Heparin

Laminarin sulfate mimics the effects of heparin on smooth muscle cell proliferation and basic fibroblast growth factor-receptor binding and mitogenic activity

Heparin and heparin-like molecules may function, apart from their effect on hemostasis, as regulators of cell growth and neovascularization. We investigated whether similar effects are exerted by laminarin sulfate, an unrelated polysulfated saccharide isolated from the cell wall of seaweed and composed of chemically O-sulfated beta-(1,3)-linked glucose residues. Laminarin sulfate exhibits about 30% of the anticoagulant activity of heparin and is effective therapeutically in the prevention and treatment of cerebrovascular diseases. We characterized the effect of laminarin sulfate on interaction of the heparin-binding angiogenic factor, basic fibroblast growth factor (bFGF), with a naturally produced subendothelial extra-cellular matrix (ECM) and with cell surface receptor sites. Laminarin sulfate (1-2 micrograms/ml) inhibited the binding of bFGF to ECM and to the surface of vascular smooth muscle cells (SMC) in a manner similar to that observed with heparin. Likewise, laminarin sulfate efficiently displaced both ECM- and cell-bound bFGF at concentrations as low as 1 microgram/ml. Both laminarin sulfate and heparin efficiently induced restoration of bFGF receptor binding in xylosyltransferase-deficient CHO cell mutants defective in initiation of glycosaminoglycan synthesis. Moreover, laminarin sulfate elicited bFGF receptor activation and mitogenic response in heparan sulfate (HS)-deficient, cytokine-dependent lymphoid cells. These results indicate that laminarin sulfate effectively replaced the need for heparin and HS in the induction of bFGF receptor binding and signaling. In other experiments, laminarin sulfate was found to inhibit the proliferation of vascular SMC in a manner similar to that observed with heparin. These effects of laminarin sulfate may have potential clinical applications in diverse situations such as wound healing, angiogenesis, and atherosclerosis.

Thrombosis and embolism

Prevention offers the best approach to limiting morbidity and mortality from deep vein thrombosis and pulmonary embolism in obstetric patients. The use of anticoagulant drugs during pregnancy, however, can be problematic, from the maternal or the fetal point of view. Deciding on the best management is further limited by the lack of controlled clinical trials in the obstetric setting. From the data available, it can be recommended that anticoagulant prophylaxis should be targeted at groups of patients at high risk of thrombosis during pregnancy and the puerperium. Heparin is the agent of choice in most situations during pregnancy for the prophylaxis of venous thrombosis, while warfarin is still the most effective agent for the prevention of systemic embolism from artificial cardiac valves. Prophylactic measures against venous thrombosis are probably underused in the puerperium. Controlled clinical studies are urgently required to optimize prophylaxis of venous thromboembolism associated with pregnancy, and large studies may be more feasible in the puerperium when the incidence of thromboembolism is highest.

Hirulog in the treatment of unstable angina. Results of the Thrombin Inhibition in Myocardial Ischemia (TIMI) 7 trial

BACKGROUND

Direct thrombin inhibitors are a new class of drugs that may offer a more effective and potentially simpler alternative to heparin. Hirulog is a synthetic peptide based on the leech-derived compound hirudin and, like hirudin, is a highly specific, direct inhibitor of free and clot-bound thrombin.

METHODS AND RESULTS

TIMI 7 was a randomized, double-blind study of Hirulog, given with 325 mg/d aspirin to 410 patients with unstable angina. Patients received a constant infusion of Hirulog for 72 hours at one of four doses: 0.02 (n = 160), 0.25 (n = 81), 0.5 (n = 88), and 1.0 (n = 81) mg.kg-1.h-1. The primary efficacy end point was "unsatisfactory outcome," defined as death, nonfatal myocardial infarction (MI), rapid clinical deterioration, or recurrent ischemic pain at rest with ECG changes by 72 hours. Unsatisfactory outcome was not different among the four dose groups: 8.1%, 6.2%, 11.4%, and 6.2% (P = NS). However, the secondary end point of death or nonfatal MI through hospital discharge occurred in 10.0% of patients treated with 0.02 mg.kg-1.h-1 compared with 3.2% of patients treated with the three higher doses of Hirulog (0.25, 0.5, and 1.0 mg.kg-1.h-1, P = .008). Only 2 of 410 patients (0.5%) experienced a major hemorrhage attributed to Hirulog.

CONCLUSIONS

The direct thrombin inhibitor Hirulog is a promising new antithrombotic agent that deserves further study. The results of TIMI 7 lend support to the use of an antithrombin agent with aspirin in patients with unstable angina.

Low molecular weight heparin versus regular heparin or aspirin in the treatment of unstable angina and silent ischemia

OBJECTIVES

This study was designed to test the hypothesis that low molecular weight heparin may lessen the severity of ischemic events in patients with unstable angina.

BACKGROUND

Unstable angina is a thrombotic process that requires intensive medical treatment. Although current treatments can reduce the number of complications, serious bleeding continues to occur. Nadroparin calcium, a low molecular weight heparin, seems to be a safe therapeutic agent that does not require laboratory monitoring.

METHODS

A total of 219 patients with unstable angina entered the study at a mean time of 6.17 h after the last episode of rest pain. Patients were randomized to receive aspirin (200 mg/day [group A]), aspirin plus regular heparin (400 IU/kg body weight per day intravenously and titered by activated partial thromboplastin time [group B]) and aspirin plus low molecular weight heparin (214 UIC/kg anti-Xa twice daily subcutaneously [group C]). The major end points determined for the in-hospital period were 1) recurrent angina, 2) myocardial infarction, 3) urgent revascularization, 4) major bleeding, and 5) death. Minor end points were 1) silent myocardial ischemia, and 2) minor bleeding. Event rates were tested by chi-square analysis.

RESULTS

Recurrent angina occurred in 37%, 44% and 21% of patients in groups A, B and C, respectively, and was significantly less frequent in group C than in either group A (odds ratio 2.26, 95% confidence interval [CI] 1 to 5.18, p = 0.03) or group B (odds ratio, 3.07, 95% CI 1.36 to 7.00, p = 0.002). Nonfatal myocardial infarction was present in seven patients in group A, four in group B and none in group C (group B vs. A, p = 0.5; group C vs. A, p = 0.01). Urgent revascularization was performed in nine patients in group A, seven in group B and one in group C (C vs. A, p = 0.01). Two episodes of major bleeding occurred in group B. Silent myocardial ischemia was present in 38%, 41% and 25% of patients in groups A, B and C, respectively, and was significantly less frequent in group C than group B (odds ratio 2.12, 95% CI 0.97 to 4.69, p = 0.04). Minor bleeding was detected in 10 patients in group B, 1 patient in group C (B vs. C, p = 0.01) and no patient in group A (A vs. B, p = 0.003).

CONCLUSIONS

In this study, treatment with aspirin plus a high dose of low molecular weight heparin during the acute phase of unstable angina was significantly better than treatment with aspirin alone or aspirin plus regular heparin.

Contemporary management of acute myocardial infarction

Acute myocardial infarction, the leading cause of death in western society, has been the focus of more randomized clinical trial effort over the past decade than any other area of medicine. As a result of this worldwide effort, involving hundreds of thousands of patients with myocardial infarction, data have accumulated showing substantially lower mortality of acute myocardial infarction with simple interventions such as i.v. thrombolytic therapy, aspirin, beta-blockers, and angiotensin-converting enzyme inhibitors. Emergency coronary angioplasty appears to be a suitable alternative to i.v. thrombolytic therapy in skilled centers. Several previously recommended therapies (routine i.v. lidocaine, calcium channel blockers, magnesium, nitrates) have not been proved to be life-saving. Whether routine coronary arteriography should be employed after myocardial infarction remains controversial, but it is generally accepted that patients with evidence of residual ischemia after infarction, either spontaneous or provoked by stress testing, should undergo prophylactic coronary revascularization.

Review of the initiation of anticoagulant therapy

The objective was to retrospectively study the initiation of anticoagulant therapy in inpatients of the two major teaching hospitals in Tasmania, Australia. The medical records of a random sample of patients with an admission diagnosis of deep venous thrombosis (DVT) or pulmonary embolism (PE) during the period February 1992 to June 1994 were studied, to examine therapeutic issues including (i) the time taken after commencing heparin to achieve a therapeutic activated partial thromboplastin time (APTT), (ii) when warfarin was commenced, (iii) the time taken after commencing warfarin to achieve a therapeutic International Normalized Ratio (INR), and (iv) the degree of anticoagulant control at the time of discharge from hospital. The medical records of 99 patients (median age: 65 years and range: 16-93 years; 52 females) were studied. Heparin was generally commenced within 4 h of admission to hospital. The median duration of heparin therapy was 5 days (range: 2-26 days). The median number of APTTs performed per patient was 6 (range: 1-24), with most results (60%) being below the optimum range. Warfarin was commenced from day 1 of hospitalization in only 34% of patients. The INR was within the therapeutic range in only 29% of cases when heparin was ceased. The median time taken to achieve a therapeutic INR after starting warfarin was 3 days (range: 1-15 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Early reactivation of ischaemia after abrupt discontinuation of heparin in acute myocardial infarction

Intravenous heparin after thrombolytic therapy for acute myocardial infarction is an effective, widely used treatment. Six cases of acute myocardial infarction are reported with early disease reactivation following the abrupt discontinuation of heparin infusion three days after alteplase thrombolysis and concomitant aspirin therapy. Immediate reinfusion of heparin resulted in regression of symptomatic ischaemia in all six patients. The activated partial thromboplastin time values, determined four hours before the discontinuation of heparin therapy, were within the therapeutic range in five of the six patients, and no difference was found in the values obtained one hour after the reinfusion of heparin (P = 0.065).

Heparin: pharmacological potentials from atherosclerosis to asthma

1. Heparin belongs to a family of polysaccharide species, whose best known property is, undoubtedly, anticoagulant activity. However, heparin has many other pharmacological effects, particularly on the cardiovascular system. 2. The therapeutic use of chronically inhaled heparin has been suggested as prophylaxis in atherosclerosis. 3. Heparin, physiologically stored in mast cells of the respiratory system, has also been recently studied in the prevention of immunological and non-immunological asthmatic attacks. 4. Experimental findings and new hypotheses of heparin action in asthma and atherosclerosis are discussed.

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.

A normal perfusion lung scan in patients with clinically suspected pulmonary embolism. Frequency and clinical validity

STUDY OBJECTIVE

To assess the frequency of a normal perfusion lung scan in a consecutive series of patients with clinically suspected pulmonary embolism, to determine the complication risk of heparin therapy in those patients treated while awaiting lung scanning, and to evaluate the clinical validity of withholding anticoagulant therapy in patients with a normal lung scan result.

DESIGN

Prospective cohort.

SETTING

Two teaching hospitals in Amsterdam, the Netherlands.

PATIENTS

Consecutive inpatients and outpatients referred for clinically suspected pulmonary embolism who underwent lung scintigraphy.

INTERVENTIONS

Initiation of intravenous heparin therapy before lung scanning was left to the discretion of the attending physician. Anticoagulant therapy was withheld or withdrawn in patients with a normal lung scan. Patients were followed-up for 6 months.

MEASUREMENTS AND RESULTS

A normal perfusion scan was obtained in 114 of 412 consecutive patients (28%; 95% confidence interval [CI] 23 to 32%). Major bleeding complications occurred in 2 of 30 patients (6.7%; 95% CI 0.8 to 22.1%) in whom heparin was administered while awaiting lung scintigraphy. One patient was lost to follow-up, and venous thromboembolism (0%; 95% CI 0 to 3.2%) did not develop in the remaining 113 patients.

CONCLUSIONS

In a substantial proportion of patients with clinically suspected pulmonary embolism (28%) the diagnosis is excluded by lung scintigraphy. The test should be performed as soon as feasible to prevent unnecessary hospitalization and bleeding complications. Long-term anticoagulant therapy can be safely withheld in symptomatic patients with a normal perfusion lung scan.

Novel antithrombotic drugs in development

Platelet activation plays a critical role in thromboembolic disorders, and aspirin remains a keystone in preventive strategies. This remarkable efficacy is rather unexpected, as aspirin selectively inhibits platelet aggregation mediated through activation of the arachidonic-thromboxane pathway, but not platelet aggregation induced by adenosine diphosphate (ADP), collagen and low levels of thrombin. This apparent paradox has stimulated investigations on the effect of aspirin on eicosanoid-independent effects of aspirin on cellular signalling. It has also fostered the search for antiplatelet drugs inhibiting platelet aggregation at other levels than the acetylation of platelet cyclo-oxygenase, such as thromboxane synthase inhibitors and thromboxane receptor antagonists. The final step of all platelet agonists is the functional expression of glycoprotein (GP) IIb/IIIa on the platelet surface, which ligates fibrinogen to link platelets together as part of the aggregation process. Agents that interact between GPIIb/IIIa and fibrinogen have been developed, which block GPIIb/IIIa, such as monoclonal antibodies to GPIIb/IIIa, and natural and synthetic peptides (disintegrins) containing the Arg-Gly-Asp (RGD) recognition sequence in fibrinogen and other adhesion macromolecules. Also, some non-peptide RGD mimetics have been developed which are orally active prodrugs. Stable analogues of prostacyclin, some of which are orally active, are also available. Thrombin has a pivotal role in both platelet activation and fibrin generation. In addition to natural and recombinant human antithrombin III, direct antithrombin III-independent thrombin inhibitors have been developed as recombinant hirudin, hirulog, argatroban, boroarginine derivatives and single stranded DNA oligonucleotides (aptanes). Direct thrombin inhibitors do not affect thrombin generation and may leave some 'escaping' thrombin molecules unaffected. Inhibition of factor Xa can prevent thrombin generation and disrupt the thrombin feedback loop that amplifies thrombin production.

Hirudin: initial results in acute myocardial infarction, unstable angina and angioplasty

The central role of thrombosis in the pathogenesis of acute myocardial infarction, unstable angina and complications after angioplasty has led to intense interest in developing more effective antithrombotic agents for these disorders. Hirudin, a direct thrombin inhibitor, has undergone extensive testing in experimental models and has recently been evaluated in patients in several pilot trials. Across these three indications, hirudin has been found to achieve a more consistent level of anticoagulation than heparin, as gauged by the activated parital thromboplastin time. Similarly, as an adjunct to thrombolytic therapy in acute myocardial infarction, in the treatment of unstable angina and in support of angioplasty, hirudin appeared to improve indexes of coronary reperfusion and patency. Initial results with clinical end points, including death or myocardial infarction, appeared to favor hirudin over heparin. In several large phase III trials, hirudin is being compared with heparin for all three indications. In the first phases of these trials, the rate of hemorrhagic events, including intracranial hemorrhage, was higher than expected in both the hirudin and heparin arms, which demonstrated that a safety ceiling had been reached. The reformulated Thrombolysis in Myocardial Infarction (TIMI) 9 and Second Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO II) trials are using lower doses of hirudin and heparin, which should allow testing of whether the initial favorable results observed in pilot trials will translate into improved clinical outcome, with an acceptable safety profile, for patients with acute myocardial infarction or unstable angina or those undergoing angioplasty.

Heparin-induced aldosterone suppression and hyperkalemia

PURPOSE

To review the effects of heparin and heparinoid compounds on aldosterone physiology and associated induction of hyperkalemia.

MATERIALS AND METHODS

A comprehensive literature search (of human and animal data) was carried out by computer and by using reference citations from primary sources.

RESULTS

Heparin and its congeners are predictable, potent inhibitors of aldosterone production. This inhibitory effect is specific for the zona glomerulosa; other corticosteroids are not affected. Aldosterone suppression occurs within a few days of initiation of therapy, is reversible, and is independent of either anticoagulant effect or route of administration. Decreases in aldosterone levels may occur with heparin dosages as low as 5,000 U BID. The most important, but probably not the only mechanism of aldosterone inhibition appears to involve reduction in both the number and affinity of the angiotensin-II receptors in the zona glomerulosa. Prolonged use of heparin causes marked reduction in the width of the adrenal zona glomerulosa.

CONCLUSIONS

Aldosterone suppression results in natriuresis and less predictably in decreased excretion of potassium. Greater than normal serum potassium levels occur in about 7% of patients, but marked hyperkalemia generally requires the presence of additional factors perturbing potassium balance (in particular, renal insufficiency, diabetes mellitus, or the use of certain medications). Heparin-induced increases in serum potassium need to be better anticipated by clinicians. Serum potassium levels should be monitored periodically in patients being given heparin for 3 or more days, and in patients at relatively high risk for hyperkalemia, the monitoring interval should probably be no greater than 4 days.

Comparison of bedside and hospital laboratory coagulation studies during and after coronary intervention

The activated clotting time is routinely used to monitor anticoagulation during coronary intervention, whereas the hospital laboratory APTT guides pre- and postprocedure heparin therapy. An optimal coagulation test for patients undergoing percutaneous revascularization would provide a rapid and accurate assessment of anticoagulation throughout a broad range of heparin therapy. We studied the relationships of the bedside whole blood APTT, ACT, and the laboratory APTT in 166 patients undergoing coronary intervation. The whole blood APTT correlated closely with the laboratory APTT (range 18-80 sec) (r = .75), whereas the ACT and laboratory APTT had only a fair correlation (r = .42). Also, the whole blood APTT demonstrated a strong correlation with the ACT throughout the range of heparin therapy for intervention (r = .81). The diagnostic accuracy of the whole blood APTT, based on the receiver operating characteristic curve, was significantly better than that for the ACT in determining the anticoagulation status. The whole blood APTT obtained by bedside monitoring provides a rapid and accurate assessment of anticoagulation throughout the range of heparin dosing associated with coronary intervention. In situations in which an adequate assessment of residual anticoagulation is necessary, the whole blood APTT is superior to the ACT and probably should be the method of choice.

Successful outcome in severe pregnancy-associated hyperlipemia: a case report and literature review

Severe hypertriglyceridemia causing pancreatitis is a rare complication of pregnancy, usually occurring in the second and third trimesters. Treatment includes a very low-fat diet, intravenous fluids, total parenteral nutrition, and plasma apheresis. In this article, the authors report the case of a pregnant woman who presented with a plasma triglyceride level of 65 mmol/L, abdominal pain, and a threatened abortion at 8 weeks of gestation. Treatment included restriction of dietary fat to below 10% of total calories, liquid protein supplementation, multiple hospitalizations for treatment with intravenous fluids, and total parenteral nutrition. Continuous intravenous heparin was started at 29 weeks of gestation for pulmonary embolism. This was associated with a dramatic decrease in plasma triglyceride levels. A normal female child was born at 37 weeks of gestation. The mother's weight at 2 weeks postpartum was 15 lb below her pregnant weight. It was concluded that a successful pregnancy is possible even when plasma triglyceride levels are very high early in the pregnancy.

Quality assurance of high-dose i.v. heparin treatment exemplified by patients implanted with coronary Palmaz-Schatz stents

The need to standardize treatment with high-dose IV standard heparin by using activated partial thromboplastin time (APTT) reagents tested for their heparin sensitivity and by establishing a standard treatment schedule led to the development of the "Lainz concept" of heparin management. The determination of heparin sensitivity of the 2 APTT reagents used (APTT Micronized Silica and APTT Actin FSL), their good agreement (r = .9977; P = .000), and their therapeutic APTT ratio of 1.5-2.5 fold of baseline APTT (therapeutic range, forty-five to seventy-five seconds) equivalent to 0.3-0.7 antifactor Xa units are presented. The "Lainz concept" was tested in 29 patients receiving high-dose heparin after coronary artery stenting. A mean dose of 1,273 U of standard heparin/hour (15.7 U/kg body weight/hour) was shown to produce APTTs in the therapeutic range. From the introduction of the "Lainz concept" 81% of the APTTs were kept within the therapeutic range by using a defined heparin-monitoring schedule based on a guideline protocol for controlling heparin treatment. Only 19% of the APTTs were below the therapeutic range. Factors underlying subtherapeutic APTTs are discussed. The reduction in the rate of subtherapeutic APTTs to less than 3% seen after the introduction of the "Lainz concept" constitutes an important contribution toward quality assurance in high-dose heparin treatment.

Rebound increase in thrombin generation and activity after cessation of intravenous heparin in patients with acute coronary syndromes

BACKGROUND

The abrupt cessation of heparin and other thrombin inhibitors when used to treat acute coronary syndromes has been accompanied by a clustering of thrombotic events. It is unknown whether these events are the result of inadequate antithrombin therapy or whether they represent a rebound increase in thrombin activity. This study was designed to determine whether there is a true rebound, as defined by an increase followed by a subsequent decrease, in thrombin activity after discontinuation of intravenous heparin therapy.

METHODS AND RESULTS

Thirty-five patients with recent acute myocardial infarction or unstable angina who had received at least 48 hours of intravenous heparin were studied. Patients underwent ST-segment monitoring, and blood samples for determination of thrombin generation and activity were drawn at 0, 3, 6, 10, and 24 hours after heparin discontinuation. Median aPTT was 65 seconds before heparin discontinuation. Median fibrinopeptide A increased from 9.5 to 16.9 ng/mL at 3 hours (P < .0004) and returned to 10.5 by 24 hours. Prothrombin fragment 1.2 likewise transiently increased, from 0.34 to 0.51 nmol/L at 6 hours (P < .0002). Modified antithrombin III decreased over time (P < .002), and activated protein C increased from 2.3 to 4.5 ng/mL at 3 hours (P < .001). Although there were no clinical thrombotic events in the first 24 hours, 4 patients had evidence of ischemia by ST-segment monitoring at a median of 12 hours after heparin discontinuation. The degree of increase in fibrinopeptide A and prothrombin fragment 1.2 was not found to be associated with baseline diagnosis, duration of heparin therapy, baseline level of antithrombin III, or activated protein C.

CONCLUSIONS

This study demonstrates a transient rebound increase in thrombin activity as well as in activated protein C upon abrupt discontinuation of intravenous heparin. Clinicians should be vigilant for associated thrombotic events. Further investigation of the significance, mechanism, and possible prevention of this rebound phenomenon is needed.

Bioavailability and pharmacokinetics of a new low molecular weight heparin (RO-11)--a three way cross-over study in healthy volunteers

This study reports on the bioavailability and pharmaco kinetics of a new low molecular weight heparin (RO-11), with a mean molecular weight of 3,600-3,800 daltons. It was administered to 12 healthy individuals in an open, cross-over study. Each subject was randomly assigned to three experimental treatments: a) 30 mg by subcutaneous route, b) 60 mg subcutaneously and c) 60 mg intravenously, leaving a wash-out period of one week between treatments. The pharmacokinetic profile was calculated by means of the anti-FXa effect, measured on serial samples taken before and during the 24 h period after each treatment. The effects of the drug on global coagulation tests, Antithrombin-III levels, tissue-factor pathway inhibitor activity and anti-FIIa activity were also assessed. After the intravenous injection, a maximal anti-FXa effect of 1.30 +/- 0.18 IU/ml was measured at 0.05 h and was not measurable after 12 h. After the subcutaneous injection of 30 and 60 mg, the maximal anti-FXa effect (0.34 +/- 0.08 IU/ml and 0.54 +/- 0.06 IU/ml) was reached after 2-4 h, and was not measurable after 12-18 h. The magnitude of this effect was dose-dependent and the absorption and elimination processes followed a first-order pattern for every dose and route. RO-11 showed a biological half-life of about 5 h and a high subcutaneous bioavailability (96%).

Effect of platelet glycoprotein IIb/IIIa integrin blockade on activated clotting time during percutaneous transluminal coronary angioplasty or directional atherectomy (the EPIC trial). Evaluation of c7E3 Fab in the Prevention of Ischemic Complications trial

The activated clotting time (ACT) has been used during percutaneous transluminal coronary angioplasty (PTCA) to monitor the extent of thrombin inhibition and anti-coagulation from heparin in an attempt to minimize untoward thrombotic events and hemorrhagic complications. With the introduction of potent platelet inhibitors, such as the chimeric monoclonal antibody c7E3, to interventional cardiology, the utility of measuring and regulating procedural ACT has not been examined. To investigate the possible influence of platelet IIb/IIIa antagonism on procedural ACT, we reviewed data from the Evaluation of c7E3 Fab in the Prevention of Ischemic Complications (EPIC) trial. In the EPIC trial, 2,099 patients undergoing PTCA with a high risk of abrupt vessel closure were randomized to receive placebo (n = 696) or the IIb/IIIa platelet receptor antagonist c7E3 Fab (n = 1,403). Despite receiving less procedural heparin, and fewer patients receiving very high heparin doses (> 14,000 U) than the placebo group, those receiving c7E3 had a higher mean (401 vs 367 seconds, p < 0.001) ACT when corrected for body weight. The ACT is increased approximately 35 seconds by the platelet IIb/IIIa receptor antagonist c7E3 Fab. This has important implications for dosing conjunctive heparin therapy and performing PTCA or directional coronary atherectomy in the setting of IIb/IIIa-directed therapy.

Activated clotting time as an appropriate test to compare heparin and direct thrombin inhibitors such as hirudin or Ro 46-6240 in experimental arterial thrombosis

BACKGROUND

Specific thrombin inhibitors are considered to be more potent antithrombotics than heparin. However, the relation between the systemic anticoagulation generated by thrombin inhibitors and their antithrombotic effect is not well defined. In a guinea pig carotid thrombosis model, the activated clotting time (ACT), the activated partial thromboplastin time (aPTT), and thrombin-generation tests were evaluated for their ability to predict the arterial antithrombotic effect of direct thrombin inhibitors such as hirudin and Ro 46-6240 compared with heparin.

METHODS AND RESULTS

Thrombosis of the carotid artery was induced by subendothelial damage in guinea pigs, and the subsequent cyclic flow variations were monitored. The effects of pretreatment with intravenous heparin, hirudin, and Ro 46-6240 were tested. After doubling the baseline aPTT, 1 IU.kg-1.min-1 heparin was inactive, whereas either hirudin or Ro 46-6240 (30 micrograms.kg-1.min-1) prevented thrombus formation by 80%. Heparin (10 IU.kg-1.min-1) induced the same antithrombotic effect but with indefinite aPTT prolongation. However, for similar prolongation of the ACT, the three compounds had equivalent antithrombotic effects. Thrombin generation was predictive of the antithrombotic effect of the thrombin inhibitors but not of heparin.

CONCLUSIONS

The arterial antithrombotic effect of direct thrombin inhibitors, when compared with those of heparin, should be evaluated by the ACT and not the aPTT or thrombin-generation assays. For a "therapeutic" aPTT prolongation, thrombin inhibitors induce higher systemic anticoagulation than does heparin and thus might unduly have higher bleeding liability.

Activation of blood coagulation by plaque rupture: mechanisms and prevention

Inhibition of thrombosis is proving to be an important treatment goal in many clinical situations, including coronary thrombolysis, angioplasty, and unstable angina. Heparin is a potent inhibitor of thrombin and thrombin generation, but its ability to accelerate thrombolysis, prevent acute reocclusion after vascular injury in angioplasty, and prevent myocardial infarction in unstable angina is relatively limited, possibly because clot-bound thrombin plays an important role in these clinical situations. Thus, when thrombin binds to fibrin, it remains enzymatically active and relatively impervious to inactivation by heparin or other fluid-phase inhibitors. However, direct thrombin inhibitors--such as D-Phe-L-Pro-L-Arg-CH2Cl (PPACK), hirudin, hirugen, and hirulog--inhibit free and clot-bound thrombin with equal efficacy, presumably because their sites of interaction are not masked when thrombin binds to fibrin. Advanced clinical trials suggest that the direct thrombin inhibitors and 7E3, an inhibitor of platelet glycoprotein IIb/IIIa, will soon be incorporated into the armamentarium against arterial thrombosis.

Do patients with the heparin-induced thrombocytopenia syndrome have heparin-specific antibodies?

PURPOSE

Patients with the heparin-induced thrombocytopenia syndrome (HIT) have heparin-associated antibodies (HAb+), which, in the presence of heparin, are responsible for platelet activation and aggregation. This study addressed the questions: (1) are the antibodies specific for heparin; and (2) how do the antibodies cause platelet aggregation?

METHODS

Plasmas from 79 patients with HIT were divided into seven plasma samples: HAb+ plasma sample 1 (24 pooled plasmas); HAb+ plasma sample 2 (50 pooled plasmas); and HAb+ plasma samples 3 through 7 (individual plasmas). Normal patient plasmas were used as controls (HAb-).

RESULTS

All seven HAb+ plasma samples caused platelet aggregation (PLA) in the presence of heparin and formed a precipitation line with heparin in gel immunodiffusion plates (HAb- plasmas did neither). The HAb+ plasma samples reacted with heparin, as determined by immunoprecipitation in sodium dodecylsulfate-polyacrylamide gel, with the production of a band at 50 kd (no band with HAb- plasmas). The plasma samples 1 and 2 were passed over heparin sepharose beads three times; the unabsorbed plasmas produced 3+ PLA, the first effluent produced 2+ PLA, and the second and third effluents produced no PLA. The heparin sepharose beads stained 3+, 2+, and 1+, after the respective passages, with fluorescein-labeled goat sera containing anti-human immunoglobulin G antibody. HAb+ plasma samples were digested with pepsin to separate the F(ab')2 fragments from the Fc fragments. The F(ab')2 fragments reacted with heparin as determined by immunoprecipitation in sodium dodecylsulfate-polyacrylamide gel with the production of a band at 25 kd, but did not cause PLA in the presence of heparin.

CONCLUSION

Patients with HIT have heparin-specific antibodies that react with heparin in a classic F(ab')2 reaction and require the Fc fragment for platelet aggregation.

Initial experience with hirudin and streptokinase in acute myocardial infarction: results of the Thrombolysis in Myocardial Infarction (TIMI) 6 trial

Hirudin is a potent, direct, and highly specific inhibitor of both free and clot-bound thrombin. Previous reports have shown hirudin to be superior to heparin when given with tissue plasminogen activator and aspirin for improving the incidence and rate of reperfusion as well as reducing reocclusion of infarct-related arteries. Patients with acute myocardial infarction were randomized to hirudin versus heparin in conjunction with streptokinase (1.5 x 10(6) U) and aspirin (325 mg/day). Study drug treatment was a 5-day infusion of either heparin, as a 5,000 U bolus, followed by a 1,000 U/hour infusion adjusted to a target activated partial thromboplastin time of 65 to 90 seconds (n = 71), or a constant infusion of hirudin at 1 of 3 doses (dose 1, n = 55: 0.15 mg/kg bolus + 0.05 mg/kg/hour infusion; dose 2, n = 31: 0.3 mg/kg bolus + 0.1 mg/kg/hour infusion; or dose 3, n = 36: 0.6 mg/kg bolus + 0.2 mg/kg/hour infusion). The incidence of major hemorrhage was similar between the heparin group (5.6%) and any of the hirudin dose groups (dose 1 = 5.5%, dose 2 = 6.5%, dose 3 = 5.6%). At hospital discharge the occurrence of death, nonfatal reinfarction, congestive heart failure, or cardiogenic shock was greater in patients receiving the lowest dose of hirudin (21.6%) than in those receiving the higher doses of hirudin (dose 2 = 9.7%, dose 3 = 11.4%).(ABSTRACT TRUNCATED AT 250 WORDS)

Enzymatic degradation of glycosaminoglycans

Glycosaminoglycans (GAGs) play an intricate role in the extracellular matrix (ECM), not only as soluble components and polyelectrolytes, but also by specific interactions with growth factors and other transient components of the ECM. Modifications of GAG chains, such as isomerization, sulfation, and acetylation, generate the chemical specificity of GAGs. GAGs can be depolymerized enzymatically either by eliminative cleavage with lyases (EC 4.2.2.-) or by hydrolytic cleavage with hydrolases (EC 3.2.1.-). Often, these enzymes are specific for residues in the polysaccharide chain with certain modifications. As such, the enzymes can serve as tools for studying the physiological effect of residue modifications and as models at the molecular level of protein-GAG recognition. This review examines the structure of the substrates, the properties of enzymatic degradation, and the enzyme substrate-interactions at a molecular level. The primary structure of several GAGs is organized macroscopically by segregation into alternating blocks of specific sulfation patterns and microscopically by formation of oligosaccharide sequences with specific binding functions. Among GAGs, considerable dermatan sulfate, heparin and heparan sulfate show conformational flexibility in solution. They elicit sequence-specific interactions with enzymes that degrade them, as well as with other proteins, however, the effect of conformational flexibility on protein-GAG interactions is not clear. Recent findings have established empirical rules of substrate specificity and elucidated molecular mechanisms of enzyme-substrate interactions for enzymes that degrade GAGs. Here we propose that local formation of polysaccharide secondary structure is determined by the immediate sequence environment within the GAG polymer, and that this secondary structure, in turn, governs the binding and catalytic interactions between proteins and GAGs.

Transient ischemic attack and minor ischemic stroke: an algorithm for evaluation and treatment. Mayo Clinic Division of Cerebrovascular Diseases

OBJECTIVE

To report a cost-effective and scientifically based algorithm for the clinical assessment and treatment of patients with transient ischemic attack (TIA) or minor ischemic stroke.

DESIGN

We comprehensively reviewed the literature on the epidemiologic features, assessment approaches, and treatment recommendations for ischemic cerebrovascular disease and developed an algorithm by using the available clinical and research data to support all decision-making steps.

MATERIAL AND METHODS

For patients with TIA or minor ischemic stroke, the appropriate setting for investigation (inpatient or outpatient), suggested diagnostic tests, use of anticoagulants and antiplatelet agents, and indications for surgical treatment are reviewed.

RESULTS

Although stroke is a common cause of death and lost productivity in the United States, the clinical assessment of patients with TIA or minor ischemic stroke has lacked consistency. The simplified algorithm clarifies patients who may be candidates for hospitalization and possible anticoagulation therapy. Initial diagnostic studies should include computed tomography of the head without use of a contrast agent, which quickly distinguishes nonhemorrhagic from hemorrhagic cerebrovascular disease. Evolving noninvasive studies of the cerebral vasculature are providing increasingly sensitive means of detecting stenoses, yet cerebral angiography remains the "gold standard." Treatment options depend on the pathophysiologic findings on diagnostic evaluation.

CONCLUSION

The assessment of patients with ischemic cerebrovascular disease is complex. The simplified algorithmic approach reported herein necessitates entry of appropriate patients into the algorithm. Because of clinical heterogeneity, an algorithm may apply to a wide spectrum of patients but will not cover every situation; hence, evaluation must be guided by a patient's unique history and findings on examination and by the physician's clinical experience.

Effects of heparin and N-acetyl heparin on ischemia/reperfusion-induced alterations in myocardial function in the rabbit isolated heart

Evidence is presented that heparin pretreatment produces protective effects on myocardial tissue distinct from its anticoagulant activity. The present study examines the ability of heparin sulfate and N-acetyl heparin (a derivative of heparin devoid of anticoagulant effects) to protect the heart from injury associated with global ischemia and reperfusion. Male New Zealand White rabbits were administered either heparin sulfate (n = 7, 300 U/kg i.v.), N-acetyl heparin (n = 6, 1.73 mg/kg i.v.), or vehicle (n = 6). Two hours after treatment, the hearts were removed, perfused on a Langendorff apparatus, and subjected to 30 minutes of global ischemia, followed by 45 minutes of reperfusion. During reperfusion, creatine kinase concentrations in the coronary sinus effluent were greater in hearts from vehicle-treated rabbits compared with hearts from N-acetyl heparin-treated and heparin-treated rabbits. Left ventricular end-diastolic pressure after 45 minutes of reperfusion in the vehicle-treated group was 64 +/- 15 mm Hg compared with 17 +/- 4 and 10 +/- 3 mm Hg in the heparin-pretreated and N-acetyl heparin-pretreated groups, respectively. Heparin, but not N-acetyl heparin, increased the activated partial thromboplastin time, consistent with its known anticoagulant action. Heparin and N-acetyl heparin inhibited complement-mediated erythrocyte lysis in a concentration-dependent manner. The glycosaminoglycans, in contrast to r-hirudin, reduced complement activation-induced injury in the rabbit isolated heart. The results demonstrate that heparin or N-acetyl heparin, administered to the intact rabbit, protects the isolated heart from subsequent myocardial dysfunction secondary to ischemia/reperfusion. The cardioprotective effects of heparin and N-acetyl heparin are independent of an antithrombin mechanism.

Bedside coagulation monitoring in heparin-treated patients with active thromboembolic disease: a coronary care unit experience

Patients with active venous and arterial thromboembolic disorders are known to benefit from systemic anticoagulation with heparin. Clinical studies have shown, however, that therapeutic anticoagulation is rarely achieved rapidly and often is not maintained over time. Prolonged laboratory turnaround time of the activated partial thromboplastin time (aPTT) may contribute directly to these common problems. A total of 272 aPTT determinations were performed on 120 heparin-treated patients admitted to the coronary care unit. The time from sample collection to data availability was 126 +/- 84 minutes with standard laboratory aPTT testing. In contrast, a bedside coagulation device provided an aPTT within 3 minutes (p < 0.001). Subtherapeutic aPTT values (< 65 seconds) were documented in 21% of all patients; in each, the heparin dose was changed and a repeat aPTT was required. In a separate study of 33 heparinized patients randomized to either bedside or central laboratory aPTT testing (264 aPTT determinations), the time to achieve a therapeutic state of systemic anticoagulation was 8.2 hours and 18.1 hours, respectively (p < 0.005). The time from aPTT determination to a decision regarding heparin titration adjustments was 14.5 minutes and 3 hours with bedside and laboratory testing, respectively (p < 0.001). Thus bedside coagulation monitoring provides a convenient, rapid, and accurate assessment of systemic anticoagulation among heparin-treated patients with active thromboembolic disease in the coronary care unit. This technology warrants further clinical investigation.

Hirudin in acute myocardial infarction. Safety report from the Thrombolysis and Thrombin Inhibition in Myocardial Infarction (TIMI) 9A Trial

BACKGROUND

The Thrombolysis and Thrombin Inhibition in Myocardial Infarction (TIMI) 9A trial compared the efficacy and safety of intravenous hirudin with heparin as adjunctive therapy to thrombolysis and aspirin in patients with acute myocardial infarction. The primary safety end point was the occurrence of major hemorrhage or anaphylaxis.

METHODS AND RESULTS

Based on experience in phase II trials, TIMI 9A used a hirudin bolus of 0.6 mg/kg followed by a fixed-dose 96-hour infusion of 0.2 mg/kg per hour. A modified weight-adjusted heparin regimen was used (5000-U bolus and infusion of 1000 U/h for patients < 80 kg or 1300 U/h for patients > or = 80 kg) with titration to a target activated partial thromboplastin time (aPTT) of 60 to 90 seconds. Because rates of hemorrhage in both treatment arms were higher than expected, randomization was suspended in TIMI 9A after 757 patients had been enrolled. Intracranial hemorrhage occurred in 1.7% of patients treated with hirudin and 1.9% of those treated with heparin (P = NS). Major spontaneous hemorrhage at a nonintracranial site occurred more frequently in hirudin--than in heparin-treated patients (7.0% versus 3.0%; P = .02), whereas major hemorrhage at instrumented sites was similar (5.2% in both hirudin and heparin groups). Patients who developed a major hemorrhage were older (P < .001) and had higher aPTT values, especially in the first 12 hours after thrombolysis (P = .001).

CONCLUSIONS

The rate of major spontaneous hemorrhage for both heparin and hirudin in TIMI 9A was higher than that seen in TIMI 5, TIMI 6, and GUSTO 1. This was possibly a result of high levels of anticoagulation at the doses of heparin and hirudin used, low previous estimates of the hemorrhage risk at the doses of hirudin used in TIMI 9A due to the relatively small number of patients receiving that dose in earlier studies, and enrollment of patients at higher risk of hemorrhage. Because a prolonged aPTT was associated with an increased risk of major hemorrhage in both heparin- and hirudin-treated patients, it now appears important to monitor aPTT on a regular basis when using either antithrombin to identify those patients who require downward adjustment of the infusion. TIMI 9B has therefore been configured with a lower hirudin bolus (0.1 mg/kg) and infusion (0.1 mg/kg per hour) and lower heparin infusion (1000 U/h without weight adjustment). Infusions of both antithrombins will be titrated to a target aPTT of 55 to 85 seconds.

In vitro model to test the thrombogenicity of coronary stents

Thrombotic occlusion is a major complication limiting the application of stents in coronary arteries. In an in vitro model we investigated the thrombogenicity of different stent materials and several medical regimens to prevent thrombotic occlusion. Experiments were conducted in a closed system of silicon tubing with circulating citrated platelet rich plasma of healthy volunteers (n = 7) and of patients (n = 7 for each condition). Patients were either treated with phenprocoumon or with high or low dose heparin in combination with aspirin alone (100 mg) or aspirin (990 mg) plus dipyridamole (225 mg). After placement of tantalum wire stents into the system platelet aggregates were visible after 13.5 +/- 3.0 min, and occlusion occurred after 15.0 +/- 3.5 min. Similarly, with implanted stainless steel stents aggregation was seen after 13.0 +/- 3.5 min and thrombosis occurred after 14.5 +/- 3.5 min (p < 0.001 vs control without stent). Microscopic examination revealed combined platelet fibrin thrombi occluding the lumen. Platelet components predominately covered stent wires, particularly at crossing points. In all experiments high-dose heparin prevented platelet aggregate formation and stent occlusion independently of additional aspirin or aspirin plus dipyridamole; perfusion time > 60 min (p < 0.001 vs no heparin). Low-dose heparin could not prevent clotting. With aspirin alone aggregates were visible after 16.0 +/- 4.0 min and clotting occurred after 23.0 +/- 5.0 min. In combination with dipyridamole aggregates were visible after 15.5 +/- 5.0 min and clotting after 21.0 +/- 4.0 min (NS vs aspirin alone). Phenprocoumon prevented platelet aggregate formation and stent occlusion; perfusion time > 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct thrombin inhibitors in cardiovascular medicine

Currently used antithrombotics such as heparin have a number of potential limitations that may be overcome by the new class of agents that directly inhibit thrombin. These agents variously block the active catalytic and/or the anion binding exosites of the thrombin molecule and are potent and specific inhibitors of thrombin's many biological actions, as demonstrated by in vitro and animal models of thrombosis. Preliminary data indicate that the direct antithrombins are safe and efficacious in humans, and their use in acute coronary syndromes and coronary angioplasty in place of heparin has yielded promising early results. Phase III trials in these clinical settings are currently under way. Newer antithrombotics that inhibit thrombin generation and thrombin activity at various strategic points within the coagulation cascade are also in the early stages of development.

Activated clotting-time variability in patients undergoing coronary angioplasty

Although the activated clotting time (ACT) is commonly used to assess adequacy of anticoagulation during percutaneous transluminal coronary angioplasty (PTCA), there is uncertainty whether measurements on samples from the arterial and venous circulations are directly comparable. We performed ACT determinations on 115 patients undergoing PTCA at our institution. Blood samples were drawn in a sequential fashion from the arterial and femoral venous sheaths at the conclusion of each case, and ACT determination were performed in the catheterization laboratory immediately thereafter. The venous ACT exceeded the arterial value in 63 patients (55%), and was identical in only 2 instances. The arterial and venous ACT differed by more than 100 s in 10 patients. In 23 patients (20%) one ACT determination was > or = 300 s, while the value from the other circulation was < 300 s. We conclude that there is substantial variability between arterial and venous ACT determinations in heparinized patients undergoing PTCA.

Anticoagulation and hemostasis in cardiac surgical patients

Optimizing anticoagulation and hemostasis during cardiopulmonary bypass and perioperatively helps to ensure the best possible clinical outcome. This article reviews the pharmacology of unfractionated and low-molecular weight heparin, aprotinin, desmopressin, dextran, antiplatelet agents, warfarin, and direct thrombin inhibitors. Their use is discussed in the context of coronary artery surgery, valvular surgery, and mechanical cardiac support devices, as well as in the management of acute ischemic syndromes, atrial fibrillation, and prevention and treatment of venous thromboembolism. Progress in the development and utilization of these anticoagulants and antiplatelet agents has supported the major advances that have been achieved in cardiac surgery.

Monitoring anticoagulation following intracoronary procedures: which method?

We have assessed bedside kits for monitoring the activated partial thromboplastin time and the activated clotting time by comparing them with laboratory activated partial thromboplastin time values. To determine the accuracy of anticoagulation we have concurrently measured the plasma heparin concentrations, and plasma prothrombin fragment F1 + 2 concentrations. Serial samples were taken from patients undergoing elective percutaneous transluminal coronary angioplasty (n = 14). Readings were taken pre-procedure, 30 min after administration of a heparin bolus (10,000 U) and 1, 2 and 3 h after commencement of a constant heparin infusion (15 U/kg/h) postprocedure. Activated partial thromboplastin time results obtained with the bedside kit compared reliably with laboratory values (r = 0.8), were rapidly available and were reflected by appropriate changes in prothrombin fragment F1 + 2 and heparin concentrations. However, the relationship between activated partial thromboplastin time values and activated clotting time was less precise (r = 0.59). Therefore, for routine and frequent monitoring of anticoagulation with heparin, a bedside activated partial thromboplastin time kit provides adequate control of therapy but in instances were particularly tight control of anticoagulation is required, use of prothrombin fragment F1 + 2 concentrations may be more appropriate.