Background: National and international guidelines on ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation acute coronary syndrome (NSTE-ACS) recommend treatment with antithrombotics and anticoagulants - so called “loading” - at time of diagnosis. Definite STEMI diagnosis with electrocardiogram is valid in pre-hospital scene. But in the absence of biomarker testing, NSTE-ACS diagnosis cannot be confirmed or ruled-out in pre-clinical setting. Despite this diagnostic uncertainty, patients with suspected NSTE-ACS are frequently loaded in pre-hospital setting with overtreatment causing potential harm.

Objective and Methods: The aims of PRELOAD were (a) to determine the pre-clinical loading routine of emergency physicians (EP) in patients with acute chest pain and suspected or definite ACS according to subtype; and (b) to investigate the effect of pretreatment with oral anticoagulants on loading decision. An online survey of pre-clinically working EP in Germany was prospectively performed in November 2022. Nine case-based scenarios including a given diagnosis were provided. Variations in scenarios included medical pre-treatment with oral anticoagulants (I: none, II: phenprocoumon or III: direct oral anticoagulants (DOAC). EP were asked to choose one loading option: a) aspirin (ASS); b) unfractionated heparin (UFH); c) ASS+UFH; or d) No loading. Complete survey forms were eligible for statistical analysis and the current analysis was restricted to STEMI and NSTE-ACS scenarios.

Results: Complete survey forms of 300 EP could be included. The median age of EP was 38 years (±7.8), 74% were male, the median experience level in emergency medicine was 6 (±7.5) years and 57.3% worked in urban areas. 60.3% of participants worked in anesthesiology followed by 27.3% working in internal medicine.

In STEMI scenario without pretreatment, loading was selected by 100% and ASS+UFH (98.7%) was the predominant strategy. In NSTE-ACS scenario without pretreatment and without indicators for urgent coronary angiography, loading was chosen by 76.7% (p<0.001). ASS+UFH (73.9%) was the preferred strategy. In NSTE-ACS with cardiogenic shock and need for urgent catheterization, 88.3% of ED decided to perform loading, ASS+UFH (90.6%) was the preferred option.

Pretreatment with oral anticoagulants resulted in a strategy shift of EP despite ACS subtype. In STEMI patient on phenprocoumon, 95.3% chose loading and ASS (57.7%) followed by ASS+UFH (41.6%) were common strategies. In STEMI patient on DOAC 97% decided to load, and ASS+UFH (52.2%) or ASS (43.3%) were mainly selected.

In NSTE-ACS, phenprocoumon pretreatment was associated with loading decision in 69.3% (p < 0.001), ASS (81.3%) was the predominant strategy (see figure 1). Accordingly, DOAC pretreatment resulted in loading decision in 68.7% (p < 0.001) and ASS (75.7%) was preferred (see figure 1).