Potential Influence of Intraluminal Thrombus on Abdominal Aortic Aneurysm as Assessed by a New Non-Invasive Method

Intraluminal thrombus may play a role in abdominal aortic aneurysm pathogenesis and rupture. The purpose of this work was to demonstrate the feasibility of a new non-invasive method for the determination of the biomechanical features of the aortic wall and luminal boundary in abdominal aortic aneurysm containing intraluminal thrombus. Automated ultrasonographic measures of infrarenal aortic cross-sectional area (A) were obtained on-line along with non-invasive arterial pressure (p) from eight patients of mean(s.e.m.) age 74(3) years, with abdominal aortic aneurysm (mean dimensions 5.9(0.4) × 5.3(0.5) cm) containing intraluminal thrombus. Luminal boundary and abdominal aortic aneurysm wall were scanned separately. Compliance (C) was computed as C = (A _max — A _min)/[A _max(p _max — p _min)], where ‘max’ and ‘min’ represent maximum and minimum values, respectively. Mean compliance was lower for the abdominal aortic aneurysm wall alone than for the luminal surface enclosed by intraluminal thrombus: 4.0(0.9) × 10⁻⁴/mmHg versus 9.8(1.7) × 10⁻⁴/mmHg (P < 0.01). Intraluminal thrombus area was nearly constant over the cardiac cycle, indicating that the thrombus is virtually incompressible. This non-invasive method to assess biomechanical features of abdominal aortic aneurysm has potential to further the understanding of the influences of intraluminal thrombus on aneurysm disease.