Explant analysis of AneuRx stent grafts: relationship between structural findings and clinical outcome

Abstract

Objective We reviewed the structural findings of explanted AneuRx stent grafts used to treat abdominal aortic aneurysms, and relate the findings to clinical outcome measures. Methods We reviewed data for all bifurcated AneuRx stent grafts explanted at surgery or autopsy and returned to the manufacturer from the US clinical trial and worldwide experience of more than 33,000 implants from 1996 to 2003. Devices implanted for more than 1 month with structural analysis are included in this article. Explant results were analyzed in relation to cause of explantation and pre-explant evidence of endoleak, enlargement, or device migration. Results One hundred twenty explanted stent grafts, including 37 from the US clinical trial, were analyzed. Mean implant duration was 22 ± 13 months (range, 1-61 months). Structural abnormalities included stent fatigue fractures, fabric abrasion holes, and suture breaks. The mean number of nitinol stent strut fractures per explanted device was 3 ± 4, which represents less than 0.2% of the total number of stent struts in each device. The mean number of fabric holes per explanted device was 2 ± 3, with a median hole size of 0.5 mm 2. Suture breaks were seen in most explanted devices, but composed less than 1.5% of the total number of sutures per device. “For cause” explants (n = 104) had a 10-month longer implant duration ( P = .007) compared with “incidental” explants (n = 16). “For cause” explants had more fractures (3 ± 5; P = .005) and fabric holes (2 ± 3; P = .008) per device compared with “incidental” explants, but these differences were not significant ( P = .3) when adjusted for duration of device implantation. Among clinical trial explants the number of fabric holes in grafts in patients with endoleak (2 ± 3 per device) was no different from those without endoleak (3 ± 4 per device; P = NS). The number of fatigue fractures or fabric holes was no different in grafts in clinical trial patients with pre-explant aneurysm enlargement compared with those without enlargement. Pre-explant stent-graft migration was associated with a greater number of stent strut fractures (5 ± 7 per device; P = .04) and fabric holes (3 ± 3 per bifurcation; P = .03) compared with explants without migration. Serial imaging studies revealed inadequate proximal, distal, or junctional device fixation as the probable cause of rupture or need for conversion to open surgery in 86% of “for cause” explants. Structural device abnormalities were usually remote from fixation sites, and no causal relationship between device findings and clinical outcome could be established. Conclusions Nitinol stent fatigue fractures, fabric holes, and suture breaks found in explanted AneuRx stent grafts do not appear to be related to clinical outcome measures. Longer term studies are needed to confirm these observations.