The proximal isovelocity surface area (PISA) method estimates the effective regurgitant orifice area (EROA) in mitral regurgitation by measuring the radius of the hemispheric flow convergence region (aliasing radius) and incorporating the aliasing velocity and the peak velocity of the MR jet.
The equation for EROA is:
EROA = (2π × r² × Va) / Vmax
Where:
r = radius of the PISA hemisphere (aliasing radius)
Va = aliasing velocity (the velocity at which color aliasing occurs)
Vmax = peak MR velocity obtained by continuous wave Doppler
This calculation does not involve the mitral annular diameter, time velocity integral of mitral annulus, or left ventricular outflow tract diameter.
Thus, the third necessary parameter after aliasing radius and velocity is the maximum MR velocity measured by continuous wave Doppler, which allows determination of flow rate through the regurgitant orifice.
This formula and its clinical application are well established in adult echocardiography literature and ASE valvular regurgitation guidelines【12:ASE Valvular Regurgitation Guidelines†p.210-220】【16:Textbook of Clinical Echocardiography, 6e†Chapter on Mitral Regurgitation Assessment】.
