Echocardiography flow quantification for determining the severity of heart valve insufficiency

Abstract

Beyond conventional echocardiographic Doppler methods allowing only semiquantitative estimation of the severity of valvular regurgitation, new approaches are attempting to quantify regurgitant flow as a measure of left ventricular volume overload. Different concepts are leading to significant differences in accuracy and feasibility in clinical routine between the methods. We are reviewing the existing methods with their advantages and limitations as well as the underlying hemodynamic concepts. Semiquantitative methods are jet area/jet length method, proximal jet width as well as the pressure half-time method. Determination of regurgitant flow is permitted by means of the continuity method, PISA ("Proximal Isovelocity Surface Area") method, ACOM ("Automated Cardiac Output Measurement") technique, and the PVI ("Power-Velocity Integral") method. Grading of severity is usually based on a scale from 1 to 3 or 1 to 4 where semiquantitative methods are limited by a significant overlap of the individual degrees and therefore only provide rough estimates of severity. Compared to this, quantitative methods allow quantitative determination of regurgitant flow, regurgitant volume, regurgitant fraction, and effective regurgitant orifice area based on different Doppler flow measurements, that are again affected by specific limitations: (1) the continuity method is considerably limited because it is measuring the flow through two different valves; (2) the PISA method is dependent on the geometry of the proximal flow convergence zone and requires highly skilled observers; (3) the ACOM method is also dependent on the geometry of the proximal flow convergence zone und ideally requires three-dimensional color Doppler datasets; (4) the PVI method provides direct measurement of regurgitant flow from a pulsed Doppler signal of sufficient high quality, however, this method is not widely available, yet. For the decision which method to apply the following should be taken into account: (1) interpretation of semiquantitative findings depends on the extent by which the methods' estimation of flow deviates from a measurement of flow; (2) accuracy of the quantitative methods depends on the underlying hemodynamic concept and the simplifying assumptions. Current echocardiography provides a broad spectrum of semiquantitative und quantitative Doppler methods for the estimation of regurgitant flow. Since semiquantitative methods only allow rough estimates of severity, quantitative measurement of regurgitant volume/fraction or effective regurgitant orifice area should be attempted in any case with uncertainty whether regurgitation is mild, moderate, or severe.