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BACKGROUND: Thoracoabdominal aortic aneurysms (TAAAs) are a life‐threatening condition which remain difficult to treat. Endovascular and open surgical repair (OSR) provide treatment options for patients, however, due to the lack of clinical trials comparing these, the optimum treatment option is unknown. OBJECTIVES: To assess the effectiveness and safety of endovascular repair versus conventional OSR for the treatment of TAAAs. SEARCH METHODS: The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase, CINAHL and AMED databases and World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers to 26 April 2021. We also searched references of relevant articles retrieved from the electronic search for additional citations. SELECTION CRITERIA: We considered all published and unpublished randomised controlled trials (RCTs) and controlled clinical trials (CCTs) comparing endovascular repair to OSR for TAAAs for inclusion in the review. The main outcomes of interest were prevention of aneurysm rupture (participants without aneurysm rupture up to 5 years from intervention), aneurysm‐related mortality (30 days and 12 months), all‐cause mortality, spinal cord ischaemia (paraplegia, paraparesis), visceral arterial branch compromise causing mesenteric ischaemia or renal failure, and rate of reintervention. DATA COLLECTION AND ANALYSIS: Two review authors independently screened all titles and abstracts identified from the searches to identify those that met the inclusion criteria. We planned to undertake data collection, risk of bias assessment, and analysis in accordance with Cochrane recommendations. We planned to assess the certainty of the evidence using GRADE. MAIN RESULTS: No RCTs or CCTs met the inclusion criteria for this review. AUTHORS' CONCLUSIONS: Due to the lack of RCTs or CCTs, we were unable to determine the safety and effectiveness of endovascular compared to OSR in patients with TAAAs and are unable to provide any evidence on the optimal surgical intervention for this cohort of patients. High‐quality RCTs or CCTs addressing this objective are necessary, however conducting such studies will be logistically and ethically challenging for this life‐threatening disease.

BACKGROUND: Type B aortic dissection can lead to serious and life‐threatening complications such as aortic rupture, stroke, renal failure, and paraplegia, all of which require intervention. Traditionally, these complications have been treated with open surgery. Recently however, endovascular repair has been proposed as an alternative. OBJECTIVES: To assess the effectiveness and safety of thoracic aortic endovascular repair versus open surgical repair for treatment of complicated chronic Type B aortic dissection (CBAD). SEARCH METHODS: The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, CINAHL, and AMED databases, as well as the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers, to 2 August 2021. We searched references of relevant articles retrieved through the electronic search for additional citations. SELECTION CRITERIA: We considered all randomised controlled trials (RCTs) and controlled clinical trials (CCTs) assessing the effects of thoracic aortic endovascular repair (TEVAR) versus open surgical repair (OSR) for treatment of complicated chronic Type B aortic dissection (CBAD). Outcomes of interest were mortality (all‐cause, dissection‐related), neurological sequelae (stroke, spinal cord ischaemia/paresis‐paralysis, vertebral insufficiency), morphological outcomes (false lumen thrombosis, progression of dissection, aortic diameters), acute renal failure, ischaemic symptoms (visceral ischaemia, limb ischaemia), re‐intervention, and health‐related quality of life. DATA COLLECTION AND ANALYSIS: Two review authors independently screened all titles and abstracts identified by the searches to identify those that met the inclusion criteria. From title and abstract screening, we did not identify any trials (RCTs or CCTs) that required full‐text assessment. We planned to undertake data collection and analysis in accordance with recommendations described in the Cochrane Handbook for Systematic Reviews of Interventions. We planned to assess the certainty of evidence using GRADE. MAIN RESULTS: We did not identify any trials (RCTs or CCTs) that met the inclusion criteria for this review. AUTHORS' CONCLUSIONS: Due to lack of RCTs or CCTs investigating the effectiveness and safety of TEVAR compared to OSR for patients with complicated CBAD, we are unable to provide any evidence to inform decision‐making on the optimal intervention for these patients. High‐quality RCTs or CCTs addressing this objective are necessary. However, conducting such studies will be challenging for this life‐threatening disease.

Advancement of subject-specific in-silico medicine requires new imaging protocols tailored to specific anatomical features, paired with new constitutive model development based on structure/function relationships. In this study we develop a new dual-VENC 4D Flow MRI protocol that provides unprecedented spatial and temporal resolution of in-vivo aortic deformation. All previous dual-VENC 4D Flow MRI studies in the literature focus on an isolated segment of the aorta, which fail to capture the full spectrum of aortic heterogeneity that exists along the vessel length. The imaging protocol developed provides high sensitivity to all blood flow velocities throughout the entire cardiac cycle, overcoming the challenge of accurately measuring the highly unsteady non-uniform flow field in the aorta. Cross sectional area change, volumetric flow rate, and compliance are observed to decrease with distance from the heart, while pulse wave velocity is observed to increase. A non-linear aortic lumen pressure-area relationship is observed throughout the aorta, such that a high vessel compliance occurs during diastole, and a low vessel compliance occurs during systole. This suggests that a single value of compliance may not accurately represent vessel behaviour during a cardiac cycle in-vivo. This high-resolution MRI data provides key information on the spatial variation in non-linear aortic compliance which can significantly advance the state-of-the-art of in-silico diagnostic techniques for the human aorta.

This paper, the second of two parts, presents a novel subject-specific in-silico framework in which we uncover the relationship between the spatially varying constituents of the aorta and the non-linear compliance of the vessel during the cardiac cycle uncovered in Part I. In Part II a novel microstructurally motivated constitutive model is developed, and simulations reveal that internal vessel contractility, due to pre-stretched elastin and actively generated smooth muscle stress, must be incorporated, along with collagen strain stiffening, in order to accurately predict the non-linear pressure-area relationship observed in-vivo. Modelling of elastin and smooth muscle contractility allows for the identification of the reference vessel configuration at zero-lumen pressure, in addition to accurately predicting high- and low-compliance regimes under a physiological range of pressures. This modelling approach is also shown to capture the key features of elastin and SMC knockout experiments. The volume fractions of the constituent components of the aortic material model were computed so that the in-silico pressure-area curves accurately predict the corresponding MRI data at each location. Simulations reveal that collagen and smooth muscle volume fractions increase distally, while elastin volume fraction decreases distally, consistent with reported histological data. Furthermore, the strain at which collagen transitions from low to high stiffness is lower in the abdominal aorta, again supporting the histological finding that collagen waviness is lower in this distally. The analyses presented in this paper provides new insights into the heterogeneous structure-function relationship that underlies aortic biomechanics. This novel subject-specific MRI/FEA methodology provides a foundation for personalised in-silico clinical analysis and tailored aortic device development.