Equis ISSN 2398-2977

Heart: sinus bradycardia

Contributor(s): Christopher Brown, Wendy Furness, Lesley Young

Introduction

  • An abnormally slow (<24 bpm) but regular heart rate.
  • Cause: variable.
  • Signs: depend on inciting cause; may show poor athletic performance if unable to elevate heart rate appropriately at exercise. Can also result in syncope and collapse.
  • Occasionally highly conditioned and very relaxed horses will have heart rates <24 bpm, but this will be rapidly reversible with exercise or excitement; such low heart rates are common with intravenous sedation.
  • Diagnosis: auscultation, ECG.
  • Treatment: indicated in profound irreversible bradycardia.
  • Prognosis: guarded to poor in symptomatic animals; excellent if bradycardia is physiological or drug-induced.

Pathogenesis

Etiology

Physiological elevation of vagal tone
  • Eyeball pressure, eg in ocular surgery.
  • Elevated intracranial pressure, eg neoplasia, trauma.
  • Hypothermia.
  • Altered carotid sinus pressure.

Pathologic

  • Systemic disease with cardiac toxicity.
  • Electrolyte imbalance.

Central nervous system lesions

  • Drug associated:
  • Calcium channel blockers.
  • Digoxin   Digoxin  .
  • Anesthetic agents: sinus bradycardia can be a warning of impending cardiac arrest during anesthesia.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Pimenta E L M et al (2011) Comparative study between atropine and hyoscine-N-butylbromide for reversal of detomidine induced bradycardia in horses. Equine Vet J 43 (3), 332-340 PubMed.


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