Posterior myocardial infarction: are we failing to diagnose this?

INTRODUCTION Isolated posterior ST-elevation myocardial infarction (STEMI) accounts for up to 7% of STEMIs. The diagnosis is suggested by indirect anterior-lead ECG changes. Confirmation requires presence of ST-elevation in posterior-leads (V7-V9). We investigated the ability of hospital doctors and paramedics to diagnose posterior STEMI (PMI). METHODS Doctors in the emergency department and acute medical unit at two teaching hospitals and West Midlands Ambulance Service Paramedics were asked to interpret a 12-lead ECG illustrating ST-depression and dominant R-wave in V1-V2 in the context of cardiac chest pain, and identify PMI as a potential diagnosis. Their ability to identify PMI was compared with their ability to diagnose anterolateral STEMI on a 12-lead ECG. We assessed whether doctors knew that posterior-leads were required to confirm PMI and whether doctors and nurses could position posterior-leads. RESULTS 44 of the 117 doctors (38%) identified PMI as a potential diagnosis. PMI was identified by 73% of registrars, 30% of senior house-officers and 18% of house-officers. 50% of doctors who identified potential PMI knew that posterior-leads were required to confirm the diagnosis. 20% of doctors correctly positioned these and 19% knew the diagnostic criteria for PMI (ST-elevation ≥1 mm in V7-V9). 13 of the 60 nurses (22%) in the emergency department and acute medical unit correctly positioned posterior-leads. Five of the 50 (10%) paramedics identified PMI as a potential diagnosis. Doctors and paramedics were significantly better at diagnosing anterolateral STEMI than PMI. CONCLUSIONS A significant proportion of doctors and paramedics were unable to diagnose PMI. Hence, the majority of PMIs may be being missed. Routine use of posterior-leads in the standard assessment of patients with chest pain may identify up to an additional 7% of STEMIs, allowing prompt reperfusion therapy, which would reduce morbidity and mortality.