Heart Valve Malformation in Cats

What is Heart Valve Malformation in Cats?

Heart valve malformation, also known as atrioventricular valve dysplasia, occurs when the atrioventricular valves are malformed and do not fully close. Instead of flowing only one way through the heart, blood backs up from the ventricle into the atria, and from there into either the lungs (mitral valve dysplasia) or the body (tricuspid valve dysplasia).

If the condition is untreated, left-sided or right-sided congestive heart failure will develop.

The feline heart is a muscle made up of four chambers ‑ two atrias and two ventricles. The atrias serve as receptacles for blood entering the heart, from the lungs on the left side, and the body on the right side. From there, blood is pumped into the ventricles and then either flows into the lungs from the right side to pick up oxygen or out from the left side to deliver oxygenated blood to the body.

The atrioventricular valves ‑ mitral and tricuspid ‑ open and close between the atria and ventricles and direct the blood flow throughout the heart. Closure of these valves is audible and results in a “lub-dub” heard when listening with a stethoscope. The tricuspid valve, which contains three cusps, lies between the right atria and right ventricle. The mitral valve, which contains two cusps, is located between the left atria and left ventricle.

If the valves are malformed and blood is no longer moving one way, the heart muscle must work harder to pump the same amount of blood out to either the lungs or the body. It will eventually bulk up, becoming enlarged either in size or thickness. Unfortunately, this process restricts the amount of blood pushed out due to a sheer decrease in volume. As the atria become enlarged stretching occurs, resulting in increased platelet activity and secondary blood clot formation which can have life-threatening consequences.

Symptoms of Heart Valve Malformation in Cats

Cats suffering from heart valve malformation often have these general symptoms:

• Failure to gain weight

• Loss of appetite

• Difficulty breathing

• Weakness

• Fainting spells

• Muscle wasting

If the malformation is in the mitral valve, your cat may have the following specific symptoms associated with left-sided heart failure because fluid accumulates in the lung and chest cavity:

• Increased heart rate

• Difficulty breathing

• “Stretching” postures

• Cough

• Pale or blue gums

• Weak pulses, felt on the inside of the cat’s thighs

• Cool extremities

If the malformation is in the tricuspid valve, your cat may have the following specific symptoms associated with right-sided heart failure:

• Ascites, or fluid buildup, in the abdomen

• Distension of the jugular veins

• Weakness or collapse

• Fluid accumulation in the lower limbs

• Enlarged liver

Unfortunately, for some pet parents, the only sign will be the sudden passing of the cat, as cats with severe congenital heart defects are likely to die prematurely. 

Causes of Heart Valve Malformation in Cats

Congenital heart defects are rare in cats. It is estimated that less than 1 percent of the population is affected, with males and purebred cats such as Maine Coons and Ragdolls having a higher incidence.

Specifically, with atrioventricular valve dysplasia, the defects are present at birth and mostly involve some sort of developmental problem where the valves are thickened, shortened or attached to the wrong location of the heart. The chordae tendineae (cords of tissue that connect the valves to the heart muscle) may be thickened or elongated which affects the valve’s ability to function.

How Veterinarians Diagnose Heart Valve Malformation in Cats

For most cats, an audible murmur can be detected, usually during one of the first of several kitten wellness exams. Further testing is then recommended.

Sometimes, the veterinarian can detect another heart sound or a “gallop” rhythm. Once detected, or if you have a cat predisposed to atrioventricular valve dysplasia, a thorough cardiac exam will be performed. This often will include:

• Diagnostic Imaging, such as chest X-rays and an ultrasound of the heart, referred to as an echocardiogram or EKG. It determines heart size, chamber thickness, pressures and valve function

• Blood pressure measurements

• Electrocardiogram

• Cardiac biomarker evaluation (NT-proBNP and cTnI), which can aid the veterinarian in detecting underlying heart disease

Blood work and urine testing are often conducted (though the results are typically unhelpful) as a baseline to serve for medication monitoring, and the effects heart valve malformation may have on the organs. 

Treatment of Heart Valve Malformation in Cats

For some cats with mild atrioventricular valve dysplasia, follow-up and careful monitoring may be the recommended therapy. Most cases require some type of medical management. Cats are usually prescribed a combination of the following:

• Diuretics (water pills), to remove excess fluid from the blood

• Blood thinners, such as aspirin or Plavix, to reduce the formation of a blood clot

• ACE-inhibitors, such as Enalapril or Benazepril to reduce blood pressure and help reduce the heart’s workload

• Pimobendan, a drug that not only improves the effectiveness of the heart’s contraction, but also helps regulate heart rate

• Atenolol, a beta-blocker, that helps regulate blood pressure and heart rate

Open-heart surgery to repair or replace the valve can be performed, although this is often limited and has been more widely used in the treatment of mitral regurgitation in dogs.

Recovery and Management of Heart Valve Malformation in Cats

Cats with mild heart defects may live for years without any clinical signs and may have a relatively normal life—or they may present with clinical signs of heart failure later in life. If the defect is severe, signs of heart failure and fatal arrhythmias may occur, and although the signs can be treated, the prognosis is often poor.

Exercise restriction, nutritional management (often geared toward sodium reduction), and use of antibiotics when undergoing surgical procedures may also be recommended. Cats diagnosed with hyperthyroidism should be monitored and screened for the presence of structural heart disease. 

Cats that have been diagnosed with atrioventricular valve dysplasia and/or heart failure should have frequent checkups and blood work to ensure that the medications prescribed are not having negative effects on the kidneys. Depending on the severity on the defect, your cat may need chest X-rays every three to six months and echocardiograms every six to 12 months.