Understanding Posterior Lead ECG

Introduction

Electrocardiography (ECG) is a crucial tool for diagnosing heart conditions. Standard ECG leads focus primarily on the anterior and lateral walls of the heart, but sometimes, additional leads are needed to detect abnormalities in less commonly assessed regions, such as the posterior wall of the left ventricle.

What Is a Posterior Lead ECG?

A posterior lead ECG is an extended ECG setup used to assess ischemia or infarction in the posterior wall of the heart, which may not be evident on a standard 12-lead ECG. Posterior myocardial infarction (MI) can be underestimated or misdiagnosed if only standard leads are used.

The Need for Posterior Leads

• Standard Lead Limitations: The traditional 12-lead ECG mostly focuses on the anterolateral and inferior walls of the heart, often missing posterior infarctions.
• Hidden Posterior Infarctions: While posterior infarctions sometimes produce indirect signs in leads V1-V3 (e.g., ST depressions), direct evidence requires additional leads.

Placement of Posterior Leads

• Lead V7: Positioned at the posterior axillary line, at the level of V6.
• Lead V8: Positioned at the midscapular line, same level.
• Lead V9: Positioned at the paraspinal line, same level.

These leads help to visualize ST elevations or Q waves in the posterior heart wall, confirming the presence of a true posterior myocardial infarction.

Clinical Significance

• Acute Coronary Syndrome (ACS): In suspected ACS with ST depressions in V1-V3, posterior leads should be recorded to identify a posterior STEMI.
• Early Diagnosis: Posterior MI often coexists with inferior or lateral infarctions but can sometimes occur in isolation.
• Improved Treatment Decisions: Recognizing a posterior MI can lead to better therapeutic choices, including urgent reperfusion strategies such as PCI (percutaneous coronary intervention).

Conclusion

A posterior lead ECG is a valuable extension of the standard ECG setup, enabling better detection of posterior myocardial infarctions. Physicians should always consider recording these leads in cases of suspected posterior involvement, ensuring timely and appropriate management of cardiac emergencies.

Source recommendations

1. American Heart Association Guidelines for ECG Interpretation

1. https://www.heart.org/en/health-topics/heart-attack/diagnosing-a-heart-attack/electrocardiogram-ecg-or-ekg
2. https://www.ahajournals.org/doi/10.1161/circulationaha.108.191095
3. https://www.heart.org/-/media/files/affiliates/mwa/kansas-city/kc-cardiac-and-stroke-symposium/2020-event-documents/cardiac-presentations/2-ecg-hockstad.pdf?la=en
4. https://www.ahajournals.org/doi/10.1161/circulationaha.108.191098
5. https://cpr.heart.org/en/courses/acls-prep-ecg-pharmacology

2. European Society of Cardiology Guidelines on STEMI

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Acute-Coronary-Syndromes-ACS-Guidelines
2. https://academic.oup.com/eurheartj/article/39/2/119/4095042
3. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines
4. https://academic.oup.com/eurheartj/article/44/38/3720/7243210
5. https://pubmed.ncbi.nlm.nih.gov/37622654/