Canis ISSN: 2398-2942

Heart: atrial premature complexes

Synonym(s): Supraventricular premature complexatrial ectopicatrial extrasystolenarrow complexpremature contraction

Contributor(s): Serena Brownlie, Jill Sammarco


  • An atrial premature complex (APC) is an electrocardiographic (ECG) abnormality.
  • Cause: indicates an extra heart beat arising from a focus of electrical activity in the atria other than the sinoatrial node, which is the primary cardiac pacemaker.
  • Signs: APCs do not usually cause clinical signs but condition may worsen and therefore should be monitored.
  • Alters the rhythm because occurs earlier than the next sinus impulse.
  • If conducted normally through the atrioventricular (AV) node and ventricles, the QRS complex on ECG is identical to the sinus complex.
  • Premature P wave is different in size or configuration from normal P wave and PR interval may be altered. Next sinus depolarization usually occurs on time but is not conducted, therefore early complex is followed by a compensatory pause.
  • Treatment: treat underlying cause if present.
  • Prognosis: rarely cause problems in their own right - often reflect underlying cardiac disease.



Predisposing factors

  • Atrial enlargement.


  • Generally considered as evidence of atrial disease in dogs, though do not cause signs on their own.
  • Irritable focus in atrial myocardium, with normal pacemaker tissue of sinoatrial node, depolarizes earlier than normal depolarization and impulse is transmitted through the conduction system causing a premature cardiac contraction.
  • Dysrhythmias result from either abnormal impulse formation or abnormal conduction.
  • Abnormal impulse formation is caused by either altered automaticity or triggered activity. Altered automaticity occurs when pacemaker tissue fires at a faster rate or at a lower resting membrane potential than normal. Triggered activity occurs when an afterdepolarization reaches threshold levels due to increased intracellular calcium levels, eg in hypokalemia or if there is catecholamine excess.
  • Abnormal conduction results when areas of slow conduction or conduction block develop in the myocardium. This results in an impulse activating a region of heart muscle and re-activating it again later (a re-entry circuit) or going in the reverse direction (retrograde conduction).


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Driehuys S et al (1998) Myocardial infarction in dogs and cats - 37 cases (1985-1994). JAVMA 213 (10), 1444-1448 PubMed.
  • Abbott J A (1997) ECG of the month. Sinus arrhythmia with occasional premature atrial complexes. JAVMA 210 (7), 900-901 PubMed.
  • Mehta A et al (1997) Caffeine and cardiac arrhythmias. An experimental study in dogs with review of literature. 52 (3), 273-283 PubMed.