Understanding Posterior Myocardial Infarction (MI) on ECG

Introduction

A posterior myocardial infarction (MI) is a type of heart attack that affects the back (posterior) wall of the left ventricle. It is often missed on a standard 12-lead electrocardiogram (ECG) because the typical leads do not directly view the posterior heart.

ECG Findings in Posterior MI

Since the standard ECG does not have direct posterior leads, we must look for indirect signs in the standard leads:

• ST-segment depression in leads V1 to V3: This is a "mirror image" of ST elevation seen in posterior leads.
• Tall R waves in V1-V2: These may be reciprocal to the Q waves that would be seen in a direct posterior lead.
• Upright T waves in V1-V2: Similar reasoning applies here as with R waves.

To confirm a posterior MI, additional posterior leads (V7-V9) should be placed on the patient’s back. If ST elevation of at least 0.5 mm (or 1 mm in men under 40) is observed, a posterior MI is confirmed.

Causes and Risk Factors

Posterior MI is usually caused by an occlusion in the circumflex artery (LCx) or, less commonly, the right coronary artery (RCA). Risk factors include: - Smoking - Hypertension - Diabetes - Dyslipidemia (high cholesterol) - Family history of cardiovascular disease

Importance of Diagnosis

Misdiagnosing a posterior MI can delay critical treatments like percutaneous coronary intervention (PCI) or thrombolysis. If a posterior MI is suspected, immediate cardiology consultation and targeted treatment are required.

Management

• Immediate interventions: Oxygen (if hypoxic), aspirin, and antiplatelet therapy.
• Reperfusion therapy: PCI is preferred if available; thrombolytics if PCI is not an option.
• Medications: Beta-blockers, ACE inhibitors, and statins are used for long-term prevention.

Conclusion

Posterior MI can be tricky to diagnose but recognizing the ECG signs and using posterior leads can ensure timely and life-saving treatment.

Source recommendations

1. American Heart Association Guidelines for the Management of ST-Elevation Myocardial Infarction

1. https://professional.heart.org/en/science-news/2021-acc-aha-scai-guideline-for-coronary-artery-revascularization
2. https://www.ahajournals.org/doi/10.1161/cir.0b013e3182742c84
3. https://www.sciencedirect.com/science/article/pii/S073510972106157X
4. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001309
5. https://pubmed.ncbi.nlm.nih.gov/18071078/

2. European Society of Cardiology Guidelines for the Management of Acute Coronary Syndromes

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Acute-Coronary-Syndromes-ACS-Guidelines
2. https://academic.oup.com/eurheartj/article/44/38/3720/7243210
3. https://pubmed.ncbi.nlm.nih.gov/37622654/
4. https://academic.oup.com/eurheartj/article/42/14/1289/5898842
5. https://pubmed.ncbi.nlm.nih.gov/21873419/