Dynamics of homemade aortic endografts: in vivo study in humans with computed tomography scanner modeling.

BACKGROUND: Several cases of aortic endograft rupture have been described. In most cases, they stem from component wear and perforation of the graft, leading to leakage. Friction of the stents on the graft can cause abrasion and perforate the textile. This friction results from movements inside the endograft implanted in the aorta exposed to blood flow, arterial pressure, and the movements of the aorta itself. METHODS: To study in vivo the movements of homemade stent grafts (HMSGs) designed and constructed by the surgeons at La Pitié Salpêtrière Hospital (Paris), the displacements of the metallic skeleton of the HMSG after implantation were measured using a dynamic CT scanner connected to the patient's ECG. The geometric structure of the HMSG was modeled using MATLAB software to specify the different displacements in the HMSG: angular displacements (A) (in degrees) at the sutures between two eyelets, radial displacements (R) (in millimeters for absolute values and percentile diameter for relative values) describing HMSG pulsation, and longitudinal displacements (L) (in millimeters) reflecting compression movements. These movements differ from the global movements of the aorta in the Windkessel wave: they are movements between the different levels of eyelets in the metallic structure. RESULTS: The results obtained were A = 4.5 + or - 1.5 degrees , R = 0.6 + or - 0.4 mm, R% = 4.2 + or - 2.4, and L = 0.4 + or - 0.2 mm. These values are the maximum displacements measured. They are located close to the junctions between the HMSG necks and body. These transition areas between the neck anchored in the aorta and the body, which not fixed in the aneurysm pouch, seem to be the areas of the maximum displacements, mainly angular and radial. On the other parts of the HMSG, displacements were less pronounced, approaching the CT scan's detection limit (0.1 to 0.2 mm). CONCLUSION: We made videos while modeling the amplitude of the displacements in the HMSG with a color code. This sequence could be a very good way to monitor the progression of HMSG displacements.

Chronology of the push pull effect on nonhuman primates-shift of the arterial pressure threshold.

Fighter pilots are frequently exposed to high Gz acceleration which may induce in-flight loss of consciousness (G-LOC). One factor reducing tolerance to accelerations is a previous exposure to negative accelerations. This phenomenon, which happens during the first few seconds after the onset of the positive plateau, is called the push pull effect. Our goal was to validate a non human primate model in order to study push pull physiological mechanisms and possible changes in arterial pressure, which may occur after the first ten seconds of the positive acceleration plateau. Eight rhesus monkeys were centrifuged in profile runs, including positive Gz accelerations (+1.4, +2 and +3 Gz) with or without previous negative Gz acceleration (-2 and -3 Gz vs. +1.4 Gz). Heart rate, blood pressure and esophageal pressure were recorded during the entire centrifugation run. Results showed that the push pull effect was observed in the non human primate model. Moreover, the reduced tolerance to acceleration lingered longer than that during the first ten seconds after exposure to +Gz acceleration. It was found that, after the fourteenth second, mean blood arterial pressure stabilizes at a lower value, when the positive acceleration is preceded by a negative acceleration (15.8 kPa for -1 Gz and 15.5 for -2 Gz vs. 16.9 for 1.4 Gz). The chronology of the push pull effect seems to involve two periods. One has a short time span. The other one has a longer time span and could be induced by shift of pressure threshold, coming from exposure to previous negative acceleration.

Static mechanical properties of custom-made aortic endografts.

Several cases of delayed aortic rupture after endovascular aneurysm repair have been attributed to in vivo endograft fatigue. Such complications could involve damage to structural components during introduction. The purpose of this study was to compare forces applied during introduction to forces needed to damage the endograft. Testing was carried out on the custom-made endograft (CMEG) that has been in almost exclusive use at our center since 1996. Findings showed that the force applied during introduction was less than the force necessary to damage the endograft. No alteration in the mechanical properties of the CMEG was observed immediately after implantation.

Custom-made stent-grafts for aortic aneurysm repair using gianturco Z stents and woven polyester: healing in an animal model.

The purpose of this study was to evaluate the healing at 6 months of aortic stent-grafts custom-made by using Z stents and woven polyester in an animal model. Stent-grafts were built by a published method using autoexpandable stainless steel stents continuously compiled with polyester sutures and covered with a woven polyester membrane. Fourteen stent-grafts of 3 different designs were deployed under fluoroscopic control into the thoracic and the abdominal aorta of 7 adult sheep. At 6 months, all the implants of the sheep that survived the implantation were angiographed and harvested for macroscopy and microscopy. All stent-grafts were implanted successfully and remained patent from then to the explantation procedure. All stent-grafts implanted among the 6 of 7 (86%) animals that survived after the implantation remained patent, stayed free from local complications, and did not migrate during more than 6 months. In all these cases during this period, the implant functioned as a satisfactory aortic substitute while the aortic segment containing the graft kept a normal structure. There was no adverse effects of the presence of the implant upon the aorta or the animal. Stent-grafts home-made according to the described methods gave results at 6 months in this animal model compatible with a safe clinical application among humans.

[Tailored endoprostheses for the endovascular treatment of aorto-iliac aneurysms: current features and perspectives]. / Endoprothèses artisanales sur mesure pour le traitement endovasculaire des anévrysmes aorto-iliaques: aspects actuels et perspectives.

We describe here our preliminary experience with the almost exclusive use of a range of made to measure stent-grafts home-made from commercially available components. From January 1996 to December 1999, 188 aortoiliac aneurysms (AIA) were treated with stent-grafts that were home-made to measure using Z autoexpandable stainless steel stents connected with polyester sutures and covered with commercially available polyester vascular prostheses. These stent-grafts were implanted through 18 to 24 (typically 20) Fr. commercially available introducers via a surgical remote access. Made to measure tubular, bifurcated, tapered, and/or blind stents combined with extra-anatomic bypass designs increased the rate of endovascular treatment (ET) of AIA in this series. This rate was further increased through the use of uncovered proximal or distal stents when dealing with short or tortuous necks near major side branches and through use of hybrid, partly surgical designs, one with stented and the other with stentless ends, the latter allowing for a surgically made anastomosis. The results of our experience with these techniques show that use of home-made to measure stent-grafts greatly increases the feasibility of the ET of AIA among unselected patients while offering enough efficiency and safety to deserve further investigation. Future perspectives are discussed.