Activation of the hemostatic system during thrombolytic therapy

The impact of platelet count on mortality in unstable angina/non-ST-segment elevation myocardial infarction

BACKGROUND

Expanding the knowledge of pathogenesis of arteriosclerosis points at a central role of platelets in the development of acute coronary syndromes. Therefore, we sought to determine the impact of platelet count on long-term outcome in unstable angina/non-ST-segment elevation myocardial infarction (UA/NSTEMI) receiving contemporary treatment.

METHODS

This prospective cohort study included 1616 consecutive patients with UA/NSTEMI. All patients underwent coronary angiography and, if appropriate, subsequent catheter-based revascularization within 24 hours of admission. Patients were divided in quintiles according to platelet count. The primary end point was all-cause mortality during long-term follow-up of up to 60 months.

RESULTS

During follow-up (median 17 months, interquartile range 6-31 months), 89 deaths and 74 nonfatal myocardial infarctions occurred. Patients with higher platelet counts were younger, more often female, and had lower height and weight as compared with patients with lower platelet counts. Mortality was significantly lower among patients in the second quintile of platelet count (181-210 x 10(9)/L) as compared with the other quintiles (hazard ratio 0.39, 95% CI 0.19 to 0.81, P = .011). Kaplan-Meier survival analysis showed cumulative 4-year mortality rates of 12.5%, 3.8%, 10.4%, 9.8%, and 11.4% for patients in the first, second, third, fourth, and fifth quintiles. This association persisted after multivariate adjustment. No association of platelet count and nonfatal myocardial infarctions was observed.

CONCLUSIONS

We found a nonlinear association between platelet count and long-term mortality. The lowest mortality was observed in patients with a platelet count between 181 and 210 x 10(9)/L.

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.

Laboratory Measurement of Thrombin Activity--What Every Clinician Scientist Needs to Know

Advances in our knowledge of the biochemistry of coagulation and fibrinolysis have facilitated the development of sensitive and specific assays that detect platelet activation, the generation of coagulation enzymes, and products of intravascular fibrin formation and dissolution. This review focuses on activation markers of blood coagulation and, in particular, on mechanistic information on the pathophysiology of blood coagulation they have provided. The methodological problems faced in employing these moieties in clinical studies are examined. Only the proper use of coagulation activation markers will enable us to establish their real clinical usefulness.

Activation markers of coagulation

Advances in our understanding of the biochemistry of the haemostatic mechanism have led to the development of sensitive methods for measuring peptides, enzyme-inhibitor complexes, and enzymes that are liberated with the activation of the coagulation system in vivo. Studies employing these markers have provided important mechanistic information regarding haemostatic mechanism function both under normal conditions and in response to pathogenic stimuli. While assays for particular components can denote the presence of a 'biochemical' hypercoagulable state prior to the appearance of overt thrombotic phenomena, most of these markers thus far have not been shown to be useful in managing individual patients. Properly designed prospective studies will be required to determine whether these assay techniques will aid in the identification of patients predisposed to thrombotic events or the monitoring of antithrombotic therapy.

Early administration of intravenous magnesium inhibits arterial thrombus formation

An antiplatelet effect of magnesium has been demonstrated in vitro and ex vivo, and this effect may be advantageous in patients with acute myocardial infarction to inhibit reocclusion after coronary angioplasty or thrombolysis. We investigated the antithrombotic in vivo effect of intravenous magnesium in a placebo-controlled, blinded study in 46 male Wistar rats. Thrombus formation was induced by standardized arteriotomy of the femoral artery and partial inversion of the vessel wall to produce a thrombogenic area. The vessel was transilluminated and visualized dynamically by in vivo microscopy. Thrombus area was measured every minute for 30 minutes after removal of the vessel clamp by image analysis techniques, and the number of visible emboli was registered. Animals were randomized into three groups: groups 1 and 2 received saline (control group, n = 15) or MgSO4 (Mg-early group, n = 15), respectively, during the entire infusion period. In group 3 intravenous saline was given during preparation of the arteriotomy followed by infusion of MgSO4 (Mg-late group, n = 16) from 10 minutes after removal of the vessel clamp. Thrombus area was significantly reduced by 75% in the Mg-early group (P < .005) but not in the Mg-late group compared with the control group. Mean number of emboli was reduced during magnesium infusion. The serum magnesium level increased to 2.2 (2.1 to 2.5) and 3.5 (3.0 to 4.2) mmol/L after infusion in the Mg-late and the Mg-early group, respectively. In the present study, intravenous infusion of MgSO4 significantly reduced thrombus formation in vivo but only when it was given before reperfusion. The antithrombotic effect of magnesium may be utilized in patients with acute myocardial infarction to reduce the rate of reocclusion. Magnesium infusion may also be of value in elective arterial angioplasty, but this option has not been investigated in clinical trials. However, correct timing of magnesium administration is critical to obtain an efficient antithrombotic effect.

[Myocardial infarction and revascularization. Current indications]

The physiopathologic role of thrombosis in the genesis of myocardial infarction, began to be suspected early in the 20th century but its logical treatment, thrombolysis, was first used on a large scale only ten years ago. Today, it is well established that short, middle and long-term mortality is correlated to coronary permeability, the delay in the revascularization treatment start-up, its efficacy, its swiftness of action, and to the maintaining of permeability following reperfusion. The importance of time elapse before reperfusion is obtained was demonstrated as early as 1986 by the GISSI study. According to this study, the administration of streptokinase (compared to a conventional treatment) reduced mortality at 21 days respectively by 47%, 23%, and 17%, depending on whether patients were treated within one hour, three hours, or between 3 and 6 hours following the onset of the painful symptoms. One of the major teachings of the GUSTO study, reported at the end of 1993, was the confirmation of the so-called "open artery" theory: mortality at 30 days was of 4.5% among patients whose coronary circulation was restored at the 90th minute, whatever thrombolytic treatment was used, compared to 8.9% when the coronary artery remained occluded. The value of aspirin in preserving coronary permeability following thrombolysis was demonstrated by the ISIS-2 study: mortality at 5 weeks was reduced by 23% in the group of patients randomised to receive only aspirin, while it was reduced by 25% in the group of patients randomised to be treated with streptokinase, and by 42% in the group randomised to receive both aspirin and streptokinase, compared to the group who received neither aspirin nor streptokinase. However, mortality during the first days following randomisation was identical among the groups, with or without aspirin, which suggested its action was rather one of prevention against reocclusion than one of accelerating dissolution of the thrombus. However, in spite of improved therapeutical protocols, a normal flow, which is the major criteria for a reduced mortality, is only obtained at the 90th minute in 54% of the patients who were administered the up-to-date treatment ie aspirin-accelerated t-PA-heparin in combination.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute myocardial infarction. Then and now

Dramatic changes in the management of acute myocardial infarction (AMI) have occurred in the past decade. While previous management strategies were primarily supportive, current strategies focus on achieving and maintaining patency of the infarct-related artery restoring blood flow to jeopardized myocytes, preserving left ventricular function, and preventing recurrences and complications in addition to promoting healing. Restoration of blood flow can be achieved pharmacologically with thrombolytic agents or mechanically with percutaneous transluminal coronary angioplasty (PTCA). Early use of antiplatelet agents and anticoagulants helps maintain patency of the infarct-related arteries and prevents thromboembolic complications. Administration of beta-blockers and angiotensin enzyme inhibitors are more specific means of conserving myocardium and preserving ventricular function. Additionally, several strategies for preventing arrhythmias such as prophylactic lidocaine use and routine long-term suppression of premature ventricular contractions with antiarrhythmic drugs are no longer routinely advocated. Basically, in the era prior to the eighth decade of this century, the primary direction of the therapeutic strategy for AMI was to reduce the oxygen demands in the infarcted myocardium; whereas in the subsequent years, the emphasis shifts to improvement in oxygen delivery, via thrombolysis, PTCA, and coronary artery bypass graft surgery. These interventional changes, when added to greater sophistication in the use of drugs to reduce oxygen demands, resulted in significant lowering of myocardial mortality.

Thrombin generation and activity during thrombolysis and concomitant heparin therapy in patients with acute myocardial infarction

OBJECTIVES

This prospective study investigated the behavior of thrombin generation and activity during thrombolysis and concomitant heparin administration.

BACKGROUND

It has been shown that during thrombolytic therapy there is an increase in thrombin generation and activity. Increased thrombin activity is suppressed by concomitant intravenous heparin, but it is unknown whether thrombin generation is also affected.

METHODS

Thrombin generation was assessed by measuring prothrombin fragment 1 + 2 and thrombin-antithrombin complex plasma levels and thrombin activity by measuring fibrinopeptide A plasma levels. Serial blood samples were obtained before and at 90 min and 24 and 48 h after the administration of streptokinase (15 patients), recombinant tissue-type plasminogen activator (15 patients) or anistreplase (13 patients). An intravenous bolus of heparin (5,000 IU) was administered before the start of thrombolytic therapy, followed by an infusion of 1,000 U/h to maintain an activated partial thromboplastin time > 1.5 times baseline.

RESULTS

During thrombolytic and concomitant heparin therapy, there was an increase in the plasma levels of prothrombin fragment 1 + 2 (baseline 1.08 vs. 2.73 nmol/liter, p < 0.001) and thrombin-antithrombin complex (baseline 6.5 vs. 17.1 micrograms/ml, p < 0.01) at 90 min, whereas no change was observed in fibrinopeptide A at 90 min (baseline 2.8 vs. 3.0 nmol/liter, p = NS).

CONCLUSIONS

During thrombolytic therapy with both fibrin-specific and non-fibrin-specific drugs, there is an increase in thrombin generation despite concomitant administration of intravenous heparin.