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

Management of Inferior Wall Myocardial Infarction

For inferior wall MI, immediately administer aspirin 160-325 mg orally, obtain a 12-lead ECG including right-sided lead V4R within 10 minutes, and initiate primary PCI within 90 minutes of first medical contact as the preferred reperfusion strategy. 1, 2

Immediate Actions (First 10 Minutes)

• Administer aspirin 160-325 mg orally immediately upon presentation 1, 3
• Obtain a 12-lead ECG within 10 minutes of arrival, including right-sided lead V4R to assess for right ventricular involvement 1, 4
• Establish continuous cardiac monitoring to detect life-threatening arrhythmias 2, 3
• Assess oxygen saturation and administer oxygen only if SaO₂ <90% or PaO₂ <60 mmHg, as routine oxygen therapy is not recommended and may cause harm 2, 3
• Provide titrated intravenous morphine for pain relief, though recognize this may delay antiplatelet drug absorption 2, 3

Critical Assessment for Right Ventricular Involvement

Right ventricular infarction occurs in up to 50% of inferior MIs and increases in-hospital mortality from 6% to 25-30%, making early identification crucial. 1, 4

• Look for the clinical triad of hypotension, clear lung fields, and elevated jugular venous pressure, though this is only 25% sensitive 1, 4
• ST-segment elevation ≥1 mm in lead V4R is the single most predictive ECG finding with 88% sensitivity and 78% specificity 4
• Record lead V4R immediately, as ST elevation can resolve within 10 hours 1, 4
• Avoid nitrates in suspected RV infarction, as they can cause profound hypotension by reducing preload 1, 4

Reperfusion Strategy

Primary PCI is the preferred reperfusion strategy when it can be performed within 90 minutes of first medical contact by experienced operators. 2, 1

• Door-to-balloon time should be ≤90 minutes for primary PCI 1
• If PCI cannot be performed within 120 minutes, consider fibrinolytic therapy followed by transfer to a PCI-capable facility 2, 3
• For high-risk patients receiving fibrinolytic therapy at non-PCI facilities, transfer immediately to a PCI-capable center for pharmacoinvasive strategy 2
• After successful fibrinolysis, perform coronary angiography within 24 hours but not within the first 2-3 hours 1

Antiplatelet and Antithrombotic Therapy

• Administer a P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) if no contraindications exist 3
• Initiate intravenous heparin, particularly for patients at high risk for left ventricular mural thrombus 1
• Consider glycoprotein IIb/IIIa inhibitors (especially abciximab) for high-risk patients undergoing PCI 5

Management of Right Ventricular Infarction

If RV infarction is identified, the management strategy differs fundamentally from standard MI care:

• Maintain RV preload through aggressive volume loading with IV normal saline 4
• Avoid nitrates, diuretics, and morphine, which reduce preload 4
• If cardiac output remains low after adequate volume loading, add dobutamine (not dopamine) starting at 2.5 μg/kg/min 4
• Maintain AV synchrony through AV sequential pacing for symptomatic high-degree heart block unresponsive to atropine 1, 4
• Consider intra-aortic balloon pump for persistent shock despite volume loading and inotropic support 4

Management of Conduction Disturbances

Inferior MI commonly causes bradyarrhythmias and conduction blocks due to involvement of the right coronary artery supplying the AV node. 4

• For symptomatic sinus bradycardia with hypotension or low cardiac output, administer atropine 0.3-0.5 mg IV, repeated up to a total of 1.5-2.0 mg 1, 4
• For symptomatic high-degree AV block unresponsive to atropine, initiate temporary transcutaneous or transvenous pacing 1, 4
• Complete AV block in inferior MI often resolves with reperfusion and may not require permanent pacing 1

Early Intravenous Beta-Blocker Therapy

Initiate early IV beta-blocker therapy followed by oral therapy for patients without contraindications. 1, 3

• Administer metoprolol tartrate 5 mg IV bolus at 2-minute intervals for three doses (total 15 mg) 6
• Monitor blood pressure, heart rate, and ECG continuously during IV administration 6
• Begin oral metoprolol 50 mg every 6 hours starting 15 minutes after the last IV dose, continuing for 48 hours 6
• Maintenance dosage is 100 mg orally twice daily thereafter 6
• Contraindications include hypotension (systolic BP <100 mmHg), severe bradycardia (HR <50 bpm), signs of shock, severe heart failure, or high-degree AV block 1, 3

Hemodynamic Management in Cardiogenic Shock

Distinguish between RV infarction (requiring volume loading) and LV dysfunction (requiring inotropic support). 4

• For LV dysfunction with cardiogenic shock, use norepinephrine initially if severely hypotensive, then transition to dopamine 5-15 μg/kg/min 4
• Target systolic BP >90 mmHg, cardiac index >2.0 L/min/m², and pulmonary wedge pressure <20 mmHg 4
• Consider emergency coronary angiography followed by PCI or CABG for persistent cardiogenic shock 4

Common Pitfalls and Critical Caveats

• Never administer nitrates before obtaining lead V4R in inferior MI, as unrecognized RV involvement can lead to catastrophic hypotension 1, 4
• Do not delay reperfusion therapy while waiting for cardiac biomarker results when ECG shows clear ST-segment elevation 3
• Avoid excessive fluid administration in patients without RV involvement, as it may worsen left ventricular failure 3, 4
• Recognize that left precordial ST-segment depression (leads V4-V6) in inferior MI predicts multivessel disease in 62.7% of cases and may require more extensive revascularization 7
• Beta-blockers and calcium channel blockers should be used cautiously in the setting of conduction abnormalities, as they may worsen bradycardia or heart block 3
• Morphine use may delay the onset and diminish the effects of oral antiplatelet agents, potentially leading to early treatment failure 2, 3