Noninvasive determination of pressure gradients in children: two methods employing pulsed Doppler echocardiography

Pulsed Doppler echocardiography has been considered poorly suited for high velocity blood flow measurement, because of the problem of signal aliasing. Two methods for reduction of aliasing in a pulsed system were evaluated in an attempt to measure flow velocities characteristic of significant pressure gradients. With the angle correction method, carrier frequency, pulse repetition frequency and intercept angle were manipulated using a commercially available two-dimensional pulsed Doppler system. Forty children undergoing cardiac catheterization were studied. Gradients of 60 to 70 mm Hg were accurately predicted by this method, and gradients above 90 mm Hg were underestimated. Overall correlation (r) value was 0.95. The method is limited primarily by the introduction of potential error in measurement of intercept angle; it is advantageous in that it can be attempted using currently available pulsed Doppler echographic systems. With the multiple sample volume method, pulse repetition frequency was increased through the addition of extra sample volumes. Carrier frequency was minimized and angle correction was not employed. Thirty-nine children underwent cardiac catheterization using a prototype instrument. Excellent agreement between Doppler predictions and actual gradients was found for gradients up to 100 mm Hg (r = 0.99). Although this method requires new instrumentation, it is advantageous in that gradients are accurately predicted and cannot be overestimated. Both methods retain the advantages of pulsed Doppler study for comprehensive flow evaluation and reference their quantitative application within a two-dimensional echographic format. Neither method is simple, and each has been validated only in pediatric subjects.