Heterogeneity of tensile strength and matrix metalloproteinase activity in the wall of abdominal aortic aneurysms.
OBJECTIVE
To measure the tensile strength of the aneurysm wall and the matrix metalloproteinase (MMP) activity in similar samples of aortic tissue.


METHODS
Detailed mechanical testing was conducted on 124 standardized specimens of aneurysm wall harvested from 24 patients undergoing elective aneurysm repair. The intrasac pressure required to cause aneurysm rupture was calculated based upon the Law of Laplace. In addition, MMP-2 and 9 were assayed from these specimens. Sixty specimens of nonaneurysmal aorta from 6 cadaveric organ donors served as controls. Intrasubject and intersubject variations were analyzed.


RESULTS
In the aneurysm specimens, the Young's modulus was 1.80x10(6) N/m(2), the load at break was 6.36 N, the strain at break was 0.30, the ultimate strength was 0.53x10(6) N/ m(2), and the MMP activity was 312 for MMP-2 and 460 for MMP-9. In the controls, the circumferential measurements were a Young's modulus of 1.82x10(6) N/m(2), a load at break of 5.43 N, strain at break of 0.29, ultimate strength of 0.61x10(6) N/m(2), and MMP activity of 395 for MMP-2 and 2019 for MMP-9. Longitudinal measurements in controls were a Young's modulus of 1.38x10(6) N/m(2), a load at break of 11.39 N, a strain at break of 0.33, and ultimate strength of 1.30x10(6) N/m(2). Intra and intersubject variation of all parameters was very high. Based upon the lowest measured tensile strength for each aneurysm, the intrasac pressure required to cause rupture varied from 142 to 982 mmHg.


CONCLUSIONS
Localized "hot spots" of MMP hyperactivity could lead to focal weakening of the aneurysm wall and rupture at relatively low levels of intraluminal pressure. These data suggest that tensile strength of the sac is just as important as intrasac tension in determining the risk of rupture. Moreover, these observations may explain why some small aneurysms rupture and larger aneurysms do not. Assessment of rupture risk based on computation or measurement of wall stress may be subject to error and inaccuracy due to variations in wall tensile strength.
Vallabhaneni
Srinivasa R
SR
Regional Vascular Unit, Royal Liverpool University Hospital, England, UK.
Gilling-Smith
Geoffrey L
GL
How
Thien V
TV
Carter
Stuart D
SD
Brennan
John A
JA
Harris
Peter L
PL
D001012:Aorta, Abdominal / Q000201:enzymology / Q000503:physiopathology*; D017544:Aortic Aneurysm, Abdominal / Q000201:enzymology* / Q000503:physiopathology*; D001019:Aortic Rupture / Q000209:etiology; D016022:Case-Control Studies; D006801:Humans; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D012307:Risk Factors; D013314:Stress, Mechanical; D013718:Tensile Strength
D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9