Eur Heart J 2004 Oct; 25(19)：1688-94 James A. de Lemosa*, Michael A. Blazingb, Stephen D. Wiviottc, William E. Bradyd, Harvey D. Whitee, Keith A.A. Foxf, Joanne Palmisanod, Karen E. Ramseyd, David W. Bilheimerd, Eldrin F. Lewisc, M. Pfefferc, Robert M. Califfb, Eugene Braunwaldc Received 2 March 2004; received in revised form 11 June 2004; accepted 17 June 2004 published online 19 August 2004. Aims In high risk patients with non-ST elevation acute coronary syndromes (ACS), enoxaparin is generally preferred to unfractionated heparin (UFH). However, less is known about the relative merits of these two forms of heparin in patients receiving concomitant glycoprotein IIb/IIIa inhibitors. Methods and results The A phase of the A-to-Z trial was an open label non-inferiority trial in which 3987 patients with non-ST elevation ACS were randomised to receive either enoxaparin or UFH in combination with aspirin and tirofiban. Inclusion required either ST depression or cardiac biomarker elevation. While the selection of an early management strategy (invasive or conservative) was at the discretion of the local investigator, investigators were asked to designate their plans for an invasive or conservative strategy on the case record form. An early conservative strategy was specified for 1778 patients (45%); this subgroup forms the population for the present analyses. Among patients with a planned conservative strategy, baseline characteristics were similar between those randomised to UFH (n=872) and those randomised to enoxaparin (n=906). The primary endpoint of death, new MI, or documented refractory ischaemia within 7 days of randomisation occurred in 10.6% of patients randomised to UFH and 7.7% of patients randomised to enoxaparin (HR 0.72; 95% CI 0.53-0.99; p=0.04). The combined rate of TIMI major, minor, or loss no-site bleeding was 1.3% in patients treated with UFH and 1.8% in those treated with enoxaparin (p=ns). Conclusions When a conservative approach to catheterisation and PCI was planned for ACS patients receiving tirofiban and aspirin, enoxaparin was associated with superior efficacy and similar bleeding vs UFH.