Second-degree atrioventricular block

From Dog
Mobitz type II block[1]

Second-degree atrioventricular block is a common heart disease in dogs characterized by bundle branch block and conduction irregularities that are usually asymptomatic.

Two forms are recognized in dogs:

  • Mobitz type I
- Usually transient in nature due to non-cardiogenic origin
- ECG is characterized by the PQ interval prolonging from beat to beat up until the drop-out of one QRS complex
- Often seen in older dogs, especially Cocker Spaniel and Dachshund
  • Mobitz type II
- More serious, and may lead to third-degree atrioventricular block
- ECG characterized by beats being dropped irregularly without PQ interval prolongation. As the drop out of beats is irregular, no clustering of QRS complexes can be seen as in second degree block type I. Second degree AV block type II marks the starting of trouble and is a class I pacemaker indication
- Usually seen in older dogs due to pericardial fibrosis or, more rarely, cardiac hemangiosarcoma

Causes include:

Most dogs with chronic second-degree atrioventricular block are treated with pacemakers[2], but emergency treatment may require dopamine (2 - 5 μg/kg/min as constant rate infusion) and atropine.


  1. ECG-pedia
  2. Estrada A et al (2011) Cardiac pacing site optimization. Compend Contin Educ Vet 33(12):E1-E4