Arrhythmias in Cats

What is an arrhythmia?

An arrhythmia is an abnormal heart rate or rhythm. It occurs when the electrical signals that tell your cat’s heart to beat are not working properly. The heart may beat too fast or too slowly, skip beats, or beat irregularly.

Normally, electrical signals tell the heart muscles to contract (squeeze) in a coordinated way to produce a heartbeat. Each signal starts in the sinoatrial (SA) node, the heart’s natural pacemaker. 

The signal first travels through the atria, the heart’s two upper chambers, causing them to contract. Then it passes through the atrioventricular (AV) node and travels to the ventricles, the two lower chambers, causing them to contract. Damage or disease anywhere along this pathway can lead to an arrhythmia.

Are all arrhythmias dangerous?

No, occasional irregular heartbeats may not be dangerous, but the cause should always be investigated. Sinus arrhythmia is a normal variation in heart rhythm that can occur in cats. The heart rate changes with breathing: it speeds up as the cat breathes in and slows down as the cat breathes out. Sinus arrhythmia can occur when cats are very relaxed or are given sedating medications.

What causes arrhythmia in cats?

The primary cause of arrhythmia is underlying heart disease:

Disease of the heart muscle: Cardiomyopathy is a disease of the heart muscle. The most common type in cats is hypertrophic cardiomyopathy (HCM). In HCM, the heart muscles lose their ability to contract normally, leading to thickening of the muscle and poor heart function.

There is a genetic predisposition to cardiomyopathy in some purebred cats, such as Maine Coons, Ragdolls, and Sphynxes. Hyperthyroidism and high blood pressure can also cause thickening of the heart muscle. Viruses such as feline infectious peritonitis and feline immunodeficiency virus have been linked to heart inflammation.

Taurine deficiency has long been recognized as a cause of cardiomyopathy in cats. Taurine is an essential amino acid that is supplemented in commercial cat foods. However, cats that are fed home-cooked or poorly balanced diets, or that eat dog food, can develop this form of heart disease.

Disease of the heart valves: The heart valves control the forward flow of blood through the heart. If these valves are abnormal at birth, or wear down over time, they become leaky. Blood can then flow backward, making the heart work harder. Bacterial infection of the heart valves (endocarditis) can also occur when bacteria spread from dental disease or other severe infections.

Other causes of arrhythmia include:

• Electrolyte imbalances (imbalances in minerals in the blood)
• Trauma (injury)
• Systemic inflammation (inflammation throughout the body) or sepsis (a life-threatening response to infection)
• Toxins such as chocolate or certain drugs like amphetamines
• Anesthetic drugs
• Tumors in or near the heart

What types of arrhythmias occur in cats?

Arrhythmias can be either tachyarrhythmias, in which the heart beats too fast, or bradyarrhythmias, in which the heart beats too slowly. Some arrhythmias can alternate between fast and slow.

Examples of tachyarrhythmias include:

• Atrial fibrillation (A-fib). The atria beat rapidly and out of sync with the ventricles. The most common cause in cats is hypertrophic cardiomyopathy.
• Ventricular premature contractions (VPCs), ventricular tachycardia (V-tach) and supraventricular tachycardia (SVT).  A heartbeat originates somewhere other than the normal conduction pathway and can be caused by a heart condition or be a sign of another disease.

Examples of bradyarrhythmias include:

• Heart block. One or more signals are blocked at the AV node, interrupting the signals that tell the ventricles to beat. Anesthetics, certain pain medications, and heart disease can cause heart block.
• Sick sinus syndrome. The SA node does not work properly. This disorder is very rare in cats. It can be associated with damage to or gradual wearing down of the heart’s electrical system, but in most cases the cause is unknown.

What are the signs of an arrhythmia?

There may be no outward signs of an arrhythmia, especially if heart disease is not advanced. With more severe disease some, or all, of the following symptoms may occur:

• Breathing faster or with more effort
• Coughing
• Exercise intolerance
• Weakness or lethargy (unusual tiredness)
• Collapse or fainting (syncope)
• Weight loss or poor appetite
• A swollen abdomen (belly) due to fluid buildup (ascites)
• Sudden hind leg pain or paralysis due to blood clots
• Pale or bluish gums 

Rarely, sudden death can occur without any warning signs.

How is an arrhythmia diagnosed?

An arrhythmia is often first suspected when your veterinarian listens to your cat’s heart with a stethoscope. They may also detect an irregular pulse. If an irregularity is found, your veterinarian may recommend additional tests to identify the arrhythmia and its cause. These may include:

• ECG (electrocardiogram). This test records the electrical signals running through your pet’s heart and displays them on a screen or paper. It can measure heart rate and detect abnormal rhythms. A Holter monitor records a continuous ECG over a longer period of time and can be fitted to your cat.
• Echocardiogram (heart ultrasound). This test looks at the valves and chambers of the heart in more detail. It can identify structural heart disease, such as abnormal valves or cardiomyopathy.
• X-rays. Chest X-rays may show an enlarged heart associated with heart disease. Fluid build-up in or around the lungs may be noted with advanced heart disease. Abdominal X-rays may detect ascites.
• Blood and urine testing. Screening tests such as a complete blood count, a biochemistry profile, and a urinalysis help rule out other causes of arrhythmias, such as electrolyte abnormalities, infectious diseases, and toxicities. 
• Thyroid hormone testing. This test screens for hyperthyroidism.
• ProBNP test. This blood test measures a substance released when heart muscle is stretched or overworked.

If your veterinarian suspects or diagnoses heart disease, they may refer you to a veterinary cardiologist (heart doctor) for further testing and management.

How is an arrhythmia treated?

Treatment depends on the underlying cause of the arrhythmia and whether it is associated with a slow or fast heart rate. If the underlying cause can be identified and removed or treated (such as electrolyte abnormalities), then the arrhythmia will often correct itself. Treatment to control the heart rate may include:

• Fast rhythms (tachyarrhythmias) may be treated with anti-arrhythmic drugs given intravenously (IV) or by mouth to control heart rate (e.g., lidocaine, atenolol, and sotalol).
• Slow rhythms (bradyarrhythmias) may be managed in the short term with medications to increase heart rate (atropine, glycopyrrolate) or treated with a surgically implanted pacemaker.

Other medications may be needed to manage underlying heart disease. These may include medications to improve the heart’s ability to contract (pimobendan), diuretics to reduce fluid buildup (furosemide), and medications to decrease blood pressure and the heart’s workload (benazepril).

A special diet may be recommended for your cat. If your cat is experiencing congestive heart failure, then a mild to moderate restriction of sodium (salt) in the diet may be advised. Omega-3 fatty acids (DHA and EPA) may also be recommended for their anti-inflammatory effects and other benefits.

When should I seek immediate veterinary care?

Contact your veterinarian if you notice any sudden change in your cat’s condition, including:

• Breathing changes: increased breathing rate or effort, or a new or worsening cough
• Weakness or severe lethargy
• Collapse, especially combined with loss of consciousness
• Pale or bluish gums
• A swollen abdomen
• Sudden hind leg pain or paralysis, especially if accompanied by cold paws

What is the long-term outlook for cats with arrhythmias?

The outlook depends on the underlying cause. If the cause can be eliminated, then the outlook is good. If heart disease is present, the outlook varies with its type and severity. With appropriate treatment, your cat may have a good quality of life for months or even years. However, if your cat does not respond well to treatment, or if symptoms are advanced, then the outlook is poorer.