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Heart: sinus block - arrest

icanis

Introduction

  • Sinus or sinoatrial block and sinus arrest are electrocardiographic (ECG) abnormalities, characterized by absence of P-QRS-T complexes.
  • Cause: they indicate a condition in which no heart beat occurs, due to temporary failure of the sinoatrial node to produce an electrical impulse, or failure of conduction from the sinoatrial node.
  • Signs: often none if short periods of no heart beat; weakness or fainting due to cerebral hypoxia with longer periods of no heart beat. 
  • Diagnosis: sinoatrial block is usually diagnosed when the pause between complexes is exactly equal to twice the previous P-P interval. Sinus arrest is the usual name for a pause which is greater than twice the previous P-P interval. Cannot be discriminated in dogs because of sinus arrhythmia.
  • Long periods of sinus arrest are usually terminated by a junctional or ventricular escape complex.
  • Treatment: drugs to increase heart rate (eg atropine) or an artificial pacemaker if appropriate.
  • Prognosis: generally reasonable unless progress; good with an artificial pacemaker.

Pathogenesis

Etiology

  • Sinoatrial node disease may be due to atrial dilatation, infiltration or fibrosis.
  • Also due to excessive vagal tone, drugs, electrolyte disturbances - particularly hyperkalemia Hyperkalemia.
  • Exaggerated sinus arrhythmia in brachycephalic breeds → long sinus pauses, especially during sleep.

Predisposing factors

Pathophysiology

  • Sinoatrial node fails to produce an impulse, usually due to depressed automaticity (high vagal tone).
  • May be described as normal in some dogs (where no clinical signs seen), especially in brachycephalic breeds.
  • Sinoatrial node fails to produce an impulse.
  • After a pause of several seconds, episode is usually terminated by an escape complex and normal sinus rhythm is re-established.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

Other sources of information

  • Ettinger S J, Feldman E C, Cote E (2017) Cardiac Arrhythmias. In: Textbook of Veterinary Internal Medicine. 8th edn. Chapter 248. Elsevier. 
  • Smith F K W Jr, Tilley L P, Oyama M, Sleeper M (2016) Electrocardiography (chapter 3); Treatment of cardiac arrhythmias (chapter 17). In: Manual of canine and feline cardiology. 5th edn, Saunders Elsevier.
  • Bonagura J D & Twedt D C (2014) Bradyarrhythmia (chapter 170); Bradyarrhythmias and Cardiac Pacing (Web Chapter 59). In: Kirks Current Veterinary Therapy XV. Elsevier Saunders.

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