Graft Inflow Stenosis Induced by the Inflatable Ring Fixation Mechanism of the Ovation Stent-Graft System: Hemodynamic and Clinical Implications

Abstract

Purpose:

To investigate the observed inflow stenosis at the O-rings of the Ovation stent-graft and evaluate its hemodynamic and clinical impact.

Methods:

The study involved 49 consecutive patients (48 men; mean age 71.2±7.7 years) treated successfully with the Ovation abdominal aortic stent-graft between June 2011 and January 2014 at a single center. Cross-sectional area and radius measurements of the infrarenal aorta just proximal to the sealing mechanism, as well at the site of stenosis, were measured from 3D reconstructions of the 1-month postoperative computed tomographic angiograms. Based on Poiseuille's law, the predicted pressure drop was calculated for each patient based on the length of the stenosis. Invasive blood pressure measurements at 3 levels (proximal to the inflatable rings, halfway inside the stenosis, and distal to the stenosis) were obtained in 10 patients intraoperatively. Ankle-brachial index (ABI) values preoperatively were compared to those after the procedure for all patients to assess the clinical impact of this phenomenon.

Results:

Median internal cross-sectional area at the site of the stenosis was significantly reduced compared to the area just proximal to the O-rings [57% reduction: 123 mm² (range 28–254) vs. 283 mm² (range 177–531), respectively; p<0.001]. The same was observed for the radius [6.5 mm (range 3–9) vs. 9.5 mm (range 7.5–13), respectively; p<0.001]. Based on the median 15 mm length of the stenosis (range 13–17) observed in the study population, a median pressure drop of 0.13 mmHg (range 0–0.25) along the stenosis was calculated. Invasive blood pressure measurements indicated a non-significant pressure change along the stenosis (e.g., 0.7 mmHg between the proximal level and halfway inside the stenosis). ABI remained practically unchanged postoperatively.

Conclusion:

The advantages of the Ovation device's unique sealing mechanism come at the expense of a median area inflow stenosis of ∼60%. This stenosis does not cause a hemodynamically significant pressure drop. Future modification of the graft ring design may be needed in order to reduce this stenosis.