Discrepancies in recommendations for optimal anticoagulation treatment in updated US and European acute coronary syndrome (ACS) management guidelines are confusing for clinicians, thrombosis management experts suggest.

"Without an opportunity to review the reasoning behind each recommendation, it is difficult for readers to decide which recommendations to follow," say John Eikelboom and colleagues from Hamilton General Hospital in Ontario, Canada.

Writing in this week's issue of The Lancet, the authors contend that the most important area of disagreement is the class of recommendation for enoxaparin and fondaparinux.

Guidelines issued by the American College of Cardiology (ACC) and American Heart Association (AHA) assign both these anticoagulants a class 1 rating for both conservatively and invasively managed patients.

In contrast, the European Society of Cardiology (ESC) guidelines give fondaparinux a class 1 rating for conservatively managed patients and none for invasively managed patients, and enoxaparin a class 2a recommendation for both conservatively and invasively managed patients.

Eikelboom and co-authors say it seems the ACC-AHA panel placed more weight on the results of a meta-analysis of randomized trials comparing enoxaparin with heparin in non-ST-elevation ACS patients, and less on the results of the individual SYNERGY (Superior Yield of the New Strategy of Enoxaparin, Revascularization, and Glycoprotein (GP) IIb/IIIa Inhibitors) and OASIS-5 trials.

Conversely, the ESC seemed to place more weight on the SYNERGY and OASIS-5 trials, leading them to downgrade the recommendation for enoxaparin.

The meta-analysis, conducted in 2004 by Petersen et al, showed that enoxaparin reduced the risk for myocardial infarction without increasing the risk for bleeding in comparison with heparin.

As previously reported, the SYNERGY trial also found enoxaparin to be as effective as heparin in NSTE-ACS patients managed by a routine invasive strategy; this trial showed enoxaparin caused more bleeding.

Meanwhile, the OASIS-5 trial showed enoxaparin was as effective as fondaparinux in both conservatively and invasively managed patients, but was associated with increased bleeding during the initial treatment period and excess strokes and deaths at 30 days.

However, an excess of catheter thrombosis with fondaparinux led the ESC not to recommend its use in invasively managed patients, Eikelboom et al note.

By contrast, the ACC-AHA appear to have judged that the increased risk for catheter thrombosis with fondaparinux is not important provided a bolus dose of heparin is administered at the time of the invasive procedure.

The authors say such disagreements could be avoided in future if the committees met and debated any differences between recommendations, and included non-conflicted methodologists to "ensure panelists applied criteria for evidence quality and strength of recommendations consistently."

They add: "Use of a grading system that facilitates explicit consideration and interpretation of criteria might also be of benefit."

Lancet 2008; 371: 1559-1561