Significance of the Doppler-derived gradient across a residual aortic coarctation

Summary

Few data exist which address the significance of the Doppler gradient across a residual narrowing in older children who have had a coarctation repaired. Therefore, we evaluated 11 patients with repaired aortic coarctation with and without residual obstruction by Doppler echocardiography. The Doppler-derived transcoarctation pressure gradient correlated poorly with catheter-measured peak-to-peak and catheter maximal instantaneous gradients when only the maximal velocity across the repair was utilized in the simplified Bernoulli equation, [r=0.73, standard of error of the estimate (SEE)=5.0 mmHg andr=0.56, SEE=7.6 mmHg, respectively]. However, when the precoarctation velocity was included in the simplified Bernoulli equation, the correlation between Doppler-derived and catheter-measured gradients became excellent. The maximal Doppler gradient correlated well with catheter peak-to-peak gradient (r=0.95, SEE=2.2 mmHg) and catheter maximal instantaneous gradient (r=0.94, SEE=3.2 mmHg). However, the maximal Doppler gradient slightly overestimated the catheter peak-to-peak gradient and underestimated the catheter maximal instantaneous gradient. The Doppler mean gradient showed excellent correlation with the catheter mean gradient (r=0.97, SEE=0.85 mmHg). Precoarctation velocities were generally twofold greater than published normals due to a spatial acceleration phenomenon. All subjects had residual hypoplasia of the transverse aorta such that its transverse diameter was 29% less than, and its crosssectional area was 50% less than, the ascending and descending aorta. Thus, it is apparent that proximal velocities must be accounted for in the modified Bernoulli equation in order to achieve an accurate gradient determination, and that this gradient is representative of a value that is between the maximal instantaneous and peak-to-peak catheter gradient. Flow acceleration within the transverse aorta may be related to significant reductions in luminal radius and crosssectional area.