Serial prehospital 12-lead electrocardiograms increase identification of st-segment elevation myocardial infarction

Background. Many prehospital protocols require acquisition of a single 12-lead electrocardiogram (ECG) when assessing a patient for ST-segment elevation myocardial infarction (STEMI). However, it is known that ECG evidence of STEMI can evolve over time. Objectives. To determine how often the first and, if necessary, second or third prehospital ECGs identified STEMI, and the time intervals associated with acquiring these ECGs and arrival at the emergency department (ED). Methods. We retrospectively analyzed 325 consecutive prehospital STEMIs identified between June 2008 and May 2009 in a large third-service emergency medical services (EMS) system. If the first ECG did not identify STEMI, protocol required a second ECG just before transport and, if necessary, a third ECG before entering the receiving ED. Paramedics who identified STEMI at any time bypassed participating local EDs, taking patients directly to the percutaneous coronary intervention (PCI) center. Paramedics used computerized ECG interpretation with STEMI diagnosis defined as an "acute MI" report by GE/Marquette 12-SL software in ZOLL E-series defibrillator/cardiac monitors (ZOLL Medical, Chelmsford, MA). We recorded the time of each ECG, and the ordinal number of the diagnostic ECG. We then determined the number of cases and frequency of STEMI diagnosis on the first, second, or third ECG. We also measured the interval between ECGs and the interval from the initial positive ECG to arrival at the ED. Results. STEMI was identified on the first prehospital ECG in 275 cases, on the second ECG in 30 cases, and on the third ECG in 20 cases (cumulative percentages of 84.6%, 93.8%, and 100%, respectively). For STEMIs identified on the second or third ECG, 90% were identified within 25 minutes after the first ECG. The median times from identification of STEMI to arrival at the ED were 17.5 minutes, 11.0 minutes, and 0.7 minutes for STEMIs identified on the first, second, and third ECGs, respectively. Conclusions. A single prehospital ECG would have identified only 84.6% of STEMI patients. This suggests caution using a single prehospital ECG to rule out STEMI. Three serial ECGs acquired over 25 minutes is feasible and may be valuable in maximizing prehospital diagnostic yield, particularly where emergent access to PCI exists.