Chambers and pre-excitation
Right heart strain and S1Q3T3
Sinus tachycardia with anterior T inversion and a right ventricle under acute load — think pulmonary embolism.
116 bpmSinus tachycardia
What you see
- Sinus tachycardia — much the commonest abnormality, and the most sensitive.
- T wave inversion in V1–V4 (right ventricular strain), often with inversion in III.
- S1Q3T3: an S wave in I, a Q wave and inverted T in III. Present in only about 20%.
- New right bundle branch block, right axis deviation, or atrial fibrillation.
Why it looks like that
An acute rise in pulmonary artery pressure dilates and strains a right ventricle unaccustomed to pressure work. The axis swings rightwards and repolarisation of the strained right ventricular free wall is delayed, inverting the anterior T waves.
What to do
- The ECG neither confirms nor excludes pulmonary embolism — use a validated pathway (Wells, PERC, D-dimer, CTPA).
- Right strain on the ECG or echo marks a submassive PE and identifies patients who need closer monitoring.
- Thrombolysis for haemodynamic instability; consider it for deterioration despite anticoagulation.
The trap
S1Q3T3 is neither sensitive nor specific and appears in any cause of acute cor pulmonale. Its absence does nothing to lower the probability of PE — a normal ECG in a breathless, tachycardic patient is entirely compatible with a large embolus.
pulmonary embolismS1Q3T3right ventricular strainsinus tachycardia