What is the next step for a 64-year-old patient presenting with chest pain for 2 days, ECG showing ST depression in leads 2 and 3, and negative troponin I (Trop I)?

Next Step: Immediate Anticoagulation and Serial Troponin Monitoring

This patient requires immediate initiation of anticoagulation (unfractionated heparin or low-molecular-weight heparin) plus dual antiplatelet therapy (aspirin and clopidogrel), followed by serial troponin measurement at 6-12 hours from symptom onset and repeat ECG monitoring. 1, 2, 3

Immediate Management Protocol

Start Anticoagulation Now—Do Not Wait for Troponin Results

• Anticoagulation must be initiated immediately upon clinical suspicion of acute coronary syndrome based on symptoms and ECG findings alone. 1
• The American College of Cardiology and European Heart Journal emphasize that heparin therapy is part of baseline treatment for suspected ACS and should begin at presentation, before troponin results are available. 1
• The acute thrombotic process is most active in the initial hours of ACS presentation, making immediate anticoagulation essential to prevent thrombus propagation and recurrent ischemic events. 1
• Troponin elevation indicates myocardial damage that has already occurred, not ongoing thrombotic risk—waiting for troponin results delays critical antithrombotic therapy during the acute thrombotic phase. 1

Anticoagulation Options:

• Unfractionated heparin: 60-70 U/kg bolus (maximum 5,000 U) followed by 12-15 U/kg/hr infusion, targeting aPTT 50-70 seconds. 1
• Low-molecular-weight heparin (enoxaparin) is a reasonable alternative with similar or improved outcomes. 1, 2

Dual Antiplatelet Therapy

• Initiate aspirin 75-150 mg immediately plus clopidogrel loading dose (300 mg). 2, 4
• The ST depression in leads 2 and 3 represents ECG changes compatible with new ischemia, meeting criteria for non-ST-elevation acute coronary syndrome. 2, 4
• Continue aspirin 75-150 mg daily indefinitely. 5, 2

Additional Baseline Medications

• Beta-blocker (unless contraindicated by bradycardia, hypotension, or heart failure). 2
• Nitrates for ongoing or recurrent chest pain. 2

Serial Troponin Measurement—Critical Timing

A single negative troponin is insufficient to exclude myocardial infarction. 2, 3

• Obtain a second troponin measurement at 6-12 hours from symptom onset (this patient presented with 2 days of chest pain, so the timing should be 6-12 hours from the most recent episode or from presentation). 5, 2, 3
• Myocardial injury may not be detectable in the first hours after symptom onset—serial measurements are mandatory. 2, 3
• The American College of Cardiology and European Society of Cardiology state that troponin results guide prognosis and treatment intensity but should not determine whether to start anticoagulation. 1, 3

Serial ECG Monitoring

• Perform repeat 12-lead ECG immediately if symptoms persist, change, or recur. 2, 3
• A 12-lead ECG should be repeated at regular intervals during the observation period. 2
• Dynamic ECG changes indicate high-risk status even with negative troponins. 3

Risk Stratification After Serial Testing

High-Risk Features Requiring Urgent Coronary Angiography (24-48 hours):

• Recurrent or persistent ischemic chest pain despite medical therapy. 2
• Dynamic ST-segment changes on serial ECGs. 2, 3
• Positive second troponin measurement. 3
• Hemodynamic instability. 2, 3
• Major arrhythmias. 2
• Diabetes mellitus. 2

If any high-risk features develop: Continue low-molecular-weight heparin, initiate GP IIb/IIIa receptor inhibitor therapy, and proceed to coronary angiography within 24-48 hours. 2

Low-Risk Pathway (If After 6-12 Hours):

• No recurrent chest pain. 3
• Normal or unchanged ECG. 3
• Twice-negative troponin measurements. 3

Then: Discontinue heparin, continue aspirin and clopidogrel, and perform stress testing before discharge. 3

Critical Pitfalls to Avoid

• Never rely on a single troponin measurement if drawn less than 6 hours from symptom onset. 3
• Do not dismiss ST depression as "non-specific"—ST depression in leads 2 and 3 with chest pain represents non-ST-elevation ACS until proven otherwise. 2, 4
• Do not delay anticoagulation while waiting for troponin results—the thrombotic process is active now. 1
• Do not use NSAIDs for pain relief due to prothrombotic effects. 5

Pain Management

• Morphine 4-8 mg IV with additional 2 mg doses at 5-15 minute intervals until pain is relieved. 5
• Avoid intramuscular injections. 5
• Administer antiemetics (metoclopramide 5-10 mg IV) concurrently with opioids. 5