Is it appropriate to withhold cardiac enzyme testing, including troponin (troponin) levels, in patients with a normal electrocardiogram (EKG)?

From the Guidelines

No, it is not appropriate to withhold cardiac enzyme testing, including troponin levels, in patients with a normal electrocardiogram (EKG). According to the 2017 AHA/ACC clinical performance and quality measures for adults with ST-elevation and non-ST-elevation myocardial infarction 1, serial cardiac troponin I or T levels should be obtained at presentation and 3 to 6 hours after symptom onset in all patients who present with symptoms consistent with acute coronary syndrome (ACS) to identify a rising and/or falling pattern of values. This is a Class I recommendation with a Level of Evidence: A, indicating that it is a strong recommendation based on high-quality evidence.

The 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes also supports this approach, stating that serial cardiac troponin I or T levels should be obtained at presentation and 3 to 6 hours after symptom onset in all patients who present with symptoms consistent with ACS 1. A normal EKG does not rule out myocardial injury or infarction, as up to 30% of patients with acute myocardial infarction may initially present with a normal or non-diagnostic EKG.

Key points to consider include:

• Troponin is a highly sensitive and specific marker for myocardial damage that can detect even small areas of cardiac injury that may not cause visible EKG changes.
• The standard protocol for evaluating chest pain typically includes serial troponin measurements (usually at presentation, 3 hours, and sometimes 6 hours after symptom onset) along with clinical assessment and EKG.
• Early detection of cardiac injury through troponin testing, regardless of EKG results, allows for timely intervention and significantly improves patient outcomes by enabling appropriate treatment decisions.
• Additional troponin levels should be obtained beyond 6 hours after symptom onset in patients with normal troponin levels on serial examination when changes on ECG and/or clinical presentation confer an intermediate or high index of suspicion for ACS 1.

Overall, troponin testing should still be performed in patients with suspected acute coronary syndrome even when the EKG appears normal, as it is a crucial component of the comprehensive approach to evaluating chest pain and identifying patients with non-ST elevation myocardial infarction (NSTEMI) or unstable angina.

From the Research

Cardiac Enzyme Testing with Normal EKG

• A normal electrocardiogram (EKG) does not necessarily rule out the need for cardiac enzyme testing, including troponin levels 2.
• According to the study on Acute Coronary Syndrome, if the ECG finding is normal, troponin levels should still be measured using one of several recommended protocols to confirm the absence of acute coronary syndrome (ACS) 2.
• The study on the approach to patients with possible cardiac chest pain emphasizes that an acute coronary syndrome cannot be excluded on clinical grounds alone, and cardiac biomarkers such as troponin are essential for diagnosis 3.
• Other studies also highlight the importance of cardiac biomarkers, including troponin, in evaluating chest pain and acute coronary syndromes, even with a normal EKG 4, 5.

Risk Stratification

• If the ECG is normal and two troponin tests are negative, risk stratification should be calculated using the Thrombosis in Myocardial Infarction (TIMI) or HEART score to determine the need for further evaluation 2.
• Further evaluation to exclude coronary artery disease (CAD) may include exercise treadmill testing, stress echocardiography, myocardial perfusion scintigraphy, or coronary computed tomography angiography 2, 5.

Exceptions and Considerations

• A case study reported a patient with grossly elevated troponin due to heterophilic antibodies, highlighting the importance of considering alternative explanations for abnormal troponin results 6.
• Clinicians should be aware of the potential for false positives or false negatives when interpreting troponin results and consider the clinical context and other diagnostic findings when making decisions about cardiac enzyme testing 6.