Doppler ultrasound in the prediction of pressure gradients across aortic coarctation

Abstract

Although pressure gradients across valvar obstructions can be estimated by incorporating peak flow velocity distal to obstruction into a modified Bernoulli equation, such attempts in aortic coarctations have not been uniformly successful. The purpose of this study was to examine the value of several Doppler flow parameters in predicting pressure gradient across the aortic coarctation. Twenty-eight patients, aged 14 days to 13 years, in whom Doppler variables and catheterization pressure gradients were measured within 24 hours of each other, were included in the study. There were 60 pairs of such data. Correlation coefficients between catheter pressure gradient on the one hand and Doppler peak flow velocity and Doppler pressure gradient (DPG) estimates using (1) distal velocity and (2) both distal and proximal velocities (DPV) in the Bernoulli equation on the other were 0.74 to 0.76. Subgrouping the subjects into native coarctations, coarctations immediately after and 6 to 30 months after balloon angioplasty did not improve the correlation coefficient. Duration-related measures of Doppler flow curve distal to the coarctation, namely, acceleration time and antegrade flow time (AFT), corrected (to heart rate) and uncorrected, improved the correlation coeffient to 0.82 ( p < 0.001). A combination of magnitude- and duration-related parameters appears to give the best fit, and the catheter gradient can be estimated by 0.31 DPG using DPV + 0.22 AFT fraction + 0.04 AFT − 16.67 ( r = 0.92). Also, the mean Doppler flow velocity decreased ( p < 0.001) from 3.62 ± 0.45 to 2.65 ± 0.53 m/sec following balloon angioplasty of aortic coarctation; this improvement persisted (2.66 ± 0.54 m/sec) on follow-up. Similarly, AFT improved and pandiastolic flow was abolished by angioplasty. Magnitude- and duration-related parameters of the Doppler curve distal to the coarctation are useful adjuncts to imaging echocardiography in quantitating the degree of aortic obstruction.