Equis ISSN 2398-2977

Heart: atrioventricular block - 3rd degree

Synonym(s): 3rd degree AVB

Contributor(s): John Keen, Lesley Young, Nicola Menzies-Gow

Introduction

  • Very uncommon arrhythmia in the horse.
  • Complete electrical and mechanical dissociation between the atria and ventricles.
  • Alternative (idionodal) pacemaker in the ventricles takes over to maintain a slower (generally <20 bpm) heart rate.
  • Cause: inflammatory or degenerative changes in the AV node; rarely in association with electrolyte or metabolic abnormalities, congenital, mediastinal lymphoma or rattlesnake envenomation.
  • Signs: severe exercise intolerance, frequent syncope.
  • Diagnosis: auscultation, ECG.
  • Treatment: pacemaker.
  • Prognosis: guarded.

Presenting signs/acute presentation

  • Severe exercise intolerance.
  • Frequent syncope.

Cost considerations

  • Cost of treatment.

Special risks, eg anesthetic

  • Affected animals should not be anesthetized.

Pathogenesis

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Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Van Loon et al (2002) Implantation of a dual-chamber, rate adaptive pacemaker in a horse with suspected sick sinus syndrome. Vet Rec 151, 541-545 PubMed.
  • Van Loon G et al (2001) Dual Chamber pacemaker implantation via the cephalic vein in healthy equids.  J Vet Intern Med 15, 564-571 PubMed.
  • Pibarot P et al (1993) Implantation of a programmable atrioventricular pacemaker in a donkey with complete atrioventricular block and syncope. Equine Vet J 25, 248-251 PubMed.
  • Reef V B et al (1986) Implantation of a permanent transvenous pacing catheter in a horse with complete heart block and syncope. JAVMA 189, 449-452 PubMed.
  • Whitton D L & Trim C M (1985) Use of dopamine hydrochloride during general anaesthesia in the treatment of advanced atrioventricular block in four foals. JAVMA 187, 1357-1361 PubMed.

Other sources of information

  • Reef V B (1999) Arrhythmias. In: Cardiology of the Horse. Ed: Marr C. W B Saunders, UK. pp 179-209.
  • Reef V B (1998) Cardiovascular System. In: Manual of Equine Emergencies. Eds: Orsini J A & Divers T J. W B Saunders, USA. pp 130-188.


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