Low molecular weight heparin decreases rebound ischemia in unstable angina or non-Q-wave myocardial infarction: the Canadian ESSENCE ST segment monitoring substudy

OBJECTIVES The goal of this study was to determine whether enoxaparin was more effective than heparin in reducing recurrent ischemic episodes. BACKGROUND Continuous ST segment monitoring is a simple tool for assessment of ischemia and identifies patients with a worse prognosis. Little is known about the impact of low molecular weight heparin on ST segment shift. METHODS Patients were randomized to receive enoxaparin or heparin (mean 3.4 days). Three-lead ST segment monitoring was performed for the first 48 h (n = 220) and an additional 48 h (n = 174) after intravenous study drug discontinuation (mean 1.9 days later). RESULTS During initial monitoring, ischemia rates were similar among the heparin and enoxaparin groups (27.2% vs. 22.6%, P = 0.44); however, the time to first ischemic episode was earlier among heparin-treated patients (11 ± 11 vs. 25 ± 18 min, P = 0.001). After drug discontinuation, ischemic episodes occurred more frequently (44.6% vs. 25.6%, P = 0.009), and the total ischemic duration was greater among heparin patients (18 ± 39 vs. 5 ± 12 min/24 h, P = 0.005). Recurrent ischemia occurred more frequently after discontinuation in the heparin (46% vs. 31%, P = 0.043), but not the enoxaparin, group (18.4% vs. 25%, P = 0.33). Regardless of treatment, patients with ischemia were more likely to die or experience (re)infarction at one year (18.4% vs. 8.3%, P = 0.023). CONCLUSIONS ST segment shift occurs frequently in unstable angina/non-Q-wave myocardial infarction despite antithrombotic therapy and is associated with worse one-year prognosis. Enoxaparin is a more effective antithrombotic treatment than unfractionated heparin and leads to greater prevention of rebound ischemia.