Bridging with Half-Therapeutic Dose Enoxaparin for Sub-Therapeutic INR among Outpatients with Ventricular Assist Devices

Abstract

Background: Long-term anticoagulation therapy with warfarin is recommended for LVAD patients. Compared to other warfarin-treated patients, the LVAD population has a higher rate of suboptimal INRs and a lower average time in the therapeutic window. Suboptimal anticoagulation is a major reason for hospital readmission. We describe our experience with the use of half-dose enoxaparin (0.5 mg/kg/dose) bridging therapy, as a potential alternative to hospital readmission for LVAD-patients with subtherapeutic INRs who may be at higher risk of thrombotic events. Methods: LVAD outpatients with sub-therapeutic INRs were selected to receive half therapeutic dose enoxaparin as bridge therapy based on our VAD anticoagulation protocol. Selection criteria included current INR, VAD type and timing of implantation, history of bleeding or thrombotic events, renal function, medication adherence, and ability to effectively administer enoxaparin injections. The general threshold for bridging was an INR ! 1.6. Enoxaparin was dosed as 0.5 mg/kg every 12 hours. Outpatient INR monitoring and follow-up was conducted by the VAD Coordinator and pharmacist. Within 24 hours of initiation of therapy, a pharmacist telephoned the patient to reinforce proper administration technique and to answer medication-specific questions. Additional telephone communications were conducted by the pharmacist and VAD Coordinator to assess for bleeding complications and duration of therapy. Patients are monitored routinely for thrombus at each ambulatory clinic visit. Results: During the initial 6 months of this program, 15 patients (11 HeartMate II, 3 HeartWare LVAD, 1 Heartware BiVad) were treated with half-dose enoxaparin. The mean INR upon initiation of therapy was 1.4 (range 1.2 to 1.7). Patients received an average of 7.2 enoxaparin doses (range 4 to 14) for a mean duration of therapy of 3.5 days (range 2 to 7). In total, 108 doses were administered accounting for 54 patient days of therapy. No patient was admitted to a hospital due to bleeding or thrombotic events. Minor bleeding, described as mild bleeding at the injection site and increased bruising, was reported in 5 patients (30%). During the observation period, 14 patients (93.3%) completed the protocol with achievement of a therapeutic INR; one patient discontinued therapy due to hospital admission not related to anticoagulation management. Conclusion: In this small series, half-dose enoxaparin appears to be a feasible strategy to bridge selected ambulatory VAD patients with sub-therapeutic INRs. Further investigation is needed to determine its safety and efficacy in a larger population of patients