Limitations of Doppler echocardiography for the post-operative evaluation of aortic coarctation

Doppler blood Row measurements and derived pressure differences. through th e Bernoulli equation. are used in the diagnosis of aortic coarctation, a co ngenital stenosis distal to the Left subclavian artery. Doppler velocities remain elevated at the coarctation site after successful repair of coarctat ion, leading to high Doppler derived pressure differences without significa nt arm-leg pressure differences. We studied this apparent contradiction of two diagnostic methods. in vivo using patient and control data, and in vitr o using a hydraulic model. Clinical and echocardiographic data from 31 pati ents, aged 13.0 +/- 4.0, 10.5 +/- 3.7 yr after coarctectomy by end-to-end a nastomosis, and 18 age-matched healthy subjects were reviewed. Doppler peak velocities at the aortic isthmus were elevated in patients (2.2 +/- 0.3 vs . 1.2 +/- 0.2m/s, P < 0.001), corresponding to significant Doppler differen ces (20 +/- 7 mmHg), however, without significant arm-leg pressure differen ces, In all patients. a mild anatomic stenosis could still be observed. Loc al stiffness was increased. The hypothesis that the less distensible surgic al scar in post-coarctectomy patients leads to a significant dynamic obstru ction in systole was validated in a latex model of the aorta. Rigid rings ( 0.5-1.5 cm), matching the unloaded aortic diameter, were mounted around the aorta. Under loading conditions. Doppler peak velocities increased by 40 /- 7%, yielding Doppler differences of 21 +/- 3 mmHg. without a significant pressure drop. An alternative expression to calculate pressure differences . using both velocity and geometric information, was validated in the model . In conclusion, post-operatively, Doppler velocities remain elevated due t o a mild anatomical and significant dynamic narrowing. but the specific geo metry, resembling a tubular hypoplasia rather than an abrupt stenosis, perm its an almost complete pressure recovery explaining the occurrence of Doppl er differences in disagreement with the negligible arm-leg pressure differe nce. (C) 2001 Elsevier Science Ltd. All rights reserved.