From the Guidelines
Posterior wall myocardial infarction (MI) is diagnosed using specific ECG criteria, including ST segment depression in leads V1-V3, and the use of additional posterior chest wall leads (V7-V9) is recommended to detect ST elevation consistent with infero-basal myocardial infarction, with a cut-point of 0.05 mV ST elevation in leads V7-V9 1. The key diagnostic findings for posterior wall MI include:
- ST segment depression in leads V1-V3 (especially V1-V2)
- Tall, upright R waves in leads V1-V2 (R/S ratio >1)
- Tall, upright T waves in leads V1-V2 These changes represent "mirror image" findings of what would be seen if electrodes were placed on the posterior chest wall. For a definitive diagnosis, these changes should be accompanied by other evidence of acute MI, such as elevated cardiac biomarkers (troponin) and clinical symptoms. Posterior MI rarely occurs in isolation and is commonly associated with inferior or lateral wall infarctions, so additional ST elevations in leads II, III, aVF (inferior) or I, aVL, V5-V6 (lateral) may be present. When suspected, additional posterior leads (V7-V9) can be placed on the patient's back to directly visualize the posterior wall, where ST elevation ≥0.05 mV would confirm the diagnosis, as recommended by the European Heart Journal guidelines 1. Prompt recognition is crucial as posterior MIs are often caused by circumflex artery occlusion and may be missed on standard 12-lead ECGs, potentially delaying appropriate reperfusion therapy. The American College of Emergency Physicians also recommends assessing for fibrinolytic therapy in patients with symptoms suggestive of AMI and presenting within 12 hours of symptom onset if ECG reveals ST depressions greater than or equal to 0.2 mV with upright T-waves in 2 or more contiguous anterior precordial leads (V1 to V4) in patients with clinical presentation suggestive of AMI involving the posterior left ventricular wall 1.
From the Research
Diagnostic Criteria for Posterior Wall Myocardial Infarction (MI)
The diagnosis of a myocardial infarction (MI) of the posterior wall involves specific electrocardiographic abnormalities and clinical findings. The key criteria include:
- Electrocardiographic abnormalities in leads V1, V2, or V3, such as:
- Horizontal ST segment depression
- A tall, upright T wave
- A tall, wide R wave
- An R/S wave ratio greater than 1.0 (in lead V2 only) 2
- The combination of horizontal ST segment depression with an upright T wave can increase the diagnostic accuracy of these findings 2
- The use of additional-lead electrocardiogram with left posterior thorax leads can be helpful, with ST segment elevation greater than 1 mm suggesting an acute posterior wall MI 2
Challenges in Diagnosing Posterior Wall MI
Diagnosing posterior wall MI can be challenging due to the limited visibility of the posterior wall on a standard 12-lead electrocardiogram 3. Additionally, posterior wall MI often occurs in conjunction with inferior or lateral MI, making it essential to consider these associated conditions in the diagnostic process.
Clinical Considerations
In clinical practice, accurate diagnosis of posterior wall MI is crucial for timely and effective management. Delays in recognition can prevent prompt revascularization, leading to significant morbidity 4. The application of the Fourth Universal Definition of Myocardial Infarction can help guide the diagnosis of peri-procedural myocardial infarction after percutaneous coronary interventions 5.