Overview of Feline Cardiac Arrhythmias (Abnormal Heart Rate or Rhythm)
Cardiac arrhythmias are abnormal heart rhythms that can occur in cats. These disorders are classified based on the area of the heart in which they originate. They originate either in the upper chambers of the heart, the lower chambers of the heart, the area of the heart responsible for creating each heart beat (the sinoatrial SA node), or the system within the heart responsible for conducting electrical impulses throughout the heart.
Below is an overview of heart arrhythmias in cats followed by in-depth information about the diagnosis and treatment of this condition.
Each heartbeat originates as an electrical signal generated in the SA node, which is in the upper right chamber of the heart. The electrical impulse then travels through the upper chambers of the heart (atria) to an intermediate station (the atrioventricular node), and finally to the lower heart chambers (ventricles). Series of these electrical impulses are responsible for the typical waveform seen on an electrocardiogram (EKG or ECG) and bring about the rhythmic mechanical contractions of the heart. Disturbances of electrical signal generation or the conduction system anywhere along its course will cause irregular heart rhythms. Some cardiac arrhythmias are temporary and do not cause illness. Others are serious and, if not treated, potentially life-threatening.
Cardiac arrhythmias can affect cats of any age, breed or sex.
The prognosis for animals with cardiac arrhythmias depends on the type of arrhythmia present, and the underlying cause and extent of heart disease. Animals in congestive heart failure have a guarded-to-poor prognosis.
What to Watch For
- Slow heart rate
- Fast heart rate
- Erratic heart rate
- Difficulty breathing
- Lack of appetite
Diagnosis of Feline Cardiac Arrhythmias
Blood work, including a complete blood count and biochemical profile, should be performed to detect any underlying abnormalities. Some animals may be anemic, have an elevated white blood cell count, or have organ dysfunction. Some diseases, such as hyperthyroidism, may underlie heart rhythm disturbances.
Cardiac arrhythmias are diagnosed with an electrocardiogram (EKG, ECG). The type of arrhythmia can be diagnosed from an ECG oscilloscope or by viewing abnormalities on a print out of the ECG trace.
Radiographs (X-rays) of the chest may help determine the extent and type of heart disease.
A cardiac ultrasound (echocardiogram) is sometimes performed to evaluate any underlying heart disease.
Treatment of Feline Cardiac Arrhythmias
Treatment depends on the type and severity of the cardiac arrhythmia and the underlying disease process. Each type of arrhythmia is managed differently. Some require medication whereas others are innocuous and do not require any treatment.
In addition to treating the arrhythmia, any underlying heart disease or other disease should be addressed.
Home Care and Prevention
There is no home care treatment for abnormal heart rhythms, except giving any medication prescribed by your veterinarian. If you suspect that your pet has an abnormal heart rate or rhythm, you should contact your veterinarian immediately.
Cardiac arrhythmias are difficult to prevent, but early diagnosis and treatment of predisposing causes can reduce the risk of arrhythmias developing.
In-depth Information on Feline Cardiac Arrhythmias
Normal heart rhythm is initiated from the sinoatrial (SA or sinus) node, which is located in the right upper chamber (atrium) of the heart. While abnormalities of the sinus node are typically a consequence of other disorders, such as thyroid problems, primary sinus disease is common and may lead to a type of arrhythmia known as sick sinus syndrome. Other atrial arrhythmias arise outside the SA node. Among the most serious of these is atrial fibrillation. Arrhythmias arising from the ventricles may also be serious. Venticular arrhythmias include premature ventricular contractions and ventricular tachycardia. Serious arrhythmias may lead to cardiac decompensation and acute or chronic heart failure. Some arrhythmias worsen to the point of fibrillation and eventually the absence of any heartbeat (asystole).
Cardiac arrhythmias may involve a very low heart rate (potentially as low at 40 beats per minute), termed bradycardia; a very fast heart rate (potentially over 300 beats per minute in a cat), termed tachycardia; or simply an erratic heart beat. Numerous different types of arrhythmias may occur. Some of the more common ones include:
- Atrial fibrillation
- Atrial tachycardia
- Ventricular escape rhythm
- Ventricular premature complex
- Ventricular tachycardia
- Ventricular fibrillation
- First degree heart block
- Second degree heart block
- Third degree heart block
Often, cardiac arrhythmias are associated with underlying heart disease caused by conditions such as hypertrophic cardiomyopathy, congestive heart failure, dilated cardiomyopathy, or congenital cardiac defects. In addition, there are a variety of other diseases or events that can cause cardiac arrhythmias, including:
- Hyperthyroidism (overactive thyroid gland)
- Chronic lung disease
- Overdose of certain medications such as digoxin, narcotics, xylazine
- Administration of anesthetic agents
- High or low blood potassium
- Tumors of the heart
- Toxicity, such as chocolate poisoning
- Urinary obstruction
- Smoke inhalation
- Head trauma
- Low blood pressure (hypotension)
- Diseases of the spleen
- Severe infections
Cardiac arrhythmias are often detected during the physical examination process. Your veterinarian will listen to your pet's heart with a stethoscope and can determine if your pet's heart rate is too slow, too fast, or is erratic. Once an arrhythmia is suspected, it is confirmed with an electrocardiogram (ECG, EKG). Your pet will be positioned on his right side and have clips or pads applied to his arms and legs. This process is painless. The machine is then turned on and a tracing is obtained of the electrical activity of the heart. The tracing is examined to determine that the heart rate or heart rhythm is normal.
Sometimes, a simple ECG is inadequate to evaluate the significance of an arrhythmia. Other methods of evaluating the heart rhythm include post-exercise ECG, hospital telemetry, ambulatory (Holter) ECG, and the use of a cardiac event monitor. These methods are particularly useful in assessing the overall frequency of an arrhythmia, the relationship of an arrhythmia to clinical signs, or the effectiveness of treatment.
In addition, other diagnostic tests are performed to determine the overall health of your cat.
- Complete blood count - This is performed to evaluate the red blood cells, white blood cells and platelets. Some animals may be anemic or have an elevated white blood cell count.
- Biochemical profile - This blood work is performed to determine the function of the body's organs and electrolyte levels. Some cats may have a high or low potassium level, elevated thyroid hormone levels or kidney or liver disease.
- Radiographs - X-rays of the chest will help determine if congestive heart failure is present or if there is underlying heart disease.
- Ultrasound - An ultrasound of the heart (echocardiogram) can help determine if underlying heart disease is present.
Treatment will vary and depends on the type of arrhythmia and underlying disease. Some arrhythmias do not require treatment and may spontaneously revert to normal. Other arrhythmias are more serious and necessitate treatment. Some of the treatment options include:
- Various medications to help control the arrhythmia, treat the underlying heart disease, or improve cardiac function. Medications that are used include digoxin, diltiazem, propranolol, enalapril, procainamide, lidocaine, and atropine.
- Certain types of cardiac arrhythmias require the placement of a pacemaker to control the arrhythmia. Severe heart blocks often require a pacemaker to keep the heart rate and rhythm normal.
- Cats in congestive heart failure may need to be treated with a diurectic (e.g. furosemide) and possibly nitroglycerine.
- Cats with underlying disease may require additional medication. For example, hyperthyroid cats may benefit from anti-thyroid medication.
Follow-up Care for Cats with Heart Arrhythmias
Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up, which may be critical, includes some or all of the following measures: