Performance assessment of prosthetic heart valves using the energy index method.

Traditional methods of characterizing valvular performance use some estimation of the effective opening area and the percent regurgitant volume. These methods are cumbersome because two parameters are used and their importance relative to one another is not revealed. The authors propose the use of a single parameter that is physically meaningful and accounts for characteristics of the valve throughout the cardiac cycle. The energy index, derived with use of a phase-by-phase analysis of the cardiac cycle, describes the energetic efficiency of the valve. The method's final form is: [Formula: see text] where Eps is the hydraulic energy available after systole, E+ is the energy dissipated in the valve while flow is positive, [Symbol: see text]_ and [Symbol: see text] are the regurgitant and forward volumes, respectively. Use of the El requires on-line measurement of valvular flow rate and pressure drop. The El was applied to a Medtronic-Hall (Minneapolis, MN), 25 mm prosthetic valve mounted in the aortic position of a cardiovascular simulator. Mild and severe degrees of valvular stenosis and regurgitance were simulated. Results indicate that the El is sensitive to either valvular condition and remains nearly constant, at 87%, for the normal valve tested over cardiac rates ranging from 50 to 100 beats per minute.