Knute Berger

Histologic fate and endothelial changes of distended and nondistended vein grafts.

Sixty-two autogenous cephalic vein segments were grafted into the femoral arteries of 31 mongrel dog: the left side receiving non-distended (control) grafts and the right side distended (experimental) grafts. Distending media were heparinized blood and saline. Veins were distended at 600 mm Hg for 2 minutes. Specimens were taken at intervals from 15 minutes to 3 months, and were studied by gross inspection, surface observations (light scanning stereoscope to X 70 scanning electron microscope to x 6,000) and routine histologic techniques (light microscope to X 1000). In general, grafting of veins in the arterial system was followed by progressive degenerative changes in all layers of the vein, including endothelial cell involution, desquamation and re-endothelialization. Often a variable degree of subendothelial fibrous and/or myoepithelial proliferation occurred which might compromise even a lumen lined by healthy endothelium. Distention caused these changes to occur earlier (2–4 weeks) and to be more pronounced. Distention with saline caused more damage to the endothelium than did distention with blood. We conclude that preimplant distention of vein grafts (to overcome spasm) should be employed sparingly, as it adversely affects the endothelial covering of the flow surface, accelerates the development of degenerative changes, and may predispose the graft to early thrombotic complications.

Presence of endothelium in an axillary femoral graft of knitted Dacron with an external velour surface

An axillary-bilateral common femoral graft of knitted Dacron with an external velour surface was examined within one hour after the patients death from non-graft-related causes. The prothesis, implanted for 20 months, was patent and was completely healed over 32% of the flow surface—that is, full wall fibrous tissue encapsulation of the graft had occurred, and 32% of the flow surface was endothelialized. The remaining flow surface was formed of fibrin, but fibrous tissue healing had reached the inner surface of the graft material, and the fibrin overlay was very thin. The healed portions of the graft included not only the areas adjacent to the anastomoses, but were scattered throughout the 45 cm length of the prosthesis. To our knowledge, this is the first report of complete healing (fibrous tissue encapsulation and endothelialization) documented at points beyond the pannus ingrowth at the prosthesis-artery anastomosis.

Experimental comparison of the thrombogenicity of fibrin and PTFE flow surfaces.

Two types of 4 mm ID prostheses were studied in the carotid arteries of the dog. These were noncrimped polypropylene-supported filamentous velour knitted Dacron® (PPSFV) and expanded polytetralfluoroethylene (e-PTFE, Gore-Tex®). Thrombus-“Free” Surface (TFS) areas and patency rates were determined at the end of the implant periods. One series of implants was subjected to controlled low flow rates for six hours; another was exposed to physiologic flow rates and observed at seven days, 14 days, and 12 weeks. At six hours the filamentous Dacron, preclotted according to a specific regimen utilizing heparin, performed as well as, and possibly better than, e-PTFE. The Gore-Tex developed surface coagulum in an irregular fashion which was related to graft wetting and blood soakage. Seven-day TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates dropped. This was sufficiently marked in the case of e-PTFE that longer-term implants were not done. However, PPSFV grafts were implanted for 12 weeks, and all grafts examined at that time had closed. It appears that patency of 4 nim ID grafts of this construction will not be reliably attained in the dog carotid artery without the use of platelet-inhibitory drugs until complete healing has occurred.

PROSTHETIC HEART VALVE REPLACEMENT

Successful prosthetic heart valve replacement, now out of its infancy, represents one of the significant advances of biomedical engineering. Yet this is only a partial accomplishment, for many problems remain. A heart valve replacement, to be judged completely successful, should (1) be easily implantable, (2) evoke minimal thrombus coverage limited to the attachment mechanism (sewing ring), (3 ) be quickly healed in permanent position by the host tissues, (4) present no resistance to forward flow, (5) allow no regurgitation, (6) do no damage to the blood, and (7) show no wear or fatigue. At present, no prosthetic heart valve completely satisfies all of these criteria. In addition, all are liable to the complications of uncontrolled thrombosis, embolism, infection and dehiscence. The ball valve has been the most widely used type of prosthesis, and hence the most significant long-term follow-up information concerns this valve. Thromboembolism, more frequent in the mitral area than in the aortic, has been a consistent c~mplication.~-l~ Complete obstruction due to thrombotic occlusion of the prosthesis4p1 -13p18-20 or to distal blockage by the ba11’8821,22 has been reported. The incidence of infection, although reduced in recent. years by the prophylactic use of antibiotics, is still a complication to be reckoned with.1~2~4~6~8~10~11~14~16Detachment of the valve may be large or small in extent, the results varying from mild incompetence to massive regurgitation and death. 1-4~6.8~10*14~18~27,28 Chronic hemolytic anemia in patients with ball valve prostheses is often associated with Ieak.2~~9 It is also thought to be due to ( 1) mechanical trauma resulting from action of the ball and from turbulence, especially in the aorta, (2) to contact of the red blood cells with the foreign materials of the p r o s t h e ~ i s , ~ * ~ ~ ~ ~ ~ and possibly (3) to an autoimmune mechanism.35 A few cases of ball wear and extrusion have been r e p ~ r t e d . ~ J * p ~ ~ ~ ~ When the left ventricular chamber has been small, the mitral ball valve has been found to cause obstruction of the outflow tract or to impinge upon the interventricular septum resulting in “rhythmic” deaths or “obstructive” d e a t h ~ . ~ ~ p ~ ~ * ~ With this in mind, prostheses have been designed with a low ventricular profile,l~,40.42,45,40,63 the moving part being a disc, lens, a centrally hinged flap or a 18.23.27

Glutaraldehyde preparation of coronary artery bypass bioprostheses

A method for glutaraldehyde (GA) fixation of canine carotid arteries has been developed for the preparation of small caliber biologic prostheses for coronary artery bypass. The biologic grafts were preserved by a static inflation technique that proved to be more advantageous than the standard stenting method. The most suitable static inflation pressure was found to be 120 mm Hg. By means of colorimetric measurements the minimal tanning time and the amount of GA required for complete fixation for canine vascular tissue were established. Stabilization of the vessel collagen and confirmation of GA-collagen cross-linking were verified by evaluation of the elastic properties and shrinkage temperature of the grafts. Stress-strain measurements were evaluated to determine the number of cross-links introduced in the vascular tissue by GA. This number was shown to be proportional to the inflation pressure. Ethyl alcohol was chosen as the storage solution because it maintained the best physical, chemical, and histologic characteristics of the grafts. Biological evaluations were performed with carotid implants that were examined following acute low flow studies and implantations up to 112 days. All implantations have yielded 100% patencies.

A healable filamentous Dacron surgical fabric. Experimental studies and clinical experience.

A strong, lightweight, highly compliant Dacron surgical fabric of warp-knit, velour construction has been developed as an outgrowth of research on filamentous tubular vascular prostheses. This material has excellent suturability and conformability, high preclotting efficiency, and is imprinted with calibration marks at 2 cm intervals. Experimentally, iliac artery and descending thoracic aorta patch grafts of this material were completely healed 28 days after implantation in dogs. Light and electron microscopy showed excellent healing. This paper reports clinical results of 119 patches implanted in 109 patients who have been followed for a mean of 26.4 months (range: 16--34 months). Of these, 20 patches were used in arterial reconstructions, and 99 were used in the heart for repair of 95 congenital and four acquired defects. The 20 patch angioplasties were performed in the carotid artery (four patches), subclavian artery, (one patch), common femoral artery, profunda femoris artery, or superficial femoral artery (10 patches), and in the popliteal artery (five patches). This new surgical fabric is easily adaptable to complex angioplasties and for repair of intracardiac abnormalities. No complications intrinsic to the surgical fabric have been observed in clinical use of this material in 109 patients.

The Carotid Artery as a Coronary Bioprosthesis: Five Potential Donor Species

Bovine, porcine, ovine, caprine and canine carotid arteries were chosen for study as potential sources of aortocoronary bypass biologic prostheses for use in patients undergoing reconstructive surgery. Anatomic and histologic evalua tions, structural measurements and static mechanical property tests were per formed. The canine carotid arteries have an average length of about 20 to 21 cm with the considerable advantage that there is only one branch, located near the distal end. They also offer the most uniform luminal diameter of 3.0 to 4.0 mm and the most uniform wall thickness (approximately 0.5 mm). The suitable lu minal diameter and wall structure provide a good match to the coronary arte rial anastomosis. Although the canine carotid artery has a thinner wall, static mechanical property tests demonstrate that wall strength and elasticity are com parable to the four other species studied. The canine carotid artery appears to best fit the suggested criteria for a biologic aortocoronary bypass prosthesis from a readily available source. As such, the canine carotid artery in a properly processed form appears worthy of experimental study for aortocoronary bypass surgery.

Influence of amount of exposed fabric on thrombotic complications of aortic ball valves in the calf

Abstract The results of ball valve replacement of the aortic valve in fifty-two calves are reported. These observations indicate that the less fabric exposed to the blood and the closer the fabric cuff to the suture line, the lower the incidence of thrombotic complications in this species.