Elastin degradation within the abdominal aortic aneurysm wall – relationship between intramural pH and adjacent thrombus formation

BACKGROUND: The natural history of abdominal aortic aneurysm (AAA) is wall remodelling potentially leading to a final rupture. The pathogenesis of AAA appears to be multifactorial. The aim of this pilot prospective study was to assess the relationship between the thickness of the thrombus within the abdominal aortic aneurysm, intramural pH and local elastin degradation. MATERIALS AND METHODS: The AAA size, intraluminal thrombus (ILT) morphology and location were evaluated in 206 consecutive patients. Thirty patients with large AAA (aortic diameter > or = 50 mm) and adjacent ILT with the thinnest part < or = 10 mm and thickest > or = 25 mm, measured in the region of the maximum diameter of AAA, were included for further study. During AAA surgery intramural pH measurements were performed and specimens taken from both thin thrombus-covered and thick thrombus-covered wall for computerized morphometric analysis. RESULTS: Mean intramural pH value was 7.21 +/- 0.18 for the wall covered by thick ILT and 7.64 +/- 0.10 for the thin one (P < 0.001). Computerized morphometric analysis demonstrated that elastin fibres in the thin thrombus-covered wall were decreased in size (for width--P < 0.0001, for length--P < 0.13), irregularly orientated (P < 0.000001) and the amount of fibres was reduced when compared to the wall covered by thick ILT (P < 0.0004). CONCLUSION: A strong relationship between intramural pH and elastin net destruction suggests that the local alkaline status within the thin thrombus-covered part of the aneurysm wall is contributing to the elastinolytic process.