What is STEMI without STE?
Posterolateral or High Posterior MI
High Lateral MI
RV infarct
- Patients presenting with acute chest pain may have clinical STEMI (acute total thrombotic occlusion of a large coronary artery) but no obvious ST-segment elevation in the ECG
- This occurs with STEMI locations that are not well represented by conventional ECG leads
- Such patients are at high for not receiving timely reperfusion therapy and for having poor outcomes
- Easily memorizable ECG signs can help raise awareness of the possibility of STEMI without STE
- If suspected, placing exploring electrodes to the area of interest can quickly uncover the STEMI
Posterolateral or High Posterior MI
- The most common type of missed STEMI
- Almost always due to acute occlusion of the LCX
- May involve the posterior papillary muscle and can cause severe mitral regurgitation
- Earliest ECG sign: ST depression in the anterior chest leads (mirror image of posterior ST elevation)
- Frequent associated findings: subtle Q waves or subtle ST elevation in the inferior or lateral leads
- Can be uncovered by placing exploring electrodes to the back (V7-V8-V9)
High Lateral MI
- The second most commonly missed STEMI
- Almost always due to acute occlusion of the first diagonal branch of the LAD (LAD-D1)
- Fortunately usually small
- Earliest ECG sign: ST elevation in leads I, aVL and V2, but not in V1 or V3, and ST depression in III and aVF
- With the conventional 4x3 lead display format, the spacing of ST deviation resembles the shape of the South African flag (the “South African Flag Sign”)
- Can be uncovered by placing the V4-V5-V6 ECG leads 1 and 2 interspaces higher
RV infarct
- Almost always due to acute occlusion of the proximal RCA
- Almost always associated with acute inferior STEMI
- Recognition of RV infarct, therefore, is now less important because code STEM is usually called anyway for the inferior MI
- Recognition can be important, however, if the ST elevation in the inferior leads is subtle or nondiagnostic
- Clues to suspect RV MI:
- Inferior STEMI with marked ST depression in I and aVL (left leads)
- Inferior STEMI with ST elevation in V1 only but not in V2
- Can be uncovered by placing right-sided chest leads
- If inferior STEMI has been diagnosed, there is no need to waste time to record right-sided chest leads
- Suspected RV MI:
- Use caution with vasodilators (nitrates)
- Consider IV fluids for hypotension with JVD