Heparin-induced thrombocytopenia and cardiovascular diseases

Heparin-induced thrombocytopenia following coronary artery bypass grafting: a diagnostic dilemma

The diagnosis of heparin-induced thrombocytopenia (HIT) is a challenge in post-cardiac surgery patients because of the high incidence of non-immune thrombocytopenia and heparin–platelet factor 4 antibodies in these groups. We present a case of HIT in a post coronary artery bypass surgery patient, which was successfully treated with prompt recognition and discontinuation of heparin products.

Structural Evidence for the Tetrameric Assembly of Chemokine CCL11 and the Glycosaminoglycan Arixtra™

Understanding chemokine interactions with glycosaminoglycans (GAG) is critical as these interactions have been linked to a number of inflammatory medical conditions, such as arthritis and asthma. To better characterize in vivo protein function, comprehensive knowledge of multimeric species, formed by chemokines under native conditions, is necessary. Herein is the first report of a tetrameric assembly of the human chemokine CCL11, which was shown bound to the GAG Arixtra™. Isothermal titration calorimetry data indicated that CCL11 interacts with Arixtra, and ion mobility mass spectrometry (IM-MS) was used to identify ions corresponding to the CCL11 tetrameric species bound to Arixtra. Collisional cross sections (CCS) of the CCL11 tetramer-Arixtra noncovalent complex were compared to theoretical CCS values calculated using a preliminary structure of the complex deduced using X-ray crystallography. Experimental CCS values were in agreement with theoretical values, strengthening the IM-MS evidence for the formation of the noncovalent complex. Tandem mass spectrometry data of the complex indicated that the tetramer-GAG complex dissociates into a monomer and a trimer-GAG species, suggesting that two CC-like dimers are bridged by Arixtra. As development of chemokine inhibitors is of utmost importance to treatment of medical inflammatory conditions, these results provide vital insights into chemokine-GAG interactions.

The non-anticoagulant heparin-like K5 polysaccharide derivative K5-N,OSepi attenuates myocardial ischaemia/reperfusion injury

Heparin and low molecular weight heparins have been demonstrated to reduce myocardial ischaemia/reperfusion (I/R) injury, although their use is hampered by the risk of haemorrhagic and thrombotic complications. Chemical and enzymatic modifications of K5 polysaccharide have shown the possibility of producing heparin-like compounds with low anticoagulant activity and strong anti-inflammatory effects. Using a rat model of regional myocardial I/R, we investigated the effects of an epimerized N-,O-sulphated K5 polysaccharide derivative, K5-N,OSepi, on infarct size and histological signs of myocardial injury caused by 30 min. ligature of the left anterior descending coronary artery followed by 1 or 24 h reperfusion. K5-N,OSepi (0.1-1 mg/kg given i.v. 15 min. before reperfusion) significantly reduced the extent of myocardial damage in a dose-dependent manner. Furthermore, we investigated the potential mechanism(s) of the cardioprotective effect(s) afforded by K5-N,OSepi. In left ventricular samples, I/R induced mast cell degranulation and a robust increase in lipid peroxidation, free radical-induced DNA damage and calcium overload. Markers of neutrophil infiltration and activation were also induced by I/R in rat hearts, specifically myeloperoxidase activity, intercellular-adhesion-molecule-1 expression, prostaglandin-E(2) and tumour-necrosis-factor-α production. The robust increase in oxidative stress and inflammatory markers was blunted by K5-N,OSepi, in a dose-dependent manner, with maximum at 1 mg/kg. Furthermore, K5-N,OSepi administration attenuated the increase in caspase 3 activity, Bid and Bax activation and ameliorated the decrease in expression of Bcl-2 within the ischaemic myocardium. In conclusion, we demonstrate that the cardioprotective effect of the non-anticoagulant K5 derivative K5-N,OSepi is secondary to a combination of anti-apoptotic and anti-inflammatory effects.

Serum Antibodies to the Heparin/Platelet Factor 4 Complex Are an Independent Predictor of Thrombotic Complications Following Pediatric Fontan Surgery

Antibodies to the heparin/platelet factor 4 complex (heparin/PF4) are linked to the pathogenesis of heparin-induced thrombocytopenia (HIT) and to the thrombotic complications. We investigated thrombotic events during early follow-up in a pediatric cardiac surgical population to ascertain whether there is a relation between heparin/PF4 antibody concentration and post-surgical thrombotic complications. One hundred and five consecutive pediatric patients treated by Fontan surgery were studied. The presence of serum heparin/PF4 immunoglobulins IgG, IgA, and IgM (collectively termed HIT antibodies) were measured in preoperative and postoperative blood samples by enzyme-linked immunosorbent assay. On day six after Fontan surgery, HIT-related thromboses was identified in total of 11 patients (10.5%). HIT antibodies were detected in 34 of 105 patients (32.4%). The post-surgical nadir platelet count was significantly lower in patients who developed antibodies ( p < 0.001). We found the odds ratio (OR) for this composite endpoint was 4.06 ( p < 0.001). Seropositive status for heparin/PF4 antibodies was an independent predictor of thrombotic events (OR 2.28; p < 0.001). Quintile analysis revealed that the median nadir platelet value was significantly lower in patients with higher HIT antibody titers. Patients in the highest quintile of HIT antibody titer all experienced thrombotic events, while only two thrombotic events occurred in patients in the lowest quintile ( p < 0.001). Heparin-induced thrombocytopenia is a rare occurrence in pediatric cardiac surgical patients. Patients who develop antibodies to the heparin/PF4 complex have a significantly higher rate of postoperative thrombotic events than patients who lack these antibodies. Within the seropositive group, the risk of developing thrombosis increased with the plasma antibody concentration.

Contribution of bleeding and thromboembolic events to in-hospital mortality among patients with thrombocytopenia treated with heparin

In a population of patients experiencing thrombocytopenia while treated with heparin, bleeding and thromboses are well-appreciated complications, but their relative contributions to mortality have been less well described. In this population, the aims of this study were (1) to identify the independent predictors of bleeding and (2) to compare the incidence and the strength of association of bleeding and of new thromboses to in-hospital mortality. The independent predictors of bleeding and in-hospital mortality were identified using multivariate logistic regression models on the 1,478 patients who developed thrombocytopenia after their enrollment in the Complications After Thrombocytopenia Caused by Heparin (CATCH) study. The independent predictors of bleeding were chronic hematologic disorders, intra-aortic balloon pump, congestive heart failure, and platelet count nadir <120 x 10(9)/L. Although bleeding (n = 141 [10%]) and thromboembolic complications (n = 135 [9%]) were equally prevalent, the former was less strongly associated than the latter with in-hospital mortality (odds ratio 1.75, 95% confidence interval 1.01 to 3.03, and odds ratio 2.77, 95% confidence interval 1.67 to 4.61, respectively). In conclusion, medical management should be directed mainly at the prevention of thromboembolic complications, while additionally considering the risk for bleeding.

Heparin/PF4 antibodies formation after heparin treatment: temporal aspects and long-term follow-up

BACKGROUND

Heparin-induced thrombocytopenia is characterized by the presence of heparin-induced antibodies against heparin/platelet factor-4 (PF4) complex and paradoxical thrombosis. Little is known on the persistence of antiheparin antibodies in blood. The aim of this study was to evaluate the time course of heparin/PF4 antibodies in patients exposed to heparin.

METHODS

We initially enrolled 500 patients treated with unfractionated heparin as part of perioperative management of coronary artery bypass graft; those who developed serologically confirmed heparin/PF4 antibodies were selected for further follow-up. Over 3 years, we repeatedly assessed serum concentration of antibodies (by enzyme-linked immunosorbent assay) and occurrence of thrombotic events.

RESULTS

One hundred thirty-one patients (26.2%) developed anti-PF4/heparin antibodies, which persisted for a median time of 90 days (Quartile 1-Quartile 3, 31-186). At 30 days, patients with antibodies had higher incidence of thrombotic events (28.2% vs 14.9%, P < .01) and death/myocardial infarction (14.5% vs 7.8%, P < .001). Of the 131 patients with antiheparin/PF4 antibodies, 78 had already developed antibodies before cardiac surgery; such patients became serologically negative more slowly than patients who developed antibodies after surgery. Over 3 years of follow-up, patients with anti-PF4/heparin antibodies developed 65 thrombotic events, 25 patients developed deep vein thrombosis and/or pulmonary embolism, and 20 patients myocardial infarction.

CONCLUSIONS

Patients with heparin-induced antibodies are more likely to develop thrombosis after cardiac surgery. Patients in whom antibodies are present before surgery show longer persistence of antibodies and increased incidence of thrombotic events over time. Persistence of antibodies suggests that these patients may be at risk for developing thrombosis; and therefore, further exposure to heparin should be limited.

Heparin-induced thrombocytopenia

Each year, 25% of all hospitalized patients are affected by venous thromboembolism, a disease comprising deep vein thrombosis and pulmonary embolism, that is responsible for up to 10% of all inpatient deaths (Alikhan, Peters, Wilmott, Cohen, 2004). Used in both the treatment and the prevention of venous thromboembolism, heparin is administered to more than 12 million patients each year in the United States, making it one of the most widely prescribed medications and the leading intravenous anticoagulant. Heparin-induced thrombocytopenia is an antibody-mediated adverse drug reaction to heparin therapy with potentially life-threatening complications. This article discusses the pathogenesis, diagnosis, and treatment of patients with heparin-induced thrombocytopenia.

Direct thrombin inhibition during percutaneous coronary intervention in patients with heparin-induced thrombocytopenia

Patients with or at risk of heparin-induced thrombocytopenia (HIT) who are undergoing percutaneous coronary intervention (PCI) are at particular risk of thrombosis due to the prothrombotic nature of HIT and the endovascular disruption from PCI. Patients require aggressive anticoagulation during PCI, and alternative, nonheparin anticoagulation is recommended over heparin in patients with acute or previous HIT. Argatroban, bivalirudin, and lepirudin are nonheparin, fast-acting, parenteral direct thrombin inhibitors (DTIs). Multicenter, prospective studies have demonstrated that argatroban and lepirudin each reduce thrombosis in HIT and that argatroban and bivalirudin each provide adequate anticoagulation during PCI in patients with or at risk of HIT. We review current therapeutic practices with direct thrombin inhibitors in patients with or at risk of HIT during PCI, including individuals requiring periprocedural anticoagulation, and the factors influencing the choice of DTI in this setting.