What ECG (electrocardiogram) changes indicate the use of antiplatelet therapy?

ECG Changes Indicating Antiplatelet Therapy

Antiplatelet drugs should be initiated in patients presenting with ST-segment depression, ST-segment elevation, or deep T-wave inversions (≥2 mm) on ECG in the setting of acute coronary syndrome, as these changes indicate acute myocardial ischemia requiring aggressive antiplatelet therapy. 1

Primary ECG Indications for Antiplatelet Therapy

ST-Segment Elevation

• ST-segment elevation ≥1 mm (0.1 mV) in at least 2 contiguous leads confirms acute myocardial infarction in >90% of patients and mandates immediate dual antiplatelet therapy (aspirin plus a P2Y12 inhibitor such as prasugrel or ticagrelor) 1
• These patients require aspirin 150-300 mg loading dose (or 75-250 mg IV) plus a potent P2Y12 inhibitor before or at the time of PCI 1
• ST elevation carries the highest early mortality risk and represents complete coronary occlusion requiring emergent reperfusion 1

ST-Segment Depression

• ST-segment depression in any leads (except V1-V3 where it may indicate posterior MI) indicates unstable angina or NSTEMI and requires antiplatelet therapy 1
• ST depression paradoxically portends the highest risk of death at 6 months, with greater degrees of depression correlating with worse outcomes 1
• These patients benefit progressively more from aggressive antiplatelet strategies including GP IIb/IIIa inhibitors as risk increases 1

Deep T-Wave Inversions

• Marked symmetrical T-wave inversion ≥2 mm (0.2 mV) in precordial leads strongly suggests acute ischemia, particularly from critical LAD stenosis, and warrants antiplatelet therapy 1
• These patients are at high risk with medical therapy alone and benefit from revascularization combined with dual antiplatelet therapy 1

Transient ST-Segment Changes

• Transient ST-segment changes ≥0.5 mm (0.05 mV) during symptomatic episodes that resolve when asymptomatic indicate acute ischemia with very high likelihood of severe CAD 1
• These dynamic changes represent the highest-risk ECG pattern and mandate aggressive antiplatelet therapy 1

Risk Stratification by ECG Pattern

The ECG provides a gradient of risk that guides antiplatelet intensity 1:

• Highest risk: Bundle-branch block, paced rhythm, or LV hypertrophy with ACS symptoms (consider GP IIb/IIIa inhibitors) 1
• High risk: ST-segment deviation (elevation or depression) - requires dual antiplatelet therapy 1
• Moderate risk: Isolated T-wave inversion - requires at least aspirin plus clopidogrel 1
• Lower risk: Normal ECG with clinical suspicion - still warrants antiplatelet therapy based on biomarkers and clinical context 1

Specific Antiplatelet Regimens by ECG Findings

For STEMI (ST elevation)

• Aspirin 150-300 mg loading dose plus ticagrelor (180 mg loading, 90 mg twice daily) or prasugrel (60 mg loading, 10 mg daily) 1
• Continue dual antiplatelet therapy for 12 months unless excessive bleeding risk 1

For NSTE-ACS (ST depression or T-wave changes)

• Aspirin plus a P2Y12 inhibitor (preferably ticagrelor or prasugrel over clopidogrel) 1
• Consider adding GP IIb/IIIa inhibitors for highest-risk patients with extensive ST depression 1

Critical Pitfalls to Avoid

• Do not withhold antiplatelet therapy based on a normal ECG if clinical suspicion for ACS is high - up to 25% of ACS patients have non-diagnostic initial ECGs 1
• Do not give fibrinolytics to patients with ST depression (except true posterior MI with ST depression in V1-V3) - these patients require antiplatelet therapy and invasive strategy instead 1
• Always obtain serial ECGs - the magnitude of ST deviation correlates with benefit from aggressive antiplatelet therapy, and changes over time provide prognostic information 1
• Compare to prior ECGs when available - new changes are far more significant than chronic abnormalities 1