Isorhythmic atrioventricular dissociation

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Third degree AV block with AV dissociation, showing the lack of relation between P waves and the (nodal) QRS complexes.[1]

Isorhythmic atrioventricular dissociation is a heart rhythm disturbance of dogs where each atria and ventricle are driven by independent pacemakers at equal or nearly equal rates.

Atrioventricular dissociation is a condition in which the atria and ventricles do not activate in a synchronous fashion but beat independent of each other[2]. AV dissociation usually refers to the situation in which the ventricular rate is the same or faster than the atrial rate. When the atrial rate is faster and the atria and ventricles are beating independently, complete bundle branch block occurs[3].

During AV dissociation the relationship between P waves and QRS complexes is lost. AV dissociations is present in third degree AV block and ventricular tachycardia.

A breed predisposition has been noted in the Labrador Retrievers[4].

Two forms have been described:

  • Type I synchronization - common form - atrioventricular conduction preceded by atrial tachycardia
  • Type II synchronization


  1. ECG-pedia
  2. Wagner GS (1994) Atrioventricular dissociation. In: Wagner GSS, Marriott HJ, eds. Marriott's Practical Electrocardiography. 9th ed. Baltimore, Md: Williams & Wilkins
  3. Braunwald E (2001) Atrioventricular dissociation. In: Braunwald E, Zipes DP, Libby P, eds. Heart Diseases: A Textbook Of Cardiovascular Medicine. 6th ed. WB Saunders Co: Philadelphia, Pa
  4. Perego M et al (2012) Isorhythmic atrioventricular dissociation in Labrador Retrievers. J Vet Intern Med 26(2):320-325