What keeps the heart pumping normally?

The natural pacemaker of the heart is located in the upper right chamber. This is called the “sinus node”. The pacemaker is responsible for generating the electrical impulses of the heart. This electrical impulse is transmitted through the heart’s upper chambers (atria) to reach the atrioventricular (AV) node. In a healthy heart, the AV node is the only electrical connection between the heart’s upper and lower chambers (ventricles). It’s the AV node that conducts the impulse to the ventricles which are the pumping chambers of the heart. Upon receiving the stimulus from the AV node, the ventricles then pump and discharge blood.

Signs of Heart Arrhythmias in Cats

Many pets with abnormal heart rhythms don’t exhibit signs of the problem unless it’s a chronic one. Most times, the symptoms are subtle and often attributed by pet parents to be part of aging. The symptoms may wax and wane depending on how often the arrhythmia occurs. These include:

• Spending more time sleeping or lying around
• Weakness
• Lethargy
• Decreased appetite

There are, however, certain types of arrhythmias that cause pets to exhibit distinct clinical symptoms and/or put them at risk for sudden death. In addition to exhibiting the above signs, pets with severe arrhythmias also exhibit the following symptoms:

• Collapse/fainting
• Poor tolerance to exercise or other forms of physical activity
• Accumulation of fluid in the abdominal cavity
• Increased respiratory rate
• Labored breathing (dyspnea)
• Sudden death

Causes of Arrhythmias in Cats

Abnormal heart rhythms in cats are generally divided into two types:

1. Cardiac causes - These are conditions that affect heart structure and function. Some of the most common cardiac causes include hypertrophic cardiomyopathy and other diseases affecting the heart muscle, congenital heart defects, heart valve defects, inflammation of the heart (myocarditis), traumatic injury to the heart, and age-related structural changes of the heart.

2. Non-cardiac causes - These include problems outside of the heart that cause arrhythmias. Common examples include severe anemia, abnormal position of the stomach, such as in gastric torsion (much more common in dogs), and diseases affecting the spleen, brain tumors, toxins, and endocrine disorders. Certain medications and anesthetic agents can also cause arrhythmias in cats.

Common Types Arrhythmias in Cats

There are many forms of arrhythmias in pets, but the most common include the following:

1. Atrial Fibrillation (AF or A-Fib)

This type of arrhythmia is common in dogs but rare in cats. The condition is generally associated with an underlying disease affecting heart structure accompanied by a severe enlargement of the left atrium. With a defect in the atria (the top chambers of the heart that receives blood from the body and lungs), the ability to pump blood into the ventricles (lower chambers of the heart) will be compromised.

The fibrillating atria lose some of their pumping power and there will be less blood reaching the ventricles and even less cardiac output. Pets with AF typically have heart rates that exceed 200 beats per minute. The problem is often associated with severe congestive heart failure.

2. Premature Beats (Premature Complexes or Depolarizations)

Premature beats are so-called because these are heartbeats that occur too early. The condition is not only caused by defects in the heart but also from extra-cardiac causes, thus further testing is needed.

There are two main types of premature beats - supraventricular premature beats and ventricular premature beats. Supraventricular premature beats (SVPC or SVPD) develop from the tissue above the ventricles (the heart’s main pumping chambers). Ventricular premature beats (VPC, VPD, or PVC) start from the ventricles themselves. Premature heartbeats are not generally a cause for concern except when they occur frequently or if the patient is at risk for other types of arrhythmias, such as ventricular tachycardia or AV.

3. Atrioventricular Block (AV Block)

This type of arrhythmia occurs when the electrical impulse in the heart cannot be conveyed from the atria to the ventricles. AV blocks can be classified as:

• 1st degree AV block - patients don’t require specific therapy
• 2nd degree AV block - conduction of impulses may occur and sometimes it doesn’t
• 3rd degree AV block - no conduction of impulses occurs from the atria to the ventricles.

Both 2nd and 3rd degree AV blocks may require medical intervention, which typically involves implantation of a permanent pacemaker. However, some cases can be managed with medication. Pets with AV block symptoms experience fainting, weakness, or collapse. They are also more prone to developing congestive heart failure as a result of long-term slow heart rate.

4. Supraventricular Tachycardia (SVT)

The condition is characterized by an abnormally fast heart rate (tachycardia) that arises or is maintained by atria. It’s called supraventricular because tachycardia is caused by tissue defects above the ventricles. The symptoms that may be exhibited by affected cats include excessive panting, weakness, shortness of breath, fainting, or collapse. SVT may occur in pets with or without structural problems of the heart.

5. Ventricular Tachycardia (VT or “V-Tach”)

Ventricular tachycardia is brought about by a serious arrhythmia that can progress to become a life-threatening problem. It’s so-called because tachycardia originates from the heart’s ventricles. Pets with VT have higher risks for sudden death. Symptoms that may be exhibited include shortness of breath, excessive panting, fainting, or even collapse. VT may occur in pets with or without structural problems of the heart.

Diagnosing Heart Arrhythmias in Cats

When your vet detects an arrhythmia when listening to your cat’s heart with a stethoscope, an electrocardiogram (EKG or ECG) is usually recommended. It’s the best diagnostic procedure that can help diagnose and identify the specific type of arrhythmia.

A Holter monitor allows the monitoring of your pet’s cardiac rhythm for 24 to 48 hours. It’s an ambulatory ECG that your pet can wear even at home. The device will record the arrhythmia’s severity and frequency.

If the EKG and Holter monitor results reveal an arrhythmia that appears to be dangerous to your cat, your vet may refer you to a veterinary cardiologist.

Treatment and Prognosis for Cats with Cardiac Arrhythmias

After evaluating the results of the different tests that were performed, the treatment regimen will be designed based on the nature of the arrhythmia, including its type, frequency, and severity.

Treatment may include anti-arrhythmic drugs (given orally or intravenously), radiofrequency ablation, electro-cardioversion, or defibrillation. In some types of arrhythmia, the implantation of a pacemaker can be the treatment of choice.

The type of arrhythmia, the presence of existing heart disease, and/or the presence of a non-cardiac cause are important variables that are considered when determining the prognosis.

Read more:

Your Pet’s Heart: A Guide to Understanding Heart Health in Dogs and Cats

Causes and Treatment for Coughing in Cats

Why is my cat not eating? 3 Common Causes of Anorexia in Cats

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