Emergency Medical Services (EMS) Agency
ECG OF THE MONTH – NOVEMBER 2018
Paramedics respond to a 58 year old male with a history of hyperlipidemia presenting with chest pain. He describes the pain as substernal pressure. The pain started 30 minutes prior to evaluation when he was doing yard work. On exam, the patient appears diaphoretic and in moderate discomfort.
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Rate: 60 bpm
Rhythm: Sinus Rhythm – there are p waves before each QRS
ST Segment Elevation >1mm
In 2 or more contiguous
Reciprocal Changes: No
Other Abnormalities: There are ST depressions in V1-V4.
This ECG and patient history is consistent with an isolated posterior myocardial infarction (MI). It is frequently missed because the ST elevations are not apparent since the infarction is occurring posteriorly. The ECG records posterior electrical activity from the anterior torso. For this reason, the ST segments appear depressed. If one were to obtain a posterior ECG (record electrical activity from the back), leads V7, V8, V9 would be elevated, signifying a posterior MI.
Figure 1: Placement of leads V7, V8, V9
Figure 2. ST elevation noted on posterior ECG on leads V7-V9.
- ST depression in the septal and anterior precordial leads V1-V3, sometimes V4. The ST segments are classically horizontal.
- Tall broad R waves in anteroseptal leads (V1-V3)
- Upright T waves in V1-V3
- Dominant R wave (R/S ratio > 1) in V2
More commonly, posterior MIs present as an extension of an inferior or lateral myocardial infarction. In these cases, ST elevation may be seen in the inferior or lateral leads and are more recognizable as STEMIs. However, isolated posterior MIs occur and are often missed if one doesn’t look for them!
Figure 3. ST elevations are present in the infero-lateral leads. Also notice the ST depressions in V1-V3 consistent with posterior involvement as well.
This patient is having a posterior MI and requires primary PCI/cardiac catheterization. Treatment should be in accordance with TP 1211 “Cardiac Chest Pain”. Contact the base and discuss your findings, including concern for a posterior MI, transmission of the ECG to a STEMI Receiving Center, and appropriate destination.