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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)

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