Andrew Eisenberger

Clinically suspected heparin-induced thrombocytopenia during extracorporeal membrane oxygenation

PURPOSE Patients receiving extracorporeal membrane oxygenation (ECMO) are at risk for thrombocytopenia including heparin-induced thrombocytopenia (HIT). The purpose of this study was to determine the frequency of suspected HIT in patients receiving ECMO and unfractionated heparin (UFH). MATERIALS AND METHODS We conducted a retrospective review in adult patients on ECMO. Patients were included if they received ECMO for at least 5 days and concomitant UFH. RESULTS There were 119 patients who met inclusion criteria. Twenty-three patients (19%) had a heparin-platelet factor 4 immunoassay performed. Patients with suspected HIT had a significantly lower platelet count within the first 3 days of ECMO, 69×10(9)/L (22-126×10(9)/L) vs 87.5×10(9)/L (63-149×10(9)/L); P=.04. The lowest platelet count on the day of HIT testing was 43×10(9)/L (26-73), representing a 71% reduction from baseline. Twenty patients (87%) had an optical density score less than 0.4, and all patients had a score less than 1.0. A functional assay was performed in 7 patients (30%), with only 1 patient having laboratory-confirmed HIT. CONCLUSIONS The evaluation of HIT occurred in a small percentage of patients, with HIT rarely being detected. Patients who had heparin-platelet factor 4 immunoassay testing exhibited lower platelet counts with a similar duration of ECMO and UFH exposure.

Clotting factor changes during the first cycle of oral contraceptive use

OBJECTIVES The risk of venous thromboembolism (VTE) is highest during the initial months of oral contraceptive (OC) use. We sought to evaluate the extent of hemostatic variable changes during the initial OC cycle and if such changes are related to systemic ethinyl estradiol (EE2) exposure. STUDY DESIGN Participants provided multiple blood samples during a 21-day OC cycle (30mcg EE2; 150mcg levonorgestrel) and after a single dose following a washout period. Analytes included D-dimer, factor VIII activity, protein C total antigen and the hepatic proteins corticosteroid-binding globulin (CBG) and sex-hormone-binding globulin (SHBG). EE2 pharmacokinetic analyses related to the 24h after the first OC tablet (OC1) and at steady state (OC21). RESULTS Seventeen women completed the study. D-dimer more than doubled by OC6 (p=.013) and remained elevated at OC21 (p=.012). D-dimer levels within women varied widely from day to day. Factor VIII increased 27% by OC2 (p<.001) but declined to a 9% increase by OC21. Protein C increased only 6%. EE2 steady-state area-under-the-curve ranged from 488 to 1103pg∙h/mL; higher levels were not correlated with greater increases in clotting variables. CBG and SHBG increased significantly but were not significantly correlated with levels of EE2 or with the hemostatic variables. CONCLUSIONS D-dimer increases during the first OC cycle were at least as great as increases seen with longer OC use. These results provide support for the increased VTE risk during initial OC use. The extreme variability in D-dimer levels may be an important component of this risk. IMPLICATIONS This study showed that increases in D-dimer are clearly evident in the first cycle of OC use and may be larger than are seen after a longer duration of use and thus provide biological support for the increased VTE risk during initial OC use found in epidemiological studies.

Effect of CYP2C9 and VKORC1 Gene Variants on Warfarin Response in Patients with Continuous-Flow Left Ventricular Assist Devices.

Bleeding and thrombotic complications continue to plague continuous-flow left ventricular assist device (CF-LVAD) therapy in patients with end-stage heart failure. Warfarin genotyping information can be incorporated into decision making for initial dosing as recommended by the Food and Drug Administration; however, clinical utility of this data in the CF-LVAD population has not been well studied. Genotypes testing for CYP2C9 and VCORC1 polymorphisms were determined in 90 CF-LVAD patients. Outcomes studied were the association of CYP2C9 (*1, *2, or *3) and VKORC1 (-1639 G>A) gene variants with time-to-target international normalized ratio (INR), total warfarin dose, maintenance warfarin dose. Continuous-flow left ventricular assist device patients carrying a rare variant in the VKORC1 gene had a significantly lower cumulative warfarin dose until target INR achieved (18.9 vs. 35.0 mg, p = 0.002), days spent until INR target achieved (4.9 vs. 7.0 days, p = 0.021), and discharge warfarin dose (3.2 vs. 5.6 mg, p = 0.001) compared with patients with wild-type genotype. Genotype-guided warfarin dosing may lead to safer anticoagulation and potentially improve outcomes in CF-LVAD patients.

Abciximab/Heparin Therapy for Left Ventricular Assist Device Implantation in Patients With Heparin-Induced Thrombocytopenia

BACKGROUND Optimal anticoagulation strategy remains uncertain in patients with heparin-induced thrombocytopenia (HIT) and undergoing left ventricular assist device (LVAD) implantation. We describe our protocol of abciximab and heparin in these patients. METHODS Our protocol is to administer abciximab, 0.25 mg/kg loading dose, followed by continuous infusion of 0.125 μg · kg-1 · min-1 throughout cardiopulmonary bypass. Full-dose heparin is then given with subsequent additional doses to maintain an activated clotting time of 400 seconds or longer. The abciximab infusion is stopped 15 minutes after heparin reversal with protamine, and platelets are transfused. RESULTS Six patients underwent LVAD implantation with this protocol in our program. HIT was confirmed in 4 patients was suspected in 2, which was negative after the operation. One patient received a HeartMate XVE (Thoratec Corp, Pleasanton, CA) and the others received HeartMate II (Thoratec Corp). There were no thromboembolic complications. One patient required chest reexploration for bleeding and temporary right VAD support. Postoperative anticoagulation with argatroban was restarted on median postoperative day 3 (range, days 1 to 6) and warfarin was started on day 5 (range, days 3 to 12). Median postoperative intensive care unit stay was 9 days (range, 5 to 76 days), and hospital stay was 22 days (range, 18 to 132 days). After the initial LVAD implantation, 1 patient required HeartMate XVE LVAD exchange to HeartMate II and subsequent heart transplant, both of which were performed with the abciximab/heparin protocol. A HeartMate II device was explanted in another patient after myocardial recovery. The remaining 4 patients are alive on device support. CONCLUSIONS This is the first report of a novel abciximab/heparin protocol for LVAD implantation in patients with HIT. The preliminary results suggest the feasibility and safety of this protocol.

Endogenous thrombin potential changes during the first cycle of oral contraceptive use

OBJECTIVES Venous thromboembolism (VTE) risk increases within months of combination oral contraceptive (COC) initiation. Because elevated endogenous thrombin potential (ETP) has been found in several studies to be a VTE risk factor, we evaluated the extent of ETP changes during the initial cycle of an ethinyl estradiol (EE) and levonorgestrel (LNG) COC. We also assessed the relationship between ETP changes and systemic EE and LNG concentrations. STUDY DESIGN Participants provided multiple blood samples during a first 21-day cycle of a 30-mcg EE/150-mcg LNG COC and after a further 7 days without an active COC. Thrombin generation measured with and without addition of activated protein C (APC) yielded ETP+APC and ETP-APC and the normalized APC sensitivity ratio (nAPCsr). EE and LNG pharmacokinetic analyses were conducted over 24 h after the first COC tablet and again at steady state. RESULTS Thrombin generation was determined in 16 of the 17 women who completed the study. Mean ETP-APC increased steadily to 21% above baseline at 24 h after the 6th COC tablet (COC624; p<.001) and to 28% above baseline at steady state (COC21; p<.001). The percentage increase in mean ETP+APC was considerably more - 54% at COC624 and 79% at steady state. Mean nAPCsr increased by 28% at COC624 and by 41% at steady state. Higher concentrations of EE or LNG were not correlated with greater increases in ETP. CONCLUSIONS ETP increases during the first COC cycle were substantial. IMPLICATIONS The early increases in ETP may provide biological support for the rapid increase in VTE risk during initial COC use. The lack of association between this clotting system perturbation and the systemic EE concentration is surprising and deserves further study.