Heparin-induced thrombocytopenia

COVID-19 Adenoviral Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT), COVID-19-Related Thrombosis, and the Thrombotic Thrombocytopenic Syndromes

Adenoviral-based vaccines such as ChadoX1 CoV-19 (AstraZeneca) and Ad26.COV2.S (J&J) were developed to prevent infection and reduce hospitalization or death in Coronavirus Disease 2019 (COVID-19) patients. Although these vaccines passed safety and efficacy trials with excellent neutralizing capabilities against SARS-CoV-2, very rare reports of acute thrombotic thrombocytopenic events following administration emerged in certain populations, which triggered a series of clinical investigations that gave rise to a novel phenomenon called vaccine-induced immune thrombotic thrombocytopenia (VITT). Several converging pathways exist between VITT and other forms of thrombotic thrombocytopenic syndromes, specifically that of heparin-induced thrombocytopenia, which involves the formation of anti-PF4 antibodies and the activation of platelets leading to thrombocytopenia and thrombin-mediated clotting. Interestingly, certain differences in the presentation also exist in VITT, and guidelines have been published in recent months to assist clinicians in recognizing VITT to achieve desired outcomes. In this paper, we first discuss the clotting phenomenon in COVID-19 and delineate it from VITT, followed by a review of current knowledge on the clinical manifestations of VITT in lieu of other thrombotic thrombocytopenic syndromes. Likewise, emerging evidence on the role of adenoviral vectors and vaccine constituents is also discussed briefly.

Quantitative interpretation of PF4/heparin-EIA optical densities in predicting platelet-activating VITT antibodies

BACKGROUND

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a prothrombotic, heparin-induced thrombocytopenia (HIT)-mimicking, adverse reaction caused by platelet-activating anti-platelet factor 4 (PF4) antibodies that occurs rarely after adenovirus vector-based COVID-19 vaccination. Strength of PF4-dependent enzyme immunoassay (EIA) reactivity-judged by optical density (OD) measurements-strongly predicts platelet-activating properties of HIT antibodies in a functional test. Whether a similar relationship holds for VITT antibodies is unknown.

OBJECTIVES

To evaluate probability for positive platelet activation testing for VITT antibodies based upon EIA OD reactivity; and to investigate simple approaches to minimize false-negative platelet activation testing for VITT.

METHODS

All samples referred for VITT testing were systematically evaluated by semiquantitative in-house PF4/heparin-EIA (OD readings) and PF4-induced platelet activation (PIPA) testing within a cohort study. EIA-positive sera testing PIPA-negative were retested following 1/4 to 1/10 dilution. Logistic regression was performed to predict the probability of a positive PIPA per magnitude of EIA reactivity.

RESULTS

Greater EIA ODs in sera from patients with suspected VITT correlated strongly with greater likelihood of PIPA reactivity. Of 61 sera (with OD values >1.0) testing negative in the PIPA, a high proportion (27/61, 44.3%) became PIPA positive when tested at 1/4 to 1/10 dilution.

CONCLUSIONS

VITT serology resembles HIT in that greater EIA OD reactivity predicts higher probability of positive testing for platelet-activating antibodies. Unlike the situation with HIT antibodies, however, diluting putative VITT serum increases probability of a positive platelet activation assay, suggesting that optimal complex formation depends on the stoichiometric ratio of PF4 and anti-PF4 VITT antibodies.

Endoluminal Recanalization in a Patient with Phlegmasia Cerulea Dolens Using a Multimodality Approach

Phlegmasia cerulea dolens is a limb-threatening form of deep venous thrombosis and should be treated aggressively. The authors report a patient who presented with iliocaval and femoral deep venous thrombosis and posed an additional therapeutic challenge based on a recent history of heparin-induced thrombocytopenia. Catheter-directed pharmacologic thrombolysis and balloon venoplasty were applied in treatment. The direct thrombin inhibitor argatroban was used in place of heparin for concurrent anticoagulation. This multimodality endovascular approach (chemical and mechanical interventions) was successful in relieving the venous occlusion and salvaging the limb, while maintaining appropriate treatment for heparin-induced thrombocytopenia.

Thrombotic Complications in Three Hemodialysis Patients With Heparin-Induced Thrombocytopenia Type I

Although unfractionated heparin is the most commonly used anticoagulant for hemodialysis and has been associated with bleeding episodes, a more devastating complication that can occur is heparin-induced thrombocytopenia (HIT). It is believed that HIT type II is much more dangerous than type I, because HIT type II is associated with thromboembolic complications whereas there are no such complications in HIT type I. However, increased clot formation in the extracorporeal circuit during hemodialysis with unfractionated heparin is sometimes experienced by not only patients with HIT type II but also those with HIT type I. Three patients with HIT type I are presented who suffered from clot formation during hemodialysis, and in whom 81 mg of aspirin and/or cessation of heparin was prescribed. All three patients had received recombinant human erythropoietin (rHuEpo). Both heparin and rHuEpo induce enhanced platelet aggregation; therefore, it is possible that even HIT type I patients may suffer clot formation in the extracorporeal circuit due to platelet activation via the synergistic effects of unfractionated heparin and rHuEpo.

Stent thrombosis caused by metal allergy complicated by protein S deficiency and heparin-induced thrombocytopenia: a case report and review of the literature

A 43-year-old woman recipient of a bare metal coronary stent during an acute anterior myocardial infarction was repeatedly hospitalized with recurrent stent thrombosis (ST) over the following 3 years. Emergent coronary angiography showed a thrombus in the in-stent segment of the proximal left anterior descending artery. We repeatedly aspirated the thrombus, which immediately reformed multiple times. The discontinuation of heparin and administration of thrombolytics and argatroban, followed by repeated balloon dilatations, ended the formation of new thrombi. The patient was found to be allergic to nickel, protein S deficient and carrier of heparin-induced thrombocytopenia antibody. We discuss this case in the context of a) literature pertaining to acute coronary syndromes in the young, and b) the detailed investigations needed to identify thrombotic risk factors. Steroids may be effective to prevent recurrent ST caused by stent allergy.

Antiplatelet drug induced isolated profound thrombocytopenia in interventional cardiology: a review based on individual case reports

A combination antithrombotic and antiplatelet therapy with clopidogrel, aspirin, glycoprotein IIb/IIIa receptor inhibitors and heparins is routinely used as adjunct therapy in patients undergoing percutaneous coronary intervention (PCI). As all substances inhibit platelet function, bleeding and thrombocytopenia may occur. We report on three patients who developed isolated profound thrombocytopenia (platelet count of < 20,000/mm(3)) within 24 h after initiation of combination antiplatelet and antithrombotic therapy during a 1 year observation period in 443 consecutive patients undergoing PCI and stent implantation. The data from our cardiology unit revealed an incidence of an isolated profound thrombocytopenia in 0.7% of all patients on combination antithrombotic therapy and in 1.5% of patients with GPIIb/IIIa-blockers. In all three cases with isolated profound thrombocytopenia GPIIb/IIIa-blockers were found to be the causative agents. Negative results of HIT-assays excluded heparin induced thrombocytopenia type II. Despite the extremely low platelet count no severe bleeding was observed and in all cases platelet counts normalized within 3-4 days without specific interventions except discontinuation of the responsible agent. These findings are discussed in conjunct with an overview of the recent literature.

The Cost-Effectiveness of Argatroban Treatment in Heparin-Induced Thrombocytopenia

A decision-tree analysis was used to estimate the average cost per patient using the direct thrombin inhibitor argatroban for early treatment (<48 hours after thrombocytopenia onset) compared with delayed treatment (> or =48 hours after thrombocytopenia onset) of immune-mediated heparin-induced thrombocytopenia (HIT) with or without thrombosis. Clinical probability data used to populate the model were obtained from argatroban clinical trials and from published clinical literature. Resource utilization data and cost data were also obtained from available literature, the 2003 Physician's Fee Reference, the Healthcare Cost and Utilization Project 2000, the 2003 Drug Topics RedBook, and a modified Delphi panel. The total per-patient cost included hospital days, diagnostic tests, heparin, argatroban, major hemorrhagic events, and patient outcomes (ie, amputation, new thrombosis, stroke, or death), multiplied by the probability of each event. The incremental cost-effectiveness ratio was calculated by dividing the incremental cost between patients with and without argatroban treatment by the incremental effectiveness, or the cost per new thrombosis event avoided. The mean cost per HIT patient without thrombosis who did not receive argatroban was $38,046. The mean cost decreased by 6.85% for patients who were treated earlier with argatroban therapy (average cost, $35,441), representing a $2605 saving per patient compared with those not treated with argatroban. For those receiving delayed argatroban therapy, the mean cost increased by $9024 per patient compared with those receiving early treatment with argatroban. The mean cost for HIT patients with thrombosis who did not receive argatroban was $48,101, which was 9.0% higher than for those receiving early argatroban therapy, representing a $3957 savings per patient. For HIT with thrombosis, mean costs increased by 18.2% in patients whose argatroban was delayed, representing a cost increase of $8020 per patient compared with early treatment (mean cost $44,144 for early treatment and $52,164 for delayed treatment). The results of this analysis support the recommendation to initiate early argatroban treatment upon suspicion of HIT to reduce the thrombotic consequences of HIT and associated healthcare costs. Argatroban therapy should not be delayed pending the results of HIT diagnostic tests.

Heparin-induced thrombocytopenia: clinical manifestations and management strategies

Thrombocytopenia is a relatively frequent and usually benign clinical complication of heparin therapy. However, some patients receiving heparin and heparin-based products experience an immune-mediated reaction due to the development of heparin-induced antibodies. This reaction leads to a highly specific and paradoxical form of thrombocytopenia, known as type II heparin-induced thrombocytopenia (HIT). Unlike other types of drug-induced thrombocytopenia, HIT promotes thrombosis rather than bleeding; therefore HIT should be suspected in patients who experience thrombotic events despite adequate anticoagulation therapy. Early identification and treatment of HIT can prevent more serious complications associated with this disorder (e.g., exacerbation of venous thromboembolism, limb gangrene, and skin necrosis). Both arterial and venous thrombosis can arise from a single episode of HIT. Routine assessment of platelet counts is necessary with heparin therapy, as a decreased platelet level is usually the only indication of HIT. Although compared with unfractionated heparin, low-molecular-weight heparin therapy is less likely to result in HIT, the use of these agents is contraindicated in HIT patients. Concomitant warfarin therapy is not contraindicated in such patients but must be carefully monitored. Treatment with a direct thrombin inhibitor, such as lepirudin or argatroban, is an effective strategy in reversing the thrombocytopenia associated with HIT and reducing its complications. This article discusses the clinical syndrome of HIT, including pathophysiology, diagnostic criteria, clinical presentations, and current available management strategies in the context of 2 case studies.

Chemical Approaches to Define the Structure-Activity Relationship of Heparin-like Glycosaminoglycans

Heparin, the drug of choice for the prevention and treatment of thromboembolic disorders, has been shown to interact with many proteins. Despite its widespread medical use, little is known about the precise sequences that interact with specific proteins. The minimum heparin binding sequence for FGF1 and FGF2 necessary to promote signaling was investigated. A characteristic pentasaccharide sequence, DEFGH, is required to accelerate the inhibition of thrombin and factor Xa in the blood-coagulation cascade. The first synthetic heparin pentasaccharide drug has been approved in Europe and the US and is sold under the trade name Arixtra. Other oligosaccharides with different composition are under clinical investigation. The enormous interest in the assembly of heparin oligosaccharides will stimulate the development of new synthetic approaches. Heparin-oligosaccharide-synthesis automation similar to that of DNA or peptide synthesis will play an important role.

Heparin-induced thrombocytopenia--recognition and treatment

Heparin, an important agent for the prophylaxis and treatment of venous and arterial thromboembolism, also can cause heparin-induced thrombocytopenia (HIT). This medication-induced immune-mediated syndrome is characterized by thrombocytopenia and life- or limb-threatening thrombotic events. The initial presentation of HIT is a decrease in platelet count with or without thrombosis. Heparin-induced thrombocytopenia frequently is overlooked in hospital settings, and it must be distinguished from other causes of thrombocytopenia. New therapies include the use of direct thrombin inhibitors argatroban and hirudin.

The incidence of heparin-induced thrombocytopenia in hospitalized medical patients treated with subcutaneous unfractionated heparin: a prospective cohort study

Although heparin-induced thrombocytopenia (HIT) is a known complication of intravenous unfractionated heparin (UFH), its incidence in medical patients treated with subcutaneous UFH is less well defined. To determine the incidence of HIT in this category of patients, the platelet count was performed at baseline and then every 3 +/- 1 days in 598 consecutive patients admitted to 2 medical wards and treated with subcutaneous UFH for prophylactic (n = 360) or therapeutic (n = 238) indications. The diagnosis of HIT was accepted in the case of a platelet drop of 50% or more and either the demonstration of heparin-dependent antibodies or (when this search could not be performed) the combination of the following features: (1) the absence of any other obvious clinical explanation for thrombocytopenia, (2) the occurrence of thrombocytopenia at least 5 days after heparin start, and (3) either the normalization of the platelet count within 10 days after heparin discontinuation or the earlier patient's death due to an unexpected thromboembolic complication. HIT developed in 5 patients (0.8%; 95% CI, 0.1%-1.6%); all of them belonged to the subgroup of patients who received heparin for prophylactic indications. The prevalence of thromboembolic complications in patients with HIT (60%) was remarkably higher than that observed in the remaining 593 patients (3.5%), leading to an odds ratio of 40.8 (95% CI, 5.2-162.8). Although the frequency of HIT in hospitalized medical patients treated with subcutaneous heparin is lower than that observed in other clinical settings, this complication is associated with a similarly high rate of thromboembolic events.

A whole blood flow cytometric determination of platelet activation by unfractionated and low molecular weight heparin in vitro

The influence of unfractionated (Heparin-Natrium) and low-molecular heparin (Fragmin(R)) on platelet activation in whole blood was investigated by FACS analysis in vitro using antibodies against glycoprotein (gp) IIb/IIIa (CD 41), GMP 140 (CD 62P), gp 53 (CD 63) and fibrinogen. Samples were also labeled with anti-gp Ib (CD 42b). Neither unfractionated heparin (UFH) nor low molecular weight heparin (LMWH) led to significant (i.e., p<0.05) changes in fluorescence intensities of platelets labeled with anti-gp IIb/IIIa or anti-gp 53. Significant platelet activation due to unfractionated heparin could be observed by labeling with anti-GMP 140 (UFH: p=0.009; LMWH: p=0.16). The proportion of platelets with surface-bound fibrinogen was significantly increased (UFH: p=0.00006; LMWH: p=0.008). After incubation with heparins, activation ability of platelets by adenosine diphosphate (ADP) was significantly increased. The potentiating action of unfractionated heparin was larger. Therefore, flow cytometric results of platelet activation in patients receiving heparin should be interpreted carefully.

Adverse dermatologic effects of cardiovascular drug therapy: part III

Cardiovascular disease is common, affecting an increasing number of persons as the population ages. To combat this growing health problem, physicians use a multitude of medications in the treatment of their patients. Although pharmacologic therapy greatly enhances quality of life for a majority of patients, there is always the potential for an unfavorable reaction. For example, cardiovascular drugs can induce a vast array of adverse dermatologic responses. This article reviews the various cutaneous reaction patterns that can occur as a result of treatment with vasodilators and other antihypertensive drugs, anticoagulants and antiplatelet drugs, thrombolytic agents, and lipid-lowering agents.

New Treatment Options for Heparin-Induced Thrombocytopenia

Heparin, in various forms, is used in a variety of conditions including prophylaxis and treatment of thromboembolic disorders. Although the most common adverse effect related to the use of heparin is bleeding, heparin-induced thrombocytopenia (HIT) can also occur. Two types of HIT exist, HIT type I and type II. HIT type I is a mild and self-limiting disease in which the patient’s platelet count may decrease slightly but will recover with continued treatment. This is in contrast to HIT type II, which may lead to potentially devastating complications. Patients with HIT type II are at increased risk for thromboembolic complications that are mediated through autoimmune reactions and therefore require anticoagulation with danaparoid or one of the direct thrombin inhibitors, including lepirudin, argatroban, or bivalirudin. Limited data are available on the use of these agents in special populations including patients who are pregnant or those undergoing procedures such as percutaneous coronary intervention, cardiopulmonary bypass and dialysis, and pregnancy. Future therapies may include the use of unfractionated heparin in combination with glycoprotein IIb/IIIa inhibitors during cardiopulmonary bypass.

Use of plasma exchange and heparin during cardiopulmonary bypass for a patient with heparin induced thrombocytopenia: a case report

Patients with documented history of heparin-induced thrombocytopenia (HIT) pose a difficult problem during surgery using cardiopulmonary bypass (CPB). Several alternatives to heparin exist, but these products either are not approved for use in the United States or have more side effects than heparin. We report on a patient with documented heparin-induced antibody and left main coronary artery disease who underwent uneventful coronary artery bypass surgery and recovery by using preoperative plasmaphresis and limited use of porcine intestinal heparin during CPB.

Development of a high-pressure liquid chromatography method for diagnosis of heparin-induced thrombocytopenia

Owing to the disadvantage of radioactivity of the carbon 14 serotonin release assay and the time-consuming procedure of the enzyme immunoassay, we developed a high-pressure liquid chromatography (HPLC) method to detect serotonin released from donor platelets in the presence of heparins and serum samples from patients with heparin-induced thrombocytopenia (HIT). Samples were analyzed from 60 healthy control subjects, 19 patients with HIT, and 20 patients without HIT after incubation with heparin, low-molecular-weight heparin (LMWH), and danaparoid. Serotonin release was measured from platelets, 300 x 10(3)/microL, by HPLC. Serotonin eluted as a single peak from the HPLC column. Serum samples from patients with HIT released 5.5 to 352.5 and 6.6 to 1,533.3 ng/mL of serotonin from platelets in the presence of 0.2 IU/mL of heparin and LMWH, respectively. In the presence of 0 IU/mL of heparin, LMWH, danaparoid, and control samples, less than 2.5 ng/mL of serotonin were released. The HPLC method permits a rapid, sensitive, and quantitative determination of serotonin released from donor platelets for laboratory confirmation of HIT.

Development of a non-human primate sub-clinical model of heparin-induced thrombocytopenia: platelet responses to human anti-heparin-platelet factor 4 antibodies

The purpose of this study was to characterize the responses of human and non-human primate (Macaca mulatta) platelets to anti-heparin-platelet factor 4 (AHPF4) antibodies. Due to the variations observed in the functionality and immunoglobulin isotypes in patients with heparin-induced thrombocytopenia (HIT), we used highly characterized human AHPF4 antibodies to study platelet activation responses. Using ELISA and 14C-serotonin release assay (SRA) systems, three patients' plasmapheresis fluid with similar responses to these assays were pooled. This pool was then used to study the platelet activation responses of human and primate platelets in the HIT platelet aggregation assay, a flow cytometry assay, and a variation of the aggregation assay in which glycoprotein IIb/IIIa inhibitors were supplemented. In the plasmapheresis fluid from three patients, the most significant AHPF4 immunoglobulin isotype present (based on optical density readings) was IgG, with less IgM (p < 0.001) and IgA (p < 0.001). The SRA yielded equivalent platelet activation results in all three patients. Using this pool in the platelet aggregation assay, without any heparin present, there was less percent aggregation (p < 0.001) with human platelets (11.8 +/- 2.35, n = 5) compared to the primate platelets (54.3 +/- 10.2, n = 9). In presence of 0.4 U/ml heparin, both platelet types had similar percent aggregations (p > 0.05). Three glycoprotein IIb/IIIa receptor inhibitors were used to evaluate the similarities in platelet activation. Eptifibatide was found to be a strong inhibitor of both species' platelet types at concentrations greater than 0.01 microg/ml. This was not the case with tirofiban which inhibited both human and monkey platelets at concentrations greater than 0.025 microg/ml. Abciximab inhibited aggregation at concentrations greater than 6.25 microg/ml. These data indicate that phylogenetic similarities in platelets of humans and primates may be used to further characterize the pathophysiology of HIT syndrome.

Pathophysiology of heparin-induced thrombocytopenia. Clinical and diagnostic implications--a review

OBJECTIVE

This review of heparin-induced thrombocytopenia (HIT), the most frequent and dangerous side effect of heparin exposure, covers the epidemiology, pathophysiology, clinical presentation, diagnosis, and treatment of this disease syndrome.

DATA SOURCES AND STUDY SELECTION

Current consensus of opinion is given based on literature reports, as well as new information where available. A comprehensive analysis of the reasons for discrepancies in incidence numbers is given. The currently known mechanism is that HIT is mediated by an antibody to the complex of heparin->platelet factor 4, which binds to the Fc receptor on platelets. New evidence suggests a functional heterogeneity in the anti-heparin-platelet factor 4 antibodies generated to heparin, and a "superactive" heparin-platelet factor 4 antibody that does not require the presence of heparin to promote platelet activation or aggregation has been identified. Up-regulation of cell adhesion molecules and inflammatory markers, as well as preactivation of platelets/endothelial cells/leukocytes, are also considered to be related to the pathophysiology of HIT. Issues related to the specificity of currently available and new laboratory assays that support a clinical diagnosis are addressed in relation to the serotonin-release assay. Past experience with various anticoagulant treatments is reviewed with a focus on the recent successes of thrombin inhibitors and platelet GPIIb/IIIa inhibitors to combat the platelet activation and severe thrombotic episodes associated with HIT.

CONCLUSIONS

The pathophysiology of HIT is multifactorial. However, the primary factor in the mediation of the cellular activation is due to the generation of an antibody to the heparin-platelet factor 4 complex. This review is written as a reference for HIT research.

Heparin-Induced thrombocytopenia: minimising the risks in the elderly patient

Heparin therapy may sometimes be seriously complicated by heparin-induced thrombocytopenia (HIT). Heparin use for treatment and prevention of thromboembolism is more common in the elderly and that may be the reason why HIT is reported more frequently in this group of patients. The first approach in the management of HIT is awareness of this disorder. The morbidity and mortality associated with HIT may be reduced by avoiding unnecessary heparin exposure, by reducing the duration of heparinisation and by using low molecular weight heparins rather than unfractionated heparin. A decrease from baseline values of at least 30% in the platelet count, any unexplained thrombotic event and the finding of a white clot at thrombectomy are clinical warning signs that should alert physicians to a possible diagnosis of HIT. Indeed, early clinical recognition of HIT may sometimes prevent the severe complications associated with this disorder. Objective confirmation of the diagnosis of HIT is difficult because none of the available biological tests possess 100% sensitivity or 100% specificity. It is, however, possible to optimise the performances of the functional assay, mainly the platelet aggregation test (PAT), by following the manoeuvres described by differ- ent investigators. The use of 2 classes of assay (functional and antigen assays) and repeat testing on another day can avoid misdiagnosis of HIT. An alternative parenteral anticoagulant treatment is most often mandatory after heparin withdrawal. Danaparoid sodium and lepirudin are 2 drugs that are currently available for the treatment of HIT, and the efficacy of argatroban needs to be confirmed in greater numbers of patients with HIT. The use of these drugs has contributed to the reduction in the mortality and morbidity associated with HIT.

Heparin-induced thrombocytopenia and thrombosis

Heparin remains the most commonly used parenteral medication in hospitalized patients. Heparin induced thrombocytopenia (HIT) and heparin induced thrombocytopenia with thrombosis syndrome or the white clot syndrome are important complications of heparin use. This article provides an in-depth review of the etiopathogenesis, clinical manifestations, diagnosis, and management options in patients with HIT. Clinical problems associated with HIT such as antiphospholipid antibody syndrome and venous gangrene are described. The management options of HIT patients during cardiac interventional procedures and coronary surgery as well as recent advances in therapeutic options are summarized.

Failure of early heparin cessation as treatment for heparin-induced thrombocytopenia

PURPOSE

The complications of heparin-induced thrombocytopenia include thrombosis and death. The purpose of the study was to determine whether early heparin cessation can prevent these outcomes.

SUBJECTS AND METHODS

We performed a retrospective analysis of consecutive patients with heparin-induced thrombocytopenia diagnosed by platelet aggregometry. Demographic, clinical, and laboratory findings were compared in patients by whether heparin treatment was stopped early (< or = 48 hours) or late (>48 hours) after the onset of thrombocytopenia, as well as between patients with and without thrombosis. Thrombocytopenia was defined as a 50% decline in baseline platelet counts or an absolute platelet count < 100,000/mm3.

RESULTS

Of the 113 patients, 38% developed thrombosis and 27% died. One-half of patients had thrombosis diagnosed >24 hours after heparin cessation. No difference in thrombosis or mortality was found in the 40 patients with early heparin cessation [mean (+/-SD) time of cessation 0.7 +/- 0.6 days] compared with the 73 patients with late heparin cessation (5 +/- 3 days). Thrombosis >24 hours after heparin cessation occurred in 61% of the patients in the early group and in 40% of the late group (P = 0.17). In a multivariate analysis, only a lower nadir of the platelet count (percent of baseline) was associated with thrombosis. Neither thrombosis nor the time to heparin cessation were associated with mortality.

CONCLUSIONS

Early heparin cessation was not effective in reducing morbid events in patients with heparin-induced thrombocytopenia. Treatment strategies other than heparin cessation alone should be considered in patients with this condition.

Orally administered dextran sulfate is absorbed in HIV-positive individuals

Preliminary in vivo studies suggested that oral dextran sulfate was poorly absorbed, but investigations were limited by inadequate methods for measuring the drug in the body. To determine absorption in HIV-positive subjects, hydrogenated dextran sulfate, average molecular weight 8000 (Usherdex 8), was orally administered in a short-term (single dose, 4 g/day for 5 days, 7 subjects) and in a long-term study (1 g, 4 times per day for 29 to 335 days, 8 subjects), which was a continuation of the short-term study with the inclusion of an additional subject. When an agarose gel electrophoresis technique with toluidine blue staining was used, the drug was recovered from plasma (67%, peak 2.2 microg/mL) and circulating peripheral blood lymphocyte (PBL) samples (50%, peak 333 microg/L blood) obtained at 5 and 15 minutes and 1, 3, 6, and 24 hours after the first day's dose and from plasma (56%) and PBL samples (38%) obtained 5 minutes after administration on 4 subsequent days in the short-term study. In the long-term study, the drug was found in plasma (67%, peak 2.4 microg/mL) and PBL samples (25%, peak 126 microg/L blood) obtained at monthly visits within 4 hours of the last dose. The drug was found in all urine samples from all subjects in both studies (short-term study, 24-hour samples up to 4 days after the final dose; long-term study, monthly samples within 4 hours of the last dose). In the long-term study, bone marrow preparations from 3 subjects showed metachromatic inclusions present in reticular cells when the cells were stained with toluidine blue, indicating the presence of sulfated polyanions. A significant rise in activated partial thromboplastin time and a drop in platelet count (P < .025) were demonstrated, with thrombocytopenia developing in 3 patients. Mild-to-moderate gastrointestinal disturbances were experienced by 6 subjects in the short-term study and by all subjects in the long-term study. One subject experienced mild central nervous system symptoms in the short-term study. These results indicate that dextran sulfate is absorbed after oral administration; therefore, further studies on its efficacy, particularly in the early stages of the disease, along with additional observations on its toxicity, are warranted.

Heparin in acute ischaemic stroke. The T wave is negative and it's time to stop

The use of heparin for acute ischaemic stroke has long been controversial. Although it may have some theoretical benefits in preventing fibrin formation and thrombus propagation, data from 16 randomised controlled trials involving more than 22,000 patients show that heparin produces no significant net benefit in eventual outcome.

Transcatheter regional urokinase therapy in the management of inferior vena cava thrombosis

PURPOSE

To study the efficacy of local infusion of urokinase (UK) in the treatment of symptomatic inferior vena cava (IVC) thrombosis.

MATERIALS AND METHODS

Eight patients (five men and three women) who ranged in age from 19 years to 75 years (mean, 56 years) with symptomatic IVC thrombosis underwent local catheter-directed infusion of UK with use of up to three access sites. Infrarenal IVC thrombus and iliac vein thrombus was identified in all patients. Four patients had extension of thrombus proximal to the renal veins. Seven of eight patients had at least one risk factor for IVC thrombosis: hypercoagulable state (n = 3), IVC filter (n = 3), malignancy (n = 2), recent surgery (n = 2), and oral contraceptive use (n = 1). No serious procedure-related complications were encountered, although one patient died 5 days after UK therapy of pulmonary failure due to advanced lung cancer. UK was infused for an average of 79 hours (range, 24-140 hours) and a mean total dose of 7.4 million U of UK (range, 2.9-14.4 million U). Adjunctive balloon angioplasty was performed in three patients. No vascular stents were placed. Clinical and/or radiographic follow-up was obtained in all eight patients.

RESULTS

Thrombolysis was successful in seven of eight (88%) IVCs with no or minimal residual thrombus. The remaining seven patients had no lower extremity swelling 2-24 months (mean, 11 months) after the procedure. Three of seven patients had computed tomographic or venographic follow-up (mean, 9 months; range, 1.5-15 months), demonstrating unchanged or improved IVC patency.

CONCLUSIONS

Transcatheter regional infusion of UK for re-establishing venous patency in acute IVC thrombosis appears to be effective with good short-term and mid-term clinical benefit.

Case managing heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) and its two subtypes, early onset (Type I) and delayed onset (Type II), are becoming an increasing concern in acute care. Also called "white clot syndrome," this condition can lead to thrombosis and loss of limb. Alternatives to heparin therapy, such as low molecular weight heparin, are discussed as ways to decrease HIT. An algorithm has been developed to guide identification and monitoring of patients at risk for HIT. The article presents the expanded role of the clinical nurse specialist as case manager in clinically managing patients with actual or potential HIT. The case manager's role for patients receiving heparin lies in increasing the awareness of this condition among all clinicians and serving as a resource for current information regarding its prevention, diagnosis, and treatment.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a potentially serious complication of heparin therapy and is being encountered more frequently in patients with cardiovascular disease as use of anticoagulant therapy becomes more widespread. Our understanding of the pathophysiology of this immune-mediated condition has improved in recent years, with heparin-platelet factor 4 complex as the culprit antigen in most patients. New sensitive laboratory assays for the pathogenic antibody are now available and should permit an earlier, more reliable diagnosis, but their optimal application remains to be defined. For patients in whom HIT is diagnosed, immediate discontinuation of heparin infusions and elimination of heparin from all flushes and ports are mandatory. Further management of patients with HIT is problematic at present, as there are no readily available alternative anticoagulant agents in the United States with proven efficacy in acute coronary disease. The direct thrombin inhibitors appear to be the most promising alternatives to heparin, when continued use of heparin is contraindicated, and the results of several multicenter trials evaluating their application in patients with HIT are awaited.

Acute profound thrombocytopenia after C7E3 Fab (abciximab) therapy

BACKGROUND

Platelets play a crucial role in the ischemic complications of percutaneous coronary procedures. The recent availability of c7E3 Fab (abciximab; ReoPro), a chimeric monoclonal antibody Fab fragment directed against the platelet glycoprotein IIb/IIIa receptor, has reduced abrupt closure and other adverse clinical events and lessened the need for revascularization procedures. As experience accrues, rare cases of acute profound thrombocytopenia have been revealed.

METHODS AND RESULTS

From November 1991 to July 1996, patients at Duke University Medical Center who underwent percutaneous coronary revascularization and received their first exposure to c7E3 Fab were evaluated for the development of acute profound thrombocytopenia, defined as a platelet count < 20 x 10(9)/L occurring within 24 hours of initial treatment. Four patients (0.5%) developed acute profound thrombocytopenia within 11 to 21 hours of receiving the c7E3 Fab bolus. Nadir platelet counts ranged from 1 to 16 x 10(9)/L and occurred within 11 to 26 hours. No patient developed a significant hemorrhagic complication, and each patient's platelet count responded to platelet transfusion. Platelet counts remained depressed for at least 3 days but returned to baseline within 2 weeks.

CONCLUSIONS

Acute profound thrombocytopenia can occur after c7E3 Fab administration. Its development was not predictable, and it requires consideration in every patient treated. A platelet count 2 to 4 hours after the bolus would likely have detected these four cases. When indicated, platelet transfusion will raise the platelet count to safer levels without adverse effects. The differential diagnosis (including heparin-induced thrombocytopenia), a plan for management, and postulates as to the mechanism are discussed.

Heparin-related thrombosis despite normal platelet counts in vascular surgery

BACKGROUND

Acute graft thrombosis is a severe complication in vascular surgery that may require limb amputation or even cause death. Because nearly all patients undergoing vascular surgery have had previous exposure to heparin, the presence of heparin-related anti-platelet antibodies typical for heparin-associated thrombocytopenia (HAT) is one underlying possible mechanism of acute graft thrombosis. Although thrombocytopenia is a typical finding of HAT, it is not clear whether the occurrence of clinically important HAT is necessarily associated with thrombocytopenia.

PATIENTS AND METHODS

Ten out of 246 patients undergoing vascular surgery were diagnosed with HAT because of otherwise unexplained acute graft thrombosis that required recurrent surgical interventions.

RESULTS

In all of the 10 patients, heparin-related anti-platelet antibodies were detected although the platelet counts were within the normal range. When HAT was diagnosed, heparin administration was stopped and, after autoantibody cross-reactivity with the heparinoid Danaparoid had been excluded, anticoagulation was continued using this anticoagulant. After heparin therapy was discontinued none of the 10 patients developed further thrombotic complications.

CONCLUSION

The data presented demonstrate clearly that a normal platelet count does not exclude the possibility of HAT. As a consequence of this, HAT should be suspected in patients who develop thrombotic complications during heparin treatment, regardless of the actual platelet counts.

The heparin-induced thrombocytopenia and thrombosis syndrome: treatment with intraarterial urokinase and systemic platelet aggregation inhibitors

We report a case of the heparin-induced thrombocytopenia and thrombosis syndrome presenting with acute ischemia of a lower limb. The patient was successfully treated by withdrawal of heparin products, intraarterial urokinase, and platelet anti-aggregation therapy consisting of Dextran and aspirin.

Skin necrosis following subcutaneous heparin injection

Heparin-induced skin necrosis is a rare but serious complication of subcutaneously administered heparin. Previous reports indicate that the skin necrosis is often accompanied by thrombocytopenia and occasionally by lethal thromboembolism. It thus shows features similar to the heparin-induced thrombocytopenia (HIT) syndrome and probably represents a localized form of this condition. Caution is required in the event of skin necrosis; heparin therapy should be ceased immediately and not used again if the complications of HIT are to be avoided.

Heparin-induced thrombocytopenia: cross-reactivity between standard heparin, low molecular weight heparin, dalteparin (Fragmin) and heparinoid, danaparoid (Orgaran)

The incidence of cross-reactivity between unfractionated heparin and LMWH, fragmin, in patients with HIT is significantly lower (6/15, 40%) than hitherto reported in the literature. 7/9 patients with a negative cross-reactivity test were treated with dalteparin sodium (Fragmin) without any untoward events.

Single amino acid mutation of Fc gamma receptor is associated with the development of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is mediated by a heparin-dependent antibody/platelet factor 4/heparin complex binding to platelets via the Fc gamma receptor (type IIA). A single base polymorphism at position 131 of Fc gamma RIIA changes the native arginine to histidine. In the presence of murine monoclonal IgG1 the former phenotype (Fc gamma RIIAArg131) is functionally characterized by strong platelet aggregation (high responder) and the latter (Fc gamma RIIAHis131) by poor aggregation (low responder). In the presence of human IgG2 the opposite response is observed. It has recently been shown that the heparin-dependent antibody is predominantly of this subclass. We hypothesize that a relationship exists between Fc gamma RIIAHis131 and the development of HIT. We studied 24 normal individuals and 20 HIT patients using VM58, a murine monoclonal IgG1, to characterize the phenotype by platelet aggregrometry, and PCR products, amplified with primers bordering the Fc gamma RIIA polymorphism and hybridized with oligonucleotide probes specific for the single base mutation, to determine the genotype. The distribution of phenotypes and genotypes in the two populations differed, with a greater prevalence of the Fc gamma RIIAHis131 allele in the HIT patient population. Homozygous Fc gamma RIIAArg131 individuals were absent from this group. We conclude that the presence of the Fc gamma RIIAHis131 allele is associated with a predisposition to HIT.

Acute myocardial infarction during coronary angioplasty associated with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia is a well-recognized complication after cardiac or vascular surgery, but it has not been previously reported during percutaneous coronary interventions. This case study describes a patient who developed an acute myocardial infarction during coronary angioplasty in association with the abrupt onset of heparin-induced thrombocytopenia. Since balloon angioplasty achieved a satisfactory angiographic result with a widely patent epicardial vessel, it is postulated that acute myocardial infarction in this patient may have been caused by platelet aggregation and activation resulting in distal small vessel thrombosis and spasm.

Severe vascular adverse effects with thrombocytopenia and renal failure following emetogenic chemotherapy and ondansetron

During late 1991, a series of severe adverse events involving thrombocytopenia, renal insufficiency and thrombotic episodes was observed in patients receiving emetogenic chemotherapy. Two patients died, one of renal failure and one of cerebral haemorrhage in the presence of thrombocytopenia. Other severe side effects included thrombosis of the aorta causing paraplegia and multifocal cerebral infarctions. Common exposure features included the use of ondansetron and dexamethasone as antiemetics, and in most of the cases high dose (100 mg/M2 or more) cisplatin. Retrospective review of a series of patients treated with similar cytotoxic regimens for similar diseases before the use of ondansetron revealed no similar adverse effects, but no substantial differences were observed in renal function or haematologic toxicity in the two groups overall. Sporadic adverse vascular events have been observed before the use of ondansetron. The mechanism remains unknown, and it is not clear whether ondansetron was a factor in the unusual incidence of such events in the present series.