Abstract 1317: Anticoagulant Responses in Patients Receiving Low Molecular Weight Heparin Compared to Unfractionated Heparin for Transesophageal Echocardiography Guided Cardioversion of Atrial Fibrillation: Results from the Assessment of Cardioversion Using Transesophageal Echocardiography Randomized Study
The ACUTE II Study compared low molecular weight heparin (LMWH) to unfractionated heparin (UFH) in patients with atrial fibrillation (AF) >2 days’ duration, undergoing TEE guided cardioversion over a 5 week study period. The present study compares the anticoagulant effects of LMWH to UFH as a prespecified endpoint. In a randomized multicenter trial of 155 patients from 17 clinical sites the anticoagulant activity of LMWH (Enoxaparin, 1 mg/kg sc bid, sanofi-aventis, n=76) was compared to UFH (aPTT 1.5 - 2.5 × control, n=79). Blood samples were drawn at enrollment, day 2 (peri cardioversion) and day 4 in both groups. Samples were taken 3 - 4 hours after the injection of LMWH in patients in the LMWH group. Blood samples were evaluated for anticoagulant activity by measuring anti-Xa, anti-IIa and tissue factor pathway inhibitor (TFPI) levels. The enrollment anti-Xa, anti-IIa and TFPI levels indicated residual circulating UFH in 80% of the patients. These patients had received UFH for ≤ 72 hours prior to enrollment. The anti-Xa levels in both groups increased on day 2. A similar increase in the anti-Xa and anti-IIa levels was observed on day 4. The anti-Xa levels and TFPI levels were higher in the LMWH group compared to the UFH group on days 2 and 4. The ACUTE II study showed that the use of LMWH for bridging therapy in patients with AF undergoing TEE guided cardioversion demonstrates a more predictable anticoagulant response than UFH. In addition, enoxaparin also causes the release of higher levels of TFPI, which contributes to the overall anticoagulantion.