Q Waves on ECG

Last updated 10.08.13

 

Definition

-  Initially negative deflection of QRS on ECG

-  Pathological Q Waves are:

-  >40ms (1mm) wide

-  >2mm deep

-  >25% depth of QRS

-  If seen in V1 – V3

 

 

Features

-  Indicates that net direction of early ventricular repolarization is >90o from positive axis of lead

-  Not usually seen in V1 – V3

-  Not all Q Waves are pathological

-  Prominent Q Waves are characteristic of AMI but not all pathological Q Waves are from AMI

-  Small Q Waves typically seen in lateral leads (I, aVL, V5, V6)

-  Deep Q Waves >2mm may be seen in III & aVR as a normal variant

-  QS complex (no R Wave) can occur in lead V1 as a normal variant (also rarely V2)

 

Causes

-  Physiological or positional

-  Mediastinal shift

-  Dextrocardia

-  Pneumothorax

-  Pectus excavatum

-  COPD: decreased R Wave voltage, Q Waves V1 to lateral chest, often seen with low limb voltage & P Pulmonale in II

-  Misplacement of chest electrodes (ie: on rather than under left breast in women)

-  Acute Myocardial Infarction (AMI)

-  May indicate prior stilent infarction

-  Prominent Q Waves are characteristic of AMI

-  Delayed conduction though ischaemic area of conduction around it results in recording potentials from opposite ventricular wall

-  Development in AMI related to duration & size of infarction

-  Ventricular enlargement: LVH, RVH, cor pulmonale

-  Altered ventricular conduction

-  LBBB: QS in right/mid precordial +/- I, II, aVF

-  WPW

-  Dilated cardiomyopathy

-  Myocarditis

-  Amyloid deposition

-  Sarcoidosis

-  Scleroderma

-  Duchenes Muscular Dystrophy

 

Ix

-  Repeat ECG

-  +/- Echo

-  +/- Tropinon as clinically indicated

 

 

 

References

 

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