Atrial premature complex

From Dog
A premature atrial complex (PAC). (In this example the atrial p-wave is difficult to discern)[1]

Atrial premature complexes are a heart disorder of dogs characterized by arrhythmia caused by supraventricular pulses originating from an atrial focus.

Atrial premature complexes are an example of ectopic beats. The result is a P wave with often a different morphology from the preceding ones. They can lead to atrial tachycardia.

The ECG usually shows a premature QRS complex (which appears normal) that may be absent when the P wave occurs too early (nonconducted atrial premature complexes). The AV node does not completely recover (refractory) and this leads to failure of ventricular conduction. Partial recovery within the AV node may lead to elongated P-R interval. Subsequent to this, a noncompensatory pause in the heart beat, followed by an ectopic atrial impulse which discharges the sinus node and resets the cycle.

A premature atral complex can have different fates:

  • Normally conducted
  • Conducted with aberrancy. Mostly bundle branch block have a longer refractory period.
  • Non-conducted. If the premature beat is very early, the AV node is refractory (cannot conduct) and the beat is not followed by a QRS complex. A non-conducted premature atrial beat is often confused with type II second degree AV block where a normal sinus beat is not followed by a QRS complex[1].

Causes include:

Depending on underlying cardiac disease, APCs are frequently treated with digoxin, atenolol or amiodarone.


  1. 1.0 1.1 ECG-pedia
  2. Duerr FM et al (2007) Prevalence of perioperative arrhythmias in 50 young, healthy dogs. Can Vet J 48(2):169-177
  3. Tidholm A et al (2006) Survival in dogs with dilated cardiomyopathy and congestive heart failure treated with digoxin, furosemide and propranolol: A retrospective study of 62 dogs. J Vet Cardiol 8(1):41-47