Heart Beat Problems (Premature Complexes) in Dogs

Atrial premature complex is a type of arrhythmia or irregular heart beat which is caused by supraventricular impulses (electrical impulses originating above ventricles) from an atrial focus other than the sinus node. This is caused by an increased automaticity of atrial myocardial tissues or a single reentrant circuit. 

The heart comprises of four chambers. Top two are called atria (atrium for singular) and bottom two are called ventricles. Sinoatrial (SA) node is the impulse-generator (pacemaker) of the heart, located in the right atrium. It generates impulses by which various atrial and ventricular structures work in exceptional synchronization, resulting in a consistent rhythmic pattern.  

The ectopic P wave is premature, and its configuration is different from that of the sinus P waves. It may be negative, positive, biphasic, or superimposed on the previous T wave.

An ECG (electrocardiogram) is a recording of the electrical impulse activity of the heart. 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.

In atrial premature complexes (APCs), this rhythmic pattern is disturbed by premature atrial beats that originate outside the sinoatrial node and disrupt the normal heart rhythm for one or two beats. The heart beats prematurely causing abnormal rhythmic disturbance.

This condition mostly affects older dogs. It can also be the result of congenital heart defect. 

Although many dogs with Atrial premature complexes may remain asymptomatic, there are some common symptoms associated with this condition including

Coughing and trouble breathing

Exercise intolerance

Fainting (syncope)

Cardiac murmur

Irregular heart rhythm

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