Management of heparin therapy: Controlled prospective trial

Clinical Studies with Anticoagulants that Have Changed Clinical Practice

Anticoagulant therapy is the cornerstone of treatment and prevention of arterial and venous thromboembolism. Taking a historical perspective, starting in the 1960s, and progressing through to 2022, we discuss key clinical trials of anticoagulants that have changed clinical practice, and examine obstacles encountered in bringing these anticoagulants to the clinic. The design of some of the early studies that shaped clinical practice was poor by current standards, but their results were influential because nothing better was available. Both heparin and vitamin K antagonists had been in clinical use for several decades before well-designed trials in the 1980s optimized their dosing and enhanced their safety and efficacy. Low-molecular-weight heparin then replaced unfractionated heparin because it had a more predictable dose-response and a longer half-life, thereby allowing it to be used conveniently in out-of-hospital settings. More recently, direct oral anticoagulants became the oral anticoagulants of choice for most indications because they were shown to be at least as safe and effective as vitamin K antagonists when used in fixed doses without the need for laboratory monitoring. The design of the trials that led to the approval of the direct oral anticoagulants was excellent, but further studies are required to optimize their dosing in selected patients who were underrepresented in these trials.

Fifty years of research on antithrombotic therapy: Achievements and disappointments

The achievements with antithrombotic therapy over the past 50 years have been monumental and the disappointments relatively few. In this review, we will discuss, chronologically, the major developments of the two recognized classes of antithrombotics - anticoagulants and antiplatelet agents.

Administration of Heparin by Continuous Intravenous Infusion in the Treatment of Deep Venous Thrombosis

In this prospective study the authors compared two approaches to heparin therapy, in the treatment of deep venous thrombosis—continuous infusion heparin and intermittent heparin therapy.

Each group was comparable with respect to age, gender, risk factors, and etiologic factors. The continuous infusion group (n=60) received a heparin bolus of 150 U/kg followed by continuous intravenous infusion of 750 U/kg/twenty-four hours. The intermittent group (n=60) received a bolus of 5000 U in every four hour period. In the infusion therapy group, the resolution of clinical symptoms was more rapid, so the hospitalization time was shorter, and the hemorrhagic complications and relapses were fewer than with intermittent therapy.

The authors conclude that administration of heparin by continuous infusion appears to be effective and safer than intermittent injection therapy.

State-of-the-Art Review: The Preclinical and Clinical Pharmacology of Novastan (Argatroban): A Small-Molecule, Direct Thrombin Inhibitor

Because of the unsatisfactory options available for safe and effective antithrombotic therapy, recent, intense research and development efforts have been focused on direct thrombin inhibitors, also known as site-directed thrombin inhibitors. The intravenous agent Novastan (argatroban) is a small-molecule, reversible, direct thrombin inhibitor that is selective for the catalytic site of the thrombin molecule. Argatroban's molecular properties (small molecule; fast, selective, and reversible inhibition of the thrombin catalytic site; and similar in vitro potency for inhibiting both clot-bound and soluble thrombin) offer the potential for significant antithrombotic efficacy with minimal systemic anticoagulant ef fects. Its clinical pharmacologic properties offer the potential for minimal risk of bleeding, very rapid achievement of therapeutic antithrombotic efficacy, predictable dose-response, and rapid restoration of the hemostatic systems to normal upon termination of intravenous infusion. Argatroban is currently approved for clinical use in Japan for the treatment of peripheral arterial occlusive disease. It is in advanced clinical development in North America, South America, and Western Europe for several clinical indications, including (1) adjunctive therapy to thrombolytic agents in the treatment of acute myocardial infarction and (2) antithrombotic therapy for patients with heparin-induced thrombocytopenia and heparin-induced thrombocytopenia and thrombosis syndrome. Key Words: Molecular properties—Novastan (argatroban)—Pharmacology—Thrombin inhibitor.

The Treatment of Proximal Vein Thrombosis with Subcutaneous Low-Mole Molecular-Weight Heparin Compared with Continuous Intravenous Heparin

Low-molecular-weight heparin, compared with unfractionated heparin, has a higher bioavailability and a more prolonged half-life. There are limited data comparing the use of low-molecular-weight heparin with unfractionated heparin for the treatment of deep vein thrombosis. We have compared fixed-dose, subcutaneous low-molecular-weight heparin given once daily with adjusted-dose intravenous heparin given by continuous infusion in a multicenter double-blind clinical trial for the initial treatment of patients with proximal vein thrombosis. Clinical outcomes were objectively documented. Six of 213 patients receiving low-molecular-weight heparin (2.8%) and 15 of 219 patients receiving intravenous heparin (6.9%) developed new episodes of venous thromboembolism (p = 0.07; 95% confidence interval for the difference, 0.02%-8.1%). During initial therapy, major bleeding occurred in one patient receiving low-molecular-weight heparin (0.5%) and in 11 patients receiving intravenous heparin (5.0%), a risk reduction of 91% (p = 0.006). This apparent protection against major bleeding was lost during long-term therapy. Minor bleeding complications were rare. During the period of the study, 10 patients receiving low-molecular-weight heparin (4.7%) died, as compared with 21 patients receiving intravenous heparin (9.6%), a risk reduction of 51%(p = 0.049). This study shows that low-molecular-weight heparin is at least as effective as classic intravenous heparin therapy and that there was a reduction in deaths and bleeding complications. Furthermore, low-molecular-weight heparin was more convenient to administer. The simplified therapy with low-molecular-weight heparin given by once-daily subcutaneous injection without monitoring may allow patients with uncomplicated proximal deep vein thrombosis to be cared for as outpatients. Key Words: Low-molecular-weight heparin—Unfractionated heparin—Deep vein thrombosis—Deaths—Bleeding complications.

Clinical Experience with Superior Vena Caval Greenfield Filters

Purpose:

To evaluate the results of superior vena caval (SVC) Greenfield filters in patients at risk for pulmonary embolism (PE) secondary to upper extremity deep venous thrombosis (UEDVT).

Methods:

Over a 46-month period, 26 patients (10 men, mean age 67 years, range 25 to 89) with UEDVT in whom anticoagulation was contraindicated (n = 22) or ineffective in preventing recurrent PE or extension of the thrombus (n = 4) were treated with placement of SVC Greenfield filters.

Results:

One SVC filter was misplaced into the innominate vein but left in place; this vein remains patent after 2 months without evidence of filter migration. Follow-up ranged from 10 days to 46 months (mean 7.8 months). Fifteen (58%) patients died inhospital of causes unrelated to the SVC filter or recurrent thromboembolism (mean time to death 36 days). Of the 11 survivors, follow-up ranged from 1 to 38 months (mean 22). Sequential chest roentgenograms in 9 (82%) patients revealed no filter migration or displacement. No evidence of PE was found in any of the survivors over the course of follow-up.

Conclusions:

Insertion of SVC Greenfield filters is a safe and feasible therapy to prevent recurrent thromboembolism in patients with UEDVT who are refractory to or inappropriate for anticoagulation therapy.

Experimental Thromboprophylaxis with Low Molecular Weight Heparin After Microsurgical Revascularization

There is great variability among microsurgeons as regards the use of prophylactic anticoagulant after revascularization and this is probably due to lack of comparative data. Also, there has been much debate regarding the benefit of anti-thrombotic therapies versus the risk of complications such as systemic bleeding and hematoma formation. To evaluate the effectiveness of postoperative low molecular weight heparin (LMWH) as a prophylactic anticoagulant therapy after microsurgical repair of the femoral artery and vein in rats. Randomized, blinded study. The femoral artery and vein of 40 Sprague Dawley rats were sectioned and repaired with microsurgical sutures under general anesthesia. They were randomly divided into 2 groups: Group (A) in which the 20 rats were injected with Enoxaparin subcutaneously at a dose 1.5 mg/kg once daily for 3 successive days; Group (B), the control group, in which 20 rats were injected with isotonic sodium chloride 0.9 % subcutaneously in a blinded fashion. After 7 days, the femoral vessels were re-explored and patency of the femoral vessels was assessed with empty-and-refill test. There were a total of 12 vascular thrombosis among 74 microsurgical repair in both groups with percentage of 16.22 % including, 5 arterial anastomosis and 7 venous anastomosis. The incidence of thrombosis in the treatment group (A) was 18.4 % while the incidence of thrombosis in the control group (B) was 13.8 %. This difference was not statistically significant using Fisher exact test. Postoperative administration of LMWH did not provide the desired protection against thrombosis after microsurgical vascular repair.

Spontaneous hemarthrosis following fibrinolytic therapy for acute myocardial infarction: a case report and literature review

Background Despite the widespread use of fibrinolytic therapy and the numerous reports on its bleeding complications, spontaneous hemarthrosis following fibrinolytic therapy is quite rare. Case Report We describe in this report a patient with no previous history of articular disease who developed a spontaneous right knee bloody effusion following fibrinolytic therapy using rt-PA for acute ST-elevation myocardial infarction. Furthermore, we provide a review of all cases of spontaneous hemarthrosis documented so far in the literature. Conclusions Several pre-existing joint diseases may predispose to hemarthrosis following fibrinolytic therapy, even in patients who deny previous or current articular disorders. Therefore, hemorrhage should be considered in the differential diagnosis of mono-arthritis following fibrinolytic therapy for STEMI.

The prevention and treatment of venous thromboembolism with LMWHs and new anticoagulants

As the risk factors for thrombosis are becoming better understood, so is the need for anticoagulation. The inherent difficulties with warfarin are such that a low-molecular-weight heparin (LMWH) is often the key therapeutic. However, there are several different species of LMWH available to the practitioner, which leads to the need for an objective guide. New agents are coming onto the marketplace, and these may supersede both warfarin and the heparins. The current report will review the biochemistry and pharmacology of different LWMHs and identify which are more suitable for the different presentations of venous thromboembolism. It will conclude with a brief synopsis of new agents which may supersede warfarin and heparin.

Heparin treatment of deep venous thrombosis in 280 patients: symptoms related to dosage

280 patients with phlebographically proven deep venous thrombosis received intravenous heparin infusion, mean duration 6.8 days, mean dose 370 U/kg/day. In 58 patients (21%) there was no apparent predisposing factor. Leg pain diminished more rapidly than edema. At discharge, 46% had edema. Symptoms suggesting pulmonary embolism (PE) occurred in 13 patients (4.6%) whose mean daily heparin dose was similar to that of the others. The only fatal PE occurred three days after cessation of heparin administration. Eight patients (3%) experienced major bleeding, the only fatal occurring after thoracocentesis. The frequency of major bleeding in patients above 70 years was 8% in females and 4% in males, in those below 70 years it was 0.5%; 22 patients (8%) had minor bleeding. Control phlebography after one week revealed completely cleared thrombus in 3%, partial clearance in 36%, unchanged in 39% and increased thrombosis in 22%. Dosage was significantly correlated to thrombus resolution.

Isolation and characterization of a heparin with low antithrombin activity from the body of Styela plicata (Chordata-Tunicata). Distinct effects on venous and arterial models of thrombosis

INTRODUCTION

A heparin preparation with low antithrombin activity and different disaccharide composition than mammalian heparin was isolated from the body of the ascidian Styela plicata (Chordata-Tunicata). The disaccharide composition and the effect of the invertebrate glycan on venous and arterial models of thrombosis was investigated.

METHODS AND RESULTS

High performance liquid chromatography of the products formed by a mixture of heparin lyases showed that the ascidian heparin is composed mainly by delta UA(2SO4)-1-->4-beta-d-GlcN(SO4) (47.5%), delta UA(2SO4)-1-->4-beta-d-GlcN(SO4)(6SO4) (38.3%) disaccharides and smaller amounts of the disaccharides delta UA(2SO4)-1-->4-beta-d-GlcN(SO4)(3SO4)(6SO4) (2.8%) and delta UA(2SO4)-1-->4-beta-d-GlcN(SO4)(3SO4) (8.0%). The invertebrate heparin has an aPTT activity of 18 IU/mg and an antithrombin-mediated antithrombin and anti-factor Xa activities 10-fold lower than that of mammalian heparin. In a venous model of thrombosis in the vena cava, S. plicata heparin inhibits only 80% of thrombosis at a dose 10-fold higher than that of the mammalian heparin that inhibits 100% of thrombosis. However, in an arterio-shunt model of arterial thrombosis, both S. plicata and mammalian heparin possess equivalent antithrombotic activities. It is also shown that at equivalent doses, ascidian heparin has a lower bleeding effect than mammalian heparin.

CONCLUSION

The antithrombin-mediated anticoagulant activity of heparin polymers is not directly related to antithrombotic potency in the arterio-venous shunt. The results of the present work suggest that heparin preparations obtained from the body of S. plicata may have a safer therapeutic action in the treatment of arterial thrombosis than mammalian heparin.

Does repeat duplex ultrasound for lower extremity deep vein thrombosis influence patient management?

The clinical significance of lower extremity deep vein thrombus (DVT) propagation in the setting of anticoagulation therapy remains unclear. The purpose of this study is to compare results of thrombus outcome found with repeat duplex ultrasonography to the incidence of pulmonary embolism and mortality. During a recent 18-month period, 457 patients were diagnosed with lower extremity DVT with duplex ultrasonography and their data were retrospectively analyzed. Repeat examinations were available for review in 118 patients (51 men, 67 women). Results of repeat duplex exams were divided into 4 groups: resolved, improved, unchanged, or extended proximally. All patients received heparin and warfarin therapy. Ventilation-perfusion (V/ Q) scans were obtained only for signs and symptoms of pulmonary embolism (n=30). Mortality, the prevalence of high-probability V/ Q scans, frequency of intracaval filter insertion, gender, mean age, mean prothrombin time (PT), mean partial thromboplastin time (PTT), mean number of repeat ultrasounds per patient, and mean time over which the repeat ultrasounds took place were compared among the 4 groups. Patients who had proximal extension of DVT (19%) on repeat duplex ultrasound had an increased prevalence of pulmonary embolism (p<0.05). Also, patients whose DVT resolved were younger (p<0.05). There was no difference among the 4 groups in mortality, placement of Greenfield filters, mean PT, mean PTT, mean number of ultrasound exams per patient, or mean follow-up time over which the exams took place. Proximal extension of DVT documented by repeat duplex ultrasound is a significant risk factor for pulmonary embolism. Repeat duplex ultrasound can identify a group of patients who may benefit from insertion of an intracaval filter device.

Unfractionated Heparin, Low Molecular Weight Heparins, and Pentasaccharide: Basic Mechanism of Actions, Pharmacology, and Clinical Use

During the past decade, a large number of new anticoagulant and antithrombotic drugs have been developed. These agents represent a wide variety of substances that are derived using natural sources, biotechnology-based methods, and synthetic approaches. Because of the structural and molecular characteristics, these agents exhibit physicochemical and functional diversities. Thus, each of these classes of drugs controls thrombogenesis by way of distinct mechanisms. The main classes of these new drugs include peptides, peptidomimetics, heparinomimetics, and recombinant proteins. Despite these significant developments, heparin and heparin-derived drugs have continued to play a major role in the management of thrombotic and cardiovascular disorders.

Antithrombotic therapy for venous thromboembolic disease: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This chapter about antithrombotic therapy for venous thromboembolic disease is part of the seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patients' values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this chapter are the following: for patients with objectively confirmed deep vein thrombosis (DVT), we recommend short-term treatment with subcutaneous (SC) low molecular weight heparin (LMWH) or, alternatively, IV unfractionated heparin (UFH) [both Grade 1A]. For patients with a high clinical suspicion of DVT, we recommend treatment with anticoagulants while awaiting the outcome of diagnostic tests (Grade 1C+). In acute DVT, we recommend initial treatment with LMWH or UFH for at least 5 days (Grade 1C), initiation of vitamin K antagonist (VKA) together with LMWH or UFH on the first treatment day, and discontinuation of heparin when the international normalized ratio (INR) is stable and > 2.0 (Grade 1A). For the duration and intensity of treatment for acute DVT of the leg, the recommendations include the following: for patients with a first episode of DVT secondary to a transient (reversible) risk factor, we recommend long-term treatment with a VKA for 3 months over treatment for shorter periods (Grade 1A). For patients with a first episode of idiopathic DVT, we recommend treatment with a VKA for at least 6 to 12 months (Grade 1A). We recommend that the dose of VKA be adjusted to maintain a target INR of 2.5 (INR range, 2.0 to 3.0) for all treatment durations (Grade 1A). We recommend against high-intensity VKA therapy (INR range, 3.1 to 4.0) [Grade 1A] and against low-intensity therapy (INR range, 1.5 to 1.9) compared to INR range of 2.0 to 3.0 (Grade 1A). For the prevention of the postthrombotic syndrome, we recommend the use of an elastic compression stocking (Grade 1A). For patients with objectively confirmed nonmassive PE, we recommend acute treatment with SC LMWH or, alternatively, IV UFH (both Grade 1A). For most patients with pulmonary embolism (PE), we recommend clinicians not use systemic thrombolytic therapy (Grade 1A). For the duration and intensity of treatment for PE, the recommendations are similar to those for DVT.

Hemorrhagic Complications of Anticoagulant Treatment

This chapter about hemorrhagic complications of anticoagulant treatment is part of the seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Bleeding is the major complication of anticoagulant therapy. The criteria for defining the severity of bleeding varies considerably between studies, accounting in part for the variation in the rates of bleeding reported. The major determinants of vitamin K antagonist-induced bleeding are the intensity of the anticoagulant effect, underlying patient characteristics, and the length of therapy. There is good evidence that vitamin K antagonist therapy, targeted international normalized ratio (INR) of 2.5 (range, 2.0 to 3.0), is associated with a lower risk of bleeding than therapy targeted at an INR > 3.0. The risk of bleeding associated with IV unfractionated heparin (UFH) in patients with acute venous thromboembolism (VTE) is < 3% in recent trials. This bleeding risk may increase with increasing heparin dosages and age (> 70 years). Low molecular weight heparin (LMWH) is associated with less major bleeding compared with UFH in acute VTE. UFH and LMWH are not associated with an increase in major bleeding in ischemic coronary syndromes, but are associated with an increase in major bleeding in ischemic stroke. Information on bleeding associated with the newer generation of antithrombotic agents has begun to emerge. In terms of treatment decision making for anticoagulant therapy, bleeding risk cannot be considered alone, ie, the potential decrease in thromboembolism must be balanced against the potential increased bleeding risk.

Prolonged bleeding time induced by anticoagulant glycosaminoglycans in dogs is associated with the inhibition of thrombin-induced platelet aggregation

INTRODUCTION

The clinical use of unfractionated heparin (UFH) is complicated by hemorrhage. This has led to a search for safer alternatives, one of which, the recently identified depolymerized holothurian glycosaminoglycan (DHG), causes less bleeding and exhibits a better antithrombotic-hemorrhagic ratio in rats and dogs than UFH and low-molecular-weight heparin (LMWH). In contrast to UFH and LMWH, which exert their anticoagulant effects by inhibiting thrombin in the presence of antithrombin III (AT), DHG exerts its anticoagulant effect by inhibiting the intrinsic factor Xase complex and thrombin in the presence of heparin cofactor II (HCII).

MATERIALS AND METHODS

The hemorrhagic effect of DHG was compared with those of UFH and LMWH in healthy dogs, and the mechanism responsible for prolonging bleeding time was examined both in dogs and with human platelets.

RESULTS

DHG prolonged template-bleeding time in dogs less than UFH and LMWH do. Although the maximum noneffective concentrations of each glycosaminoglycan (GAG) that prolong the bleeding time are almost the same as the concentrations that inhibit thrombin-induced platelet aggregation, they are not related to those that inhibit ADP-induced platelet aggregation. Results of experiments on gel-filtered platelets from humans indicate that the inhibition of thrombin-induced platelet aggregation caused by UFH and LMWH in the presence of AT is more prominent than that caused by DHG with HCII.

CONCLUSIONS

These results suggest that the prolongation of bleeding time caused by GAGs are associated with the inhibition of thrombin-induced platelet aggregation, and DHG may cause less bleeding than UFH and LMWH because of its different thrombin inhibition mechanism in platelet-rich plasma (PRP).

Heparin-induced thrombocytopenia, paradoxical thromboembolism, and other adverse effects of heparin-type therapy

This article discusses the common and uncommon side effects of heparin and heparin-like therapy. Most attention is devoted to heparin-induced thrombocytopenia, as it is the most clinically aggressive adverse reaction. Additionally, less common and several newly reported side effects are discussed.

The effect of subcutaneously administered low-molecular-weight heparin on microarterial thrombosis in the rat

OBJECTIVE

To examine the effect of administration of a low-molecular-weight heparin derivative, enoxaparin, on the rate of arterial thrombosis in a rat model.

STUDY DESIGN

Prospective, randomized, blinded study.

METHODS

A standard microarterial anastomosis tuck injury was created in both femoral arteries of 25 Long Evans retired breeder rats. Thirteen animals received a subcutaneous injection of 50 IU/kg of enoxaparin 2 hours before the procedure, while 12 control animals received vehicle (isotonic sodium chloride solution) alone. Sites of injury/repair were assessed 2 hours after the procedure for anastomotic patency or thrombosis.

RESULTS

Six (23%) of 26 vessels in the drug-treated group developed an arterial thrombosis at the site of repair, while 6 (25%) of 24 vessels in the control group developed thrombosis. There was no statistically significant difference at the 95% confidence limit between the 2 groups based on a comparison-of-proportions test.

CONCLUSION

The preoperative subcutaneous administration of 50 IU/kg of enoxaparin did not alter the rate of arterial thrombosis following the creation of a thrombogenic tuck injury/repair of the rat femoral artery.

The effects of danaparoid, dalteparin and heparin on tissue factor-induced experimental disseminated intravascular coagulation and bleeding time in the rat

Danaparoid and heparin, on the basis of anti-activated factor X (anti-FXa) activity, were equipotent in accelerating the rate of interaction of FXa and antithrombin III. In rat tissue factor-induced disseminated intravascular coagulation (DIC) models, an intravenous administration of danaparoid inhibited the decrease in plasma fibrinogen and platelet counts and the increase in serum fibrinogen degradation products. Expressed on the basis of anti-FXa activity, these effects were comparable with those of dalteparin and heparin. In rat mesenteric small artery and vein, less bleeding was observed after intravenous administration of danaparoid than after dalteparin or heparin. Danaparoid did not affect adenosine diphosphate- or collagen-induced platelet aggregation, and showed weaker inhibitory effects on aggregation induced by thrombin, or collagen + thrombin, than did dalteparin or heparin. These findings suggest that danaparoid may be useful for the prevention of DIC and has less tendency to cause bleeding than dalteparin or heparin, probably as a result of its weaker ability to inhibit platelet aggregation.

Effects of a low-molecular-weight heparin on thrombus regression and recurrent thromboembolism in patients with deep-vein thrombosis

BACKGROUND

Low-molecular-weight heparins are frequently used to treat venous thromboembolism, but optimal dosing regimens and clinical outcomes need further definition.

METHODS

In this multicenter, open-label study with blinded adjudication of end points, we randomly assigned patients with acute deep-vein thrombosis to one of three treatment regimens: intravenous administration of unfractionated heparin; subcutaneous administration of a low-molecular-weight heparin, reviparin, twice a day for one week; or subcutaneous administration of reviparin once a day for four weeks. The primary end point was evidence of regression of the thrombus on venography on day 21; secondary end points were recurrent venous thromboembolism, major bleeding within 90 days after enrollment, and death.

RESULTS

Of the patients receiving unfractionated heparin, 40.2 percent (129 of 321) had thrombus regression, as compared with 53.4 percent (175 of 328) of patients receiving reviparin twice daily and 53.5 percent (167 of 312) of the patients receiving reviparin once daily. With regard to thrombus regression, reviparin administered twice daily was significantly more effective than unfractionated heparin (relative likelihood of thrombus regression, 1.28; 97.5 percent confidence interval, 1.08 to 1.52), as was reviparin administered once daily (relative likelihood, 1.29; 97.5 percent confidence interval, 1.08 to 1.53). Mortality and the frequency of episodes of major bleeding were similar in the three groups.

CONCLUSIONS

In acute deep-vein thrombosis, reviparin regimens are more effective than unfractionated heparin in reducing the size of the thrombus. Reviparin is also more effective than unfractionated heparin for the prevention of recurrent thromboembolism and equally safe.

Hemorrhagic complications of oral anticoagulant therapy

Hemorrhage is the major complication of anticoagulant therapy. The criteria for classifying the severity of bleeding has varied between studies, which has resulted in variability in the rate of bleeding reported in the literature. The major determinants of oral anticoagulant-related bleeding are the intensity of the anticoagulant effect, baseline patient characteristics, and the length of therapy. Older patients have characteristics that may place them at higher risk for anticoagulant-related bleeding, but they also have characteristics that make them more likely to benefit. The risk for anticoagulant-related bleeding cannot be considered in isolation and the potential benefits need to be weighed carefully in each individual patient, irregardless of age.

Hemorrhagic complications of anticoagulant treatment

Bleeding is the major complication of anticoagulant therapy. The criteria for defining the severity of bleeding varied considerably between studies, accounting in part for the variation in the rates of bleeding reported. Since the last review, there have been several meta-analyses published on the rates of major bleeding in trials of anticoagulants for atrial fibrillation and ischemic heart disease. The major determinants of oral anticoagulant-induced bleeding are the intensity of the anticoagulant effect, underlying patient characteristics, and the length of therapy. There is good evidence that low-intensity oral anticoagulant therapy (targeted INR of 2.5; range, 2.0 to 3.0) is associated with a lower risk of bleeding than therapy targeted at a higher intensity. Lower-intensity regimens (INR < 2.0) are associated with an even smaller increase in major bleeding. In terms of treatment decision making for anticoagulant therapy, bleeding risk cannot be considered alone, ie, the potential decrease in thromboembolism must be balanced against the potential increased bleeding risk. The risk of bleeding associated with IV heparin in patients with acute venous thromboembolism is < 3% in recent trials. There is some evidence to suggest that this bleeding risk increases with the heparin dosage and age (> 70 years). LMW heparin is not associated with increased major bleeding compared with standard heparin in acute venous thromboembolism. Standard heparin and LMW heparin are not associated with an increase in major bleeding in ischemic coronary syndromes, but are associated with an increase in major bleeding in ischemic stroke.

Management of heparin therapy in the high-risk, chronically anticoagulated, oral surgery patient: a review and a proposed nomogram

PURPOSE

This study analyzes the use of a standard nomogram that can help reduce the level of anticoagulation preoperatively to effectively manage perioperative heparin therapy in chronically anticoagulated oral surgery patients who are at high risk for thromboembolism.

PATIENTS AND METHODS

Twenty patients with significant cardiovascular disease, ranging in age from 56 to 79 years and requiring oral surgery, were randomly divided into 2 groups. All patients were on chronic warfarin therapy, and perioperative heparinization was recommended by their cardiologist. Group A (n = 10) had their anticoagulation therapy managed with the use of a standard nomogram. The heparin therapy for group B (n = 10) was managed without the use of the nomogram. The records of all patients were analyzed for therapeutic efficacy of heparinization, number of laboratory tests required, duration of hospitalization, and complications related to heparinization.

RESULTS

Patients in group A did significantly better in all parameters when compared with group B patients. There were no complications in group A, whereas there was a 20% incidence of complications related to anticoagulation therapy in group B.

CONCLUSIONS

The use of a standard nomogram to manage anticoagulation therapy in the oral surgery patient requiring heparinization is strongly recommended. This provides optimal therapeutic benefit, decreases the incidence of complications, and makes the hospitalization less costly and more comfortable for the patient.

Clinical experience with superior vena caval Greenfield filters

PURPOSE

To evaluate the results of superior vena caval (SVC) Greenfield filters in patients at risk for pulmonary embolism (PE) secondary to upper extremity deep venous thrombosis (UEDVT).

METHODS

Over a 46-month period, 26 patients (10 men, mean age 67 years, range 25 to 89) with UEDVT in whom anticoagulation was contraindicated (n = 22) or ineffective in preventing recurrent PE or extension of the thrombus (n = 4) were treated with placement of SVC Greenfield filters.

RESULTS

One SVC filter was misplaced into the innominate vein but left in place; this vein remains patent after 2 months without evidence of filter migration. Follow-up ranged from 10 days to 46 months (mean 7.8 months). Fifteen (58%) patients died inhospital of causes unrelated to the SVC filter or recurrent thromboembolism (mean time to death 36 days). Of the 11 survivors, follow-up ranged from 1 to 38 months (mean 22). Sequential chest roentgenograms in 9 (82%) patients revealed no filter migration or displacement. No evidence of PE was found in any of the survivors over the course of follow-up.

CONCLUSIONS

Insertion of SVC Greenfield filters is a safe and feasible therapy to prevent recurrent thromboembolism in patients with UEDVT who are refractory to or inappropriate for anticoagulation therapy.

Clinical aspects of heparin-induced thrombocytopenia and thrombosis and other side effects of heparin therapy

Heparin, first used to prevent the clotting of blood in vitro, has been clinically used to treat thrombosis for more than 50 years. Although several new anticoagulant drugs are in development, heparin remains the anticoagulant of choice to treat acute thrombotic episodes. The clinical effects of heparin are meritorious, but side effects do exist. Bleeding is the primary untoward effect of heparin. Major bleeding is of primary concern in patients receiving heparin therapy. However, additional important untoward effects of heparin therapy include heparin-induced thrombocytopenia, heparin-associated osteoporosis, eosinophilia, skin reactions, allergic reactions other than thrombocytopenia, alopecia, transaminasemia, hyperkalemia, hypoaldosteronism, and priapism. These side effects are relatively rare in a given individual, but given the extremely widespread use of heparin, some are quite common, particularly HITT and osteoporosis. Although reasonable incidences of many of these side effects can be "softly" deduced from current reports dealing with unfractionated heparin, at present the incidences of these side effects with newer low molecular weight heparins appear to be much less common. However, only longer experience will more clearly define the incidence of each side effect with low molecular weight preparations.

The use of heparin in patients in whom a pulmonary embolism is suspected after total hip arthroplasty

BACKGROUND

The morbidity and mortality associated with pulmonary embolism are well known, as is the benefit of the use of heparin in patients who have a pulmonary embolism. However, the patterns of heparin use as well as its undesirable effects, especially in patients who have recently had a total hip arthroplasty, have been less well studied. Thus, concern arises regarding the use of heparin in patients who have no firm evidence of a pulmonary embolism. The purpose of the current study was to track the use of heparin and associated orthopaedic complications in patients in whom a pulmonary embolism was suspected after a total hip arthroplasty.

METHODS

The records of 150 patients in whom a pulmonary embolism had been suspected after a total hip arthroplasty were reviewed retrospectively. The rates of individual complications (such as stroke, infection, and hematoma) and those of groups of complications (such as medical complications, orthopaedic complications, and all complications combined) were recorded and then were stratified according to the treatment (with or without heparin), the presence or absence of pulmonary embolism, and other variables.

RESULTS

Thirty-two (47 percent) of sixty-eight patients who were managed with heparin had complications compared with sixteen (20 percent) of eighty-two patients who were not thus managed (p = 0.0006). Specifically, patients who were managed with heparin were more likely to have gastrointestinal bleeding, hematological complications, a loose prosthesis, a hematoma, or an early revision arthroplasty (p<0.05 for all). With the numbers available, the use of heparin was not found to be significantly associated with an increased risk of death, stroke, or infection at the site of the prosthesis. Interestingly, thirty-one (31 percent) of ninety-nine patients who had ventilation-perfusion scans that demonstrated normal findings or findings indicating a low probability of pulmonary embolism were given heparin before the diagnosis of a pulmonary embolism was excluded, and sixteen (52 percent) of these thirty-one had complications.

CONCLUSIONS

Given this risk profile, we advise against the use of heparin before the diagnosis of pulmonary embolism is established in patients who have had a total hip arthroplasty. This recommendation is supported by algorithms, in widely read medical texts, pertaining to the use of heparin in patients in whom a pulmonary embolism is suspected.

Modern management of pulmonary embolism

BACKGROUND

Pulmonary embolism is a significant cause of morbidity and death after operation. The introduction of new technologies in the diagnosis, and thrombolysis in the treatment, of pulmonary embolism has led to a need to reappraise the management of this condition.

METHODS

This review encompasses a comprehensive discussion of diagnostic modalities and therapeutic strategies used in the current management of pulmonary embolism. Relevant papers on the diagnosis and treatment of pulmonary embolism were identified from a Medline search for the period 1967-1998. Additional papers were derived from the reference lists of retrieved articles. Articles presenting prospectively gathered data have been referenced preferentially.

RESULTS AND CONCLUSION

Algorithms for the diagnosis and treatment of pulmonary embolism are presented.

Deep venous thrombosis and pulmonary embolism in bilateral lower-extremity amputee patients

OBJECTIVE

To determine the incidence of deep venous thrombosis and pulmonary emboli and the value of an inferior vena cava filter in patients with bilateral lower-extremity amputations, and to determine the incidence of pulmonary emboli after filter placement.

DESIGN

Retrospective study with a follow-up of 3 to 64 months.

SETTING

Inner-city university hospital.

PATIENTS

Twenty-seven consecutive patients with bilateral lower-limb amputation.

RESULTS

Age, sex, and race were assessed, and had no impact on the incidence of pulmonary embolus in these patients with lower-extremity amputation.

CONCLUSION

No clinical objective evidence of pulmonary emboli occurred after placement of an inferior vena caval filter.

Investigation of a whole blood fluidized bed Taylor-Couette flow device for enzymatic heparin neutralization

The use of clinical bioreactors will increase as more therapeutic proteins are being cloned, expressed, and produced at a reduced cost. The proposed use of an immobilized heparinase I reactor to make heparin anticoagulation a safer therapy is an example of how the specificity and high activity of an enzyme could be incorporated into a system to ultimately benefit a patient. However, the development of a safe and efficient bioreactor is important for the use of immobilized heparinase I and other therapeutic proteins designed for use in medical extracorporeal procedures. This study examined the possibility of using Taylor-Couette flow and "flow-induced" recirculation of the agarose beads as a way to fluidize agarose-bound heparinase in whole blood. Heparinase I was immobilized onto agarose beads via cyanogen bromide activation. A reactor based on Taylor-Couette flow was designed and modified with a tangential recirculation line. The reactor was tested for efficacy and safety in vitro in human blood. Visualization studies in water and 42% glycerol were used to determine the minimum rotation rate for efficient fluidization. The strategic placement of the recirculation line allowed recirculation of the agarose without the use of an external pump. The device removed 90% of the heparin activity within 2 min from 450 cc of human blood at a blood flow rate of 100 mL/min. Furthermore, the device maintained inlet and outlet clotting times of 269 +/- 10 and 235 +/- 6 s, respectively, demonstrating the potential for regional heparinization. Blood damage was a function of gel volume fraction and rotation rate of the inner cylinder. Hemolysis of the red cells is an important issue when Taylor vortices are combined with macroscopic solid particles such as agarose beads. A modified Taylor-Couette flow device was developed to treat whole blood and operational criteria were established to minimize hemolysis.