Canis ISSN: 2398-2942

Heart: first degree atrioventricular block

Synonym(s): Prolonged P-Q interval

Contributor(s): Jill Sammarco

Introduction

  • Cause: slowed conduction through the atrioventricular node:
    • Can be due to excessive vagal tone, metabolic disorders, cardiomyopathies or idiopathic.
    • Can be found in clinically normal dogs - may be benign in many cases.
  • Signs: usually an incidental finding; if advanced, there can be weakness or syncope.
  • Diagnosis: clinically, usually no abnormality on auscultation; electrocardiography.
  • Treatment: usually none, but may respond temporarily to atropine Atropine.
  • Prognosis: usually very good.

Pathogenesis

Etiology

  • Congential: brachycephalic breeds?
  • Iatrogenic: cardiac glycosides (digitalis Digoxin ); alpha-2 adrenoceptor stimulant sedatives (xylazine Xylazine ). Class IA anti-arrhythmic agents, eg quinidine Quinidine , procainamide Procainamide , calcium antagonists.
  • Functional: often occurs with increased vagal tone:
    • Especially in brachycephalic dogs, associated with sinus arrhythmia.
    • Occasionally with CNS diseases, eg head trauma Brain: trauma , brain trauma Brain: trauma , encephalitis Encephalitis.
  • Metabolic: can be found occasionally with hyperkalemia.

Predisposing factors

General
  • Brachycephalic breeds, often in combination with sinus arrhythmia.

Specific

Pathophysiology

  • Prolonged conduction through the atrioventricular node usually results from a high vagal tone.
  • This can be caused iatrogenically, secondary to other diseases or be functional.
  • Usually benign and will disappear at elevated heart rates.
  • May be associated with second degree AV block Heart: second degree atrioventricular block (Mobitz Type I).

Timecourse

  • Non-progressive in most cases.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

Other sources of information

  • Lunney J & Ettinger S J (1995)Cardiac arrhythmias.In:Textbook of Veterinary Internal Medicine.4th edn. Eds S J Ettinger & E C Feldman. Philadelphia: W B Saunders.
  • Smith F W K, Tilley L P & Miller M S (1994)Electrocardiography.In:Saunders Manual of Small Animal Practice.Eds S J Birchard & R G Scherding. Philadelphia: W B Saunders.
  • Tilley L P (1992)Essentials of Canine and Feline Electrocardiography.3rd edn. Philadelphia: Lea & Febiger.
  • Sisson D D (1989)Bradyarrhythmias and cardiac pacing.In:Current Veterinary Therapy X.Ed R W Kirk. Philadelphia: W B Saunders.


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