AV Dissociation

  Independent activation of the atria and the ventricles is seen.

  By definition, retrograde conduction from the ventricules to the atria is not seen.

  AV dissociation can be continuous or intermittent.




AV dissociation developes when there is

  3rd degree (complete) AV block (ventricular rate is slower than the atrial rate)

  Slow atrial rate with a faster junctional or ventricular rate (there is no AV block).




Isorhythmic AV dissociation

  Sometimes, the rate of the junctional or ventricular rhythm during AV dissociation is

      only slightly different from that of the atrial rhythm.

  Transient AV dissociation caused by competing atrial and junctional or ventricular rhythms

      with similar rates (so-called isorhythmic AV dissociation).

  Temporary atrial pacing will accelerate the atrial rate and overdrive the competing junctional or

      ventricular arrhythmia, demonstrating intact AV conduction.





References:

  Clinical Arrhythmology and Electrophysiology: A Companion to Braunwald's Heart Disease
      2nd Edition, Elsevier Saunders, 2012: pp 189-190. ISBN:1455737682, 9781455737680

  Clinical Cardiac Pacing, Defibrillation and Resynchronization Therapy.
      Ellenbogen, Kenneth A. 4th ed. Philadelphia, PA : Saunders. 2011. pp 323-360.





ECG 1. The ECG above is from a patient with coronary artery disease and severe left ventricular dysfunction.
Ventricular tachycardia (VT) is seen in leads II, C4, C5 and C6.
The P wave activity due to atrioventricular dissociation
supports the diagnosis of VT.
Ventricular rate during VT is higher than the atrial (P wave) rate.

Click here for a more detailed ECG





ECG 2. The Holter tracing above is from a 29 years-old woman with mild mitral stenosis.
The rhythm is isorhythmic AV dissociation.
The AV dissociation is intermittent (some P waves are conducted to the ventricles).
The cause of intermittent isorhythmic AV dissociation in this woman was increased vagal activity.
During the recording of the above tracing, she was experiencing near-syncope.
Her Holter recording also showed infrequent ventricular premature contractions (VPCs).

Click here for a more detailed ECG