Study protocol. Laboratory determinations. Definitions

Transcription

1 Effects of platelet glycoprotein IIb/IIIa inhibition with abciximab on thrombin generation and activity during percutaneous coronary intervention George Dangas, MD, Jonathan D. Marmur, MD, Traci E. King, BS, Joshua De Leon, MD, Samin K. Sharma, MD, Raghuraman Vidhun, MD, Dmitriy Feldman, BA, Michael Y. Stoynov, BA, Juan J. Badimon, PhD, and John A. Ambrose, MD New York, NY Background Antagonists of the platelet glycoprotein IIb/IIIa decrease acute ischemic complications after percutaneous coronary interventions (PCI). Abciximab (c7e3 Fab, ReoPro) has been reported to decrease thrombin generation in vitro. We investigated in vivo the effect of abciximab therapy on thrombin generation, thrombin activity, and the activated clotting time (ACT) during PCI. Methods We studied 32 consecutive patients who underwent PCI for unstable coronary syndromes. Group I (n = 11) was treated with heparin plus aspirin, and group II (n = 21) was treated with heparin plus aspirin plus standard-dose abciximab, administered 5 minutes after the initial heparin bolus. Patients received a standardized heparin bolus at time 0, and arterial blood specimens for prothrombin fragment F1.2, fibrinopeptide A (FPA), and ACT were obtained from the guiding catheter at 5 minutes, 10 minutes (ACT only), 20 minutes, and at the end of the PCI. Standard-dose abciximab was administered in group II only. Each patient served as his or her own control, and the changes against the baseline were compared between the 2 groups. Results There were no significant differences between the 2 groups regarding baseline characteristics, hematocrit, and platelet count. Group I patients had higher ACT and lower F1.2 and FPA compared with group II at baseline. Subsequent measurements demonstrated a gradual decrease in FPA and F1.2 in group II; the end of procedure versus baseline changes that occurred in F1.2 were significantly different compared with group I (decrease of 0.59 ± 0.22 nmol/l in group II vs increase of 0.22 ± 0.3 nmol/l in group I, P =.04), and a trend in the same direction was evident for FPA changes (decrease of 1.46 ± 1.16 ng/ml in group II vs increase of 2.25 ± 1.58 ng/ml in group I, P =.07). The ACT response to abciximab was variable, but a 6.3% increase (+20 sec) in ACT was documented 5 minutes after abciximab bolus in group II compared with the 3.4% decrease ( 10 sec) observed in group I at the same time point (P =.1). Conclusion Addition of abciximab to heparin plus aspirin during PCI was associated with a significant decrease in thrombin generation and a borderline decrease in thrombin activity. (Am Heart J 1999;138:49-54.) Percutaneous transluminal coronary revascularization procedures (PCI) traumatize the arterial wall, leading to platelet activation, increased thrombin generation and activity, and intracoronary thrombosis. 1-6 Activation of the platelet glycoprotein (GP) IIb/IIIa receptor is the final common pathway of platelet aggregation. 7 Treatment of patients with inhibitors of the GPIIb/IIIa integrin during interventional procedures has been shown From the Cardiovascular Institute, Mount Sinai School of Medicine. Supported in part by grants and from the National Heart Lung and Blood Institute and by grant 5 M01 RR00071 to the Mount Sinai General Clinical Research Center from the National Center for Research Resources, National Institutes of Health. Submitted June 26, 1998; accepted September 18, Reprint requests: Jonathan D. Marmur, MD, Box 1030, Mount Sinai Medical Center, New York, NY [email protected] Copyright 1999 by Mosby, Inc /99/$ /1/95343 to decrease acute ischemic complications in large prospective studies The mouse-human chimeric monoclonal antibody abciximab (c7e3 Fab, ReoPro), which blocks GPIIb/IIIa and the related α V β 3 receptor, 13 inhibits platelet aggregation. 14,15 Although abciximab has also been shown to decrease thrombin generation in vitro, 16 it has not been determined whether it exerts an antithrombin effect in vivo.we have recently shown that the addition of abciximab to aspirin plus heparin during coronary interventional procedures decreases both platelet thrombus formation and fibrin deposition in an ex vivo model of thrombosis on an injured vascular surface under dynamic flow conditions. 17 In this study, we investigated the effect of abciximab treatment during coronary interventional procedures on thrombin generation and thrombin activity in vivo as assessed by the change induced in activated clotting time (ACT) and plasma levels of prothrombin fragment

2 50 Dangas et al American Heart Journal July 1999 Figure 1 Table I. Nomogram calculation of initial bolus of heparin (at time 0) for patients already receiving heparin infusion before procedure Heparin bolus (U/Kg) ACT (sec) < >300 None None Outline of study protocol. All blood specimens were obtained from coronary ostium through guiding catheter after discarding first 10 ml of blood withdrawn. F1.2 and fibrinopeptide A (FPA). 18,19 We report that the addition of abciximab was associated with significantly decreased thrombin generation. Methods All patients transferred to the Mount Sinai Hospital, New York, for PCI after diagnostic angiography performed at the City Hospital Center at Elmhurst, Queens, from March to July 1997 were eligible for enrollment in this study.a single interventionalist (J.D.M.) performed all procedures. Inclusion criteria were the presence of an unstable coronary syndrome or an angiographically high-risk lesion. Exclusion criteria included restenosis, acute myocardial infarction (primary or rescue intervention), thrombocytopenia, or bleeding disorders.the values of F1.2, FPA, and ACT were periodically measured during the intervention according to the study protocol.the study was approved by the Institutional Review Board at Mount Sinai Hospital, and all enrolled patients gave written informed consent. Definitions In this study, unstable coronary syndrome was defined as unstable angina Braunwald classes II (rest pain), III (rest pain within 48 hours), B (primary) or C (postinfarction). 20 High-risk lesions were defined as complex lesions by Ambrose criteria 21 or lesions of type B 2 or C according to the American Heart Association/American College of Cardiology classification. 22 Study protocol Patients were divided into 2 groups: group I was composed of patients treated with heparin plus aspirin during the intervention; group II was composed of patients treated with abciximab in addition to heparin plus aspirin.abciximab was administered in patients with Braunwald class III or C unstable angina (group II), whereas patients in classes II and B were treated with heparin and aspirin only (group I, control). The study protocol is outlined in Figure 1.All patients had a complete blood count, platelet count, and prothrombin time/international normalized ratio preprocedure. Patients received a heparin bolus at time 0 (Table I); the first blood drawing was performed at 5 minutes, and then group II received standard-dose abciximab. Further blood drawings were performed at the 10-minute and 20-minute time points and at the end of the procedure.all arterial blood specimens were obtained from the 8F guiding catheter, positioned at the coronary ostium, after discarding the first 10 ml of blood. During blood withdrawal, the guiding catheter was either empty (beginning and end of procedure), or had a inch diameter coronary guide wire (during the procedure). Blood samples were never drawn with devices other than the coronary guide wire inside the guiding catheter lumen. The initial heparin bolus was adjusted according to the ACT value in patients already treated with heparin (Table I). During all procedures, the ACT was targeted at 350 to 400 seconds for the control group (group I) and at 300 to 350 seconds for the abciximab group (group II), with administration of additional heparin boluses as needed after obtaining the 10-minute specimen. Laboratory determinations At each time point the ACT value was calculated as the mean of 2 measurements performed simultaneously with a Hemochron 8000 (INC, Edison, NJ) in the catheterization laboratory. Blood for F1.2 (4 ml) was collected in a citrated tube, and blood for FPA (4 ml) was collected in a PPACK-coated tube (Hematologic Technologies, Inc).All specimens were centrifuged at 3000g for 15 minutes, and the plasma was separated and frozen at 70 C.The plasma F1.2 and FPA levels were measured with commercially available enzyme-linked immunosorbent assays (Enzygnost F1.2 by Behring Diagnostics,Westwood, Mass, and Asserachrom FPA by Diagnostica Stago,Asnieres-sur-Seine, France) by a single operator (T.E.K.) blinded to the specimen origin.

3 American Heart Journal Volume 138, Number 1, Part 1 Dangas et al 51 Table II. Patient characteristics (n = 11) (n = 21) P value Age (y) 61.3 ± ± 2.8 NS Male 9 (81.2) 18 (85.7) NS Diabetes mellitus 2 (18) 7 (33) NS Hypertension 3 (27) 14 (67) 0.03 Hyperlipidemia 1 (9) 11 (52) 0.01 Smoking 4 (36) 4 (19) NS Heparin before procedure 3 (27) 13 (62) NS Prior infarction 7 (63) 10 (48) NS LAD intervention 5 (45) 10 (47) NS LCX intervention 1 (9) 4 (19) NS RCA intervention 5 (45) 7 (33) NS Values as mean ± SE or n (%). LAD, Left anterior descending coronary artery; LCX, left circumflex coronary artery; RCA, right coronary artery. Revascularization procedure All interventions were performed with the transfemoral approach by an 8F arterial sheath.all stents were electively deployed with high pressure (16 to 18 atm for 30 sec, balloonto-artery ratio 1.0) and without intravascular ultrasound guidance.the balloon-to-artery ratio during balloon angioplasty was 1.0 to 1.1 with an inflation pressure 6 to 8 atm for 100 seconds. Patients who received stents received the first dose of ticlopidine after completion of the intervention. Rotational atherectomy was performed when appropriate with the stepped burr approach, a final burr-to-artery ratio of 0.7, and with adjunctive balloon postdilatation at 2 to 4 atm for 100 seconds. Procedural success was defined as <30% final diameter stenosis and absence of dissection or major complications, such as death, infarction, or need for bypass surgery. Statistical analysis The study design allowed each patient to serve as his or her own control.the changes that occurred at 20 min versus baseline and at the end of the procedure versus baseline in plasma F1.2 and FPA were obtained in each group.the primary end points were the differences in these observed changes in F1.2 and FPA in the abciximab group (group II) compared with the control group (group I).A secondary end point was the comparisons of the observed changes in ACT values between the 2 groups at the 10-minute specimen versus baseline. Continuous variables were expressed as mean ± SE and compared with a 2-tail Student t test; categoric variables were compared with Fisher s exact test.the statistical software JMP 3.2 (SAS Institute, Cary, NC) was used for all analyses.with respect to the primary end points, the Bonferroni correction (multiple comparisons) was used and the corrected statistical significance was considered a 2-tailed probability value.04. Other between-group comparisons were considered significant if the 2-tail P value was <.05. Results Of 46 patients transferred for coronary interventions during the study period, 14 were excluded because of acute myocardial infarction (n = 3), restenosis (n = 4), Table III. Prothrombin fragment F1.2 values F1.2 (nmol/l) (n = 11) (n = 21) P value F1.2 at 5 min 0.95 ± ± F1.2 at 20 min 1.06 ± ± 0.26 NS F1.2 at end 1.17 ± ± 0.18 NS F1.2 at 20-5 min 0.11 ± ± F1.2 at end-5 min 0.22 ± ± Time points are after administration of the heparin bolus (time 0). Abciximab was administered in group II immediately after obtaining the 5-minute specimen. Braunwald class I angina (n = 3), or stable angina without a high-risk lesion (n = 4).The remaining 32 patients comprised the entire population: 11 patients in group I (control) 21 patients in group II (abciximab treated). There were no significant differences between the 2 groups of patients regarding clinical or angiographic characteristics (Table II). Groups I and II had similar values in platelet count (236 ± /dl vs 218 ± /dl), hematocrit (38.6% ± 1.2% vs 38.5% ± 0.9%), and international normalized ratio (1.0 ± 0.1 vs 1.1 ± 0.1).Total procedural heparin doses were 8036 ± 561 U in group I versus 4700 ± 406 U in group II (P <.01). The procedural duration was 74 ± 13 minutes in group I compared with 96 ± 9 minutes in group II (P = not significant [NS]). Rotational atherectomy was performed in 4 patients in group I and 12 patients in group II (40% vs 57%, P = NS), and stents were placed in 2 patients in group I and 3 patients in group II (20% vs 14%, P = NS).All other patients were treated with balloon angioplasty.all procedures were successful and all patients were discharged home the day after the intervention without any complications. Thrombin generation and activity Changes in thrombin generation as assessed by the plasma F1.2 levels are shown in Table III.At the 5- minute specimen after heparin bolus (baseline F1.2), there was evidence of significantly higher F1.2 levels in group II versus group I (1.99 ± 0.27 nmol/l vs 0.95 ± 0.38 nmol/l, P =.03). During the procedure, F1.2 levels gradually increased in group I but gradually decreased in group II.The observed changes from baseline were borderline different at 20 minutes into the procedure (P =.08) and significantly different at the end of procedure (decrease of 0.59 ± 0.22 nmol/l in group II vs increase of 0.22 ± 0.3 nmol/l in group I, P =.04). Plasma FPA levels were also somewhat higher in group II compared with group I at the 5-minute specimen after heparin bolus (baseline FPA), but the difference was statistically nonsignificant (Table IV).At subsequent blood specimens, FPA levels decreased gradually in group II, and the observed end of procedure versus baseline change was of borderline significance when

4 52 Dangas et al American Heart Journal July 1999 Table IV. FPA values FPA (ng/ml) (n = 11) (n = 21) P value FPA at 5 min 4.18 ± ± 0.67 NS FPA at 20 min 3.77 ± ± 0.67 NS FPA at end 6.43 ± ± FPA at 20-5 min 0.41 ± ± 0.60 NS FPA at end-5 min 2.25 ± ± Time points are after administration of the heparin bolus (time 0). Abciximab was administered in group II immediately after obtaining the 5-minute specimen. compared with the change observed in group I: a decrease of 1.46 ± 1.16 ng/ml in group II versus an increase of 2.25 ± 1.58 ng/ml in group I (P =.07). ACT values (Table V) were within the target range in both groups in all specimens obtained.act was significantly lower in group II compared with group I at the 5-minute specimen (baseline ACT) and at 20 minutes into the intervention, and there was a trend in the same direction in specimens taken at the end of the procedure.abciximab was administered in group II patients immediately after obtaining the 5-minute specimen (Figure 1); therefore the 10-minute specimen is the first one obtained after the initiation of abciximab administration in group II and before the administration of additional heparin in any patient. In the 10-minute specimens, we observed wide variation in ACT. Overall, an increase was noted in the ACT in group II patients compared with baseline, and this change was of borderline significance compared with the respective change in group I: a 20 ± 13 second increase in group II versus a 13 ± 18 second decrease in group I, P =.1.The observed changes at the 20- minute and the end of procedure specimens compared with baseline were not statistically different between the 2 groups. Discussion The antiplatelet effect of GPIIb/IIIa receptor blockade with abciximab has been previously documented. 14,15 In a recent study, we quantified ex vivo thrombus formation under dynamic flow conditions and demonstrated that abciximab significantly inhibited both platelet thrombus and fibrin deposition on an injured arterial surface compared with heparin and aspirin therapy alone. 17 Cadroy et al 23 have also documented decreased fibrinogen deposition when nonhuman primates were treated with a GPIIb/IIIa receptor antagonist, but Weiss et al 24 have described increased fibrin deposition when the blood of patients with Glanzmann s thrombasthenia (ie, absent GPIIb/IIIa receptor) was passed through a flow chamber.although not entirely consistent, these results suggest that inhibitors of GPIIb/IIIa may exert an antithrombin effect. Table V. ACT values ACT (min) (n = 11) (n = 21) P value ACT at 5 min 384 ± ± 11 <.01 ACT at 10 min 371 ± ± 14 NS ACT at 20 min 374 ± ± ACT at end 364 ± ± ACT at 10-5 min 13 ± ± ACT at 20-5 min 10 ± 15 1 ± 11 NS ACT at end-5 min 20 ± ± 15 NS Time points are after administration of the heparin bolus (time 0). Abciximab was administered in group II immediately after obtaining the 5-minute specimen. In this study, we sought to determine in human beings the in vivo effect of abciximab in thrombin generation and activity by determining the plasma levels of F1.2 and FPA and the ACT values during coronary interventional procedures. Our results indicate that decreased thrombin generation and trends toward decreased thrombin activity and increased ACT values are evident with abciximab.this in vivo report is consistent with prior experimental findings of our group and others. 17,23,24 Effect on thrombin generation and activity The abciximab-treated group had higher levels of F1.2 and FPA at the beginning of the procedure compared with the control group.this finding was rather expected because the study population was not randomly assigned to the treatment offered.abciximab was administered in a relatively higher risk group of patients, including those with severe unstable angina 21 and angiographically high-risk lesions.additionally, more patients in the same group were already receiving heparin therapy before the procedure. In accordance with the clinical expectation, this group demonstrated increased thrombin generation and activity at the initial blood drawing, suggesting greater predisposition to active thrombosis, compared with the control group. Although the prespecified target ACT during the procedure was lower, as was the total heparin dose, there was a significant decrease in thrombin generation and a trend toward decreased thrombin activity in the abciximab group compared with the control group. The mechanism through which abciximab decreases thrombin generation may be caused by the decrease in the total platelet aggregate mass because activated platelets facilitate thrombin generation by providing a surface on which coagulation reactions occur and possibly through other actions.7,16 However, abciximab has been shown to reduce thrombin generation when defibrinated plasma is treated with tissue factor,16 indicating a possible qualitative effect of abciximab on thrombin generation. Group I (control) patients had an increase in thrombin

5 American Heart Journal Volume 138, Number 1, Part 1 Dangas et al 53 generation and activity despite heparin and aspirin therapy.these changes were not statistically significant, implying that there was a mixed response within the group.this finding is consistent with our previous reports that showed increased thrombin generation and activity after procedures compared with before procedures in selected cases treated with various types of coronary interventions. 25,26 The fact that abciximab therapy reduced thrombin generation and activity in a higher risk group (group II) suggests that this agent may inhibit the procedure-related activation of blood coagulation.these effects of abciximab may contribute to the mechanism of action underlying its clinical benefit in decreasing ischemic complications after intervention. Abciximab has also been previously reported to prolong ACT both when administered to patients 27 and when added to heparinized blood in vitro. 28 In our study,we found a mixed response of ACT after abciximab administration. In group II, abciximab treatment prolonged the ACT 5 minutes after the bolus but had little effect on subsequent ACT values. However, the within-group response was mixed at all time points, the post heparin bolus ACT was not a predictor of the 5-minute post abciximab bolus ACT,and an ACT >350 seconds after heparin bolus did not necessarily predict further prolongation after abciximab bolus. Overall the average increase in ACT after abciximab bolus compared with baseline was 20 second, which was smaller than that seen in the EPIC trial, although the latter study did not use each patient as his or her own control. 27 Abciximab has been shown to decrease the rate of postprocedure asymptomatic non-q-wave myocardial infarction (creatine phosphokinase release) A possible mechanism of this complication may be intracoronary thrombosis during the interventional procedure. Decrease of thrombin generation and activity with abciximab may be specifically targeted against this specific mechanism of ischemic complication and may explain this particularly accentuated efficacy of abciximab compared with other GPIIb/IIIa inhibitors in decreasing the incidence of these complications Study limitations In this study, abciximab therapy was directed by the physician to patients who were considered to be at higher risk for ischemic complications than the control group.the fact that patients were not randomly assigned likely resulted in the inclusion of higher risk cases in group II.This potentiality could mask an existing effect of abciximab or decrease the magnitude of a possible antithrombin effect of abciximab.the fact that group II had higher thrombin generation and activity at baseline is consistent with previous studies demonstrating increased thrombin generation with more complex lesion morphologic characteristics. 25,26 Although various types of interventional procedures were performed, their distribution between the 2 groups was similar, and patients receiving stents were given the first dose of ticlopidine after the end of the procedure. Although procedure duration was not different between the 2 groups, it was somewhat longer in the abciximab group.this may be an indicator of more technically difficult interventions, which may indicate that these patients had more reasons for increased thrombotic action. In contrast, thrombin generation and activity were shown to decrease steadily along the procedure in this group, whereas they increased in the control group despite the shorter duration of the procedure. On the other hand, the normal range of FPA and F1.2 levels has not been well defined, and it is possible that their variability might have affected our findings. However, both groups had baseline FPA and F1.2 levels higher than those observed previously by us in stable angina. 25,26 The efficacy of antithrombotic medications may differ in static compared with dynamic flow conditions.the peptides measured in this study were withdrawn from the coronary ostium, proximal to the lesion, and therefore represent systemic levels, which may differ from those existing at the lesion site. However, because the evaluated antithrombotic regimen was administered systemically, the importance of this potential error may be small. Finally, to minimize the variability in the laboratory assays, we had the same investigator perform all the studies in a blinded fashion after completion of the study, and individual patient specimens were run on the same plate. Conclusion Our data suggest that treatment with the platelet GPIIb/IIIa inhibitor abciximab reduces thrombin generation during coronary interventions and provides an additional mechanism through which GPIIb/IIIa inhibition, and abciximab in particular, produce the clinically beneficial effects observed in coronary interventional trials. 10 The antiplatelet and antithrombin effects of abciximab may contribute to the mechanism of action underlying its clinical benefit in decreasing ischemic complications after interventions. References 1. Fernandez-Ortiz A, Badimon JJ, Falk E, Fuster V, Meyer B, Mailhac A, et al. Characterization of the relative thrombogenicity of atherosclerotic plaque components: implications for consequences of plaque rupture. J Am Coll Cardiol 1994;23: Marmur JD, Thiruvikraman SV, Fyfe BS, Guha A, Sharma SK, Ambrose JA, et al. Identification of active tissue factor in human coronary atheroma. Circulation 1996;94: Kirchhofer D, Tschopp B, Steiner B, Baumgartner HR. Role of collagen-adherent platelets in mediating fibrin formation in flowing whole blood. Blood 1995;86: Kumar R, Beguin S, Hemker HC. The influence of fibrinogen and fibrin on thrombin generation. Evidence for feedback activation of the clotting system by clot bound thrombin. Thromb Haemost 1994;72:

6 54 Dangas et al American Heart Journal July Toschi V, Gallo R, Lettino M, Fallon JT, Gertz SD, Fernandez-Ortiz A, et al. Tissue factor modulates the thrombogenicity of human atherosclerotic plaques. Circulation 1997;95: Dangas G, Fuster V. Management of restenosis after coronary intervention. Am Heart J 1996;132: Coller BS, Anderson K, Weisman HF. New antiplatelet agents: platelet GP IIb/IIIa antagonists. Thromb Haemost 1995;74: EPIC investigators. Use of a monoclonal antibody directed against the platelet glycoprotein IIb/IIIa receptor in a high risk coronary angioplasty. N Engl J Med 1994;330: The EPILOG investigators. Platelet glycoprotein IIb/IIIa receptor blockade and low-dose heparin during percutaneous coronary revascularization. N Engl J Med 1997;336: The CAPTURE investigators. Randomized placebo-controlled trial of abciximab before and during coronary intervention in refractory unstable angina: the CAPTURE study. Lancet 1997;349: The RESTORE Investigators. Effects of platelet glycoprotein IIb/IIIa blockade with tirofiban on adverse cardiac events in patients with unstable angina or acute myocardial infarction undergoing coronary angioplasty. Circulation 1997;96: The IMPACT II Investigators. Randomized placebo-controlled trial of effect of eptifibatide on complication of percutaneous coronary intervention: IMPACT II. Lancet 1997;349: Coller BS. A new murine monoclonal antibody reports and activation-dependent change in the conformation and/or microenvironment of the platelet glycoprotein IIb/IIIa complex. J Clin Invest 1985;76: Konstantopoulos K, Kamat SG, Schafer AI, Banez EI, Jordon R, Kleiman NS, et al. Shear-induced platelet aggregation is inhibited by in vivo infusion of an anti-glycoprotein IIb/IIIa antibody fragment, abciximab, in patients undergoing coronary angioplasty. Circulation 1995;91: Turner NA, Moake JL, Kamat SG, Schafer AI, Kleiman NS, Jordan R, et al. Comparative real-time effects on platelet adhesion and aggregation under flowing conditions of in vivo aspirin, heparin, and monoclonal antibody fragment against glycoprotein IIb/IIIa. Circulation 1995;91: Reverter JC, Beguin S, Kessels H, Kumar R, Coller BS. Inhibition of platelet-mediated, tissue factor-induced thrombin generation by the mouse/human chimeric 7E3 antibody. Potential implications for the effects of abciximab treatment on acute thrombosis and clinical restenosis. J Clin Invest 1996;98: Dangas G, Badimon JJ, Coller BS, Fallon JT, Sharma SK, Hayes RM, et al. Administration of abciximab during percutaneous coronary intervention reduces both ex vivo platelet thrombus formation and fibrin deposition: implications for a potential anticoagulant effect of abciximab. Arterioscl Thromb Vasc Biol 1998; 18: Teitel JM, Bauer KA, Lau HK, Rosenberg RD. Studies of the prothrombin activation pathway using radio-immunoassays for the F2/F1+2 fragment and thrombin-anitithrombin complex. Blood 1982;59: Nossel HL, Ti M, Kaplan KL, Spanondis K, Soland T, Butler VP Jr. The generation of fibrinopeptide A in clinical blood samples. Evidence for thrombin activity. J Clin Invest 1976;58: Braunwald E. Unstable angina: a classification. Circulation 1989; 80: Dangas G, Mehran R, Wallenstein S, Courcoutsakis NA, Kakarala V, Hollywood J, et al. Correlation between angiographic morphology and clinical presentation in unstable angina. J Am Coll Cardiol 1997;29: Ryan TJ, Faxon DP, Gunnar RM. Guidelines for percutaneous transluminal coronary angioplasty: A report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures (Subcommittee on Percutaneous Transluminal Coronary Angioplasty). J Am Coll Cardiol 1988;12: Cadroy Y, Hanson SR, Andrew BK, Marzec UM, Evatt BL, Kunicki TJ, et al. Relative antithrombotic effects of monoclonal antibodies treating different platelet glycoprotein-adhesive molecule interactions in nonhuman primates. Blood 1994;83: Weiss HJ, Turitto VT, Baumgartner HR. Role of shear rate and platelets in promoting fibrin formation on rabbit subendothelium. Studies utilizing patients with quantitative and qualitative platelet defects. J Clin Invest 1986;78: Marmur JD, Merlini PA, Sharma SK, Khaghan N, Torre SR, Israel DH, et al. Thrombin generation in human coronary arteries after percutaneous transluminal balloon angioplasty. J Am Coll Cardiol 1994;24: Marmur JD, Sharma SK, Weinrauch M, Kantrowitz N, Dangas G, Kokkinakis S, et al. Thrombin generation and activity during coronary angioplasty: influence of angiographic lesion morphology. J Invas Cardiol 1997;9: Moliterno DJ, Califf RM, Aguirre FV, Anderson K, Sigmon KN, Weisman HF, et al for the EPIC study investigators. Effect of platelet glycoprotein IIb/IIIa integrin blockade on activated clotting time during percutaneous transluminal coronary angioplasty or directional atherectomy. Am J Cardiol 1995;75: Ammar T, Scudder LE, Coller BS. In vitro effects of the platelet glycoprotein IIb/IIIa receptor antagonist abciximab on the activated clotting time. Circulation 1997;95:614-7.