Canis ISSN: 2398-2942

Heart: dysrhythmia

Synonym(s): arrhythmia

Contributor(s): Serena Brownlie, Mark Rishniw

Introduction

  • Most dysrhythmias are clinically unimportant.
  • Abnormalities of heart rate +/- conduction (rhythm).
  • Cause: systemic disease, primary cardiac disease.
  • Signs: many are subclinical, frequent finding in cardiac disease.
  • Diagnosis: auscultation, ECG, must make accurate diagnosis before considering treatment.
  • Treatment: may be inappropriate - anti-dysrhythmic drugs if necessary.
  • Prognosis: often depends on etiology.
    Follow the diagnostic trees for Common Cardiac Arrhythmias Common cardiac arrhythmias and Bradyarrhythmia and Tachyarrythmia Bradyarrhythmia and Tachyarrhythmia.

Pathogenesis

Pathophysiology

  • May occur as a primary entity or secondary to systemic or cardiac disease.
  • Depolarization of pacemaker cells in sino-atrial node (dictates intrinsic heart rate):
    • Increased by sympathetic stimulation (excitement, fear and pain).
    • Decreased by parasympathetic stimulation.
    • Altered by drugs, hormone levels, electrolytes.
    • Reflected by damage to conduction tissues → AV or branch bundle block.
  • Ectopy:
    • Myocardial hypoxia, electrolyte imbalances or sympathetic stimulation → ectopic foci.
    • Abnormal automaticity refers to site of depolarization in non-pacemaker tissue.
    • Re-entry refers to second depolarization when part of impulse is delayed by passage through diseased tissue (due to hypoxia or fibrosis).
    • After-potentials are oscillations in resting membrane potential following repolarization which may reach threshold potential and trigger an impulse.
    • After-potentials are enhanced by adrenergic stimulation, digitalis toxicity and increased intracellular calcium.
  • Can be classified according to site of origin.

Supraventricular

Atrioventricular nerve block

Ventricular

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.
  • Moïse N S (1998) Autonomic influences on cardiac rhythms in dogs. JSAP 39 (10), 460-468 PubMed.

Other sources of information

  • Knight D (1999)Reason must supercede dogma in the management of ventricular arrhthymias.In:Kirk's Current Veterinary Therapy13. Ed J Bonagura. Saunders Co. pp 730-733.
  • Moise N S (1999)CVT update - ventricular arrhythmias.In:Kirk's Current Veterinary Therapy13. Ed J Bonagura. Saunders Co. pp 733-737.


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