Pressure gradient across the pulmonary valve is estimated from the continuous wave Doppler derived velocity across the pulmonary valve using the simplified Bernoulli equation: Pressure gradient = 4*V*V (4 x V squared). Sample volume of Doppler has to be aligned parallel to the flow, guided by colour Doppler imaging in the parasternal short axis view. Subcostal view may be better in children. Highest value obtained from multiple views should be used. Doppler derived gradient has good correlation with cath derived gradient. It should be remembered that Doppler measures peak instantaneous gradient while cath measures peak to peak gradient.
