What is the management of a suspected posterior myocardial infarction (MI) on an electrocardiogram (ECG)?

Management of Posterior Myocardial Infarction on ECG

A posterior MI identified on ECG should be treated as a STEMI-equivalent requiring immediate reperfusion therapy with primary PCI as the preferred strategy, with fibrinolytic therapy as an alternative if PCI is not immediately available. 1

ECG Recognition and Diagnosis

Standard 12-Lead ECG Findings

• Posterior MI presents with ST-segment depression in leads V1-V4 (often horizontal with upright T-waves), which represents reciprocal changes from the posterior wall injury 1, 2
• The key distinguishing feature: horizontal ST-segment depression with upright precordial T-waves in ≥2 contiguous leads V1-V4 differentiates true posterior MI from anterior non-STEMI 1
• Patients with downsloping ST-depression and T-wave inversion more likely have anterior non-STEMI rather than posterior MI 1

Enhanced ECG Lead Placement

• Obtain posterior leads V7-V9 when posterior MI is suspected to confirm the diagnosis 1
• ST-elevation ≥0.5 mm in posterior leads V7-V9 confirms posterior STEMI 1
• This additional lead placement increases diagnostic yield and identifies patients at higher risk 1, 2

Immediate Management Algorithm

Time-Critical Actions

1. ECG within 10 minutes of ED arrival with immediate evaluation by experienced physician 1
2. Decision for reperfusion therapy within 10 minutes of ECG diagnosis 1
3. Continuous cardiac monitoring with defibrillation equipment immediately available 1

Reperfusion Strategy

• Primary PCI is the preferred reperfusion strategy for posterior STEMI 1
• Fibrinolytic therapy is a Class II recommendation for posterior MI with symptom onset <12 hours when PCI is not immediately available 1
• Posterior MI represents 15-21% of all MIs and involves significant myocardium at risk, typically from circumflex or posterior descending artery occlusion 1

Supportive Care

Pain Management

• Titrated intravenous opioids (morphine) should be considered for pain relief 1
• Important caveat: morphine delays absorption and diminishes effects of oral antiplatelet agents (clopidogrel, ticagrelor, prasugrel), potentially causing early treatment failure 1

Oxygen Therapy

• Oxygen is indicated only if SaO2 <90% or PaO2 <60 mmHg 1
• Routine oxygen is NOT recommended when SaO2 ≥90% due to evidence suggesting hyperoxia may increase myocardial injury 1

Anxiety Management

• Benzodiazepines should be considered in very anxious patients 1
• Reassurance of patient and family is important 1

Critical Pitfalls to Avoid

Misdiagnosis Risk

• Do NOT withhold reperfusion therapy based solely on ST-depression if clinical suspicion for posterior MI exists 1
• The heterogeneous group with ST-depression includes both benign conditions (LVH, electrolyte abnormalities) and high-risk ACS—posterior MI must be actively excluded 1
• Fibrinolytic therapy in undifferentiated ST-depression patients (without confirmed posterior MI) may increase mortality (15.2% vs 13.8% in controls) 1

Antiplatelet Considerations

• Be aware that both morphine and hypothermia (if used post-cardiac arrest) reduce effectiveness of oral antiplatelet agents 1
• Consider intravenous antiplatelet strategies in these scenarios 1

Special Circumstances

Post-Cardiac Arrest with Posterior MI

• Primary PCI is the strategy of choice in resuscitated cardiac arrest patients with ST-elevation or posterior MI pattern 1
• Urgent angiography within 2 hours should be considered even in unresponsive survivors with high suspicion of ongoing infarction 1
• Targeted temperature management (32-36°C for ≥24 hours) is indicated in unconscious post-arrest patients but should not delay PCI 1