ECG Case: Posterior STEMI

• 66 year old male presented to the ER with chest pain that began 2 hours ago. Associated with diaphoresis and nausea. 

• HR 60. BP 110/70 mmHg. 

• Alert + oriented x 3. Appears uncomfortable on stretcher. 

• Normal heart sounds, no murmurs. 

• Lungs clear.

• An ECG was called for immediately and performed within 6 minutes of patient’s arrival. 

The 12-lead ECG shows:

• Sinus rhythm

• ST depression in leads V2-V3

• Dominant R wave in V2 (R/S ratio > 1)

• Subtle ST elevation in leads III and aVF

Based on the ST depression in leads V2-V3, a 15 lead was immediately performed.

• The 15 lead ECG shows ST elevation > 0.5 mm in leads V7-V9

• This confirms the diagnosis of a posterior infarct

Key takeaways: While isolated posterior STEMIs are less common, it is an important diagnosis to think of, especially with the right clinical situation. As the posterior myocardium is not directly seen in the 12-lead ECG, what we will see is reciprocal ST depression in V1-V3. A 15-lead ECG is important to confirm the diagnosis of posterior infarct (ST elevation in V7-V9).