Ibuprofen in experimental vascular surgery.

Animal studies have been conducted to determine the effectiveness of ibuprofen in reducing early platelet deposition on small diameter (4 mm) Gore-Tex (polytetrafluoroethylene) arterial grafts and larger (10 mm) Gore-Tex grafts placed in the inferior vena cava. These studies demonstrated a significant reduction in platelet deposition at one and three hours. Additional studies of animals undergoing treatment with ibuprofen and subjected to arterial replacement with 1 or 4 mm Gore-Tex grafts demonstrated enhanced patency at 30 days. Cautious evaluation of ibuprofen as an adjunct in vascular surgery appears warranted.

The relationship of clinical outcomes to status as a Medicare-approved heart transplant center.

This study reports the evaluation of the validity and utility of the Medicare heart transplant center selection process, as outlined in its 1986 Heart Coverage Regulations. A total of 9401 heart transplants performed in the U.S. between 1986 and 1991 were analyzed. The outcomes assessed were mortality and the occurrence of infection during the hospital stay. Outcomes experienced by centers with and without Medicare approval were compared directly and following adjustment for patient risk factors. Patients at centers that satisfied the Medicare criteria experienced lower mortality. The risk-adjusted hazard ratio for death over the five years of observation was 0.874 (P = 0.005). The probability of death following a transplant at a Medicare-approved center was 7.0 +/- 0.4% at 30 days and 16.2 +/- 0.6% at one year, and 9.2 +/- 0.4% and 19.2 +/- 0.6%, respectively, at centers without Medicare approval (P = 0.001). The difference appeared to be principally associated with death within 30 days of admission due to nonspecific graft failure. The posttransplant infection rate at Medicare-approved centers was 0.743 (P < 0.001) but this result is strongly confounded with differences in reporting patterns of the two types of centers. Criteria used by HCFA identify medical centers where outcomes of heart transplantation, as measured by mortality, are superior. This difference is established early, persists over time, and is not attributable to the numerous risk factors considered in our models. Overall, the results of the present study suggest that "centers of excellence" can be identified through the evaluation of center characteristics and outcomes, and that this approach chosen by HCFA may have broad health care systems applications.

A new concept for successful long-term pulmonary preservation in a dog model.

We developed a dextran-glucose-based extracellular perfusion solution (DGX) that supports limited aerobic metabolism to maintain cellular integrity of an inflated donor lung during long-term ischemia and a storage temperature of 10 degrees C. In a dog model, we compared respiratory and hemodynamic function of orthotopically transplanted left lungs preserved using this method (DGX, group I, n = 6) with function of those preserved with EuroCollins solution (EC) stored at a temperature of 4 degrees C (group II, n = 6). All lungs were inflated with room air and stored for 12 hr. Pulmonary function was monitored for 5 hr of reperfusion. Values expressed below are group means with standard deviation. Statistical significance was calculated using a two-tailed t test. For PO2 (mmHg) (FiO2 = 0.4), group I (EC): control = 193 +/- 8, 30 min p.o. = 87 +/- 20*, 300 min p.o. = 174 +/- 13*; and group II (DGX): control = 217 +/- 28, 30 min p.o. = 184 +/- 46*, 300 min p.o. = 248 +/- 5*. For pulmonary vascular resistance (dynes), group I: control = 389 +/- 22, 30 min p.o. = 1209 +/- 301, 300 min p.o. = 1025 +/- 204*; and group II: control = 401 +/- 31, 30 min p.o. = 522 +/- 129, 300 min p.o. = 458 +/- 137* (*P < 0.05 DGX vs. EC). Gas analysis performed on air samples taken from the ischemic donor lung immediately after harvest and after 12-hr storage showed (calculated as group means) a significant decrease of PO2 and a significant increase of PCO2, respectively. Histology of the lungs after 5 hr of reperfusion showed essentially normal-appearing lungs in the DGX group, whereas lungs in the EC group showed thickening of the intra-alveolar septi, marked cellular infiltration, and accumulation of protein-like material in the alveoli. In this study, preservation with DGX resulted in satisfactory respiratory and hemodynamic function of the transplanted lung even after 12 hr of ischemia. It does not cause an increase of pulmonary vascular resistance as seen after preservation with EC. Data from the intrabronchial air analysis of the donor lung suggest that aerobic metabolism continues even under preservation conditions.

Reduction of thrombosis in canine coronary bypass vein grafts with dipyridamole and aspirin.

The potential benefit of platelet inhibitor drugs in reducing early thrombosis of coronary arterial vein bypass grafts was assessed in dogs. There were 26 control dogs and 24 dogs treated with dipyridamole, 55 mg/day plus aspirin, 325 mg/day. The dogs in both groups were killed at 2 hours and 1, 2, 3, 7 and 14 days after operation. The grafts were perfused with fixative in vivo, harvested and examined with light microscopy. Severe alterations of the graft wall were observed in the dogs in both groups. The grafts in the control group had a high incidence rate of thrombosis, which occurred early after the operation; those in the treated group had a significantly reduced incidence of thrombosis (p = 0.025). Our study indicates that a combined regimen of dipyridamole and aspirin is effective in reducing early graft thrombosis in dogs.

Reduction of intimal thickening in canine coronary bypass vein grafts with dipyridamole and aspirin.

The potential benefit of platelet inhibitor drugs on coronary arterial bypass vein grafts was assessed in dogs with magnification-corrected angiographic luminal measurements and quantitative histologic evaluation of the vein grafts. There were 11 control animals and 11 animals treated with dipyridamole, 55 mg/day, plus aspirin, 325 mg/day. Eighteen animals with patent grafts were studied when electively killed 2, 4 or 6 months after grafting. At 14 days, there was greater angiographic narrowing in the most distal 1 cm of vein grafts in control than in treated dogs (P less than 0.01). This same angiographic narrowing persisted in control dogs until they were killed (P less than 0.03). Computer-assisted measurements of the entire area of intimal thickening were done on vein graft cross sections taken 1 cm from the distal anastomosis. The circumference of the vein grafts at the intimal-media junction was measured from the same section and the potential maximal luminal area calculated. The calculated luminal narrowing due to intimal thickening was greater in control than in treated dogs (P less than 0.03). These data correlate well with the demonstrated angiographic narrowing. The findings indicate that the degree of early intimal thickening that persists 2 to 6 months postoperatively in canine coronary bypass vein grafts may be reduced by the platelet inhibitor combination of dipyridamole plus aspirin.

Comparison of the antithrombotic action of calcium antagonist drugs with dipyridamole in dogs.

Because platelet activation is associated with fluxes of intracellular calcium, calcium antagonist drugs such as verapamil and nifedipine may have useful platelet inhibitor effects. Accordingly, the effect of these drugs was compared with that of dipyridamole, an established platelet inhibitor, in preventing the deposition of indium-111-labeled autologous platelets and thrombus development in polytetrafluoroethylene (Gore-Tex) grafts interposed in both femoral arteries in mongrel dogs. Eight dogs received verapamil 7.5 micrograms/kg/min perioperatively, 8 dogs received nifedipine 4 micrograms/kg/h perioperatively, 8 dogs received dipyridamole 50 mg orally given twice during the 24 hours before operation, and 16 control dogs received isotonic saline solution perioperatively. After 3 hours of perfusion, the median weight of the grafts and luminal thrombus was less in dogs treated with dipyridamole (465.1 mg), verapamil (453.7 mg), or nifedipine (389.7 mg) than in control dogs (680.2 mg) (p less than 0.001). In addition, the estimated total platelet deposition along the graft was reduced in dogs treated with dipyridamole was reduced in dogs treated with dipyridamole (2,073.2 X 10(6)) (p less than 0.01), verapamil (1,898.9 X 10(6)) (p less than 0.001), and nifedipine (1,474.8 X 10(6)) (p less than 0.001) as compared with controls (3,056.2 X 10(6)). When the mural thrombus was removed from 14 grafts, a median 73% of the platelets were located in the interface between thrombus and graft. We conclude that all 3 drugs prevent thrombus formation by inhibiting platelet activity in this model, and that the calcium antagonist drugs are as effective as dipyridamole.

Cardiac dysrhythmias in the conscious dog after surgically induced autonomic imbalance.

The ventrolateral cardiac nerve in the dog is a primary branch of the left sympathetics and represents a direct neural link between the central nervous system and the heart. Its electric excitation elicits characteristic shifts in pacemaker and tachydysrhythmias related to its explicit innervation of the inferior atrial, atrioventricular (A-V) junctional and ventricular tissues. Total denervation of the canine heart, sparing the ventrolateral cardiac nerve, produced a long-term model in which only these portions of the heart retained their sympathetic innervation. The trained unanesthetized model dog was subjected to severe exercise in order to determine the effects of elevated levels of sympathetic tone upon these important regions of the conduction system. Reproducible tachydysrhythmias were elicited in all six animals completing the regimen of periodic testing over a period of 136 to 378 days after operation. The abnormal rhythms consisted of shifting cardiac pacemakers and supraventricular A-V junctional and ventricular tachycardias with frequent premature systoles. Comparable abnormalities were not observed in a similarly tested sham-operated animal or in dogs with a totally denervated heart. The exercise-induced dysrhythmias gradually disappeared with time, presumably in relation to autonomic reinnervation of the heart. The characteristic patterns of ventrolateral cardiac nerve and upon its presumed influence upon Purkinje fiber and A-V nodal automaticity and temporal dispersion of refractoriness in myocardial tissues.

Function of expanded-polytetrafluoroethylene laminated trileaflet valves in animals.

A stent-mounted trileaflet cardiac valve prosthesis has been developed in which the valve leaflets were fabricated from 0.003-mm films of expanded polytetrafluoroethylene laminated in 4 to 15 layers. A total of 28 valves of varying leaflet thickness were implanted in the tricuspid position in dogs. Cardiac catheterization performed during the follow-up period between 1 week and 15 months after valve replacement in 20 surviving animals showed that the initial good function was maintained in 12 dogs for up to 15 months, whereas valve dysfunction developed in 8 other dogs within 6 months. Autopsy revealed that the cause of valve dysfunction among the eight dogs was cusp stiffening with or without retraction in six, dehiscence of the suture ring in one, and strut entrapment in one. This study demonstrated that the thickness of the leaflet material is an important factor affecting the long-term function in vivo.

Myocardial ultrastructural changes after experimental ventricular fibrillation and anoxic arrest.

A transmural myocardial biopsy method was used to study changed in ultrastructure after induced ventricular fibrillation or anoxic arrest in the canine heart. Interstitial edema, mitochondrial derangement, contraction bands, and swelling of capillary endothelium were more extensive in subendocardial than in subepicardial layer after anoxic arrest. Significant numbers of contraction bands were also seen in the myocardium after induced ventricular fibrillation. These changes appeared to be reversible at least in part in the group with induced ventricular fibrillation but generally not in the anoxic arrest animals. After anoxic arrest, preservation of the endocardial layer was significantly poorer than that of the epicardium; after ventricular fibrillation, there appeared to be no such difference. Myocardial mitochondria and glycogen granules were intact and more numerous after ventricular fibrillation than after anoxic arrest. The lesser damage after ventricular fibrillation than after anoxic arrest suggest that the myocardium may be affected less by the no-reflow phenomenon after normal coronary circulation is restored in ventricular fibrillation.

Imaging platelet deposition with 111In-labeled platelets in coronary artery bypass grafts in dogs.

At 8 and 32 hours after saphenous vein aortocoronary artery bypass graft surgery in four dogs, images of the grafts were obtained with a gamma camera after intravenous injection, 2 hours postoperatively, of autologous platelets labeled with indium-111. The location of platelet deposition could be accurately estimated from the scintiphotos. In vitro radioactivity counting of the segments of the isolated grafts showed 4 to 15 times greater activity in the grafts than in blood and 25 to 100 times greater activity than in normal myocardium. This was sufficient for delineating accurately the area of platelet deposition. This noninvasive technique may be a promising tool for a better understanding of the role played by platelets in the process of occlusion of saphenous vein bypass grafts in man.

Noninvasive radioisotopic technique for detection of platelet deposition in mitral valve prostheses and quantitation of visceral microembolism in dogs.

A noninvasive technique has been developed in the dog model for imaging, with a gamma camera, the platelet deposition on Björk-Shiley mitral valve prostheses early postoperatively. At 25 hours after implantation of the prosthesis and 24 hours after intravenous administration of 400 to 500 microCi of platelets labeled with indium-111, the platelet deposition in the sewing ring and perivalvular cardiac tissue can be clearly delineated in a scintiphotograph. An in vitro technique was also developed for quantitation of visceral microemboli in brain, lungs, kidneys, and other tissues. Biodistribution of the labeled platelets was quantitated, and the tissue/blood radioactivity ratio was determined in 22 dogs in four groups: unoperated normal dogs, sham-operated dogs, prosthesis-implanted dogs, and prosthesis-implanted dogs treated with dipyridamole before and aspirin and dipyridamole immediately after operation. Fifteen to 20% of total platelets were consumed as a consequence of the surgical procedure. On quantitation, we found that platelet deposition on the components of the prostheses was significantly reduced in prosthesis-implanted animals treated with dipyridamole and aspirin when compared with prosthesis-implanted, untreated dogs. All prosthesis-implanted animals considered together had a twofold to fourfold increase in tissue/blood radioactivity ratio in comparison with unoperated and sham-operated animals, an indication that the viscera work as filters and trap platelet microemboli that are presumably produced in the region of the mitral valve prostheses. In the dog model, indium-111-labeled platelets thus provide a sensitive marker for noninvasive imaging of platelet deposition on mechanical mitral valve prostheses, in vitro evaluation of platelet microembolism in viscera, in vitro quantitation of surgical consumption of platelets, and evaluation of platelet-inhibitor drugs.

Quantification of deposition of neutrophilic granulocytes on vascular grafts in dogs with 111In-labeled granulocytes.

A new radioisotopic technique has been developed for quantification of deposition of neutrophilic granulocytes on vascular grafts. Nine healthy mongrel dogs underwent bilateral femoral artery resection and reconstruction with grafts of femoral vein and Gore-Tex. Pure granulocytes that had been separated from whole blood by centrifugal elutriation were labeled with 111In-tropolone in plasma. The granulocyte harvesting efficiency was 25 +/- 12%, and the labeling efficiency was 87 +/- 7%. Three hours after injection of labeled granulocytes and 2 hours after reperfusion, the grafts were harvested and cut into several segments for study of areas of anastomoses and midsections. On the basis of the radioactivity in the blood and in anastomotic and graft sections, the area of graft sections, and the neutrophilic granulocyte and differential leukocyte counts, the number of neutrophilic granulocytes adherent to a unit area and the total number of neutrophilic granulocytes on graft sections were calculated. These quantifications of the deposition of neutrophilic granulocytes indicated that the midsections of Gore-Tex grafts retained more neutrophilic granulocytes than did the midsections of vein grafts. Although the anastomotic areas retained more neutrophilic granulocytes than did the midsections of vein grafts, the opposite finding prevailed for the Gore-Tex grafts. A major fraction of neutrophilic granulocytes on Gore-Tex grafts was incorporated into thrombus. Semiquantitative information obtained by scintigraphy of the deposition of neutrophilic granulocytes on vascular grafts also confirmed this observation.

Light and electron microscopic evaluation of canine hearts orthotopically transplanted after 24 hours of extracorporeal preservation.

The hearts of 19 dogs were subjected to in vitro, moderately hypothermic, whole blood perfusion through the aorta for 24 hours. Sixteen of the hearts were reimplanted into recipient animals in the conventional orthotopic fashion and three were subjected to histologic study without reimplantation. Fourteen of the 16 reimplanted hearts successfully supported the recipients. Histologic and ultrastructural studies of the reimplanted hearts 24 hours and 7 days after implantation demonstrated good preservation of cellular and ultracellular structures. Some mild widening of the interstitium was noted.

Quantitative evaluation of myocardial ultrastructure following hypothermic anoxic arrest.

Thirty-six anesthetized mongrel dogs were subjected to systemic hypothermia and anoxic cardiac arrest while on cardiopulmonary bypass. Myocardial fine structure in the left ventricle was evaluated by quantitative analysis in the subepicardial, mid-myocardial, and subendocardial layers. The specimens were obtained by a transmural myocardial biopsy method. Graded hypothermia was employed at 36 degrees, 30 degrees, 28 degrees, 25 degrees, and 22 degrees C. The aorta was cross-clamped for 30 minutes at 36 degrees, 30 degrees, 28 degrees, and 25 degrees C. or for 45 minutes at 25 degrees and 22 degrees C. Observations indicated that pathological changes of the myocardial fine structure were significant after anoxic arrest in the normothermic group. Lesions were most extensive in the subendocardial layer after normothermic anoxic arrest, whereas hypothermia below 30 degrees C. preserved the myocardium throughout all layers without difference in pathological changes in the fine structure among the layers. Mitochondria and glycogen granules in the mid-myocardial layer and the subendocardial layer were best preserved with hypothermia at 25 degrees and 22 degrees C. after 30 minutes or 45 minutes of anoxic arrest, and dogs in these groups had a survival rate of 100 percent. Quantitative analysis of ultrastructural changes induced in these experiments suggest that a safe duration of anoxic arrest at 22 degrees to 25 degrees C. is between 30 and 45 minutes.

Fate of indium 111-labeled platelets during cardiopulmonary bypass performed with membrane and bubble oxygenators.

To elucidate the effects of bubble and membrane oxygenators on platelet integrity, we developed a quantitative method of determining platelet lysis during cardiopulmonary bypass. Two groups of dogs whose platelets had been labeled with indium 111 were subjected to 1 hour of cardiopulmonary bypass. In Group A (bubble oxygenator), platelet lysis as measured by free plasma 111In levels increased from 6% +/- 1% to 33% +/- 7% during bypass. In Group B (membrane oxygenator), plasma 111In levels increased from 5% +/- 2% to 10% +/- 6% during bypass (p less than 0.01). After 1 hour of bypass, the ratio of 111In-labeled platelets to prebypass levels was 36% +/- 8% in Group A and 67% +/- 9% in Group B. Platelet deposition on the oxygenator was greater in bubble oxygenators (19% +/- 4% of total injected 111In) than in membrane oxygenators (12% +/- 3% of total injected 111In). These data indicated that membrane oxygenators maintain a higher circulating platelet count both intraoperatively and postoperatively and result in less platelet destruction than bubble oxygenators following 1 hour of cardiopulmonary bypass in dogs.

Gore-Tex (polytetrafluoroethylene) in canine coronary artery bypass.

Because of the occasional need for a prosthesis in coronary artery operations, we investigated the potential use of microporous polytetrofluoroethylene (PTFE) with and without antiplatelet drugs as an aorta-coronary bypass graft in 43 dogs. In 13 animals without antiplatelet drugs, no grafts were patent at 1 month. When antiplatelet drugs were used (25 dogs), the 1 month patency rate increased to 64%. The addition of antibiotic treatment 1 month patency rate to 80%. The 6 month patency rate in dogs treated with antiplatelet drugs, preoperative bowel preparation, and systemic antibiotics was 60%. Our data indicate that microporous PTFE grafts used as coronary artery bypass grafts in dogs can be maintained patent for at least 6 months when the animals are treated with antiplatelet drugs.

Flow capacity of the canine internal mammary artery.

The internal mammary artery has excellent long-term patency when used as a conduit for coronary artery bypass, and clinical and experimental studies have shown that blood flow through an internal mammary artery graft is satisfactory for most coronary artery branches. Multiple distal anastomoses from a single internal mammary artery, either with sequential anastomoses or with a Y-graft, might require additional blood flow through the vessel, and there has been concern that the flow capacity of the internal mammary artery is insufficient with these techniques. To better define the immediate postoperative flow capacity and pattern of the internal mammary artery, we performed experiments in seven dogs in which the left internal mammary artery was anastomosed to the circumflex coronary artery. In situ, blood flow in the internal mammary artery was 27 ml/min. Blood flow was 63 ml/min in the circumflex coronary artery and 42 ml/min in the left anterior descending coronary artery. After anastomosis of the left internal mammary artery to the circumflex coronary artery, the left main coronary artery was ligated; flow through the bypass graft increased to 92 ml/min, and systemic hemodynamics remained stable. Isoproterenol stimulation further increased flow through the left internal mammary artery graft to 160 ml/min. This study suggests that the canine internal mammary artery is capable of substantial early increase in flow and can, in fact, support the entire left coronary circulation.

Simplified method of heterotopic cardiac transplantation for left ventricular assist.

A method of heterotopic cardiac transplantation has been developed which is performed through a left thoracotomy and requires only two vascular anastomoses. Systemic heparinization and cardiopulmonary bypass are not necessary. Preliminary experiments demonstrated that this heterotopic transplant technique was effective for left ventricular assist; in some experiments, a multimode atrioventricular programmable pacemaker was used to provide sequential pacing for "counterpulsation." This technique or similar techniques may have potential clinical benefit for patients with intractable left ventricular failure.

The effect of preclotting on surface thrombogenicity and thromboembolic complications of Dacron grafts in the canine thoracic aorta.

Previous reports have advocated preclotting and autoclaving of Dacron grafts to prevent graft hemorrhage, yet no data delineate possible changes in surface thrombogenicity or thromboembolic risks. To assess these factors, preclotted and preclotted-autoclaved woven Dacron prostheses were implanted in the thoracic aorta of 31 dogs. Grafts were harvested 1 week to 1 month following implantation, and the thrombus-free surface of each graft was calculated by computerized morphometry. Values for thrombus-free surface were lowest in autoclaved grafts preclotted in nonheparinized blood (72%) or in heparinized blood (78%). Grafts preclotted in platelet-rich plasma and autoclaved had a thrombus-free surface value of 85%. Regular preclotted grafts or grafts without preclotting had the greatest thrombus-free surface value (97% and 99%). Distal embolization to the kidneys was detected in seven of 31 animals (23%). No emboli were found in animals with grafts that were not preclotted or if grafts were preclotted with platelet-rich plasma and autoclaved. Thrombus-free surface values were lower (p less than 0.01) in grafts with embolic complications (71% versus 91%). These data suggest that, if the risk of severe bleeding in fully heparinized patients precludes the use of a woven Dacron graft without preclotting, autoclaving a graft preclotted with platelet-rich plasma appears to be the method of choice.

Quantification of regional platelet and calcium deposition on pericardial tissue valve prostheses in calves and effect of hydroxyethylene diphosphonate.

Mitral valves were replaced with 25 mm bovine pericardial tissue valve prostheses (Ionescu-Shiley) in 45 calves (23 controls and 22 treated daily with hydroxyethylene diphosphonate). Before being killed 1, 14, 30, and 90 days later, the calves received In-labeled autologous platelets intravenously. Regional variations in platelet deposition were measured by a new technique. Thrombus was noted early on the flexion zone of the valve; with time it increased on the free edge and central zone. Platelet deposition was initially high on the flexion zone, attachment zone, sewing ring, and perivalvular tissue but decreased with time. Hydroxyethylene diphosphonate treatment tended to decrease platelet deposition in all zones. Calcium content was high in thrombus and increased in all zones with time, in both groups, but the deposition was less in the group treated with hydroxyethylene diphosphonate. Collagenous tissue and adherent thrombus appear to provide nucleation sites for calcification.