S1, Q3, T3 Pattern: ECG Finding in Acute Pulmonary Embolism
The S1, Q3, T3 pattern is an electrocardiographic finding suggestive of acute pulmonary embolism, characterized by an S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III. 1
Clinical Significance
- This ECG pattern indicates right ventricular strain from acute pulmonary artery obstruction and should prompt immediate evaluation for pulmonary embolism in patients presenting with sudden-onset dyspnea, hypoxia, tachycardia, or hypotension 1
- The pattern is not specific to pulmonary embolism but when present in the appropriate clinical context (preceding DVT history, sudden dyspnea, syncope), it strongly supports the diagnosis 1
Aspirin Recommendations for S1, Q3, T3 Pattern
Do NOT administer aspirin to patients with suspected pulmonary embolism showing the S1, Q3, T3 pattern. 2
Critical Decision Points
- If chest pain suggests cardiac origin (substernal, crushing, radiating to jaw/arm): Aspirin 150-300 mg should be administered immediately for suspected acute coronary syndrome 3
- If presentation suggests pulmonary embolism (sudden dyspnea, hypoxia, S1Q3T3 pattern, preceding DVT): Withhold aspirin and initiate anticoagulation therapy instead 1
- If uncertain about the diagnosis: Do not encourage aspirin administration, as giving aspirin when the cause is not cardiac could be harmful 2
Management Algorithm for S1, Q3, T3 Pattern
Immediate Actions
- Call EMS/activate emergency response immediately for any patient with S1, Q3, T3 pattern and acute symptoms 2
- Perform bedside echocardiography urgently to visualize potential pulmonary artery thrombus 1
- Assess for signs of hemodynamic instability: tachycardia, hypotension, hypoxia, syncope 1
Treatment Pathway
- For confirmed/highly suspected pulmonary embolism: Initiate thrombolytic therapy (tenecteplase or streptokinase) without delay in hemodynamically unstable patients 1
- For stable patients: Arrange immediate transfer to facility with capability for advanced imaging (CT pulmonary angiography) and interventional procedures 1
- Anticoagulation: Begin therapeutic anticoagulation (enoxaparin or unfractionated heparin) as soon as pulmonary embolism is suspected, unless contraindications exist 1
Common Pitfalls to Avoid
- Do not assume all chest pain with ECG changes requires aspirin - the S1, Q3, T3 pattern specifically indicates right heart strain from pulmonary embolism, not left ventricular ischemia 2, 1
- Do not delay thrombolysis while waiting for confirmatory imaging in hemodynamically unstable patients with visible thrombus on bedside echo 1
- Do not give aspirin if bleeding risk is present or if the diagnosis is uncertain, as this could worsen outcomes in pulmonary embolism requiring anticoagulation 2