ISSN 2398-2977      

Heart: atrioventricular block - 2nd degree

pequis

Introduction

  • Cause: impulse of supraventricular origin (from sinus node or an atrial ectopic beat) is blocked at the AV node and does not progress to activate the ventricles.
  • Significance: usually non-pathologic.
  • Signs: dropped beat.
  • Diagnosis: ECG and/or auscultation.
  • Treatment: usually condition is physiological and no treatment is required, very rarely an artificial pacemaker, or sympathomimetic agents may be indicated in advanced (pathological) 2nd  degree atrioventricular block (AVB).
  • Prognosis: generally excellent due to physiological nature of the condition, but conversely prognosis is guarded to poor if arrhythmia is not abolished by exercise and horse is symptomatic.

Pathogenesis

Etiology

  • Usually a normal homeostatic mechanism to regulate blood pressure. Mediated by the vagus.
  • During the conducted beats, blood pressure gradually rises. This stimulates baroreceptors which act via the vagus to slow or block conduction at the atrioventricular and sinoatrial node.
  • In advanced (pathological) second degree AVB:
    • Occasionally structural conduction system disease, eg congenital, degenerative, inflammation or neoplasia.
    • Drug induced, eg α2 agonists (detomidine Detomidine hydrochloride, romifidine Romifidine and xylazine Xylazine).
    • Electrolyte imbalances.
    • Digitalis toxicity.

Pathophysiology

  • Usually a normal homeostatic mechanism to regulate blood pressure. Mediated by the vagus.
  • Rarely pathological.

Diagnosis

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Treatment

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Outcomes

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Matsui K et al (1985) Second-degree atrioventricular block observed in a Thoroughbred foal on 2.5 months of age. Nippon Juigaku Zasshi 47 (1), 175-178 PubMed.
  • Smetzer D L et al (1969) Second-degree atrioventricular block in the horse. Am J Vet Res 30 (6), 933-946 PubMed.
  • Smetzer D L et al (1969) High-grade second-degree atrioventricular block in a horse. Am J Vet Res 30 (3), 337-343 PubMed.

Other sources of information

  • Marr C M & Bowen I M (2010) Eds. Cardiology of the Horse. 2nd edn. Saunders Ltd, UK. ISBN: 9780702028175.

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!

 
 
 
 

To show you are not a Bot please can you enter the number showing adjacent to this field

 Security code