Abstract 2008: Characterizing Changes In Abdominal Aortic Aneurysm Principal Wall Strain Using Ultrasound Elastography

Abstract

Pressure-normalized aortic principal wall strain (ep+/pp, %/mmHg) is a biomechanical parameter for abdominal aortic aneurysm (AAA) stability correlated with aneurysm growth rate. We hypothesized that ep+/pp decreases as AAAs degenerate. This study aimed to characterize ep+/pp change over time using ultrasound elastography (USE). Axial ultrasound images of patient AAAs were collected at two consecutive clinic visits. The USE algorithm applied a finite element mesh over the aneurysm wall at the point of maximum diameter. A custom image-registration protocol tracked frame-to-frame displacement fields of the images over one cardiac cycle to calculate maximum ep+/pp (Fig 1). Clinical data were collected from patient records. The cohort was separated by index ep+/pp terciles. Thirty-one patients with a mean age of 71.7 ± 10.1 at index visit were included, with follow-up imaging at an interval of 7.1 ± 3.4 months. For the cohort, maximum ep+/pp decreased from 2.3 ± 1.0 %/mmHg to 2.0 ± 0.9 %/mmHg (p=0.08), and average AAA diameter increased from 4.4 ± 0.6 cm to 4.5 ± 0.7 cm (p=0.04). The “high-strain” tercile was associated with a strain reduction of -1.7 ± 0.8 %/mmHg, compared to “low” (0.1 ± 1.0 %/mmHg, p<0.01) and “intermediate” (-0.4 ± 0.5 %/mmHg, p=0.04) terciles (Fig 2). There was no difference in AAA growth or rupture between terciles. The present findings indicate that AAA ep+/pp at baseline predicts the degree of ep+/pp decrease over time. These data suggest that biomechanical changes in the aortic wall related to aneurysmal degeneration can be quantized by a novel ultrasound technique. Research correlating these results with histopathologic AAA remodeling may inform monitoring.