve Stenosis Severity: A New Index Based on the Energy Loss Concept

Abstract

Background —Fluid energy loss across stenotic aortic valves is influenced by factors other than the valve effective orifice area (EOA). We propose a new index that will provide a more accurate estimate of this energy loss. Methods and Results —An experimental model was designed to measure EOA and energy loss in 2 fixed stenoses and 7 bioprosthetic valves for different flow rates and 2 different aortic sizes (25 and 38 mm). The results showed that the relationship between EOA and energy loss is influenced by both flow rate and aortic cross-sectional area (A A ) and that the energy loss is systematically higher (15±2%) in the large aorta. The coefficient (EOA×A A )/(A A −EOA) accurately predicted the energy loss in all situations ( r 2 =0.98). This coefficient is more closely related to the increase in left ventricular workload than EOA. To account for varying flow rates, the coefficient was indexed for body surface area in a retrospective study of 138 patients with moderate or severe aortic stenosis. The energy loss index measured by Doppler echocardiography was superior to the EOA in predicting the end points, which were defined as death or aortic valve replacement. An energy loss index ≤0.52 cm 2 /m 2 was the best predictor of adverse outcomes (positive predictive value of 67%). Conclusions —This new energy loss index has the potential to reflect the severity of aortic stenosis better than EOA. Further prospective studies are necessary to establish the relevance of this index in terms of clinical outcomes.