Cardiac Muscle Tumor in Cats

Cardiac muscle tumors are a class of tumor or mass that occurs in the cat’s heart and related tissues. The tumor will either be benign or malignant. Benign tumors are not cancerous, grow more slowly, and are unlikely to spread. A malignant tumor is cancerous and capable of rapid growth, spreading throughout the heart and other parts of the body, and recurring even after removal. Both types of tumor can cause cardiac or heart issues for your pet, but malignant tumors are more dangerous and can be fatal. Your cat will require medical treatment if symptoms of a cardiac tumor appear.

Many cats with cardiac muscle tumors will not demonstrate symptoms. This is especially true of benign tumors. The most common clinical signs, like heart murmur or an irregular heartbeat, are not easily observable for a pet owner. If the tumor begins to impair heart function or if it is malignant clinical signs may become apparent. The tumor can impair heart function either because of growth or its location in the heart.

Symptoms Include:

• Heart murmurs
• Arrhythmia or irregular heartbeat
• Muffled heart sounds
• Pulse deficits
• Exercise intolerance
• Lethargy or fatigue
• Poor blood circulation
• Congestive heart failure on one or both sides
• Coughing
• Difficulty breathing
• Collapse or fainting 
• Fluid retention
• Abdominal bloating
• Lack of appetite or anorexia
• Loss of lean muscle mass
• Internal bleeding

Types

Numerous types of tumors can occur in the heart and related tissues. Additionally, it is possible for cancer in other parts of the body to spread to the heart resulting in tumors. The most common types of tumors that can affect cardiac muscles include:

• Lymphosarcoma: this is the most common cardiac tumor found in cats
• Rhabdomyoma or Rhabdomyosarcoma: the benign and malignant version of the same type of tumor, these are common in the walls of the ventricle
• Fibroma or Fibrosarcoma: the benign and malignant version of the same type of tumor, this typically occurs in the valves
• Hemangioma or Hemangiosarcoma: the benign and malignant version of the same type of tumor, this is more common in dogs than cats

The exact cause of cardiac tumors in cats is unknown. Unlike infectious diseases, it is not something that can be easily traced back to a specific source. Many tumors, like the benign Rhabdomyoma, are believed to be congenital or present at birth. These birth defects may never require treatment, or may be discovered within the first few years of life. Malignant tumors are caused by an overgrowth of cells that do not follow the normal cell life cycle. The reason this occurs in cats is unconfirmed. Older pets are more likely to have a malignant cardiac tumor.

Tumors of the cardiac muscles can be difficult to diagnose. This is due to a combination of factors including a lack of clinical signs and inability to easily biopsy or observe the tumor. Your veterinarian will likely begin with an electrocardiogram. Ultrasonography is a common imaging technique that helps a veterinarian to identify a mass in the heart that might indicate a tumor. Angiography, which uses an injectable contrast material, or pneumopericardiography, which uses air or carbon dioxide to outline shapes, are more invasive techniques that are used in conjunction with X-rays to create imaging that will identify the tumor. It is also possible your veterinarian will want to biopsy the mass to confirm if it is benign or malignant. This may be possible without surgical intervention, but this depends on the location of the tumor. The diagnosis is often confirmed only during surgery to correct the issue or during a necropsy.

In the case of a benign tumor that is not affecting heart function, your cat will not require any treatment. If the tumor is causing problems with heart function or severe symptoms, your veterinarian will have to determine the best treatment for your pet. In some cases, there will be very little the veterinary staff can do your cat other than treating the symptoms. Hospitalization is often required and may be prolonged or required return visits. Some possible treatments include:

Surgery: Surgically removing the tumor is one of the most effective ways to resolve the issue. The risk associated with cardiac surgery is very high, however, and it requires a certain level of expertise. It is also possible that your pet will not be a candidate for surgery, either due to their health or the location of the tumor. 

Chemotherapy: Just like in humans, this treatment is used to attack and shrink the tumor. This practice has only just begun to be tested in cats, but has shown promise as a treatment in dogs and cats. Chemotherapy can be very hard on your pet’s overall health. 

Oxygen Therapy: In cases where the cat is having difficulty breathing, oxygen will be administered. This could be done using tubes, masks, or an oxygen cage. This will help maintain your pet’s blood oxygen level and keep their immune system working. 

Steroids: This category of drugs may be administered to help the symptoms associated with the tumor. Steroids depress the immune system and help control the cat’s response to this chronic condition. 

Analgesics: A type of painkiller, these may be administered to reduce inflammation and help your pet cope with pain. They may not be needed if the animal is not experiencing pain related to the tumor. Your veterinarian will choose the appropriate dose for your pet to minimize risks.

Your cat’s prognosis will depend on a variety of factors. Pets with a benign tumor are at a lower risk of complications, including death. With malignant tumors, the prognosis is less positive, and inoperable malignant tumors can result in the death of your pet. Early detection and treatment can reduce this risk. As your pet is recovering, they will require physical, nutritional, and emotional support. Restrict your pet’s movements by keeping food, water, and their litter box in close proximity until they are stronger and able to move around with less assistance. Your cat may not be able to cover much distance while dealing with the tumor or recovering from surgery because their heart is not performing at its normal level. You can also support your cat’s healing process by providing them healthy, nutritious food and giving them lots of love and affection.