Are aortic biomechanical properties early markers of dilatation in patients with Marfan syndrome? A systematic review and meta-analysis

Although tissue stiffness is known to play an important role in aortic dilatation, the current guidelines for offering preventative surgery in patients with Marfan syndrome rely solely on the aortic diameter. In this systematic review and meta-analysis, we analyze and compare literature on in vivo aortic stiffness measures in Marfan patients. Our aim is to assess the potential of these measurements as early indicators of aortic dilatation. Following the PRISMA guidelines, we collected literature on diameter and three in vivo stiffness measures: Pulse wave velocity (PWV), β -stiffness index (SI) and distensibility, at five different aortic locations in patients with Marfan syndrome. Results were reviewed and compared against each other. For meta-analysis, an augmented dataset was created by combining data from the literature. Regression with respect to age and statistical comparisons were performed. Thirty articles reporting data from 1925 patients with Marfan and 836 patients without Marfan were reviewed. PWV was found to be higher in Marfan, but only in dilated aortas. Distensibility was found to be lower even in non-dilated aortas, and its decrease was associated with higher chances of developing aortic dilatation. β -SI was higher in Marfan patients and was positively correlated with the rate of aortic dilatation, emphasizing its role as a valuable indicator. In our meta-analysis, all stiffness measures showed a significant variation with age. Distensibility and β -stiffness index were different in Marfan patients at all locations, and the difference was more pronounced after accounting for age-related variation. From the literature, β -SI and distensibility emerge as the best predictors of future aortic dilatation. Our meta-analysis quantifies age-related changes in aortic stiffness and highlights the importance of accounting for age in comparing these measurements. Missing diameter values in the literature limited our analysis. Further investigation of criteria combining stiffness and diameter is recommended to better assist clinical decisions for prophylactic surgery.

Impact of Genotype-Phenotype Interactions on Cardiovascular Function in Paediatric Loeys-Dietz Syndrome

Background

The relationship between genotype and phenotypical vascular and cardiac properties in paediatric Loeys-Dietz syndrome (LDS) patients are not well characterized. This study explores the phenotypical differences in aortic properties and cardiac structural and functional parameters between paediatric LDS patients with TGFBR1 and TGFBR2 mutations.

Methods

We included 32 LDS patients with either TGFBR1 (n = 17) or TGFBR2 (n = 15) mutations. Echocardiographic data included aortic dimensions, distensibility, strain, and stiffness at the level of the annulus, sinuses of Valsalva, sinotubular junction, ascending aorta, and descending aorta. Parameters for left ventricular size and function were also recorded.

Results

Demographics were similar between the groups. Patients with TGFBR2 were more likely to have undergone aortic surgery (47% vs 12%, P = 0.057) and use angiotensin receptor blockers (93% vs 47%, P = 0.015). Aortic z scores were significantly larger in the TGFBR2 group at the level of the aortic valve annulus (P = 0.007), sinuses of Valsalva (P = 0.001), sinotubular junction (P = 0.001), and ascending aorta (P = 0.054). Patients with TGFBR2 also had significantly lower aortic distensibility and strain coupled with higher stiffness index at the level of the annulus, sinotubular junction, and ascending aorta. Parameters for the descending aorta, cardiac morphology, and cardiac function were similar between the groups.

Conclusions

Paediatric LDS patients with TGFBR2 present with more severe cardiovascular phenotypes than patients with TGFBR1 with larger aortic dimensions and increased aortic stiffness. Our findings suggest that genotypes should be taken into consideration in the clinical management of paediatric LDS patients.

Echogenomics: Echocardiography in Heritable Aortopathies

PURPOSE OF REVIEW

The aim of this article is to review the current echocardiographic considerations in the diagnosis and monitoring of patients with inherited aortopathies.

RECENT FINDINGS

Aortic dilation is a key feature in heritable aortopathies, and dissection is a leading cause of morbidity and mortality. New genetic and histopathologic findings are helpful in better understanding these conditions. Non-invasive imaging modalities, including echocardiogram, computerized tomography, and magnetic resonance imaging, are essential in monitoring these patients, as well as providing new prognostic factors of arterial stiffness that may help with risk stratification in the future. Diagnosis of heritable aortopathies should be considered with identification of aortic root dilation, particularly in children and young adults, or when there is a family history of aortic disease. Recent adult consensus guidelines highlight the importance of underlying genotype and phenotypic features when considering prophylactic surgical intervention. There are currently no consensus pediatric guidelines.

A hiPSC-derived lineage-specific vascular smooth muscle cell-on-a-chip identifies aortic heterogeneity across segments

Aortic aneurysm (AA), a potentially lethal condition with the characteristic of aortic dilatation, can only be treated by surgical or endovascular procedures. The underlying mechanisms of AA are unclear and early preventive treatment is still insufficient due to segmental aortic heterogeneity and the limitations of current disease models. Here, we firstly established a comprehensive lineage-specific vascular smooth muscle cell (SMC)-on-a-chip model using human induced pluripotent stem cells to yield cell lineages representing different segments of the aorta and tested the constructed organ-on-a-chip model under various tensile stress conditions. Bulk RNA sequencing, RT-qPCR, immunofluorescence, western blot and FACS analyses were performed to discover the segmental aortic heterogeneity of response for tensile stress and drug testing. The appropriate stretching frequency for all lineages of SMCs was 1.0 Hz, paraxial mesoderm (PM) SMCs were more sensitive to tensile stress than lateral mesoderm (LM) SMCs and neural crest (NC) SMCs. These differences may be related to the different transcriptional profiles of the tension-stressed distinct lineage-specific vascular SMCs, specifically in relation to the PI3K-Akt signaling pathway. Also, the organ-on-a-chip displayed contractile physiology, perfect fluid coordination, and was conducive to drug testing, displaying heterogeneous segmental aortic responses. Compared with LM-SMCs and NC-SMCs, PM-SMCs were more sensitive to ciprofloxacin. The model is evaluated as a novel and suitable supplement to AA animal models for determining differential physiology and drug response in different parts of the aorta. Furthermore, this system could pave the way for disease modeling, drug testing, and the personalized treatment of patients with AA in the future.

Patient-derived microphysiological model identifies the therapeutic potential of metformin for thoracic aortic aneurysm

Background

Thoracic aortic aneurysm (TAA) is the permanent dilation of the thoracic aortic wall that predisposes patients to lethal events such as aortic dissection or rupture, for which effective medical therapy remains scarce. Human-relevant microphysiological models serve as a promising tool in drug screening and discovery.

Methods

We developed a dynamic, rhythmically stretching, three-dimensional microphysiological model. Using patient-derived human aortic smooth muscle cells (HAoSMCs), we tested the biological features of the model and compared them with native aortic tissues. Drug testing was performed on the individualized TAA models, and the potentially effective drug was further tested using β-aminopropionitrile-treated mice and retrospective clinical data.

Findings

The HAoSMCs on the model recapitulated the expressions of many TAA-related genes in tissue. Phenotypic switching and mitochondrial dysfunction, two disease hallmarks of TAA, were highlighted on the microphysiological model: the TAA-derived HAoSMCs exhibited lower alpha-smooth muscle actin expression, lower mitochondrial membrane potential, lower oxygen consumption rate and higher superoxide accumulation than control cells, while these differences were not evidently reflected in two-dimensional culture flasks. Model-based drug testing demonstrated that metformin partially recovered contractile phenotype and mitochondrial function in TAA patients’ cells. Mouse experiment and clinical investigations also demonstrated better preserved aortic microstructure, higher nicotinamide adenine dinucleotide level and lower aortic diameter with metformin treatment.

Interpretation

These findings support the application of this human-relevant microphysiological model in studying personalized disease characteristics and facilitating drug discovery for TAA. Metformin may regulate contractile phenotypes and metabolic dysfunctions in diseased HAoSMCs and limit aortic dilation.

Funding

This work was supported by grants from National Key R&D Program of China (2018YFC1005002), National Natural Science Foundation of China (82070482, 81771971, 81772007, 51927805, and 21734003), the Science and Technology Commission of Shanghai Municipality (20ZR1411700, 18ZR1407000, 17JC1400200, and 20YF1406900), Shanghai Municipal Science and Technology Major Project (2017SHZDZX01), and Shanghai Municipal Education Commission (Innovation Program 2017-01-07-00-07-E00027). Y.S.Z. was not supported by any of these funds; instead, the Brigham Research Institute is acknowledged.

Aorta smooth muscle-on-a-chip reveals impaired mitochondrial dynamics as a therapeutic target for aortic aneurysm in bicuspid aortic valve disease

Background:

Bicuspid aortic valve (BAV) is the most common congenital cardiovascular disease in general population and is frequently associated with the development of thoracic aortic aneurysm (TAA). There is no effective strategy to intervene with TAA progression due to an incomplete understanding of the pathogenesis. Insufficiency of NOTCH1 expression is highly related to BAV-TAA, but the underlying mechanism remains to be clarified.

Methods:

A comparative proteomics analysis was used to explore the biological differences between non-diseased and BAV-TAA aortic tissues. A microfluidics-based aorta smooth muscle-on-a-chip model was constructed to evaluate the effect of NOTCH1 deficiency on contractile phenotype and mitochondrial dynamics of human aortic smooth muscle cells (HAoSMCs).

Results:

Protein analyses of human aortic tissues showed the insufficient expression of NOTCH1 and impaired mitochondrial dynamics in BAV-TAA. HAoSMCs with NOTCH1-knockdown exhibited reduced contractile phenotype and were accompanied by attenuated mitochondrial fusion. Furthermore, we identified that mitochondrial fusion activators (leflunomide and teriflunomide) or mitochondrial fission inhibitor (Mdivi-1) partially rescued the disorders of mitochondrial dynamics in HAoSMCs derived from BAV-TAA patients.

Conclusions:

The aorta smooth muscle-on-a-chip model simulates the human pathophysiological parameters of aorta biomechanics and provides a platform for molecular mechanism studies of aortic disease and related drug screening. This aorta smooth muscle-on-a-chip model and human tissue proteomic analysis revealed that impaired mitochondrial dynamics could be a potential therapeutic target for BAV-TAA.

Funding:

National Key R and D Program of China, National Natural Science Foundation of China, Shanghai Municipal Science and Technology Major Project, Shanghai Science and Technology Commission, and Shanghai Municipal Education Commission.

To function properly, the heart must remain a one-way system, pumping out oxygenated blood into the aorta – the largest artery in the body – so it can be distributed across the organism. The aortic valve, which sits at the entrance of the aorta, is a key component of this system. Its three flaps (or ‘cusps’) are pushed open when the blood exits the heart, and they shut tightly so it does not flow back in the incorrect direction.

Nearly 1.4% of people around the world are born with ‘bicuspid’ aortic valves that only have two flaps. These valves may harden or become leaky, forcing the heart to work harder. This defect is also associated with bulges on the aorta which progressively weaken the artery, sometimes causing it to rupture.

Open-heart surgery is currently the only way to treat these bulges (or ‘aneurysms’), as no drug exists that could slow down disease progression. This is partly because the biological processes involved in the aneurysms worsening and bursting open is unclear.

Recent studies have highlighted that many individuals with bicuspid aortic valves also have lower levels of a protein known as NOTCH1, which plays a key signalling role for cells. Problems in the mitochondria – the structures that power up a cell – are also observed. However, it is not known how these findings are connected or linked with the aneurysms developing.

To answer this question, Abudupataer et al. analyzed the proteins present in diseased and healthy aortic muscle cells, confirming a lower production of NOTCH1 and impaired mitochondria in diseased tissues. They also created an ‘aorta-on-a-chip’ model where aortic muscle cells were grown in the laboratory under conditions resembling those found in the body – including the rhythmic strain that the aorta is under because of the heart beating. Abudupataer et al. then reduced NOTCH1 levels in healthy samples, which made the muscle tissue less able to contract and reduced the activity of the mitochondria. Applying drugs that tweak mitochondrial activity helped tissues from patients with bicuspid aortic valves to work better.

These compounds could potentially benefit individuals with deficient aortic valves, but experiments in animals and clinical trials would be needed first to confirm the results and assess safety. The aorta-on-a-chip model developed by Abudupataer et al. also provides a platform to screen for drugs and examine the molecular mechanisms at play in aortic diseases.

Aortic flow dynamics and stiffness in Loeys-Dietz syndrome patients: a comparison with healthy volunteers and Marfan syndrome patients

AIMS

To assess aortic flow and stiffness in patients with Loeys-Dietz syndrome (LDS) by 4D flow and cine cardiovascular magnetic resonance (CMR) and compare the results with those of healthy volunteers (HV) and Marfan syndrome (MFS) patients.

METHODS AND RESULTS

Twenty-one LDS and 44 MFS patients with no previous aortic dissection or surgery and 35 HV underwent non-contrast-enhanced 4D flow CMR. In-plane rotational flow (IRF), systolic flow reversal ratio (SFRR), and aortic diameters were obtained at 20 planes from the ascending (AAo) to the proximal descending aorta (DAo). IRF and SFRR were also quantified for aortic regions (proximal and distal AAo, arch and proximal DAo). Peak-systolic wall shear stress (WSS) maps were also estimated. Aortic stiffness was quantified using pulse wave velocity (PWV) and proximal AAo longitudinal strain. Compared to HV, LDS patients had lower rotational flow at the distal AAo (P = 0.002), arch (P = 0.002), and proximal DAo (P < 0.001) even after adjustment for age, stroke volume, and local diameter. LDS patients had higher SFRR in the proximal DAo compared to both HV (P = 0.024) and MFS patients (P = 0.015), even after adjustment for age and local diameter. Axial and circumferential WSS in LDS patients were lower than in HV. AAo circumferential WSS was lower in LDS compared to MFS patients. AAo and DAo PWV and proximal AAo longitudinal strain revealed stiffer aortas in LDS patients compared to HV (P = 0.007, 0.005, and 0.029, respectively) but no differences vs. MFS patients.

CONCLUSION

Greater aortic stiffness as well as impaired IRF and WSS were present in LDS patients compared to HV. Conversely, similar aortic stiffness and overlapping aortic flow features were found in Loeys-Dietz and Marfan patients.

A scoping review presenting a wide variety of research on paediatric and adolescent patients with Marfan syndrome

Aim

The present study aimed to map and summarise the research on children, aged 0‐18 years, with Marfan syndrome, identify research gaps and point to research agendas.

Methods

A scoping review was systematically performed by searching multiple databases from January 1996 to April 2019. Primary studies presenting results on at least six individuals aged 0‐18 years with Marfan syndrome, diagnosed according to the Ghent nosology, were selected.

Results

From 2341 de‐duplicated records, 92 papers were included, mapped and described. Their topics were diagnostics (12%), cardiovascular matters (50%), skeletal matters (22%), ocular matters (9%), other medical aspects (5%) and psychosocial perspectives (2%). Most studies were from Europe and North America and published between 1999 and 2019 in subject‐specific or paediatric journals, while a few were published in genetics journals. All studies had quantitative designs, and very few were multicentre studies. Each study had six to 608 subjects for a total of approximately 5809.

Conclusion

A wide range of research topics on adolescent and paediatric Marfan syndrome was found, but qualitative studies and a focus on psychosocial matters were lacking. Future investigations addressing noncardiovascular consequences and patient experiences are needed, as well as studies reaffirming or replicating existing intervention study results.

Unreliable Estimation of Aortic Pulse Wave Velocity Provided by the Mobil-O-Graph Algorithm-Based System in Marfan Syndrome

Background Several devices have been proposed to assess arterial stiffness in clinical daily use over the past few years, by estimating aortic pulse wave velocity (PWV) from a single measurement of brachial oscillometric blood pressure, using patented algorithms. It is uncertain if these systems are able to provide additional elements, beyond the contribution carried by age and blood pressure levels, in the definition of early vascular damage expressed by the stiffening of the arterial wall. Methods and Results The aim of our study was to compare the estimated algorithm-based PWV values, provided by the Mobil-O-Graph system, with the standard noninvasive assessment of aortic PWV in patients with Marfan syndrome (ie, in subjects characterized by premature aortic stiffening and low blood pressure values). Aortic stiffness was simultaneously evaluated by carotid-femoral PWV with a validated arterial tonometer and estimated with an arm cuff-based ambulatory blood pressure monitoring Mobil-O-Graph device on 103 patients with Marfan syndrome (50 men; mean± SD age, 38±15 years). Aortic PWV, estimated by the Mobil-O-Graph, was significantly ( P<0.0001) lower (mean± SD, 6.1±1.3 m/s) than carotid-femoral PWV provided by arterial tonometry (mean± SD , 8.8±3.1 m/s). The average of differences between PWV values provided by the 2 methods (±1.96×SD) was -2.7±5.7 m/s. Conclusions The Mobil-O-Graph provides PWV values related to an ideal subject for a given age and blood pressure, but it is not able to evaluate early vascular aging expressed by high PWV in the individual patient. This is well shown in patients with Marfan syndrome.

Aortic Strain Correlates with Elastin Fragmentation in Fibrillin-1 Hypomorphic Mice

Background

High frequency ultrasound has facilitated in vivo measurements of murine ascending aortas, allowing aortic strains to be gleaned from two-dimensional images. Thoracic aortic aneurysms associated with mutations in fibrillin-1 (FBN1) display elastin fragmentation, which may impact aortic strain. In this study, we determined the relationship between elastin fragmentation and aortic circumferential strain in wild type and fibrillin-1 hypomorphic (FBN1 ^mgR/mgR) mice.

Methods and Results

Luminal diameters of the ascending aorta from wild type and FBN1 hypomorphic (FBN1 ^mgR/mgR) mice were measured in systole and diastole. Expansion of the ascending aorta during systole in male and female wild type mice was 0.21±0.02 mm (16.3%) and 0.21±0.01 mm (17.0%) respectively, while expansion in male and female FBN1 ^mgR/mgR mice was 0.11±0.04 mm (4.9%) and 0.07±0.02 mm (4.5%) respectively. Reduced circumferential strain was observed in FBN1 ^mgR/mgR mice compared to wild type littermates. Elastin fragmentation was inversely correlated to circumferential strain (R^2 = 0.628 p = 0.004) and significantly correlated with aortic diameter. (R^2 = 0.397, p = 0.038 in systole and R^2 = 0.515, p =0.013 in diastole).

Conclusions

FBN1 ^mgR/mgR mice had increased aortic diameters, reduced circumferential strain, and increased elastin fragmentation. Elastin fragmentation in FBN1 ^mgR/mgR and their wild type littermates was correlated with reduced circumferential strain.

Preventing a Catastrophe: Increasing Awareness of Loeys-Dietz Syndrome

Loeys-Dietz syndrome is a genetic disorder that predisposes patients to aortic aneurysms. If left untreated, the natural history of the associated aortopathy often culminates in fatal aortic dissection. We describe the case of a 21-year-old man who was diagnosed with Loeys-Dietz syndrome after 2 family members died of aortic dissection. This case highlights the importance of increased physician awareness of this syndrome, which can play a crucial role in preventing premature sudden cardiac death caused by aortic catastrophe.

Central artery stiffness and thoracic aortopathy

Thoracic aortopathy, especially aneurysm, dissection, and rupture, is responsible for significant morbidity and mortality. Uncontrolled hypertension and aging are primary risk factors for such conditions, and they contribute to an increase in the mechanical stress on the wall and an increase in its structural vulnerability, respectively. Select genetic mutations also predispose to these lethal conditions, and the collection of known mutations suggests that dysfunctional mechanosensing and mechanoregulation of the extracellular matrix may contribute to pathogenesis and disease progression. In the absence of a well-accepted pharmacotherapy, nonsurgical treatments tend to focus on reducing the mechanical loading on the aorta, particularly via the use of antihypertensive medications and recommendations to avoid strenuous exercises such as weight lifting. In this brief review, we discuss the important effects of central artery stiffening on global hemodynamics and, in particular, on the increase in pulse pressure that acts on the proximal thoracic aorta. We consider Marfan syndrome as an illustrative aortopathy but discuss other conditions leading to thoracic aortic aneurysm and dissection. We highlight the importance of phenotyping the aorta biomechanically, not just clinically, and emphasize the utility of mouse models in elucidating molecular and mechanical mechanisms of disease. Notwithstanding the widely recognized role of central artery stiffening in driving end-organ disease, we suggest that there is similarly a need to consider its key role in thoracic aortopathy.

In vivo quantification of regional circumferential Green strain in the thoracic and abdominal aorta by 2D spiral cine DENSE MRI

INTRODUCTION

Regional tissue mechanics play a fundamental role in patient-specific cardiovascular function. Nevertheless, regional assessments of aortic kinematics remain lacking due to the challenge of imaging the thin aortic wall. Herein, we present a novel application of DENSE (Displacement Encoding with Stimulated Echoes) MRI to quantify the circumferential Green strain of the thoracic and abdominal aorta.

METHODS

2D spiral cine DENSE and steady-state free procession (SSFP) cine images were acquired at 3T at the infrarenal aorta (IAA), descending thoracic aorta (DTA), or distal aortic arch (DAA) in a pilot study of 6 healthy volunteers. DENSE data was processed with multiple custom noise-reduction techniques to calculate circumferential Green strain across 16 equispaced sectors around the aorta. Each volunteer was scanned twice to evaluate interstudy repeatability.

RESULTS

Circumferential strain was heterogeneously distributed in all volunteers and locations. Spatial heterogeneity index by location was 0.37 (IAA), 0.28 (DTA), and 0.59 (DAA). Mean peak strain by DENSE for each cross-section was consistent with the homogenized linearized strain estimated from SSFP cine. The mean difference in peak strain across all sectors following repeat imaging was -0.1±2.2%, with a mean absolute difference of 1.7%.

CONCLUSIONS

Aortic cine DENSE MRI is a viable non-invasive technique for quantifying heterogeneous regional aortic wall strain and has significant potential to improve patient-specific clinical assessments of numerous aortopathies, as well as to provide the lacking spatiotemporal data required to refine computational models of aortic growth and remodeling.

Truncated C-terminus of fibrillin-1 induces Marfanoid-progeroid-lipodystrophy (MPL) syndrome in rabbit

Various clinical differences have been observed between patients with the FBN1 gene mutation and those with the classical Marfan phenotype. Although FBN1 knockout (KO) or dominant-negative mutant mice are widely used as an animal model for Marfan syndrome (MFS), these mice cannot recapitulate the genotype/phenotype relationship of Marfanoid-progeroid-lipodystrophy (MPL) syndrome, which is caused by a mutation in the C-terminus of fibrillin-1, the penultimate exon of the FBN1 gene. Here, we describe the generation of a rabbit MPL model with C-terminal truncation of fibrillin-1 using a CRISPR/Cas9 system. FBN1 heterozygous (FBN1 Het) rabbits faithfully recapitulated the phenotypes of MFS, including muscle wasting and impaired connective tissue, ocular syndrome and aortic dilation. Moreover, skin symptoms, lipodystrophy, growth retardation and dysglycemia were also seen in these FBN1 Het rabbits, and have not been reported in other animal models. In conclusion, this novel rabbit model mimics the histopathological changes and functional defects of MPL syndrome, and could become a valuable model for studies of pathogenesis and drug screening for MPL syndrome.

Summary: A novel genetically engineered rabbit model of MPL syndrome, generated by CRISPR/Cas9-mediated mutation of FBN1, mimics the histopathological changes and functional defects of MPL syndrome seen in the clinic.

Comparison of 10 murine models reveals a distinct biomechanical phenotype in thoracic aortic aneurysms

Thoracic aortic aneurysms are life-threatening lesions that afflict young and old individuals alike. They frequently associate with genetic mutations and are characterized by reduced elastic fibre integrity, dysfunctional smooth muscle cells, improperly remodelled collagen and pooled mucoid material. There is a pressing need to understand better the compromised structural integrity of the aorta that results from these genetic mutations and renders the wall vulnerable to dilatation, dissection or rupture. In this paper, we compare the biaxial mechanical properties of the ascending aorta from 10 murine models: wild-type controls, acute elastase-treated, and eight models with genetic mutations affecting extracellular matrix proteins, transmembrane receptors, cytoskeletal proteins, or intracellular signalling molecules. Collectively, our data for these diverse mouse models suggest that reduced mechanical functionality, as indicated by a decreased elastic energy storage capability or reduced distensibility, does not predispose to aneurysms. Rather, despite normal or lower than normal circumferential and axial wall stresses, it appears that intramural cells in the ascending aorta of mice prone to aneurysms are unable to maintain or restore the intrinsic circumferential material stiffness, which may render the wall biomechanically vulnerable to continued dilatation and possible rupture. This finding is consistent with an underlying dysfunctional mechanosensing or mechanoregulation of the extracellular matrix, which normally endows the wall with both appropriate compliance and sufficient strength.

Aortic elasticity and carotid intima-media thickness in children with mitral valve prolapse

Aim We aimed to study the dimensions, systolic and diastolic functions of the left ventricle; dimensions and elasticity of the aorta; and carotid intima-media thickness and flow-mediated dilatation of the brachial artery in mitral valve prolapse.

METHODS

The study group consisted of 43 patients (mean age=13.3±3.9) and 42 healthy children (mean age=12.9±3.4). Left ventricular end-diastolic, end-systolic, left atrial diameters, interventricular septum, and left ventricular posterior wall thickness were measured. Ejection and shortening fractions were calculated by M-mode. Measurements were adjusted to the body surface area. Mitral annulus, and systolic and diastolic diameters of the aortic annulus and aorta at each level were obtained; z-scores, aortic strain, distensibility, stiffness index were calculated. Carotid intima-media thickness and flow-mediated dilatation were studied. Patients were classified as classical/non-classical mitral valve prolapse and younger/older patients.

RESULTS

Left ventricular end-systolic, end-diastolic, and left atrial diameters (p=0.009, p=0.024, p=0.001) and aortic z-scores at annulus, sinus valsalva, and sinotubuler junction were larger (p=0.008, p=0.003, p=0.002, respectively) in the mitral valve prolapse group. Aortic strain and distensibility increased and stiffness decreased at the ascending aorta in the patient group (p=0.012, 0.020, p=0.019, respectively). Classical mitral valve prolapse had lower strain and distensibility and higher stiffness of the aorta at sinus valsalva level (p=0.010, 0.027, 0.004, respectively). Carotid intima-media thickness was thinner in the patient group, especially in the non-classical mitral valve prolapse group (p=0.037). Flow-mediated dilatation did not differ among the groups.

CONCLUSION

Mitral valve prolapse is a systemic disease of the connective tissue causing enlarged cardiac chambers and increased elasticity of the aorta. Decreased carotid intima-media thickness in this group may indicate low atherosclerosis risk.

Impaired Central Pulsatile Hemodynamics in Children and Adolescents With Marfan Syndrome

Background

Marfan syndrome is characterized by aortic root dilation, beginning in childhood. Data about aortic pulsatile hemodynamics and stiffness in pediatric age are currently lacking.

Methods and Results

In 51 young patients with Marfan syndrome (12.0±3.3 years), carotid tonometry was performed for the measurement of central pulse pressure, pulse pressure amplification, and aortic stiffness (carotid‐femoral pulse wave velocity). Patients underwent an echocardiogram at baseline and at 1 year follow‐up and a genetic evaluation. Pathogenetic fibrillin‐1 mutations were classified between “dominant negative” and “haploinsufficient.” The hemodynamic parameters of patients were compared with those of 80 sex, age, blood pressure, and heart‐rate matched controls. Central pulse pressure was significantly higher (38.3±12.3 versus 33.6±7.8 mm Hg; P=0.009), and pulse pressure amplification was significantly reduced in Marfan than controls (17.9±15.3% versus 32.3±17.4%; P<0.0001). Pulse wave velocity was not significantly different between Marfan and controls (4.98±1.00 versus 4.75±0.67 m/s). In the Marfan group, central pulse pressure and pulse pressure amplification were independently associated with aortic diameter at the sinuses of Valsalva (respectively, β=0.371, P=0.010; β=−0.271, P=0.026). No significant difference in hemodynamic parameters was found according to fibrillin‐1 genotype. Patients who increased aortic Z‐scores at 1‐year follow‐up presented a higher central pulse pressure than the remaining (42.7±14.2 versus 32.3±5.9 mm Hg; P=0.004).

Conclusions

Central pulse pressure and pulse pressure amplification were impaired in pediatric Marfan syndrome, and associated with aortic root diameters, whereas aortic pulse wave velocity was similar to that of a general pediatric population. An increased central pulse pressure was present among patients whose aortic dilatation worsened at 1‐year follow‐up.

Cardiovascular Benefits of Moderate Exercise Training in Marfan Syndrome: Insights From an Animal Model

BACKGROUND

Marfan syndrome (MF) leads to aortic root dilatation and a predisposition to aortic dissection, mitral valve prolapse, and primary and secondary cardiomyopathy. Overall, regular physical exercise is recommended for a healthy lifestyle, but dynamic sports are strongly discouraged in MF patients. Nonetheless, evidence supporting this recommendation is lacking. Therefore, we studied the role of long-term dynamic exercise of moderate intensity on the MF cardiovascular phenotype.

METHODS AND RESULTS

In a transgenic mouse model of MF (Fbn1^C1039G/+), 4-month-old wild-type and MF mice were subjected to training on a treadmill for 5 months; sedentary littermates served as controls for each group. Aortic and cardiac remodeling was assessed by echocardiography and histology. The 4-month-old MF mice showed aortic root dilatation, elastic lamina rupture, and tunica media fibrosis, as well as cardiac hypertrophy, left ventricular fibrosis, and intramyocardial vessel remodeling. Over the 5-month experimental period, aortic root dilation rate was significantly greater in the sedentary MF group, compared with the wild-type group (∆mm, 0.27±0.07 versus 0.13±0.02, respectively). Exercise significantly blunted the aortic root dilation rate in MF mice compared with sedentary MF littermates (∆mm, 0.10±0.04 versus 0.27±0.07, respectively). However, these 2 groups were indistinguishable by aortic root stiffness, tunica media fibrosis, and elastic lamina ruptures. In MF mice, exercise also produced cardiac hypertrophy regression without changes in left ventricular fibrosis.

CONCLUSIONS

Our results in a transgenic mouse model of MF indicate that moderate dynamic exercise mitigates the progression of the MF cardiovascular phenotype.