Hypertrophic-Cardiomyopathy-in-Cats by thevetscare.com

Hypertrophic Cardiomyopathy in Cats – 10 important things you must know

This post include on query Hypertrophic Cardiomyopathy in Cats, symptoms, treatment and prevention by thevetscare.com

Doctor veterinarian at clinic.
 Vasyl Dolmatov / Getty Images

While everything often looks alright on the outside, your cat may have something going on internally. Hypertrophic cardiomyopathy is one of those silent diseases that cats are unfortunately very prone to developing. Some breeds of cats are more likely to develop this disease than others, but it is still something all cat owners should be aware of. Knowing what signs to look for can help this problem from going undetected.

What Is Hypertrophic Cardiomyopathy in Cats?

Hypertrophic cardiomyopathy, often abbreviated as HCM, is a condition of the heart that causes the walls, specifically the left ventricle, to thicken.1 This makes it harder for the heart to work properly. The heart is a muscle with chambers inside of it that pump blood. If the walls of the heart become too thick, then it won’t be able to properly pump blood. The left ventricle is one of four heart chambers, but it specifically takes primary responsible for pumping blood through the body. If it can’t do its job, the rest of the body does not get proper blood flow.

Blood can also back up and clots can form if the heart isn’t working properly. In HCM, the heart tries to beat faster to compensate for the lack of proper blood flow. In doing so, it depletes the body of oxygen, which then kills heart cells. When the cells die, the heart function decreases even more and abnormal heartbeats occur. Congestive heart failure is also a common occurrence in cats who have HCM, partially due to the backup of blood.1

Signs of Hypertrophic Cardiomyopathy in Cats

Because HCM happens internally, it often comes as a surprise to cat owners. Heart issues may not be obvious until a cat is having problems, so it is important to know what to watch for.

A good physical examination will include auscultation, where your doctor will listen to your cat’s heart with a stethoscope. Your vet will be searching for normal heart rhythm, a murmur, or an arrhythmia. If an arrhythmia or murmur is heard, it may be an indication of heart disease such as hypertrophic cardiomyopathy. An X-ray and an ultrasound of the heart, called an echocardiogram, may be recommended to further assess your cat’s heart.1 These tests won’t fix a heart problem, but they can give your veterinarian a diagnosis and therefore a potential treatment plan.

Labored breathing is usually identifiable by observing your cat taking quick breaths. A cat struggling to breathe may also have audible wheezes, its abdomen rising and falling instead of the chest, an open mouth or heavy panting, and pale or blue gums. If your cat isn’t able to move oxygen through its lungs, it will have difficulties breathing and may be weak or collapse.

Sudden hind limb paralysis is a scary symptom that can also be a result of HCM.1 If a clot travels out of the heart and blocks blood flow to the hind limbs, your cat will appear to be paralyzed. This can happen quite suddenly, and due to the lack of blood flow, the leg will feel cold to the touch. Sudden death can also occur due to clots, but this is rare.

Symptoms of Hypertrophic Cardiomyopathy in Cats

  • Labored breathing
  • Open-mouth breathing
  • Pale or blue gums
  • Collapse
  • Weakness
  • Irregular heartbeat
  • Hind limb paralysis
  • Sudden death

Causes of Hypertrophic Cardiomyopathy in Cats

Certain breeds of cats are more likely to develop hypertrophic cardiomyopathy than others. Maine Coons, Ragdolls, Persians, Sphynx, Chartreux, and British Shorthair breeds have shown to have a suspected genetic predisposition to HCM and are therefore more prone to developing it.1 It is unknown why these breeds are more likely to get HCM than others. But, if you have one of these cats, it is especially important to closely monitor your cat’s heart health so you can catch HCM early.

Other breeds of cats can also develop hypertrophic cardiomyopathy, but the reason why is still unknown. Some dietary components and obesity may play a role in heart disease in cats, but there is no definitive link between hypertrophic cardiomyopathy and a specific cause.

Treatment of Hypertrophic Cardiomyopathy in Cats

Since hypertrophic cardiomyopathy cannot be cured, the goal of treatment is to keep the heart rate normal, prevent blood clots from forming inside your cat, and make it easy for your cat to breathe. While this is more of a management plan than a treatment plan, it’s the best option until a cure or further research has been done.

  • Nutrition: Taurine and L-carnitine are amino acids that are often recommended as supplements for cats with heart disease. These ingredients are often added to pet food and are also produced naturally within a cat’s body. Research has shown that they may be beneficial in supporting a healthy heart but they are not treatments of hypertrophic cardiomyopathy specifically, just overall heart health. Omega-3 fatty acids and special diets formulated for cats with heart disease may also be beneficial in supporting cats with hypertrophic cardiomyopathy.
  • Medications: There are several drugs that might be prescribed to help manage the symptoms of HCM. Some medications may be injected, applied topically, or administered in pill form. Different drugs will help make breathing easier, assist the heart’s function, stabilize blood pressure, and address other potential symptoms of HCM.
  • Activity level: Your veterinarian may recommend keeping your cat’s activity level low in order to decrease the amount of work its heart has to do.

Medications commonly used for HCM:

Beta-adrenergic blockers such as atenolol (Tenormin) or propanolol (Inderal). These medications slow the heart rate, which enhances filling and relaxation of the pumping chambers. Beta-blockers also allow more time for blood flow to the heart muscle itself, and reduce the amount of oxygen used by the heart. In some cases, the incidence of arrhythmias is also lessened. Side effects may include bronchospasm (spasm of the airways) (propranolol), fatigue, and in excessive doses,  slow heart rate and low blood pressure.

Calcium-channel blockers such as diltiazem (Cardizem CD, Dilacor XR). This class of drug has similar actions to the beta-blockers. Some differing characteristics of the calcium-blockers include little or no anti-arrhythmic activity in some cases, possible a greater ventricular relaxing effect, and a greater propensity for low blood pressure at higher doses.

Other medications may be prescribed in some patients. Diuretics (furosemide, spironolactone, etc.) may be needed to control edema and effusions (congestive heart failure). In pets that have had or may be prone to blood clot formation, anti-coagulants such as aspirin, warfarin, or heparin may be prescribed.

Medical therapy is always chosen to meet the needs of the individual patient. Frequent recheck examinations and adjustments may be needed especially early in the course of treatment to individualize a medication regimen.

Prevention of Hypertrophic Cardiomyopathy in Cats

Since there is no known definitive cause, there is not a concrete way to know if you are preventing hypertrophic cardiomyopathy. Providing proper nutrition to support the heart and ensuring your cat gets an annual veterinarian examination will help keep your cat healthy and hopefully decrease the likelihood of diseases, including hypertrophic cardiomyopathy.

Diagnosis of Hypertrophic Cardiomyopathy in Cats

If hypertrophic cardiomyopathy is suspected, your cat will most likely have blood work, X-rays, blood pressure testing, and an echocardiogram performed to fully assess the health of your cat. Based on the findings of those tests, your veterinarian will recommend a treatment plan to help diminish the symptoms or delay the progression of the disease.

How Do Cats with HCM Present?

The clinical signs of HCM are variable. To some degree, the clinical signs depend on the severity – mild disease doesn’t cause obvious problems, but severe disease often does. Additionally, cats are masters at masking problems until they become severe, so cats with severe HCM may appear completely normal or have only subtle signs that go unnoticed (i.e., mildly increased respiratory rate) or they may be very nonspecific to heart disease (i.e., decreased appetite). On the other hand, an owner may notice signs such as respiratory distress secondary to congestive heart failure or leg paralysis secondary to a thromboembolic (blood clot) event.

In many cases, the first an owner knows about the disease is when a veterinarian informs them that they heard an abnormality during a regular or routine examination.  A veterinarian can clue in on signs when he or she listens to your cat’s chest during their physical exam. A heart murmur, and/or gallop rhythm (extra heart sound) or an arrhythmia can be heard in many cats with HCM that are showing no outward signs of disease.

How is HCM Diagnosed?

An echocardiogram (ultrasound of the heart) with color flow and spectral Doppler imaging offers the best means to diagnose HCM. Echocardiography allows a veterinarian to observe the physical structure and dynamic function of the heart. Fortunately, the test is non-invasive and poses essentially no risk to the cat. Unfortunately, it is a relatively specialized procedure and can be expensive.

Electrocardiograms and radiographs provide additional useful information and are often used to assist a veterinarian in diagnosing HCM, but cannot be used alone to diagnose the disease. Since very subtle structural and functional changes can occur within the heart in the early stages of HCM, it is strongly recommended that a veterinary cardiologist be consulted for diagnosis as well as subsequent management of the disease.

Some veterinarians will run a blood test looking for changes in proteins produced exclusively by the heart (NT-proBNP).  Elevations in this protein can be seen in cats with HCM, but are not a specific or sensitive means of detecting the disease.  As previously mentioned, additional tests might be needed to rule out underlying diseases such as systemic hypertension or hyperthyroidism which can cause hypertrophy of the left ventricle similar to that seen with HCM. If no other causes are found, the diagnosis of HCM is made.

Two breeds (Maine Coon and Ragdoll) have been identified with mutations in the same gene (Myosin-binding protein C) as a cause of HCM.  A genetic test has been developed to test these breeds for the mutation, and is offered through North Carolina State University.  The test does not work in other breeds.

How is HCM Treated?

Currently, there is no cure for HCM. The changes occurring to the heart muscle are irreversible. However, if your pet’s left ventricular hypertrophy is secondary to some other underlying heart disease, such as hyperthyroidism, treatment of the primary disease can result in some or complete resolution of the heart condition.

As previously mentioned, hypertrophy of the heart muscle affects the ability of the left ventricle to relax properly, and therefore, function appropriately. While veterinarians might prescribe one or more medications to try to improve the heart’s relaxing ability, it is important to recognize that no drugs have been shown to be effective in achieving this. Thus, attempts to reduce the risk of heart failure and to help the heart function efficiently are largely theoretical and may ultimately be of no value.

Some treatment options that may be prescribed include:

  • Drugs that are thought to alter relaxation of heart muscle, or slow down the heart rate to allow a longer time for the heart to fill, or both. No proof exists that either of these approaches actually benefits cats with HCM. It is quite acceptable to not treat cats with HCM prior to the onset of CHF – when information becomes available showing a benefit of any treatment, guidelines might change.
  • Drugs to treat congestive heart failure (diuretics and ACE inhibitors). These medications are not specific for HCM, but are used in cats with heart failure secondary to any heart condition. With severe fluid build-up in the chest cavity, the veterinarian may physically remove the fluid with a catheter to help the cat breathe.
  • Drugs that are thought to reduce the risk of clot formation, or clot recurrence. A medication that reduces the ability of the blood to clot might be prescribed if the veterinarian believes the cat is at risk for blood clot formation or currently has a blood clot in one of its arteries or heart chambers. The use of certain drugs for this purpose must be closely monitored to insure the patient is not placed at risk for hemorrhage. Treatment does not guarantee that a blood clot will not form, nor is it designed to break down previously formed clots. One study has demonstrated that cats given clopidogrel after surviving an initial clotting event have a lower risk of another event, compared with cats receiving aspirin.

As an owner of a cat with HCM, you should be very sensitive to changes in your pet’s condition and should not hesitate to seek veterinary advice. Your veterinarian might show you how to monitor your cat’s respiratory rate as an increased rate may be a sign that congestive heart failure is developing or worsening. Cats with congestive heart failure do not generally cough, but often exhibit open mouth breathing and panting. A cat that is having difficulty breathing from heart failure or has loss of function of hindlimbs or front limbs, requires veterinary care as quickly as possible. In the acute setting, these problems often need specific treatments (oxygen therapy, injectable medications, anticoagulation medications, or pain medications) that can only be offered by a veterinarian.

What is the Prognosis of a Cat with HCM?

The prognosis of a cat with HCM is highly variable. Some cats might develop only mild hypertrophy and suffer little compromise of heart function, while others progress to more severe disease. HCM might worsen quickly over a period of months, or it may progress slowly over several years. Its severity might not change for many years and then suddenly worsen. Some cats with HCM die very suddenly even though they had no clinical signs of heart disease.

A cat with mild to moderate disease may enjoy an essentially normal life for a number of years. However, the prognosis is much more guarded once the cat has more severe disease. The risk of developing congestive heart failure is proportional to disease severity, which is often classified by measuring wall thicknesses and left atrial size. Although congestive heart failure can be treated medically, severe heart failure may become difficult to manage over time as the disease progresses. The prognosis for a cat with heart failure, unfortunately, is guarded to poor. On average, survival for cats with HCM and heart failure is 12 to 18 months after diagnosis.

Thromboembolism is a severe uncommon complicating condition in HCM. It can cause acute pain and various clinical signs such as loss of function of the hindlimbs (most commonly, although other organs or limbs can be affected). Although treatment to break down or remove the clot is available, the high treatment costs of the procedure, death during administration of the drugs and high recurrence rate of thromboembolism dissuades most from attempting this type of therapy. With supportive care, about 40 to 50% of patients with thromboembolic disease will break down clots on their own and regain limb function over time. However, despite the best medical efforts to prevent their reoccurrence, a cat that has survived a thromboembolic event has a significant risk of developing another over the following weeks to months.

To Breed or Not to Breed?

In some forms of HCM, an autosomal dominant pattern of inheritance has been documented in some breeds. Not only does that mean it can be passed on genetically, but also that males and females are equally affected; every affected cat will have at least one affected parent; and all carriers of even a single copy of the gene can show the disease and transmit a mutant gene to half of their offspring.

In two breeds (Maine Coon and Ragdoll), a specific genetic mutation has been identified and a test has been developed to identify cats with the mutation. So what does this mean if you want to breed Maine Coon or Ragdoll cats?

If the DNA test is positive for that mutant gene, the cat may develop HCM. As in people, not all individuals with the mutation will develop the disease. Breeding recommendations are currently all over the place. Some people currently recommend that if the cat has two copies of the gene, the cat should not be used for breeding. Rather, the cat should be screened periodically to see if he has the disease. But if the cat has one copy of the gene, he should also be screened periodically for the disease, although his status for breeding is much better.

On the flip side, some veterinarians feel that any cat with the mutation should be spayed or neutered. However, the gene pool for purebred cats is pretty small, which colors all breeding considerations. If all the cats with the mutation in one generation are not bred, you might end up with far too much inbreeding, which would ruin the breed anyway. Therefore, some people recommend that cats who have one copy of the mutation and who have no clinical evidence of the disease may be used to breed to a mutation-negative cat. Offspring of that cat should be carefully evaluated and, if possible, a mutation-negative kitten should be used for a breeding replacement.

Before breeding your cat, be sure you understand all of the possibilities of what could happen. Genetics is an area that not all veterinarians are comfortable discussing. Discuss with your veterinarian whether referral to a geneticist or cardiologist or would be best for you and your pet