What is the initial evaluation and treatment for a patient with suspected Acute Coronary Syndrome (ACS)?

Diagnosis of Acute Coronary Syndrome

Obtain a 12-lead ECG within 10 minutes of presentation and measure high-sensitivity cardiac troponin immediately—these two tests form the cornerstone of ACS diagnosis and guide all subsequent management decisions. 1

Immediate Diagnostic Evaluation

ECG Acquisition and Interpretation

• Perform and interpret a 12-lead ECG within 10 minutes of arrival for any patient with chest discomfort or symptoms suggestive of ACS 1, 2
• If the initial ECG is non-diagnostic but clinical suspicion remains high, obtain serial ECGs at 15-30 minute intervals to detect evolving ST-segment changes 1
• ST-segment elevation ≥1mm in two contiguous leads indicates STEMI and requires immediate reperfusion therapy 1, 3
• ST-segment depression in anteroseptal leads (V1-V3) may represent posterior STEMI—obtain posterior lead ECG if suspected 1
• Non-ST-elevation ACS may show ST-depression, T-wave inversions, transient ST-elevation, or completely normal ECG findings 1, 3

Cardiac Biomarker Measurement

• Measure cardiac troponin immediately upon presentation, preferably using high-sensitivity troponin (hs-cTn) assays 1, 2
• For hs-cTn assays: repeat measurement at 1-2 hours after initial sample if first result is non-diagnostic 1
• For conventional troponin assays: repeat measurement at 3-6 hours after initial sample 1
• If symptoms began within 6 hours of presentation and initial biomarkers are negative, remeasure at 8-12 hours after symptom onset 1
• Elevated troponin above the 99th percentile upper reference limit with a rising or falling pattern indicates myocardial infarction 2, 3
• Men and women may have different hs-cTn cutoff values—use sex-specific thresholds when available 1

Clinical Assessment

History Taking—Specific High-Risk Features

• Chest discomfort lasting >20 minutes at rest is the most concerning symptom 1
• Substernal chest pain radiating to arms, jaw, or back increases ACS likelihood 2, 3
• Associated symptoms: diaphoresis, dyspnea, nausea, or lightheadedness 3
• Prior MI, known coronary disease, or previous revascularization significantly increases risk 1
• Age >70 years, diabetes mellitus, or renal failure elevate risk 1

Physical Examination—Critical Findings

• Hemodynamic instability (hypotension, tachycardia) indicates high-risk ACS 1
• Pulmonary edema suggests ischemia-related left ventricular dysfunction 1
• New mitral regurgitation murmur may indicate papillary muscle dysfunction 1
• Signs of cardiogenic shock require urgent echocardiography 1

Risk Stratification

High-Risk Features Requiring Immediate Invasive Strategy

• Recurrent or ongoing ischemic chest pain despite medical therapy 1, 4
• Hemodynamic instability or cardiogenic shock 1
• Life-threatening arrhythmias (ventricular tachycardia, ventricular fibrillation) 1
• Elevated troponin levels with dynamic changes 2, 4
• ST-segment depression ≥0.5mm or transient ST-elevation 1
• Early post-infarction unstable angina 4

Intermediate-Risk Features

• Age >70 years without other high-risk features 1
• Diabetes mellitus 1
• Prior MI or known coronary disease 1
• Prolonged chest pain (>20 minutes) now resolved 1
• Slightly elevated cardiac biomarkers (troponin 0.01-0.1 ng/mL) 1

Low-Risk Features

• Normal or unchanged ECG 1
• Normal cardiac biomarkers measured at appropriate intervals 1
• New-onset angina (within 2 weeks to 2 months) without rest symptoms 1
• Age <70 years without other risk factors 1

Differential Diagnosis Considerations

Always consider non-coronary causes during initial evaluation, including aortic dissection, pulmonary embolism, pericarditis, esophageal disorders, and musculoskeletal pain 1

Common Pitfalls to Avoid

• Do not rely on telephone assessment alone—patients with possible ACS require in-person evaluation with ECG and biomarkers 1
• A normal initial ECG does not exclude ACS—approximately 41% of NSTE-ACS patients have non-diagnostic initial ECGs 3
• Chest pain that resolves with nitroglycerin does not rule out ACS and still requires full evaluation 1
• Do not use total CK, AST, or LDH as primary markers for myocardial injury—these are inadequate for ACS diagnosis 1
• Troponin elevation can occur from non-ACS causes (demand ischemia from SVT, renal failure, myocarditis)—interpret in clinical context 2

Immediate Management During Diagnostic Workup

• Place patient in monitored environment with continuous ECG monitoring and defibrillation capability 1, 4
• Administer aspirin 162-325 mg immediately (chewed, non-enteric coated) unless contraindicated 1, 4
• Provide supplemental oxygen if oxygen saturation <90% 4
• Give sublingual nitroglycerin 0.4 mg every 5 minutes (up to 3 doses) for ongoing chest pain 1, 4
• Initiate anticoagulation therapy once ACS diagnosis is confirmed 4