Morphology and Hemodynamics in Isolated Common Iliac Artery Aneurysms Impacts Proximal Aortic Remodeling

Elongation of the proximal descending thoracic aorta and associated hemodynamics increase the risk of acute type B aortic dissection

BACKGROUND

Acute type B aortic dissection (ATBAD) is a life-threatening aortic disease. However, little information is available on predicting and understanding of ATBAD.

OBJECTIVE

The study sought to explore the underlying mechanism of ATBAD by analyzing the morphological and hemodynamic characteristics related to aortic length.

METHODS

The length and tortuosity of the segment and the whole aorta in the ATBAD group (n= 163) and control group (n= 120) were measured. A fixed anatomic landmark from the distal of left subclavian artery (LSA) to the superior border of sixth thoracic vertebra was proposed as the proximal descending thoracic aorta (PDTA), and the dimensionless parameter, length ratio, was introduced to eliminate the individual differences. The significant morphological parameters were filtrated and the associations between parameters were investigated using statistical approaches. Furthermore, how aortic morphology influenced ATBAD was explored based on idealized aortic models and hemodynamic-related metrics.

RESULTS

The PDTA length was significantly increased in the ATBAD group compared with the control group and had a strong positive correlation with the whole aortic length (r= 0.89). The length ratio (LR2) and tortuosity (T2) of PDTA in the ATBAD group were significantly increased (0.15 ± 0.02 vs 0.12 ± 0.02 and 1.73 ± 0.48 vs 1.50 ± 0.36; P< 0.001), and LR2 was positive correlation with T2 (r= 0.73). In receiver-operating curve analysis, the area under the curve was 0.835 for LR2 and 0.641 for T2. Low and oscillatory shear (LOS) was positive correlation with LR2, and the elevated LOS occurred in the distal of LSA.

CONCLUSION

Elongation of PDTA is associated with ATBAD, and the length ratio is a novel predictor. Elongated PDTA induced more aggressive hemodynamic forces, and high LOS regions may correspond to the entry tear location. The synergy of the morphological variation and aggressive hemodynamics creates contributory conditions for ATBAD.

Aortic hemodynamic and morphological analysis before and after repair of thoracoabdominal aortic aneurysm using a G-Branch endograft

Background and objective: The G-Branch endograft is a novel multibranched "off-the-shelf" device used to repair thoracoabdominal aortic aneurysms (TAAAs). This report describes the hemodynamic and morphological performance of the G-Branch endograft in a human patient with TAAA. Materials and methods: We retrospectively reviewed the computed tomography angiography scans and clinical data of a woman in whom TAAA was treated using a G-Branch endograft. Patient-specific three-dimensional models were reconstructed, and computational fluid dynamics and morphological and hemodynamic indicators were analyzed before and after implantation of the device. Results: From a morphological perspective, there was an increase in cross-sectional area in the G-Branch endograft and all bridging stent grafts over time. Blood flow was redistributed among the renovisceral arteries, with a decrease in flow rate in the celiac artery and an increase in the left renal artery. Laminar blood flow was smoother and more rapid after implantation of the G-Branch device and remained stable during follow-up. In the bridging stent grafts, flow recirculation zones were found in the bridging zones of the celiac artery and superior mesenteric artery as well as the distal sealing zones of both renal arteries. Furthermore, higher time-averaged wall shear stress and a lower oscillatory index and relative resident time were found in the G-Branch endograft and bridging stent grafts. Quantitative analysis showed obvious reduction in the surface area ratio of the elevated time-averaged wall shear stress area and surface area ratio of the relative resident time after G-branch implantation. Conclusion: The revascularization of branch vessels occurred following G-branch implantation, with improvements arising not only from morphological changes but also from hemodynamic alterations. The long-term performance of the G-Branch endograft needs further investigation and clinical validation.

Effect of aortic bifurcation geometry on pressure and peak wall stress in abdominal aorta: Fluid-structure interaction study

BACKGROUND AND OBJECTIVE

Geometry of aorto-iliac bifurcation may affect pressure and wall stress in aorta and thus potentially serve as a predictor of abdominal aortic aneurysm (AAA), similarly to hypertension.

METHODS

Effect of aorto-iliac bifurcation geometry was investigated via parametric analysis based on two-way weakly coupled fluid-structure interaction simulations. The arterial wall was modelled as isotropic hyperelastic monolayer, and non-Newtonian behaviour was introduced for the fluid. Realistic boundary conditions of the pulsatile blood flow were used on the basis of experiments in literature and their time shift was tailored to the pulse wave velocity in the model to obtain physiological wave shapes. Eighteen idealized and one patient-specific geometries of human aortic tree with common iliac and renal arteries were considered with different angles between abdominal aorta (AA) and both iliac arteries and different area ratios (AR) of iliac and aortic luminal cross sections.

RESULTS

Peak wall stress (PWS) and systolic blood pressure (SBP) were insensitive to the aorto-iliac angles but sensitive to the AR: when AR decreased by 50%, the PWS and SBP increased by up to 18.4% and 18.8%, respectively.

CONCLUSIONS

Lower AR (as a result of the iliac stenosis or aging), rather than the aorto-iliac angles increases the BP in the AA and may be thus a risk factor for the AAA development.

Long-term outcomes of endovascular aortic repair with flared iliac limb endografts in patients with abdominal aortic aneurysm and aneurysmal common iliac arteries

BACKGROUND

The aim of this study was to evaluate the long-term outcomes of endovascular aneurysm repair with flared iliac limb grafts in patients with abdominal aortic aneurysm (AAA) and aneurysmal common iliac arteries (CIAs).

METHODS

This is a multicenter, retrospective, observational cohort study that involves four tertiary referral hospitals between May 1, 2005, and April 30, 2019. Primary outcomes were freedom from aneurysm-related mortality (ARM), and freedom from iliac-related reintervention.

RESULTS

We studied 995 aneurysmal iliac limbs in 795 (85.2%) patients who met the inclusion criteria. Median AAA diameter was 55mm (IQR: 51-60). Early mortality occurred in 3 (0.4%) patients. The median of follow-up time was 52 months (IQR: 26-88). Estimated freedom from ARM was 99±0.002% (95% CI: 99-99.9) at 1 year, and 99±0.004% (95% CI: 97.9-99.6) at 5-years. Chronic obstructive pulmonary disease (HR=6.4, 95% CI: 1.7-24.0, P=0.006), chronic kidney disease (HR=5.5, 95% CI: 1.4-21.9, P=0.016), and the presence of an aneurysmal left CIA (HR=5.3, 95% CI: 1.0.5-27.4, P=0.044) was associated with ARM. There were 42 (7.3%) late iliac-related events (limb occlusion, N.=5; iliac-related endoleaks, N.=37). Estimated freedom from iliac-related reintervention was 98±0.003% (95% CI: 97-99) at 1 year, and 95±0.01% (95% CI: 92.7-96.7) at 5-years, which was associated with an aneurysmal right CIA (HR=2.2, 95% CI: 1.3-3.9; P=0.005), and age ≥78 years (HR=1.9, 95% CI: 1.01-1.3; P=0.039).

CONCLUSIONS

EVAR flared iliac limb grafts showed a high rate of freedom from ARM and a low reintervention rate. Owing to these results, it can be a durable and stable alternative for patients aged >78 years.

Impact of Altered Vena Cava Flow Rates on Right Atrium Flow Characteristics

The right atrium (RA) combines the superior (SVC) and inferior vena cava (IVC) flows. Treatments like extracorporeal membrane oxygenation (ECMO) and hemodialysis by catheter alter IVC/SVC flows. Here we assess how altered IVC/SVC flow contributions impact RA flow. Four healthy volunteers were imaged with CT, reconstructed and combined into a patient-averaged model. Large Eddy Simulations (LES) were performed for a range of IVC/SVC flow contributions (30-70% each, increments of 5%) and common flow metrics were recorded. Model sensitivity to reconstruction domain extent, constant/pulsatile inlets and hematocrit was also assessed. Consistent with literature, a single vortex occupied the central RA across all flowrates with a smaller counter-rotating vortex, not previously reported, in the auricle. Vena cava flow was highly helical. RA turbulent kinetic energy (TKE) (P=0.027) and time-averaged wall shear stress (WSS) (P<0.001) increased with SVC flow. WSS was lower in the auricle (2 Pa, P<0.001). WSS in the vena cava were equal at IVC/SVC =65/35%. The model was highly sensitive to the reconstruction domain with cropped geometries lacking helicity in the vena cavae, altering RA flow. RA flow was not significantly affected by constant inlets or hematocrit. The rotational flow conventionally described in the RA is confirmed however a new, smaller vortex was also recorded in the auricle. When IVC flow dominates, as is normal, TKE in the RA is reduced and WSS in the vena cavae equalize. Significant helicity exists in the vena cava, a result of distal geometry and this geometry appears crucial to accurately simulating RA flow.

Low Shear Stress at Baseline Predicts Expansion and Aneurysm-Related Events in Patients With Abdominal Aortic Aneurysm

BACKGROUND

Low shear stress has been implicated in abdominal aortic aneurysm (AAA) expansion and clinical events. We tested the hypothesis that low shear stress in AAA at baseline is a marker of expansion rate and future aneurysm-related events.

METHODS

Patients were imaged with computed tomography angiography at baseline and followed up every 6 months >24 months with ultrasound measurements of maximum diameter. From baseline computed tomography angiography, we reconstructed 3-dimensional models for automated computational fluid dynamics simulations and computed luminal shear stress. The primary composite end point was aneurysm repair and/or rupture, and the secondary end point was aneurysm expansion rate.

RESULTS

We included 295 patients with median AAA diameter of 49 mm (interquartile range, 43-54 mm) and median follow-up of 914 (interquartile range, 670-1112) days. There were 114 (39%) aneurysm-related events, with 13 AAA ruptures and 98 repairs (one rupture was repaired). Patients with low shear stress (<0.4 Pa) experienced a higher number of aneurysm-related events (44%) compared with medium (0.4-0.6 Pa; 27%) and high (>0.6 Pa; 29%) shear stress groups (P=0.010). This association was independent of known risk factors (adjusted hazard ratio, 1.72 [95% CI, 1.08-2.73]; P=0.023). Low shear stress was also independently associated with AAA expansion rate (β=+0.28 mm/y [95% CI, 0.02-0.53]; P=0.037).

CONCLUSIONS

We show for the first time that low shear stress (<0.4 Pa) at baseline is associated with both AAA expansion and future aneurysm-related events. Aneurysms within the lowest tertile of shear stress, versus those with higher shear stress, were more likely to rupture or reach thresholds for elective repair. Larger prospective validation trials are needed to confirm these findings and translate them into clinical management.

Middle cerebral arterial bifurcation aneurysms are associated with bifurcation angle and high tortuosity

PURPOSE

To investigate the association of middle cerebral artery (MCA) bifurcation aneurysms with bifurcation morphology.

MATERIALS AND METHODS

205 patients were enrolled, including 61 patients with MCA bifurcation aneurysms and 144 non-aneurysmal subjects. Aneurysmal cases were divided into types C (aneurysm neck on extension of the parent artery centerline) and D (deviating neck). The radius of the parent artery M1 (R_P) and bilateral branches (R_S and R_L, respectively), smaller (φ_S) and larger (φ_L) lateral angles, bifurcation angle, and arterial tortuosity from parent vessel to bilateral branches (T_S and T_L, respectively) were analyzed. Logistic regression and receiver operator characteristic (ROC) curve analysis were performed to identify risk factors and predictive values for MCA aneurysm presence and types.

RESULTS

In aneurysmal MCA bifurcations, bifurcating angle, T_S, T_L and R_L were significantly larger (P<0.01), while φ_S was significantly smaller (P<0.001) than those in controls. The bifurcation angle, T_S and LogitP were better morphological parameters for predicting MCA aneurysm presence with the AUC of 0.795, 0.932 and 0.951, respectively. Significant (P<0.05) differences were observed in the bifurcation angle, φ_L, R_P, R_L and T_L between types C and D aneurysmal bifurcations. T_L was an independent factor in discriminating types C from D aneurysms with an AUC of 0.802.

CONCLUSIONS

Bifurcation angle and arterial tortuosity from the parent artery to the branch forming a smaller angle with the parent artery have a higher value in distinguishing MCA aneurysmal from non-aneurysmal ones, and the tortuosity from the parent artery to the contralateral branch is the best indicator for distinguishing types C from D aneurysmal bifurcations.

Proximal False Lumen Thrombosis is Associated with Low False Lumen Pressure and Fewer Complications in Type B Aortic Dissection

BACKGROUND

Improved risk stratification is a key priority for type B aortic dissection (TBAD). Partial false lumen thrombus morphology is an emerging predictor of complications however, partial thrombosis is poorly defined and its evaluation in clinical studies is inconsistent.

PURPOSE

This work aims to characterise hemodynamic pressure in TBAD and determine how pressure relates to false lumen thrombus morphology and clinical events.

METHODS

Retrospective admission computed tomography angiography of 69 patients with acute TBAD was used to construct three-dimensional computational models for simulation of cyclical blood flow and calculation of pressure. Patients were categorised based on false lumen thrombus morphology: minimal; proximal; distal; or extensive thrombosis. Linear regression analysis compared the luminal pressure difference between the true and false lumen for each morphology group. The impact of morphology classification on acute complications within 14 days was studied using logistic regression adjusted for clinical parameters. A survival analysis for adverse aortic events at one-year was also performed using Cox regression.

RESULTS

44 patients experienced acute complications and 45 had an adverse aortic event at one-year. Mean (±standard deviation) age was 62.6 (±12.6) years and 75.4% were male. Compared to patients with minimal thrombosis, those with proximal thrombosis had reduced false lumen pressure by 10.1mmHg (95% CI 4.3-15.9mmHg, p=.001). Individuals that did not experience an acute complication had reduced relative false lumen pressure (-6.35mmHg vs -0.62mmHg, p=.03). Proximal thrombosis was associated with fewer acute complications (OR 0.17, 95% CI 0.04-0.60 p=.01) and one-year adverse aortic events (HR 0.36, 95% CI 0.16-0.80, p=.01).

CONCLUSIONS

Proximal false lumen thrombosis is a marker of reduced false lumen pressure. This may explain how proximal false lumen thrombosis appears protective of acute complications (refractory hypertension or pain, aortic rupture, visceral or limb malperfusion and acute expansion) and adverse aortic events within the first year.

Prediction model of isolated iliac and abdominal aneurysms

OBJECTIVES

We analyse the cardiovascular risk factors in patients undergoing screening for Isolated Iliac Aneurysm (IIA) and Abdominal Aortic Aneurysm (AAA) and propose a logistic regression model to indicate patients at risk of IIA and/or AAA.

METHODS

A screening programme was carried out to identify the presence of aneurysm based on Duplex scan examination. Cardiovascular risk factors information was collected from each subject. A descriptive analysis for the incidence of IIA and AAA stratified by age and sex was carried out to evaluate factors incidence. A logistic regression model was developed to predict the probability of developing an aneurysm based on the observed risk factor levels. A threshold probability of aneurysm risk for a datum patient was also identified to effectively direct screening protocols to patients most at risk.

RESULTS

A cohort of 10 842 patients was evaluated: 1.52% affected by IIA, 2.69% by AAA and 3.90% by at least one. Risk factors analysis showed that: IIA was correlated with cardiological status, diabetes, cardiovascular disease family history, and dyslipidaemia; AAA was correlated with cardiological status, body mass index, hypertension, and dyslipidaemia; diabetes and dyslipidaemia were the most relevant factors with at least one aneurysm. The prediction tool based on the logistic regression and the threshold probability predict the presence of IIA and AAA in 69.7% and 83.8% of cases, under k-fold cross-validation.

CONCLUSIONS

The proposed regression model can represent a valid aid to predict IIA and AAA presence and to select patients to be screened.

Recent Advances in Vascular Imaging

Recent advances in vascular imaging have enabled us to uncover the underlying mechanisms of vascular diseases both ex vivo and in vivo. In the past decade, efforts have been made to establish various methodologies for evaluation of atherosclerotic plaque progression and vascular inflammatory changes in addition to biomarkers and clinical manifestations. Several recent publications in Arteriosclerosis, Thrombosis, and Vascular Biology highlighted the essential roles of in vivo and ex vivo vascular imaging, including magnetic resonance image, computed tomography, positron emission tomography/scintigraphy, ultrasonography, intravascular ultrasound, and most recently, optical coherence tomography, all of which can be used in bench and clinical studies at relative ease. With new methods proposed in several landmark studies, these clinically available imaging modalities will be used in the near future. Moreover, future development of intravascular imaging modalities, such as optical coherence tomography-intravascular ultrasound, optical coherence tomography-near-infrared autofluorescence, polarized-sensitive optical coherence tomography, and micro-optical coherence tomography, are anticipated for better management of patients with cardiovascular disease. In this review article, we will overview recent advances in vascular imaging and ongoing works for future developments.

Computational Hemodynamic Modeling of Arterial Aneurysms: A Mini-Review

Arterial aneurysms are pathological dilations of blood vessels, which can be of clinical concern due to thrombosis, dissection, or rupture. Aneurysms can form throughout the arterial system, including intracranial, thoracic, abdominal, visceral, peripheral, or coronary arteries. Currently, aneurysm diameter and expansion rates are the most commonly used metrics to assess rupture risk. Surgical or endovascular interventions are clinical treatment options, but are invasive and associated with risk for the patient. For aneurysms in locations where thrombosis is the primary concern, diameter is also used to determine the level of therapeutic anticoagulation, a treatment that increases the possibility of internal bleeding. Since simple diameter is often insufficient to reliably determine rupture and thrombosis risk, computational hemodynamic simulations are being developed to help assess when an intervention is warranted. Created from subject-specific data, computational models have the potential to be used to predict growth, dissection, rupture, and thrombus-formation risk based on hemodynamic parameters, including wall shear stress, oscillatory shear index, residence time, and anomalous blood flow patterns. Generally, endothelial damage and flow stagnation within aneurysms can lead to coagulation, inflammation, and the release of proteases, which alter extracellular matrix composition, increasing risk of rupture. In this review, we highlight recent work that investigates aneurysm geometry, model parameter assumptions, and other specific considerations that influence computational aneurysm simulations. By highlighting modeling validation and verification approaches, we hope to inspire future computational efforts aimed at improving our understanding of aneurysm pathology and treatment risk stratification.

Morphology and Computational Fluid Dynamics Support a Novel Classification of Common Iliac Aneurysms

OBJECTIVE

Isolated common iliac artery aneurysms (CIAAs) are uncommon, and evidence concerning their development, progression, and management is weak. The objective was to describe the morphology and haemodynamics of isolated CIAAs in a retrospective study.

METHODS

Initially, a series of 25 isolated CIAAs (15 intact, 10 ruptured) in 23 patients were gathered from multiple centres, reconstructed from computed tomography, and then morphologically classified and analysed with computational fluid dynamics. The morphological classification was applied in a separate, consecutive cohort of 162 patients assessed for elective aorto-iliac intervention, in which 55 patients had intact CIAAs.

RESULTS

In the isolated CIAA cohort, three distinct morphologies were identified: complex (involving a bifurcation); fusiform; and kinked (distal to a sharp bend in the CIA), with mean diameters of 90.3, 48.3, and 31.7 mm, and mean time averaged wall shear stresses of 0.16, 0.31, and 0.71 Pa, respectively (both analysis of variance p values < .001). Kinked cases vs. fusiform cases had less thrombus and favourable haemodynamics similar to the non-aneurysmal contralateral common iliac artery (CIA). Ruptured isolated CIAAs were large (mean diameter 87.5 mm, range 55.5-138.0 mm) and predominantly complex. The mean CIA length for aneurysmal arteries was greatest in kinked cases followed by complex and fusiform (100.8 mm, 91.1 mm, and 80.6 mm, respectively). The morphological classification was readily applicable to a separate elective patient cohort.

CONCLUSION

A new morphological categorisation of CIAAs is proposed. Potentially this is associated with both haemodynamics and clinical course. Further research is required to determine whether the kinked CIAA is protected haemodynamically from aneurysm progression and to establish the wider applicability of the categorisation presented.

Ultrasound Assisted On-Table Management of Type III Endoleak at Endovascular Repair of Isolated Giant Common Iliac Aneurysm

Objectives

This report presents the endovascular treatment of a large isolated common iliac artery aneurysm, focusing on the use of on table ultrasonography to characterise and treat an early endoleak that could not be defined by angiography alone.

Report

A 58 year old man presented with an asymptomatic, large (13cm) left common iliac artery aneurysm (LCIAA) whilst being investigated for change in bowel habit. This was treated successfully via a percutaneous approach using left internal iliac embolisation followed by endovascular aneurysm repair (EVAR) with deployment of an aorto-uni-iliac converter system from the LCIA origin to the external iliac artery. A non-characterised endoleak at the end of the procedure was shown to be a type IIIb endoleak by application of immediate on table ultrasonography, allowing immediate supplementary targeted stent graft deployment to cover the leaking segment.

Discussion

The patient was discharged uneventfully and will remain on follow up. On table ultrasonography allowed both localisation and characterisation of an immediate intra-procedural endoleak and confirmed cessation of the endoleak with supplementary stent grafting and thrombosis within the sac.

Conclusions

Isolated CIAA is rare, and endovascular therapy is appropriate for them, given that open surgery, whilst feasible, carries a high morbidity and mortality risk. Application of on-table ultrasound allows definition and targeted treatment of endoleaks, reducing the need for further intervention at a later stage, and thus also reducing the risk of continued pressurisation of the large sac post-EVAR till the next surveillance episode.

•

Isolated common iliac artery aneurysms (CIAAs) are very rare.

•

They can be asymptomatic but have a high risk of rupture.

•

Open repair is high risk and associated with high morbidity/mortality.

•

This paper highlights successful endovascular repair of a giant isolated CIAA.

•

On table ultrasound helps immediately to characterise and treat endoleaks at EVAR.