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.