When should an electrocardiogram (ECG) be repeated in the emergency room (ER) for evaluation of chest pain if the initial ECG is unremarkable?

When to Repeat ECG in the ER for Chest Pain with Initial Unremarkable ECG

Repeat the ECG immediately if symptoms persist or recur, if the clinical condition deteriorates, or when clinical suspicion for acute coronary syndrome (ACS) remains intermediate-to-high, regardless of the initial normal ECG. 1

Core Principle: A Single Normal ECG Never Rules Out ACS

• A normal or nondiagnostic initial ECG is insufficient to exclude ACS—up to 6% of patients with evolving ACS are discharged from the ED with a normal ECG. 1
• Decision-making should never be based solely on a single normal or nondiagnostic ECG, as this is a critical pitfall that can lead to missed myocardial infarction. 1, 2
• Left ventricular hypertrophy, bundle branch blocks, and ventricular pacing can mask signs of ischemia or injury on the initial ECG. 1

Specific Indications for Repeat ECG

Symptom-Driven Timing (Class I Recommendation)

• Repeat ECG immediately when chest pain recurs or persists during the ED evaluation, as ongoing symptoms increase the likelihood of capturing evolving ischemic changes. 1
• Repeat ECG if the clinical condition deteriorates, including development of dyspnea, diaphoresis, hemodynamic instability, or arrhythmias. 1
• Continue serial ECGs until other diagnostic testing (troponins, imaging) definitively rules out ACS. 1

Risk-Stratified Approach

• When clinical suspicion for ACS remains intermediate-to-high, perform serial ECGs even if symptoms have temporarily abated, as the diagnostic accuracy does not differ significantly between ongoing and abated pain. 1, 3
• High-risk features warranting serial ECGs include: diabetes mellitus, known coronary artery disease, elevated troponin levels, recurrent ischemia, or hemodynamic instability. 2, 4

Additional ECG Strategies

Supplemental Leads for Occult Infarction

• Consider posterior leads (V7-V9) in patients with intermediate-to-high ACS suspicion and nondiagnostic standard ECG (Class IIa recommendation), as left circumflex or right coronary artery occlusions causing posterior wall ischemia are often "electrically silent" on standard 12-lead ECG. 1

Comparison with Prior ECGs

• Always compare the current ECG with previous ECGs if available, as a normal but changed ECG may reveal subtle new abnormalities. 1

Integration with Other Diagnostic Testing

• Serial ECGs should be performed in conjunction with serial high-sensitivity cardiac troponin measurements, as troponin is the most sensitive test for myocardial injury. 1, 2, 4
• The timing of repeat ECGs should align with troponin measurement intervals (typically at presentation and 1-3 hours later depending on the assay). 2
• Continue ECG monitoring until troponin results and risk stratification are complete. 1

Critical Pitfalls to Avoid

• Never rely on a single normal ECG to discharge a patient with ongoing chest pain or high clinical suspicion for ACS—this is the most dangerous error in chest pain evaluation. 1, 2, 5
• Do not delay repeat ECGs waiting for scheduled intervals if symptoms change; symptom-driven timing takes priority. 1
• Recognize that 1-4% of patients with completely normal initial ECGs ultimately have acute myocardial infarction, reinforcing that history and serial evaluation are paramount. 5