Monitoring of fibrin generation during thrombolytic therapy of acute myocardial infarction with recombinant tissue-type plasminogen activator

Management of adjunctive antithrombotic therapy in STEMI patients treated with fibrinolysis undergoing rescue or delayed PCI

Although primary percutaneous coronary intervention (PCI) is the recommended method of reperfusion in patients presenting with ST-segment elevation myocardial infarction (STEMI), fibrinolysis remains a beneficial alternative in patients who cannot be reperfused timely with primary PCI, and is still the preferred revascularisation strategy in many parts of the world where PCI facilities are unavailable. Because fibrinolysis is known to activate platelets and promote thrombin activity, concomitant administration of antiplatelet and anticoagulant therapies is needed to lower the risk for re-occlusion and to support mechanical interventions in patients undergoing rescue or delayed PCI. However, the addition of oral antiplatelet and parenteral anticoagulant drugs on top of fibrinolysis may come at the price of an increased risk of bleeding. The current availability of several antiplatelet and anticoagulant therapies often leads to questions about the optimal selection in STEMI patients treated with fibrinolytics. This article appraises current evidences for the management of adjunctive antiplatelet and anticoagulant therapies in patients with STEMI undergoing fibrinolysis followed by rescue or delayed PCI.

Plasmin-induced procoagulant effects in the blood coagulation: a crucial role of coagulation factors V and VIII

Plasminogen activators provide effective treatment for patients with acute myocardial infarction. However, paradoxical elevation of thrombin activity associated with failure of clot lysis and recurrent thrombosis has been reported. Generation of thrombin in these circumstances appears to be owing to plasmin (Plm)-induced activation of factor (F) XII. Plm catalyzes proteolysis of several coagulant factors, but the roles of these factors on Plm-mediated procoagulant activity remain to be determined. Recently developed global coagulation assays were used in this investigation. Rotational thromboelastometry using whole blood, clot waveform analysis and thrombin generation tests using plasma, showed that Plm (> or =125 nmol/l) shortened the clotting times in similar dose-dependent manners. In particular, the thrombin generation test, which was unaffected by products of fibrinolysis, revealed the enhanced coagulation with an approximately two-fold increase of peak level of thrombin generation. Studies using alpha2-antiplasmin-deficient plasma revealed that much lower dose of Plm (> or =16 nmol/l) actually contributed to enhancing thrombin generation. The shortening of clotting time could be observed even in the presence of corn trypsin inhibitor, supporting that Plm exerted the procoagulant activity independently of FXII. In addition, using specific coagulation-deficient plasmas, the clot waveform analysis showed that Plm did not shorten the clotting time in only FV-deficient or FVIII-deficient plasma in prothrombin time-based or activated partial thromboplastin time-based assay, respectively. Our results indicated that Plm did possess procoagulant activity in the blood coagulation, and this effect was likely attributed by multicoagulation factors, dependent on FV and/or FVIII.

Is heparin still necessary after primary angioplasty in the era of platelet glycoprotein IIb/IIIa receptor inhibitors? A review of the literature

While there is clear evidence for administering unfractionated heparin after systemic thrombolysis, there are not randomised trials supporting the usefulness of postprocedural heparin in the setting of primary angioplasty, especially in the era of glycoprotein IIb/IIIa inhibitors, and this issue is still a matter of debate. In this review we analysed the 30-day cardiac events of patients treated with primary angioplasty and abciximab, with or without postprocedural unfractionated heparin. We conducted a Medline search and eight studies were selected: in four of them heparin was continued for at least 12 h after the procedure (group 1), in the others heparin was used only during the procedure (group 2). The composite incidence of 30-day major adverse cardiac events was similar in the two groups (5.1 vs. 5.1%; 95% confidence interval 0.66-1.45; P = 0.91), whereas total bleeding occurred in 5.5% of group 1 compared with 3% of group 2 (relative risk 1.82; 95% confidence interval 1.19-2.80; P = 0.005). In conclusion, this review suggests that in the setting of primary angioplasty with concomitant glycoprotein IIb/IIIa inhibitors, postprocedural heparin does not appear to favourably affect cardiac and systemic ischaemic events and turns out to be associated with an increase in haemorrhagic complications.

Factor XII-dependent increases in thrombin activity induce carboxypeptidase-mediated attenuation of pharmacological fibrinolysis

Activation of the contact system in patients treated with fibrinolytic agents may be an important source of thrombin that activates thrombin-activated fibrinolysis inhibitor (TAFI) and attenuates fibrinolysis. Factor (F)XIIa in plasma increased 2-fold over 60 min in patients given either tissue plasminogen activator (t-PA) or streptokinase (SK). To determine whether FXIIa-mediated generation of thrombin and activated TAFI (TAFIa) attenuates fibrinolysis in vitro, plasma clots were incubated with SK (250 U mL-1) or t-PA (2.5 g mL-1) and the rate of lysis was measured. Plasma FXIIa impaired lysis judging from marked acceleration when 2.5 micro m corn trypsin inhibitor were added (lysis increased by 172 +/- 144% for SK and 40 +/- 31% for t-PA vs. no inhibitor, n = 16, P < 0.01). Moreover, inhibition of thrombin with hirudin and TAFIa with carboxypeptidase inhibitor accelerated lysis. We conclude that activation of FXII increases thrombin generation, which promotes TAFIa-mediated attenuation of fibrinolysis.

Antithrombotic properties of a direct thrombin inhibitor with a prolonged half-life and AT-mediated factor Xa inhibitory activity

Rebound thrombin generation after successful thrombolysis might be related to (i) too short-term anticoagulant therapy and to (ii) the inability of heparin derivatives to inhibit clot-bound thrombin. To meet these shortcomings, a compound was synthesized, which consists of a pentasaccharide conjugated to a direct thrombin inhibitor. This compound (Org 42675) has a 10 times longer half-life compared with the original half-life of the direct thrombin inhibitor, while the thrombin inhibitory activity is maintained. An extra advantage of this product is the inhibitory activity on thrombin generation via antithrombin III (AT)-mediated factor (F)Xa inhibition. Org 42675 inhibited in vitro clot-bound thrombin with similar activity to the direct thrombin inhibitor argatroban. In experimental models in rats, Org 42675 showed on a molar base similar antithrombotic activity to unfractionated heparin, was more active than argatroban and was more active than fondaparinux sodium (AT-mediated FXa inhibitor) in arterial thrombosis. Finally, Org 42675 was far more active than the three reference compounds in an experimental thrombolysis model in rabbits. These properties of Org 42675, with its FXa and (clot-bound) thrombin inhibitory activity in combination with its long half-life, make this compound a powerful drug that is likely to be effective in the prevention of re-occlusion after successful thrombolysis in man.

Thrombin generation and fibrinolytic activities among patients receiving reduced-dose alteplase plus abciximab or undergoing direct angioplasty plus abciximab for acute myocardial infarction

The purpose of this study was to determine the impact of these 2 reperfusion strategies (reduced-dose alteplase plus abciximab or direct angioplasty plus abciximab) on fibrinolytic and thrombin generation activities. The effect of reduced-dose alteplase plus abciximab and direct angioplasty plus abciximab on hemostatic factors is unknown. Of 70 patients with acute myocardial infarction of < or = 6 hours, 34 were randomized to reduced-dose alteplase (35 to 50 mg in 1 hour) and 36 to direct angioplasty. A standard bolus and infusion dose of abciximab was administered to all patients. Blood specimens were collected at baseline, and at 1, 4, 12, and 24 hours. The following parameters were assayed: fibrinogen, plasminogen and antiplasmin activities, tissue plasminogen activator antigen, D-dimer, prothrombin fragments F1 + 2, and thrombin/antithrombin III complexes. Among patients treated with reduced-dose alteplase plus abciximab, the fibrinogen level decreased by 28.4% in the first hour (11.7 +/- 3.4 vs 7.8 +/- 2.5 micromol/L, p <0.001). Correspondingly, plasminogen and antiplasmin activities decreased by 43.8% (p <0.001) and 59.1% (p <0.001), respectively. Prothrombin fragments F1 + 2 increased from 2.2 +/- 1.7 to 4.2 +/- 1.6 nmol/L (1 hour) (p <0.001) and thrombin/antithrombin III increased from 16.3 +/- 15.0 to 33.5 +/- 19.9 microg/L (1 hour) (p <0.001). Conversely, in the direct angioplasty group, there was a marginal elevation in fibrinogen level at 1 hour (10.2 +/- 2.4 vs 10.6 +/- 2.0 micromol/L, p = 0.064) despite a significant reduction in plasminogen and an increase in tissue plasminogen activator levels. There was no significant change in prothrombin fragments F1 + 2 and thrombin/antithrombin III levels. Thus, there was considerable fibrinolytic activity with reduced-dose alteplase plus abciximab; thrombin generation was not prevented. Among patients treated with direct angioplasty, there was some endogenous fibrinolytic activity, but there was no significant thrombin generation.

The thrombolytic paradox

Thrombolytic drugs do not only stimulate the plasmin system but also induce thrombin activation additionally to the preexisting hypercoagulative state in patients with acute myocardial infarction. Testing the in vitro-derived hypothesis of a plasmin-mediated activation of the contact phase of the coagulation leading to the procoagulant effect, several thrombolytic regimen have been evaluated. Paradoxical thrombin activation (referred to as "thrombolytic paradox") was related to absence of fibrin specificity. Highly fibrin-specific drugs like tenecteplase did not cause additional thrombin activation, while non-fibrin-specific drugs like streptokinase caused a marked additional activation of the contact phase and of thrombin. It could be shown that the thrombolytic paradox was related to the extent of systemic plasmin activation confirming the hypothesis of a plasmin-mediated factor XII/kallikrein system activation as cause of the thrombolytic paradox.

Fibrin specificity and procoagulant effect related to the kallikrein-contact phase system and to plasmin generation with double-bolus reteplase and front-loaded alteplase thrombolysis in acute myocardial infarction

This study was undertaken to compare the effects of reteplase and alteplase regimens on hemostasis and fibrinolysis in acute myocardial infarction (AMI). Thrombolytic treatment in patients with AMI is hampered by paradoxical procoagulant effects that favor early reocclusion. In vivo data comparing this effect and the fibrin specificity of double-bolus reteplase and front-loaded alteplase regimens are not available. In a prospective, randomized study, 50 patients with AMI were either treated with double bolus (10 + 10 U) reteplase or with front-loaded alteplase (up to 100 mg) within 6 hours of symptom onset. Thirty apparently healthy persons served as controls. Molecular markers of coagulation and fibrinolysis were serially examined for up to 5 days. Paradoxical thrombin activation at 3 hours after initiation of therapy was comparable between reteplase and alteplase. Reteplase (65 +/- 5 U/L) and alteplase (72 +/- 8 U/L) caused significantly elevated kallikrein activity at 3 hours after adminstration (p <0.01 vs controls 30 +/- 1 U/L). Fibrin specificity was less for reteplase (p <0.05) with a decrease in fibrinogen at 3 hours to 122 +/- 27 mg/dl versus 224 +/- 28 mg/dl for alteplase (p <0.01 and p <0.05 vs controls). D-Dimer levels at 3 hours were higher (p <0.05) after reteplase (5,459 +/- 611 ng/ml) versus alteplase (3,445 +/- 679 ng/ml) (both p <0.01 vs controls 243 +/- 17 ng/ml). Plasmin generation (plasmin-antiplasmin complexes) was significantly (p <0.01) increased at 3 hours with both regimens to 27,079 +/- 3,964 microg/L (reteplase) and 19,522 +/- 2,381 microg/L (alteplase). The data from 3 hours after start of thrombolytic therapy proved less marked fibrin specificity of the reteplase regimen (in vivo) compared with front-loaded alteplase. Both regimens have a moderate procoagulant effect without differences in activation of the kallikrein system.

Issues Regarding the Use of Heparin Following Streptokinase Therapy

The success of thrombolytic therapy is dependent upon the balance of fibrinolytic activity and procoagulant activity. Streptokinase produces fibrin degradation products that have anticoagulant effects and may potentially protect against reocclusion. However, streptokinase also activates platelets and thrombin, and the prothrombotic effects may be more marked than after administration of recombinant tissue plasminogen activator (rt-PA). Administration of high-dose, delayed subcutaneous heparin after streptokinase and aspirin has been shown to have some benefits and some risks. The benefits and risks of adding intravenous heparin to aspirin and streptokinase have not been clearly defined.

Novel Antithrombotic Strategies for the Treatment of Coronary Artery Thrombosis: A Critical Appraisal

Large-scale clinical trials have demonstrated that treatment of patients with acute myocardial infarction and unstable angina with antithrombotic agents significantly improves outcome. Despite the proven benefit of current therapies, there is a widespread perception that outcome could be enhanced further with novel antithrombotic agents. Enthusiasm for novel antithrombotic strategies has been stimulated by recent advances in the understanding of the mechanisms responsible for coronary artery thrombosis, which has led to the development of diverse inhibitors of platelet function and coagulation factors. In experimental models of coronary artery thrombosis, aspirin and heparin have been ineffective in preventing recurrent thrombosis after coronary thrombolysis and in preventing the progression of thrombosis in response to strong thrombogenic stimuli. In contrast, inhibitors of the platelet fibrinogen receptor, direct-acting thrombin inhibitors, and inhibitors of coagulation factors that promote elaboration of thrombin have been shown to be effective in attenuating arterial thrombosis in a variety of experimental preparations. Initial clinical trials with these agents have also documented efficacy in attenuating thrombotic events in patients treated with coronary thrombolysis and in those with unstable angina. However, optimal doses of novel antithrombotic agents, the degree to which combination antiplatelet and anticoagulant therapies are needed, and the risk/benefit ratio associated with specific novel antithrombotic drugs are still relatively undefined. With regard to the latter, it is possible that the large-scale clinical trials now in progress may show an increase in bleeding complications with novel anticoagulants compared with conventional therapy. Nonetheless, there are considerable data that suggest that treatment with aspirin and heparin is not completely effective in preventing the progression of thrombosis or its recurrence after interventions in high-risk subgroups of patients with coronary artery thrombosis and unstable coronary artery disease. Accordingly, continued investigation of a large variety of antithrombotic agents, both currently available and in development, should improve the treatment of high-risk patients with coronary disease if regimens with appropriate efficacy but without serious hemorrhagic effects can be designed.

Achieving Optimal Reperfusion without Adjunctive Antithrombotic Therapy: Novel Thrombolytic Dosing Strategies

There is firm evidence that reperfusion therapy, to be effective must establish and maintain coronary arterial blood flow at a level sufficient to allow myocardial perfusion. However, current thrombolytic regimens have clear limitations, including a relatively low capacity to achieve TIMI Grade 3 blood flow and an unacceptable incidence of coronary reocclusion. Although it has been assumed that the key to achieving optimal reperfusion lies with adjunctive antithrombotic therapy, it may be that novel thrombolytics and dosing strategies can address the problem adequately. This possibility is attractive and requires careful consideration.

Activation of coagulation factor VII by tissue-type plasminogen activator

To investigate the effect of tissue-type plasminogen activator (t-PA) on blood coagulation, we examined the effects of the addition of t-PA to normal pool plasma (NPP) on clotting times such as diluted prothrombin time (PT) and kaolin clotting time (KCT). The diluted PT but not the KCT was significantly shortened by the addition of t-PA to NPP compared with the normal controls, suggesting a t-PA-induced activation of blood coagulation through factor VII (FVII) activation. The activated factor VII (FVIIa) concentration in the NPP was significantly increased by the addition of t-PA. Although the FVIIa formation was not observed following the incubation of purified FVII with only t-PA or plasminogen, an increase in the FVIIa level was observed after the incubation of purified FVII with t-PA together with plasminogen, or only plasmin. This plasmin-mediated FVIIa formation was also confirmed by Western blotting. These findings suggest that t-PA enhances the activation of the coagulation system through FVII activation.

Tetranectin levels in patients with acute myocardial infarction and their alterations during thrombolytic treatment

Tetranectin (TN), a new regulator of fibrinolysis, was studied in the plasma of 60 patients with acute myocardial infarction (AMI) and 30 healthy subjects (HS), in relation to D-dimer (DD) and alpha 2-plasmin inhibitor (alpha 2-PI), to investigate its possible involvement in the pathophysiology of AMI. Thirty patients underwent thrombolytic treatment with fibrin-specific plasminogen activator (rt-PA) (group A); the other 30 patients, according to the exclusion criteria, were conventionally treated (group B). Twenty of the thrombolysized patients established early recanalization (subgroup A1), while 10 failed to respond to thrombolytic treatment (subgroup A2). Median (interquartile range), baseline plasma TN levels were lower in AMI patients compared to HS [8.27 (2.75) mg/L versus 12.1 (0.55) mg/L, P < 10(-6)]. In subgroup A1, TN increased at the end of rt-PA infusion and returned to the baseline levels 12 h later. A positive association between DD and TN release (3 h level minus baseline level) was found (rs = 0.48, P = 0.03) in subgroup A1. No significant alterations of TN levels were observed during therapy in subgroup A2 and group B. TN, DD and alpha 2-PI concentrations in group B remained relatively constant during the study period. This study provides evidence of a significant decrease of TN levels in AMI patients compared to healthy subjects and of a remarkable difference in the evolution of TN levels during thrombolytic treatment with rt-PA between recanalized and non-recanalized AMI patients. Thus, an involvement of TN in the formation and dissolution of fibrin clot in AMI patients is worthy of further investigation.

Thrombin generation, inhibition and clinical outcomes in patients with acute myocardial infarction treated with thrombolytic therapy and heparin: results from the GUSTO-I Trial. GUSTO-I Hemostasis Substudy Group. Global Utilization of Streptokinase and TPA for Occluded Coronary Arteries

OBJECTIVES

We sought to assess the effects of antithrombotic therapy after thrombolysis for acute myocardial infarction on markers of thrombin generation and activity and to determine the relation of these markers with clinical outcomes.

BACKGROUND

Thrombin activation and generation often occur with thrombolysis for acute myocardial infarction. Antithrombotic regimens have been developed to reduce the resulting thrombotic complications.

METHODS

We sampled plasma markers of thrombin generation and activity after thrombolysis in 292 patients. We assessed the relations of these markers with clinical outcomes at 30 days.

RESULTS

Fibrinopeptide A (FPA), a marker of thrombin activity toward fibrinogen, was elevated at baseline (12.3 ng/ml) and increased to 18.4 ng/ml by 90 min after streptokinase and subcutaneous heparin treatment. With intravenous heparin, this increase was attenuated, but intravenous heparin did not prevent thrombin generation, as measured by prothrombin fragment 1.2 (F1.2). Heparin level, measured by anti-Xa activity, correlated with activated partial thromboplastin time (aPTT, r = 0.62 to 0.67). Thrombin activity, measured by FPA, was as closely related to aPTT as to the heparin level. Baseline levels of F1.2 were significantly related to the risk of death or reinfarction at 30 days (p = 0.008); values 12 h after enrollment also were related to 30-day mortality (p = 0.05).

CONCLUSIONS

Although intravenous heparin partly suppresses the increased thrombin activity associated with thrombolysis, it does not inhibit thrombin generation. The aPTT was as good a measure of suppression of thrombin activity as the heparin level itself. Hematologic markers of thrombin generation were found to be related to the subsequent risk of thrombotic events.

Exaggerated luminal loss a few minutes after successful percutaneous transluminal coronary angioplasty in patients with recent myocardial infarction compared with stable angina: an intracoronary ultrasound study

This study investigates the mechanisms of exaggerated acute luminal loss after successful coronary angioplasty in patients with recent myocardial infarction compared with stable angina by angiography and intracoronary ultrasound (ICUS). We studied 15 consecutive patients (group 1) who, after a successful thrombolysis for myocardial infarction, underwent delayed (8 +/- 2 days after the myocardial infarction) successful balloon coronary angioplasty. Group 1 patients were individually matched with 15 stable angina patients (group 2). The percentage of stenosis and acute luminal loss were measured by quantitative coronary analysis. The ultrasound characteristics of lumen pathology were described as soft, hard, calcified, eccentric, concentric, thrombotic, and dissection lesions. Matching by stenosis location, reference diameter, sex, and age resulted in 2 comparable groups of 15 lesions with identical baseline characteristics. Immediately after percutaneous transluminal coronary angioplasty (PTCA), the minimal luminal diameter increased from 0.5 +/- 0.3 mm to 2.4 +/- 0.3 mm and from 0.5 +/- 0.2 mm to 2.4 +/- 0.3 mm in groups 1 and 2, respectively. Similar balloon sizes were used in both groups. The acute luminal loss (the difference between the maximal dilated balloon diameter and the minimal luminal diameter) immediately after PTCA was 0.4 +/- 0.2 mm and 0.3 +/- 0.3 mm (14 +/- 8% and 10 +/- 11% of balloon size) (P = not significant [NS]) in groups 1 and 2, respectively. After ICUS (mean 24 min after the last balloon deflation), the acute luminal loss was 0.9 +/- 0.3 mm and 0.5 +/- 0.4 mm (29 +/- 11% and 17 +/- 8% of balloon size) (P = 0.01) in groups 1 and 2, respectively. There was a significantly higher prevalence of intracoronary thrombus formation as detected by ICUS in group 1 compared with group 2 (80% vs. 20%; P < 0.001). In matched groups of successfully treated coronary angioplasty, patients with recent myocardial infarction had a similar magnitude of acute gained luminal loss immediately after the procedure. However, an exaggerated luminal loss a few minutes after the last balloon deflation in patients with recent myocardial infarction was noted because of mural thrombus formation compared with patients with stable angina.

TIMI grade 3 flow and reocclusion after intravenous thrombolytic therapy: a pooled analysis

Early and sustained flow of grade 3 according to Thrombolysis in Myocardial infarction (TIMI) criteria and reocclusion rates are the key measures that define the physiologic efficacy of thrombolytic agents in the treatment of acute myocardial infarction. We performed a systematic overview of angiographic studies after intravenous thrombolysis with accelerated and standard-dose tissue-plasminogen activator (TPA), anisoylated plasminogen streptokinase activator complex (APSAC), and streptokinase. There were 5475 angiographic observations from 15 studies for TIMI flow analysis and 3147 angiographic observations from 27 studies for reocclusion. At 60 and 90 minutes, the rates of TIMI grade 3 flow were 57.1% and 63.2%, respectively, with accelerated TPA, 39.5% and 50.2% with standard-dose TPA, 40.2% and 50.1% with APSAC, and 31.5% at 90 minutes with streptokinase. Overall reocclusion with standard-dose TPA was 11.8% versus 6.0% for accelerated TPA, 4.2% for streptokinase, and 3.0% for APSAC. Although the incidence of TIMI grade 3 flow increased over time with all thrombolytic regimens, decreased patency was observed at 180 minutes with accelerated TPA. Still, accelerated TPA is the most effective agent to establish early (90-minute) TIMI grade 3 flow.

Usefulness of fibrinogenolytic and procoagulant markers during thrombolytic therapy in predicting clinical outcomes in acute myocardial infarction. TIMI-5 Investigators. Thrombolysis in Myocardial Infarction

Thrombin activity is increased in the setting of acute myocardial infarction (AMI) and has been shown to increase further after the administration of thrombolytic therapy for acute infarction. This increase in thrombin activity may play an important role in the 15% to 25% rate of failure to achieve initial reperfusion and in the 5% to 15% rate of early reocclusion after initially successful thrombolysis. To investigate potential mechanisms of thrombin formation in vivo, to understand better the balance of coagulation and fibrinolysis during treatment with recombinant tissue-type plasminogen activator (rt-PA), and to investigate the role of hemostatic markers as predictors of clinical events, we measured 3 markers of procoagulant activity: fibrinopeptide A (FPA), thrombin-antithrombin III complexes (TAT), and prothrombin fragment 1.2 (F1.2), and a marker of fibrinogenolytic activity (B beta 1-42) in patients enrolled in the Thrombolysis in Myocardial Infarction (TIMI)-5 study. This trial was a randomized, dose-ranging, pilot trial of hirudin versus heparin as adjunctive antithrombotic therapy with rt-PA administered to patients with AMI. Correlation of markers at 1 hour with clinical outcomes revealed that increased FPA and TAT levels were associated with increased mortality and TIMI grades 0, 1, or 2 flow at 90 minutes; increased F1.2 levels were associated with TIMI grade 0 or 1 flow at 90 minutes; and increased levels of all 3 procoagulant markers were associated with hemorrhagic events. Late (12 to 24 hours) increases in F1.2, TAT, and B beta 1-42 may be predictive of recurrent ischemia. These results suggest that selected markers of procoagulant and fibrinogenolytic activity may be useful in predicting clinical outcomes in patients treated with thrombolytic therapy for AMI.

Antiplatelet and anticoagulant use after myocardial infarction

Coronary thrombosis leading to myocardial infarction is a complex process involving the interaction of the arterial wall, the coagulation cascade, and platelets. Increased understanding of the molecular biology of thrombosis has prompted an evolution in antithrombotic therapy, from the early use of warfarin following myocardial infarction to agents targeting specific receptors or modulators in the thrombotic process. The complexity of thrombosis allows for numerous sites of pharmacologic intervention; the multiple pathways leading to platelet aggregation and thrombin formation provide the opportunity for combined therapies. This review presents the current clinical data on antiplatelet, anticoagulant, and specific antithrombin therapies following myocardial infarction.

Lesion-directed administration of alteplase with intracoronary heparin in patients with unstable angina and coronary thrombus undergoing angioplasty

Percutaneous coronary revascularization in patients with unstable angina and coronary thrombus carries a high complication rate. A new strategy to reduce thrombus burden before revascularization was tested in a multicenter prospective trial. Patients with unstable angina and coronary thrombus (n = 45) received alteplase through an infusion catheter at the proximal aspect of the target lesion and concomitant intracoronary heparin via a standard guiding catheter. Angiography was performed before and alter lesion-directed therapy and post-intervention. Systemic fibrinogen depletion and thrombin activation were not observed, while fibrinolysis was evident for > or = 4 hr after treatment. Target lesion stenosis did not change significantly after lesion-directed therapy, but thrombus score was reduced, particularly among patients who had large thrombi (mean 2.2 vs. 1.6, P = 0.02). Revascularization was successful in 89% of patients. Median final stenosis was 30% and mean final thrombus score was 0.4. Complications included recurrent ischemia (11%), MI (7%), abrupt closure (7%), severe bleeding (4%), and repeat emergency angioplasty (2%). Patients with overt thrombus appeared to derive the most angiographic benefit from lesion-directed alteplase plus intracoronary heparin. Later revascularization was highly successful. This strategy may be a useful adjunct to percutaneous revascularization for patients with unstable angina and frank intracoronary thrombus.

Reocclusion: the flip side of coronary thrombolysis

Since the introduction of thrombolytic therapy for acute myocardial infarction, the incidence of coronary artery reocclusion has been intensively studied. Also, the prediction and diagnosis of reocclusion by angiographic and clinical variables, as well its invasive and pharmacologic prevention, have gained much attention. By angiographic definition, reocclusion requires three angiographic observations: one with an occluded artery, one with a reperfused artery and a third for the assessment of subsequent occlusion (true reocclusion). Since the introduction of early intravenous reperfusion therapy, most studies use only two angiograms: one with a patent and one with a nonpatent infarct-related artery. A search for all published reocclusion studies revealed 61 studies (6,061 patients) with at least two angiograms. The median time interval between the first angiogram after thrombolysis and the second was 16 days (range 0.1 to 365). Reocclusion was observed in 666 (11%) of 6,061 cases. Interestingly, the 28 true reocclusion studies showed an incidence of reocclusion of 16 +/- 10% (mean +/- SD), and the 33 studies with only two angiograms 10 +/- 8% (p=0.04), suggesting that proven initial occlusion of the infarct-related artery is a risk factor for reocclusion after successful thrombolysis. The other predictors for reocclusion are probably severity of residual stenosis of the infarct-related artery after thrombolysis and perhaps the flow state after lysis. Reocclusion is most frequently seen in the early weeks after thrombolysis. The clinical course in patients with reocclusion is more complicated than in those without this complication. Left ventricular contractile recovery after thrombolysis is hampered by reocclusion. Routine invasive strategies have not been proven effective against reocclusion. In the prevention of reocclusion, both antiplatelet and antithrombin strategies have been tested, including hirudin and hirulog, but the safety of these agents in thrombolysis is still questionable. Thus, reocclusion after thrombolysis is an early phenomenon and is more frequent after proven initial occlusion of the infarct-related artery. Reocclusion can be predicted by angiography after thrombolysis. Because reocclusion is detrimental, strategies to prevent it should be developed and carried out after thrombolytic therapy for acute myocardial infarction as soon as they are deemed safe.

Relationship between intracoronary thrombolysis and fibrino-coagulation--special reference to TAT/PIC and FPA/PIC

To clarify the relationship between the results of intracoronary thrombolytic therapy (ICT) and fibrino-coagulation in patients with acute myocardial infarction (AMI), the thrombin-antithrombin III complex (TAT) and fibrinopeptide A (FPA), as indices of accelerated coagulation, and the plasmin- alpha 2-plasmin inhibitor complex (PIC), as an index of accelerated fibrinolysis in peripheral blood, were measured just before and after heparin injection (5,000 U), and immediately after ICT. Twenty-four patients with AMI were divided into 2 groups according to the results of ICT; successful ICT (group S) and unsuccessful ICT (group F). As a control group (group C), 14 age-matched normal volunteers were also studied. The levels of TAT and FPA before ICT were significantly higher in groups S and F than in group C (p < 0.01). The TAT level before ICT in group F was higher than that in group S (p = 0.07), however, the TAT, FPA and PIC levels showed no significant differences between groups S and F at each sampling time. TAT/PIC before ICT was significantly higher in group F than in group S (F: 0.026 +/- 0.020 vs S: 0.008 +/- 0.004, p < 0.05), whereas there was no remarkable difference in FPA/PIC between groups S and F. These results indicate that hyper-coagulation had occurred in the AMI cases and that coagulation had been more accelerated in group F. TAT/PIC might be an index of the equilibrium of the fibrino-coagulating system. Therefore, TAT/PIC measurement before thrombolytic therapy may be more useful than TAT measurement alone for evaluating recanalization in ICT.

Changes in circulatory indices of thrombosis and fibrinolysis during total knee arthroplasty performed under tourniquet

Deep vein thrombosis may begin during surgery with the tourniquet inflated. Arterial levels of fibrinopeptide A, thrombin-antithrombin complexes, D-dimer, tissue plasminogen activator (t-PA) activity, and t-PA antigen were measured before surgery, during surgery with the tourniquet inflated, and following deflation of the tourniquet in 12 patients undergoing total knee arthroplasty. Minimal increases in fibrinopeptide A, thrombin-antithrombin complexes, and D-dimer were noted during surgery with the tourniquet inflated, but significant increases occurred immediately following deflation of the tourniquet. In 10 patients, intravenous heparin administration significantly suppressed the rise in fibrinopeptide A, but did not significantly alter the increases in either thrombin-antithrombin complexes, D-dimer, t-PA antigen, or t-PA activity. This study provides further evidence that deep vein thrombosis begins during surgery.

Heparin as adjunctive therapy to coronary thrombolysis in acute myocardial infarction

For many years anticoagulation has played a role in the prevention and management of thromboembolic complications associated with acute myocardial infarction. However, the role of heparin therapy after pharmacologic thrombolysis in myocardial infarction remains controversial. Debate continues regarding the necessity of heparin treatment after thrombolytic therapy as well as the mode by which it is administered. The purpose of this review is to summarize the findings of clinical trials designed to evaluate the effectiveness and safety of heparin as an adjuvant agent to thrombolytic therapy in acute myocardial infarction. Data regarding the clinical effectiveness of heparin are presented. Information and recommendations regarding the optimal dose, route of administration, timing of initiation, and duration of heparin treatment are provided.

Rational approach to use of heparin during cardiac catheterization in children

OBJECTIVES

We sought to determine an anticoagulation protocol for use during cardiac catheterization in children.

BACKGROUND

There are few data to indicate which dose of heparin represents adequate anticoagulation or how best to monitor its efficacy. In this study, adequate anticoagulation was defined as the amount of heparin needed to prevent a significant increase in serum fibrinopeptide A, a sensitive marker for thrombin activity. The degree of heparinization was estimated by the activated clotting time.

METHODS

Thirty-six children (1 month to 19.5 years old) with congenital heart disease underwent diagnostic cardiac catheterization; 13 of these 36 patients had an additional interventional procedure. Sheaths and catheters were flushed with heparinized saline (1 IU/ml); during the procedure, 33 of the 36 patients received either a 50- or a 100-IU/kg heparin bolus. Paired fibrinopeptide A and activated clotting time samples were obtained throughout each procedure.

RESULTS

Increasing the activated clotting time with heparin resulted in a dose-related decrease in fibrinopeptide A levels. A single heparin bolus of either 50 or 100 IU/kg elevated the activated clotting time above baseline level (209 +/- 52 s after 50 IU/kg, 270 +/- 57 s after 100 IU/kg vs. 133 +/- 20 s at baseline [p < 0.0001]) and reduced fibrinopeptide A levels below baseline (7.9 +/- 14 ng/ml after 50 IU/kg, 4.8 +/- 3.7 ng/ml after 100 IU/kg vs. 38 +/- 59 ng/ml at baseline [p < 0.0001]). Heparin flush alone did not increase the activated clotting time above baseline and failed to suppress an increase in fibrinopeptide A levels. There were no differences in activated clotting time and fibrinopeptide A values between patients undergoing diagnostic or interventional procedures.

CONCLUSIONS

Administration of a heparin bolus to maintain an activated clotting time > 200 s prevented a significant increase in thrombin activity. Heparin flush alone did not provide adequate anticoagulation. Patients undergoing an interventional procedure did not require more heparin than that needed for a diagnostic procedure.

A pooled analysis of coronary arterial patency and left ventricular function after intravenous thrombolysis for acute myocardial infarction

Individual studies of patency rates and left ventricular (LV) function after thrombolysis have generally been limited by small numbers of observations, wide confidence intervals, and limited numbers of time points. To obtain a more reliable estimate of patterns of patency and LV ejection fraction, a systemic overview of angiographic studies was performed after intravenous thrombolytic therapy. A total of 14,124 angiographic observations from 58 studies evaluating patency after no thrombolytic agent, streptokinase, standard dose tissue-type plasminogen activator (t-PA), accelerated dose t-PA, or anistreplase (anisoylated plasminogen streptokinase activator complex [APSAC]) were included. At 60 and 90 minutes, streptokinase had the lowest patency rates of 48% and 51%, respectively, standard dose t-PA and APSAC had similar intermediate rates of approximately 60% and 70%, and accelerated t-PA had the highest patency rates of 74% and 84%. By 2 to 3 hours and longer, the patency rates were similar for the various regimens. Reocclusion rates in studies including 1,172 patients randomized to t-PA versus a nonfibrin-specific agent were higher after t-PA (13.4% vs 8.0%, p = 0.002). Ten studies enrolling 4,088 patients treated with thrombolytic therapy versus control demonstrated a modest improvement in mean LV ejection fraction in the thrombolytic group at each of the times after thrombolytic therapy: hour 4, day 1, day 4, day 7 to 10, and day 10 to 28 after thrombolysis. By 4 days, mean ejection fraction was 53% versus 47% (thrombolytic vs control therapy, p < 0.01); by 10 to 28 days it was 54.1% and 51.5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of fixed dose intravenous heparin to suppress increases in thrombin activity after coronary thrombolysis with streptokinase

OBJECTIVES

This study was designed to define the extent of inhibition of thrombin activity achieved with conjunctive fixed dose intravenous sodium heparin compared with fixed dose subcutaneous calcium heparin in patients receiving intravenous streptokinase for acute myocardial infarction.

BACKGROUND

The role of heparin therapy during coronary thrombolysis with streptokinase is controversial, in part because the efficacy of different conjunctive heparin regimens in inhibiting early increases of thrombin activity is not known.

METHODS

Twenty-eight patients treated with 1.5 million U of streptokinase and 165 mg of aspirin for acute myocardial infarction were randomly assigned to receive fixed dose subcutaneous heparin therapy (12,500 U every 12 h delayed until 4 h after the end of streptokinase therapy [n = 14]) or fixed dose intravenous heparin (5,000-U bolus followed by 1,000-U/h infusion [n = 14]). Anticoagulation was assessed with serial measurements of activated partial thromboplastin time, and thrombin activity by measuring fibrinopeptide A and thrombin-antithrombin III complex levels. Plasma concentrations of creatine kinase (CK) MM isoforms were measured for 3 h to determine recanalization (increase in activity > 0.18%/min).

RESULTS

Recanalization occurred in 27%, 64% and 79% of patients given subcutaneous heparin versus 43%, 76% and 86% of those given intravenous heparin at 1, 2 and 3 h, respectively (p = 0.6). Concentrations of fibrinopeptide A (mean +/- SEM) at 1 h were higher in patients without (n = 5) than in those with (n = 23) CK-MM isoform criteria for recanalization (76.4 +/- 25.7 vs. 25.2 +/- 5.2 nmol/liter, p = 0.02), and at 1, 2 and 3 h were significantly lower with fixed dose intravenous heparin (18.4 +/- 4.8 vs. 46.7 +/- 10.2 nmol/liter at 1 h, p = 0.004) than without heparin. After fixed dose subcutaneous heparin at 4 h, fibrinopeptide A levels were similar in both groups despite lower activated partial thromboplastin times in patients who received fixed dose subcutaneous heparin. However, fibrinopeptide A was not consistently suppressed in either group (fixed dose subcutaneous heparin 8.7 +/- 1.8 nmol/liter vs. fixed dose intravenous heparin 11.8 +/- 5.2 nmol/liter) at 48 h (p = 0.4). No significant changes in the concentration of thrombin-antithrombin III complexes were found between the two groups.

CONCLUSIONS

Fixed dose intravenous heparin attenuates increases in fibrinopeptide A early after streptokinase. Subsequent fixed dose intravenous and subcutaneous heparin have similar effects but are relatively ineffective in suppressing thrombin activity, suggesting a role for more potent antithrombin agents during coronary thrombolysis with streptokinase.

Beta-thromboglobulin plasma levels in the first week after myocardial infarction: influence of thrombolytic therapy

In vitro and in vivo studies have shown both an inhibition and an activation of platelets after thrombolysis in acute myocardial infarction. Plasma beta-thromboglobulin, a marker of platelet activity, was evaluated daily during the first week after myocardial infarction in 24 patients who received intravenous streptokinase (group 1) and 26 who did not (group 2). On admission, levels of beta-thromboglobulin, as compared to those in healthy subjects (35 +/- 9 IU/ml), were similarly augmented in group 1 (105 +/- 27 IU/ml) and in group 2 (115 +/- 30 IU/ml); 3 hours later, values averaged 191 +/- 58 IU/ml in group 1 (p < 0.001 vs baseline) and 95 +/- 28 IU/ml in group 2 (not significant vs baseline; p < 0.001 between the two groups). From the second to the seventh day, beta-thromboglobulin augmented in those patients in both groups with postinfarction angina. From day 5 to day 7, patients of group 1 without angina had lower beta-thromboglobulin levels than patients of group 2 who had no symptoms. The lowest levels of platelet activity were observed in group 1 reperfused patients. These data indicate that in myocardial infarction an early platelet activation takes place that is enhanced by thrombolytic treatment; recurrence of angina is associated with persistent activation; in the absence of recurrent angina, thrombolysis can limit late platelet activation.

Serial changes in coagulant activities after thrombolytic therapy for acute myocardial infarction

Early reocclusion and bleeding complications are still unresolved problems in thrombolytic therapy for acute myocardial infarction (AMI). In the present study, 16 patients treated with either fibrin-specific tissue-type plasminogen activator (t-PA) or nonspecific urokinase (UK) were studied to determine the effects of thrombolytic therapy on serial hemostatic states. Hemostatic states of each patient were estimated by measuring various plasma markers at one- to two-hour intervals during the first six hours of therapy, daily during the next three days, and subsequently on day 7. Two markers of plasma thrombin generation, thrombin antithrombin III complex (TAT) and prothrombin fragment 1 + 2 (F 1 + 2), showed an activated coagulant state immediately after thrombolytic therapy. The amount of thrombin generation indicated by these markers showed significant positive correlation with direct markers of fibrinolysis such as fibrin degradation products (FDP), while it did not show any correlation with the markers for plasmin generation. The potential for coagulation as indicated by prothrombin time (%) decreased with thrombolysis using fibrin nonselective agents, owing perhaps to destruction of coagulant factors by free plasmin. Fibrinolytic activity induced by thrombolytic therapy for AMI caused transient activation of the coagulant system, which could contribute to early reocclusion. Fibrin nonselective agents decreased the potential for coagulation by destroying clotting factor through the generation of free plasmin. These data provide theoretical support for simultaneous administration of anticoagulant therapy with fibrin-specific thrombolytic agents.

Thrombolytic retreatment with tissue plasminogen activator for threatened reinfarction and thrombotic coronary reocclusion

Following successful coronary arterial thrombolysis, thrombogenic substrate persists, increasing the risk of recurrent thrombosis, reocclusion, and reinfarction. The preferred treatment in this setting has not been established. Although many patients receive mechanical revascularization, it is conceivable that repeat thrombolysis, primarily with tissue plasminogen activator, represents the most readily available and effective alternative.

Plasma level changes of fibrinopeptide A after uncomplicated coronary angioplasty

Fibrinopeptide A (FPA) is a small polypeptide cleaved from fibrinogen by thrombin, has a short half-life, and is considered a sensitive biochemical marker of thrombin activity, fibrin generation, and ongoing thrombosis. Increased plasma levels of FPA have been reported in various procoagulable and thrombotic medical and cardiovascular disorders, including acute myocardial infarction, unstable angina, and sudden cardiac death. However, activation of thrombosis by the arterial injury incurred during coronary angioplasty has not been systematically examined with use of plasma FPA measurements. To detect and monitor activation of thrombosis by coronary angioplasty, plasma levels of FPA were obtained by venipuncture and measured by radioimmunoassay before, immediately after, 24 to 48 h later, and 1 and 3 months after uncomplicated coronary angioplasty. From December 1990 through June 1991, FPA was measured in 30 patients (28 men and 2 women, aged 54 +/- 9 years) with coronary artery disease who were undergoing coronary angioplasty. The mean left ventricular ejection fraction was 55 +/- 7%. The dilated vessel was the left anterior descending coronary artery in 20 patients (together with a second vessel in 2), the right coronary artery in 9, and the left circumflex in 1. The procedure was successful and free of major complications in all patients. Before angioplasty the FPA levels averaged 6.50 +/- 1.18 ng/ml. Shortly after angioplasty they rose to 20.20 +/- 7.91 ng/ml (p = 0.08) despite intravenous heparin. At 24 to 48 h and after heparin had been discontinued for at least 4 h, the mean FPA levels were significantly higher (32.33 +/- 10.86 ng/ml) compared with baseline values (p = 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)

Emergency coronary angioplasty for acute myocardial infarction: predictors of early occlusion of the infarct-related artery after balloon inflation

THE FACTORS RESPONSIBLE FOR EARLY OCCLUSION OF THE INFARCT VESSEL AFTER emergency percutaneous transluminal coronary angioplasty (PTCA) were retrospectively examined in 191 patients with acute myocardial infarction. During the 24-hour period after the initial balloon inflation, 47 patients (25%) had occlusion of the vessel (occlusion group), whereas 144 did not (nonocclusion group). The former patients immediately underwent repeat PTCA, which was successful in 37. Univariate correlates of early occlusion were a shorter time interval between the onset of symptoms and PTCA (3.5 +/- 2.2 vs 4.5 +/- 2.9 hours, p = 0.025), right coronary artery involvement (53% vs 30%, p = 0.015), prior thrombolytic therapy (49% vs 32%, p = 0.035), and undersized inflation (43% vs 17%, p < 0.001). With multivariate analysis the three independent predictors were undersized inflation (p < 0.001), right coronary artery involvement (p = 0.004), and a shorter time interval until PTCA (p = 0.011). Thus patients undergoing early PTCA and having right coronary artery involvement appear to be at greater risk of having early occlusion. Thrombolytic agents and undersized inflation may also play an important role in its development.

Anticoagulant effects of hirulog, a novel thrombin inhibitor, in patients with coronary artery disease

Selective thrombin inhibitors are a new class of antithrombotic drugs that, unlike heparin, can effectively inhibit clot-bound thrombin and escape neutralization by activated platelets. Hirulog is a 20 amino acid hirudin-based synthetic peptide that has shown promise in experimental models of thrombosis. Little information is available about the effects of hirulog in patients with coronary artery disease. Forty-five patients undergoing cardiac catheterization, who were taking aspirin, were randomized to receive either (1) hirulog, 0.05 mg/kg intravenous bolus followed by 0.2 mg/kg/hour intravenous infusion until the end of the catheterization; (2) hirulog, 0.15 mg/kg intravenous bolus followed by 0.6 mg/kg/hour intravenous infusion; or (3) heparin; 5,000 U intravenous bolus. Serial activated partial thromboplastin time (APTT), prothrombin time, activated clotting time and fibrinopeptide A were measured. Hirulog produced a dose-dependent prolongation of all coagulation parameters; the 0.6 mg/kg/hour dose prolonged the APTT to 218 +/- 50% of baseline after 2 minutes and 248 +/- 50% of baseline after 15 minutes. The half-life of the effect on APTT was 40 minutes. The hirulog blood level correlated well with the APTT, prothrombin time and activated clotting time (r = 0.77, 0.73, and 0.82 respectively, all p < 0.001). Both doses of hirulog potently suppressed the generation of fibrinopeptide A (p < 0.05). There were no major hemorrhagic, thrombotic or allergic complications in patients treated with hirulog or heparin. Thus, hirulog, a direct thrombin inhibitor, provides a predictable level of anticoagulation and appears to have a potent yet well-tolerated anticoagulant profile in patients with coronary artery disease.

An overview of the patency and stroke rates following thrombolysis with streptokinase, alteplase, and anistreplase used to treat an acute myocardial infarction

The results of an overview of early (90-240 min) and late (24 hours or more) patency and of stroke rates for each of the three commercially available thrombolytic agents, streptokinase, alteplase, and anistreplase are presented. Studies included in this analysis are all those published between 1985 and March 1992 and focus on the licensed dosage regimens of each agent. The rates of early and late patency for streptokinase were 64.7% and 80.8%; for alteplase, 66.6% and 73.7%; and for anistreplase, 72.1% and 84.5%. The rates of total and hemorrhagic stroke for streptokinase were 0.69% and 0.17%; for alteplase, 1.27% and 0.50%; and for anistreplase 0.91% and 0.38%. These results provided evidence that the rates of early and late patency appeared to be greatest for anistreplase and that the rates of stroke are within "acceptable" ranges for all three thrombolytic agents with streptokinase affording the lowest rate.

Principles underlying the use of conjunctive agents with plasminogen activators

Pharmacological thrombolysis is a dynamic situation in which fibrin degradation occurs concomitant to procoagulant activity. The consequences of enhanced procoagulant and platelet activity may delay or prevent thrombolysis or lead to reocclusive events following successful recanalization. Although heparin and aspirin may attenuate ongoing thrombin and thromboxane generation, respectively, a relatively high percentage (10-20%) of patients treated with heparin and aspirin still have complications associated with thrombolysis. This suggests that heparin and aspirin are not universally effective as the heparin-antithrombin III complex may be inaccessible to fibrin-bound thrombin in the microenvironment of the thrombus and aspirin eliminates only thromboxane-dependent platelet aggregation. Therefore, careful consideration must be given to small molecule, active-site thrombin inhibitors which may prove to be more effective than heparin and to fibrinogen receptor antagonists which block aggregation to all known platelet agonists and have a much broader spectrum of activity than aspirin. Hopefully, well-designed clinical trials will be conducted with safe and effective thrombin inhibitors and/or fibrinogen receptor antagonists in thrombolysis and compared to heparin and aspirin such that potentially the overall efficiency of thrombolysis can be improved upon.

Tissue plasminogen activator for treatment of livedoid vasculitis

Livedoid vasculitis, a hyalinizing vasculopathy, is characterized by extensive formation of microthrombi and deposition of fibrin in the middermal vessels, which result in epidermal infarction, ulceration, and formation of stellate scars. In a prospective study of nonhealing ulcers in patients with livedoid vasculitis, we found a high incidence of anticardiolipin antibodies, lupus anticoagulants, increased levels of plasminogen activator inhibitor, and low levels of endogenous tissue plasminogen activator (t-PA) activity. This procoagulant tendency and decreased fibrinolysis may provide an explanation for the occlusive vasculopathy often noted in biopsy specimens from these patients. On the basis of these findings, we proposed that fibrinolysis with recombinant t-PA would lyse microvascular thrombi, restore circulation, and promote wound healing. In six patients who had nonhealing ulcers caused by livedoid vasculitis and in whom numerous conventional therapies had failed, low-dose t-PA (10 mg) was administered intravenously during a 4-hour period daily for 14 days. Five of the six patients had dramatic improvement; almost complete healing of the ulcers occurred during hospitalization, and tissue oxygenation, as measured by transcutaneous oximetry, increased. The one treatment failure was due to rethrombosis of the microvasculature; this patient was subsequently re-treated but with concurrent anticoagulation, and her leg ulcers healed. We conclude that daily administration of a low dose of t-PA is safe and effective treatment for nonhealing ulcers due to occlusive vasculopathy.

Correlation between level of heparinization and patency of the infarct-related coronary artery after treatment of acute myocardial infarction with alteplase (rt-PA)

BACKGROUND AND OBJECTIVES

The conjunctive use of intravenous heparin may influence the efficacy of alteplase for coronary thrombolysis in patients with acute myocardial infarction. In this study we examined the relation between the level of intravenous anticoagulation with heparin and sustained coronary artery patency in a subgroup of patients of the European Cooperative Study Group (ECSG) trial.

METHODS

In the ECSG trial, patients treated with alteplase and aspirin were randomized to concomitant fixed doses of intravenous heparin (a bolus dose of 5,000 U followed by a continuous infusion of 1,000 U/h or placebo). The current study group comprised 149 of 324 ECSG patients allocated to heparin therapy and 132 of 320 ECSG patients allocated to placebo administration who had both an interpretable coronary angiogram obtained within 6 days of treatment and sufficient plasma samples to assess the level of anticoagulation. Activated partial thromboplastin times, fibrinogen and D-dimer levels were determined on plasma samples at baseline and at 45 min and 3, 12, 24 and 36 h after the start of alteplase administration.

RESULTS

The coronary artery patency rate was higher in patients allocated to heparin therapy than in those allocated to placebo (80% and 71%, respectively, p = 0.05). Patients allocated to heparin were classified into three subgroups: 48 patients (32%) with all activated partial thromboplastin times at least twice their own baseline value (optimal anticoagulation), 40 patients (27%) with the lowest activated partial thromboplastin time at 3, 12, 24 or 36 h between 130% and 200% of the baseline value (suboptimal anticoagulation) and 61 patients with at least one activated partial thromboplastin time less than 130% of baseline (inadequate anticoagulation). In the heparin group, coronary artery patency correlated with the level of anticoagulation: 90%, 80% and 72%, respectively, in patients with optimal, suboptimal and inadequate anticoagulation (p = 0.02, optimal vs. inadequate anticoagulation). Heparin administration was associated with a smaller reduction in fibrinogen and a smaller increase in D-dimer level during and after alteplase administration. No correlation was found between fibrinogen or D-dimer levels and coronary artery patency. No intracerebral hemorrhage occurred in these patients; however, bleeding was more frequent in the subgroup with optimal anticoagulation (p = 0.05).

CONCLUSIONS

Intense anticoagulation with intravenous heparin enhances coronary artery patency after alteplase treatment of acute myocardial infarction.

Adjunctive therapy with low molecular weight heparin with recombinant tissue-type plasminogen activator causes sustained reflow in canine coronary thrombosis

Rethrombosis of the infarct-related artery after pharmacologic thrombolysis is a major limitation of the thrombolytic therapy. Platelet and fibrin deposition in the coronary artery after recombinant tissue-type plasminogen activator (rTPA) may play a leading role in reformation of thrombus. Therefore we examined the effect of low molecular weight heparin (LMWH) as adjunctive treatment with rTPA in a dog model of electrically induced intracoronary thrombus. Fourteen dogs, in which a stable coronary thrombus was induced with delivery of 100 microA of anodal direct current, were randomly given an intravenous bolus of LMWH, 75 IU/kg (n = 6), or saline (n = 8), followed by intravenous rTPA, 1 mg/kg over 20 minutes. LMWH (75 IU/kg) or saline was continuously infused over 90 minutes after rTPA-induced thrombolysis. Reperfusion occurred at 29 +/- 7 minutes in six of eight dogs receiving rTPA plus saline (reperfusion rate 75%), while reperfusion occurred at 18 +/- 3 minutes in all six dogs receiving rTPA plus LMWH (both p = NS versus rTPA plus saline group). Coronary reocclusion occurred in 83% of dogs given rTPA plus saline, but only in one dog (17%) given rTPA plus LMWH (p less than 0.05). Magnitude of reflow at 60 minutes of reperfusion was higher in the rTPA plus LMWH group than in the rTPA plus saline group (51 +/- 14 ml/min versus 10 +/- 9 ml/min; p less than 0.05). As expected, partial thromboplastin time was greater in rTPA plus LMWH than in rTPA plus saline-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The Role of Heparin in the Thrombolytic Treatment of Acute Myocardial Infarction

Objective:

To review the literature to determine the most appropriate role of heparin when using thrombolytic therapy.

Data Sources:

English-language journal articles published between 1985 and 1991.

Study Selection:

Ten trials comparing the effects of thrombolytic therapy with and without heparin. Desired outcomes that the authors were interested in were coronary vessel patency, reocclusion, recurrent ischemia, reinfarction, mortality, and bleeding complications.

Data Extraction:

Studies were assessed based on methodology.

Data Synthesis:

The concurrent use of heparin with tissue plasminogen activator (tPA) enhances coronary vessel patency without significantly increasing the risk of bleeding complications. The concurrent use of heparin with streptokinase enhances survival; however, the risk of bleeding associated with heparin use is unclear at present. Data are not currently available for anistreplase. Studies are underway to further address the role of heparin with thrombolytic therapy.

Conclusions:

Based on data currently available, it appears that beginning intravenous heparin during the first hour of the tPA infusion and continuing heparin for 24 hours appears most appropriate and has a minimal risk of bleeding. Delaying heparin for 9–12 hours after the streptokinase infusion appears to produce clinical benefits; however, it is not clear whether these benefits outweigh the potential risks of bleeding.