Posts Tagged ‘regular cannon waves in avnrt svt’

Cannon waves occur when Atria contracts against a closing tricuspid valve of  right ventricle .( There  would be a equivalent left atrial cannon which  goes into pulmonary vein as well  , it is discussed elsewhere !)

Cannon waves  happen only when P waves fall within QT interval in ECG as QT represents the electro-mechanical systole of  ventricles.  (Since P wave represents atrial systole , it is simple to understand when it falls within QT both atria and ventricular contractions collide to produce a cannon wave into the neck or pulmonary veins.)

The following two images of cannon waves  taken from the legend  Dr Paul woods own tracing  .

irregular cannon waves in jvp  complete heart block

regular cannon waves in jvp  svt avnrt  11 va conduction  002

Regular cannon waves

Occur during SVT  with 1:1 VA conduction.*

1 : 1  VA conduction  can be considered as  absence of  AV dissociation  (Rather  disciplined  VA association with every beat ) This is essential to create a hemodynamic  milieu for regular cannon waves.

* In AVNRT , VA conduction in strict  sense  is a misnomer  .It is simply a retrograde conduction thorough  the AV node .

Irregular cannon waves 

  1. Complete heart block .
  2. Multiple random VPDs
  3. Some patients with VT.*(Who are those patients ?  Those with AV dissociation when retrograde “P” wave falls  within QT interval cannon occurs. As expected this occurs in random fashion  which makes  the cannon fire irregular.

Can we get regular cannon in VT ?

Yes , but rare . As explained earlier this can happen only if AV  association occur on a retrograde fashion.

Further reading in this site

What-is-a-cannon-sound  , how is it related to cannon wave ?

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