Heterogeneity in the Segmental Development of the Aortic Tree: Impact on Management of Genetically Triggered Aortic Aneurysms

Marfan and Loeys-Dietz aortic phenotype: A potential tool for diagnosis and management

Objective

In heritable aortic diseases, different vascular involvement may occur with potential variable implications in aortic dilation/dissection risk. This study aimed to analyze the aortic anatomy of individuals with Marfan syndrome and Loeys-Dietz syndrome to identify possible morphological differences.

Methods

Computed tomography and magnetic resonance imaging of the thoracoabdominal aorta from the proximal supra-aortic vessels to the femoral bifurcation level of 114 patients with Marfan and Loeys-Dietz syndromes and 20 matched control subjects were examined. Aortic diameters, areas, length, and tortuosity were measured in different aortic segments using specific vessel analysis software.

Results

Patients with Marfan syndrome showed a higher prevalence of ascending aorta and aortic root dilation (P = .011), larger and longer aortic roots (P = .013) with pear-shaped phenotype, larger isthmus/descending aorta diameter ratio (P = .015), and larger suprarenal aorta and iliac arteries. Patients with Loeys-Dietz syndrome showed longer indexed segments and a significantly longer arch (P = .006) with type 2/3 arch prevalence (P = .097). Measurement ratios analysis provided cut-off values (aortic root to ascending aorta length/aortic root diameter, aortic root/sinotubular junction, aortic root/ascending aorta diameter) differentiating patients with Marfan syndrome from patients with Loeys-Dietz syndrome, even in the early stage of the disease.

Conclusions

Both syndromes show peculiar anatomic patterns at different aortic levels irrespective of aortic dilation and disease severity. These features may represent the expression of different genetic mutations on aortic development, with a potential impact on prognosis and possibly contributing to better management of the diseases. The systematic adoption of whole body imaging with magnetic resonance or computed tomography should always be considered, because they allow a complete vascular assessment with practical indicators of differential diagnosis.

Ex vivo biaxial load testing analysis of aortic biomechanics demonstrates variation in elastic energy distribution across the aortic zone zero

OBJECTIVES

We hypothesized that tissue characteristics vary significantly along zone zero, which may be reflected by regional differences in stored elastic energy. Our objectives were to (1) characterize the regional variation in stored elastic energy within tissues of the aortic zone zero and (2) identify the association between this variation and patient characteristics.

METHODS

From February 2018 to January 2021, 123 aortic tissue samples were obtained from the aortic root and proximal and distal ascending aortas of 65 adults undergoing elective ascending aorta replacement. Biaxial biomechanics testing was performed to obtain tissue elastic energy at the inflection point and compared with patient demographics and preoperative computed tomography imaging. Coefficient models were fit using B-spline to interrogate the relationship among elastic energy, region, and patient characteristics.

RESULTS

Mean elastic energy at inflection point was 24.3 ± 15.6 kJ/m3. Elastic energy increased significantly between the root and proximal, and root and distal ascending aorta and decreased with increasing age. Differences due to history of connective tissue disorder and bicuspid aortic valve were significant but diminished when controlled for other patient characteristics. Among covariates, age and region were found to be the most important predictors for elastic energy.

CONCLUSIONS

Aortic tissue biomechanical metrics varied across regions and with patient characteristics within the aortic zone zero. Assessment of endovascular outcomes in the ascending aorta must closely consider the region of deployment and variable tissue qualities along the length of the landing zone. Regional variation in tissue characteristics should be incorporated into existing patient-specific models of aortic mechanics.

Murine model of elastase-induced proximal thoracic aortic aneurysm through a midline incision in the anterior neck

Objective

This study was performed to develop a murine model of elastase-induced proximal thoracic aortic aneurysms (PTAAs).

Methods

The ascending thoracic aorta and aortic arch of adult C57BL/6J male mice were exposed through a midline incision in the anterior neck, followed by peri-adventitial elastase or saline application. The maximal ascending thoracic aorta diameter was measured with high-resolution micro-ultrasound. Twenty-eight days after the operation, the aortas were harvested and analyzed by histopathological examination and qualitative polymerase chain reaction to determine the basic characteristics of the aneurysmal lesions.

Results

Fourteen days after the operation, the dilation rate (mean ± standard error) in the 10-min elastase application group (n = 10, 71.44 ± 10.45%) or 5-min application group (n = 9, 42.67 ± 3.72%) were significantly higher than that in the saline application group (n = 9, 7.37 ± 0.94%, P < 0.001 for both). Histopathological examination revealed aortic wall thickening, degradation of elastin fibers, loss of smooth muscle cells, more vasa vasorum, enhanced extracellular matrix degradation, augmented collagen synthesis, upregulated apoptosis and proliferation capacity of smooth muscle cells, and increased macrophages and CD4⁺ T cells infiltration in the PTAA lesions. Qualitative analyses indicated higher expression of the proinflammatory markers, matrix metalloproteinase-2 and -9 as well as Collagen III, Collagen I in the PTAAs than in the controls.

Conclusion

We established a novel in vivo mouse model of PTAAs through a midline incision in the anterior neck by peri-adventitial application of elastase. This model may facilitate research into the pathogenesis of PTAA formation and the treatment strategy for this devastating disease.

Different ascending aortic phenotypes with similar mutations in 2 patients with Loeys-Dietz syndrome type 2

Our goal was to present 2 infants with confirmed Loeys-Dietz syndrome. The missense mutations in exon 7 of the TGFBR2 gene are only 5 codons apart (c.1597T>C and c.1582C>G). Phenotypically, the aneurysms of the ascending aorta were restricted to different segments of the aorta: the suprajunctional segment in 1 patient and the aortic root in another. These cases highlight the complexity of signaling pathways and gene expression in the pathogenesis of aortic aneurysms.

Geotemporospatial and causal inference epidemiological analysis of US survey and overview of cannabis, cannabidiol and cannabinoid genotoxicity in relation to congenital anomalies 2001–2015

Background

Cannabinoids including cannabidiol have recognized genotoxic activities but their significance has not been studied broadly epidemiologically across the teratological spectrum. We examined these issues including contextual space-time relationships and formal causal inferential analysis in USA.

Methods

State congenital anomaly (CA) rate (CAR) data was taken from the annual reports of the National Birth Defects Prevention Network 2001–2005 to 2011–2015. Substance abuse rates were from the National Survey of Drug Use and Health a nationally representative longitudinal survey of the non-institutionalized US population with 74.1% response rate. Drugs examined were cigarettes, monthly and binge alcohol, monthly cannabis and analgesic and cocaine abuse. Early termination of pregnancy for abortion (ETOPFA) rates were taken from the published literature. Cannabinoid concentrations were from Drug Enforcement Agency. Ethnicity and income data were from the US Census Bureau. Inverse probability weighted (IPW) regressions and geotemporospatial regressions conducted for selected CAs.

Results

Data on 18,328,529 births from an aggregated population of 2,377,483,589 for mid-year analyses 2005–2013 comprehending 12,611 CARs for 62 CAs was assembled and ETOPFA-corrected (ETOPFACAR) where appropriate. E-Values for ETOPFACARs by substance trends were elevated for THC (40 CAs), cannabis (35 CAs), tobacco (11 CAs), cannabidiol (8 CAs), monthly alcohol (5 CAs) and binge alcohol (2 CAs) with minimum E-Values descending from 16.55, 1.55x107, 555.10, 7.53x1019, 9.30 and 32.98. Cardiovascular, gastrointestinal, chromosomal, limb reductions, urinary, face and body wall CAs particularly affected. Highest v. lowest substance use quintile CAR prevalence ratios 2.84 (95%C.I. 2.44, 3.31), 4.85 (4.08, 5.77) and 1.92 (1.63, 2.27) and attributable fraction in exposed 0.28 (0.27, 0.28), 0.57 (0.51, 0.62) and 0.47 (0.38, 0.55) for tobacco, cannabis and cannabidiol. Small intestinal stenosis or atresia and obstructive genitourinary defect were studied in detail in lagged IPW pseudo-randomized causal regressions and spatiotemporal models confirmed the causal role of cannabinoids. Spatiotemporal predictive modelling demonstrated strongly sigmoidal non-linear cannabidiol dose-response power-function relationships (P = 2.83x10−60 and 1.61x10−71 respectively).

Conclusions

Data implicate cannabinoids including cannabidiol in a diverse spectrum of heritable CAs. Sigmoidal non-linear dose-response relationships are of grave concern.

These transgenerational genotoxic, epigenotoxic, chromosomal-toxic putatively causal teratogenic effects strongly indicate tight restrictions on community cannabinoid penetration.

Nitric oxide in the Marfan vasculature: Friend or foe?

Marfan syndrome (MFS) is a connective tissue disorder caused by mutations in the FBN1 gene, which encodes fibrillin-1, a protein essential for the formation and stabilization of elastic fibers as well as signaling homeostasis. Progressive aortic root widening is the most serious manifestation of MFS as it can lead to aortic dissection, aneurysm formation and rupture. However, despite their ability to decrease the hemodynamic stress the aorta is subjected to, anti-hypertensive medications often lead to underwhelming reductions in the rate of aortic root dilation, which illustrates how fragmental our understanding of MFS-associated aortic remodeling is. This manuscript summarizes recent evidence that document nitric oxide (NO) synthase (NOS)-related changes to the vasculature during the pathogenesis of MFS and how they result in a unique state of vascular dysfunction that likely plays a causal role in the aortic root widening process. We also review how clinic-approved and experimental therapies as well lifestyle approaches may promote aortic root stability by correcting NO homeostasis, which if properly optimized may improve outcomes in this population afflicted by a notoriously refractory type of aortopathy.

A Dual-VENC Four-Dimensional Flow MRI Framework for Analysis of Subject-Specific Heterogeneous Nonlinear Vessel Deformation

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-velocity encoding coefficient (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 nonuniform 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 (PWV) is observed to increase. A nonlinear 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 behavior during a cardiac cycle in vivo. This high-resolution MRI data provide key information on the spatial variation in nonlinear aortic compliance, which can significantly advance the state-of-the-art of in-silico diagnostic techniques for the human aorta.

A review of thoracic aortic aneurysm disease

Aortic diseases may be diagnosed after a long period of subclinical development or they may have an acute presentation. Acute aortic syndrome is often the first sign of the disease, which needs rapid diagnosis and decision making to reduce the extremely poor prognosis. Aortic dilatation is a well-recognised risk factor for acute events and can occur as a result of trauma, infection, or, most commonly, from an intrinsic abnormality in the elastin and collagen components of the aortic wall. Over the years it has become clear that a few monogenic syndromes are strongly associated with aneurysms and often dictate a severe presentation in younger patients while the vast majority have a multifactorial pathogenesis. Conventional cardiovascular risk factors and ageing play an important role. Management strategy is based on prevention consisting of regular follow-up with cross-sectional imaging, chemoprophylaxis of further dilatation with drugs proved to slow down the disease progression and preventative surgery when dimension exceeds internationally recognised cut-off values for aortic diameters and the risk of rupture/dissection is therefore deemed very high.

Thoracic aortic aneurysm in patients with loss of function Filamin A mutations: Clinical characterization, genetics, and recommendations

The frequency and gender distribution of thoracic aortic aneurysm as a cardiovascular manifestation of loss-of-function (LOF) X-linked FilaminA (FLNA) mutations are not known. Furthermore, there is very limited cardiovascular morbidity or mortality data in children and adults. We analyzed cardiac data on the largest series of 114 patients with LOF FLNA mutations, both children and adults, with periventricular nodular heterotopia (PVNH), including 48 study patients and 66 literature patients, median age of 22.0 years (88 F, 26 M, range: 0-71 years), with 75 FLNA mutations observed in 80 families. Most (64.9%) subjects had a cardiac anomaly or vascular abnormality (80.8% of males and 60.2% of females). Thoracic aortic aneurysms or dilatation (TAA) were found in 18.4% (n = 21), and were associated with other structural cardiac malformations in 57.1% of patients, most commonly patent ductus arteriosus (PDA) and valvular abnormalities. TAA most frequently involved the aortic root and ascending aorta, and sinus of Valsalva aneurysms were present in one third of TAA patients. Six TAA patients (28.5%) required surgery (median age 37 yrs, range 13-41 yrs). TAA with its associated complications was also the only recorded cause of premature, non-accidental mortality in adults (2 M, 2 F). Two adult patients (1 F, 1 M, median 38.5 yrs), died of spontaneous aortic rupture at aortic dimensions smaller than current recommendations for surgery for other aortopathies. Data from this largest series of LOF FLNA mutation patients underscore the importance of serial follow-up to identify and manage these potentially devastating cardiovascular complications.

Differences in manifestations of Marfan syndrome, Ehlers-Danlos syndrome, and Loeys-Dietz syndrome

Many different heritable connective tissue disorders (HCTD) have been described over the past decades. These syndromes often affect the connective tissue of various organ systems, including heart, blood vessels, skin, joints, bone, eyes, and lungs. The discovery of these HCTD was followed by the identification of mutations in a wide range of genes encoding structural proteins, modifying enzymes, or components of the TGFβ-signaling pathway. Three typical examples of HCTD are Marfan syndrome (MFS), Ehlers-Danlos syndrome (EDS), and Loeys-Dietz syndrome (LDS). These syndromes show some degree of phenotypical overlap of cardiovascular, skeletal, and cutaneous features. MFS is typically characterized by cardiovascular, ocular, and skeletal manifestations and is caused by heterozygous mutations in FBN1, coding for the extracellular matrix (ECM) protein fibrillin-1. The most common cardiovascular phenotype involves aortic aneurysm and dissection at the sinuses of Valsalva. LDS is caused by mutations in TGBR1/2, SMAD2/3, or TGFB2/3, all coding for components of the TGFβ-signaling pathway. LDS can be distinguished from MFS by the unique presence of hypertelorism, bifid uvula or cleft palate, and widespread aortic and arterial aneurysm and tortuosity. Compared to MFS, LDS cardiovascular manifestations tend to be more severe. In contrast, no association is reported between LDS and the presence of ectopia lentis, a key distinguishing feature of MFS. Overlapping features between MFS and LDS include scoliosis, pes planus, anterior chest deformity, spontaneous pneumothorax, and dural ectasia. EDS refers to a group of clinically and genetically heterogeneous connective tissue disorders and all subtypes are characterized by variable abnormalities of skin, ligaments and joints, blood vessels, and internal organs. Typical presenting features include joint hypermobility, skin hyperextensibility, and tissue fragility. Up to one quarter of the EDS patients show aortic aneurysmal disease. The latest EDS nosology distinguishes 13 subtypes. Many phenotypic features show overlap between the different subtypes, which makes the clinical diagnosis rather difficult and highlights the importance of molecular diagnostic confirmation.

Recent progress in understanding the natural and clinical histories of the Marfan syndrome

Over the past 4 decades, remarkable progress in understanding the cause, pathogenesis, and management of the MFS has led to an increase in life expectancy to near normal for most patients. Accompanying this increased life span has been the emergence of previously rare or unanticipated clinical problems. Despite much more detailed knowledge of the molecular, cellular, and tissue effects of a mutation in FBN1, targeted, effective therapy remains elusive. Until such precision medicine takes hold, management will depend on early diagnosis, regular scrutiny by imaging, chronic β-blockade, and perhaps ARBs, and prophylactic cardiothoracic surgery. Without question, MFS will remain a fertile subject for basic, translational, and clinical research for the foreseeable future.