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

Immediate Management of Inferior Wall Myocardial Infarction

Administer aspirin 162-325 mg (chewed, non-enteric coated) immediately upon arrival, initiate continuous cardiac monitoring, assess for right ventricular involvement with right-sided ECG leads (particularly V4R), and pursue urgent reperfusion therapy with primary PCI if available within 90 minutes or fibrinolytic therapy if PCI is unavailable. 1, 2

Initial Assessment and Monitoring

Assess for Right Ventricular Infarction

• Obtain right-sided ECG leads immediately, particularly V4R, as ST elevation ≥1 mm is highly predictive of RV infarction, which occurs in up to 50% of inferior MIs and significantly increases mortality from 6% to 25-30% 3, 1
• Record V4R early as ST elevation can resolve within 10 hours of symptom onset 3, 1
• Look for the clinical triad of hypotension, clear lung fields, and elevated jugular venous pressure, though this has sensitivity <25% 3, 1
• Kussmaul's sign or distended neck veins alone may indicate RV involvement 3
• Right atrial pressure ≥10 mm Hg and >80% of pulmonary wedge pressure is relatively sensitive and specific for RV ischemia 3

Establish Monitoring

• Initiate continuous cardiac monitoring for arrhythmias and conduction disturbances (sinus bradycardia and AV block are common in inferior MI) 1
• Have emergency equipment readily available: atropine, lidocaine, transcutaneous pacing patches, transvenous pacemaker, defibrillator, and epinephrine 1
• Consider pulmonary artery catheter monitoring for progressive hypotension unresponsive to fluid administration 1
• Use intra-arterial pressure monitoring for cardiogenic shock 1

Immediate Pharmacological Management

Antiplatelet Therapy

• Administer aspirin 162-325 mg orally (chewed, non-enteric coated formulation for more rapid buccal absorption) immediately unless contraindicated 3, 1, 2
• Maintenance dose should be 75-162 mg daily to minimize bleeding risk while maintaining efficacy 3
• Add clopidogrel 75 mg daily (or preferably prasugrel or ticagrelor if proceeding to PCI) and continue dual antiplatelet therapy for 12 months 3, 1, 2

Analgesia and Symptom Management

• Provide appropriate analgesia with narcotic medications (morphine) to minimize pain and anxiety 1
• Administer sublingual nitroglycerin unless systolic BP <90 mmHg, heart rate <50 or >100 bpm, or RV infarction is suspected 2
• Begin intravenous nitroglycerin for 24-48 hours if no hypotension, bradycardia, or RV involvement 1
• Avoid nitrates completely in patients with RV infarction as they can cause profound hypotension by reducing preload 3, 1

Beta-Blocker Therapy

• Administer early IV beta-blocker therapy (metoprolol 5 mg IV every 2 minutes for 3 doses) followed by oral therapy (50 mg every 6 hours for 48 hours, then 100 mg twice daily) if no contraindications 1, 4
• Avoid beta-blockers in patients with hypotension, acute heart failure, high-degree AV block, severe bradycardia, or low-output state due to pump failure 1, 2

Anticoagulation

• Administer high-dose IV unfractionated heparin during primary PCI 2
• Consider anticoagulation with IV heparin, particularly if thrombolytic therapy was administered, and continue until revascularization or for hospital stay up to 8 days 1, 2

ACE Inhibitors

• Initiate ACE inhibitors (lisinopril 5 mg) within first 24 hours in hemodynamically stable patients, particularly those with heart failure, LV systolic dysfunction, diabetes, or anterior infarct 2, 5
• Reduce dose to 2.5 mg if systolic BP <120 mmHg at baseline 5

Reperfusion Strategy

Primary PCI (Preferred)

• Primary PCI is the preferred reperfusion method and should be performed within 90 minutes of first medical contact if available at a center with 24/7 capability 1, 2
• Patients should bypass the emergency department and go directly to the catheterization laboratory 2
• Reperfusion therapy is indicated for all patients with symptoms ≤12 hours duration and persistent ST-segment elevation 1, 2

Fibrinolytic Therapy (Alternative)

• Consider fibrinolytic therapy if no contraindications exist and PCI is not available within 90-120 minutes 1, 2
• Administer thrombolytic agents within 3 hours of symptom onset for optimal benefit 6

Special Management for Right Ventricular Infarction

Hemodynamic Management

• Maintain RV preload through aggressive volume loading with IV normal saline for hypotension 3, 1
• Avoid nitrates and diuretics as they can cause profound hypotension by reducing preload 3, 1
• Recognize that volume depletion may mask signs of RV involvement; findings may only become evident after adequate volume loading 3, 1

Inotropic Support

• Provide inotropic support with dobutamine if cardiac output fails to increase after volume loading 3, 1
• Consider intra-aortic balloon pump for persistent shock despite pharmacological therapy 3, 1
• Use arterial vasodilators (sodium nitroprusside, hydralazine) or ACE inhibitors to reduce RV afterload if left ventricular dysfunction is present 3

Maintain AV Synchrony

• Maintain AV synchrony through AV sequential pacing for symptomatic high-degree heart block, as loss of atrial contraction profoundly affects hemodynamics in RV infarction 3, 1
• Prompt cardioversion for hemodynamically significant supraventricular tachycardia 3

Management of Conduction Disturbances

Bradycardia and AV Block

• Treat symptomatic sinus bradycardia with IV atropine 0.5 mg, repeated up to 2.0 mg total 1
• Second-degree type I (Mobitz I/Wenckebach) AV block is usually associated with inferior wall MI and seldom causes adverse hemodynamic effects, often requiring no treatment if hemodynamically stable 1
• Consider temporary pacing for symptomatic high-degree AV block, especially if unresponsive to atropine 1
• AV block associated with inferior wall infarction is usually supra-Hisian and typically resolves spontaneously or after reperfusion 1

Activity and Monitoring

• Limit physical activities for at least 12 hours 1
• Perform routine echocardiography to assess LV and RV function, detect mechanical complications, and exclude LV thrombus 1, 2
• Monitor for sudden hypotension, recurrence of chest pain, new cardiac murmurs (suggesting mitral regurgitation or ventricular septal defect), pulmonary congestion, or jugular vein distension, which should raise suspicion for mechanical complications requiring immediate echocardiographic assessment 1

Medications to Avoid

• Avoid calcium channel blockers as they have not been shown to reduce mortality and may be harmful 1
• Discontinue any nonsteroidal anti-inflammatory drugs (except aspirin) due to increased risks of mortality, reinfarction, and other complications 1

Common Pitfalls

• Administering nitrates to patients with RV infarction can cause catastrophic hypotension 3, 1
• Failing to obtain right-sided ECG leads early, as ST elevation in V4R may resolve within 10 hours 3, 1
• Treating all hypotension with vasopressors rather than volume loading in RV infarction 3, 1
• Using diuretics in patients with elevated jugular venous pressure without recognizing RV infarction 3, 1