Atrial Premature Complexes in Dogs
There are four chambers in the heart. The two top chambers are the atria (single: atrium), and two bottom chambers are the ventricles. Under normal circumstances, the heart works with exceptional synchronization between the various atrial and ventricular structures, resulting in a consistent rhythmic pattern. Atrial premature complexes result in an abnormal rhythmic disturbance, where the heart beats prematurely, before the normal timing, or pacing.
Excluding animals born with a congenital heart disease, atrial premature complexes often affect older dogs, especially small-breed dogs. Atrial premature complexes (APCs) can be seen on an electrocardiogram (EKG) as a premature wave called a P wave. This P wave may be biphasic, negative, positive or superimposed on the previous T wave on the EKG.
The P wave on an EKG represents the electrical conduction from the sinoatrial node in the heart to and through the atria of the heart. The QRS complex -- a recording of a single heartbeat on the EKG -- following the P wave represents the passing of this impulse through the heart’s ventricles after it passes through the atrioventricular node. The last wave on an EKG reading is the T wave which measures ventricular recovery (from charging) before the next cardiac contraction.
An increase in automaticity of atrial heart muscle fibers or a single reentrant circuit can cause a premature P wave to occur. These premature atrial beats begin outside of the sinoatrial node (ectopic) -- the pacemaker of the heart -- and disrupt the normal "sinus" heart beat rhythm for one or more beats.
Symptoms and Types
Although there may be no symptoms associated with atrial premature complexes, especially in older dogs or in dogs that are normally not very active, some common signs include:
- Coughing and trouble breathing
- Exercise intolerance
- Fainting (syncope)
- Cardiac murmur
- Irregular heart rhythm
- Chronic heart valve disease
- Congenital heart disease (defect from birth)
- Disease of heart muscle
- Electrolyte disorders
- Toxemias (toxic elements in blood)
- Drug toxicity (for example, overdose of digitalis, a heart medicine)
- Normal variation in many older dogs
You will need to provide your veterinarian with a thorough history of your dog's health leading up to the onset of symptoms. The full physical exam will include a chemical blood profile, a complete blood count and an electrolyte panel.
It is crucial to search for an underlying cause for the heart disease that is bringing about the APCs. An electrocardiogram (EKG) recording can be used to examine the electrical currents in the heart muscles, and may reveal any abnormalities in cardiac electrical conduction (which underlies the heart’s ability to contract/beat). Other diagnostic tools, like echocardiograph and Doppler ultrasound, can be used to visualize the heart and its performance (rhythms, velocity of contraction).