Heparins reduce the number of heart attacks but caused more minor bleeding after non-ST elevation acute coronary syndromes compared with placebo

Blood clots in the arteries leading to the heart can cause acute coronary syndromes: unstable angina (a feeling of tightness in the chest) or a type of heart attack (non-ST segment myocardial infarction - NSTEMI). Drugs that prevent clots from forming (such as aspirin) or thin the blood (such as heparin) can relieve the problem. Unfractionated heparin (UFH) and low molecular weight heparin (LMWH) are two types of heparin. This review of trials found that UFH and LMWH when given to patients with high-risk unstable angina or NSTEMI in the acute phase of treatment, in addition to standard therapy with aspirin, prevent more heart attacks than placebo but do not reduce mortality, the need for revascularization procedures or recurrent angina. Although there was limited reporting of side-effects, heparins caused more cases of minor bleeding.

Authors' conclusions: 

Compared with placebo, patients treated with heparins had a similar risk of mortality, revascularization, recurrent angina, and thrombocytopenia. However, those treated with heparins had a decreased risk of myocardial infarction and a higher incidence of minor bleeding. Overall, the evidence assessed in this review was classified as low quality according to the GRADE approach. The results presented in this review must therefore be interpreted with caution.

Read the full abstract...

Non-ST elevation acute coronary syndromes (NSTEACS) represent a spectrum of disease including unstable angina and non-ST segment myocardial infarction (NSTEMI). Despite treatment with aspirin, beta-blockers and nitroglycerin, unstable angina/NSTEMI is still associated with significant morbidity and mortality. Although evidence suggests that low molecular weight heparin (LMWH) is more efficacious compared to unfractionated heparin (UFH), there is limited data to support the role of heparins as a drug class in the treatment of NSTEACS. This is an update of a review last published in 2008.


To determine the effect of heparins (UFH and LMWH) compared with placebo for the treatment of patients with non-ST elevation acute coronary syndromes (unstable angina or NSTEMI).

Search strategy: 

For this update the Cochrane Heart Group Trials Search Co-ordinator searched the Cochrane Central Register of Controlled Trials on The Cochrane Library (2013, Issue 12), MEDLINE (OVID, 1946 to January week 1 2014), EMBASE (OVID, 1947 to 2014 week 02), CINAHL (1937 to 15 January 2014) and LILACS (1982 to 15 January 2014). We applied no language restrictions.

Selection criteria: 

Randomized controlled trials of parenteral UFH or LMWH versus placebo in people with non-ST elevation acute coronary syndromes (unstable angina or NSTEMI).

Data collection and analysis: 

Two review authors independently assessed quality of studies and independently extracted data.

Main results: 

There were no new included studies for this update. Eight studies (3118 participants) were included in this review. We found no evidence for difference in overall mortality between the groups treated with heparin and placebo (risk ratio (RR) = 0.84, 95% confidence interval (CI) 0.36 to 1.98). Heparins compared with placebo, reduced the occurrence of myocardial infarction in patients with unstable angina and NSTEMI (RR = 0.40, 95% CI 0.25 to 0.63, number needed to benefit (NNTB) = 33). There was a trend towards more major bleeds in the heparin studies compared to control studies (RR = 2.05, 95% CI 0.91 to 4.60). From a limited data set, there appeared to be no difference between patients treated with heparins compared to control in the occurrence of thrombocytopenia (RR = 0.20, 95% CI 0.01 to 4.24). Assessment of overall risk of bias in these studies was limited as most of the studies did not give sufficient detail to allow assessment of potential risk of bias.