Simple method for estimating regurgitant volume with use of a single radius for measuring proximal isovelocity surface area: An in vitro study of simulated mitral regurgitation

The proximal isovelocity surface area (PISA) color Doppler method with use of a hemielliptic formula is reported to be accurate for quantitating regurgitant volume (RV). However, this formula ideally requires the measurement of 2 or 3 radii and therefore is not widely used clinically. The purpose of this in vitro study was to derive a simple PISA formula for estimating RV with use of a single radius axial to the valve orifice and to compare it with the clinically used single-radius hemispherical formula (2 x pi x R-2 x AV x TVI/Vp), where AV is the apparent color Doppler aliasing velocity, R is the PISA. color Doppler aliasing radius, TVI is time-velocity integral of the jet by continuous wave Doppler, and Vp is the peak velocity of the jet by continuous wave Doppler. Pulsatile flow studies were performed across a convex curvilinear surface, which more closely approximates the shape of the mitral valve than does a planar surface. Pulse rates (60 to 80 bpm), peak now velocities (4.0 to 6.0 m/s), and regurgitant orifice areas (0.2 to 1.0 cm(2))were varied to simulate mitral regurgitation. The AVs were varied from 11 to 39 cm/s, and a single PISA aliasing radius was measured at each AV. Excellent linear correlations were obtained between the PISA radius and the actual RV measured with use of a beaker (r = 0.94 to 0.97, P < .0001). A series of simplified formulas was derived from the regression line of the PISA radius versus the RV. For example, with an AV of 21 cm/s, RV was estimated by a simplified PISA formula (where RV [mL] = 10 x R [mm] - 30) with are accuracy of 3.3 +/- 6.3 mL versus -20.3 +/- 8.7 mt for the standard single-radius PISA method (P < .0001). By using the standard single-radius hemispherical PISA formula, RV was underestimated if the radius was <20 mm. By using simplified regression equations, the PISA radius accurately estimated RV at a PISA radius <20 mm. Clinical studies are necessary to validate this concept.