In vitro and in vivo evaluation of a small caliber vascular prosthesis fixed with a polyepoxy compound.

A small caliber vascular prosthesis obtained from an ovine internal thoracic artery (3.8-4.5 mm ID) fixed with a polyepoxy compound and treated with heparin has been evaluated. Cytocompatibility was evaluated in vitro using human endothelial cells (HEC). HEC were obtained from human saphenous vein and cultivated in culture medium supplemented with 25% human serum. Graft segments were rinsed using a standard protocol proposed by the manufacturer. Tissue reaction was tested on a rabbit model of subcutaneous implantation. The patency rate and healing patterns were evaluated comparatively with polytetrafluorethylene (PTFE) 4 mm ID prosthesis in a canine model of carotid interposition. Cytocompatibility assay showed that there was low adhesion on vascular grafts (20 +/- 2% of endothelial cells seeded) and no growth of HEC on the graft surface. The graft patency rate was 55% in both groups, and actuarial freedom from occlusion was not different at 3 months (37.7 +/- 15% in Denacol-fixed grafts versus 38.1 +/- 14% in PTFE). Histological studies on the biological grafts shows a frequent neointimal hyperplasia at the anastomosis (5/12), a lack of endothelial cells lining the graft surface, a good preservation of the media, and a moderate inflammatory response in the adventicia. The Denacol-fixed graft has presented excellent surgical properties and preservation of the histological structure. Nevertheless, the patency rate was not improved when compared with the PTFE control graft.

Deterioration of bioprosthetic heart valves.

The aim of this study was to detect biologic factors in the structural deterioration of bioprosthetic heart valves. Prostheses were removed from patients after 4-8 years of implantation and submitted to biochemical and morphologic assays. Successive staining of biologic sections revealed colocalization of lipids and glycosaminoglycans underneath calcifications in the disintegrated extracellular matrix. On biochemical assays, the amidolysis of synthetic peptide substrates indicated thrombin, plasmin, and tissue plasminogen activator activities in the nonhemocompatible leaflets; 0.15 mol NaCl, 0.05 mol Tris, and 5 mmol CaCl2 extracts from the prostheses cleaved the peptide substrate for collagenase and lysed gelatin gels. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate disclosed the presence of low molecular mass polypeptides in extracts of the deteriorated prostheses. The detection of plasmin and collagenolytic enzyme(s), and the known broad proteolytic activity of plasmin, may point to the role of activation of the fibrinolytic system in the proteolytic degradation of bioprosthetic valves.

A new device for endothelial cell seeding of a small-caliber vascular prosthesis.

A device permitting homogeneous endothelial cell seeding of a small-caliber arterial prosthesis has been developed. The prosthesis is maintained firmly attached to a rotative scaffolding device. This device is activated by an electrical motor at constant and adjustable speed. The whole system is maintained at 37 degrees C in a cell culture incubator. The 4 mm internal diameter polytetrafluoroethylene (PTFE) prosthesis was coated with biological glue and seeded with human saphenous vein endothelial cells obtained by mechanical detachment. Cell seeding density was 2.10(4) cells/cm2 (Group A, n = 6) or 10(5) cells/cm2 (Group B, n = 6). Rotation speed was 8 revolutions per hour (rph) during 90 min. Analysis of the homogeneity of cell seeding was permitted by cell counts on five different segments of the prosthesis. Each longitudinal segment was analyzed at three different subsegments of the circumference. The average adhesion was 43 +/- 4% in Group A and 38% +/- in Group B of seeded cells. No difference could be observed between the different segments and subsegments. In the two groups, cells were spread, and in Group B, a complete endothelial cell layer was obtained on the graft surface. This study permits validation of the device to allow homogeneous cell seeding in an arterial prosthesis.

[Discordant heart xenografts. Experimental study in pigs conditioned by total lymphoid irradiation and cyclosporine A]. / Xénogreffes cardiaques discordantes. Etude expérimentale chez le porc conditionné par irradiation lymphoïde totale et ciclosporine A.

The use of discordant xenografts may solve some of donor shortage problems. The beneficial effects of treatment with total lymphoid irradiation (TLI) and classical drugs on this discordant model of transplantation rejection was evaluated. Twenty-four lamb hearts were transplanted heterotopically in the abdomen of 24 pigs. Group I received no treatment (control). Group II received continuous intravenous medical treatment cyclosporin A (CyA) (5 mg/kg) and azathioprine (3 mg/kg) 3 days prior to transplantation. Group III received the same medical treatment and simultaneously 12 grays of irradiation in 5 equal fractions with a high rate (100 cGy/min) or a low rate (1.6 cGy/min) prior to transplantation. Group IV also received 12 grays in 5 fractions at a high rate followed by the medical treatment started 5 days after TLI and continued until the day of transplantation. Antibody and serum cyclosporine levels were monitored. Histology specimen were analyzed at the end of the experiment. Mean GST (graft survival time) in group I and II was 140 +/- 35 min and 117 +/- 27.4 min respectively. The histological features of these hearts suggested acute humoral rejection (hemorrhage, thrombosis, and edema) without cellular infiltration. In group III, one heart functioned 4.5 days with pathological features of cellular rejection and a second animal died at 6 hours with a functioning graft with no evidence of an acute rejection. Both had been treated with the low rate TLI protocol (1.6 cGy/min). The mean GST in this group was 1080 +/- 794 min. In Group IV, one graft functioned for 6.5 days and another for 3.25 days. Mean GST was significantly increased in this group to 4800 +/- 2647 min (p < 0.05). A cellular infiltration was seen in this two grafts. The remaining graft was rejected in 6 hours with histological lesions typical of acute humoral rejection. Antibodies levels at the time of transplantation were lowest (40%) in group IV and in the low rate irradiation group. The ability of TLI to induce tolerance and to prolong survival in a discordant xenograft model depends upon cumulative dose, rate of irradiation, delay between TLI and graft placement, and combined treatment with immunosuppressive drugs. A high rate of TLI and graft placement is delayed. Low rates of irradiation may be beneficial when there is a very short period between treatment and transplantation. These findings highlight the potential usefulness of TLI in combination with immunosuppressive drug therapy when antibody-mediated rejection occurs, such as with xenograft and in sensitized patient.

Mode of failure of the Mitroflow pericardial valve.

A consecutive series of 188 Mitroflow pericardial bioprostheses were inserted in 166 patients between 1st January 1983 and 31st December 1985. Twenty-two valves had to be removed from 16 patients after a mean follow up period of 78 months (range 58-92 months) for aortic, 73 months (65-79 months) for mitral and 78 months (48-103 months) for double valve replacements. All but one reoperations for primary tissue failure were carried out as elective surgical procedures. The most important cause of failure was collagen degeneration, seen in all explanted valves. The areas of degeneration were the major sites of origin of calcification, which was seen in 11 valves (50%). Ten valves (45%) showed features suggestive of lipid infiltration, extensive fatty acid deposition being identified in one and a typical atheromatous reaction in another. In contrast to the Ionescu-Shiley valve, the mode of failure was tear originating at the top of the commissure, associated with major structural changes in the tissue. Excessive pannus ingrowth was observed in 11 valves (50%). The universal presence of tissue degeneration in the glutaraldehyde treated pericardial leaflets of the Mitroflow bioprostheses explanted and examined in this study questions the adequacy of the methods employed in the harvesting and/or processing and/or preservation of this valve. We have, therefore, discontinued using the Mitroflow bioprosthesis. However, the slow deterioration of the Mitroflow bioprosthesis permits elective reoperation; preventive removal of functioning valves is therefore not indicated.

Enhanced O2 transportation during cardiopulmonary bypass in piglets by the use of inositol hexaphosphate loaded red blood cells.

A continuous lysing and resealing of erythrocytes permitted internalization of inositol hexaphosphate (IHP), a strong allosteric effector of Hb, leading to significant rightward shifts of the HbO2 dissociation curve. Twelve piglets were put on cardiopulmonary bypass (CPB) with the heart beating, cooled to 25 degrees C then rewarmed to 37 degrees C before weaning off CPB. AoP, LV pressure, PAP, and cardiac output (CO) were monitored. Blood samples were taken before CPB, at 25 degrees C, at 30 degrees C, at 37 degrees C and after CPB for assessment of blood gases, arterio-venous difference in O2 content, lactates, P50 (partial pressure of O2 at 50% Hb saturation), and ionogram. Control group I included five pigs where the CPB circuit was primed with Ringer's lactate solution and porcine blood. In group II (n = 5), priming was done with Ringer's lactate solution and IHP loaded erythrocytes. P50 was significantly higher during CPB than before surgery in group II (20%), but not in group I (1%). There was a significant increase in VO2 in group II (6.02 ml/min) compared to group I (4.03 ml/min) (p less than 0.05) after CPB. Hemodynamics improved after CPB in group II (mean AoP 42 mmHg and syst LVP 70 mmHg) compared to group I (AoP 25 mmHg and syst LVP 22.5 mmHg). These preliminary results show that O2 transportation at the end of CPB is enhanced and myocardial function is improved in piglets with the use of IHP erythrocytes.

In vitro endothelialization of carbon-coated Dacron vascular grafts.

Physical vapour deposition is used to coat vascular prostheses with pyrolytic carbon. This coating may facilitate the development of an endothelial monolayer in grafts implanted in laboratory animals. This in vitro study compared the adherence and growth of cultured porcine aortic endothelial cells (EC) seeded in vitro on carbon-coated Dacron, to uncoated prostheses. The cells were incubated at 5 x 10(4) cells/cm2. Progress was monitored at different times (TO + 2 hours, D 1, D 4, D 8) by microscopic observation, when cell counts were made; and by scanning electronic microscopy (SEM) to evaluate morphological EC-graft interactions. Cell adherence was independent of the carbon coating but cellular growth occurred only on carbon-coated Dacron. The SEM observations showed both the shape of the adherent cells, which were rounded on uncoated Dacron and extensively spread on carbon-coated prostheses, and the morphology of the carbon coating.

[Conflicting xenograft. Role of preoperative total lymphoid irradiation]. / Xénogreffes discordantes. Le rôle de l'irradiation lymphoïde totale pré-opératoire.

This study deals with an experimental model of discordant cardiac xenograft between 24 donor lambs of the Préalpes race and 24 recipient Camborough pigs divided up into 4 groups: I control (6) without immunosuppressive treatment; II (5) with pharmacological immunosuppression (IP); III (13) with PI and total lymphoid irradiation (TLI) and immediate graft, divided up into IIIa (5) with high-rate (HR) TLI and IIIb with low-rate (LR) TLI; IV (4) with a two-week lapse between TLI and grafting. The best graft survival rate (GSR) is obtained either after delayed LR-TLI or after LR-TLI without delay. This study seems to be the first one demonstrating that for discordant xenogenic grafts, TLI associated to PI with cyclosporin A (Cy A) significantly prolongs the survival of the graft (30 times).

Palliative treatment of bile duct tumoral compression by an endoprosthesis: clinical results.

The palliative therapy of stenoses of the biliary tract is a difficult choice. Because percutaneous or endoscopic drainage methods are fraught with complications, an endoprosthesis for surgical intubation of the biliary tract has been developed. Thirty patients were treated by this method. After choledochotomy, the endoprosthesis is positioned surgically above the sphincter of Oddi, thereby avoiding ascending cholangitis. Twenty-nine patients (13 with gallbladder cancer, 11 with cholangiocarcinomas, 5 with metastases) presented with neoplastic compression, and one patient had an early postoperative stricture with loss of substance after right hepatectomy for hepatic metastases. The operative mortality was 3.3% (one pulmonary complication). Resolution of jaundice was obtained in all but two patients, and pruritus always resolved. The mean survival time for the patients with cholangiocarcinoma was 12.2 months and 6.33 months for those with gallbladder cancer. Indices of satisfaction (Bismuth's method) were 71% (gallbladder cancer), 93.5% (hilar cholangiocarcinoma), and 92% (metastatic compressions). This new type of surgical endoprosthesis is an alternative in the palliative treatment of neoplastic hilar compression because it is well tolerated, has a low rate of operative mortality or morbidity, and affords an acceptable quality of life for the patients.

Protection of the small intestine against irradiation by means of a removable prosthesis.

In radiation therapy of tumors, several techniques are used to prevent injury of the intestinal loops. Their purpose is to drive the intestine out of the external beam. Understanding the disadvantages they present, a temporary prosthesis which effectively protects the small bowel, and is easy to remove, has been developed. The device is a 600 to 1,000 ml, silicone rubber, expandable balloon. When implanted in the pelvis or retroperitoneal cavity, and filled, this balloon displaces the intestinal loops out of the pelvic irradiation field. It may remain either filled or empty between each irradiation session. Due to its particular elliptical shape, once empty, the balloon can be removed through a 3 cm incision under local or peridural anesthesia at the completion of radiotherapy. Eleven patients with recurrent (8) or primary (3) cancer have been implanted. The protective effect has been evaluated on successive biologic tests, performed during treatment. No problem related to the prosthesis, no alteration of the biologic tests, nor bowel injury have been observed after several months follow-up. This device is suitable for preventing intestinal complications during therapy, allowing a higher dose of radiations in some cases.

[New surgical procedure for the protection of the small intestine before postoperative pelvic irradiation]. / Nouveau procédé chirurgical de protection du grêle avant irradiation pelvienne post-opératoire.

A prosthesis was designed to protect the intestinal loop from external beam radiation therapy when post-operative radiation is indicated. It is a silicone inflatable balloon, which, when implanted displaces the intestinal loops out of the pelvic irradiation field. The prosthesis can be deflated between each course of irradiation, without surgery. The device has been used in 8 patients: 6 patients with recurrent pelvic tumor (2 rectal cancers, 1 anal cancer, 1 cancer of the endometrium, 1 cervical carcinoma, 1 ovarian carcinoma), 2 patients with primary tumor (1 malignant paraganglioma, 1 cervical carcinoma). Radiotherapy was administered by means of high power appliances. After radiotherapy, the prosthesis was deflated, then removed through a 3 cm incision under local or peridural anesthesia. The tolerance of the small intestine to the radiation therapy has been satisfactory in each case with no bowel injury due to radiation. Therefore, this simple device might be useful to prevent bowel injury during postoperative radiation in the treatment of abdominal and retroperitoneal tumor masses.

[Experimental study of arterial microanastomoses under tension in the Wistar rat. Morphologic and histologic effects]. / Etude expérimentale des microanastomoses artérielles sous tension chez le rat Wistar. Effets morphologiques et histologiques.

An experimental study was performed to evaluate the effects of tension on microsurgical anastomoses. A variable length of the common carotid artery in Wistar rats was resected to give variable degrees of tension and the artery was reanastomosed microsurgically. 42 Wistar rats were divided into 7 groups of 6 rats each according to the relative length resected. Repaired arteries were then compared histologically and functionally with the artery of the contralateral side, submitted to simple section followed by microsurgical anastomosis. Significant histological changes occurred when the length of the resected segment was greater than 13.33% of the vessel's total length. These changes included subendothelial hyperplasia, medial necrosis and thrombosis. The results of this study lead us to conclude that small degrees of tension (less than 13.33% of total vessel length in this study), have no significant effects on patency of microanastomoses. Greater tension results in changes in the laminar flow through vessels that can adversely effect patency. There are also significant histological changes that may have detrimental effects in the long term.

The Mitroflow pericardial valve. First five years of follow-up evaluation.

The first 5 years durability study on a substantial number of Mitroflow pericardial valves makes the substance of the present report. One hundred eighty-eight valves were implanted on 166 patients before December 1985: 149 patients were discharged and are recalled annually. Follow up is 99% complete. In October 1988, mean follow up was 3.5 years (3-5.5). Total patients times years is 582. Sixty-two percent of the patients are asymptomatic, 58% in sinus rhythm. Forty-seven percent do not receive any anticoagulant therapy. The linearized rates of thromboembolism (1.2% per patient-year) and endocarditis (0.17 per patient-yr) is minimal. Seven patients only had valve dysfunction requiring explantation (1.2% per patient-yr). At 5 years, freedom of structural deterioration is 95.2% +/- 2.1. Single cusp tear at a stent post is the most frequent lesion (86%) as calcifications are observed in three only (major in two, microscopical in one). Histology does not permit to ascertain whether the tear is due to tissue fatigue or abrasion. Moderate microscopic architectural disruption of the valvular tissue is observed. Composite indices of all valve mortality and morbidity show at 5 years a 89.7% +/- 2.9 freedom of events. These data, associated to the high mechanical and optimal clinical characteristics of the valve, published previously, confirm the satisfactory performances of the valve at 5 years.

An original inflow cannula for paracorporeal assist devices.

Cannulae for paracorporeal ventricular assist devices have been clinically shown to be limiting factors in optimal circulatory support. A new inflow cannula has been manufactured according to an original silicone rubber molding process, permitting a hemocompatible inner surface. The cannula is 200 mm in length, with a 10 mm internal diameter. The wall is 3 mm thick and reinforced by a stainless steel spiral spring embedded in the silicone. An external ring permits adequate interface between the cannula and the endocardial surface of the atrium. A compliant external segment on the inflow cannula, free of any spiral spring, allows adjustment of vacuum to optimal values, thus avoiding inflow obstruction. The cannula has been tested during 1 to 5 days of left ventricular bypass in calves (n = 15). A Symbion AVAD, Utah 85 VAD, or Centrimed pumps were used. Adequate heparinization was maintained throughout. Paracorporeal flow was 0.045 L min-1 kg-1. In vivo evaluation was made by hemodynamic studies and the incidence of thromboembolism. The cardiac cavities, cannulae, and peripheral vessels were carefully searched for thrombi and emboli at autopsy. The atrium, the interface between atrium and silicone cannula, and the cannula itself were found free of any deposit. This aspect differed from that observed previously with available PU or PVC cannulae.

Centrifugal pump or pneumatic ventricle for short-term mechanical circulatory support?

Two comparable groups of four Holstein calves were implanted with different left ventricle assist devices: the Centrimed centrifugal pump (CP) (Sarns Inc.) or the UTAH 85 VAD pneumatic ventricle (University of Utah). Operative procedure, inflow and outflow cannulae, monitoring, heparinization, were identical in both groups. No transfusion was ever required. The study was terminated after three days and autopsy was performed on the calves. Left ventricular unloading provided by both devices was complete (LVEDP less than 1 mmHg) and identical. LV bypassed flow rate was higher in CP (0.045 L/min/kg) than in UTAH 85 VAD (0.035 L/min/kg) but with no statistical difference. Blood trauma was comparable in the two groups. Daily blood samples did not show any significant changes from baseline values in creatinine, hematocrit, fibrinogen. Platelet loss from initial level was 30%; serum lactate dehydrogenase rose 150% with no significant difference in the two groups; plasma free hemoglobin never reached significant values. At autopsy, thrombotic deposits on cannuale and renal infarction rate were similar. CP housing had to be changed every day, whereas no technical failure was ever observed with the UTAH 85 VAD. Clinical response and blood damage of the two pumps used as LVAD were the same. Considering the CP has to be replaced every 24 h, the cost of three CP's would be comparable to one Utah UVAD-85 if polyurethane tricusp semi-lunar valves are used in the latter. Until the UTAH-85 VAD becomes commercially available, simple valveless low-cost CP are very attractive for short-term mechanical support.