How should I assess and manage a patient presenting with MI (myocardial infarction) symptoms such as chest pressure, radiation to the arm or jaw, dyspnea, diaphoresis, and nausea?

Management of Patient Presenting with MI Symptoms

Immediately obtain a 12-lead ECG within 10 minutes of patient arrival and administer 162-325 mg aspirin (chewed, non-enteric coated) while placing the patient on continuous cardiac monitoring with a defibrillator at bedside. 1, 2

Immediate Actions (First 10 Minutes)

Do not evaluate patients with suspected MI symptoms over the telephone—they must be seen in person with ECG capability. 1

Patient Arrival Protocol

• Instruct patients or bystanders to call 9-1-1 immediately rather than driving themselves or having family transport them, as approximately 1 in 300 patients transported by private vehicle experiences cardiac arrest en route 1

• Place patient on continuous cardiac monitor immediately with defibrillator and advanced cardiac life support equipment at bedside 1, 2

• Obtain 12-lead ECG within 10 minutes to identify ST-segment elevation ≥1 mm in contiguous leads or new left bundle branch block 1, 2

• Administer aspirin 162-325 mg (chewed, non-enteric coated) immediately upon suspicion of acute coronary syndrome—this is the single most important pharmacologic intervention 1, 2

Initial Assessment Focus

Look specifically for:

• Chest pressure/discomfort (may be described as pressure rather than pain) radiating to arm, jaw, neck, back, or epigastrium 1
• Dyspnea, diaphoresis, nausea, lightheadedness 1
• Autonomic activation signs: pallor, sweating, hypotension or narrow pulse pressure 1
• Cardiac examination: irregular pulse, bradycardia/tachycardia, third heart sound, basal rales 1

Critical caveat: One-third of MI patients present without chest discomfort, particularly elderly patients, women, and diabetics—these patients have 2.2 times higher in-hospital mortality (23.3% vs 9.3%) because they are often misdiagnosed and undertreated 1

Oxygen and Nitroglycerin Administration

• Give supplemental oxygen ONLY if oxygen saturation <90% or PaO₂ <60 mmHg—routine oxygen in patients with adequate saturation may increase myocardial injury and is classified as Class III harm 2

• Administer sublingual nitroglycerin (up to 3 doses, 5 minutes apart) UNLESS systolic BP <90 mmHg, heart rate <50 or >100 bpm 1, 2

ECG-Based Reperfusion Decision (Within 20 Minutes Total)

If ST-Elevation MI or New LBBB Present:

Primary PCI is the preferred reperfusion strategy if door-to-balloon time can be achieved within 90 minutes of first medical contact. 2

• Transfer immediately to PCI-capable facility if not already at one, particularly for high-risk patients (anterior MI, shock, pulmonary congestion, heart rate >100 bpm, systolic BP <100 mmHg) 1, 2

• If primary PCI cannot be performed within 120 minutes, initiate fibrinolytic therapy with door-to-needle time ≤30 minutes 2

• Do NOT wait for cardiac biomarker results before initiating reperfusion therapy—ECG findings alone warrant immediate treatment 2, 3

Time-critical context: The greatest benefit occurs within the first hour ("golden hour"), saving 35 lives per 1,000 patients treated. Benefit progressively diminishes, with reperfusion beyond 12 hours offering little benefit in most patients. 1, 3

If No ST-Elevation (Possible NSTEMI/Unstable Angina):

• Draw cardiac troponin at presentation with repeat measurement at 6-hour intervals 2

• Administer P2Y12 inhibitor (ticagrelor or prasugrel preferred over clopidogrel) in addition to aspirin 2

• Continue cardiac monitoring for at least 24 hours or until alternative diagnosis established 1

• Obtain cardiology consultation immediately if diagnosis or treatment plan unclear 1

Critical System Requirements

• Do NOT send patient to physician's office—transport directly to hospital with 24-hour emergency cardiac care capability, cardiac catheterization, and revascularization services 1

• Do NOT delay treatment for insurance authorization or administrative procedures 2

• Establish direct communication between EMS and receiving hospital to activate catheterization lab before patient arrival 2

• For critically ill patients (cardiac arrest, recurrent ventricular arrhythmias, severe bradycardia, cardiogenic shock), triage directly to facilities with both catheterization and cardiac surgery capability 1, 2

Common Pitfalls to Avoid

• Do not dismiss atypical presentations: Severe epigastric pain, unexplained dyspnea without chest pain, or unexplained indigestion should trigger immediate MI protocol activation 1, 2

• Do not rely on normal initial ECG to exclude MI: 10% of patients with normal ECG and 8% with minimal nonspecific changes ultimately develop confirmed MI 4

• Do not delay for biomarkers in ST-elevation: Reperfusion decisions are based on ECG, not troponin results 2, 3

• Recognize silent MI risk factors: Older age, female sex, diabetes, and prior heart failure increase likelihood of atypical presentation 1