Heart: 3rd degree atrioventricular block

Buy now to access the full article, existing subscribers login

Sections available in full article Introduction, Presenting signs, Acute presentation, 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, Standard treatment, Sequelae, Prognosis, Expected response to treatment, Reasons for treatment failure, Sources, Publications, Vetstream contributor(s),
Contributors Dr Barrett Bulmer DVM MS DACVIM-Cardiology
Mr Simon Swift MA VetMB CertSAC MRCVS
Mr Mark Rishniw BVSc MS DipACVIM
Synonyms Complete heart block

Introduction

  • Cause : complete failure of conduction from the atria to the ventricles.
  • Signs : causes weakness, syncope and (rarely), congestive heart failure.
  • Diagnosis : electrocardiograph shows no relationship of P waves to QRS complexes. Ventricles develop their own pacemaker independent of the atrial pacemaker.
  • Treatment : medical treatment usually ineffective. Requires pacemaker implantation.
  • Prognosis : guarded with medical therapy. Can be good following successful pacemaker implantation.

Diagnosis

Clinical signs

  • Lethargy.
  • Exercise intolerance.
  • Weakness.
  • Syncope.
  • Evidence of congestive heart failure (dyspnea, coughing, or ascites).
  • On occasion owners will report their dogs is asymptomatic because they mistakenly believe reductions in activity are age-related.

Diagnosis

Differential diagnosis

  • Causes of exercise intolerance /syncope:
    • Other arrhythmias Heart: dysrhythmia.
      Escape beats should not be confused with ventricular premature contractions (VPCs) on ECG.

Sequelae

Prognosis

  • Poor for those treated with sympathomimetic drugs.
  • A recent study reported a median survival time of approximately 350 days for dogs (n=63) with high-grade second degree or third degree AV block that did not receive pacemakers.
  • Administration of anticholinergics, sympathomimetics, furosemide Furosemide or angiotensin converting enzyme inhibitors were not associated with duration of survival.
  • The study further identified that dogs with high-grade second grade and third degree AV block that received pacemakers (n=12) had a significantly longer survival time (>900 days) than those that did not receive pacemakers (approximately 350 days).

Expected response to treatment

  • Increased exercise tolerance, control of congestive failure if present.
  • If the bradyarrhythmias was responisble for the syncopal episodes they should resolve.
  • Response time variable depending on treatment option and presence of underlying disease.

Reasons for treatment failure

  • Progression of underlying disease.
  • Pacemaker failure - lead dislodged, infection or seroma formation, battery fatigue.

Sources

Publications

Refereed papers

  • Recent references from PubMed.
  • Bulmer B J, Sisson D D, Oyama M A et al(2006) Physiologic VDD versus non-physiologic VVI pacing in canine third degree atrioventricular block. J Vet Intern Med 20 , 257-271 PubMed.
  • Schrope D P, Kelch W J (2006) Signalment, clinical signs, and prognostic indicators associated with high-grade second- or third-degree atrioventricular block in dogs: 124 cases (January 1, 1997-December 31, 1997). JAVMA 228 , 1710-1717 PubMed.
  • Wess G, Thomas W P, Berger D M et al(2006) Applications, and outcomes of transvenous pacemaker implantation in 105 dogs (1997-2002). J Vet Intern Med 20 , 877-884.
  • Oyama M A, Sisson D D, Lehmkuhl L B (2001) Practices and outcome of artificial cardiac pacing in 154 dogs. J Vet Intern Med 15 , 229-239 PubMed.

Other sources of information

  • Ettinger S (2005) Electrocardiography and Cardiac Arrhythmias. In: Textbook of Veterinary Internal Medicine.6th edn. Eds Ettinger & Feldman. pp 1065-1066 and 1075-1076.
  • Martin M (1998) Arrhythmias. In: Manual of Small Animal Cardiorespiratory Medicine and Surgery.Eds V Luis-Fuentes & S Swift. Cheltenham BSAVA.
  • Darke P G G et al(1996) Color Atlas of Veterinary Cardiology. pp 154-159.
  • Tilley L P (1992) Essentials of Canine and Feline Electrocardiography. 3rd edn. pp 175-178.

Sample content only, to unlock the full article login or buy now

Loading...