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Between May 1975 and March 1977, 193 bovine heterografts and 184 polytetrafluoroethylene (PTFE) grafts (Impragrafts) have been placed for hemodialysis access. A comparison of these materials demonstrates that Impragrafts have significantly fewer late thromboses, increased resistance to infection, and comparable longevity, and they are easier to repair.
Pulmonary valve replacement is an uncommon surgical procedure, yet lifesaving when performed under the appropriate circumstances. The patient reported on here had the classic indications for valve replacement: increased pulmonary vascular resistance and associated pulmonary valve incompetence following repair of a congenital heart defect resulting in right heart failure and secondary tricuspid insufficiency. A review of the literature provides the basis for the decision to replace the pulmonary valve with a glutaraldehyde-preserved porcine heterograft.
A patient who had aortic and mitral valves replaced by Carpentier porcine heterografts for bacterial endocarditis developed severe heart failure 18 days after operation. A second emergency operation revealed that the mitral prosthesis had become severely stenosed and calcified. A loud Graham Steell murmur had developed during the 12 hours before reoperation but no distinct murmurs of mitral stenosis had been detected.
Three patients with porcine atrioventricular valves (two mitral, one tricuspid) with diastolic rumbles and presystolic murmurs are presented. Full hemodynamic and angiographic studies demonstrated moderate to severe prosthetic stenosis, even in the one patient who was minimally symptomatic. Diastolic murmurs across atrioventricular porcine heterografts indicate prosthetic stenosis until proved otherwise by full hemodynamic and angiographic studies. If the studies indicate normal function of the device and calculated prosthetic valve area that is small for the patient, then it must be recognized that the device is hemodynamically "stenotic" for that particular patient (valve prosthesis--patient mismatch).
In this study, L-Asparaginase has been bound to collagen heterografts derived from carotid bovine arteries. The immobilization procedure utilizes both non-covalent and covalent interactions to fix the enzyme. Binding of the enzyme to the graft material was shown to the pH dependent, with optimum binding occurring at pH 6.0 and pH 8.5. Amidohydrolysis by the bound enzyme exhibited zero-order kinetic behavior at substrate saturating conditions. Total apparent asparaginase activity expressed by the grafts as a function of the number of repeated in vitro assay trials demonstrated that over a span of 3 months of intermittent storage and use, the enzyme-grafts retained as much as 62% of their initial activities. Implantation of 4 asparaginase-collagen grafts in various locations of the thoracic and abdominal aorta resulting in prolonged reductions of plasma asparagine levels in 3 of the 4 implants. Presence of plasma asparaginase was checked in one of the four implants and determined to be less than 2 X 10(-4) I.U./ml. Removal of grafts from 3 of the 4 animal subjects showed reductions in the apparent asparaginase activity expressed by the grafts of 7 to 70 percent after in vivo contact times which varied from 6 to 15 days.
As compared with previous methods of donor site care, procine heterograft dressings allow the donor site to heal faster, require less postoperative care, are associated with a lower infection rate and eliminate virtually all of the pain of the split-thickness wound. Our experience supports that of others. We believe our modifications of this technique to be superior to previous modalities of donor site care.
Two commercially prepared, glutaraldehyde-treated porcine heterograft valves mounted on flexible stents have been tested in a pulsatile-flow water tunnel. Measurements of the radial deflections of the stent posts have been made for various applied pressures across the valve. A previous claim of 90 percent reduction in leaflet stress as a result of stent flexibility is of doubtful validity because the measurement technique used was inappropriate for the magnitude of strain involved. Photographs of the valve at various steady forward flow rates show that the leaflets do not open as readily as the antibiotic-treated homograft valve.
Transplantation of the superior cervical ganglion of rat, after by organe culture retains ultrastructural integrity of the cells for a longer period than transplantation alone. Whatever the graft--homo or heterograft--neuronal survival is extended. Apart from minuts differences, S.I.F. cells show the same evolution. Ultrastructural features modified after culture always return to their initial state. Numerous after the culture always return to their initial state. Numerous after the culture, the lysosomes disappear in the first weeks following the graft. This cytoplasmic epuration is very important, since it might regenerate the cell and dilate its antigenic properties. Without the graft, the cytoplasmic epuration does not take place; vascularization is considered as a favourable factor of evolution. The association graft-culture has a double impact on survival of SCG cells. The culture initiates a cellular epuration, the graft quickens and perfects the return to a normal morphology.
In sequence with an earlier publication on the results of heterograft tracheal transplants in animals, changes in the Formol-Cialit preserved heterogenous tracheal grafts were studied by light microscopy, and by scanning and transmission electron microscopy. Two main queries arise. Where does the graft respiratory epithelium come from, and what happens to the grafted tracheal cartilage? We found that in the epithelium of graft the number of ciliated cells decreased and that there was ultrastructure evidence of cilial destruction, the goblet cells increased in number, there was a loss of strict polarity of the respiratory epithelium, subepithelial accumulations of cells of probable epithelial origin appeared, and there was a subepithelial accumulation of lymphocytes just beneath the basal lamina. Resorption and transformation of the grafted tracheal cartilage into connective tissue was also observed. Hence, the following conclusions may be made. (1) Small tracheal defects can be corrected by Formol-Cialit preserved heterologous grafts. (2) The mucosa of the host trachea produces a functioning respiratory epithelium in the graft. (3) Tracheal grafts should not exceed 2 x 3 cm in size otherwise a new stenosis from resorption and transformation of grafted cartilage into connective tissue will occur.
Use of the Hancock, glutaraldehyde-preserved, stented heterograft for aortic valve replacement has gained wide acceptance in the past 7 years. Nevertheless, very little is known about the long-term mechanical and pathological characteristics following implantation. A rare case is presented in which mechanical valve failure occurred secondary to leaflet disruption in the absence of infection 23 months after implantation. The literature is reviewed and the implications of this unusual complication are discussed.
Details are reviewed of a case of transient cerebral ischemic attacks which probably resulted from thromboembolism from a Hancock porcine heterograft prosthesis. Cause of the embolism probably was thrombus formation on the worn cloth covering of the supporting valve stent. Technical and antomic factors which assure precise seating of the prosthesis in the mitral anulus without contacting the ventricular wall appear to be important in preventing this complication.
Of 200 patients who received porcine heterograft cardiac valves, the first 100 did not receive postoperative anticoagulant therapy. In the second 100 patients anticoagulant measures were used when thrombogenic factors not related to the prosthesis were evident. Anticoagulation should be employed following mitral valve replacement while factors contributing to thromboembolism prevail. The conditions that tend to induce vascular stasis in the left atrium followed by embolism are chronic atrial fibrillation, a large dilated left atrium and a calcified left atrial wall. The results of our study provide assurance of the continued use of the porcine bioprosthesis.
Mitral valve replacement for congenital mitral stenosis has been performed infrequently in infants. In all but two previously reported infants, the valve has been replaced with a mechanical prosthesis. The case history of an infant is reported in whom emergency mitral valve replacement was successfully performed with a porcine heterograft excised from a tubular prosthesis. This approach is an acceptable alternative when a valve of appropriate size is unavailable.
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The production of prosthetic valve incompetence during atriotomy closure is among the operative maneuvers utilized to prevent air embolism in mitral valve replacement. The leaflets of a porcine bioprosthesis may be retracted safely and effectively, thereby producing temporary valve incompetence, by placing three polypropylene sutures through the valve orifice and around the sewing ring to encircle the leaflets. These traction sutures are eaily pulled out through the atriotomy suture line after all air has been displaced from the heart. The technique has been effective, easily accomplished, and without complications.