Effect of compliance on Doppler diastolic flow patterns seen in coarctation of the aorta: a numerical study

In the echocardiographic evaluation of coarctation of the aorta, the degree of antegrade diastolic flow (diastolic runoff) noted on spectral Doppler tracings traditionally was felt to be solely dependent on lesion severity. However, recent in-vitro experiments suggest the presence of this saw-toothed spectral Doppler pattern has less to do with severity than it has to do with changes in aortic compliance. Using state of the art multidisciplinary numerical analysis tools, the purpose of this study was to investigate the specific fluid and wall mechanics in coarctation of the aorta. Three models of coarctation were developed with high, low, and zero wall compliance. In both the low output and high output states, the degree of diastolic runoff increases with increasing vessel compliance. The high compliance model had larger changes in aortic dilatation in the pre-coarctation region compared to the low compliance model. In conclusion, increased aortic compliance brings about greater dilatation of the precoarctation aorta in systole leading to an increase in stored energy in systole. This increased stored energy, released in diastole as the walls contract, leads to increased degrees of diastolic runoff. Numerical methods offer a unique perspective into the understanding of the mechanisms behind such clinical measures.