Comparison of two treatment durations (6 days and 14 days) of a low molecular weight heparin with a 6 day treatment of unfractionated heparin in the initial management of unstable angina or non-Q-wave myocardial infarction: FRAXIS (FRAXiparine in Ischaemic Syndrome) - The FRAX.I.S. study Group (Eur Heart J, 1999)