Activated partial thromboplastin time overestimates anti-coagulation in left ventricular assist device patients

Abstract

Patients with continuous-flow left ventricular assist devices (LVADs) require long-term systemic anti-coagulation after implantation to prevent thrombotic events. Thrombosis of an LVADmay result in cerebrovascular accidents, device exchange or death. Over the past several years, there has been a reported increase in the risk of device thrombosis in the United States, without a clear explanation for the increase. Proper anticoagulation management in patients with an LVAD is essential for thrombosis prevention. Unfractionated heparin (UFH) is often used to bridge LVAD patients early after surgical implantation or when oral anti-coagulation is sub-therapeutic. Due to its mechanism of action, the activated partial thromboplastin time (aPTT) reflects the function of heparin’s effects on the intrinsic pathways of the coagulation cascade, whereas the anti-factor Xa (anti-Xa) assay measures heparin’s impact on anti-thrombin. The aPTT is currently the most commonly used laboratory test for monitoring UFH. A large number of variables can affect the aPTT, rendering the patient receiving UFH at risk of supraor sub-therapeutic anticoagulation. Routine monitoring of UFH using the anti-Xa assay has been reported to provide a more accurate reflection of anti-coagulation. Since the 1990s, the American College of Chest Physicians and the College of American Pathologists have recommended that aPTT goals be titrated to a corresponding anti-Xa level according to individual institutions. It is currently unknown whether the aPTT and anti-Xa levels reflect the same level of anti-coagulation in LVAD patients. Due to a higher-than-expected LVAD thrombosis rate at our institution, we hypothesized that the aPTT may not adequately reflect the level of anti-coagulation with UFH in LVAD patients; therefore, we simultaneously measured the aPTT and anti-Xa activity in both LVAD recipients and patients admitted with acute decompensated heart failure (ADHF). We performed a prospective, single-center quality improvement project that included all hospitalized patients receiving