The term “S1Q3T3” in the context of an EKG (electrocardiogram) refers to a specific pattern often associated with pulmonary embolism (PE), a potentially life-threatening condition where a blood clot blocks an artery in the lung. This pattern is not diagnostic on its own but can be a clue when combined with clinical symptoms and other findings.

Breakdown of S1Q3T3 Pattern:

• S1: A deep S wave in Lead I (indicating rightward deviation of the QRS axis).
• Q3: A prominent Q wave in Lead III (a small initial negative deflection in the QRS complex).
• T3: An inverted T wave in Lead III (suggesting right ventricular strain or ischemia).

This pattern reflects right heart strain, often caused by acute pulmonary embolism, as the right ventricle struggles against increased pulmonary artery pressure. It’s seen in a minority of PE cases (estimated 10-25%) and is not specific, as it can occur in other conditions like chronic lung disease or right ventricular hypertrophy.

Clinical Relevance:

• Sensitivity and Specificity: S1Q3T3 is neither highly sensitive nor specific for PE. It’s a supportive finding but not definitive. Other EKG findings in PE may include sinus tachycardia (most common), right bundle branch block, or right axis deviation.
• Action: If S1Q3T3 is observed in a patient with symptoms like sudden dyspnea, chest pain, tachycardia, or hypoxia, urgent evaluation for PE is warranted. This may involve:
  • D-dimer testing (if low pretest probability).
  • CT pulmonary angiography (gold standard for PE diagnosis).
  • Echocardiography to assess right ventricular strain.
  • Clinical scoring (e.g., Wells Score or Geneva Score) to guide diagnostic workup.

Example Scenario:

A 45-year-old patient presents with acute shortness of breath and chest pain. EKG shows sinus tachycardia, a deep S wave in Lead I, a Q wave in Lead III, and T-wave inversion in Lead III (S1Q3T3). Combined with a high Wells Score (e.g., recent surgery, immobility), this raises suspicion for PE, prompting immediate imaging and possibly anticoagulation therapy pending confirmation.