• Open Access

Isorhythmic Atrioventricular Dissociation in Labrador Retrievers


  • Preliminary data were presented at the European College of Veterinary Internal Medicine (ECVIM) Forum, Ghent, Belgium, September 4–8, 2008.

Corresponding author: Roberto A. Santilli Dr Med.Vet., PhD, D.E.C.V.I.M.-C.A. (Cardiology), Clinica Veterinaria Malpensa, Viale Marconi, 27, 21017 Samarate, Varese, Italy; e-mail:rasantil@tin.it.



Isorhythmic atrioventricular dissociation (IAVD) is a rhythm disturbance in which atria and ventricles are driven by independent pacemakers at equal or nearly equal rates.


To describe electrocardiographic and electrophysiologic features of IAVD in a group of 11 Labrador Retrievers and its possible correlation with focal junctional tachycardia (FJT).


Between December 2004 and October 2010, medical records of 11 Labrador Retrievers with surface electrocardiographic findings compatible with IAVD were retrospectively analyzed.


Twelve-lead surface electrocardiograms, thoracic radiographs, and echocardiographic findings of each dog and electrophysiologic mapping results of 3 dogs were retrospectively analyzed.


In 10 of 11 dogs, the ECG pattern revealed the presence of IAVD with type I synchronization. In 5 of 10 dogs, IAVD with type I synchronization was interrupted by periods of junctional tachycardia with 1 : 1 ventriculo-atrial conduction. One of 11 dogs presented IAVD with type II synchronization. The ECG diagnosis of IAVD with type I and type II synchronization, and junctional rhythm with 1 : 1 ventriculo-atrial conduction was confirmed in 3 of 11 dogs with endocardial mapping in which the diagnosis of focal junctional tachycardia was made.

Conclusion and Clinical Importance

IAVD with type I synchronization is more common than IAVD with type II synchronization in Labrador Retrievers, and a correlation between IAVD and FJT can be hypothesized.