Compliance is defined by the relationship between the variation of volume and the variation of pressure. The thoracic aorta has a certain level of compliance enabling it to cushion the systolo-diastolic wave of pressure generated by the cardiac muscle. This is an important physical concept, because the interposition of a less compliant vascular substitute will drive a total rigidification of the aortic axis, source of complications. The objective of this study was to measure the compliance of various usually implanted thoracic stentgrafts (TS) and to propose a comparative analysis adjusted with their structure.

For about ten year, the endovascular treatment of the thoracic aorta became accepted as the technique of first intention for pathologies of the thoracic aorta. Proximal anchoring of thoracic stentgrafts (TS) is based on the application of a radial force (RF) generated by the TS on the aortic wall. This force depends at the same time on the intrinsic properties of the stent and on the coefficient of oversizing (OS) of the stent compared to the aortic neck. The instructions for use from the manufacturers recommend a percentage of OS ranging between 10 and 20% and a proximal neck >20 mm. On the basis of this postulate, we studied and compared the radiate force of the various available TS. We studied 10 TS from five manufacturers. Each TS was placed on an experimental test bench including a cylinder of compression 25 mm deep connected to the force sensor of a tensile testing machine. Each sample was tested on two segments: 0-25 and 25-50 mm. Recording of RFs was continuous for compressions going between 0 to 50%. RFs were analyzed according to the model of TS and to the zones, and for three levels of OS: 10, 15 and 20%. RF varied according to the models of TS between 0.4 and 2.4 N with 10% of OS and between 1.8 and 3.2 N with 20% of OS. The analysis of RFs showed very different mechanical behaviors according to the type of TS. For one TS, RFs increased in an important way according to the percentage of OS (multiplying coefficient of 5.8) while for four other types of SG this coefficient did not exceed 1.5. We also highlighted that for nine models of TS, RFs were more important (on average of 0.6 N) at the level of the second segment. These experimental results consolidate the need for knowing the mechanical properties of the TS we implant. The current recommendations for OS cannot apply in the same manner to all the models of TS. It would be advisable to refine OS according to the implanted type but also according to the length of the aortic neck and the treated pathology.

The endovascular treatment of the thoracic aorta profited of the improvement of the design of thoracic stentgrafts (TS) in particular for the procedures including the aortic arch (AA). This progress in the conformability of the second generation TS made it possible to widen the indications with more technical aortic necks (AN). However, this improvement in conformability does not preclude the quality of anchoring of the SG, which depends on the radial force of the stent. An important force exposes to the risk of traumatism of the arterial wall, whereas a lesser force exposes to the risk of migration. These are the mechanical characteristics that we wanted to study on the various models of SG available on the market.

BACKGROUND:Compliance mismatch between native artery and a prosthetic graft used for infrainguinal bypass is said to be a factor for graft failure. The aim of this study was to develop a technique for measuring the compliance of collagen-coated polyethylene terephthalate (PET) vascular prostheses and to analyze the influence of several key properties on the elastic behavior of the grafts.METHODS:Compliance testing was performed on 3 prostheses with and without internal compliant membrane (ICM). The principle of this test was to study the dimensional changes of prostheses submitted to internal pressure from 30 to 240 mm Hg at intervals of predetermined values.RESULTS:We demonstrated that the ICM created links with the inner surface of the crimps and considerably modified the graft behavior when submitted to internal pressure. The results showed that compliance properties were dependent on the wall thickness and the crimping geometry of textile vascular prostheses. Mechanical analysis predicts the circumferential tensile behavior of these arterial grafts and validates tests for measuring compliance.

Vascular textile prostheses (VTP) are proof to be reliable structures in terms of their resistance. However, longitudinal ruptures were described in literature. Explanations were given. But, overal...