S1Q3T3

What it is

The S1Q3T3 is the ECG manifestation of acute pressure and volume overload of the right ventricle.

It is characterised by:

• Lead I - an S wave signifying a complete or more often incomplete RBBB.
• Lead III - a Q wave, slight ST elevation, and an inverted T wave. These findings are due to the pressure and volume overload over the right ventricle which causes repolarization abnormalities.

Causes

Any cause of acute cor pulmonale can cause the S1Q3T3 finding on the ECG. This includes PE, acute bronchospasm, pneumothorax, and other acute lung disorders. In addition, transient LPFB may cause this finding as well.

What this means for Dx'ing PE

The ECG is often abnormal in PE, but findings are not sensitive & not specific. S1Q3T3 pattern is present in only in 20% of cases of PE.

The ECG is a poor diagnostic tool for PE. The greatest utility of the ECG in the patient with suspected PE is ruling out other potential life-threatening diagnoses such as MI.


References:

• http://medicine.ucsf.edu/housestaff/Chiefs_cover_sheets/ecg_pe.pdf
• http://www.ispub.com/ostia/index.php?xmlFilePath=journals/ijem/vol3n1/cor.xml