Fixed region of nondistensibility after coarctation repair: In vitro validation of its influence on Doppler peak velocities

After coarctectomy, local loss of distensibility is noted in addition to mi ld anatomic narrowing. We hypothesize that the increased Doppler peak veloc ities measured at the aortic isthmus in these patients partly reflect obstr uction secondary to the stiff surgical scar. The hypothesis was studied in a pulsatile hydraulic model. Thirty-one patients (13.0 +/- 4.0 years of age ), 10.5 +/- 4.7 years after coarctectomy by end-to-end anastomosis, were st udied clinically and echocardiographically. Indexes of distensibility were calculated. The effect of isolated increased stiffness was studied in vitro with a stiff and a com pliant 1:1 scale latex model of the aorta mounted i n a pulsatile full-scale circulation loop. Local stiffening was obtained by a rigid ring mounted around the aorta, fitted to the dimension of the unlo aded aorta. For different pressure and flow regimens, pressures and Doppler velocities were measured across the ring. Mean peak velocities at the surg ical scar were 2.2 +/- 0.4 m/s. Mild anatomic stenosis was present. All dis tensibility indexes indicated locally increased stiffness (P < .001). In th e stiff latex model, Doppler peak velocities increased from 1.89 +/- 0.04 m /s to 2.32 +/- 0.06 m/s (P < .03); in the compliant model, from 1.15 +/- 0. 03 m/s to 1.79 +/- 0.05 m/s (P < .001). The increase of Doppler peak veloci ties depends on model compliance only and is independent of now rate, lengt h of the noncompliant segment, and viscosity of the perfusion fluid. Veloci ties do not change when semicircular stiffening is applied. We have demonst rated in vitro that isolated local nondistensibility leads to vessel narrow ing during vascular distension. The relative contribution of local scar sti ffness in the increase of Doppler peak velocities after coarctectomy was he reby assessed.