Assessment of myocardial oxidative stress in

patients after myocardial revascularization

A homogeneous group of six patients, who underwent coronary artery bypass surgery, was studied to determine the presence of oxidative stress caused by oxygen-derived free radicals and its relationship with reperfusion cell damage. Biopsies were performed before ischemia and 10 minutes after reperfusion. The samples were assayed for hydroperoxide-initiated chemiluminescence and histochemical succinic dehydrogenase activity; the specimens were also studied by electron microscopy. The preischemic biopsy specimens showed chemiluminescence of 40 rt 2 (cpm/mg protein) X 103, normal succinic dehydrogenase activity (grade 41, and generally preserved ultrastructure (necrotic/normal cells 51100). However, the reperfusion biopsy specimens showed an increase in chemiluminescence to 91 i 19 (cpm/mg protein) x lo3 (p < 0.025), a partial loss of enzymatic activity (grade 2.6), and ultrastructural changes characterized by mitochondrial swelling and focal myofibrillar disorganization (necrotic/normal cells: 15/ 100; p < 0.001). These observations seem to indicate the presence of oxidative stress during reoxygenation, a situation that may play a major role in the genesis of reperfusion injury. It appears to be the first observation relating free radical-induced oxidative stress to reperfusion injury in humans. (AM HEART J 1988;115:307.)

Ricardo Ferreira, M.D., Susana Llesuy, Ph.D., Jose Milei, M.D., Domingo Scordo, M.D., Hector Hourquebie, M.D., Luis Molteni, M.D., Carlos de Palma, M.D., and Albert0 Boveris, Ph.D. Buenos Aires, Argentina

Preservation of myocardial function is a major con- cern during open-heart surgery requiring interrup- tion of coronary blood flow. It has been demon- strated that, prolonged ischemia or inadequate car- dioplegic techniques produce structural, biochemi- cal, and functional lesions that occur mainly during restoration of arterial flow. This reperfusion injury, originally described by Jennings et a1.l and later by Engelman et a1.,2 has recently been related to the cytotoxic action of oxygen-derived free radicals.3,4

In 1982, Parks et a1.5 and Shlafer et a1.6 postulated that reperfusion lesions are caused by increased superoxide anion generation and peroxidation of polyunsaturated membrane lipids, This process of lipoperoxidation is probably initiated by the highly cytotoxic and reactive hydroxyl radica1.l However, all of these studies have been done in experimental

From the Sectioc of Pathology, Institute of Cardiology, National Academy of Medicine; the Department of Biological Chemistry, School of Pharmacy and Biochemistry, University of Buenos Aires; the Latin American Insti- tute for Medical Investigations, University of Salvador; and the Depart- ment of Cardiovascular Surgery, Sanatorio Colegiales.

Supported by the National Research Council of Argentina and Secretaria de Ciencia y T&mica.

Received for publication Feb. 19, 1987; accepted Aug. 22, 1987.

Reprint requests: Jose Milei, M.D., Instituto de Cardiologia, Coronel Diaz 2423, 1425 Buenos Aires, Argentina.

models, and until now there has been no clinical experience with cell damage produced in the ische- mic heart by oxygen-derived free radicals.

The present study affords an opportunity for assessment of changes in ultrastructure, succinic dehydrogenase activity, and hydroperoxide-initi- ated chemiluminescence in a group of patients with surgically treated coronary artery disease that involved a cycle of ischemia and reperfusion. Hydro- peroxide-initiated chemiluminescence integratively measures the level of endogenous free radical scav- engers; increased chemiluminescence is defined as a reduced endogenous antioxidant defense resulting from a situation of oxidative stress.8sg

METHODS

Patients. Six patients who underwent coronary bypass surgery, and who constituted a highly homogeneous group, were selected for the study. Participants were 37 to 57 years of age (49.3 I 3.1; mean +- SEM) and had no evidence of recent (<4 weeks) acute myocardial infarction. The average preoperative ejection fraction was 52 t 2. Only patients in whom satisfactory revascularization was achieved were considered for this study. Written informed consent for myocardial biopsy was obtained from each patient. The study protocol was approved and controlled by the ethics committee of the Institute of Cardiology of the National Academy of Medicine (Argentina).

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308 Ferreira et al. February 1988

American Heart Journai

1 XrESM X+ESM

CONTROL SAMPLES REPERFUSION SAMPLES

Fig. 1. Mean and total values for control and reperfusion determinations of hydroperoxide-initiated chemiluminescence in six patients.

Cardiopulmonary bypass was instituted and the tem- perature of the perfusate was lowered to 28” C. Topical hypothermia with crushed-iced saline solution was applied. Before the aorta was cross clamped, three full- thickness needle biopsy specimens were obtained from the apex of the heart. The biopsy sample for the chemilumi- nescence study was immersed in saline solution, immedi- ately frozen, and rushed to the laboratory. The specimen for the study of succinic dehydrogenase activity was frozen in an empty beaker. The third biopsy specimen, for electron microscopy, was immersed in cold 3 % glutaralde- hyde in 0.1 mol/L phosphate buffer (pH 7.4).

After placement of the aortic cross clamp, 500 ml of Saint Thomas-type cardioplegic solution was injected at 80 mm Hg, into the aortic root. A needle thermistor was inserted into the septum for continuous monitoring of the myocardial temperature, which ranged from 18’ to 22’ C. There were 2.8 -+ 0.3 grafts per patient. After completion of the distal anastomoses, the aortic cross clamp was removed and the heart was defibrillated. The average aortic cross-clamp time was 55 + 5 minutes. In most instances one countershock was necessary for the heart to return to sinus rhythm (mean value of applied counter- shocks: 1.6 * 0.3). After 10 minutes of reperfusion and with the patient rewarmed, three new myocardial biopsy specimens were obtained and processed as described previously.

Specimens taken before the ischemic period were desig- nated as control and those obtained 10 minutes after the aortic cross clamp was removed were designated as reper- fusion biopsies.

Hydroperoxide-initiated chemiluminescence. Biopsy specimens (40 mg approximate weight) were homogenized in a small Potter-Elvejhem Teflon homogenizer in 2 ml of 140 mmol/L KC1 and 20 mmol/L phosphate buffer (pH 7.3). The proteins of the homogenate were assayed by the method of Lowry et a1.,8 and the homogenate was diluted to 1 mg of protein/ml in the same buffer solution. The

suspension was added to 3 mmol/L tert-butyl hydroperox- ide and assayed for chemiluminescence in a Tri-Carb model 3320 scintillation counter (Packard Instrument Co., Santa Ana, Calif.) in the out-of-coincidence.gj lo

Succinic dehydrogenase activity. The histochemical technique used has been described elsewhere.” Briefly, succinate and nitroblue tetrazolium are added to the tissue slice to stain the intracellular granules. A clear differentiation between normal cells and those showing early damage was obtained by applying Barbeito Lopez trichrome stain to the slides. The entire tissue area was examined by light microscopy and staining of the granules was scored semiquantitatively. We used a scale ranging from 0 (no enzyme activity plus yellow cytoplasm) to 4 (dense concentration of granules and green cyto- plasm) .I22 I3

Electron microscopy. Tissues to be used for transmis- sion electron microscopy were fixed in cold 3% glutaralde- hyde in 0.1 mol/L cacodylate buffer (pH 7.4), postfixed in 1% osmium tetroxide, dehydrated, and embedded in Araldite. One-micrometer thick sections were cut, stained with 1% toluidine blue, and examined for light microscop- ic alterations and to select appropriate areas for thin sectioning. Ultrathin sections were then stained with lead citrate and orange acetate and examined with a Siemens Elmiskop 101 electron microscope (Siemens AG, Munich, W. Germany). A single score was given for each area, and the observations were conducted in a blind manner by two different observers.

For a detailed analysis of organelle changes in the myocardial cells, electron micrographs (magnification ~5000 to ~10,000) were examined morphometrically under a grid as described by Kloner et a1.14 Overall myocardial cell injury was ranked independent of mito- chondrial structure on a scale of 0 to 4 as follows: 0 = normal; 1 = minimal ischemic changes (glycogen loss, nuclear chromatin clumping, and margination, I bands); 2 = moderate ischemic changes (as in grade 1, and inter-

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Number 2 Oxidative stress and reperfusion injury 309

Fig. 2. Control vs reperfusion biopsies. A, Transmission electron micrographs of control biopsy specimen. Mitochondria show normal morphology or early damage. There is clearing of matrix density and separation of cristae. Amorphous matrix density and linear density are present. (~30,000.) B, Transmis- sion electron micrographs of reperfusion biopsy specimen. Mitochondria show massive swelling and rupture of inner and outer membranes (arrow). (~30,000.)

myofibrillar and sarcoplasmic reticular edema); 3 = severe ischemic changes (as in grade 2, plus subsarcolemmal blebs, sarcolemmal gaps, and marked edema); and 4 = complete architectural disruption (absent sarcolem- ma1 membrane and loss of sarcomere structure). A necrot- ic index such as the number of damaged myocytes (grades 3 and 4)/100 counted myocytes, was used.

The severity of mitochondrial swelling was also graded on a scale of 0 to 4 as follows: 0 = normal mitochondria; 1 = early swelling (clearing of matrix density and separa- tion of cristae); 2 = increased swelling (as in grade 1, but more evident); 3 = massive swelling with disruption of cristae; and 4 = findings as in grade 3, plus rupture of inner and outer mitochondrial membranes.

When a point on the grid fell on a mitochondrion, this mitochodrion was assigned a numerical value of 0 to 4, depending on the morphologic degree of damage. A mean mitochondrial grade for each cell was obtained. Approxi- mately 50 cells per sample and 750 to 1000 mitochondria per field were graded in this manner.

Student’s t test was used to compare the two groups of biopsy specimens.

RESULTS

The six patients had a satisfactory postoperative outcome and did not require treatment with inotro- pit drugs. No evidence of perioperative myocardial

infarction was observed by the appearance of new Q waves in the ECG or by increased values for serum creatine phosphokinase. The average interval between surgery and discharge was 7 days.

Hydroperoxide-initiated chemiluminescence. Fig. 1 shows a markedly increased (approximately 3.5 times) hydroxyperoxide-initiated chemilumines- cence in the reperfusion samples compared to the control samples. The mean value for the six control samples was 40 rt 2 (cpm/mg protein) x lo3 and for the six reperfusion samples, 91 + 19 (cpm/mg pro- tein X lo3 (p < 0.025).

Succinic dehydrogenase activity. Reperfusion sam- ples had a mean value of 2.6, whereas all of the control samples had a score of 4.0.

Electron microscopy Qualitative anaZysis. The morphologic changes in

the reperfusion biopsy specimens consisted of focal myofibrillar disorganization with myocytolysis, sar- coplasmic vacuolization, and mitochondrial swelling or disruption (Fig. 2). Distension of sarcoplasmic reticulum and T tubules was frequently seen and diffusely scattered in damaged myocytes. Mitochon- dria showing swelling, clearing of matrix density, and separation of cristae with granular and linear

February 1983 310 Ferreira et al. American Heart Journal

Table I. Morphometric analysis of electron micrographs (X5000 and X10,000) by stereologic count point methods

Biopsies G?lZde Grade

0 1 Grade

2 Grade

3 Grade

4 Total cell damage

Necrotic index

Control 43 iz 1* 36 f lt 15 + 1* 5 k 1t 0 57 * 2* 5 + 1* Reperfusion 15 + 1* 40 iz 17 31 + 1* 11 k 2t 4kl 86 i l* 15 * 1*

Grade indicates percentage of myocardial cell damage (see Methods for explanation); values are expressed as mean I standard error of mean; p = Probability. *p < 0.001. tp < 0.025.

Table II. Mitochondrial changes in injured myocytes

No. of No. of damaged checked mitochondria % of Damaged

Biopsies mitochondria (grades 3 to 4) mitochondria

Control 824 +- 35 93 t 9 11.16 k 0.67 Reperfusion 790 ir 22 244 + 18 30.80 + 1.72

P NS <O.OOl <O.Ol

Values are expressed as mean ? standard error of mean; grade indicates grade of mitochondrial damage (see Methods for explanation); p = proba- bility; NS = not significant.

densities or myeline figures and membrane disrup- tion were observed in the most advanced stages.

Quantitative analysis. Morphologic quantitative analysis of the biopsy specimens showed that the reperfusion samples were significantly more dam- aged than the control samples. Values for the necrotic index and total cell damage were 15/100 and 86/100, respectively, for the reperfusion biopsies compared to the corresponding values of 5/100 and 56/100 for the control biopsies (Table I). The num- ber of severely swollen mitochondria (grades 3 and 4) was also significantly higher in the perfusion samples (30.9%) than in the control specimens (11.3%) (Table II).

DlS6xSSlON

Open-heart surgery with interruption of coronary blood flow frequently leads to structural, biochemi- cal, and functional alterations of the myocardium. It has been shown that these changes occur mainly during the reperfusion period.2,4i I52 I6

Although topical hypothermia combined with cold potassium cardioplegia has demonstrated an extended myocardial protective effect,17,1s the capa- bilities are limited. To enhance myocardial protec- tion, alternate techniques that add oxygenated crys- talloid, blood, or calcium blocking agents to the cardioplegic solution are widely used.20,21 However, when the ischemic period is prolonged, histochemi- cal and structural changes are apparently always

present. Experimental studies over the past few years have indicated a major role of oxygen-derived free radicals as the cause of cell damage in cycles of ischemia and reperfusion in mammalian organs5,22 and in cardiac surgery.23,24

Oxygen free radicals have an extremely short life and, hence, they are exceedingly difficult to assay.7 A classical approach to detection of free radical generation is based on assessment of lipoperoxida- Lion. This has been achieved in the past by assay of malondialdehyde, a byproduce of lipid peroxida- tion,7125 or more recently by measurement of chemi- luminescence.7, g, 26* 27

Chemiluminescence is the photoemission of ex- cited molecules generated in end reactions of the peroxy-free radicals produced during lipoperoxida- tion and constitutes a reliable method for determin- ing the presence of these metabolites in vivo.25,26 Moreover, for in vitro assays, chemiluminescence appears to have a higher sensitivity than malondial- dehyde formation. 27, 2s We have selected hydroperox- ide-initiated chemiluminescence to test the hypoth- esis that production of oxygen-derived free radicals during reperfusion is associated with myocardial injury in patients undergoing cardiac surgery.

Tissue homogenates and suspensions of subcellu- lar fractions show chemiluminescence when added to external hydroperoxides.8,g*27~28 Hydroperoxide- initiated chemiluminescence has been used to detect decreased levels of endogenous antioxidants in liver homogenates from ethanol-treated rats8 and from tumor-bearing mice30 and in heart homogenates from Adriamycin-treated rabbits and mice.10,3L The assay seems to be adequate for organs in which increased lipid peroxidation has occurred.8z9,30,31 Accordingly, the increased chemiluminescence observed with reperfusion biopsies would indicate a decreased level of antioxidants derived from oxida- tive stress imposed on the myocardium during the ischemia-reperfusion cycle.

Cell damage was assessed both by ultrastructural study of myocytes and mitochondria and by histo-

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chemical determination of succinic dehydrogenase activity. Decrease in the activity of this enzyme is a current method for showing a decrease in the capac- ity of the mitochondria to generate metabolic energy. 11,13 A relatively preserved ultrastructure with high succinic dehydrogenase activity was char- acteristic of the preischemic control samples. How- ever, reperfusion biopsy specimens showed a decrease in succinic dehydrogenase activity and an increase in the degree of ultrastructural damage. A close correlation was observed between increases in mitochondrial damage and hydroperoxide-initiated chemiluminescence after completion of the isch- emia-reperfusion cycle.

The six patients had normal hemodynamic parameters in the postoperative period, probably because the ischemic time was not substantially prolonged. This also points out the effectiveness of standard cardioplegic techniques. Apparently, the histochemical, structural, and biochemical altera- tions reported here indicate minor and reversible myocardial damage. However, these lesions may be sufficient to induce postoperative arrhythmias32 or show a predisposition to low myocardial output syndrome in those patients with impaired ejection fractions.

The role of oxygen-derived free radicals as an important source of cell damage during reperfusion has been demonstrated up to the present time in experimental models. This study indicates that a decrease in tissue antioxidants, probably as a result of an increased rate of generation of oxygen-derived free radicals accompanies myocardial damage after reperfusion in patients undergoing open-heart sur- gery.

REFERENCES

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Jennings RB, Sommers HM, Symth GA, Flack HA, Linn H. Myocardial necrosis induced by temporary occlusion of a coronary artery in the dog. Arch Path01 1960;70:82. Engelman RM, Chandra R, Baumann FG. Myocardial reper- fusion, a cause of ischemic injury during cardiopulmonary bypass. Surgery 1972;80:266. Hess ML, Manson NH, Okabe E. The role of free radicals in the pathophysiology of ischemic heart disease. Can J Physiol Pharmacol 1982;60:1382. Dermopoulous HB, Flamm ES, Pietronigro DD, Seligman ML. The free radical pathology and the microcirculation in the major central nervous system disorders. Acta Physiol Stand 1980;492:91. Parks DA, Bulkley GB, Granger DN, Hamilton SR, McCord NM. Ischemic injury in the cat small intestine. Role of superoxide radicals. Gastroenterology 1982;82:9. Shlafer M, Kane PF, Wiggins VY, Kirsh MM. Possible role of cytotoxic oxygen metabolites in the pathogenesis of cardiac ischemic iniurv. Circulation 1982:66:185. ” _ Chance B, Sies H, Boveris A. Hydroperoxide metabolism in mammalian organs. Physiol Rev 1979;62:527.

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Lowry OH, Rosenbrough AL, Farr AL, Randall RI. Protein measurement with the Folin phenol reagent. J Biol Chem 1951;193:265. Boveris A, Fraga CG, Varsavsky AI, Koch OR. Increased chemiluminescence and superoxide production in the liver of chronically ethanol-treated rats. Arch Biochem Biophys 1983;227:534. Milei J, Boveris A, Llesuy S, et al. Amelioration of adriamy- tin-induced cardiotoxicity in rabbits by prenylamine and vitamins A and E. AM HEART J 1986;111:95. Pearson B. Improvement in hystochemical localization of succinic dehydrogenase by use of nitroneotetrazolium chlo- ride. J Biochem Cvtochem 1958:6:112. Milei J, Bolomo Nj. A routine method for diagnosis of early myocardial infarction. Int J Cardiol 1983;4:319. Milei J, Storino R. Early myocardial infarction. A feasible histologic diagnostic procedure. Jnn Heart J 1986:27:307. Kloner-RA, Fishbein-MC, Braunwald E, Maroko PR. Effect of propranolol on mitochondrial morphology during acute myocardial ischemia. Am J Cardiol 1978;41:881. Hearse DJ, Humphrey SM, Chain EB. Abrupt reoxygenation of the anoxic potassium-arrested perfused rat heart. A study of myocardial enzyme release. J Mol Cell Cardiol 1973; 5:395. Hearse DJ, Humphrey SM, Nayler WG, Slade A, Border D. Ultrastructural damage associated with oxygenation of the anoxic myocardium. J Mol Cell Cardiol 1975;7:315. Slack JD, Zeok JV, Cole JS, Hanley HG, Cornish AL, McKean HE. Influence of potassium cardioplegia versus ischemic arrest on regional left ventricular diastolic compli- ance in humans. Ann Thorac Surg 1981;31:214. Roberts AJ, Sanders Jr JH, Moran JM, et al. Nonrandomized matched pair analysis of intermittent ischemic arrest versus potassium crystalloid cardioplegia during myocardial revas- cularization. Ann Thorac Surg 1981;31:502. Flameng W, Borgers M, Daenen W, et al. Thomas cardiople- gia versus topical cooling: ultrastructural and biochemical studies in humans. Ann Thorac Surg 1981;31:340. Singh AK, Farrugia R, Teplitz C, Karlson KA. Electrolyte versus blood cardioplegia: randomized clinical and myocardi- al ultrastructural study. Ann Thorac Surg 1982;33:219. Christakis GT, Fremes SE, Weisel RD, et al. Diltiazem cardioplegia. A balance of risk and benefit. J Thorac Cardio- vast Surg 1986;91:647. McCord JM. Oxygen-derived free radicals in postischemic tissue injury. N Engl J Med 1985;312:159. Nayler WG, Elz JF. Reperfusion injury: laboratory artifact or clinical dilemma? Circulation 1986;74:215. Braunwald E, Kloner R. Myocardial reperfusion: a double- edged sword? J Clin Invest 1985;76:1713. Stewart JR, Blackwell MS, Crute SL, Loughlin V, Greenfield LJ, Hess ML. Inhibition of surgically induced ischemia/ reperfusion injury by oxygen free radical scavengers. J Tho- rat Cardiovasc Surg 1983;86:262. Boveris A, Cadenas E, Reiter R, Filipowsky M, Nakase Y, Chance B. Organ chemiluminescence: noninvasive assay for oxidative radical reactions. Proc Nat1 Acad Sci USA 1980;77:347. Boveris A, Cadenas E, Chance B. Ultraweak chemilumines- cence: a sensitive assay for oxidative radical reactions. Fed Proc 1981;40:23. Cadenas E, Varsavsky A, Boveris A, Chance B. Oxygen of organic hydroperoxide-induced chemiluminescence of brain and liver homogenates. Biochem J 1981;198:645. Cadenas E, Boveris A, Chance B. In: Pryor WB, ed. Free radicals in biology. New York: Academic Press, Inc., 1984; 6:211. Boveris A, Llesuy SF, Fraga CG. Increased liver chemilumi- nescence in tumor-bearing mice. J Free Radicals Biol Med 1985;1:131.

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31. Llesuy SF, Milei J, Molina H: Boveris A, Milei S. Comparison of lipid peroxidation and myocardial damage induced by adriamycin and 4’-epiadriamycin in mice. Tumori 1985; 71:241.

32. Bernier M, Hearse DJ, Manning AS. Reperfusion-induced

arrhythmias and oxygen derived free radicals. Studies with “anti-free radical” interventions and a free radical-generat- ing system in the isolated perfused rat heart. Circ Res 19%; 58:331.

Fiberoptic study on the effects of transluminal angioplasty in experimental occlusive arterial thrombosis

Percutaneous transluminal coronary angioplasty has been proposed as definitive therapy for coronary recanalization of occluded coronary arteries in patients with acute myocardial infarction (AMI). The effects of transluminal angioplasty (TA) on experimental occlusive canine arterial thrombi that closely simulated the clinical condition was examined by a fiberoptic method. Experimental arterial thrombosis was produced by endothelial denudation and induction of iuminal stenosis. Eighteen dogs that showed total occlusion of the iliac artery with thrombi were evaluated. Seven dogs (group A) with 6hour-old thrombi received 20,000 IU/kg intravenous urokinase (UK) but did not show recanalization. TA was performed with a Gruentzig or Simpson-Robert balloon catheter and its effect was evaluated by a vascular fibroscope. Eight dogs (group B) with 6-hour-old thrombi underwent primary TA. After TA, less than 50% luminal obstruction with residual thrombi was visualized in five dogs (71%) of group A and four dogs (50%) of group B. Residual thrombi showed a doughnut-like or globular type shape and consisted of dense fibrin networks and compact platelet aggregates. All dogs in group B received 20,000 IU/kg intravenous UK after TA, but most of them showed progression of thrombus size despite UK infusion. In conclusion, the results suggest (1) that TA is effective in recanalization of an occluded artery with aged thrombus that is resistant to thrombolytic therapy and (2) that vascular fiberscope is a useful method for evaluation of the effects of TA on occlusive arterial thrombus. (AM HEART J 1988;115:312.)

Takanobu Tomaru, Yasumi Uchida, and Tsuneaki Sugimoto. Tokyo, Japan

Percutaneous transluminal coronary recanalization (PTCR) has been widely used to dissolve the coro- nary thrombi and restore coronary flow in patients with acute myocardial infarction (AMI).1-8 However, in most cases, significant coronary stenosis remains after the treatment. To open persisting high-grade atherosclerotic stenosis in AM1 patients, percutane- ous transluminal coronary angioplasty (PTCA) has been used after thrombolytic therapy.vp10 PTCA has also been recommended as initial therapy for coro- nary recanalization of coronary arteries occluded

From the Second Department of Internal Medicine, University of Tokyo.

Received for publication May 26, 1987; accepted Aug. 21, 1987.

Reprint requests: Takanobu Tomaru, M.D., 2nd Department of Internal Medicine, University of Tokyo, 7-3-l Hongo, Bunkyo-ku, Tokyo, Japan.

with atherosclerosis and thrombi.g-‘l Compared with PTCR with urokinase (UK) or streptokinase (SK), which often results in a tendency to bleeding, prima- ry PTCA is often beneficial because it can restore coronary flow without the use of thromboiytic agents.

Recently, the vascular fiberscope (angioscope) has been used for direct visualization of the coronary or peripheral arteries in clinical or experimental condi- tions,12-l5 and it is considered a useful method for direct visualization of arterial recanalization. In this study, we report an initial experience with direct fiberoptic visualization of transluminal angioplasty (TA) of experimental occlusive canine arterial thrombi that closely simulated the clinical condi- tion.

312