Jean-Pierre Favre

Cryopreserved arterial homografts: preliminary study.

The use of arterial or venous allografts for vascular reconstruction was first reported in 1951, but long-term results have been disappointing. Rejection and inappropriate methods of preservation are the main reasons for failure. A successful solution to this problem could be achieved by programmed cryopreservation with cryoprotectant. Our study had two aims: to define the biomechanical properties of cryopreserved arterial allografts and to study their histologic appearance. Arteries were removed as part of a protocol for multiorgan harveting for transplantation. Cryopreservation was performed within the first 24 hours after harvesting. Programmed cryopreservation with 15% dimethyl sulfoxide (cryoprotectant) was used. Mechanical testing was done immediately after thawing. Two groups were tested: a control group of fresh aortas and a group of cryopreserved aortas. Axial and circumferential strips were tested. High strain modulus and stress and strain characteristics were calculated for each strip. There was no statistically significant difference between the mechanical properties of fresh and cryopreserved human descending thoracic aortas. Biochemical tests were performed in the preservative solution at 1 and 7 days in both groups. There was no statistically significant difference between the two groups at day 1 or day 7 (p > 0.05). Histologic studies before and after arterial cryopreservation included standard and electron microscopy and showed that arteries had normal structure after cryopreservation. These results confirm that programmed cryopreservation with cryoprotectant does not alter the molecular or geometric configuration of collagen or elastic fibers. Endothelial cells were still present; however, their viability and function were not assessed. The results of our studies have encouraged us to use cryopreserved arterial allografts for clinical application, and to date 27 patients have received cryopreserved arterial allografts. Definitive results including histologic and immunologic findings will be reported in the future when the length of follow-up is adequate.

Editor's Choice – Hybrid Treatment of Thoracic, Thoracoabdominal, and Abdominal Aortic Aneurysms: A Multicenter Retrospective Study

OBJECTIVESnThe aim of this study was to assess the results of hybrid techniques for the treatment of thoracic, thoracoabdominal, and abdominal aortic aneurysms based on multicenter results and the various series regarding hybrid procedures reported in the literature.nnnMETHODSnThe results of 76 hybrid procedures performed in 19 French university hospital centers between November 2001 and October 2011 were collected. There were 50 men and 26 women, mean age 68.2 (35-86) years. All patients were considered at high risk (ASA≥3) for conventional surgery. Aneurysms involved the thoracic, abdominal, and thoracoabdominal aorta in five, 14, and 57 cases respectively. There were 11 emergent repairs. The revascularization of four visceral arteries was performed in 38 cases. Between one and three visceral arteries were revascularized in the other cases. Visceral artery debranching and stent graft deployment were performed in a one-stage procedure in 53 cases and in a two-stage procedure in 23 cases.nnnRESULTSnThere were 26 (34.2%) postoperative deaths. Nine of the survivors developed paraplegia, of which one resolved completely. Bowel ischemia occurred in 13 cases (17.1%), and one patient was treated by a superior mesenteric artery bypass. Four patients required long-term hemodialysis. Postoperative computed tomography scan showed a type II endoleak in two patients.nnnCONCLUSIONSnMorbidity and mortality in this study were greater than previously reported. Candidates for hybrid aortic repair should be carefully selected.

In vitro analysis of localized aneurysm rupture

In this study, bulge inflation tests were used to characterize the failure response of 15 layers of human ascending thoracic aortic aneurysms (ATAA). Full field displacement data were collected during each of the mechanical tests using a digital image stereo-correlation (DIS-C) system. Using the collected displacement data, the local stress fields at burst were derived and the thickness evolution was estimated during the inflation tests. It was shown that rupture of the ATAA does not systematically occur at the location of maximum stress, but in a weakened zone of the tissue where the measured fields show strain localization and localized thinning of the wall. Our results are the first to show the existence of weakened zones in the aneurysmal tissue when rupture is imminent. An understanding these local rupture mechanics is necessary to improve clinical assessments of aneurysm rupture risk. Further studies must be performed to determine if these weakened zones can be detected in vivo using non-invasive techniques.

Cryopreserved Arterial Allografts for Limb Salvage in the Absence of Suitable Saphenous Vein: Two-Year Results in 20 Cases

From January 1992 to November 1992, 20 cryopreserved arterial allografts were used as below-knee bypasses for repeated limb salvage in 18 patients lacking saphenous vein grafts. Arteries were obtained during multiorgan harvesting. A scheduled program of cryopreservation with 15% dimethylsulfoxide was used. Mean storage period was 37 days. All cases were matched for blood group compatibility. Patency was checked at 10 and 90 days and twice a year thereafter. Conventional arteriography was routinely performed 3 months postoperatively. Average follow-up was 26.8 months for the 18 patients and 20.8 months for the 20 bypass grafts. No patients were lost to follow-up. Aneurysmal dilation developed in one graft, which was replaced by another homograft. During follow-up 10 grafts occluded: five once, four twice, and one four times. These 10 grafts underwent a total of 16 reinterventions. Thrombectomy with angioplasty was performed 15 times and graft replacement once because of proximal and distal arterial deterioration. Primary actuarial patency was 68% at 1 year and 42% at 2 years. Secondary actuarial patency was 89% at 1 year and 72% at 2 years. Preliminary results of cryopreserved arterial allografts for repeated limb salvage in the absence of available saphenous veins are encouraging. Further studies are needed to determine the long-term deterioration rate of cryopreserved arterial allografts.

Carotid surgery in the octogenarian

The records of 52 patients aged 80 years or older who underwent 56 carotid artery reconstructions were analyzed retrospectively. Four patients had amaurosis fugax, 27 patients had experienced one or more transient ischemic attacks, eight had a completely or partially reversible stroke, and 10 had vertebrobasilar insufficiency. Three patients were asymptomatic. Arteriograms documented stenosis >80% on the operated side in 48 cases, whereas the contralateral carotid artery was occluded or had >80% stenosis in 10 cases each. Two or more cerebral arteries were involved in 37 patients. CT scans were normal in only 21 (40%) patients. General anesthesia was used in 54 of 56 operations. Thirty-six endarterectomies, 18 bypasses, and two resection-anastomoses (for tortuosity) were performed. A shunt was employed in eight (14.3%) cases. One lethal stroke (1.9%) occurred during the first postoperative month. Three patients experienced nonfatal strokes, two of which gave rise to residual deficits. Two patients were lost to follow-up. For the remaining 49 patients the mean follow-up was 24 months. Two-year actuarial survival was 76.3% for the entire series and 67% for those surviving without neurologic events. This study shows that when properly selected the elderly population can safely undergo carotid surgery.

Biaxial rupture properties of ascending thoracic aortic aneurysms.

UNLABELLEDnAlthough hundreds of samples obtained from ascending thoracic aortic aneurysms (ATAA) of patients undergoing elective surgical repair have already been characterized biomechanically, their rupture properties were always derived from uniaxial tensile tests. Due to their bulge shape, ATAAs are stretched biaxially in vivo. In order to understand the biaxial rupture of ATAAs, our group developed a novel methodology based on bulge inflation and full-field optical measurements. The objective of the current paper is threefold. Firstly, we will review the failure properties (maximum stress, maximum stretch) obtained by bulge inflation testing on a cohort of 31 patients and compare them with failure properties obtained by uniaxial tension in a previously published study. Secondly, we will investigate the relationship between the failure properties and the age of patients, showing that patients below 55years of age display significantly higher strength. Thirdly, we will define a rupture risk based on the extensibility of the tissue and we will show that this rupture risk is strongly correlated with the physiological elastic modulus of the tissue independently of the age, ATAA diameter or the aortic valve phenotype of the patient.nnnSTATEMENT OF SIGNIFICANCEnDespite their medical importance, rupture properties of ascending thoracic aortic aneurysms (ATAA) subjected to biaxial tension were inexistent in the literature. In order to address this lack, our group developed a novel methodology based on bulge inflation and full-field optical measurements. Here we report rupture properties obtained with this methodology on 31 patients. It is shown for the first time that rupture occurs when the stretch applied to ATAAs reaches the maximum extensibility of the tissue and that this maximum extensibility correlates strongly with the elastic properties. The outcome is a better detection of at-risk individuals for elective surgical repair.

Severe Bending of Two Aortic Stent-Grafts: An Experimental and Numerical Mechanical Analysis

Stent-grafts (SGs) are commonly used for treating abdominal aortic aneurysms (AAAs) and numerical models tend to be developed for predicting the biomechanical behavior of these devices. However, due to the complexity of SGs, it is important to validate the models. In this work, a validation of the numerical model developed in Demanget et al. (J. Mech. Behav. Biomed. Mater. 5:272–282, 2012) is presented. Two commercially available SGs were subjected to severe bending tests and their 3D geometries in undeformed and bent configurations were imaged from X-ray microtomography. Dedicated image processing subroutines were used in order to extract the stent centerlines from the 3D images. These skeletons in the undeformed configurations were used to set up SG numerical models that are subjected to the boundary conditions measured experimentally. Skeletons of imaged and deformed stents were then quantitatively compared to the numerical simulations. A good agreement is found between experiments and simulations. This validation offers promising perspectives to implementing the numerical models in a computer-aided tool and simulating the endovascular treatments.

Dysplastic lesions of renal artery branches: Late results of ex vivo repair

Between November 1980 and July 1989, 29 ex vivo reconstructions were performed in 12 women and five men (mean age: 42 years) for dysplastic lesions of renal artery branches. Fifteen patients had hypertension, associated with advanced renal failure in one case. The internal iliac artery was used routinely for reconstruction. The saphenous vein was used on one side where bilateral repairs were necessary. A total of 52 distal anastomoses were performed, an average of 2.6 per revascularized kidney. Mean follow-up was four years and 10 months. No patients were lost to follow-up. There were no early or late deaths. At least one follow-up arteriogram and technetium99 diethylene triamine pentacetic acid scintiscan was obtained for all patients. Forty-five (86%) of 52 anastomoses remained patent. Eleven of 15 hypertensive patients completely recovered while four were improved. Systolic arterial blood pressure decreased by an average of 42 mmHg (p < 0.001), and results remained stable with time. For fibromuscular dysplasia occurring in young patients whose life expectancy is usually long, this type of surgery provides excellent long-term clinical and anatomical results.

Predictive Models with Patient Specific Material Properties for the Biomechanical Behavior of Ascending Thoracic Aneurysms

AbstractnThe aim of this study is to identify the patient-specific material properties of ascending thoracic aortic aneurysms (ATAA) using preoperative dynamic gated computed tomography (CT) scans. The identification is based on the simultaneous minimization of two cost functions, which define the difference between model predictions and gated CT measurements of the aneurysm volume at respectively systole and cardiac mid-cycle. The method is applied on five patients who underwent surgical repair of their ATAA at the University Hospital Center of St. Etienne. For these patients, the aneurysms were collected and tested mechanically using an in vitro bench. For the sake of validation, the mechanical properties found using the in vivo approach and the in vitro bench were compared. We eventually performed finite-element stress analyses based on each set of material properties. Rupture risk indexes were estimated and compared, showing promising results of the patient-specific identification method based on gated CT.

Do Collagen-Impregnated Knitted Dacron Grafts Reduce the Need for Transfusion in Infrarenal Aortic Reconstruction?

The purpose of this study was to evaluate the benefits of collagen-impregnated Dacron grafts in patients undergoing infrarenal aortic reconstruction. We therefore prospectively compared two consecutive series of patients undergoing infrarenal aortic reconstruction with Dacron grafts between January 1991 and December 1992. The first group (group A) included 83 high-density knitted prosthetic grafts (Dialine I), whereas the second included 82 grafts of the same type but impregnated with collagen (Dialine II). The two groups were comparable with regard to age, sex, and operative risk factors. They were also comparable in terms of the proportion of patients with occlusive disease or aneurysms, that is, there were 39 and 36 patients with occlusive disease and 44 and 46 patients with aneurysms in groups A and B, respectively. The type of bypass was similar in both groups with 17 and 19 tubular grafts and 66 and 63 bifurcated grafts being inserted in groups A and B, respectively. Thirteen parameters were studied and compared within each group including (1) number of infected grafts, (2) number of postoperative occlusions, (3) maximum postoperative temperature, (4) number of positive postoperative blood cultures, (5) number of postoperative deaths, (6) intraoperative and (7) postoperative quantities of blood transfused, (8) difference between pre- and postoperative hemoglobin concentrations, (9) difference between pre- and postoperative fibrinogen levels, (10) difference between pre- and postoperative platelet counts, (11) duration of aortic clamping,(12) date of return of intestinal function, and (13) mean duration of pre- and postoperative hospital stays. One death, one graft occlusion, and one postoperative infection were observed in group A, whereas there were three deaths, two occlusions, and one postoperative infection in group B (difference not significant). Of all the parameters studied, the only significant difference concerned the reduction in transfusion requirements of units when a collagen-impregnated graft was inserted (p<0.05). These results are similar to those observed with other standard or collagen-coated knitted grafts. Less loss of blood, resulting in a reduced theoretic risk of viral contamination, appears to be the main advantage of collagen-coated grafts.