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

Management of Posterior Myocardial Infarction on ECG

Posterior myocardial infarction should be managed as a STEMI with immediate reperfusion therapy, preferably primary percutaneous coronary intervention (PCI) if available within 120 minutes, or fibrinolysis if PCI is not available within this timeframe.

Diagnosis of Posterior MI

Posterior MI can be challenging to diagnose as it may not show typical ST-segment elevation on standard 12-lead ECG. Key diagnostic features include:

• ST depression and dominant R waves in leads V1-V3 on standard 12-lead ECG
• Additional posterior leads (V7-V9) should be used to confirm the diagnosis, with ST elevation ≥0.5mm considered diagnostic 1
• Continuous ECG monitoring should be established immediately upon suspicion 2

Initial Management

1. Immediate Assessment:

   • Place patient on cardiac monitor with defibrillation capability
   • Obtain 12-lead ECG within 10 minutes of first medical contact
   • Add posterior leads (V7-V9) when posterior MI is suspected
   • Establish IV access and draw blood for cardiac biomarkers (but do not delay reperfusion)

2. Supportive Care:

   • Administer oxygen only if SaO2 <90% or patient is breathless 1
   • Provide pain relief with titrated IV opioids 1
   • Consider mild tranquilizer (benzodiazepine) for anxious patients 1

Reperfusion Strategy

Posterior MI should be managed according to STEMI protocols:

1. Primary PCI (preferred strategy):

   • Transfer immediately to a PCI-capable center if available within 120 minutes 2
   • Aim for door-to-balloon time <90 minutes

2. Fibrinolytic Therapy (if PCI not available within 120 minutes):

   • Administer within 30 minutes of hospital arrival 2
   • Use fibrin-specific agents (tenecteplase, alteplase, or reteplase)
   • Transfer to PCI-capable center after fibrinolysis for routine angiography within 2-24 hours

Pharmacological Therapy

1. Antiplatelet Therapy:

   • Aspirin 160-325mg loading dose, then 75-100mg daily
   • P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) 2

2. Anticoagulation:

   • Unfractionated heparin or low-molecular-weight heparin during PCI
   • Enoxaparin preferred over UFH if fibrinolysis is used 2

3. Additional Medications:

   • Beta-blockers if hemodynamically stable (avoid if hypotensive, in acute heart failure, or with AV block) 2
   • ACE inhibitors within 24 hours (especially for anterior infarction, heart failure, or LVEF <40%)
   • High-intensity statin therapy regardless of baseline cholesterol

Monitoring and Complications

• Continuous ECG monitoring for at least 24 hours 1
• Echocardiography to assess LV and RV function and detect mechanical complications 2
• Monitor for reperfusion arrhythmias
• Watch for complications including heart failure, cardiogenic shock, and mechanical complications

Common Pitfalls in Posterior MI Management

1. Diagnostic Challenges:

   • Posterior MI is frequently missed due to lack of ST elevation on standard 12-lead ECG 3
   • Only 38% of doctors and 10% of paramedics correctly identify potential posterior MI 3
   • Failure to use posterior leads (V7-V9) when indicated

2. Treatment Delays:

   • Misclassification as NSTEMI or unstable angina, leading to delayed reperfusion 4
   • Waiting for cardiac biomarker results before initiating reperfusion therapy

3. Anatomical Considerations:

   • Left circumflex artery is the most common culprit vessel (94% of cases) 4
   • May be associated with inferior or lateral wall involvement

Post-Discharge Management

• Dual antiplatelet therapy for 12 months
• Long-term beta-blocker therapy, especially with heart failure or reduced LVEF
• ACE inhibitors/ARBs for patients with heart failure, hypertension, diabetes, or LVEF <40%
• High-intensity statin therapy
• Cardiac rehabilitation referral
• Risk factor modification and lifestyle changes

By recognizing the unique ECG patterns of posterior MI and treating it as a STEMI with urgent reperfusion therapy, mortality and morbidity can be significantly reduced in these patients.