Peak wall stress measurement in elective and acute abdominal aortic aneurysms.
BACKGROUND
Abdominal aortic aneurysm (AAA) rupture occurs when wall stress exceeds wall strength. Engineering principles suggest that aneurysm diameter is only one aspect of its geometry that influences wall stress. Finite element analysis considers the complete geometry and determines wall stresses throughout the structure. This article investigates the interoperator and intraoperator reliability of finite element analysis in the calculation of peak wall stress (PWS) in AAA and examines the variation in PWS in elective and acute AAAs.


METHODS
Full ethics and institutional approval was obtained. The study recruited 70 patients (30 acute, 40 elective) with an infrarenal AAA. Computed tomography (CT) images were obtained of the AAA from the renal vessels to the aortic bifurcation. Manual edge extraction, three-dimensional reconstruction, and blinded finite element analysis were performed to ascertain location and value of PWS. Ten CT data sets were analyzed by four different operators to ascertain interoperator reliability and by one operator twice to ascertain intraoperator reliability. An intraclass correlation coefficient was obtained. The Mann-Whitney U test and independent samples t test compared groups for statistical significance.


RESULTS
The intraclass correlation coefficient was 0.71 for interoperator reliability and 0.84 for intraoperator reliability. There was no statistically significant difference in the mean (SD) maximal AAA diameter between elective (6.47 [1.30] cm) and acute (7.08 [1.39] cm) patients (P = .073). The difference in PWS between elective (0.67 [0.30] MPa) and acute (1.11 [0.51] MPa) patients (P = .008) was statistically significant, however.


CONCLUSIONS
Interoperator and intraoperator reliability in the derivation of PWS is acceptable. PWS, but not maximal diameter, was significantly higher in acute AAAs than in elective AAAs.
Academic Vascular Surgery, Hull Royal Infirmary, Anlaby Road, Hull, United Kingdom.
Michael S
MS
Heng
Michael J
MJ
Fagan
Jason W
JW
Collier
Grishma
G
Desai
Peter T
PT
McCollum
Ian C
IC
Chetter
D000208:Acute Disease; D000368:Aged; D000369:Aged, 80 and over; D017544:Aortic Aneurysm, Abdominal / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D001019:Aortic Rupture / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology*; D001027:Aortography / Q000379:methods; D015331:Cohort Studies; D017558:Elective Surgical Procedures; D004632:Emergency Medical Services; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D015588:Observer Variation; D018579:Patient Selection; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted; D015203:Reproducibility of Results; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed; D014656:Vascular Surgical Procedures