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

ECG LIBRARY 700

ECG LIBRARY

Electrocardiogram

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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