What is the initial management for an inferior myocardial infarction (MI) on an electrocardiogram (EKG)?

Initial Management of Inferior Myocardial Infarction on EKG

Immediately activate the cardiac catheterization lab for primary PCI as the preferred reperfusion strategy, or administer fibrinolytic therapy if PCI cannot be performed within 120 minutes of first medical contact. 1, 2

Immediate Actions (Within 10 Minutes)

ECG Evaluation and Risk Stratification

• Obtain right-sided leads (V3R, V4R) in all inferior MI patients to identify right ventricular involvement, which occurs in 40-50% of cases and fundamentally changes management 3, 4
• Record posterior leads (V7-V9) if ST-depression ≥0.05 mV is present in V1-V3, as this represents posterior wall extension requiring STEMI-equivalent treatment 1, 2, 5
• Assess for precordial ST-depression in V1-V6, which predicts multivessel disease (62.7% prevalence) and worse outcomes comparable to anterior MI 6, 7

Immediate Supportive Care

• Initiate continuous ECG monitoring and establish IV access 1
• Administer aspirin 160-325 mg (non-enteric coated, chewed) immediately unless contraindicated by active bleeding, severe hepatic disease, or known hypersensitivity 1
• Give oxygen only if SaO2 <90%—routine oxygen administration when saturations are adequate may increase myocardial injury 2
• Administer sublingual nitroglycerin for ongoing chest pain, but withhold entirely if right ventricular involvement is suspected (see below) 1, 2

Reperfusion Strategy Decision

Primary PCI (Preferred)

• Primary PCI is the definitive treatment and should be performed as soon as possible, ideally within 90 minutes of first medical contact 1, 2
• This is particularly critical in inferior MI with RV involvement, where PCI may produce rapid hemodynamic improvement 3

Fibrinolytic Therapy (Alternative)

• Administer fibrinolytics if PCI cannot be achieved within 120 minutes and symptom onset is <12 hours 2
• Do NOT give fibrinolytics to patients with isolated ST-depression without confirmed posterior MI, as this increases mortality 2
• Fibrinolytic therapy is appropriate even in hypotensive patients with RV infarction if PCI is unavailable 3

Critical Management for Right Ventricular Infarction

If ST-elevation ≥0.5 mm in V3R/V4R is present, management differs fundamentally from standard MI:

Hemodynamic Support

• Aggressively administer IV fluids (rapid boluses of 500-1000 mL normal saline) to maintain RV preload—this is the cornerstone of RV infarction management 3
• Strictly avoid all vasodilators: no nitrates, no morphine, no diuretics, no ACE-inhibitors, as these cause catastrophic hypotension in RV infarction 3

Arrhythmia Management in RV Infarction

• Immediately cardiovert atrial fibrillation to restore atrial contribution to RV filling, which is critically important 3
• Institute dual-chamber pacing immediately if any degree of heart block develops, as AV synchrony is essential for adequate cardiac output 3

Management of Bradycardia and Heart Block

Sinus Bradycardia

• Common in the first hour of inferior MI 1
• Treat with atropine 0.3-0.5 mg IV (repeat up to total 1.5-2.0 mg) only if accompanied by hypotension 1
• Later bradycardia without hypotension requires no treatment 1

Heart Block

• First-degree AV block: no treatment required 1
• Mobitz I (Wenckebach): typically benign in inferior MI; give atropine if hemodynamically significant, consider pacing if atropine fails 1
• Mobitz II or complete heart block: immediate temporary pacing indicated if causing hypotension or heart failure 1

Pain Management

• Administer titrated IV morphine for pain relief, but recognize this delays absorption of oral antiplatelet agents 2
• Avoid morphine entirely if right ventricular involvement is present due to vasodilatory effects 3

Beta-Blocker Administration

• Initiate metoprolol 5 mg IV every 2 minutes for three doses (total 15 mg) once hemodynamically stable, followed by oral metoprolol 50 mg every 6 hours for 48 hours, then 100 mg twice daily 8
• Contraindicated in patients with RV infarction, heart block, or hemodynamic instability 1, 8

Common Pitfalls to Avoid

• Failing to obtain right-sided leads misses RV involvement in nearly half of inferior MIs, leading to inappropriate vasodilator use and potential cardiovascular collapse 3, 4
• Treating RV infarction like standard LV infarction with nitrates and diuretics causes catastrophic hypotension—instead give aggressive IV fluids 3
• Ignoring precordial ST-depression as "reciprocal changes" when it actually indicates either posterior extension (requiring STEMI treatment) or multivessel disease (requiring more aggressive intervention) 2, 6
• Routine lidocaine prophylaxis increases risk of asystole and mortality—do not use prophylactically 1