What is the management plan for a patient with an inferior wall myocardial infarction (MI)?

Management of Inferior Wall Myocardial Infarction

Patients with inferior wall MI require immediate reperfusion therapy within 12 hours of symptom onset, with critical assessment for right ventricular involvement using lead V4R before administering nitrates, as RV infarction occurs in up to 50% of cases and dramatically increases mortality from 6% to 25-30%. 1, 2

Immediate Actions (First 10 Minutes)

• Administer aspirin 160-325 mg orally immediately (chewed, not swallowed) upon arrival, which reduces 35-day mortality by 21% when combined with reperfusion therapy 1, 2
• Obtain 12-lead ECG within 10 minutes to confirm ST-segment elevation ≥1 mm in inferior leads (II, III, aVF) 1, 2
• Record lead V4R immediately to detect right ventricular involvement—ST elevation ≥1 mm in V4R is the single most predictive finding for RV infarction, though this finding may resolve within 10 hours 1, 2
• Establish continuous cardiac monitoring with emergency equipment immediately available (atropine, lidocaine, transcutaneous pacing patches, defibrillator, epinephrine) 1
• Provide oxygen only if oxygen saturation <90%—avoid routine oxygen in non-hypoxemic patients 1
• Administer morphine sulfate or meperidine for adequate analgesia 1

Critical Assessment for Right Ventricular Involvement

Before administering any nitrates, assess for RV infarction because nitrate administration in RV infarction causes profound hypotension by reducing preload 2

Clinical Features of RV Infarction:

• Classic triad: hypotension, clear lung fields, and elevated jugular venous pressure (specific but <25% sensitive) 1
• Distended neck veins or Kussmaul's sign 1
• Right atrial pressure ≥10 mm Hg and >80% of pulmonary wedge pressure 1
• RV infarction increases in-hospital mortality to 25-30% compared to 6% without RV involvement 1

Reperfusion Strategy (Within 12 Hours)

Maximum benefit occurs within the first hour ("golden hour"), with 35 lives saved per 1,000 patients treated within the first hour versus 16 lives saved per 1,000 when treated 7-12 hours after symptom onset. 1

Primary PCI (Preferred):

• Perform primary PCI if available within 90 minutes of first medical contact by experienced operators with access to emergency CABG 1, 2
• Door-to-balloon time should be ≤90 minutes 2
• Administer high-dose intravenous heparin during primary PCI 1
• Patients with RV infarction are high-priority candidates for reperfusion due to significantly higher mortality 1

Fibrinolytic Therapy (If PCI Unavailable):

• Initiate fibrinolytic therapy if PCI cannot be performed within 120 minutes and patient presents within 12 hours of symptom onset 1
• Door-to-needle time should be ≤30 minutes 2
• Use fibrin-specific agents: tissue plasminogen activator (tPA), streptokinase, or urokinase 1
• Reperfusion therapy beyond 12 hours offers little benefit 1
• Thrombolytic therapy in older patients (>70 years) with RV infarction remains ineffective with mortality of 38.5% versus 7.7% in younger patients 3

Management of Conduction Disturbances

Sinus bradycardia and AV block are common in inferior MI, especially with RV involvement, and often resolve spontaneously with reperfusion. 1

• For sinus bradycardia with severe hypotension: administer atropine 0.3-0.5 mg IV, repeated up to 1.5-2.0 mg total 1, 2
• Second-degree type I (Wenckebach) AV block: usually requires no treatment unless causing adverse hemodynamics; use atropine first, then pacing if needed 1
• Second-degree type II or complete AV block: consider transvenous pacing 1
• For complete AV block with RV infarction and hemodynamic compromise: use AV sequential pacing to maintain AV synchrony 1
• AV block associated with inferior MI is usually supra-Hisian and typically resolves spontaneously or after reperfusion 1
• Avoid agents that slow AV conduction (beta-blockers, digitalis, verapamil, amiodarone) in the setting of AV block 1

Pharmacological Management

If NO Right Ventricular Involvement:

• Give sublingual nitroglycerin (up to 3 doses, 5 minutes apart) unless systolic BP <90 mmHg or heart rate <50 or >100 bpm 1
• Initiate intravenous nitroglycerin at 5 µg/min, increase gradually until mean systolic arterial pressure falls by 10-15% but not below 90 mm Hg 1

If Right Ventricular Involvement Present:

• Avoid nitrates and diuretics completely—they cause profound hypotension by reducing RV preload 1
• Volume loading with IV normal saline is the cornerstone of treatment for hypotension when the right ventricle is ischemic 1
• If cardiac output fails to increase after volume loading: administer dobutamine for inotropic support 1
• Consider intra-aortic balloon pump for refractory cases 1
• If concomitant LV dysfunction present, use arterial vasodilators (sodium nitroprusside, hydralazine) or ACE inhibitors to reduce RV afterload 1

Standard Medical Therapy (First 24-48 Hours):

• Continue aspirin 160-325 mg daily indefinitely 1
• Add clopidogrel 75 mg daily (or other P2Y12 inhibitor) 4
• Initiate early IV beta-blocker therapy followed by oral therapy if no contraindications (hypotension, severe bradycardia, shock, severe heart failure) 1, 2
• Administer intravenous heparin for 48 hours, particularly for large inferior MI or LV mural thrombus 1
• Initiate ACE inhibitors within first 24 hours 1
• Do not use prophylactic antiarrhythmic agents in the first 24 hours 1
• Avoid calcium channel blockers—they have not been shown to reduce mortality and may be harmful 1

Post-Fibrinolytic Management

• For STEMI with successful fibrinolytic therapy, perform coronary angiography within 24 hours, but NOT within the first 2-3 hours after fibrinolytic administration due to increased bleeding risk 5, 2
• Immediate transfer for catheterization (within 24 hours) reduces recurrent MI and ischemia compared to delayed approaches 5

Critical Pitfalls to Avoid

• Never administer nitrates before obtaining lead V4R in inferior MI—nitrates can cause catastrophic hypotension in RV infarction 2
• Do not delay recording lead V4R, as ST elevation in this lead can resolve within 10 hours 1, 2
• Avoid volume depletion, diuretics, and nitrates in RV infarction—these reduce preload and worsen hemodynamics 1
• Do not perform routine catheterization within 2-3 hours of fibrinolytic administration unless rescue PCI is needed 5, 2
• Do not delay reperfusion therapy beyond 12 hours unless there is evidence of ongoing ischemia 1
• Recognize that older patients (>70 years) with RV infarction have significantly worse prognosis (32% mortality vs 10% in younger patients) and thrombolytic therapy is less effective in this subgroup 3
• Do not send patients to physician's office—transport directly to hospital with 24-hour emergency cardiac care capability 1