Treatment of heparin-associated thrombocytopenia and thrombosis with low molecular weight heparin (CY 216)

Management of Heparin-Induced Thrombocytopenia and Heparin-Induced Thrombocytopenia and Thrombosis Syndrome

Summary: Heparin-induced thrombocytopenia (HIT) is an immune mediated response to heparin in which antibody driven thrombosis can have a dramatic life-threatening expression. There is much interest on this subject including studies on the pathophysiologic mechanism, the clinical managements of the initial stages of HIT versus the HIT-positive patient requiring continued anticoagulation versus the HIT patient with thrombosis, the pros and cons of available alterr~aci~~ anticoagulants, and the laboratory assays to aid in the diagnosis of HIT with particular reference to the sensitivity/specificity of the new heparin-platelet factor 4 antibody titer assay. A comprehensive account of these timely issues is given in this article.

Heparin-induced thrombocytopenia: natural history, diagnosis, and management

Heparin-induced thrombocytopenia (HIT) is an under-recognized, limb- and life-threatening complication of pharmacologic heparin administration. Antibody formation against heparin complexed to platelet factor 4 (PF4) is central to the pathogenesis of HIT. Heparin: PF4 antibodies promote platelet activation and aggregation as well as excess thrombin generation which may lead to clinical thrombosis. HIT should be suspected in patients who develop thrombocytopenia with or without associated arterial or venous thrombosis while on heparin. HIT is a clinical diagnosis. Specialized HIT assays should be interpreted with care. The cornerstone of HIT management is the discontinuation of all forms of heparin exposure and the institution of anticoagulation with an alternative agent. The direct thrombin inhibitors lepirudin and argatroban are currently available and approved for use in patients with HIT.

Hirudin therapy during thrombolysis for venous thrombosis in heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is the most common drug-related thrombocytopenia. Thromboembolic complications occur in approximately 50% of patients with HIT and result in limb amputation and death in up to 20% and 30% respectively. Because patients with a history of HIT may require future intravenous anticoagulation but have a high-risk of thromboembolism if re-challenged with heparin, alternative therapies are necessary when further anticoagulation is indicated. The use of direct thrombin inhibitors in HIT patients who also require thrombolytic therapy offers unique challenges to anticoagulant monitoring and safety. We present a case of progressive ileofemoral deep venous thrombosis in a patient with a history of HIT in order to review the combined use of hirudin and thrombolysis in this setting.

Heparin-Induced Thrombocytopenia

Heparin's anticoagulation effect makes it the principal component in the immediate treatment of all thrombotic diseases. After hemorrhage, the most important complication of heparin is thrombocytopenia, the decrease in the number of blood platelets. Ten cases of "heparin-induced thrombocytopenia" are described, and guidelines for diagnosing heparin-induced thrombocytopenia in patients who present for cardiac and vascular surgery are given. Methods of treating patients with heparin-induced thrombocytopenia, including use of arachidonic acid derivatives, antiplatelet agents, other anticoagulants, heparinoids, natural and synthetic thrombin inhibitors, hirudin, and defibrinogenation with ancrod, are discussed.

Lack of In Vitro Cross-Reactivity Predicts Safety of Low-Molecular Weight Heparins in Heparin-Induced Thrombocytopenia

Alternative anticoagulation in patients with heparin-induced thrombocytopenia (HIT) is often problematic. The relatively high cross-reactivity rate reported for the low-molecular-weight heparins (LMWH) has discouraged their use in this setting. This study has investigated the safety of using the LMWH Fragmin, based on a negative heparin-dependent platelet aggregation test using the latter, in patients with proven HIT. Fifty-three evaluable patients with clinical and laboratory evidence of HIT were evaluated for cross-reactivity with Fragmin using a Fragmin-dependent platelet aggregation test. In 20 of 38 patients who showed no in vitro cross-reactivity. Fragmin was substituted for unfractionated heparin. The outcome of these 20 patients was evaluated and compared to that of the remaining 33 patients, in whom anticoagulates were ceased or warfarin or Orgaran was used. Eighteen of 20 patients treated with Fragmin increased their platelet count by ≥50 x 109/l from a mean nadir of 57.9 ± 4.7 x 109/l within 2.8 ± 0.29 days following substitution of Fragmin for unfractionated heparin. Twenty-eight of the 33 remaining patients who did not receive Fragmin increased their platelet count by ≥50 x 109/l from a mean nadir of 53.0 ± 4.8 x 109/l within 3.0 ± 0.29 days. In seven patients (two treated with Fragmin), response could not be evaluated due to death within 36 h of cessation of heparin or discharge from hospital. The results indicate that in vitro cross-reactivity testing employing a heparin-dependent platelet aggregation assay can be safely used to select patients with HIT for further anticoagulation with LMWH. Key Words: Fragmin—Crossreactivity—Heparin-induced thrombocytopenia.

Weight-based argatroban dosing nomogram for treatment of heparin-induced thrombocytopenia

BACKGROUND

Manufacturer recommendations for argatroban use in the setting of heparin-induced thrombocytopenia (HIT) state that the dosage should be titrated to a goal activated partial thromboplastin time (aPTT) of 1.5-3 times the baseline aPTT. The lack of a clear dosing strategy with argatroban may result in delayed stabilization of aPTT. There are no published nomograms to guide the dosing of argatroban.

OBJECTIVE

To study the anticoagulant effect and incidence of bleeding and thrombotic events in patients receiving argatroban, with doses determined using a weight-based nomogram.

METHODS

Patients with suspected or documented HIT at an 800-bed teaching community hospital were prospectively treated, in a nonrandomized, nonblinded manner, with argatroban; dosage adjustments were made according to 1 of 2 variations of a dosing nomogram: standard or hepatic/critically ill. The primary outcomes were time to aPTT stabilization and percentage of patients whose aPTTs were within the therapeutic range of 45-90 seconds at 6, 12, 24, 48, 72, and 96 hours. Secondary outcomes were the percentage of patients whose aPTTs were subtherapeutic, supratherapeutic, or above the therapeutic threshold of 45 seconds at each time interval; incidence of thrombotic events; number of dosage adjustments to achieve stabilization; and number of major bleeding events.

RESULTS

Fifty-one patients were prospectively treated using the standard (n = 34) and hepatic/critically ill (n = 17) nomograms. Mean time to aPTT stabilization was 16.25 hours with the standard nomogram and 27.05 hours with the hepatic/critically ill nomogram. The percentages of patients with aPTTs within the therapeutic range at each time interval were 82.4%, 82.4%, 88.2%, 96.4%, 100%, and 100% with the standard nomogram and 58.8%, 82.4%, 76.5%, 93.3%, 100%, and 90.9% with the hepatic/critically ill nomogram. There were no thrombotic events after the initiation of argatroban. Three cases of major bleeding occurred.

CONCLUSIONS

The nomogram is an effective dosing tool for achieving and maintaining therapeutic levels of anticoagulation.

The homozygous FcγRIIIa-158V genotype is a risk factor for heparin-induced thrombocytopenia in patients with antibodies to heparin-platelet factor 4 complexes

We hypothesized that Fcγ receptor IIIa (FcγRIIIa), a polymorphic receptor for the Fc portion of immunoglobulin G (IgG) other than FcγRIIa, was involved in heparin-induced thrombocytopenia (HIT). FcγRIIa-131 and FcγRIIIa-158 genotypes were determined in 102 patients with definite HIT and in 2 control groups of patients treated by heparin (86 subjects without detectable antibodies [Abs] to heparin-platelet factor 4 [H/PF4], Ab- group; 84 patients with Abs to H/PF4 without HIT, Ab+ group). There were no significant differences in genotype distribution or allele frequencies between the 3 groups for FcγRIIa-131H/R polymorphism. In contrast, FcγRIIIa-158V homozygotes were more frequent in the HIT group than in the Ab+ group (P = .02), a difference that was more pronounced in patients with high levels of anti-H/PF4 Abs (P = .01). Since anti-H/PF4 Abs are mainly IgG1 and IgG3, clearance of sensitized platelets may be increased in patients homozygous for the FcγRIIIa-158V allotype, thus contributing to the development of thrombocytopenia. (Blood. 2004;104:2791-2793)

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.

On the prophylactic and therapeutic use of danaparoid sodium (Orgaran) in patients with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a rare but dangerous complication of heparin prophylaxis or treatment. The present laboratory tests to measure heparin-associated antibodies are not specific. The diagnosis of HIT mainly depends on the decrease in platelet count and on clinical symptoms. To evaluate clinical outcome, bleeding complications and platelet counts were evaluated in 45 patients with HIT type II (HIT II) treated prophylactically (subcutaneous injections) or therapeutically (intravenous infusion) with danaparoid. Group I included 24 patients with HIT II without thromboembolic complications who received danaparoid twice daily subcutaneously (10 IU/kg) for a mean of 16 days. Group II included 21 patients with thromboembolic complications. They were treated with intravenous danaparoid (2.6 IU/kg/h +/- 1.1) for a mean of 17 days. During subcutaneous prophylaxis, mean anti-Xa levels of 0.2 U/mL and during intravenous treatment, mean anti-Xa levels of 0.4 U/mL were reached. No deaths, amputations, or serious bleeding complications occurred, and no new thromboses were observed in both patient groups. Treatment with danaparoid led to a fast normalization of the platelet counts. This normalization occurred earlier and the concentration of platelets was higher in patients treated with intravenous doses. Danaparoid with subsequent vitamin K-antagonist treatment effectively prevents thromboembolic complications in patients with HIT.

Pharmacodynamic characterization of the interaction between abciximab or tirofiban with unfractionated or a low molecular weight heparin in healthy subjects

AIMS

The objective of our study was to define the interaction between either unfractionated heparin (UFH) or a low molecular weight heparin, reviparin (REV), and the pharmacodynamic profile of the GPIIb/IIIa-antagonists abciximab (ABC) or tirofiban (T).

METHODS

Two studies each containing 18 healthy subjects were performed, and all were pretreated with aspirin (ASA) for 3 days. Volunteers then received UFH (5000 IU bolus/infusion 7 IU kg(-1) h(-1) for 7 h, n = 6), REV (4200-anti-Xa-IU s.c., n = 6) or placebo (n = 6). One hour later, ABC (study I) or T (study II) were given by i.v. infusion for 6 h. The pharmacodynamic effects measured were bleeding time (BT), fibrinogen-binding at the GPIIb/IIIa-receptor (FIB), expression of the platelet secretion marker CD62, and ADP (20 microM)- and collagen (5 microg ml(-1))-induced platelet aggregation.

RESULTS

After treatment with both GPIIb/IIIa-antagonists, prolongation of BT occurred to a similar magnitude (approximately 25-30 min) and was not affected by UFH or REV-comedication. ABC or T with ASA alone resulted in nearly the same magnitude of reduction in FIB and platelet aggregation. After coadministration with UFH, FIB was significantly higher (thus less inhibited) than after after T + ASA alone (19 +/- 16% vs 55 +/- 36%) or ABC + ASA alone (8 +/- 9% vs 32 +/- 11%). This attenuation of FIB was not seen with REV. Inhibition of ADP-and collagen-induced aggregation tended to be attenuated by treatment with UFH (e.g. ADP-induced aggregation at 0.25 h after ABC + ASA alone =13 +/- 4%; after coadministration with UFH = 40 +/- 26%). No such changes were noted with REV. Minor reductions in CD62-expression were seen in subjects given ABC or T alone, but expression was not affected by UFH or REV.

CONCLUSIONS

Co-medication with UFH attenuated platelet inhibition during treatment with GPIIb/IIIa-antagonists, but these effects were not seen with the low molecular weight heparin reviparin. The results show that administration of reviparin together with abciximab or tirofiban did not adversely affect the pharmacodynamic profile of these GPIIb/IIIa-antagonists.

Argatroban anticoagulant therapy in patients with heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an immune-mediated syndrome caused by heparin. Complications range from thrombocytopenia to thrombocytopenia with thrombosis. We report a prospective, historical- controlled study evaluating the efficacy and safety of argatroban, a direct thrombin inhibitor, as anticoagulant therapy in patients with HIT or HIT with thrombosis syndrome (HITTS).

METHODS AND RESULTS

Patients with HIT (isolated thrombocytopenia, n=160) or HITTS (n=144) received 2 microgram. kg(-1). min(-1) IV argatroban, adjusted to maintain the activated partial thromboplastin time 1.5 to 3.0 times baseline value. Treatment was maintained for 6 days, on average. Clinical outcomes over 37 days were compared with those of 193 historical control subjects with HIT (n=147) or HITTS (n=46). The incidence of the primary efficacy end point, a composite of all-cause death, all-cause amputation, or new thrombosis, was reduced significantly in argatroban-treated patients versus control subjects with HIT (25.6% versus 38.8%, P=0.014). In HITTS, the composite incidence in argatroban-treated patients was 43.8% versus 56.5% in control subjects (P=0.13). Significant between-group differences by time-to-event analysis of the composite end point favored argatroban treatment in HIT (P=0.010) and HITTS (P=0.014). Argatroban therapy, relative to control subjects, also significantly reduced new thrombosis and death caused by thrombosis (P<0.05). Argatroban-treated patients achieved therapeutic activated partial thromboplastin times generally within 4 to 5 hours of starting therapy and, compared with control subjects, had a significantly more rapid rise in platelet counts (P=0.0001). Bleeding events were similar between groups.

CONCLUSIONS

Argatroban anticoagulation, compared with historical control subjects, improves clinical outcomes in patients who have heparin-induced thrombocytopenia, without increasing bleeding risk.

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.

Heparin-induced thrombocytopenia: historical review

Heparin-induced thrombocytopenia (HIT) and heparin-induced thrombosis (HITT), recognized as clinical entities only in the past 30 years, have become a major concern for all who work in the field of thromboembolism, its prevention, and treatment. Studies of the 1930 to 1970 era were primarily devoted to the interaction of heparin with platelets in vivo with no knowledge that such interaction could lead to serious morbidity and mortality in as many as 3-5% of patients receiving the drug. When this was recognized in the 1970s, concerns arose regarding recognition and diagnoses. Clinicians, laboratory investigators, and drug companies entered into many research collaborations. The advent of low molecular weight heparin (LMWH) and heparinoids led to studies of their interaction with the IgG antibody that was identified as the mechanism for heparin-induced thrombocytopenia of the immune type. Newer, more sensitive test systems were developed and applied to studies comparing the new low LMWHs and heparinoids. These studies showed a lower incidence of immune-mediated thrombocytopenia with LMWH. The specificity of the antibody for platelet factor 4-heparin complexes led to the development of new tests in the early 1990s. This was soon followed by experiments with antithrombin drugs such as hirudin and argatroban as replacements for heparin in the HIT-HITT syndrome. Shorter courses of heparin therapy and the use of LMWH in place of heparin had become more standard practice in the 1990s.

Determination of heparin-induced thrombocytopenia: a rapid flow cytometric assay for direct demonstration of antibody-mediated platelet activation

Heparin-induced thrombocytopenia (HIT) and thrombosis are serious complications of heparin therapy. Recently, we have reported a practical and rapid functional flow cytometric assay (FCA) for the diagnosis of HIT with high specificity and sensitivity compared with the radioactive serotonin-release assay (SRA). In the present study, we added an immune-neutralization assay to directly demonstrate the antibody-mediated process, and tested the immune compatibility of low-molecular-weight heparin (LMWH) Lovenox and the heparinoid Orgaran (danaproid) using plasma from 18 patients with HIT confirmed by both FCA and SRA. The clinical utility of this modified method is demonstrated by a pediatric patient with a complex clinical presentation who developed thrombocytopenia with multiple thromboses while on heparin therapy. ELISA and SRA (performed in three independent laboratories) for diagnosis of HIT were both negative. In contrast, the FCA for detecting activated platelets expressing anionic phospholipids, was highly and reproducibly positive with both unfractionated and LMWH. Another FCA also demonstrated the surface expression of the alpha-granule membrane p-selectin (CD62p). Compatibility testing with the heparinoid Orgaran was also positive (and with plasma from 4 of the 18 patients with HIT). Heparin was discontinued, along with full recovery of the platelet count. The capacity of the patient's plasma to activate platelets in the presence of heparin gradually decreased over 4 weeks consistent with antibody clearance. The responsible mechanism was clarified using an immune-neutralization assay, which showed a dose response neutralization of the plasma activity by antibodies against human Immunoglobulin G (IgG) and IgM. This assay was also reproducible in the 18 patients with HIT. We conclude that the functional FCA with its modification is practical, sensitive, and specific for reliable diagnosis of HIT. It can simultaneously assess the compatibility of alternative therapies and directly confirm the antibody-mediated process. Further, it is particularly useful to clarify mechanisms of thrombocytopenia and thrombosis and to direct therapy in patients with a complex presentation and confounding laboratory results who often need prompt diagnosis and treatment.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia with or without thrombosis has been recognized increasingly as a serious complication of heparin use. This article reviews type II heparin-induced thrombocytopenia, which is mediated by an antibody that in most cases has specificity for a complex between heparin and platelet factor 4, a secreted platelet alpha-granule protein. The antibody-heparin-platelet factor 4 complex can activate platelets and endothelial cells, thereby initiating thrombosis. Clinical thrombosis in this syndrome may be arterial or venous. Treatment of the syndrome requires discontinuation of heparin and institution of an alternative anticoagulant.

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.

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

Although several new anticoagulant drugs are in development, heparin remains the drug of choice for most anticoagulation needs. The clinical effects of heparin are meritorious, but side effects do exist. Important untoward effects of heparin therapy including heparin-induced thrombocytopenia, heparin-associated osteoporosis, eosinophilia, skin reactions, allergic reactions other than thrombocytopenia and alopecia will be discussed in this article.

Heparin-induced thrombocytopenia with thrombosis: incidence, analysis of risk factors, and clinical outcomes in 108 consecutive patients treated at a single institution

Heparin-induced thrombocytopenia with thrombosis (HITT) can lead to serious morbidity and may be potentially fatal. We reviewed our experience with this entity over a 4-year period, to determine the following: 1) incidence and type of thrombosis in patients with heparin-induced thrombocytopenia (HIT), 2) clinical consequences of thrombosis, i.e., amputation, cerebrovascular accidents and death, 3) risk factors associated with development of thrombosis, and 4) impact of therapy on clinical outcomes in patients with HITT. Between 1991-1994, 108 patients were diagnosed to have HIT by heparin-induced platelet aggregation test. Thirty-two (29%) of these developed thrombotic complications, of which 20 were venous, 8 arterial, and 4 both. Five of the 32 died, 3 underwent amputations, and 3 had cerebrovascular accidents. The patients who developed thrombotic complications, when compared to those with HIT alone, were older (68.7 +/- 11.5 vs. 63.3 +/- 16 years, P = .05), had more severe thrombocytopenia (platelet count 46,300 +/- 30,400/mm3 vs. 62,500 +/- 34,400/mm3, P = .02), and developed it earlier (6.0 +/- 2.9 vs. 7.4 +/- 3.1 days, P = .03). Multivariate analysis showed that severity of thrombocytopenia and early fall in platelet count were independent risk factors for development of thrombotic complications. We did not find an association between development of thrombosis and clinical events (myocardial infarction, cardiac procedures or surgery, noncardiac surgery, and sepsis) that occurred immediately prior to onset of thrombocytopenia. Heparin was stopped in all 32 patients with HITT. Six received no additional therapy, and one received a single dose of aspirin. Three of these 7 died. The other 25 received anticoagulant or multiagent therapy, with 2 deaths. The death rate was lower in those who were treated with anticoagulant or multiagent therapy (P = .05). We conclude that: 1) Thrombotic complications occur in about 29% of hospitalized patients who develop HIT. 2) Early, severe fall in platelet count in elderly patients receiving heparin appears to be associated with development of thrombotic complications. 3) Our data do not show an association between development of thrombotic complications and clinical events immediately preceding the diagnosis of HIT. 4) In addition to discontinuation of heparin, anticoagulant or thrombolytic therapy should be considered in patients with HITT.

Report of successful use of argatroban as an alternative anticoagulant during coronary stent implantation in a patient with heparin-induced thrombocytopenia and thrombosis syndrome

Heparin-induced thrombocytopenia and thrombosis syndrome (HITTS) is a severe complication of heparin caused by an antibody response to the heparin-platelet factor 4 complex which results in severe thrombosis. Heparin rechallenge in HITTS patients carries a high risk of inducing thrombosis. Antithrombin agents represent treatment alternatives in HITTS patients who require anticoagulation. We report successful coronary stent implantation in a HITTS patient using the antithrombin agent argatroban.

Use of enoxaparin in patients with heparin-induced thrombocytopenia syndrome

PURPOSE

To determine whether low molecular weight heparin (LMWH) can be an alternative to unfractionated heparin (UH) for patients with heparin-induced thrombocytopenia syndrome (HIT).

METHODS

The diagnosis of HIT was established in 126 patients by platelet aggregometry with UH (1 U/ml). These plasma samples were also tested for the ability to aggregate platelets in the presence of the LMWH enoxaparin (1 U/ml). Two patients with the HIT syndrome, after negative platelet aggregometry testing with enoxaparin, were anticoagulated with enoxaparin.

RESULTS

Fifteen plasma samples that tested negative to UH also tested negative to enoxaparin. Forty-three of 126 (34%) UH-positive plasma samples aggregated platelets in the presence of enoxaparin. Twenty-two of 102 (22%) plasma samples with limited positive aggregation responses (minimal or no change in optical density) aggregated platelets in the presence of enoxaparin. However, 21 of 24 (88%) strongly positive plasma samples (30% to 60% change in optical density at 3 to 27 minutes) also aggregated platelets in the presence of enoxaparin. Two patients with HIT who received enoxaparin after aggregation testing demonstrated no cross-reactivity to enoxaparin achieved adequate anticoagulation and did not develop HIT.

CONCLUSIONS

Thirty-four percent of plasma samples from patients with HIT (88% of those strongly positive) aggregated platelets in the presence of enoxaparin. Patients with HIT may safely receive enoxaparin if their plasma does not aggregate platelets in the presence of enoxaparin.

Cross-reactivity study of low molecular weight heparins and heparinoid in heparin-induced thrombocytopenia

Previous studies suggested that the cross-reactivity rates of low molecular weight (LMW) heparins with the antibody in heparin-induced thrombocytopenia (HIT) are more than 80%, whilst that of the LMW heparinoid (Orgaran) is relatively low at about 10%. These earlier studies were limited either in the number of patients studied, or in investigating only a single drug. They were also inadequate due to non-standardisation of testing conditions. This study compares three LMW heparins (Fragmin, Clexane, Fraxiparin) and a heparinoid (Orgaran) in their cross-reactivity rates with the HIT antibody. The sera of 45 HIT patients were tested using platelet aggregometry under standardised conditions. The cross-reactivity rates are: 7% (Orgaran), 89% (Fragmin), 83% (Clexane) and 86% (Fraxiparin). Although there are no controlled trials to determine the in vivo cross-reactivity rates of LMW heparins and heparinoid, the low in vitro cross-reactivity rate of the latter favours its use in HIT. Nevertheless, the therapeutic use of these drugs in HIT should be preceded by exclusion of in vitro cross-reactivity.

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.

Heparin-induced thrombocytopenia: an improved method of detection based on lumi-aggregometry

Heparin-induced thrombocytopenia (HIT) is a recognized complication of heparin administration. Early detection of this syndrome is essential in the prevention of immune-mediated thromboembolic sequelae. The 14C-serotonin release assay (SRA) has been used in reference laboratories to identify sera from patients on heparin therapy capable of inducing platelet dense granule release. In an attempt to improve existing methodologies, we employed luminographic detection of platelet-dense granule ATP release as an endpoint of HIT antibody-mediated platelet activation. Sera tested included 10 SRA confirmed positive and five SRA confirmed negative samples (to establish the assay), five samples from patients with thrombocytopenia not on heparin therapy and 34 patients suspected of HIT syndrome. All SRA confirmed positive sera (n = 19) were positive by the luminographic procedure. 24/26 SRA confirmed negative sera and five sera from thrombocytopenic patients not on heparin therapy were negative using luminography. Two of four sera yielding equivocal SRA results were found to be positive by the luminographic technique. The data suggest that the use of a lumiaggregometer in the coagulation laboratory to detect HIT antibody-induced platelet activation is a reliable alternative to the SRA. The luminographic procedure is both rapid and sensitive, and does not require the use of biohazardous radio-isotopes.

Thrombolysis to treat arterial thrombotic complications of heparin-induced thrombocytopenia

An 80-year-old man with diabetes developed acute ischemia of the right leg secondary to heparin-induced thrombocytopenia while being treated for a pulmonary embolism. For fear of recurrent thrombosis at the operative site, he was treated with cessation of heparin, placement of a Greenfield filter, and intra-arterial infusion of urokinase into the popliteal artery for 36 hours. All arterial thrombus resolved with no complications. One week later he underwent a below-knee popliteal to anterior tibial artery translocated cephalic vein bypass and transmetatarsal amputation for progressive gangrene of the right toes. The graft remains patent 2 years later. This patient represents the eighth case reported in the world literature in which thrombolytic therapy was used to treat arterial thrombotic complications of heparin-induced thrombocytopenia. Five patients were successfully treated without complications, two others required major amputations, and one died of adrenal hemorrhage. Although thrombolytic therapy should be used cautiously for treatment of arterial thrombotic complications of heparin-induced thrombocytopenia, this adjunct may prove useful and safe in selected cases.

Clotting by heparin of hemoaccess for hemodialysis in an end-stage renal disease patient

Clotting of vascular access in hemodialysis patients remains a significant problem. The routine use of heparin to anticoagulate the blood during hemodialysis has been helpful in increasing the life span of vascular access in these patients. However, the use of heparin is not without complications. Heparin-induced thrombocytopenia is one of the well-recognized drug-induced thrombocytopenic disorders that by itself usually does not cause serious morbidity. A small proportion of these patients concomitantly develop "paradoxic" acute thrombotic complications. Myocardial infarction, ischemic damage to lower extremities leading to amputation, and cerebrovascular accident with permanent neurologic deficits or leading to death are just some of the disastrous complications. We report a case of paradoxic clotting of the hemoaccess in a patient receiving hemodialysis treatment associated with the use of heparin that has not been previously described. The patient had heparin-dependent platelet antibody resulting in a decrease in platelet count and clotting of the hemoaccess.

Platelet aggregation in response to four low molecular weight heparins and the heparinoid ORG 10172 in patients with heparin-induced thrombocytopenia

A simple rapid platelet aggregation test was used to evaluate cross-reactivity of four low molecular weight heparins and the heparinoid ORG 10172 in three patients with heparin-induced thrombocytopenia. The low molecular weight heparins cross-reacted in 11 out of 12 tests. The heparinoid ORG 10172 did not cross-react in any of the patients. One patient was treated with ORG 10172 and thrombocytopenia resolved.

Complications from heparin-induced thrombocytopenia in patients undergoing cardiopulmonary bypass

The purpose of this study was to evaluate retrospectively the incidence and severity of heparin-induced thrombocytopenia (HIT)-related complications in patients undergoing cardiopulmonary bypass. We reviewed the records of 1,500 consecutive patients who underwent cardiopulmonary bypass between August 1987 and December 1991 at Thomas Jefferson University Hospital. During this period of time, there were 1,155 coronary artery bypass graft operations (77 percent); 225 valve replacements and repairs, or both (15 percent); 60 combination coronary artery bypass graft or valve operations, or both (4 percent); and 60 miscellaneous procedures (4 percent). Although not all patients with postoperative complications were tested for the HIT antibody, 11 patients (0.75 percent) were diagnosed with HIT. There were 17 complications in these 5 men and 6 women including 6 cases of ischemic limbs which required amputation, 4 strokes, 2 instances of saphenous vein graft occlusion with resulting myocardial infarction, 2 cases of pulmonary emboli, 1 case of phlegmasia cerulea dolens, and 2 deaths. The complications occurred an average of 3.6 days postoperatively, with a range of occurrence of 1 to 11 days postoperatively. The mean nadir platelet count at the time of recognition was 123,000/mm3 (range 32,000 to 193,000/mm3) with 9 of 11 patients (81.8 percent) having counts greater than 100,000/mm3. There was, however, a mean percent decrease in the platelet count of 50 percent (range, 31 to 75 percent) from the time of first exposure to heparin to the time of recognition of HIT. In our patients, HIT was not related to the type, duration of treatment with or amount of heparin, or to pretreatment with aspirin.

Dipyridamole in the Management of Severe Heparin-associated Thrombocytopenia

Severe heparin-associated thrombocytopenia (SHAT) is a rare, life-threatening condition. The aim of this prospective pilot study was to determine the safety and efficacy of dipyridamole-heparin infusion (DHI) in the management of the condition. We studied 6 patients (4 males and 2 females) aged 28 to 80 years (mean 50.5±14.2) with deep venous thrombosis and/or pulmonary embolism who developed SHAT a few days following heparin therapy. Heparin-dependent platelet aggregating factor was demonstrated ex vivo in the plasma of 4 patients. 240-300 mg of dipyridamole/day (4 mg/kg/day) was mixed with heparin in the same bag and given as a continuous intravenous infusion. Anticoagulation was continued successfully along with significant platelet recovery over a few days. This regimen was without side-effects. We conclude that DHI may provide an effective therapy for patients with SHAT.