S1-Q3-T3 refers to an EKG pattern first described in the 1930s suggestive of cor pulmonale in a case series of patients with pulmonary embolism (PE).
This pattern has the following findings:
- Prominent S wave in lead I.
- Large Q wave in lead III. ST depression with an ascent to the T-wave in lead II (red arrows).
- T wave inversion in lead III (blue arrows).
It’s important to remember that this pattern is NOT pathognomonic for PE. In fact, S1-Q3-T3 should be LESS associated with PE and MORE with causes of cor pulmonale such as COPD, pneumothorax, pneumonia, ARDS, airway obstruction, and yes, PE.
Gotta keep the differential wide and consider pre-test probabilities for all pathologies!
