Effect of intravenous heparin infusion on thrombin-antithrombin complex and fibrinopeptide A in unstable angina

A pilot study documenting increased thrombin generation following abrupt withdrawal of heparin therapy in healthy dogs

OBJECTIVE

To document if a transient hypercoagulable state occurs in healthy dogs following abrupt cessation of unfractionated heparin (UFH) therapy.

DESIGN

Prospective experimental pilot study.

SETTING

University research facility.

ANIMALS

Seven adult random-source male dogs.

INTERVENTION

Thromboelastography (TEG) and thrombin-antithrombin (TAT) complex formation were used to assess coagulation status in healthy dogs. Seven adult research dogs received 200-300 IU/kg subcutaneous UFH every 8 hours for 4 days. A final IV bolus of 100 IU/kg was given on day 4 and the peak measured heparin concentration 1 hour later is defined as the start of heparin withdrawal (time 0). Citrated whole blood samples were collected at baseline (prior to heparin administration) and 3, 6, 12, 30, and 48 hours after UFH withdrawal. At all time points, a kaolin-activated TEG was performed and citrated plasma for measurement of TAT concentration was collected for batch analysis. Fibrinogen concentration, PCV, total plasma proteins, and platelet count were measured at baseline and 48 hours after heparin withdrawal.

MEASUREMENTS AND MAIN RESULTS

Compared to baseline, TAT was increased 12 hours after heparin withdrawal and returned to baseline by 30 hours. TEG clot formation time (K) was decreased 30 and 48 hours after heparin withdrawal.

CONCLUSION

TAT results suggest that a transient increase in thrombin generation developed 12 hours after withdrawal of UFH therapy. Though clot kinetics were rapid compared to baseline beginning 30 hours after heparin withdrawal, a return to baseline was not documented. Future studies are warranted to determine the clinical relevance of these results and to evaluate the effect of UFH withdrawal in critically ill animals.

The use of low molecular weight heparin to predict clinical outcome in patients with unstable angina that had undergone percutaneous coronary intervention

BACKGROUND

Antithrombotic therapy with heparin reduces the rate of ischemic events in patients with acute coronary syndrome. Low-molecular-weight heparin, given subcutaneously twice daily, has a more predictable anticoagulant effect than standard unfractionated heparin. Moreover, it is easier to administer and does not require monitoring.

METHODS

We prospectively analyzed 180 patients with unstable angina who had undergone percutaneous coronary intervention (PCI) between 1999 and 2001 at Chonnam National University Hospital and had received either 120 U/kg of dalteparin (Fragmin), administered subcutaneously twice daily (Group I; n = 90, 61.8 +/- 8.9 years, male 67.8%), or had received continuous intravenous unfractionated heparin (Group II; n = 90, 62.6 +/- 9.7 years, male 70.0%). During hospitalization and at 6 month after PCI, major adverse cardiac events such as acute myocardial infarction, target vessel revascularization, death, and restenosis were examined.

RESULTS

During hospitalization, the incidence of acute myocardial infarction, target vessel revascularization and death were not different between the two groups. At follow-up coronary angiography 6 months after PCI, the incidence of restenosis was lower in group I than in group II (Group I; 26/90, 28.8% vs. Group II; 32/90, 35.6%, p = 0.041) and the incidence of target vessel revascularization was lower in group I than in group II (Group I; 21/90, 23.3% vs. Group II; 27/90, 30.0%, p = 0.039). No difference was found in the rates of major and minor hemorrhages, ischemic strokes or thrombocytopenia between two groups. By multivariate analysis, the factors related to restenosis were lesion length, postprocedural minimal luminal diameter, CRP on admission, diabetes mellitus, the type of heparin, and stent use.

CONCLUSION

Dalteparin, a low molecular weight heparin, is superior to standard unfractionated heparin in terms of reducing the restenosis rate and target vessel revascularization without increasing bleeding complications.

The role of low-molecular-weight heparin in cardiovascular diseases

Unfractionated heparin continues to have important limitations in clinical practice. It has an inconsistent anticoagulant effect, needs frequent monitoring, and is inactivated by several plasma proteins. Low-molecular-weight heparins have a more predictable anticoagulant effect than unfractionated heparin, are easier to administer, and may not require monitoring. The anticoagulation effect of low-molecular-weight heparins is caused by a combination of inhibition of thrombin generation and inhibition of thrombin activity. Low-molecular-weight heparins have now been evaluated for a number of cardiovascular conditions and have been found to be safe and effective. We review and summarize the existing data regarding the use of low-molecular-weight heparins in cardiovascular diseases, including venous thromboembolism, percutaneous coronary interventions, and acute coronary syndromes such as ST-segment elevation myocardial infarction.

Persistence of the prothrombotic state after acute coronary syndromes: implications for treatment

BACKGROUND AND RESULTS

Acute coronary syndromes (unstable angina and acute myocardial infarction) are generally caused by thrombosis over a disrupted atherosclerotic plaque. During the acute phase, antithrombotic therapy (including aspirin and heparin) has been shown to reduce the risk of death or myocardial infarction (MI). The purpose of this review is to examine the high-risk period for clinical thrombotic events that extends for several weeks after presentation and to review the treatments aimed at reducing these events.

RESULTS

More than half of clinical events reported during the first month occur after the first 3 to 5 days that comprise the standard in-hospital treatment period. Several different antithrombotic approaches have been tested, including longer duration of antiplatelet therapy, anticoagulant treatment, and oral glycoprotein (GP) IIb/IIIa inhibitors. Aspirin is effective at reducing risk, and clopidogrel provides additional benefit, as does dalteparin for at least the first month. Warfarin in addition to aspirin, while generally disappointing, has not been adequately tested at higher doses. Oral GP IIb/IIIa inhibitors cause a paradoxic increased risk of death for unclear reasons.

CONCLUSION

Further reduction of risk during the weeks after presentation with acute coronary syndromes remains an important therapeutic goal.

Risk stratification in non-ST segment elevation acute coronary syndromes with special focus on recent guidelines

Patients with unstable angina or non-ST segment elevation (non-Q-wave) myocardial infarction are a heterogeneous group with respect to their risk of developing clinically significant adverse events such as subsequent myocardial infarction and death. Recent guidelines promote risk stratification of these patients, targeting high-risk patients for maximal antithrombotic and antiischemic therapy and low-risk patients for early discharge. We reviewed current and future modalities for risk stratification of patients and the predictive value of these methods in context with available pharmacologic agents. Unfortunately, most of the data identifying a particular pharmacologic regimen as beneficial in high-risk patients are retrospectively derived from large trials. Until prospective studies that use markers to guide therapy are available, clinicians should be familiar with the use of these risk markers and their application to the role of a given management strategy, including pharmacologic therapy.

Reactivation of ischemic events in acute coronary syndromes: results from GUSTO-IIb. Gobal Use of Strategies To Open occluded arteries in acute coronary syndromes

OBJECTIVES

We sought to determine the incidence of and risk factors for thrombotic events early after discontinuing antithrombin therapy in patients with acute coronary syndromes.

BACKGROUND

Discontinuation of treatment with heparin and other thrombin inhibitors in patients with unstable coronary syndromes has related to clinical and biochemical evidence of early reactivation of thrombosis.

METHODS

We studied 8,943 of the 12,142 patients with acute coronary syndromes enrolled in the Global Use of Strategies To Open occluded arteries in acute coronary syndromes trial of hirudin versus heparin. We excluded patients who received no study drug, lacked timing data, died or had myocardial (re)infarction [(re)MI] during study-drug infusion, or began heparin treatment within 2 h after treatment with the study drug was stopped. We assessed the incidence and timing of (re)MI by type and timing of antithrombin treatment.

RESULTS

In all, 215 patients (2.4%) suffered (re)MI, 49 within 12 h of antithrombin therapy discontinuation and 166 between hour 12 and hospital discharge. The duration of infusion did not differ between the hirudin and heparin groups. The rate of early re(MI) after drug therapy discontinuation was significantly higher in patients given heparin versus hirudin (0.8% vs. 0.3%, p = 0.002). Patients with (re)MI had higher mortality at 30 days (23.6% vs. 2.4%, p = 0.001) and 1 year (35.2% vs. 6.7%, p = 0.001) compared with patients without (re)MI.

CONCLUSIONS

The incidence of (re)MI was clustered within 12 h of heparin therapy discontinuation, with the greatest risk within 4 h. There was no evidence of early reactivation of thrombotic events after hirudin. Patients who had (re)infarction had worse outcomes. Better understanding of the mechanism and possible prevention of recurrent thrombosis is needed.

Assessment of the treatment effect of enoxaparin for unstable angina/non-Q-wave myocardial infarction. TIMI 11B-ESSENCE meta-analysis

BACKGROUND

Two phase III trials of enoxaparin for unstable angina/non-Q-wave myocardial infarction have shown it to be superior to unfractionated heparin for preventing a composite of death and cardiac ischemic events. A prospectively planned meta-analysis was performed to provide a more precise estimate of the effects of enoxaparin on multiple end points.

METHODS AND RESULTS

Event rates for death, the composite end points of death/nonfatal myocardial infarction and death/nonfatal myocardial infarction/urgent revascularization, and major hemorrhage were extracted from the TIMI 11B and ESSENCE databases. Treatment effects at days 2, 8, 14, and 43 were expressed as the OR (and 95% CI) for enoxaparin versus unfractionated heparin. All heterogeneity tests for efficacy end points were negative, which suggests comparability of the findings in TIMI 11B and ESSENCE. Enoxaparin was associated with a 20% reduction in death and serious cardiac ischemic events that appeared within the first few days of treatment, and this benefit was sustained through 43 days. Enoxaparin's treatment benefit was not associated with an increase in major hemorrhage during the acute phase of therapy, but there was an increase in the rate of minor hemorrhage.

CONCLUSIONS

The accumulated evidence, coupled with the simplicity of subcutaneous administration and elimination of the need for anticoagulation monitoring, indicates that enoxaparin should be considered as a replacement for unfractionated heparin as the antithrombin for the acute phase of management of patients with high-risk unstable angina/non-Q-wave myocardial infarction.

Clinical trials of low-molecular-weight heparins in cardiology

Our understanding of the pathophysiology of acute coronary syndromes is evolving as the role of prognostic coagulation markers and the different effects unfractionated heparin and low-molecular-weight heparins have on these coagulation markers are investigated. The results of recent clinical trials of low-molecular-weight heparins in acute coronary syndromes are summarized, and an economic evaluation of enoxaparin for these indications is reviewed.