First-degree atrioventricular block

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1st degree AV block. Although the PQ interval is prolonged, all P waves are followed by QRS complexes: there is no dropout of complexes[1]

First-degree atrioventricular block is a common degenerative heart disease of dogs characterized by a benign bundle branch block with resulting prolonged P-R intervals.

This condition is frequently observed in dogs over 8 years of age and is associated with neuronal degeneration within the through the atrioventricular junction and bundle of His.

A breed predisposition has been noted in the Cocker Spaniel and Dachshund.

ECG studies usually show P-R intervals >0.13 secs in the presence of normal sinus rhythm.

In most dogs, this is usually an incidental finding on ECG, but comprehensive thoracic radiography, echocardiography and blood pressure measurement should be taken to exclude underlying cardiac diseases[2].


  1. ECG-pedia
  2. Kovacevic A & Sastravaha A (2007) Clinically silent atrial dissociation in a dog. J Vet Cardiol 9(2):135-137