Chimeric 7E3 Fab (ReoPro) decreases detectable CD11b on neutrophils from patients undergoing coronary angioplasty.

OBJECTIVES: The purpose of this study was to monitor the effects of chimeric 7E3 Fab (ReoPro) on leukocyte and platelet activation and interaction during coronary angioplasty. BACKGROUND: Increased expression of CD11b on monocytes and neutrophils promotes their adhesion to endothelial cells, extracellular matrix and smooth muscle cells. Thrombin-activated platelets adhere via P-selectin to monocytes and neutrophils. These cell interactions may affect the outcome of coronary angioplasty. METHODS: During coronary angioplasty, venous blood was obtained for flow cytometric detection of leukocyte CD11b; platelet CD41a, CD61a and CD62P; the percentage of leukocytes with adherent platelets and the intensity of bound platelet fluorescence. RESULTS: Leukocyte CD11b expression increased after angioplasty in control patients (neutrophils 171+/-25 to 255+/-31 mean fluorescence intensity [MFI, mean+/-SEM], n=25, p < 0.0001; monocytes 200+/-40 to 248+/-36 MFI, n=17, p < 0.05) and decreased in the patients selected to receive chimeric 7E3 Fab (neutrophils 146+/-30 to 82+/-22 MFI, n=25, p < 0.0001; monocytes 256+/- 53 to 160+/-38 MFI, n= 17, p < 0.05). Neutrophil CD11b decreased after in vitro incubation of whole blood with chimeric 7E3 Fab (n=5, p=0.01), but fMLP-induced increases in CD11b were not prevented. The CD11b expression was unchanged and increased with fMLP stimulation after in vitro incubation of isolated neutrophils with chimeric 7E3 Fab. Direct-labeled chimeric 7E3 Fab was not detected bound to neutrophils in whole blood or isolated cells using flow cytometric techniques. Adhesion of isolated neutrophils to protein-coated glass was not prevented by in vitro incubation with chimeric 7E3 Fab. Platelet activation increased after angioplasty in control patients (CD62P 8.9+/-0.8 to 12.3+/-1.2 MFI, n=25, p < 0.05; CD41a 382+/-25 to 454+/-26 MFI, n=25, p < 0.05, CD61a 436+/-52 to 529+/-58 MFI, n=11, p < 0.05); it did not increase in the patients selected to receive chimeric 7E3 Fab (CD62P 13.2+/-1.0 to 9.0+/-0.9 MFI, n=25, p < 0.05; CD61a 398+/-32 to 410+/-38 MFI, n=7, p=NS). Leukocytes with adherent platelets tended to increase in the control group of patients and decrease after the procedure in patients selected to receive chimeric 7E3 Fab; individual and procedure-related variability were marked. CONCLUSIONS: Despite standard aspirin and heparin therapy, leukocyte and platelet activation with platelet adherence to leukocytes occurs after coronary angioplasty. Although chimeric 7E3 Fab does not bind to leukocytes directly, it influences CD11b expression in whole blood. Modulation of platelet and leukocyte activation and interaction by chimeric 7E3 Fab may contribute to an improved outcome after coronary angioplasty.

Is computer interpretation of the exercise electrocardiogram a reasonable surrogate for visual reading? Veterans Affairs ACME Investigators.

BACKGROUND: Interpretation of exercise tests as positive or negative is primarily based upon exercise-induced ST segment changes. Consistently accurate measurements are difficult to obtain during exercise. HYPOTHESIS: This study compared on-line computer-generated electrocardiographic (ECG) analysis with visual interpretation. The goals were to document the extent of agreement, establish reasons for disagreements, characterize ST-segment depression (extent, onset, duration), and determine the sensitivity and ability to localize coronary artery disease for each method. METHODS: Comparisons were made in 120 patients at eight Veterans Affairs Medical Centers. An exercise test was considered positive if > 1.0 mm horizontal or downsloping ST-segment depression was detected 0.08 s after the J point during exercise or recovery. The ST-segment depression had to be present on at least two successive ECG recordings 15 s apart. Computer interpretation was based on median averaged beats. RESULTS: There was an 88% agreement of visual and computer interpretations [106/120 (both positive, n = 62; both negative, n = 44)]. The disagreements involved visual negative, computer positive in 10 cases and visual positive, computer negative in 4 cases. Correlation was excellent between methods for characterization of ST-segment depression (p < 0.0001). Sensitivity for detecting and the ability to localize coronary artery disease (> or = 70% stenosis) were similar for both methods. CONCLUSION: This computer algorithm using median averaged beats is a reasonable surrogate for visual interpretation of the exercise ECG, making it a valuable source of confirmation of physician readings in large research trials and in clinical settings.

Acute myocardial infarction: clinical characteristics, management and outcome in a metropolitan Veterans Affairs Medical Center teaching hospital.

OBJECTIVES: The influence of race and age on thrombolytic therapy, invasive cardiac procedures and outcomes was assessed in a Veterans Affairs teaching hospital. The influence of Q wave evolution on the use of invasive cardiac procedures and outcome was also assessed. BACKGROUND: It is not well known how early revascularization procedures for acute myocardial infarction are delivered or influence survival in a Veterans Affairs patient population. METHODS: From October 1993 to October 1995, all patients with myocardial infarction were identified by elevated creatine kinase, MB fraction (CK-MB) and one of the following: chest pain or shortness of breath during the preceding 24 h or electrocardiographic (ECG) abnormalities. RESULTS: Racial groups were similar in terms of age, time to ECG, peak CK and length of hospital stay. Mortality increased with age (odds ratio [OR] 1.93, 95% confidence interval [CI] 1.33 to 2.81). A trend toward increased mortality occurred for race other than Caucasian. Patients meeting ECG criteria were given thrombolytic agents in 49% of cases, but age, comorbidity count and Hispanic race decreased the probability of thrombolytic use. Cardiac catheterization was performed more often after thrombolytic agents (OR 1.85, 95% CI 0.97 to 3.54), but less often in African-Americans (OR 0.59, 95% CI 0.35 to 1.02), older patients (OR 0.39, 95% CI 0.24 to 0.64) or patients with heart failure (OR 0.30, 95% CI 0.17 to 0.52). Patients evolving non-Q wave infarctions were older and had increased comorbidity counts and trends toward increased mortality. Angioplasty was chosen less for patients > or = 65 years old (p = 0.02); angioplasty and coronary artery bypass graft surgery were performed less in patients > or = 70 years old (p = 0.02). Patients treated invasively had lower mortality rates than those treated medically (p < 0.02). CONCLUSIONS: The use of thrombolytic agents and invasive treatment plans declined with age, and mortality increased with age. Trends toward increased mortality occurred with non-Q wave infarctions and race other than Caucasian.

CD18 integrin and CD54-dependent neutrophil adhesion to cytokine-stimulated human hepatocytes.

We investigated the hypothesis that CD54 (intercellular adhesion molecule-1) expressed on hepatocytes will support beta2-integrin (CD18)-dependent adhesion of neutrophils. An in vitro model using C3A cells (a human hepatoblastoma cell line exhibiting many characteristics of normal hepatocytes) and human neutrophils was utilized. C3A cells were stimulated with interleukin-1beta (IL-1beta), tumor necrosis factor-alpha, or interferon-gamma (IFN-gamma) for 24 h to induce expression of CD54, and adhesion of neutrophils was found to be markedly increased. Detailed studies with IFN-gamma-stimulated (100 U/ml) C3A cells revealed that this adhesion involved CD11a/CD18 [lymphocyte function-associated antigen-1 (LFA-1)] and CD54 and was dependent on low levels of IL-8 produced by the stimulated hepatocytes. Addition of higher concentrations of chemotactic factor (e.g., IL-8) further augmented adhesion and recruited contributions of CD11b/CD18 (Mac-1). In contrast to LFA-1, Mac-1 appeared to recognize a CD54-independent ligand constitutively expressed on the hepatocytes. Such close apposition of neutrophils to hepatocytes may increase the potential for parenchymal cell injury by providing a short distance through which cytotoxic factors such as reactive oxygen or proteolytic enzymes could act.

Leukocyte activation with platelet adhesion after coronary angioplasty: a mechanism for recurrent disease?

OBJECTIVES: The purpose of this pilot study was to determine whether leukocyte activation occurs, whether leukocyte-platelet complexes develop and whether there is any association between these findings and clinical outcome after coronary angioplasty. BACKGROUND: Increased expression of CD11b on monocytes and neutrophils promotes their adhesion to endothelial cells, extracellular matrix and smooth muscle cells. Thrombin-activated platelets adhere to monocytes and neutrophils through P-selectin. These cell complexes may affect the inflammatory process and, thus, the outcome of coronary angioplasty. METHODS: During elective single-vessel coronary angioplasty in 11 men, samples were obtained for flow cytometric detection of CD11b, as well as the percent of leukocytes with adherent platelets and the intensity of bound platelet fluorescence (number of platelets/leukocyte). RESULTS: After angioplasty, there was an increase in CD11b (monocytes: p = 0.001, neutrophils: p = 0.02) and leukocytes with adherent platelets (p = 0.02). During follow-up, five patients remained in stable condition and six had subsequent clinical events: restenosis and progression of disease requiring coronary artery bypass grafting (n = 3), myocardial infarction involving the dilated artery (n = 1) and unstable angina (n = 2). Values for leukocyte CD11b expression, the percent of leukocytes with adherent platelets and the intensity of bound platelet fluorescence were higher both before and after angioplasty in the six patients experiencing clinical events. CONCLUSIONS: Despite standard aspirin and heparin therapy, leukocyte activation with platelet adherence occurs after coronary angioplasty. The magnitude of leukocyte activation and platelet adherence appears to be higher in patients experiencing late clinical events.

Differential expression and release of CD54 induced by cytokines.

Intercellular adhesion molecule-1 (ICAM-1, CD54) is upregulated in many cell types stimulated by cytokines. A human hepatoblastoma cell line (C3A, a subclone of HepG2/C3 that is currently being used as a surrogate liver) and human lung adenocarcinoma cells (A549) were stimulated with interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF alpha), interferon-gamma (IFN gamma), or IL-6 to determine any differences in cell type responsiveness to individual cytokines for ICAM-1 upregulation. Time courses were performed with each cytokine evaluating ICAM-1 mRNA, surface expression, and cICAM-1 in the cell culture media. Between 3 and 6 hours, IL-1 beta (30 U/mL) stimulated the greatest increase in hepatocyte ICAM-1 mRNA, followed by IFN gamma (100 U/ mL), and IL-6 (100 U/mL) in order of potency. Except for IL-6, cytokine-induced hepatocyte surface levels of ICAM-1 (immunofluorescence flow cytometry, mAb R6.5) were dose dependent, with inhibition at higher concentration. Highest levels followed stimulation with INF gamma (P < .05). Significantly less was found after both IL-1 beta and TNF alpha; none was detected after IL-6 (P < .05). In contrast, IL-1 beta stimulated significantly more cICAM-1 release from hepatocytes than the other cytokines (P < .001), and IL-6 stimulated modest cICAM-1. Between 3 and 6 hours in the A549 cells, IL-1 beta stimulated the greatest increase in ICAM-1 mRNA, followed by TNF alpha. Both responses were greater than that observed in the hepatocytes. IFN gamma- and IL-6-induced ICAM-1 mRNA synthesis was not different from unstimulated A549 cells. Cytokine-induced A549 surface levels of ICAM-1 (immunofluorescence flow cytometry, mAb R6.5) was highest for IL-1 beta (peak levels similar to hepatocyte response), modest with TNF alpha (peak levels less than hepatocytes), detectable with IFN gamma (much less than hepatocytes), and nondetectable after IL-6. No ICAM-1 release from A549 cells was induced under any condition. In hepatocytes the amount of ICAM-1 mRNA was best accounted for by considering both cell surface levels of ICAM-1 and cICAM-1 levels. In human lung adenocarcinoma cells, the cytokine induction of ICAM-1 mRNA could potentially be accounted for by observing cell surface levels of ICAM-1 because no cICAM-1 was produced. These results suggest that surface ICAM-1 and cICAM-1 may be differentially controlled by each cytokine and by each parenchymal cell type.

Myocardial contrast echocardiography: relation of collateral perfusion to extent of injury and severity of contractile dysfunction in a canine model of coronary thrombosis and reperfusion.

OBJECTIVES: This study sought to determine whether myocardial contrast echocardiography could be used to detect and quantitate collateral blood flow capable of limiting the effects of ischemia in an experimental model of coronary thrombosis and reperfusion. BACKGROUND: Myocardial contrast echocardiography has been used to assess collateral blood flow in humans, but this technique has not been extensively validated in the experimental laboratory. METHODS: Myocardial ischemia occurred after electrically induced left circumflex coronary artery thrombosis in a canine model. Ischemia was intensified by administration of vasodilators. Reperfusion was induced with recombinant tissue-type plasminogen activator. Myocardial perfusion was assessed with contrast echocardiography and radiolabeled microspheres. Infarct size was determined by histochemical staining methods. Myocardial samples were evaluated histologically. RESULTS: The dogs were classified into two groups on the basis of contrast echocardiographic detection of perfusion in the ischemic region: those with (n = 13) and without collateral flow (n = 10). Collateral perfusion detected by contrast echocardiography paralleled changes detected by radiolabeled microspheres during thrombosis and vasodilator administration. A 91% agreement was observed between the two techniques in detecting collateral flow > 0.3 ml/min per g (p < 0.0001). Collateral perfusion correlated directly with radial shortening fractions of the ischemic myocardium (p < 0.01). Recovery of function after reperfusion was faster, infarct size was smaller (mean [+/- SD] 4 +/- 1% vs. 11 +/- 3%, p = 0.05), and histopathologic injury was less in dogs with than without collateral flow, respectively (p < 0.05). CONCLUSIONS: Myocardial contrast echocardiography can identify physiologically significant collateral vessels capable of limiting the degree of ischemic damage during coronary thrombosis. The magnitude of collateral flow and the change in flow induced by vasodilators can be assessed and compares favorably with the microsphere standard.

Myocardial contrast echocardiography: relation between on-line and off-line assessment of myocardial perfusion.

BACKGROUND: Quantitative assessment of myocardial perfusion by myocardial contrast echocardiography has been made possible by the use of custom-made off-line video-intensity programs. A standardized program that could be used by all investigators would improve the reproducibility of results and enhance its clinical utility. METHODS AND RESULTS: The purpose of this study was to determine if the assessment of myocardial perfusion by contrast echocardiography using a new commercially available, quantitative on-line software program correlates with an off-line custom-made video-intensity program previously validated by our laboratory and with radiolabeled microspheres, under various experimental myocardial perfusion conditions. Two of the measured myocardial contrast echocardiographic parameters (peak intensity, area under the time-intensity curve {area}) correlated well among on-line and off-line methods and radiolabeled microspheres, especially when the data were "normalized" by comparing percent change from baseline or a ratio of ischemic to nonischemic myocardium. The third myocardial contrast echocardiographic parameter examined, half-time of the peak intensity on the washout limb of the curve (t 1/2), correlated only when the percent change from baseline was compared between the two methods or when the off-line method was compared with radiolabeled microspheres. CONCLUSION: The results of this investigation add further support to the potential use of myocardial contrast echocardiography to evaluate serial changes in myocardial perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

High dose intravenous aspirin, not low dose intravenous or oral aspirin, inhibits thrombus formation and stabilizes blood flow in experimental coronary vascular injury.

OBJECTIVES: The purpose of this study was to assess the anti-thrombotic potential of various forms of aspirin administration. BACKGROUND: Platelet activation in response to endothelial injury has been implicated in acute coronary syndromes. METHODS: Delivering 100-microA anodal direct current to the intima of the left circumflex coronary artery in dogs at a site of moderate external stenosis provides a thrombogenic model of vascular injury. Animals were treated with aspirin (Group I, 20 mg/kg intravenously [n = 11]; Group II, 4.6 mg/kg intravenously [n = 6]; Group III, 4.6 mg/kg orally 18 h before the experiment [n = 7]) or vehicle (Group IV, control [n = 11]). RESULTS: The time required for thrombotic occlusion to occur was longer and the incidence of thrombosis was lower in Group I (Group I, 238 +/- 7 min [n = 2]; Group II, 127 +/- 25 min [n = 3]; Group III, 156 +/- 35 min [n = 6]; Group IV, 90 +/- 11 min [n = 11]) (p < 0.05). Thrombus mass was smaller in Group I (Group I, 5.0 +/- 0.8 mg; Group II, 12.2 +/- 2.6 mg; Group III, 11.6 +/- 3.9 mg; Group IV, 9.1 +/- 1.6 mg) (p < 0.05). Initial hemodynamic variables did not differ among groups. An increase in mean arterial pressure was noted for several hours after intravenous aspirin administration in Group I (99 +/- 5 to 110 +/- 4 mm Hg) (p < 0.05). Left circumflex coronary artery blood flow was stable for 5 h in Group I (Group I, 31 +/- 2 to 26 +/- 4 ml/min) but decreased in all the other groups (Group II, 26 +/- 4 to 10 +/- 5 ml/min; Group III, 27 +/- 5 to 7 +/- 7 ml/min; Group IV, 29 +/- 4 to 0 ml/min) (p < or = 0.05). The in vivo area of left ventricle perfused by the left circumflex coronary artery was not different among groups. Platelet counts were similar and did not change over the course of the protocol. Ex vivo arachidonic acid-induced platelet aggregation decreased in all groups after aspirin (p < or = 0.001). Indium-111-labeled platelet adherence to the coronary vasculature was decreased in distal vessel segments after all doses of aspirin (p < 0.05). Platelet deposition in thrombi was similar for all treatment groups. CONCLUSIONS: High dose intravenous aspirin has salutary effects. It stabilizes left circumflex coronary artery blood flow, prolongs the time to thrombosis, reduces the incidence of thrombotic occlusion, reduces thrombus mass and limits platelet adherence to sites of arterial injury. Low dose aspirin given intravenously or orally was ineffective. When persistent intracoronary thrombi precipitate unstable coronary syndromes, high dose intravenous aspirin may be useful in the acute period even though platelets continue to interact with injured vascular segments through aspirin-insensitive mechanisms.

Doppler quantification of echo-contrast injections in vivo.

It is difficult to quantify myocardial perfusion using contrast echocardiography because the echogenicity of injected contrast is unknown. We propose that a measurement of Doppler amplitude from blood in a systemic artery during the passage of contrast could define the needed input function. Time-amplitude curves from pulsed Doppler cuffs on coronary and carotid arteries of 7 dogs were analyzed during aortic root and left atrial injections of Albunex. We found in individual animals that the areas under the Doppler time-amplitude curves were correlated to the amount of Albunex injected (R = 0.87-0.99), inversely correlated to cardiac output (R = 0.83), and uncorrelated to coronary flow (R = 0.18). Due to better mixing, the coronary and carotid response areas correlated better for left atrial injections (R = 0.96) than for aortic root injections (R = 0.56). We conclude that Doppler amplitude detection can be used to quantify the passage of echo-contrast agents, that the measurements comply with indicator-dilution principles, and that systemic measurements in the carotid artery could be used to predict the coronary input function for injection sites with good systemic mixing.

A monoclonal antibody against the platelet glycoprotein IIb/IIIa receptor complex prevents platelet aggregation and thrombosis in a canine model of coronary angioplasty.

BACKGROUND: The comparative effects of aspirin and F(ab')2 fragments of monoclonal antibody 7E3 against the platelet glycoprotein IIb/IIIa receptor on ex vivo platelet aggregation and in vivo thrombosis were studied in a canine coronary balloon angioplasty model. METHODS AND RESULTS: Three groups were studied. Group 1 (n = 8) was pretreated with saline placebo, group 2 (n = 8) was pretreated with 325 mg aspirin, and group 3 (n = 8) was pretreated with 0.8 mg/kg 7E3 F(ab')2. Coronary angioplasty was performed in the left anterior descending coronary artery of open-chest dogs under fluoroscopic control; serial measurements of basal and hyperemic coronary blood flows were then made for 2 hours after application of an external stenosis that decreased hyperemic flow by 50%. There were no significant differences in platelet counts or hemodynamic measurements during the experiments. Platelet aggregation was decreased by treatment: group 1, 64 +/- 13% versus 50 +/- 13% (p = NS); group 2, 57 +/- 4% versus 25 +/- 4% (p less than 0.001); and group 3, 77 +/- 5% versus 10 +/- 6% (p less than 0.0002). Compared with initial measurements, the 7E3 antibody was superior to aspirin in maintaining hyperemic coronary blood flow after release of the external stenosis: group 1, 177 +/- 14 versus 21 +/- 14 ml/min (p less than 0.0003); group 2, 189 +/- 9 versus 110 +/- 28 ml/min (p less than 0.008); and group 3, 194 +/- 12 versus 181 +/- 15 ml/min (p less than 0.02). In group 1, arterial occlusion developed in five dogs, and nonocclusive thrombus was seen in three dogs. In group 2, arterial occlusion developed in one dog, and nonocclusive thrombus was seen in five dogs. No thrombotic material was visualized in group 3 dogs treated with 7E3 F(ab')2. CONCLUSIONS: In this animal model, the 7E3 antiplatelet antibody is superior to aspirin in inhibiting platelet aggregation, thrombosis, and acute closure after deep arterial injury caused by coronary balloon angioplasty.

Prospective, double-blind, placebo-controlled trial of low-dose amiodarone in patients with severe heart failure and asymptomatic frequent ventricular ectopy.

Sudden cardiac death is a common cause of mortality in patients with congestive heart failure. To determine if low-dose amiodarone could reduce sudden death among these patients, a prospective, placebo-controlled, double-blind pilot trial was conducted. One hundred one patients with ejection fractions less than 30%, New York Heart Association class III or IV symptoms, and frequent but asymptomatic spontaneous ventricular ectopy (Lown class II to V) were randomly assigned to treatment with low-dose amiodarone (400 mg/day for 4 weeks and then 200 mg/day) or placebo. Mean follow-up was 357 days (range 4 to 1009 days). Side effects were infrequent and there was no difference in the incidence of side effects between the treatment groups. The frequency of spontaneous ventricular ectopy in the group receiving amiodarone fell from 4992 +/- 1240 beats/24 hours at baseline to 1135 +/- 494 beats/24 hours after 1 month of treatment (p = 0.02) and remained low after 6 months, while there was no change in ventricular ectopy among the patients receiving placebo. Despite the reduction in ectopy, there was no improvement in mortality or decrease in the incidence of sudden death. One-year mortality by Kaplan-Meier analysis was 28% in the group receiving amiodarone and 19% in the group receiving placebo (p = NS). One-year mortality in patients with greater than 75% reduction in ventricular ectopy after 1 month of treatment was 31% versus 17% in patients with less than or equal to 75% ectopic suppression (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Antiplatelet antibody [7E3 F(ab')2] prevents rethrombosis after recombinant tissue-type plasminogen activator-induced coronary artery thrombolysis in a canine model.

Coronary artery rethrombosis can complicate initially effective thrombolytic therapy. Platelets interacting with injured vascular endothelium in a region along the coronary artery with reduced luminal cross-sectional area contribute to rethrombosis. The purpose of this study was to investigate the potential of the F(ab')2 fragment of the murine monoclonal antibody 7E3 [7E3 F(ab')2] to prevent rethrombosis after intracoronary clot lysis with recombinant tissue-type plasminogen activator (rt-PA) in an experimental model. The 7E3 F(ab')2 binds to the platelet glycoprotein IIb/IIIa complex (GPIIb/IIIa), thereby preventing platelet-fibrinogen interaction and intravascular thrombus formation. Experimental coronary artery thrombosis was produced in the anesthetized dog by application of direct anodal current to the intimal surface of the left circumflex coronary artery in the region of an external stenosis. Lysis of the established intracoronary thrombus was achieved with the intravenous administration of rt-PA (25 mg) after which the animals were randomized into two groups. Group 1 (n = 10) served as the control, receiving the saline diluent, and group 2 (n = 9) received 7E3 F(ab')2, given as a single intravenous injection (0.8 mg/kg). The times required for occlusive thrombus formation, rt-PA-induced thrombolysis, and rethrombosis (if it occurred) were similar in the animals treated with saline and those treated with 7E3 F(ab')2. The initial left circumflex coronary artery blood flow was similar in both groups but decreased to a negligible level in group 1. In group 2, left circumflex coronary artery blood flow declined modestly (24 +/- 2 to 10 +/- 2 ml/min). Rethrombosis occurred in all animals in group 1 but in only two of nine animals in group 2 (p less than 0.05). Oscillations in coronary blood flow preceded rethrombosis in group 1, whereas 7E3 F(ab')2 stabilized left circumflex coronary artery blood flow patterns during the course of teh experimental protocol (5.2 +/- 0.9 vs. 0.7 +/- 0.4 oscillations, respectively; p less than 0.05). Thrombus mass recovered from the left circumflex coronary artery at the conclusion of each experiment was greater in group 1 as compared with group 2 (7.0 +/- 2.3 vs. 1.5 +/- 0.7 mg, respectively; p less than 0.05). The area of left ventricle at risk for infarction was similar in both groups but infarct size, infarction/at risk assessed histochemically, was larger in group 1 than group 2 (35 +/- 9% vs. 6 +/- 4%, respectively; p less than 0.05). Platelet aggregation induced by ADP and arachidonic acid was similar at baseline for all of the animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Sustained limitation of myocardial reperfusion injury by a monoclonal antibody that alters leukocyte function.

Pentobarbital anesthetized dogs were subjected to 90 minutes of left circumflex coronary artery (LCCA) occlusion followed by 72 hours of reperfusion. Control or anti-Mo1 (904) F(ab')2 fragments of monoclonal antibodies were administered intravenously at a dose of 1 mg/kg beginning 45 minutes after occlusion and at a dose of 0.5 mg/kg at 12, 24, 36, and 48 hours after reperfusion. Myocardial infarct size expressed as a percentage of the area at risk (IN/AR) measured postmortem after 72 hours of reperfusion was significantly reduced by 904 F(ab')2 (21.6 +/- 2.8%, n = 8) compared with control F(ab')2 (37.4 +/- 5.8%, n = 8; p less than 0.025). There were no significant differences between groups in heart rate, mean arterial blood pressure, rate-pressure product, or LCCA blood flow that could account for a reduced infarct size. Regional myocardial blood flow (RMBF) was determined with 15-microns radiolabeled microspheres. Transmural blood flows (ml/min/g) within the region of myocardium at risk were not statistically different between treatment groups. Infarct size in both groups was related to regional myocardial blood flow, and the relation was shifted downward in the group treated with the anti-Mo1 F(ab')2 antibody (analysis of covariance, p = 0.01). Thus, anti-Mo1 F(ab')2 produces a sustained limitation of myocardial infarct size compared with controls under similar hemodynamic conditions and a similar degree of myocardial ischemia as determined by RMBF. These data suggest that inhibition of neutrophil adhesive interactions (as suggested by the inhibitory effect of anti-Mo1 on canine neutrophil aggregation) may be an effective mechanism for protection against myocardial injury secondary to myocardial ischemia and reperfusion.

Induction of ventricular arrhythmia by high and low osmolarity ionic and nonionic contrast media.

Studies that used prolonged contrast media infusion in canine arteries have generated controversy regarding the arrhythmogenic potential of low osmolarity, nonionic contrast agents. In order to establish the relative safety of these agents in the more typical setting of bolus injections, 4 ml intracoronary bolus injections of Hypaque-76 (n = 54), Iohexol-350 (n = 51), and Iohexol-140 (n = 51) were given in random order to 10 anesthetized, open-chest dogs undergoing programmed cardiac stimulation. Hemodynamics and electrocardiogram were monitored during stimulation, both during and for 2 minutes after the end of contrast infusion. Occurrence of evoked single and coupled premature ventricular contractions and nonsustained ventricular tachycardia did not differ statistically among agents. Sustained ventricular tachycardia (five episodes) and ventricular fibrillation (seven episodes) occurred only after Hypaque-76 injections (p less than 0.002). These results differ from those in studies that use continuous contrast infusion and suggest that low osmolarity nonionic contrast agents are as safe as high osmolarity nonionic contrast media. Both appear safer than ionic contrast material.

Streptokinase improves reperfusion blood flow after coronary artery occlusion.

Streptokinase is an effective thrombolytic agent which, with early restoration of coronary blood flow, has the potential for limiting infarct size. Distinct from thrombolysis, we studied the effects of streptokinase on reperfusion coronary blood flow and infarct size. Open-chest anesthetized canines underwent a 90 minute snare occlusion of the left circumflex coronary artery followed by release and reperfusion through a critical stenosis for 6 hours. The animals were assigned randomly to two groups. Intracoronary streptokinase [group 1 (n = 8): 6000 IU/kg in 3 ml of saline] or saline [group 2 (n = 8): 3 ml of saline] was infused at 0.05 ml/min for 60 minutes beginning 30 minutes before reperfusion. Coronary blood flow was stable in group 1 during reperfusion, while in group 2 it fell during 6 hours of reperfusion (30 +/- 4 ml/min to 18 +/- 2 ml/min, P = 0.05). The ST-segment elevation on the limb lead II electrocardiogram 15 minutes after coronary artery occlusion was similar in both groups (group 1: 3.9 +/- 0.6 mV, group 2: 2.3 +/- 0.5 mV), suggesting the extent of myocardial ischemia was also similar in both groups. The infarct sizes were similar when expressed both as a percent of the total left ventricular mass [(IZ/LV) group 1: 17 +/- 2.5%, group 2: 17.5 +/- 2.5%] or as a percent of the area at risk of infarction [(IZ/AR) group 1: 39 +/- 6%, group 2: 39 +/- 5%]. In both groups, the mass of left ventricle dependent on the blood flow distribution of the left circumflex coronary artery was similar when compared to total left ventricular mass [(AR/LV) group 1: 41 +/- 3%, group 2: 44 +/- 4%]. These results demonstrate that streptokinase maintains reperfusion coronary blood flow through a critical stenosis at a rate similar to baseline levels. Despite the fact that coronary blood flow remained stable with streptokinase during reperfusion, infarct size was not limited after 90 minutes of fixed coronary artery occlusion in this canine model of myocardial injury.

Antiplatelet monoclonal F(ab')2 antibody directed against the platelet GPIIb/IIIa receptor complex prevents coronary artery thrombosis in the canine heart.

Interactions between platelets with injured vascular endothelium contribute to thrombotic occlusion. A murine monoclonal antibody [7E3 F(ab')2] to the platelet GPIIb/IIIa receptor complex was used to inhibit platelet aggregation in an experimental model of coronary artery thrombosis. Prevention of thrombotic occlusion by 7E3 F(ab')2 (0.8 mg/kg bolus i.v.) was studied in dogs with direct current induced intimal injury (100 microA for 5 h) and critical stenosis of the left circumflex coronary artery (LCCA). Baseline LCCA blood flow (CBF) was similar in 7E3 F(ab')2 and control groups, but decreased in the controls [24 +/- 2 ml/min to 0 +/- 0 ml/min, n = 13 (mean +/- S.E.M.)] due to thrombotic occlusion in each case (time to thrombosis 136 +/- 15 min). In the group treated with 7E3 F(ab')2, CBF did not change significantly (27 +/- 3 ml/min to 22 +/- 3 ml/min, n = 6) and thrombotic occlusion did not occur during the 5-h observation period in which intimal injury was produced in the LCCA (P less than 0.001). Oscillations in CBF preceded thrombosis in the control group, but did not occur with 7E3 F(ab')2 treatment (2.2 +/- 0.7 vs. 0 +/- 0, P less than 0.05). The thrombus mass recovered from the LCCA 30 min after occlusion was 8.8 +- 1.3 mg in the controls compared to 2.2 +/- 1.2 mg determined 5 h after administration of 7E3 F(ab')2 (P less than 0.05). When studied ex vivo, before the administration of the test agents, platelets from both groups of dogs aggregated in response to ADP and arachidonic acid. However, after treatment, the ex vivo aggregation of platelets from 7E3 F(ab')2 animals was inhibited whereas platelets from the control animals continued to aggregate ex vivo throughout the period of the experimental protocol (P less than 0.05). The labeling of platelets with 111indium showed accumulation of radioactivity within the thrombus and upon the vascular endothelium which was less in 7E3 F(ab')2 treated dogs as compared to the control group (P less than 0.05). The murine monoclonal antibody 7E3 F(ab')2 did not affect hemodynamic values or the circulating platelet count during the experimental protocol. In conclusion, antibody to platelet GPIIb/IIIa receptors: (1) prevented thrombotic LCCA occlusion, (2) inhibited ex vivo platelet aggregation, (3) minimized platelet deposition on injured vascular endothelium and within formed thrombi, and (4) stabilized CBF during 5 h of continuous direct current induced intimal injury of the LCCA.

Identification of a time window for therapy to reduce experimental canine myocardial injury: suppression of neutrophil activation during 72 hours of reperfusion.

The cardio-protective effects of neutrophil depletion or inhibition of neutrophil activation early in the course of myocardial reperfusion has been established. Whether these treatments would be effective during extended periods of reperfusion has not been ascertained. Open-chest anesthetized dogs were subjected to left circumflex artery (LCX) occlusion for 90 minutes followed by 72 hours of reperfusion. Dogs were randomized into one of four groups: 1) control; 2) Ilo-2 (iloprost 100 ng/kg/min administered via the left atrium beginning 10 minutes after LCX occlusion and continuing 2 hours into reperfusion); 3) Ilo-48 (iloprost 100 ng/kg/min administered as above until 1 hour after reperfusion then 25 ng/kg/min for 48 hours of reperfusion; or 4) antibody (neutrophil antibody administered before occlusion and 1/2 hourly for 2 hours of reperfusion and then every 24 hours). Myocardial infarct size, as a percentage of the area at risk assessed after 72 hours of reperfusion, was significantly smaller in the antibody-treated group (32.1 +/- 5.0% mean +/- SEM) or Ilo-48 (22.6 +/- 4.0%) treatment group compared with control (48.7 +/- 5.6%) or Ilo-2 (57.6 +/- 5.2%) groups. Regional myocardial blood flow studies demonstrated that all groups developed similar degrees of ischemia. The iloprost-treated groups had lower mean arterial blood pressures during occlusion and reperfusion than groups 1 and 4 (p less than 0.05). Circulating neutrophil counts were increased in groups 1 and 2 at 24 and 48 hours after reperfusion compared to groups 3 and 4 (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Protection of myocardial function and coronary vasculature by streptokinase.

Coronary artery reperfusion established by thrombolytic agents early in the evolution of an acute myocardial infarction is known to result in the salvage of otherwise jeopardized heart muscle. Recently, experimental evidence has suggested that reactive products of oxygen are formed as a result of reperfusion and can increase the amount of myocardial tissue that becomes irreversibly damaged. The purpose of the present study was to determine if the thrombolytic agent, streptokinase, could serve to scavenge reactive species of oxygen, thereby protecting the myocardium by a mechanism independent of its ability to lyse an occlusive thrombus. Rabbit isolated hearts were perfused at a constant rate with Krebs-Henseleit buffer (25 ml/min, 31 degrees C, pH 7.4) using a modified Langendorff method. Changes in the permeability of the coronary vascular bed were determined with 125I-labeled albumin added to the perfusion buffer. An intraventricular fluid-filled latex balloon connected to a pressure transducer maintained the left ventricle in an isovolumic state and was used to detect changes in myocardial contractility throughout the study protocol. Electrolysis of the oxygenated Krebs-Henseleit perfusion buffer with a 20 mA direct current for 2 min, delivered with a stainless-steel anode (proximal) and a platinum cathode (distal), resulted in the generation of reactive products of oxygen. Perfusion of the isolated heart with buffer containing the products of electrolysis resulted in an increase in mean coronary artery perfusion pressure, from 48 +/- 3 to 121 +/- 6 mm Hg [mean +/- SEM (n = 17)], and an increase in the left ventricular end-diastolic pressure, from 10 +/- 1 to 54 +/- 6 mm Hg. The addition of streptokinase (150 U/ml) or heparin (20 U/ml) to the perfusion medium attenuated the observed increase in coronary artery perfusion pressure from 42 +/- 3 to 73 +/- 9 mm Hg (n = 9) or from 43 +/- 2 to 98 +/- 9 mm Hg (n = 9), respectively. In addition, streptokinase prevented the increase in the left ventricular end-diastolic pressure (11 +/- 1 to 36 +/- 5 mm Hg, n = 9) and preserved left ventricular function as determined by the pressure-volume relationship. Myocardial accumulation of 125I-labeled albumin after exposure of the heart to the reactive products of oxygen was attenuated by the addition of streptokinase or heparin to the buffer solution. The data suggest that streptokinase and, to a lesser extent, heparin may preserve myocardial and coronary vascular function by scavenging reactive oxygen species.

Recombinant single-chain urokinase-type plasminogen activator (rscu-PA) induces thrombolysis and systemic fibrinolysis in a canine model of coronary artery thrombosis.

The thrombolytic efficacy of recombinant single-chain urokinase-type plasminogen activator (rscu-PA) was studied in an open-chest canine model of coronary artery thrombosis. Dogs (n = 16) were anesthetized, a left thoracotomy performed, and a two cm segment of the left circumflex coronary artery was isolated and instrumented with an electromagnetic flow probe, an intracoronary stimulation electrode, and an adjustable mechanical occluder. Anodal direct current (100 microA) was applied to the stimulation electrode until thrombosis occurred (n = 14). After 30 min of thrombotic occlusion, rscu-PA was administered intravenously. Dogs were sacrificed either 6 h after thrombolysis or 6.5 h after initiation of rscu-PA when thrombolysis did not occur. In group A (30-50 micrograms/kg bolus rscu-PA + 20-40 micrograms/kg/min infusion rscu-PA for 30 min, n = 5) thrombolysis occurred in one case (20%) and this artery reoccluded. In group B (250 micrograms/kg bolus rscu-PA + 25 micrograms/kg/min infusion rscu-PA for 30 min, n = 6) all reperfused and only one reoccluded (16.6%). In group C (200 micrograms/kg bolus rscu-PA + 100 micrograms/kg/min rscu-PA infusion for 30 min, n = 2) both reperfused and neither reoccluded. Infarct size, determined as a percentage of left ventricle, was smaller when thrombolysis was followed by persistent reperfusion (n = 7), than when reperfusion did not occur (n = 4): 16.9 +/- 3.7% vs 31.3 +/- 2.2%, respectively (mean +/- SEM, p less than 0.02). If thrombolysis was followed by reocclusion, infarct size was 27.0 +/- 10.0%. In this study thrombolysis occurred when changes in prothrombin time, partial thromboplastin time, fibrinogen and fibrin split products were suggestive of systemic finbrinogenolysis. In conclusion, effective thrombolysis with rscu-PA appears to limit infarct size and to be accompanied by evidence of systemic fibrinolysis.