Congestive Heart Failure in Cats

What is congestive heart failure?

Congestive heart failure (CHF) refers to the heart's inability to pump adequate blood to the body. When the heart is unable to pump blood efficiently throughout the body, fluid backs up. This extra fluid causes increased pressure inside the blood vessels, and they become leaky. When fluid starts to leak out of the blood vessels, it is CHF.

Where the fluid backs up and leaks out depends on if the CHF is right-sided or left-sided. 

• With left-sided heart disease, fluid backs up into the lungs, a condition called pulmonary edema. 
• With right-sided heart disease, fluid backs up in the chest around the lungs (pleural effusion) and/or in the abdomen (abdominal effusion or ascites). 

What causes CHF?

CHF occurs when heart disease becomes severe enough that the heart can no longer compensate by working harder. There are two types of heart disease in cats: congenital and acquired. Acquired is by far the most common in cats.

Congenital heart disease is a heart condition your cat was born with. 

• The heart valves usually prevent blood from moving in the wrong direction. With congenital heart disease, these valves can be malformed, leading to back-flow of blood when the heart pumps.
• Defects or “holes” can occur between the right and left sides of the heart (ventricular septal defect [VSD] and atrial septal defect [ASD]) or between the large blood vessels leaving the lungs (patent ductus arteriosus or PDA). These holes are present in utero but should be closed at the time of birth. Blood can flow in the wrong direction through these holes.

Acquired heart disease develops over time. 

• The most common type of heart disease in cats is hypertrophic cardiomyopathy (HCM) – a disease of the heart muscle, primarily the left ventricle, which pumps blood to the whole body. With hypertrophic cardiomyopathy, the muscle becomes thicker (hypertrophied) over time. This abnormal muscle does not pump as efficiently, and there is less space inside the chamber for blood, which causes blood to back up into the atrium. The atrium will stretch over time.
• Other cardiomyopathies are rare in cats, but include dilated cardiomyopathy (DCM), where the heart muscle weakens and thins over time, and restrictive cardiomyopathy (RCM), in which scar tissue forms, causing the heart muscle to stiffen.
• Acquired valve disease is uncommon in cats.

Are some cats predisposed to heart disease?

• HCM can occur in any breed of cat. Males are more commonly affected. 
• HCM occurs at a higher frequency in Maine coon cats, sphynx, and ragdolls, due to a higher incidence of genetic mutations in these breeds. One study showed 33% of Maine coon cats carry the mutation. 
• Siamese cats are more prone to DCM and congenital PDA. 
• Older cats with hyperthyroidism and/or high blood pressure can develop secondary HCM due to the increased workload that the heart must endure.

What are the clinical signs of congestive heart failure in cats?

The most common sign of heart failure in cats is difficulty breathing. This sign may develop rapidly. Your cat will breathe faster and work harder to breathe. If they are very stressed, they may breathe with their mouth open. 

These breathing changes can be seen in both left-sided and right-sided heart disease. In left-sided heart disease, fluid that builds up in the lungs reduces oxygen absorption. In right-sided heart disease, fluid around the lungs restricts the expansion of the lungs for oxygen exchange. Coughing is not a common sign of heart failure in cats, in contrast to dogs. 

Right-sided heart disease can also cause fluid to build up in the abdomen, which leads to a large, round abdomen. This condition can be uncomfortable and lead to decreased appetite. Other less specific clinical signs may include exercise intolerance, lethargy, hiding, weight loss, and poor appetite.

A complication called arterial thromboembolism (ATE) can also occur in cats, due to severe heart disease. Blood clots, called thrombi, form in the heart due to abnormal blood flow. Pieces of these clots, called emboli, can become dislodged and leave the heart, traveling through the bloodstream. Most commonly, these blood clots lodge where the aorta (a large blood vessel that supplies blood to the body) splits into the femoral arteries (the arteries that supply blood to each back leg). This condition is also known as a saddle thrombus. When this condition occurs, the cat can experience a sudden loss of function in one or both back legs. The affected limb(s) can become paralyzed and cold to the touch. It is a painful condition.

How is CHF diagnosed?

Any cat with breathing changes should be assessed by a veterinarian immediately. Your veterinarian will assess your cat’s breathing rate and effort. They will listen to your cat’s chest with a stethoscope. Affected cats often have a fast heart rate and may have a heart murmur, which is an abnormal sound due to turbulent blood flow.

It is important to note that murmurs do not always signify heart disease, as some cats have a murmur at faster heart rates, and it can be normal for them. An abnormal heart rhythm (arrhythmia) or extra heart sounds (gallop rhythm) may be detected. 

Conversely, some cats with heart disease do not have any abnormalities that can be heard with a stethoscope. In cats with fluid around the lungs, the heart and lung sounds can be muffled. Low body temperature and gums that look pale or bluish are other common signs and signify lack of adequate blood and oxygen flow to the tissues.

If your cat is stable enough, X-rays of the chest should be done. Sedation may be needed for this procedure. X-rays look at the size and shape of the heart and lungs. Heart disease often causes the heart to be enlarged. Pulmonary edema, or fluid in the lungs, can make the lungs look whiter on X-ray. Fluid around the lungs can compress and outline the lungs. If there is fluid in the abdomen, it can make it difficult to see the other abdominal organs.

Other tests that can be done at the veterinary clinic include checking blood oxygen levels with a sensor, measuring blood pressure, and performing an electrocardiogram (EKG). The EKG monitors the electrical activity of the heart and assesses irregularities in the heart rhythm. Blood and urine testing is done to determine if there are any other abnormalities in the body, including an overactive thyroid (see handout “Hyperthyroidism in Cats”).

Differentiating between heart failure and other causes of breathing difficulty is not always straightforward. There is a blood test called NTpro-BNP that measures levels of a compound released by damaged heart muscle. This can be a useful test when X-rays are inconclusive or cannot be performed.

An echocardiogram is an ultrasound of the heart. This is a useful diagnostic test that looks at the heart muscle, valves, and chambers. This may be best done by a cardiologist at a referral center, though some regular clinics have the necessary equipment and expertise. An echocardiogram is the best way to accurately identify the type and severity of heart disease. It can also look for the presence of blood clots within the heart, and fluid in the chest.

A thromboembolism can be diagnosed based on clinical signs. Sudden onset of hind-end paralysis and pain will be evident. The affected leg(s) will feel cold to the touch and have absent pulses. The toe pads will look white or purple (cyanotic).

How is CHF treated?

• Severely affected cats will require hospitalization and oxygen therapy. Sedation may be warranted if your cat is distressed, as distress exacerbates breathing difficulties. 
• In cats with left-sided heart disease, diuretics such as furosemide will be administered to remove fluid in the lungs (pulmonary edema). 
• In cats with right-sided heart disease, any fluid around the lungs (pleural effusion) may be drained with a needle in a process called thoracocentesis.
• Once your cat is stabilized, other heart drugs may be added for maintenance therapy. Pimobendan (Vetmedin®) is a drug to improve contractility; other drugs such as angiotensin-converting enzyme (ACE) inhibitors and anti-arrhythmic drugs can be considered. 
• In cats with evidence of blood clotting within the heart, anti-coagulant medications such as Clopidrogel (Plavix®) will be given to reduce the risk of thromboembolism. Medication choices and dosages will be tailored specifically for your cat and may be adjusted as needed.

Cats diagnosed with hyperthyroidism should be started on treatment for that disease as soon as possible. Congenital heart defects such as septal defects and PDAs may be corrected surgically by a trained cardiovascular surgeon.

What monitoring is needed for cats with CHF?

When your cat has been stabilized with appropriate treatment, it is important they are closely monitored. At home, regularly observe your cat’s breathing, preferably when they are asleep. Your veterinarian can show you how to count the number of breaths per minute. Notify your veterinarian if the breathing rate is increasing over time or consistently above 30 breaths per minute. You can also observe your cat’s appetite, weight, and energy level at home.

Your veterinarian will perform bloodwork regularly to assess kidney function and other parameters. Chest X-rays, EKG, blood pressure, and echocardiogram can be repeated as needed to monitor your cat’s response to treatment.

What is the prognosis for CHF?

With rapid diagnosis and proper treatment, many cats can be stabilized and managed for a period of time. The cause and severity of heart disease will affect prognosis. In cats with HCM that occurs secondary to hyperthyroidism, correction of the hyperthyroidism often allows heart function to improve on its own. Cats with thromboembolism have a guarded to poor prognosis and, even if they recover, recurrence is common.