[Pulsed Doppler echocardiographic estimation of pressure gradient across a ventricular septal defect: with particular reference to potential factors of error].

The clinical validity and some problems concerning pulsed Doppler echocardiography (PD) in non-invasive estimates of pressure difference (delta P) across a ventricular septal defect were studied. The maximum velocity (max V) of the left to right shunt flow in the right ventricle was converted to delta P using the simplified Bernoulli equation: delta P = 4V2. We also used the equation: delta P = 4(V2(2) - V1(2)) to estimate the delta P in cases who had left to right shunt flows of high velocity in the left ventricle. Simulatenous recordings of both left and right ventricular pressures and PD were obtained during cardiac catheterization of 11 cases. Accurate Doppler estimates of delta P only from the maximum velocity of the left to right shunt flow in the right ventricle were impossible in nine cases whose actual delta P's were large (more than 41 mmHg) and also in eight cases whose right ventricular systolic pressure was high (either equal to or higher than left ventricular systolic pressure). Besides these 17 cases, delta P estimated by PD using the simplified Bernoulli equation in 39 cases, with pansystolic left to right shunt flows in the right ventricle, correlated well with the actually measured delta P (Y = 0.99X + 2.77, r = 0.91, p less than 0.01). The difference in the maximal instantaneous pressure gradient and Doppler delta P was considered insignificant (between 0 and 7 mmHg, mean 4 mmHg). In nine cases, the left to right shunt flows of relatively high speed (0.63 approximately 2.00 m/sec, mean 1.31 m/sec) were observed also in the left ventricle, and calculated delta P using the simplified Bernoulli equation overestimated the actually measured delta P by 2 to 16 mmHg (Y = 1.52X + 4.88, r = 0.95, p less than 0.01). However, if the delta P is estimated by using the equation, delta P = 4(V2(2) - V1(2)), without ignoring the maximum speed in the left ventricle (V1), it correlates well with the actually measured delta P (Y = 1.07X + 0.76, r = 0.98, p less than 0.01). Thus, in cases with left to right shunt flows with high speeds in the left ventricle, the equation: delta P = 4(V2(2) - V1(2)) was more accurate in estimating the delta P by pulsed Doppler echocardiography.