Ascending aorta curvature and flow displacement are associated with accelerated aortic growth at long-term follow-up: A MRI study in Marfan and thoracic aortic aneurysm patients

Regional differences in biomechanical properties of the ascending aorta in aneurysmal and normal aortas

OBJECTIVE

To understand regional biomechanical differences within the healthy and aneurysmal ascending aorta.

METHODS

Aortic tissue was collected from the inner (IC) and outer (OC) curvature of aneurysms excised during elective surgery (n = 102) and normal aortas from organ donors (n = 25). Biaxial tensile testing and peel testing were performed to derive a comprehensive set of biomechanical parameters.

RESULTS

In normal aortas, the OC exhibited greater energy loss, lower tangent modulus at low strain, and lower transition zone stress compared to the IC. In aneurysmal aortas, similar findings were observed. All IC and OC biomechanical parameters were linearly correlated in aneurysmal aortas, including delamination strength. Healthy and aneurysmal aortas exhibited similar degrees of difference between IC and OC for most biomechanical properties. Aneurysms with greater biomechanical differences between IC and OC trended toward being older (p = 0.096) with larger diameters (p = 0.051) compared to other aneurysms. Asymmetric bulging exhibited lower stiffness and transition zone stress in the OC, but no difference in delamination strength between regions.

CONCLUSIONS

Regional biomechanical differences exist in aneurysms of the ascending aorta to a similar extent as in healthy aortas. In aneurysms, biomechanical properties of the IC and OC regions were strongly linearly correlated, suggesting that the regional differences in ascending aortic biomechanics are less important than the large biomechanical variability that exists between patients.

Thoracic Aortic Aneurysm Growth Rates and Predicting Factors: A Systematic Review and Meta-Analysis

BACKGROUND

Thoracic aortic aneurysm (TAA) is an indolent, potentially fatal disease, which progresses at variable rates that are influenced by pathogenesis and patient characteristics. We conducted a systematic review and meta-analysis to synthesize the current evidence on growth rate (GR) and predictive factors among patients with syndromic and nonsyndromic heritable thoracic aortic disease, bicuspid aortic valve, and sporadic TAA.

METHODS AND RESULTS

Online databases were searched for studies that reported aortic growth on adult patients with asymptomatic TAA. Pooled GRs were calculated for 3 different TAA groups: syndromic heritable thoracic aortic disease, bicuspid aortic valve, and sporadic TAA. The search yielded 6297 studies, of which 85 were included in the systematic review, and 55 in the meta-analysis of growth rate (10 syndromic heritable thoracic aortic disease, 31 bicuspid aortic valve, and 34 sporadic subgroups). Mean observed TAA GR was 0.25 mm/y (95% CI, -0.18 to 0.68) in Turner syndrome, 0.45 mm/y (95% CI, 0.00-0.90) in Marfan syndrome, and 0.81 mm/y (95% CI, -0.46 to 2.08) in Loeys-Dietz syndrome. The mean observed GR in patients with bicuspid aortic valve before aortic valve surgery was 0.37 mm/y (95% CI, 0.29-0.46), compared with 0.18 mm/y (95% CI, 0.14-0.33) in postsurgical studies. Mean observed GR in sporadic ascending TAA was 0.33 mm/y (95% CI, 0.13-0.52) and 2.71 mm/y (95% CI, 0.53-4.88) in descending TAA.

CONCLUSIONS

Considering all pathogeneses, ascending TAAs typically grow at 0.25 to 1 mm/y, and thus annual surveillance is likely too frequent to detect growth in most patients. Studies vary widely in populations, methodology, and outcomes, with few high-quality longitudinal studies and no predictors of aortic GR.

Ascending aorta over-angulation is a risk factor for acute type A aortic dissection: evidence from advanced finite element simulations

OBJECTIVES

To assess whether ascending aorta over-angulation, a morphological feature recently found to be associated with acute type A aortic dissection, precedes dissection and how it affects wall stress distribution.

METHODS

A baseline finite element model, previously created by a neural network tool from end-diastolic computed tomography angiography measurements in 124 healthy subjects, was modified to simulate the over-angulation accompanying aortic elongation, obtaining paradigmatic models with different ascending angulations (ascending-arch angle 145°-110°). The models were discretized and embedded in a deformable continuum representing surrounding tissues, aortic wall anisotropy and nonlinearity were accounted for, pre-tensioning at diastolic pressures was applied and peak systolic stresses were computed. Then, from 15 patients' pre-dissection geometries, patient-specific finite element models of pre-dissection aorta were created through the same framework. The sites of maximum longitudinal stress were compared with the respective sites of dissection entry tear in post-dissection imaging.

RESULTS

Paradigmatic models showed that progressive narrowing of the ascending-arch angle was associated with increasing longitudinal stress (becoming significant for angles <130°), whereas the impact on circumferential stress was less consistent. In pre-dissection patient-specific models, the ascending-arch angle was narrowed (113°±11°), and the region of peak longitudinal stresses corresponded to the entry tear location in the respective post-dissection computed tomography angiography.

CONCLUSIONS

This study strongly supports the hypothesis that the ascending-arch angle, as quantifier of aorta over-angulation, can be a good predictor of aortic dissection, since its narrowing below 130° increases longitudinal wall stress, and the dissection entry tears develop in the aortic wall in areas of highest longitudinal stress.

The future of cardiovascular magnetic resonance imaging in thoracic aortopathy: blueprint for the paradigm shift to improve management

Thoracic aortopathies result in aneurysmal expansion of the aorta that can lead to rapidly fatal aortic dissection or rupture. Despite the availability of abundant non-invasive imaging tools, the greatest contemporary challenge in the management of thoracic aortic aneurysm (TAA) is the lack of reliable metrics for risk stratification, with absolute aortic diameter, growth rate, and syndromic factors remaining the primary determinants by which prophylactic surgical intervention is adjudged. Advanced cardiovascular magnetic resonance (CMR) techniques present a potential key to unlocking insights into TAA that could guide disease surveillance and surgical intervention. CMR has the capacity to encapsulate the aorta as a complex biomechanical structure, permitting the determination of aortic volume, morphology, composition, distensibility, and fluid dynamics in a time-efficient manner. Nevertheless, current standard-of-care imaging protocols do not harness its full capacity. This state-of-the-art review explores the emerging role of CMR in the assessment of TAA and presents a blueprint for the required paradigm shift away from aortic size as the sole metric for risk-stratifying TAA.

Growth rates in non-syndromic aneurysms of the ascending aorta: a systematic review

The maximum aortic diameter is the main risk predictor for type A acute aortic syndromes and understanding the growth rate of ascending thoracic aortic aneurysms (aTAAs) is pivotal for risk assessment and stratification for pre-emptive aortic surgery. Prevailing guidelines recommend serial imaging of aTAA patients until the thresholds for prophylactic surgery are met. Based on early landmark studies, it was thought that the growth rate of aTAAs is substantially higher than that of the normal-sized aorta. However, more recent studies have reported that aTAA growth is generally slow, questioning the need for frequent imaging during follow-up. The current systematic review provides an overview of studies reporting annual diameter growth rates of non-syndromic aTAAs and explains differences in findings between early and recent studies.

Computer-aided shape features extraction and regression models for predicting the ascending aortic aneurysm growth rate

OBJECTIVE

ascending aortic aneurysm growth prediction is still challenging in clinics. In this study, we evaluate and compare the ability of local and global shape features to predict the ascending aortic aneurysm growth.

MATERIAL AND METHODS

70 patients with aneurysm, for which two 3D acquisitions were available, are included. Following segmentation, three local shape features are computed: (1) the ratio between maximum diameter and length of the ascending aorta centerline, (2) the ratio between the length of external and internal lines on the ascending aorta and (3) the tortuosity of the ascending tract. By exploiting longitudinal data, the aneurysm growth rate is derived. Using radial basis function mesh morphing, iso-topological surface meshes are created. Statistical shape analysis is performed through unsupervised principal component analysis (PCA) and supervised partial least squares (PLS). Two types of global shape features are identified: three PCA-derived and three PLS-based shape modes. Three regression models are set for growth prediction: two based on gaussian support vector machine using local and PCA-derived global shape features; the third is a PLS linear regression model based on the related global shape features. The prediction results are assessed and the aortic shapes most prone to growth are identified.

RESULTS

the prediction root mean square error from leave-one-out cross-validation is: 0.112 mm/month, 0.083 mm/month and 0.066 mm/month for local, PCA-based and PLS-derived shape features, respectively. Aneurysms close to the root with a large initial diameter report faster growth.

CONCLUSION

global shape features might provide an important contribution for predicting the aneurysm growth.

Endothelial dysfunction in Marfan syndrome mice is restored by resveratrol

Patients with Marfan syndrome (MFS) develop thoracic aortic aneurysms as the aorta presents excessive elastin breaks, fibrosis, and vascular smooth muscle cell (vSMC) death due to mutations in the FBN1 gene. Despite elaborate vSMC to aortic endothelial cell (EC) signaling, the contribution of ECs to the development of aortic pathology remains largely unresolved. The aim of this study is to investigate the EC properties in Fbn1C1041G/+ MFS mice. Using en face immunofluorescence confocal microscopy, we showed that EC alignment with blood flow was reduced, EC roundness was increased, individual EC surface area was larger, and EC junctional linearity was decreased in aortae of Fbn1C1041G/+ MFS mice. This modified EC phenotype was most prominent in the ascending aorta and occurred before aortic dilatation. To reverse EC morphology, we performed treatment with resveratrol. This restored EC blood flow alignment, junctional linearity, phospho-eNOS expression, and improved the structural integrity of the internal elastic lamina of Fbn1C1041G/+ mice. In conclusion, these experiments identify the involvement of ECs and underlying internal elastic lamina in MFS aortic pathology, which could act as potential target for future MFS pharmacotherapies.

4D Flow MRI in Ascending Aortic Aneurysms: Reproducibility of Hemodynamic Parameters

(1) Background: Aorta hemodynamics have been associated with aortic remodeling, but the reproducibility of its assessment has been evaluated marginally in patients with thoracic aortic aneurysm (TAA). The current study evaluated intra- and interobserver reproducibility of 4D flow MRI-derived hemodynamic parameters (normalized flow displacement, flow jet angle, wall shear stress (WSS) magnitude, axial WSS, circumferential WSS, WSS angle, vorticity, helicity, and local normalized helicity (LNH)) in TAA patients; (2) Methods: The thoracic aorta of 20 patients was semi-automatically segmented on 4D flow MRI data in 5 systolic phases by 3 different observers. Each time-dependent segmentation was manually improved and partitioned into six anatomical segments. The hemodynamic parameters were quantified per phase and segment. The coefficient of variation (COV) and intraclass correlation coefficient (ICC) were calculated; (3) Results: A total of 2400 lumen segments were analyzed. The mean aneurysm diameter was 50.8 ± 2.7 mm. The intra- and interobserver analysis demonstrated a good reproducibility (COV = 16–30% and ICC = 0.84–0.94) for normalized flow displacement and jet angle, a very good-to-excellent reproducibility (COV = 3–26% and ICC = 0.87–1.00) for all WSS components, helicity and LNH, and an excellent reproducibility (COV = 3–10% and ICC = 0.96–1.00) for vorticity; (4) Conclusion: 4D flow MRI-derived hemodynamic parameters are reproducible within the thoracic aorta in TAA patients.