How should I manage a patient with an acute inferior ST‑segment elevation myocardial infarction?

Management of Acute Inferior ST-Segment Elevation Myocardial Infarction

Activate immediate reperfusion therapy—primary PCI is preferred if door-to-balloon time ≤90 minutes; otherwise, initiate fibrinolysis within 10 minutes of STEMI diagnosis if anticipated PCI delay exceeds 120 minutes. 1

Immediate ECG Acquisition and Diagnostic Confirmation

• Obtain and interpret a 12-lead ECG within 10 minutes of first medical contact in any patient with chest discomfort or anginal-equivalent symptoms 2
• Confirm inferior STEMI by identifying ST-elevation ≥1 mm (0.1 mV) at the J-point in at least two contiguous inferior leads (II, III, aVF) 1
• For men <40 years, the threshold in V2-V3 is ≥2.5 mm; for men ≥40 years, ≥2.0 mm; for women, ≥1.5 mm 1

Critical Additional Leads for Inferior STEMI

Always record right precordial leads V3R and V4R to identify concomitant right ventricular (RV) infarction, which occurs in up to 50% of inferior STEMIs 1. ST-elevation ≥1 mm in V4R confirms RV involvement and mandates specific hemodynamic management 1, 3.

Record posterior leads V7-V9 when ST-depression appears in V1-V3 with upright terminal T-waves, as this pattern represents posterior wall extension; ST-elevation ≥0.5 mm in V7-V9 confirms posterior STEMI 1.

High-Risk ECG Patterns Requiring Urgent Recognition

ST-Depression in Lead aVL

• ST-depression >1 mm in lead aVL has 87% sensitivity and 91% specificity for RV involvement in inferior STEMI 3
• This simple 12-lead sign identifies patients at higher risk for hemodynamic compromise 3

ST-Elevation in Leads V5-V6

• ST-elevation >2 mm in V5-V6 during inferior STEMI indicates a larger perfusion territory at risk and predicts impaired myocardial reperfusion 4
• When ST-elevation in lead III exceeds that in V6, the culprit is typically the right coronary artery (96% of cases) 4
• When ST-elevation in V6 equals or exceeds that in lead III, the culprit is usually the left circumflex artery (96% of cases), often proximal (74%) 4

ST-Changes in Lead aVR

• ST-elevation or depression in lead aVR occurs in 42% of inferior STEMI patients and carries significantly worse prognosis 5
• In-hospital mortality is 27.7% with ST-elevation in aVR, 16.5% with ST-depression in aVR, versus only 1.0% with no aVR changes (p<0.001) 5
• ST-elevation in aVR combined with widespread ST-depression (≥8 leads) suggests left main or severe multivessel disease and mandates immediate angiography 6

Isolated ST-Elevation in Lead III

• Approximately 8% of inferior STEMIs present with ST-elevation only in lead III 7
• When maximal precordial ST-depression occurs in V4-V6 (rather than V1-V3), the risk of severe heart failure (pulmonary edema or cardiogenic shock) increases six-fold (62% vs 10%) 7
• These patients require aggressive interventional strategy 7

Reperfusion Strategy Selection

Primary PCI is the preferred reperfusion modality when door-to-balloon time can be achieved within 90 minutes of first medical contact 1. Transfer patients directly to a 24/7 high-volume PCI center, bypassing the emergency department 1.

Initiate fibrinolytic therapy immediately (within 10 minutes of STEMI diagnosis) if the anticipated time from diagnosis to PCI-mediated reperfusion exceeds 120 minutes 1. Door-to-needle time for fibrinolysis must be ≤30 minutes 2.

Immediate Pharmacologic Management

Antiplatelet Therapy

• Administer aspirin 162-325 mg (non-enteric coating) immediately, chewed for rapid absorption 1, 8
• For primary PCI: loading dose of prasugrel 60 mg or ticagrelor 180 mg (preferred over clopidogrel due to faster onset and greater platelet inhibition) 1
• For fibrinolysis: loading dose of clopidogrel 300 mg 1, 8
• Continue dual antiplatelet therapy (aspirin plus P2Y12 inhibitor) for 12 months 1

Anticoagulation

• Primary PCI: unfractionated heparin is standard; enoxaparin or bivalirudin are acceptable alternatives 1
• Fibrinolysis: enoxaparin is preferred; unfractionated heparin is an alternative 1

Pain Management

• Titrated intravenous opioids (e.g., morphine) should be considered for pain relief (Class IIa, Level C) 1
• Caution: morphine delays absorption and reduces efficacy of oral antiplatelet agents (clopidogrel, ticagrelor, prasugrel), potentially leading to early treatment failure 1

Oxygen Therapy

• Oxygen is indicated only in hypoxemic patients (SaO₂ <90% or PaO₂ <60 mmHg) (Class I, Level C) 1
• Routine oxygen is contraindicated in patients with SaO₂ ≥90% due to evidence of increased myocardial injury from hyperoxia (Class III, Level B) 1

Special Management Considerations for Right Ventricular Infarction

When RV involvement is confirmed (ST-elevation ≥1 mm in V4R):

• Avoid nitrates and diuretics, which reduce preload and can precipitate severe hypotension 1
• Maintain preload with intravenous normal saline boluses 1
• Monitor closely for hemodynamic instability, as RV infarction increases risk of cardiogenic shock 3, 5

STEMI Equivalents Requiring Immediate Reperfusion

New or Presumed New Left Bundle Branch Block (LBBB)

• In patients with LBBB and ongoing ischemic symptoms, emergency coronary angiography should be performed immediately without awaiting definitive ECG criteria 1
• Concordant ST-elevation (elevation in leads with positive QRS deflection) is the most reliable marker of acute coronary occlusion in LBBB 1

Posterior MI Pattern

• Isolated ST-depression ≥0.5 mm in V1-V3 with upright terminal T-waves represents posterior STEMI and must be managed identically to anterior STEMI 1

Ventricular Pacing

• Pacemaker rhythm obscures ST-segment interpretation 1
• Consider reprogramming to allow evaluation of intrinsic rhythm in non-pacemaker-dependent patients, without delaying invasive investigation 1

Post-Reperfusion Monitoring and Care

• Continuous ECG monitoring for at least 24 hours to detect reperfusion arrhythmias (sinus bradycardia, accelerated idioventricular rhythm, ventricular tachycardia) 9
• Have anti-arrhythmic therapy immediately available for bradycardia and ventricular irritability 9
• Perform bedside echocardiography to assess left ventricular function, regional wall motion abnormalities, and mechanical complications 10

Management of Non-Infarct-Related Lesions

• Assess all coronary anatomy before hospital discharge 1
• Treat severe stenoses (evaluated by angiography or FFR) either during the index PCI or in a staged procedure before discharge 1
• In cardiogenic shock, consider PCI of non-infarct-related arteries during the index procedure 1

Technical Aspects of Primary PCI

• Radial artery access is the standard of care (lower bleeding risk) 1
• Drug-eluting stent implantation is routine 1
• Routine thrombus aspiration is contraindicated (no mortality benefit, increased stroke risk) 1
• Deferred stenting is contraindicated 1

Common Pitfalls to Avoid

• Do not wait for troponin results before activating reperfusion therapy in patients meeting ECG STEMI criteria 2
• Do not dismiss single-lead ST-elevation in lead III, especially when accompanied by maximal precordial ST-depression in V4-V6 7
• Do not overlook ST-changes in lead aVR, which independently predict in-hospital mortality 5
• Do not administer routine oxygen to non-hypoxemic patients 1
• Do not use nitrates or diuretics in RV infarction 1
• Do not combine tenecteplase with planned PCI as primary strategy, as this increases mortality, cardiogenic shock, heart failure, recurrent MI, and repeat revascularization compared to PCI alone 9

In-Hospital Mortality and Risk Stratification

• Overall in-hospital mortality for unselected inferior STEMI patients ranges 4-12% in European registries 1
• Independent predictors of ST-elevation in aVR (high-risk marker) include female gender, diabetes, hypertension, lower ejection fraction, and cardiogenic shock on admission 5
• Early ambulation and early discharge are optimal for uncomplicated patients 1