Atrial Premature Complexes in Cats
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 cats. 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.
There are four chambers in the heart. The two top chambers are the atria (single: atrium), and two bottom chambers are the ventricles. 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 cats or in cats 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 animals
You will need to provide your veterinarian with a thorough history of your cat'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).
The treatment your veterinarian administers will depend on exactly what kind of heart disease is affecting your cat and how severe it is. There are several different types of medicines that can be used, depending on the type of heart disease present. A drug to dilate the blood vessels (vasodilator) may be prescribed for hypertrophic cardiomyopathy, and digitoxin may be prescribed to decrease the heart rate and increase cardiac contractility in cases of dilated cardiomyopathy.
Living and Management
Underlying cardiac diseases must be treated and kept as controlled as possible by your veterinarian. This means that you will need to take your cat to the veterinarian for frequent follow-up appointments. Sometimes, despite drug therapy, some animals will have an increased frequency of APCs, or will deteriorate to more severe signs of heart disease as the underlying disease progresses.
Depending on the underlying cardiac disease, you may need to change your cat's diet to a low sodium diet. Your veterinarian will advise you on the diet and amount of activity your cat will need to be of optimum health.