Atrioventricular Valvular Stenosis in Cats

 

There are four chambers in the heart. The top two chambers of the heart are the atria, and the bottom two chambers of the heart are the ventricles. The valves that communicate between the atria and ventricles are the atrioventricular valves. The mitral valve communicates between the left atrium and left ventricle, and the tricuspid valve communicates between the right atrium and the right ventricle.

 

Abnormalities in the mitral valve, on the left, affect blood flow to the lungs. The tricuspid valve, on the right side of the heart, is responsible for blood flow to the body.  Abnormalities seen here result in poor blood flow throughout the body.

 

Stenosis (narrowing) of these valves can occur due to the valves being malformed from birth, bacterial heart muscle infection, cancer of the heart, or hyptertrophic cardiomyopathy (a disease often seen in cats suffering from a thyroid tumor). Stenosis of these valves causes the valves to become leaky, increasing the diastolic pressure gradient between the atrium and the ventricle (the pressure gradient is the period in which the heart's chambers dilate and fill with blood – diastole of the ventricles follows diastole of the atria). 

 

Mitral valve narrowing can cause high blood pressure in the lungs, trouble breathing, and coughing. Mitral valve stenosis is more commonly seen more in Siamese breeds.

 

Tricuspid valve stenosis can lead to swelling of the legs and paws, and an enlarged liver may be seen on radiographis images.

 

Both mitral and tricuspid valve stenosis can lead to congestive heart failure (CHF).

 

Symptoms and Types

 

• Exercise intolerance
• Fainting (syncope)
• Trouble breathing
• Coughing (mitral valve narrowing)
• Pale or bluish skin color (cyanosis)
• Fluid in the abdomen, swelling (tricuspid valve stenosis)
• Stunted growth
• Spitting up blood

 

Causes

 

There are a variety of causes that narrow a cat's heart valves, much of it depending on the type of valve stenosis. Mitral valve stenosis, for example, is congenital and commonly affects Siamese. Tricuspid valve stenosis, meanwhile, is also congenital in nature and may be due to cancer of the heart and bacterial infection of the heart muscle. Moreover, both of these are usually diagnossed at an early age.

 

Diagnosis

 

You will need to give your veterinarian a thorough history of your cat's health and onset of symptoms, including any information you have on your cat's family line. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis. The results of these tests typically return normal levels. Based on the apparent symptoms and the results of the initial physical exam, your veterinarian should be able to narrow the cause down to which type of heart valve disease is present. This will need to be confirmed with further testing.

 

For diagnostic purposes, your veterinarian will need to view the heart using imaging tools. X-rays can help your veterinarian to determine if there is enlargement of the valves or atrium on either side of the heart, and echocardiography will show atrial dilation, and possibly abnormal flow of the blood through the heart. Electrocardiograph readings can also help your doctor to determine if the heart's electrical functioning is being affected. An abnormal rhythm, and the exact measurement of the abnormality can be a great help in determining which side of the heart is most affected. 

 

Your doctor may also use a diagnostic method called angiography, which utilizes X-ray imaging along with a radio-opaque contrasting agent (dye) that is injected into the blood vessels. This dye makes it possible to visualize the vessels internally and evaluate the flow of blood through the heart and surrounding vessels.

 

In rare instances, a veterinarian may also want to check for pressure disparities within the heart (intracardial) and within the vessels (intravascular) by catheterizing it, a process called cardiac catheterization. This method can also be used for injection of contrasting agents, to take a sample for biopsy, if cancer is suspected, and to assess the severity of the disease.

 

 

Treatment

 

Medicine is essential to treating heart valve disorders. Diuretics may be used to reduce fluid retention, but other drugs of choice will be based on the final diagnosis. While it is possible to surgically replace or repair damaged valves, it is expensive and has limited availability. An alternative treatment to surgery is a method called balloon valvuloplasty, which may be performed by a specialist after a referral from your veterinarian. Intensive care hospitalization will be necessary for medical treatment of your cat if it is suffering from congestive heart failure. 

 

Living and Management

 

Your cat will need to be rechecked about every three months or sooner to see if there are continuing signs of chronic heart failure and to adjust the treatment accordingly. Chest X-rays, an electrocardiogram (EKG – to measure the electrical activity of the heart) and echocardiography will very likely be performed at the follow-up appointments.  Your veterinarian will discuss precautions and home treatment with you, but generally, cats that are diagnosed with AVD need to be restricted to a low-salt diet and exercise should be restricted. 

 

Because this is a genetically based disease, if your cat is diagnosed with it, your veterinarian will strongly advise against breeding your cat out. Spaying or neutering is indicated.