Think of HIT When Thrombosis Follows Heparin

ISTH DIC subcommittee communication on anticoagulation in COVID-19

Hypercoagulability is an increasingly recognized complication of SARS-CoV-2 infection. As such, anticoagulation has become part and parcel of comprehensive COVID-19 management. However, several uncertainties exist in this area, including the appropriate type and dose of heparin. In addition, special patient populations, including those with high body mass index and renal impairment, require special consideration. Although the current evidence is still insufficient, we provide a pragmatic approach to anticoagulation in COVID-19, but stress the need for further trials in this area.

Pregnancy and thrombophilia

The physiological changes that occur during pregnancy create a hypercoagulable milieu. This hypercoagulable state is thought to be protective, especially at the time of labor, preventing excessive hemorrhage. The presence of hereditary or acquired causes of thrombophilia during pregnancy tilts the balance in favor of unwanted venous thromboembolism and adverse pregnancy outcomes due to vascular uteroplacental insufficiency. These adverse pregnancy outcomes include recurrent pregnancy losses, intrauterine fetal death, intrauterine growth retardation, preeclampsia and placental abruption. Much of the current data with regards to the association of the different thrombophilias and pregnancy-related complications are based on retrospectively designed studies. This lack of randomization, in-homogeneity of patient populations, varying case definitions, selection biases and inadequately matched control populations, have given rise to conflicting data with regard to screening for, and treatment of, pregnant women with suspected thrombophilias. The limited data that we have support the use of anticoagulant drugs for the prevention of pregnancy-related complications in the setting of thrombophilia. Heparin and low-molecular-weight heparins are the anticoagulant drugs of choice as they do not cross the placental barrier and, hence, do not cause fetal anticoagulation or teratogenicity. Warfarin can be used from the 12th week of gestation onwards but is preferably reserved for the postpartum period.

Heparin-induced thrombocytopenia in patients with ventricular assist devices: are new prevention strategies required?

Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating antiplatelet factor 4/heparin antibodies. However, clinical HIT (thrombocytopenia or thrombosis, or both) develops in only a minority of patients who form antibodies. It is difficult to distinguish HIT from non-HIT thrombocytopenia in patients after ventricular assist device (VAD) implantation. Further, the risks of heparin-induced immunization and clinical HIT approach 65% and 10%, respectively, in this patient population, with a particularly high risk of cerebrovascular ischemia/infarction. Given the apparent high risk of HIT and its complications, and the diagnostic challenges, we suggest that the VAD patient population be evaluated using alternative, nonheparin agents for routine postimplantation anticoagulation.

Reducing thrombotic complications in the perioperative setting: an update on heparin-induced thrombocytopenia

Heparins are widely used in the perioperative setting. Immune heparin-induced thrombocytopenia (HIT) is a serious, antibody-mediated complication of heparin therapy that occurs in approximately 0.5%-5% of patients treated with heparin for at least 5 days. An extremely prothrombotic disorder, HIT confers significant risks of thrombosis and devastating consequences on affected patients: approximately 38%-76% develop thrombosis, approximately 10% with thrombosis require limb amputation, and approximately 20%-30% die within a month. HIT antibodies are transient and typically disappear within 3 mo. In patients with lingering antibodies, however, re-exposure to heparin can be catastrophic. In the perioperative setting, heightened awareness is important for the prompt recognition, diagnosis, and treatment of HIT. HIT should be considered if the platelet count decreases 50% and/or thrombosis occurs 5-14 days after starting heparin, with other diagnoses excluded. On strong clinical suspicion of HIT, heparin should be discontinued and a parenteral alternative anticoagulant initiated, even before laboratory confirmation of HIT is obtained. Subsequent laboratory test results may help with the decision to continue with nonheparin therapy or switch back to heparin. Heparin avoidance in patients with current or previous HIT is feasible in most clinical situations, except perhaps in cardiovascular surgery. If the surgery cannot be delayed until HIT antibodies have disappeared, intraoperative alternative anticoagulation is recommended.

Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse drug effect that is characterized by platelet activation, hypercoagulability, and a resulting increased risk for thrombosis, both venous and arterial. This disorder is autoimmune-like, because the target antigen is a multimolecular complex of the "self" protein, platelet factor 4, and heparin. HIT usually begins 5 to 10 days after starting heparin, especially when administered intra- or perioperatively, although a rapid onset of thrombocytopenia can occur if heparin is given to a patient with circulating HIT antibodies that resulted from a recent heparin exposure. The clinical diagnosis is supported if heparin-dependent, platelet-activating antibodies are detectable. Treatment includes cessation of heparin and use of an alternative non-heparin anticoagulant, such as danaparoid, lepirudin, or argatroban. Warfarin must be avoided or postponed, as the acute phase of HIT poses a high risk for coumarin necrosis, particularly limb loss due to venous limb gangrene.