Abstract
Endovascular aneurysm repair (EVAR) is a minimally invasive treatment option for abdominal aortic aneurysm (AAA). However, a major EVAR complication is endoleak, the reoccurrence of blood flow into the residual aneurysmal sac. Detection of endoleak is critical in post-EVAR surveillance, as endoleak can lead to further aneurysm growth and rupture. Usual surveillance is by ultrasound imaging, but this has some limitations. Proof-of-concept studies have suggested shear wave elastography (SWE) is a possible imaging modality for the detection of endoleak in EVAR patients. The overall aim of this study was to investigate SWE’s application in the Otago Vascular Diagnostic Laboratory (OVD) post-EVAR surveillance cohort.
This project aimed to first validate the novel use of SWE within the OVD. One, healthy, 21- year-old female consented to undergo repeated SWE scans of her liver and three gelatine phantom models of different densities were also imaged. Results were consistent with published results, and demonstrated good inter- and intra-observer reliability from observers with varying levels of ultrasound experience.
The other aims of the project were to use SWE technology to detect changes in intraluminal thrombus (ILT) density over time, and determine if SWE values in post-EVAR residual aneurysm sac (RAS) can detect endoleak. Patients enrolled in the OVD EVAR surveillance programme between May and August 2023 were invited to participate. Forty-six patients (40 men), with a median age of 77 years (range 58 – 91 years), provided informed consent for SWE alongside their routine B-mode and colour Doppler (CDUS) ultrasound surveillance. The entire circumferential RAS was insonated at three points along its axis: its maximum diameter, as well as levels above and below this point.
Overall, no relationship between ILT stiffness and post-EVAR time was found. However, in a small subset of patients with repeated early scans (n = 3), a significant (p = 0.0063, paired Student’s t-test) increase of 0.39 ± 0.05 m/s (mean ± SD) was found between one- and three- months post-EVAR. Upon completion of all data collection, the occurrence of endoleak was unblinded, and 13/46 patients had type-II endoleak detected by CDUS and/or CEUS. Across the whole RAS, average SWE was 3.40 ± 1.0 m/s, with no significant difference (p = 0.22, unpaired Student’s t-test) between the SWE in patients with (3.42 ± 0.54 m/s) and without (3.16 ± 0.67 m/s, n = 43) endoleak. The hypothesised reduction in SWE in endoleak was only observed (p = 0.035, paired Student’s t-test) when SWE acquisition was targeted to the exact location of endoleak within the RAS.
The data of this project indicate that SWE can detect changes in ILT stiffness in the first three months post-EVAR, but is not able to detect long-term changes in ILT stiffness. The presence of endoleak could be identified by SWE, but only if acquisitions were taken from the exact location of endoleak. Therefore, SWE is not suitable as a clinical tool to diagnose endoleak, but may have potential use as a research tool.