The aim of this trial is to implement record of posterior ECG leads (V7, V8 and V9) in addition to the standard 12-lead ECG in the pre-hospital setting and to evaluate the clinical impact of this implementation: In comparison to a control cohort of STEMI patients diagnosed with a pre-hospital standard 12-lead ECG prior study start, the investigators hypothesize that introducing V7-V9 leads as a clinical routine in the pre-hospital setting will identify patients with STEMI involving LCX and with a non-diagnostic standard 12-lead ECG.