Changes in intraoperative aortic strain as detected by ultrasound elastography in patients following abdominal endovascular aneurysm repair

Abstract

Objective: Predicting success after endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms (AAAs) relies on measurements of aneurysm sac regression. However, in the absence of regression, morphometric analysis alone is insufficient to reliably predict the successful remodeling of AAAs after EVAR. Biomechanical parameters, such as pressure-normalized principal strain, might provide useful information in the post-EVAR AAA assessment. Our objective was to assess the feasibility of our novel ultrasound elastography (USE) technique to detect changes in the aortic wall principal strain in patients who had undergone EVAR and determine the temporal nature of the biomechanical changes in the aorta. Methods: USE images were obtained from patients undergoing elective EVAR intraoperatively, immediately before and after endograft implantation, and at their 30-day follow-up. The maximal mean principal strain (ερ+¯) for each scan was assessed using our novel technique, which uses a finite element mesh to track the frame-to-frame displacements of the aortic wall over one cardiac cycle. The ερ+¯ in the user-defined aortic wall was then divided by the pulse pressure at the time of the scan to produce a pressure-normalized strain measurement (ερ+¯/PP), a surrogate for tissue stiffness. Paired t tests were used to compare the pre- and postoperative ερ+¯/PP and the postoperative and 30-day ερ+¯/PP. Patient 30-day sac regression and endoleak data were collected by a review of 30-day follow-up computed tomography scans. Results: USE analysis of the data from 12 patients demonstrated a significant reduction in aortic wall ερ+¯/PP (average, 0.191% ± 0.09%/kPa vs 0.087% ± 0.04%/kPa; P = .002) immediately after graft implantation, with a nonsignificant change in the ερ+¯/PP (0.091% ± 0.04%/kPa vs 0.102% ± 0.05%/kPa; P = .47) from postoperatively to 30-day follow-up. This represents an average 46.5% reduction after stent placement, with a nonsignificant 18.1% increase at 30-day follow-up. All the patients showed sac stability, except for two patients who had demonstrated 7.3-mm and 6.8-mm sac regressions. Conclusions: Our analysis has demonstrated that the presented USE technique is a feasible method for detecting significant reductions in aortic ερ+¯/PP intraoperatively after EVAR. We found that patients undergoing EVAR will experience large reductions in the ερ+¯/PP intraoperatively after graft implantation, with stabilization found at their 30-day follow-up. These preliminary data have shown that an intraoperative ερ+¯/PP reduction could be a promising correlate of post-EVAR aneurysm remodeling. Our results have also suggested that endograft design likely plays a large role in determining the aneurysm biomechanical changes immediately after implantation.

Keywords

• Abdominal aortic aneurysm
• Elasticity imaging techniques
• Endovascular procedures
• Ultrasonography