What is the initial diagnostic test for a patient presenting with chest pain?

Initial Diagnostic Test for Chest Pain

For patients presenting with chest pain, an electrocardiogram (ECG) should be obtained and interpreted within 10 minutes of arrival as the initial diagnostic test. 1

Rationale for ECG as First-Line Test

The 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guidelines strongly recommend an ECG as the initial diagnostic test for several critical reasons:

• Early recognition of ST-elevation myocardial infarction (STEMI) significantly improves outcomes
• An ECG can rapidly identify potentially life-threatening conditions requiring immediate intervention
• The test is non-invasive, widely available, and provides immediate results
• It helps direct subsequent diagnostic and treatment pathways

ECG Acquisition Protocol

• ECG should be obtained and interpreted within 10 minutes of arrival regardless of setting 1
• If an ECG cannot be obtained in an office setting, immediate transfer to the ED by EMS is recommended 1
• For patients with intermediate-to-high clinical suspicion for ACS but nondiagnostic initial ECG, supplemental leads V7-V9 are reasonable to rule out posterior MI 1

ECG Interpretation and Next Steps

If ECG shows evidence of ACS:

• ST-elevation, ST depression, or new left bundle branch block: Treat according to STEMI and NSTE-ACS guidelines 1
• Immediate activation of appropriate treatment pathways

If initial ECG is nondiagnostic:

• Serial ECGs should be performed, especially when:
  • Clinical suspicion of ACS is high
  • Symptoms are persistent
  • Clinical condition deteriorates 1
• Compare with previous ECGs if available
• A normal or unchanged ECG is useful but not sufficient to rule out ACS

Follow-up Testing After Initial ECG

After the initial ECG, the next appropriate test is cardiac troponin (cTn):

• cTn is the most sensitive test for diagnosing acute myocardial injury 1
• Should be measured as soon as possible after presentation to the ED 1
• Serial measurements may be necessary to detect rising/falling patterns

Important Caveats

• A normal ECG does not exclude ACS - up to 6% of patients with evolving ACS are discharged from the ED with a normal ECG 1
• Left ventricular hypertrophy, bundle branch blocks, and ventricular pacing may mask signs of ischemia or injury 1
• Left circumflex or right coronary artery occlusions and posterior wall ischemia may be "electrically silent" on standard ECG leads 1
• Women are at risk for underdiagnosis, and potential cardiac causes should always be considered 1
• In patients ≥75 years of age, ACS should be considered when accompanying symptoms such as shortness of breath, syncope, or acute delirium are present 1

Clinical Pearls

• Decision-making should never be based solely on a single normal or nondiagnostic ECG 1
• Delayed transfer to the hospital for determination of cTn or other diagnostic testing beyond the ECG in the office setting can be detrimental and should be avoided 1
• For patients with chest pain and normal ECGs, the risk of AMI is extremely low (approximately 1-4%) but not zero 2
• The timing for repeat ECG should be guided by symptoms, especially if chest pain recurs or clinical condition changes 1

By following this evidence-based approach with the ECG as the initial diagnostic test, clinicians can rapidly identify patients requiring urgent intervention while appropriately risk-stratifying others for further evaluation.