Mrinal K. Dewanjee

Balloon angioplasty. Natural history of the pathophysiological response to injury in a pig model.

The restenosis or occlusion that frequently follows balloon angioplasty is poorly understood. Thus, the pathophysiological response to angioplasty of the common carotid artery in 38 heparinized normal pigs was investigated by quantification of the 111In-labeled platelet deposition and histological and electron microscopic examination from 1 hour to 60 days after angioplasty. At 1 hour, the following findings were noted: complete endothelial denudation in all arteries, marked platelet deposition (44.7 +/- 20.7 X 10(6)/cm2), mural thrombus in seven of 10 pigs, and a medial tear extending through the internal elastic lamina in nine of 18 arteries. All nine arteries with tears had associated mural thrombus and severe platelet deposition (76 X 10(6)/cm2); in contrast, the nine arteries without a tear had no mural thrombus and much lower platelet deposition (6 X 10(6)/cm2). Necrosis of medial smooth muscle cells was evident at 24 hours. Platelet deposition remained high at 24 hours (40.5 +/- 20.6 X 10(6)/cm2), but was markedly reduced at 4 days (4.4 +/- 1.5 X 10(6)/cm2), coincident with partial regrowth of endothelium or periluminal lining cells. No significant platelet deposition was noted at 7 days, when the endothelial cell type of regrowth was largely complete. Intimal proliferation of smooth muscle cells was mild and patchy at 7 days, significantly greater and more uniform at 14 days, and unchanged at 30 and 60 days after angioplasty. Complete thrombotic occlusion occurred in four (11%) of the 38 pigs. A significant stenosis present at 30 days after angioplasty was shown by histological examination to be due to organization of mural thrombus.(ABSTRACT TRUNCATED AT 250 WORDS)

Deep arterial injury during experimental angioplasty: Relation to a positive indium-111-labeled platelet scintigram, quantitative platelet deposition and mural thrombosis

Although it is not clear why coronary occlusion and restenosis occur after successful coronary angioplasty, factors related to the procedure may influence early and late results. The possible adverse effects of a medial tear documented histologically and produced during balloon angioplasty of the common carotid arteries were studied in 30 fully heparinized (100 U/kg body weight) normal pigs. Scanning electron microscopy showed endothelial denudation and extensive platelet deposition in all dilated arterial segments. Visible macroscopic mural thrombus was present within an hour of the procedure in 29 (91%) of the 32 arteries that had a medial tear documented by histologic study; the tear produced an indium-111-labeled platelet deposition of 116.4 +/- 26.5 X 10(6)/cm2 (mean +/- SE) and total thrombotic occlusion in 2 arteries (4%). None of the 24 arteries without a medial tear had a thrombus, and the mean platelet deposition in that group was 7.0 +/- 0.5 X 10(6)/cm2 (p less than 0.0008). In 12 pigs scanned with a gamma camera, visible thrombus was associated with platelet deposition in excess of 20 X 10(6)/cm2 in 12 arteries, 9 of which had a positive indium-111-labeled platelet scintigram. Thus, arterial angioplasty causes deep arterial injury, which appears to be a major cause of mural thrombosis, heavy platelet deposition, a positive indium-111-labeled platelet scintigram and acute arterial occlusion. A positive indium-111-labeled platelet scintigram was always associated with macroscopic thrombus of at least 20 > 10(6) platelets/cm2 and underlying deep arterial injury.

Noninvasive radioisotopic technique for detection of platelet deposition in coronary artery bypass grafts in dogs and its reduction with platelet inhibitors.

SUMMARYAt 8 and 32 hours after saphenous vein bypass graft surgery in six dogs, in vivo images of the graft were obtained with a gamma camera after intravenous injection, 2 hours postoperatively, of autologous platelets labeled with indium-111. Platelet deposition in the grafts could be imaged in vivo from the scintiphotos. In vitro images of the excised heart showed saphenous vein graft uptake confirming the in vivo image. In vitro determination of radioactivity in the graft averaged 17 ± 14 times greater than in blood and 33 ± 26 times greater than in the lung.Under identical conditions, in eight dogs treated with dipyridamole (55 mg/day) plus aspirin (325 mg/day), the grafts appeared to have considerably less platelet deposition as estimated by imaging. In vitro determination of radioactivity in the graft averaged 5 ± 2 times greater than in blood and 8 ± 4 times greater than in the lung (P < 0.01).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 and its prevention with platelet inhibitors.

In vivo quantitation of platelet deposition on human peripheral arterial bypass grafts using indium-111-labeled platelets. Effect of dipyridamole and aspirin

Indium-111-labeled autologous platelets, injected 48 hours after operation, were used to evaluate the thrombogenicity of prosthetic material and the effect of platelet inhibitor therapy in vivo. Dacron double-velour (Microvel) aortofemoral artery bifurcation grafts were placed in 16 patients and unilateral polytetrafluoroethylene femoropopliteal grafts were placed in 10 patients. Half the patients in each group received platelet inhibitors before operation (dipyridamole, 100 mg 4 times a day) and after operation (dipyridamole, 75 mg, and acetylsalicylic acid, 325 mg 3 times a day); the rest of the patients served as control subjects. Five-minute scintigrams of the graft region were taken with a gamma camera interfaced with a computer 48, 72, and 96 hours after injection of the labeled platelets. Platelet deposition was estimated from the radioactivities of the grafts and expressed as counts per 100 pixels per microcurie injected. Dipyridamole and aspirin therapy significantly reduced the number of platelets deposited on Dacron grafts and prevented platelet accumulation over 3 days. With the small amount of platelet deposition on polytetrafluoroethylene femoropopliteal artery grafts even in control patients, platelet inhibitor therapy had no demonstrable effect on platelet deposition on these grafts. It is concluded that (1) platelet deposition on vascular grafts in vivo can be quantitated by noninvasive methods, and (2) dipyridamole and aspirin therapy reduced platelet deposition on Dacron aortofemoral artery grafts.

Quantification of platelet retention in aortocoronary femoral vein bypass graft in dogs treated with dipyridamole and aspirin.

Autologous femoral vein segments were implanted as aortocoronary bypass grafts in 50 dogs, 25 of which were treated with dipyridamole and aspirin to inhibit platelet deposition and 25 that were not. Autologous platelets labeled with indium-111 were injected into some dogs 48 hr before they were killed on the first day after surgery; other dogs were injected 24 hr before they were killed (3, 7, 30, and 90 days after surgery). Radioactivity on the grafts and on control specimens of contralateral femoral veins was converted to quantification of platelets adhering to the vessel wall (platelets/cm2). The treated group had fewer graft platelets per square centimeter than the untreated group on postoperative days 3, 7 (p less than .01), and 30 (p less than .05). Graft and control vein platelets per square centimeter were nearly equal by day 90. Comparison of graft and control specimens by scanning electron microscopy nearly equal by day 90. Comparison of graft and control specimens by scanning electron microscopy revealed deendothelialization at 1 and 7 days after grafting and reendothelialization at 30 and 90 days. The data suggest that indefinite prolongation of therapy to inhibit platelet deposition after bypass grafting may be unnecessary (although other atherosclerotic vessels may benefit from therapy).

Cardiac and vascular imaging with labeled platelets and leukocytes

The contribution of platelets in atherosclerosis and thrombosis in animal models and in clinical studies has been quantified with 111In-platelet scintigraphy. New in vitro quantitative techniques have been developed using 111In-labeled platelets to determine the number of adherent platelets on deendothelialized surfaces of damaged vessel walls and synthetic vascular grafts. In vivo imaging techniques are semi-quantitative in nature; in these studies 111In radioactivity on thrombotic vessels or graft surfaces of iliac, femoral, or popliteal arteries is compared with contralateral vessels. Background 111In radioactivity in the circulating blood pool of venous and capillary networks and radioactivity in marrow decreases the sensitivity of these techniques. Despite these limitations, the dynamic process of platelet deposition in most of the denuded, atherosclerotic vessels and prostheses in the circulatory system can be recorded. This ongoing thrombosis and embolization has been observed in 5-10-year-old vascular grafts of Teflon and Dacron biomaterials. Currently used platelet function inhibitor drugs, eg, aspirin, Persantine, sulfinpyrazone, and Motrin, have a demonstrable effect on platelet deposition. Slight changes in reduction of platelet deposition on these surfaces due to medical intervention have been observed by noninvasive imaging with 111In-platelets. Subtraction of blood pool radioactivity with 99mTc-labeled autologous red cells and calculation of 111In radioactivity associated with platelet thrombus on vessel walls also have been performed for coronary, carotid, and femoral arteries. Although platelet concentrates are used frequently after open heart surgery (one to six per patient), consumption of platelets in the artificial lung or oxygenator, lysis of platelets during pumping, and suction of blood only recently have been quantified with the use of 111In-labeled platelets. These studies also demonstrated far less trauma to platelets with the use of a membrane rather than a bubble oxygenator. Further reduction in platelet consumption and trauma was observed with the use of prostacyclin, a short-acting drug with significant beneficial effect on platelet thrombus reduction and disaggregation of aggregated platelets. The role of polymorphonuclear leukocytes in inflammation, infection and myocardial infarction, and in vivo evaluation with 111In-leukocyte scintigraphy in animals and humans has been described.(ABSTRACT TRUNCATED AT 400 WORDS)

Heterotopic splenic autotransplantation in prevention of overwhelming postsplenectomy infection

An experimental study was undertaken to evaluate the protective effect of heterotopic splenic autotransplantation in weanling rats. Rats were divided into three experimental groups: splenectomy, control, and splenic autotransplantation. Rats were challenged with i.v. type I pneumococcus. Bacterial bloodstream clearance and survival were determined. Splenic bacterial uptake was measured by determining the isotopic activity of technetium-99m-labeled pneumococci. Autoradiographs and material stained with hematoxylin and eosin and Gram strains were examined for histologic features. All autografts survived and were histologically compatible with normal splenic tissue. Bloodstream clearance of pneumococci was significantly greater in rats with splenic autotransplantation. Splenic autografts had 10 to 30 times greater uptake of pneumocci than did the liver. Rats with autotransplantation had a prolonged survival time. Heterotopic splenic autotransplantation may prove to be an important adjunctive surgical measure in the treatment of children undergoing splenectomy.

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.

Distribution of Mesalamine Enemas in Patients With Active Distal Ulcerative Colitis

Mesalamine (5-aminosalicylic acid), a topically administered anti-inflammatory agent, is effective treatment by enema for distal ulcerative colitis; it lacks many of the side effects of orally administered sulfasalazine. In this study, we determined the colonic distribution of a 60-ml mesalamine enema in eight patients (five women and three men, 18 to 48 years old) with active distal ulcerative colitis that ranged from 12 to 40 cm proximal to the anal verge. On 3 consecutive days, each patient self-administered a 4-g (60-ml) 5-aminosalicylic acid enema that contained 3.7 MBq of [99mTc]technetium-sulfur colloid. Anterior and posterior images were obtained at 0, 30, 60, 120, and 240 minutes. During the 4-hour study period, all patients retained the enemas. The enemas spread to the sigmoid region in 24 of 24 studies, to the splenic flexure region in 22 of 24, and to the transverse colon in 1 of 24. Most of the enema was retained in the sigmoid colon. Therefore, we conclude that a 60-ml enema, when administered as recommended clinically, routinely flows retrograde as far as the splenic flexure but rarely spreads beyond this point. These results support the use of intrarectally administered 5-aminosalicylic acid for segmental colitis of the descending colon.

Methods of assessment of thrombosis in vivo

The contributions of platelets and clotting factors in thrombosis on injured vessel and cardiovascular prostheses have been quantified with several tracers. Thrombus formation in vivo could be measured semiquantitatively in animal models and humans with 111In-labeled platelets, 123I- and 131I-labeled fibrinogen, 111In-labeled antibody to the fibrinogen receptor on the platelet membrane and to fibrin. Thrombus localization by imaging was possible for large thrombus in vessel with deep injury of thrombogenic surface in the acute phase. A single layer of adherent platelet could not be imaged, due to the high background radioactivity present in blood. Thrombogenicity of graft was compared with that of contralateral vessel. The dynamic process of platelet deposition could be followed accurately using the in vivo imaging technique. In addition, in vitro quantification permits determination of platelet and fibrin density and of the number of fibrin monomers per platelet in thrombus. The roles of prostacyclin, thromboxane inhibitors, and nonsteroidal antiinflammatory drugs have also been evaluated in animals models and humans. The tracer techniques thus provide invaluable information about platelet-fibrin deposition, its organization and dissolution, and for development of less thrombogenic surfaces for use in cardiovascular prostheses.