S1 , Q3 , T3
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In a patient who has suffered a pulmonary embolus there may be transient non-specific changes in the patient's ECG:

  • often no changes are seen on the ECG
  • classical changes are S1, Q3, T3

The detailed changes are as follows:

  • tall R waves in V1
  • P pulmonale (peaked P waves) best seen in the inferior leads
  • there may be right axis deviation and clockwise rotation
  • atrial arrhythmias may occur
  • there may be T wave inversion in the leads V1, V2, V3
  • possible right bundle branch block
  • there may be a shift of transition point to the left, so that the R wave equals the S wave in V5 or V6 rather than V3 or V4
  • in this condition there is often a Q wave in lead 3, resembling an inferior infarction
  • right ventricular strain is very occasionally seen, causing an S wave in lead I, Q wave and inverted T wave in lead III
    • right ventricular strain pattern on ECG is associated with adverse short-term outcome and adds incremental prognostic value to echocardiographic evidence of right ventricular dysfunction in patients with acute pulmonary embolism and normal blood pressure (1)

Click here for an example ECG and further information

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