Mechanical Characterization of Ascending Aorta in Patients With and Without Aortic Dissection

Study Overview
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Brief Summary
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Acute type A aortic dissection is a frequent (3 cases per 100 000 people per year) and severe (spontaneous mortality 70%), needing an emergency surgical treatment. Surgical outcomes have improved with the development of surgical techniques, but the postoperative mortality remains high (15-30% at 30 days). Endovascular approach with the deployment of endoprosthesis sealing the proximal intimal tear is an attractive minimally invasive technique, which can represent an alternative to surgical repair especially in high risk patients.

Detailed Description
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Objectives: this study aims to characterize mechanical properties of ascending aorta (AA) in patients, with and without aortic dissection. Materials and methods : comprised an in vivo and ex vivo studies performed in 2 groups of patients : (1) patients admitted for acute type A dissection and treated with surgical procedure ; (2) healthy control group selected among patients without any ascending aorta pathology and who underwent transoesophageal echocardiography for various indications. In vivo study : Strain, distensibility, stiffness index and pressure strain elastic modulus (Ep) were calculated from aortic diameter variation in response to pressure variation. Aortic diameters were measured using transoesophageal echocardiography. Ex vivo study : biaxial tensile testing were performed on aortic wall samples. Dissected aortic samples were collected from patients who underwent surgical repair and healthy samples from unused donors hearts and lungs. Mechanical characterization was combined to a histological and microstructural analysis of aortic wall. The latter was conducted using multiphoton microscopy to visualize elastin and collagen fibers. Results : In vivo study: 22 patients in healthy control group and 13 patients in dissection group were prospectively investigated. In vitro study : Biaxial testing was performed on 4 samples of dissected aorta and 6 samples of non dissected aorta. Anisotropic and non linear behavior of aortic tissue was shown in the 2 types of samples. Dissected tissue were stiffer than the intimal flap which was in turn stiffer than non dissected tissue. Histological data showed that in dissection group global elastin density was lower than in control. Microstructural analysis in dissection specimens revealed a higher collagen signal in the media mainly in circumferential plane, contrasting with a roughly similar intensity between the two planes in control. This higher signal reflects higher collagen fiber density and/or thicker fibers in this tunica. Conclusion : Both in vivo and in vitro data revealed that dissected aorta was stiffer than healthy ascending aorta. These findings has consequences on the choice of futur devices dedicated to AA

Official Title
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Mechanical Characterization of Ascending Aorta in Patients With Acute Type A Dissection and in Healthy Control Group Combined to Structural and Ultrastructural Analysis of Aortic Tissue

Conditions
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Acute Type A Dissection

Intervention / Treatment
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* Other: measure the elastic properties of aortic wall


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patients aged 50 to 85 years The information given search, Aortic dissection evolving for less than 15 days confirmed Exclusion Criteria: the acute aortic dissections against-indicated for aortic surgery (patient age, stroke or multiple organ failure) Iatrogenic dissections, Dissections related to congenital or hereditary disorder (abnormal connective tissue) or those occurring in subjects with a bicuspid aortic valve, Intramural hematomas type A, Patients under guardianship or trusteeship deprived of liberty.

Ages Eligible for Study
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Minimum Age: 50 Years
Maximum Age: 85 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| experimental<br>patients with acute type A dissection | Other: measure the elastic properties of aortic wall<br> <br> |
| control<br>patients without any pathology of the ascending aorta, but having the same characteristics as the sick patients, in terms of age and vascular risk factors including high blood pressure | Other: measure the elastic properties of aortic wall<br> <br> |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| measure the elastic properties of aortic wall | The distensibility, aortic strain will be measured as a function of changes of aortic diameter and pulse pressure. | one day | 
| Measurement of aortic diameters | The measurement will be done by transesophageal echocardiography simultaneously to the cuff brachial artery pressure. | one day |