Posterior Myocardial Infarction and ECG Diagnosis

Introduction

A posterior myocardial infarction (PMI) is a type of heart attack affecting the back (posterior) portion of the left ventricle. It often occurs in conjunction with an inferior or lateral myocardial infarction due to shared blood supply from the right coronary artery (RCA) or the left circumflex artery (LCx).

ECG Characteristics of Posterior Myocardial Infarction

Diagnosing a posterior MI on a standard 12-lead ECG can be challenging because the posterior wall is not directly represented by standard leads. Instead, physicians look for reciprocal changes in the anterior leads (V1–V3):

Key ECG Findings:

1. ST-segment depression in leads V1–V3 (reciprocal change reflecting posterior ST elevation).
2. Tall, broad R waves in V1–V3 (reciprocal of Q waves that form in posterior infarction).
3. Upright T waves in V1–V3 (opposite of the expected T-wave inversion seen in infarction).
4. Dominant R waves in V2 and V3 (R-wave > S-wave suggests a posterior infarct).

Confirming Diagnosis: Posterior Leads

To confirm a posterior MI, additional posterior ECG leads (V7, V8, and V9) should be recorded: - ST-segment elevation of >=0.5 mm in V7–V9 is diagnostic for posterior infarction.

Associated Risks and Comorbidities

Since posterior infarctions often occur alongside inferior or lateral infarctions, they may involve: - Right ventricular infarction (if the RCA is involved → check right-sided ECG leads like V4R). - Conduction abnormalities (AV block with inferior infarcts due to RCA involvement). - Heart failure or cardiogenic shock if a large myocardial area is affected.

Management and Treatment

Treatment of posterior MI follows standard myocardial infarction protocols:

Acute Management:

1. Dual antiplatelet therapy (DAPT) – Aspirin and P2Y12 inhibitor (clopidogrel, ticagrelor, or prasugrel).
2. Anticoagulation – Heparin or enoxaparin.
3. Reperfusion therapy – Primary PCI (preferred) or fibrinolysis if PCI is unavailable.
4. Oxygen, nitrates, and analgesia (if no contraindications).

Post-MI Care:

• Beta-blockers, ACE inhibitors, and statins to reduce further risk.
• Monitoring for arrhythmias and heart failure.

Conclusion

A posterior myocardial infarction requires detailed ECG interpretation, often looking for reciprocal anterior lead changes. Early recognition and appropriate management significantly improve outcomes.

Source recommendations

1. European Society of Cardiology (ESC) Guidelines for the Management of Acute Myocardial Infarction in Patients Presenting with ST-Segment Elevation

1. https://pubmed.ncbi.nlm.nih.gov/28886621/
2. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Acute-Coronary-Syndromes-ACS-Guidelines
3. https://academic.oup.com/eurheartj/article/39/2/119/4095042
4. https://www.escardio.org/static-file/Escardio/Guidelines/2017%20STEMI%20ehx393_web%20addenda%20-%20FOR%20WEB.pdf
5. https://academic.oup.com/eurheartj/article/42/14/1289/5898842

2. American Heart Association (AHA) Guidelines for the Management of ST-Elevation Myocardial Infarction (STEMI)

1. https://www.ahajournals.org/doi/10.1161/cir.0b013e3182742c84
2. https://pubmed.ncbi.nlm.nih.gov/23247304/
3. https://www.ncbi.nlm.nih.gov/books/NBK532281/
4. https://www.ahajournals.org/doi/10.1161/circulationaha.107.188209
5. https://pubmed.ncbi.nlm.nih.gov/18071078/