Management of Suspected ACS Without ST-Segment Elevation on ECG
In patients with suspected coronary artery disease and no EKG ST changes, immediately obtain serial cardiac troponins (at presentation and 3-6 hours later), perform serial ECGs at 15-30 minute intervals if symptoms persist, and stratify risk to determine whether early invasive management or stress testing is appropriate. 1
Immediate Assessment and Serial Monitoring
Obtain serial ECGs every 15-30 minutes during the first hour if clinical suspicion remains high or symptoms persist, as up to 15% of additional STEMI cases may be identified on subsequent tracings that were not present initially 1
Measure cardiac troponin I or T at presentation and repeat at 3-6 hours after symptom onset using contemporary or high-sensitivity assays, which provide >95% negative predictive value for myocardial infarction 1
A normal ECG does not exclude ACS and occurs in 1-6% of patients with acute coronary syndromes; absence of ST changes during active symptoms does not reliably exclude ischemia 1, 2, 3
Risk Stratification Based on Clinical and Biochemical Findings
High-Risk Features (Requiring Early Invasive Strategy)
Patients should be classified as high-risk and undergo coronary angiography if they have any of the following 1:
- Elevated troponin levels (indicating myocardial necrosis) 1
- Recurrent chest pain or dynamic ST-segment changes (even without persistent elevation) during the observation period 1
- Hemodynamic instability (hypotension, pulmonary rales, new heart failure) 1
- Major arrhythmias (repetitive ventricular tachycardia, ventricular fibrillation) 1
- Diabetes mellitus as a comorbidity 1
- Early post-infarction unstable angina 1
For high-risk patients, coronary angiography should be performed as soon as feasible (though not necessarily emergently unless severe ongoing ischemia, major arrhythmias, or hemodynamic instability are present), with continuation of antiplatelet and anticoagulation therapy 1
Low-Risk Features (Stress Testing Pathway)
Patients are considered low-risk if they have ALL of the following 1:
- No recurrence of chest pain during the 6-12 hour observation period 1
- No ST-segment depression or elevation, but may have negative T waves, flat T waves, or completely normal ECG 1
- No elevation of troponin on both initial and repeat measurements (at 6-12 hours) 1
Medical Management During Observation Period
For All Patients With Suspected NSTE-ACS
Initiate the following therapies while awaiting risk stratification 1:
- Aspirin 75-150 mg daily (or clopidogrel if aspirin contraindicated) 1
- Clopidogrel loading dose 300 mg followed by 75 mg daily 1
- Beta-blocker (unless contraindicated) 1
- Low-molecular-weight heparin or unfractionated heparin 1
- Nitrates (oral or intravenous) for persistent or recurrent chest pain 1
Discontinuation Criteria
Low-molecular-weight heparin may be discontinued after the observation period if no ECG changes appear and the second troponin measurement remains negative 1
Stress Testing for Low-Risk Patients
A stress test is mandatory for low-risk patients to confirm or exclude coronary artery disease and assess future risk 1
Standard exercise ECG testing is appropriate for patients who can exercise and have no baseline ECG abnormalities that would preclude interpretation 1
Stress imaging (echocardiography or nuclear perfusion) should be used if the patient cannot exercise, has baseline ECG abnormalities (left bundle branch block, >1mm ST depression at rest, paced rhythm, pre-excitation), or had equivocal standard exercise test results 1
If significant ischemia occurs at low workload during stress testing, coronary angiography and revascularization should be considered 1
Common Pitfalls to Avoid
Do not assume a normal ECG during symptoms excludes ACS—patients with normal or nonspecific ECGs during active symptoms have similar rates of adverse events as asymptomatic patients with ECG abnormalities 3
Do not rely on a single troponin measurement—serial measurements are essential as troponins rise within hours and may be initially negative 1
Do not discharge patients with ongoing symptoms even if the initial ECG and troponin are normal—these patients require continued observation and serial testing 1
Consider posterior leads (V7-V9) in patients with isolated ST depression in V1-V3, as this may represent posterior wall STEMI from left circumflex occlusion 1
Patients with extremely low risk (normal ECG throughout observation, negative serial troponins, normal stress test with good exercise tolerance) likely have a non-cardiac cause and can undergo additional non-cardiac evaluation as outpatients 1