Heart: second degree atrioventricular block

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Sections available in full article Introduction, Presenting signs, Age predisposition, Cost considerations, Special risks (e.g. anesthetic), Pathogenesis, Etiology, Predisposing factors, Pathophysiology, Timecourse (incubation, duration), Diagnosis, Presenting problems, Client history, Clinical signs, Diagnostic investigation, Confirmation of diagnosis, Gross autopsy findings, Histopathology findings, Differential diagnosis, Treatment, Initial symptomatic treatment, Standard treatment, Monitoring, Sequelae, Prognosis, Expected response to treatment, Reasons for treatment failure, Sources, Publications, Vetstream contributor(s),
Contributors Dr Peter Darke BVSc PhD DVR DVC MRCVS DipECVIM(CA)
Ms Jill Sammarco BVSc MRCVS DipACVS DipECVS
Synonyms Partial AV block

Introduction

  • Cause : slowed conduction throughout 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 some cases.
  • Signs : may be incidental finding; if advanced, there can be weakness or syncope.
  • Diagnosis : signs, missed beats may be heard at auscultation, electrocardiography.
  • Treatment : may respond temporarily to atropine if vagally mediated; may not require therapy; permanent, advanced and symptomatic block should be treated with a cardiac pacemaker.
  • Prognosis : very variable, from good to sudden death through asystole.

Diagnosis

Clinical signs

  • Irregular heart - missed ('dropped') beats evident on auscultation and pulse palpation.
  • May be pronounced sinus arrhythmia (regular irregularity).

Diagnosis

Differential diagnosis

  • Other arrhythmias Heart: dysrhythmia.
  • Third degree (complete) AV block Heart: 3rd degree atrioventricular block.
  • Other causes of weakness/collapse.
  • Other causes of sudden death.

Sequelae

Prognosis

  • Relatively good for Mobitz Type I.
  • Guarded for Mobitz Type II or advanced second degree AV block.

Expected response to treatment

  • Improved exercise tolerance.
  • Reduction in episodes of weakness or collapse.

Reasons for treatment failure

  • Progression of any underlying myocardial disease may occur.
  • Failure of pacemaker or lead system is not uncommon.
  • Mobitz Type II cases may not respond to any medical therapy.

Sources

Publications

Other sources of information

  • Lunney J & Ettinger S J (1995) Cardiac arrhythmias. In: Textbook of Veterinary Internal Medicine4th ed. Eds S J Ettinger & E C Feldman. Philadelphia: W B Saunders & Co.
  • Smith F W K, Tilley L P & Miller M S (1994) Electrocardiography. In: Saunders Manual of Small Animal PracticeEds S J Birchard & R G Scherding. Philadelphia: W B Saunders & Co.
  • Tilley L P (1992) Essentials of Canine and Feline Electrocardiography. 3rd edn. Philadelphia: Lea and Febiger.
  • Sisson D D (1989) Bradyarrhythmias and cardiac pacing. In: Current Veterinary Therapy X.Ed R W Kirk. Philadelphia: W B Saunders & Co.

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