Noninvasive evaluation of the effectiveness of endovascular AAA exclusion

To evaluate the relationship between aneurysm sac pressure and endograft wall motion in vitro and in vivo and to compare this to sac volume changes after endovascular aneurysm repair.

In a flow model of an aneurysm with a stent-graft in situ, sac pressure was incrementally increased by adding volume to an otherwise excluded sac; sac pressure waves were registered. Clinically, 43 patients who had unsupported endografts were monitored for stent-graft wall motion using electrocardiographically-guided M-mode ultrasonography. At 3 predetermined points in the cardiac cycle, 2 independent observers measured the maximal endograft diameter. Graft wall motion was then compared to changes in aneurysm thrombus volume (shrinking, static, growth) based on serial spiral computed tomographic angiography measurements.

In the in vitro model, as the sac was incrementally pressurized, the initially static pressure waveform changed to a more dynamic waveform identical to that of the systemic pressure. Additionally, graft wall motion was noted visually when the pressure exceeded 40 mm; it became increasingly vigorous at higher pressures. The 0.13-cm wall motion in the growth group (n=5) was significantly larger than the 0.04 cm in the static group (n=19; p=0.012) and the 0.03 cm in the shrinking group (n=19; p=0.002). No significant difference was found between the static and the shrinking groups (p=0.209).

Increases in sac pressure are reflected as increased wall motion in unsupported endografts. Clinically, increased endograft wall motion can be demonstrated by M-mode ultrasound; in growing aneurysms, the significant change in wall motion may suggest increased sac pressures as the etiology of the aneurysm growth.