What is the approach to a patient presenting with chest pain and suspected myocardial infarction (MI) according to the latest American Heart Association (AHA) guidelines?

Approach to Chest Pain and Myocardial Infarction: 2021 AHA/ACC Guidelines

Immediate Actions Upon Presentation (Within 10 Minutes)

All patients presenting with chest pain must have a 12-lead ECG performed and interpreted within 10 minutes of arrival at any medical facility, regardless of setting. 1 This is a Class I recommendation and represents the single most critical initial step in the evaluation pathway.

• Simultaneously measure cardiac troponin (cTn) as soon as possible after presentation, with high-sensitivity troponin strongly preferred because it enables more rapid detection or exclusion of myocardial injury and increases diagnostic accuracy 1
• Administer oxygen only if oxygen saturation is low (not routinely to all patients) 1
• Give aspirin 160-325 mg orally immediately unless contraindicated 1
• Provide sublingual nitroglycerin unless systolic blood pressure <90 mmHg or heart rate <50 or >100 bpm 1
• Administer adequate analgesia with morphine sulfate if needed 1

ECG-Directed Management Algorithm

If ST-Segment Elevation or New LBBB Present:

Treat immediately as STEMI with reperfusion therapy—do not wait for troponin results. 1

• Activate catheter lab for primary PCI if available within 90-120 minutes 2
• If PCI unavailable within this window, initiate fibrinolytic therapy within 30 minutes of arrival (greatest benefit occurs within first hour of symptom onset: 35 lives saved per 1000 patients versus 16 lives saved per 1000 when given 7-12 hours after symptoms) 1
• Portable chest X-ray should be ordered simultaneously but must never delay reperfusion therapy 2
• Initiate IV metoprolol (5 mg bolus every 2 minutes for 3 doses) once hemodynamically stable, followed by oral metoprolol 50 mg every 6 hours starting 15 minutes after last IV dose 3

If ST-Depression, New T-Wave Inversions, or Diffuse ST Changes:

Manage as NSTE-ACS according to non-STEMI guidelines—do not give thrombolytics. 1

• Serial troponin measurements at presentation and 3-6 hours after symptom onset (not from presentation time) 1
• Risk stratification using validated scores (TIMI, GRACE) to guide invasive versus conservative strategy 1
• High-risk features requiring immediate angiography: persistent chest pain despite medical therapy, dynamic ECG changes, positive or rising troponin pattern, hemodynamic instability, life-threatening arrhythmias 4, 5

If Initial ECG Nondiagnostic or Normal:

A normal ECG occurs in 1-6% of patients with acute MI and does NOT exclude ACS—serial testing is mandatory. 1, 4, 5

• Repeat ECG every 15-30 minutes during the first hour if symptoms persist, recur, or clinical condition deteriorates 1, 5
• Obtain supplemental leads V7-V9 if intermediate-to-high suspicion for ACS, as left circumflex or right coronary artery occlusions causing posterior MI are often "electrically silent" on standard 12-lead ECG 1, 5
• Continue serial ECGs until troponin results and risk stratification are complete 4, 5
• Serial troponin at 3-6 hours from symptom onset; if both ECG and troponins remain normal but clinical suspicion persists, obtain additional troponin beyond 6 hours 1, 4

Biomarker Strategy

High-sensitivity cardiac troponin I or T is the preferred and only recommended biomarker—CK-MB and myoglobin are not useful when troponin is available. 1, 5

• Clinicians must know the 99th percentile upper reference limit for their institution's specific troponin assay 1
• Serial measurements identify rising or falling patterns indicative of acute myocardial injury versus chronic elevation 1
• A single negative troponin drawn <6 hours from symptom onset is insufficient to exclude MI—this is a critical pitfall 4

Risk Stratification and Disposition

High-Risk Criteria (Admit to Monitored Bed, Consider Invasive Strategy):

• Recurrent ischemic chest pain despite medical therapy 4, 5
• Elevated or rising troponin pattern 1, 4
• Dynamic ECG changes on serial testing 1, 4
• Hemodynamic instability or signs of heart failure 1, 4
• Life-threatening arrhythmias 1, 4

Low-Risk Criteria (May Discharge with Outpatient Testing):

• No recurrent chest pain after 6-12 hours of observation 4, 5
• Normal or unchanged ECG on serial testing 4, 5
• Two negative troponin measurements (at presentation and 6 hours from symptom onset) 4, 5
• No high-risk features present 4, 5

Additional Diagnostic Considerations

• Obtain chest radiograph to evaluate for alternative causes (aortic dissection, pulmonary embolism, pneumothorax, pneumonia, pulmonary edema) but do not delay reperfusion therapy in clear STEMI 1, 2
• Compare current ECG with any available prior ECGs, as subtle new changes may be significant even if current ECG appears "normal" 5
• Left ventricular hypertrophy, bundle branch blocks, and ventricular pacing can mask ischemic changes—maintain high suspicion in these patients 1, 6

Critical Pitfalls to Avoid

Never discharge a patient with ongoing chest pain based on a single normal ECG—this is the most dangerous error in chest pain evaluation. 4, 5

• Do not administer thrombolytics without clear ST-elevation or new LBBB, as this causes harm in non-STEMI patients 4
• Do not delay transfer to ED for troponin testing from office settings—transport immediately if ACS suspected 1
• Do not rely on symptom quality alone: chest pain described as "sharp," "stabbing," or "pleuritic" does not exclude ACS, though these descriptors lower probability 1
• In patients ≥75 years, maintain high suspicion even with atypical presentations (dyspnea, syncope, delirium, unexplained falls without classic chest pain) 1

Office Setting Considerations

• If ECG unavailable in office, refer patient to ED immediately 1
• Patients with clinical evidence of ACS should be transported urgently to ED by EMS, not driven by family 1
• Advise patients to call 911 after 3 doses of sublingual nitroglycerin (one every 5 minutes) if chest pain persists—do not come to office 1