What are the immediate interventions and assessments for a suspected myocardial infarction (MI) or cardiac rhythm problem?

Immediate Interventions and Assessment for Suspected MI or Cardiac Rhythm Problem

For patients with suspected myocardial infarction (MI) or cardiac rhythm problems, immediate evaluation should be performed within 10 minutes of arrival to the emergency department, with initial management including oxygen by nasal prongs, sublingual nitroglycerin (unless contraindicated), adequate analgesia, aspirin, and a 12-lead ECG. 1

Initial Assessment and Stabilization

• Perform rapid evaluation within 10 minutes of arrival to the emergency department, with no more than 20 minutes elapsing before assessment is complete 1
• Immediately initiate cardiac monitoring to identify potential life-threatening arrhythmias 2
• Obtain a 12-lead ECG to identify ST-segment elevation or left bundle branch block that may indicate need for reperfusion therapy 1
• Administer oxygen therapy only if arterial oxygen saturation <90% or PaO₂ <60 mmHg (avoid routine oxygen when SaO₂ ≥90%) 3, 2
• Obtain vital signs frequently, at least every 30 minutes while in the emergency department 2
• Treat hyperthermia (temperature >99.6°F) with acetaminophen as it is associated with poor outcomes 2

Immediate Pharmacological Interventions

• Administer aspirin 160-325 mg orally immediately 1, 4
• Give sublingual nitroglycerin unless systolic blood pressure is <90 mmHg or heart rate is <50 or >100 beats per minute 1
• Provide adequate analgesia with morphine sulfate or meperidine 1, 5
• Administer a P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel if no contraindications) 3, 4
• Initiate anticoagulation with unfractionated heparin, enoxaparin, or bivalirudin according to protocol 3

Reperfusion Strategy Decision Making

• ST-segment elevation (≥1 mm) in contiguous leads or new LBBB indicates need for immediate reperfusion therapy 1
• Primary PCI is the preferred reperfusion strategy when available within 90 minutes of first medical contact 3, 4
• Consider fibrinolytic therapy if PCI cannot be performed in a timely manner (within 120 minutes) 4
• Patients without ST-segment elevation should not receive thrombolytic therapy 1

Management of Cardiac Rhythm Disturbances

• Have transcutaneous pacing capabilities immediately available for bradyarrhythmias 3
• For symptomatic or hemodynamically significant bradycardia, administer atropine 0.5-1.0 mg IV (may repeat to maximum of 3 mg) 3
• Monitor for ventricular arrhythmias, which are common complications in acute MI 6, 7
• Treat ventricular fibrillation or pulseless ventricular tachycardia immediately with defibrillation 6
• For patients with inferior wall MI, monitor closely for conduction abnormalities and right ventricular involvement 3

Diagnostic Workup

• Obtain cardiac biomarkers (preferably high-sensitivity cardiac troponin) with at least one value above the 99th percentile upper reference limit for diagnosis 4, 8, 9
• Consider emergency echocardiography if diagnosis is uncertain, but do not delay angiography if indicated 2
• Monitor for signs of cardiogenic shock, which would require additional hemodynamic support 3

Common Pitfalls and Caveats

• Avoid nitrates in patients with inferior STEMI with suspected right ventricular involvement as they can cause profound hypotension 3
• Avoid excessive fluid administration in patients without right ventricular involvement as it may worsen left ventricular failure 3
• Do not delay reperfusion therapy while waiting for cardiac biomarker results when ECG shows clear ST-segment elevation 3
• Be cautious with beta-blockers and calcium channel blockers in the setting of conduction abnormalities, as they may worsen bradycardia or heart block 3
• Recognize that early and successful reperfusion therapy is the best anti-arrhythmic therapeutic approach in patients with MI 6
• In rural settings, develop protocols for initiating thrombolytic therapy before transfer to tertiary centers when appropriate 1