Q Wave

The Q Wave

A Q wave is any negative deflection that precedes an R wave

  • The Q wave represents the normal left-to-right depolarisation of the interventricular septum
  • Small ‘septal’ Q waves are typically seen in the left-sided leads (I, aVL, V5 and V6)
Normal Q wave in V6

Q waves in context

ECG basics: waves, segments and intervals LITFL ECG library

Q waves in different leads

  • Small Q waves are normal in most leads
  • Deeper Q waves (>2 mm) may be seen in leads III and aVR as a normal variant
  • Under normal circumstances, Q waves are not seen in the right-sided leads (V1-3)

Pathological Q Waves

Q waves are considered pathological if:

  • > 40 ms (1 mm) wide
  • > 2 mm deep
  • > 25% of depth of QRS complex
  • Seen in leads V1-3

Pathological Q waves usually indicate current or prior myocardial infarction.

Differential Diagnosis

Loss of normal Q waves

  • The absence of small septal Q waves in leads V5-6 should be considered abnormal.
  • Absent Q waves in V5-6 is most commonly due to LBBB.

ECG Examples

Example 1

Inferior Q waves with STEMI
  • Inferior Q waves (II, III, aVF) with ST elevation due to acute MI

Example 2

Q waves with old inferior AMI
  • Inferior Q waves (II, III, aVF) with T-wave inversion due to previous MI

Example 3

Lateral Q waves with STEMI
  • Lateral Q waves (I, aVL) with ST elevation due to acute MI

Example 4

Anterior Q waves STEMI
  • Anterior Q waves (V1-4) with ST elevation due to acute MI

Example 5

Anterior Q waves post recent MI
  • Anterior Q waves (V1-4) with T-wave inversion due to recent MI

ECG Library Basics

LITFL Further Reading

Advanced Reading




Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

One comment

  1. Thankyou for this Dr Burns,

    I wonder what your thoughts are on finding inferior Q waves in a patient with an indeterminate axis? Should we still expect the small inferior R waves seen in a superior axis?

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