Cardiomyopathy In Your Cat
When Your Pet's Heart Fails
If your pet is a Dog, go here.  

Ron Hines DVM PhD.......................................................

 

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This is a disease that usually strikes the family with little warning. Once most owners are aware that their pet is ill, the condition is quite advanced and serious.

Cardiomyopathy means heart (cardio) muscle (myo) disease (pathy).

Veterinarians divide cardiomyopathy in cats into three types:

In the first, Dilated Cardiomyopathy, the walls of the pet's heart balloon out, causing an enlarged, rounded, thin-walled weakened heart.

In the second form, Hypertrophic Cardiomyopathy, the heart retains it classic shape but the walls of the heart thicken, reducing this muscle’s ability to pump blood.

The third type is called Restrictive Cardiomyopathy. In this form, scarring of the heart muscles prevent normal pumping action. The signs of all three forms in cats are similar and are ultimately due to a lack of oxygen supply to cells throughout the pet's body.

What Causes Cardiomyopathy ?

We do not know what causes most cases of cardiomyopathy in cats. But we do know a few of the factors that seem to make the disease more likely to occur.

Cardiomyopathy was a relatively common disease in cats fed generic cat foods or dog food. These foods were sometimes deficient in an essential amino acid of cats, taurine. A deficiency in this amino acid was discovered to be the cause of heart failure in these cats. When this link was found, most cat food manufacturers added taurine to their diets or periodically analyzed it to be sure there was sufficient taurine in it.

Another known association with cardiomyopathy in cats is hyperthyroidism. Hyperthyroidism is quite common in older cats and becoming more so. In this disease, the pet’s metabolic rate increases due to over-secretion of the thyroid hormone, thyroxine. The number of cases hyperthyroidism in cats has increased significantly in the last 25 years. Some experts think that hyperthyroidism in cats is more common in cats feed tuna or fish-based diets and those fed a variety of canned diets marketed in “pop-top” or “peel-back” cans or the chemicals coating these cans. Others believe that increased iodine in commercial cat food is the cause. (ref) Still others blame the modern home environment. But nothing has been scientifically proven.

When a cat's thyroid is overactive, the pet's blood pressure and the workload on its heart muscle increase. This can cause cardiac enlargement or heart muscle thickening.

We also suspect that prior viral infections, genetics or the lack of antioxidants may predispose the pet to heart failure.

Cardiomyopathy seems to be an inherited disease in Maine Coon and American Shorthair cats. It appears to also be more common in Persians cats than ordinary domestic shorthair cats. More male than female cats develop the disease.

What Symptoms Might I See In My Cat ?

Although dogs and humans often develop a moist cough when the heart looses its efficiency, cats rarely cough with this disease. Instead, they are often brought to veterinarians due to listlessness, rapid labored respiration, poor appetite and loss of body condition. At first glance these cats may look plump. But they are bony over their back and loins and what appears to be a plump tummy is actually an enlarged liver with fluid accumulation in the abdomen (see the blood tests). These signs signify that the disease is already quite advanced.

On the microscopic level, failing hearts that no longer pump sufficient blood, allow the liquid portion of the blood (serum) to leak into the smallest chambers of the lungs (the alveoli and bronchioles) where oxygen and waste CO2 exchange should be occurring. This is called pulmonary edema. When this fluid seeps out and surrounds the lungs themselves it is called plural effusion. Both conditions make respiration difficult and are quite uncomfortable.

The sluggish flow of blood through damaged hearts commonly results in another serious problem, the formation of blood clots blocking major arteries. These clots form in stagnant blood pooling within the enlarged left atrium of the heart and then move out into the peripheral circulation. A common place for these clots (saddle thrombi) to lodge is the bifurcation (where it divides) of the primary artery of the abdomen called the descending aorta. The portion of the aorta that becomes blocked is the portion supplying the rear legs and tail. When circulation to the rear legs and tail is interrupted, the muscles of the legs and tail become limp because they are starved of oxygen. This condition mimics spinal cord damage and paralysis. When I examine these cats I note that the femoral pulse within the rear legs is weak or absent and the limbs are cold to the touch. Although the clots usually dissolve slowly and limb function returns the underlying heart problem remains.

The hypertrophic form of cardiomyopathy often results in increased blood pressure or hypertension (systolic blood pressure exceeds 160mm Hg). Smaller blood vessels may burst under increased pressure particularly vessels within the retina of the eye. This can lead to retinal detachment and sudden blindness. To reduce the blood pressure anti-hypertensive drugs should be used. A number of agents called calcium channel blockers are available for treatment of hypertension and cardiac failure although many of these are not specifically licensed for cats. Examples of two drugs commonly used are benazepril (Fortekor®, Lotensin) and amlodipine ( Istin®, NORVASC).

How Do Veterinarians Diagnose Cardiomyopathy ?

Any combination of signs I have discussed can lead us to suspect cardiomyopathy in your cat. Cats suffering from this disease are usually over the age of five. A firm diagnosis requires at a minimum a chest X-ray, echocardiography or ultrasound image of the heart. An EKG (electrocardiogram) can also be diagnostic. An elevated free T-4 level will diagnose the presence of hyperthyroidism - a common finding in older cats with heart problems.

When veterinarians can not decide if the cat has sudden (acute) cardiomyopathy or a slower, progressive heart failure (Congestive Heart Failure, CHF), a 2010 study found that a lab test (NT-proANP) can be useful in deciding. You can read the report here.

What Treatments Are Available For My Cat ?

Treatment is first directed at correcting any underlying cause that may be responsible for the disease. Hyperthyroid cats need to have their thyroid condition alleviated with medication (methimazole, Tapazole®) , thyroid surgery or radioactive iodine therapy.

Where no underlying cause is found, I treat the cat with a class of medications called ACE inhibitors (angiotensin converting enzyme) that improve cardiac function (enalapril, Enacard), and diuretics to remove pooled fluids (furosemide, Lasix). Low salt diets may also be helpful. The calcium channel blockers I mentioned previously help the heart muscle relax and fill more completely.

Beta-blocking drugs (atenolol, metoprolol, propranolol) are sometimes used to slow the heart rate down in cases where the heart rate is excessively fast so there is no time for filling to occur.

Vetmedin (pimobendan)

Although not yet approved for use in cats in 2012, Vetmedin works by increasing the amount of calcium available to the heart muscle and also lowers vascular resistance and blood pressure (increased blood vessel diameter or vasodilatation). In doing so, the pet’s heart needs to do less work. Studies show that it appears to help the hearts of cats as well as the dogs for which it is an approved use. (ref)

Vetmedin increases blood calcium levels. The more calcium that is present, the stronger are the heart’s contractions. The Drug was originally used in human medicine about 10 years ago. At the time, it was thought that it might offer hope to people with heart conditions similar to your pet’s. It did increase the force of human heart contractions, but it sometimes made the hearts pump too forcefully. Dogs and cats do not develop coronary artery disease as humans do. But human hearts with blocked or occluded coronary arteries became starved for oxygen when on this drug. This led to heart attacks and angina (chest pain). Because dog and cat hearts differ from human hearts in this respect it is permissible to use pimobendan in pets. It should be given about an hour before meals with half the dose given before breakfast and half before supper. An occasional pet will experience vomiting on this drug.

Digoxin, which acts to slow heart rate and also to improve the force of heart contractions, is often prescribed in cases of dialative cardiomyopathy when other drugs are no longer sufficient. I no longer use it because of its strong side effects and disappointing results.

Very cautious use of aspirin in cats can decrease the likelihood of clots (thromboemboli). Cats should never receive over 60 milligrams of aspirin in a forty-eight hour period and their blood chemistry, clotting and bleeding time must be closely monitored.

Some veterinarians physically remove excess fluid from the chest of cats in heart failure. I rarely do this because the fluid rapidly reoccurs and important proteins are lost when the fluid is siphoned off. Instead I try to rely on oral diuretics to remove excess fluids.

Unfortunately, the disease will slowly worsen in your pet - despite treatment. Some cats remain stable for years while others deteriorate more rapidly. In general cats with thromboembolic disease, and those with heart failure which does not respond well to ACE inhibitors or calcium channel blockers have a bleaker outlook. Cats are quite successful in hiding the early stages of heart failure from their owners so many cats are not brought to my attention until the disease is in its later stages.
What

In cases where a taurine deficiency is suspected, taurine should be supplemented (about 250mg twice a day). Fat cats should be put on a diet program. A low salt diet may also be helpful.

Restrictive cardiomyopathy is another form of heart muscle disease. This form can be a later stage of hypertrophic disease or it may be the primary entity. Unfortunately, restrictive cardiomyopathy is quite refractory to the treatments I have outlined. Cats with this condition tend to have a very distended left atrium and are at a high risk of development of blood clots and heart failure.

Cats suffer from a number of heart conditions. The most common two are disease of the left atrio-ventricular valve (mitral valve insufficiency) and a generalized enlargement, and weakening of the heart called dilative cardiomyopathy.

What Other Drugs Might Help ?

Benazepril (Forticor)

This is another angiotensin-converting enzyme (ACE inhibitor) drug. Benazepril is similar in it’s effect to enalapril (Enacard) and some vets prefer it. Forticor is used to increase the efficiency with which failing hearts pump blood and is also used to treat high blood pressure in pets. In the liver, the drug is metabolized to benazeprilat, the active compound. The dose of Forticor is best divided into two daily doses. It can be given with or without food. It is also effective in lowering blood pressure (hypertension) in cats with kidney failure.

Spirolactone (Aldactone)

When the maximum dose of furosemide diuretic is not sufficient to eliminate fluid buildup in the tummy (ascites) and lungs (pulmonary edema) of your pet, another diuretic, such as spirolactone, can be added to the medications your pet receives. You need to be patient - it takes 2-4 days for the full effect of the drug to be reached. Spirolactone can increase the toxicity and effect of digoxin so your pet’s digitoxin dose may need to be lowered. It can also cause an increase in serum potassium, which can be dangerous. To monitor potassium, a blood sample should be taken and measured for serum electrolytes and kidney function on the 3rd or 4th day, the 7th day and periodically there after.

Are There Some Medications It Might Be Best To Avoid ?

Perhaps corticosteroids given orally or by injection. (ref)

How Much Longer Will My Cat Live ?

Unfortunately, cats do not tend to survive as long as dogs or humans do when they develop the signs of a cardiac problem. In a study I referred to earlier (ref) ; of 164 Massachusetts cat diagnosed with this problem, the average additional life span, with intensive treatment, was 151 days.