What are the immediate management steps for a patient with suspected myocardial infarction (MI) and how do you differentiate it from other potential causes of chest pain?

Immediate Management and Differential Diagnosis of Myocardial Infarction

For suspected MI, obtain a 12-lead ECG within 10 minutes of arrival, immediately administer aspirin 160-325 mg orally, and initiate cardiac monitoring—do not wait for biomarkers if ST-elevation or new LBBB is present, as ECG findings alone warrant immediate reperfusion therapy. 1, 2, 3

Time-Critical Initial Actions (Complete Within 10 Minutes)

• Obtain 12-lead ECG immediately to identify ST-segment elevation ≥1 mm in contiguous leads or new left bundle branch block, which indicates thrombotic coronary occlusion requiring immediate reperfusion 2, 3, 4
• Initiate continuous cardiac monitoring to detect life-threatening arrhythmias, with transcutaneous pacing capabilities immediately available 5, 2
• Administer aspirin 160-325 mg orally without delay—this is the single most important immediate pharmacologic intervention 1, 2, 3, 6
• Assess oxygen saturation and provide supplemental oxygen only if SaO₂ <90% or PaO₂ <60 mmHg; routine oxygen is not recommended when saturation is adequate 1, 2, 3

Immediate Pharmacological Management

• Give sublingual nitroglycerin unless systolic BP <90 mmHg or heart rate <50 or >100 bpm 1, 2, 3
• Administer intravenous morphine or meperidine for pain control, titrated to effect, though be aware this may delay oral antiplatelet absorption 1, 2, 7
• Administer P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) immediately 1, 2

Reperfusion Decision Algorithm (Based on ECG Findings)

If ST-Elevation ≥1 mm in Contiguous Leads or New LBBB:

• Primary PCI is preferred if available within 90 minutes of first medical contact (door-to-balloon time ≤90 minutes) 1, 2, 3
• Initiate fibrinolytic therapy if PCI cannot be performed within 120 minutes, with door-to-needle time ≤30 minutes 1, 2, 3
• Greatest 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 patients treated between 7-12 hours 1
• Reperfusion therapy beyond 12 hours offers little benefit in most patients unless there is evidence of ongoing ischemia 1

Post-Fibrinolytic Management:

• Avoid catheterization within 2-3 hours of fibrinolytic administration due to increased bleeding risk 1
• Perform coronary angiography within 24 hours after successful fibrinolysis, but not within the first 2-3 hours 1
• Immediate transfer for catheterization (within 24 hours) reduces recurrent MI and ischemia in high-risk patients 1

Differentiating MI from Other Causes of Chest Pain

Classic MI Presentation:

• Chest pain lasting ≥20 minutes, not responding to nitroglycerin, often radiating to neck, lower jaw, or left arm 3
• Associated symptoms include shortness of breath, sweating, nausea, vomiting, abnormal heart rhythm, anxiety, fatigue 7

Atypical Presentations (Especially in Elderly):

• Fatigue, dyspnea, faintness, or syncope without chest pain 3
• Epigastric pain or unexplained indigestion should trigger immediate MI protocol activation 1

ECG Patterns Requiring Advanced Interpretation:

• Modified Sgarbossa criteria allow identification of acute MI in the presence of left bundle branch block or ventricular pacing 4
• Lead aVL changes help recognize inferior MI 4
• 3- and 4-variable formulas differentiate normal ST elevation from subtle left anterior descending coronary artery occlusion 4
• Differentiate ST elevation of left ventricular aneurysm from acute anterior MI 4

Prevalence of Coronary Occlusion:

• Coronary occlusion or flow limitation is present in 75% of STEMI and 63% of NSTEMI patients at presentation 8
• Significant coronary lesions are found in 94% of suspected STEMI and 90% of suspected NSTEMI patients 8

Critical Pitfalls to Avoid

• Do not delay reperfusion waiting for cardiac biomarkers when ECG shows ST-elevation or new LBBB—ECG findings alone warrant immediate treatment 1, 2
• Avoid nitrates in inferior STEMI with suspected right ventricular involvement as they can cause profound hypotension 2
• Do not perform routine catheterization within 2-3 hours of fibrinolytic administration unless rescue PCI is needed for failed reperfusion 1
• Do not wait beyond 12 hours to initiate reperfusion unless there is evidence of ongoing ischemia or mechanical complications 1
• Avoid excessive fluid administration in patients without right ventricular involvement as it may worsen left ventricular failure 2
• Use beta-blockers and calcium channel blockers with caution in the setting of conduction abnormalities, as they may worsen bradycardia or heart block 2

Management of Bradyarrhythmias

• For symptomatic or hemodynamically significant bradycardia, administer atropine 0.5-1.0 mg IV (may repeat to maximum of 3 mg) 2
• Monitor patients with inferior wall MI closely for conduction abnormalities and right ventricular involvement 2

Organizational Requirements

• All emergency vehicles must contain a defibrillator with staff trained in its use 5
• Target call-to-needle time of 90 minutes for thrombolytic treatment from alerting medical services 5
• Direct communication between ambulance and admitting hospital should be established 5
• Hospitals should implement "fast tracking" of patients with obvious MI 5