Implantable Pressure-Sensing Devices for Monitoring Abdominal Aortic Aneurysms in Post-Endovascular Aneurysm Repair.

Over the past two decades, there has been extensive research into surveillance methods for the post-endovascular repair of abdominal aortic aneurysms, highlighting the importance of these technologies in supplementing or even replacing conventional image-screening modalities. This review aims to provide an overview of the current status of alternative surveillance solutions for endovascular aneurysm repair, while also identifying potential aneurysm features that could be used to develop novel monitoring technologies. It offers a comprehensive review of these recent clinical advances, comparing new and standard clinical practices. After introducing the clinical understanding of abdominal aortic aneurysms and exploring current treatment procedures, the paper discusses the current surveillance methods for endovascular repair, contrasting them with recent pressure-sensing technologies. The literature on three commercial pressure-sensing devices for post-endovascular repair surveillance is analyzed. Various pre-clinical and clinical studies assessing the safety and efficacy of these devices are reviewed, providing a comparative summary of their outcomes. The review of the results from pre-clinical and clinical studies suggests a consistent trend of decreased blood pressure in the excluded aneurysm sac post-repair. However, despite successful pressure readings from the aneurysm sac, no strong link has been established to translate these measurements into the presence or absence of endoleaks. Furthermore, the results do not allow for a conclusive determination of ongoing aneurysm sac growth. Consequently, a strong clinical need persists for monitoring endoleaks and aneurysm growth following endovascular repair.

Design and Characterisation of a Read-Out System for Wireless Monitoring of a Novel Implantable Sensor for Abdominal Aortic Aneurysm Monitoring.

Abdominal aortic aneurysm (AAA) is a dilation of the aorta artery larger than its normal diameter (>3 cm). Endovascular aneurysm repair (EVAR) is a minimally invasive treatment option that involves the placement of a graft in the aneurysmal portion of the aorta artery. This treatment requires multiple follow-ups with medical imaging, which is expensive, time-consuming, and resource-demanding for healthcare systems. An alternative solution is the use of wireless implantable sensors (WIMSs) to monitor the growth of the aneurysm. A WIMS capable of monitoring aneurysm size longitudinally could serve as an alternative monitoring approach for post-EVAR patients. This study has developed and characterised a three-coil inductive read-out system to detect variations in the resonance frequency of the novel Z-shaped WIMS implanted within the AAA sac. Specifically, the spacing between the transmitter and the repeater inductors was optimised to maximise the detection of the sensor by the transmitter inductor. Moreover, an experimental evaluation was also performed for different orientations of the transmitter coil with reference to the WIMS. Finally, the FDA-approved material nitinol was used to develop the WIMS, the transmitter, and repeater inductors as a proof of concept for further studies. The findings of the characterisation from the air medium suggest that the read-out system can detect the WIMS up to 5 cm, regardless of the orientation of the Z-shape WIMS, with the detection range increasing as the orientation approaches 0°. This study provides sufficient evidence that the proposed WIMS and the read-out system can be used for AAA expansion over time.

BMI-Adapted Double Low-Dose Dual-Source Aortic CT for Endoleak Detection after Endovascular Repair: A Prospective Intra-Individual Diagnostic Accuracy Study.

PURPOSE: To assess the diagnostic accuracy of BMI-adapted, low-radiation and low-iodine dose, dual-source aortic CT for endoleak detection in non-obese and obese patients following endovascular aortic repair. METHODS: In this prospective single-center study, patients referred for follow-up CT after endovascular repair with a history of at least one standard triphasic (native, arterial and delayed phase) routine CT protocol were enrolled. Patients were divided into two groups and allocated to a BMI-adapted (group A, BMI < 30 kg/m2; group B, BMI ≥ 30 kg/m2) double low-dose CT (DLCT) protocol comprising single-energy arterial and dual-energy delayed phase series with virtual non-contrast (VNC) reconstructions. An in-patient comparison of the DLCT and routine CT protocol as reference standard was performed regarding differences in diagnostic accuracy, radiation dose, and image quality. RESULTS: Seventy-five patients were included in the study (mean age 73 ± 8 years, 63 (84%) male). Endoleaks were diagnosed in 20 (26.7%) patients, 11 of 53 (20.8%) in group A and 9 of 22 (40.9%) in group B. Two radiologists achieved an overall diagnostic accuracy of 98.7% and 97.3% for endoleak detection, with 100% in group A and 95.5% and 90.9% in group B. All examinations were diagnostic. The DLCT protocol reduced the effective dose from 10.0 ± 3.6 mSv to 6.1 ± 1.5 mSv (p < 0.001) and the total iodine dose from 31.5 g to 14.5 g in group A and to 17.4 g in group B. CONCLUSION: Optimized double low-dose dual-source aortic CT with VNC, arterial and delayed phase images demonstrated high diagnostic accuracy for endoleak detection and significant radiation and iodine dose reductions in both obese and non-obese patients compared to the reference standard of triple phase, standard radiation and iodine dose aortic CT.

Dynamic, Time-Resolved CT Angiography After EVAR: A Quantitative Approach to Accurately Characterize Aortic Endoleak Type and Identify Inflow Vessels.

PURPOSE: Our purpose was to study the accuracy of dynamic computed tomography angiography (d-CTA) in characterizing endoleak type, inflow vessels as compared with digital subtraction angiography (DSA) using qualitative and quantitative analysis. METHODS: Between March 2019 and January 2021, all patients who underwent d-CTA imaging after EVAR were retrospectively reviewed. Two blinded independent reviewers qualitatively reviewed d-CTA and DSA images. Quantitative region of interest (ROI) analysis was performed by measuring time-resolved contrast enhancement within the aorta and endoleak lesion(s) in the aneurysm sac. Differences between time-to-peak enhancement (Δ TTP) across different ROIs were quantified. RESULTS: A total of 48 patients underwent d-CTA during the study period, of whom 24 patients had abdominal EVAR and DSA imaging for comparison. Qualitative review of DSA imaging showed type I (n=4), type II (n=16), and type III (n=2) and no endoleak (n=2). In 23 of 24 patients (95.8%), d-CTA findings correlated with DSA findings for endoleak type. One patient had a type III endoleak that was demonstrated only in d-CTA (arising from defect in polymer sealing ring of Ovation stent graft) imaging. In type II endoleak cases, d-CTA identified more inflow vessels than DSA imaging (33 vs 21 vessels, p=0.010). Quantitative analysis showed mean (±SD) Δ TTP values for type I endoleak as 1.8 (±1.8) seconds, type II as 9.6 (±3.5) seconds, and for type III endoleak as 5.6 (±1.3) seconds. CONCLUSION: Dynamic CTA can accurately characterize aortic endoleak type, inflow vessels as compared with DSA imaging. Quantitative parameters such as Δ TTP enhancement can help better differentiate endoleak types and provide an objective approach to endoleak diagnosis.

The Role of Aortic Volume in the Natural History of Abdominal Aortic Aneurysms and Post-Endovascular Aortic Aneurysm Repair Surveillance.

There has been a debate about whether maximum diameter can be solely used to assess the natural history of abdominal aortic aneurysm. The aim of the present review is to collect all the available evidence on the role of abdominal aortic aneurysm (AAA) volume in the natural history of AAAs, including small untreated AAAs and AAAs treated by EVAR. The current literature appears to reinforce the role of volume as a supplementary measure for evaluating the natural history of AAA, in both intact AAAs and after EVAR. The clinical impact of AAA volume measurements remains unclear. Several studies show that volumetric analysis can assess changes in AAAs and predict successful endoluminal exclusion after EVAR more accurately than diameter. However, most studies lack strict standardized measurement criteria and well-defined outcome definitions. It remains unclear whether volumetry could replace diameter assessment in defining the risk of rupture of AAAs and identifying clinically relevant sac growth.

Dynamic, Time-Resolved Computed Tomography Angiography Technique to Characterize Aortic Endoleak Type, Inflow and Provide Guidance for Targeted Treatment.

PURPOSE: To illustrate dynamic, time-resolved CTA (d-CTA) imaging technique in characterizing aortic endoleak type/inflow using quantitative parameters and its value in providing image guidance for targeted treatment approach. TECHNIQUE: Dedicated endoleak protocol involved acquiring multiple time-resolved contrast enhanced scans using third-generation CT scanner (Somatom Force®, Siemens Healthineers). Parameters such as scan field of view (FOV), kV, number/timing of scans were customized based on patient's body-mass-index, timing bolus, and prior imaging findings. D-CTA image datasets were evaluated qualitatively and quantitatively using time-attenuation curves (TAC) analysis after motion correction using a dedicated software (syngo.via®, Siemens). D-CTA findings from 4 illustrative cases demonstrating type I, type II (inferior mesenteric and lumbar artery inflow), and type III endoleak were illustrated. TAC analysis with time to peak parameter enabled better characterization of endoleak type and inflow. During endoleak intervention, target vessels from d-CTA images were electronically annotated and overlaid on fluoroscopy using 2D-3D image fusion to provide image guidance for targeted treatment. CONCLUSION: D-CTA imaging with TAC analysis characterizes aortic endoleak type and inflow, in addition to providing image guidance for targeted endoleak treatment. Such dynamic, time-resolved imaging techniques may provide further insights into understanding aortic endoleak that remains an Achilles heel for endovascular aortic aneurysm repair.

Three-dimensional ultrasound is a reliable alternative in endovascular aortic repair surveillance.

OBJECTIVE: Three-dimensional ultrasound (3D-US) has already demonstrated improved reproducibility with a high degree of agreement (intermodality variability), reproducibility (interoperator variability), and repeatability (intraoperator variability) compared with conventional two-dimensional ultrasound (2D-US) when estimating the maximum diameter of native abdominal aortic aneurysms (AAAs). The aim of the present study was, in a clinical, multicenter setting, to evaluate the accuracy of 3D-US with aneurysm model quantification software (3D-US abdominal aortic aneurysm [AAA] model) for endovascular aortic aneurysm repair (EVAR) sac diameter assessment vs that of computed tomography angiography (CTA) and 2D-US. METHODS: A total of 182 patients who had undergone EVAR from April 2016 to December 2017 and were compliant with a standardized EVAR surveillance program were enrolled from five different vascular centers (Rigshospitalet, Copenhagen, Denmark; Catharina Ziekenhuis, Eindhoven, Netherlands; L'hospital de la Timone, Paris, France; Cleveland Clinic, Cleveland, Ohio; and The Christ Hospital, Cincinnati, Ohio) in four countries. All image acquisitions were performed at the local sites (ie, 2D-US, 3D-US, CTA). Only the 2D-US and CTA readings were performed both locally and centrally. All images were read centrally by the US and CTA core laboratory. Anonymized image data were read in a randomized and blinded manner. RESULTS: The sample used to estimate the accuracy of the 3D-US AAA model and 2D-US included 164 patients and 177 patients, respectively. The Bland-Altman analysis revealed that the mean difference between CTA and 3D-US was -2.43 mm (95% confidence interval [CI], -5.20 to 0.14; P = .07) with a lower and upper limit of agreement of -8.9 mm (95% CI, -9.3 to -8.4) and 2.7 mm (95% CI, 2.3-3.2), respectively. For 2D-US and CTA, the mean difference was -3.62 mm (95% CI, -6.14 to -1.10; P = .002), with a lower and upper limit of agreement of -10.3 mm (95% CI, -10.8 to -9.8) and 2.5 mm (95% CI, 2-2.9), respectively. CONCLUSIONS: The 3D-US AAA model showed no significant difference compared with CTA for measuring the anteroposterior diameter, indicating less bias for 3D-US compared with 2D-US. Thus, 3D-US with AAA model software is a viable modality for anteroposterior diameter assessment for surveillance after EVAR.

Editor's Choice - Detection of Late Complications After Endovascular Abdominal Aortic Aneurysm Repair and Implications for Follow up Based on Retrospective Assessment of a Two Centre Cohort.

OBJECTIVE: Endovascular aortic aneurysm repair (EVAR) is associated with the risk of late complications and mandates follow up. This retrospective study assessed post-EVAR complications in a two centre cohort. The study evaluated the rate of complications presenting with symptoms vs. those detected by imaging follow up. Additionally, the agreement between DUS and CTA in detecting complications was assessed in patients with both. METHODS: All EVAR patients from 1998 to 2012 in two centres were included. Complications were classified based on whether they were symptomatic or detected by imaging, as well as based on imaging detection modality (DUS or CTA). For patients who had undergone DUS and CTA within three months of each other, the kappa coefficient of agreement was assessed. RESULTS: Four hundred and fifty-four patients treated by EVAR were identified. The median follow up time was 5.2 (IQR 2.8-7.6) years. One hundred and eighteen patients (26%) developed 176 complications. One hundred and six (60.2%) of the complications were asymptomatic, and 70 (39.8%) were symptomatic. Two hundred and fifty-three patients had imaging with both modalities within three months of each other; the kappa coefficient for agreement between CTA and DUS for detecting clinically significant complications was 0.91. Regarding CTA as the standard modality, DUS had a sensitivity of 88.8% (95% CI 77.3-95.8%) and a specificity of 99.4% (95% CI 97.1-99.9%). Three of the complications missed by DUS were related to loss of proximal and distal seal, all occurring in patients with short sealing length on first post-operative CT scan. CONCLUSION: Approximately a quarter of the patients developed complications, the majority of which were asymptomatic, underlining the importance of adequate surveillance. There was good agreement between CTA and DUS in detecting complications. Clinically significant complications related to inadequate seal were missed by DUS, suggesting that CTA still plays an important role in EVAR surveillance.

Cutdown Technique is Superior to Fascial Closure for Femoral Artery Access after Elective Endovascular Aortic Repair.

OBJECTIVES: Arterial access closure after endovascular aneurysm repair (EVAR) can be achieved using three different approaches: percutaneous closure devices, surgical exposure and direct suture ("cutdown"), and the less invasive fascial closure technique. The aim of this study was to report on the intra-operative, in hospital, and three month outcome of fascial closure and cutdown, and to determine risk factors for failure. METHODS: The primary outcome was assessed in 439 groins in 225 elective EVAR patients recruited consecutively and prospectively from February 1, 2011 to August 31, 2014. During the study period, fascial closure and cutdown were first and second line closing techniques. Compared with fascial closure, procedures completed with cutdown had lower BMI, thinner subcutaneous tissue of the groin and more complex femoral anatomy. Computed tomographic angiography (CTA) and duplex ultrasound (DUS) of the groin were performed pre-operatively and three months after EVAR. Retrospective review of medical records and CTA were used to determine intra-operative and in hospital outcome, and risk factors for failure. RESULTS: In total, 64%, 33%, and 3% were completed with fascial closure, cutdown, and closure device, respectively. Intra-operative, in hospital, and three month technical success rates of fascial closure vs. cutdown were 91% (283/310 groins) vs. 99% (114/115 groins), 89% (277/310 groins) vs. 99% (114/115 groins), and 89% (275/310 groins) vs. 99% (114/115 groins) (p < .001). Wound complications within three months were infrequent for both methods. No risk factor was significantly associated with failure after fascial closure. CONCLUSION: This study shows that cutdown is superior to fascial closure for femoral artery access after elective EVAR. In acute EVAR, however, fascial closure is still considered to be a good and fast method, and it has been kept in the present authors' armamentarium for this indication.

Efficacy of volumetric analysis of aorta as surveillance tool after EVAR.

OBJECTIVE: Compared to the diameter measurement, volume measurement of the aneurysm can be an alternative option for accurate evaluation. This study was undertaken to analyze the relationship between the diameter and the volume measurement of the aorta after EVAR. METHODS: From January 2012 to December 2016, 82 patients underwent EVAR in our institution. The infrarenal aorta after EVAR was evaluated with regard to maximal aortic diameter (DMAX) and aortic volume. The relationship between the DMAX and the aortic volume measurement after EVAR were analyzed. RESULTS: The rate of enlargement of aortic volume with endoleak over time was 0.02 cm3/month. The rate of enlargement of DMAX with endoleak over time was 0.007 mm/month. The mean rate of enlargement of aortic volume was significantly different from the mean enlargement rate of DMAX (p = 0.02). A ≥12% of increase rate of aortic volume was equivalent to an increase of ≥5 mm in the DMAX after EVAR. Significantly more endoleak occurred in the DMAX-enlargement group than no-enlargement group (100% vs. 26.76%, p < 0.001). Significantly more patients need secondary intervention and treatment of endoleak in the DMAX-enlargement group (p = 0.02 and p < 0.001, respectively). Significantly more endoleak occurred in the aortic volume-enlargement group than no-enlargement group (90.91% vs. 16.67%, p < 0.001). Significantly more patients needed secondary intervention and treatment for endoleak in the aortic volume-enlargement group (p = 0.02 and p < 0.001, respectively). CONCLUSION: Volumetric analysis can predict successful EVAR more accurate than diameter measurement. A ≥12% increase in aortic volume was equivalent to a ≥5 mm increase in aortic diameter.

Patient satisfaction and chronic illness are predictors of postendovascular aneurysm repair surveillance compliance.

OBJECTIVE: Although lifelong surveillance is recommended by the Society for Vascular Surgery for patients undergoing endovascular aneurysm repair (EVAR) reported that compliance with long-term follow-up has been poor. We sought to identify factors that predict compliance with EVAR surveillance through analysis of patient variables and post-EVAR questionnaire results. METHODS: We analyzed 28 patient variables gathered from our computerized registry, patient charts, and phone questionnaires of patients who underwent EVAR between January 1, 2010, and December 31, 2014. These factors included patient demographics, education, postoperative complications, satisfaction with vascular surgery care, transportation mode, distance to our medical center, and living situation. Compliance was defined as a patient who underwent the most recent recommended follow-up surveillance study within the prescribed timeframe. Post-EVAR surveillance protocol consisted of office evaluation and duplex ultrasound examination performed in our accredited noninvasive vascular laboratory at 1 week, 6 months, then annually. Computed tomography angiography was obtained only if duplex ultrasound examination suggested endoleak, sac enlargement of more than 5 mm, or a failing limb. RESULTS: Of 144 patients who underwent EVAR during this time period, 89 patients (62%) were compliant with the most recent recommended follow-up study. One hundred two patients completed the questionnaire or their families did if patients died or were incapacitated. Of those, 80 were compliant with follow-up and 22 were not. Based on the questionnaires of these 102 patients, estimated compliance at 3 years after EVAR was 69.6 ± 6.0% based on Kaplan-Meier analysis. In the compliant vs noncompliant groups, the estimated 3-year survival rate was 93.2 ± 3.4% vs 52.4 ± 12.7%, respectively (P < .001), and the estimated 5-year survival rate was 83.1 ± 6.4% vs 34.4 ± 13.4%, respectively (P < .001), respectively. However, none of the mortalities observed in the noncompliant group were aneurysm related. Adverse neurologic events after EVAR demonstrated a trend predicting noncompliance after 5 years based on multivariate Cox regression analysis (hazard ratio [HR], 2.57; 95% confidence interval [CI], 0.95-6.90; P = .062). Patient dissatisfaction with their vascular surgeon and hospital care predicted noncompliance with recommended postoperative surveillance (HR, 5.0; 95% CI, 1.52-16.7; P = .008). College education or higher was associated with compliance (HR, 0.28; 95% CI, 0.06-1.23; P = .092). No other variables, including postoperative complications or distance from the hospital, predicted follow-up noncompliance. CONCLUSIONS: Patient satisfaction with their vascular surgeon and hospital experience predicted compliance with post-EVAR surveillance regardless of postoperative complications. Noncompliant patients had decreased survival, but mortality and surveillance noncompliance were likely due to disabling chronic disease.

Three-dimensional Ultrasound in the Management of Abdominal Aortic Aneurysms: A Topical Review.

Three-dimensional (3D) ultrasound is an evolving modality that may have numerous applications in the management of abdominal aortic aneurysms. Many vascular specialists will not be familiar with the different ways in which 3D vascular ultrasound data can be acquired nor how potential applications are being explored by researchers. Most of the current literature consists of small series and single-centre experience, although clinical themes such as measurement of abdominal aortic aneurysm volume and surveillance following endovascular repair are emerging. The aim of this topical review is to introduce clinicians to the current concepts of 3D ultrasound, review the current literature, and highlight avenues for further research in this new and exciting field of vascular imaging.

Standardized 2D ultrasound versus 3D/4D ultrasound and image fusion for measurement of aortic aneurysm diameter in follow-up after EVAR.

PURPOSE: To compare standardised 2D ultrasound (US) to the novel ultrasonographic imaging techniques 3D/4D US and image fusion (combined real-time display of B mode and CT scan) for routine measurement of aortic diameter in follow-up after endovascular aortic aneurysm repair (EVAR). METHOD AND MATERIALS: 300 measurements were performed on 20 patients after EVAR by one experienced sonographer (3rd degree of the German society of ultrasound (DEGUM)) with a high-end ultrasound machine and a convex probe (1-5 MHz). An internally standardized scanning protocol of the aortic aneurysm diameter in B mode used a so called leading-edge method. In summary, five different US methods (2D, 3D free-hand, magnetic field tracked 3D - Curefab™, 4D volume sweep, image fusion), each including contrast-enhanced ultrasound (CEUS), were used for measurement of the maximum aortic aneurysm diameter. Standardized 2D sonography was the defined reference standard for statistical analysis. CEUS was used for endoleak detection. RESULTS: Technical success was 100%. In augmented transverse imaging the mean aortic anteroposterior (AP) diameter was 4.0±1.3 cm for 2D US, 4.0±1.2 cm for 3D Curefab™, and 3.9±1.3 cm for 4D US and 4.0±1.2 for image fusion. The mean differences were below 1 mm (0.2-0.9 mm). Concerning estimation of aneurysm growth, agreement was found between 2D, 3D and 4D US in 19 of the 20 patients (95%). Definitive decision could always be made by image fusion. CEUS was combined with all methods and detected two out of the 20 patients (10%) with an endoleak type II. In one case, endoleak feeding arteries remained unclear with 2D CEUS but could be clearly localized by 3D CEUS and image fusion. CONCLUSION: Standardized 2D US allows adequate routine follow-up of maximum aortic aneurysm diameter after EVAR. Image Fusion enables a definitive statement about aneurysm growth without the need for new CT imaging by combining the postoperative CT scan with real-time B mode in a dual image display. 3D/4D CEUS and image fusion can improve endoleak characterization in selected cases but are not mandatory for routine practice.

Duplex Ultrasound versus Computed Tomography for the Postoperative Follow-Up of Endovascular Abdominal Aortic Aneurysm Repair. Where Do We Stand Now?

In the last decade, endovascular aneurysm repair (EVAR) has rapidly developed to be the preferred method for infrarenal abdominal aortic aneurysm repair in patients with suitable anatomy. EVAR offers the advantage of lower perioperative mortality and morbidity but carries the cost of device-related complications such as endoleak, graft migration, graft thrombosis, and structural graft failure. These complications mandate a lifelong surveillance of EVAR patients and their endografts. The purpose of this study is to review and evaluate the safety of color-duplex ultrasound (CDU) as compared with computed tomography (CT), based on the current literature, for post-EVAR surveillance. The post-EVAR follow-up modalities, CDU versus CT, are evaluated questioning three parameters: (1) accuracy of aneurysm size, (2) detection and classification of endoleaks, and (3) detection of stent-graft deformation. Studies comparing CDU with CT scan for investigation of post-EVAR complications have produced mixed results. Further and long-term research is needed to evaluate the efficacy of CDU versus CT, before CDU can be recommended as the primary imaging modality for EVAR surveillance, in place of CT for stable aneurysms.