A Heart to Know: The Truth about HCM in Cats.

Hypertrophic Cardiomyopathy or HCM is one of the most common diagnosed heart diseases found in felines. But what exactly is HCM and what causes it? Before we start I just want to note that PurrCozi kitties are not veterinarians and our information is for education purposes only and should not replace the advice of professionals! Always ask your veterinarian if you suspect health issues in your kitty!

What exactly is HCM and how does it work?

Hypertrophic Cardiomyopathy (HCM) in cats is the most common diagnosed heart disease affecting about 10-15% of the feline population. HCM causes the muscle walls in the heart to thicken, making it difficult for the heart to pump blood efficiently. The thickening of the walls is known as hypertrophy and it primarly affects the left ventricle which is the hearts main pumping chamber.

To go a little more in depth... Like the human heart, feline hearts consist of four chambers. These chambers each play a very important role in the production of blood and getting it to where it needs to go. There are two smaller chambers on the top, these are called the left and right atrium. Then there are two larger chambers on the bottom of the heart, these are the left and right ventricle. What do these chambers do you may ask, well the right atrium pumps deoxygenated blood from the body into the right ventricle, which then pumps the blood into the lungs. This in exchange picks up more oxygen for the body to use and releases carbon dioxide for disposal. Now, the function of the left atrium is kinda similar to the right, but its function is to pump oxygen-rich blood from the lungs into the left ventricle. This then will pump blood back into the body and allows for proper cellular and organ functions. Because the left ventricle needs to push oxgenated blood into the rest of the body, the muscular walls are thicker then those of the right ventricle. When the walls of the left ventricle become englarged and excessively thickened, this results in Hypertrophic Cardiomyopathy (HCM). The thickening of the walls results in the narrowing of the inner chamber of the heart. The inner chamber narrowing, due to the result of the thickening, prevents the heart from filling with blood properly. This all effects the effiency of the heart, resulting in less oxygen-rich blood reaching the body to keep it functioning correctly. This causes the heart to beat faster, which increases the need for oxygen and causing heart cells to ultimatly parish.

What causes HCM in cats?

While the mechanisms and triggers of HCM are still not 100% understood, we do know that HCM is most commonly an inharent disease of the heart that it is often related to a genetic predisposition of HCM that is present in many cat breeds. The breeds that are most commonly affected are American Shorthairs, Bengals, British Shorthairs, Chartruex, Maine Coons, Norwegian Forest, Persian, Ragdoll, Sphynx, and Turkish Van. Those cat breeds are most commonly affected because they have been found to be more at risk of carrying a mutation of the gene A31P.  The mutation is a single base pair change in MYBPC3 that disrupts the production of the cardiac myosin binding protein C that is needed for normal heart development. The gene produces HCM in cats that carry two copies of this mutation. Cats that carry one copy of this mutation have a longer life expectancy but can still develop HCM.

On top of genetics, there are several medical causes of HCM in cats. Hormonal conditions such as hyperthyroidism or acromegaly (excessive secretion of a growth hormone because of a tumor in the anterior pituitary gland near the brain) can stimulate growth of the muscular walls of the left ventricle. Cancer in the heart can also cause an increase of size in the muscular walls of the left ventricle.

There have also been cases of heath issues unrelated to the heart that can cause high blood pressure in the body, this can put an additional strain on the left ventricle as it works harder than normal to pump blood to the body against elevated pressure in the vessels. Over time, this increased effort causes the ventricle walls to become thicker, and the interior chamber narrower which eventually results in HCM.

Progression & Complications

Below are some of the most common symptoms of HCM. Note that while these symptoms are common in HCM they are not always a sign of HCM and can be the result of another serious health issue. It is important to talk to your vet if your cat is experiencing any of these symptoms.

• Loss of appetite 

• Heart murmur 

• Arrhythmias (abnormal heart rhythms) 

• Blood clots, which can cause pain/vocalization, trouble walking, cold rear limbs, vomiting, and trouble breathing 

• Heart failure 

• Fluid in lungs, causing crackles and wheezes when breathing 

• Difficulty breathing 

• Fluid in abdomen, causing visible abdominal swelling 

• Abnormal gum color... pale, gray, or blue gums 

• Blue foot pads and nailbeds 

• Weak or unstable pulse 

• Tiring easily during play/exercise 

• Lethargy/weakness 

• Fainting/collapse 

• Sudden death 

HCM is often a slow progressive disease, but in some cases it can progress more rapidly. Once symptoms appear most cats with HCM survive less than two years. Up to 7% of cats that have shown signs of HCM will develop heart failure by a year of age. Studies have shown that if the first symptom is a blood clot then the average survival time is 6 months.

How to Diagnose and Treatment options...

The most common way to diagnose HCM is through an Echocardiography (Echo) which is an ultrasound of the heart and can reveal characteristics of thickening of the muscular walls that result in HCM.

Example of an Echocardiograph

Along with an Echo there are other tests that the veterinarian can provide to diagnose HCM. These include, blood tests, chest x-rays, and electrocardiograms. These tests can also confirm if there is another underlying health issue that is contributing to HCM.

DNA testing is also a good tool for testing if a cat carries a mutation of the gene A13P that results in HCM. However it is important to note that it does not definatively confirm if HCM is present or not. We recommend yearly echos for high risk breeds as a precauction and to stay on top of any underlying issues.

While unfortunatly there is not a cure for HCM, there are different options to slow the progression if caught soon enough. We found this amazing list on PetMD that gives the different medications that can be used and details on what it is used for.

• Clopidogrel: medication that helps prevent blood clots. 

• Diltiazem: a medication that can prevent some fluid buildup and reduce the thickness of the left ventricular wall in some cats. 

• Beta blockers: medications such as atenolol can help cats with severe HCM by slowing heart rate in cats with tachycardia (an overly fast heart rate), correcting abnormal heart rhythms, and improving the function of the valves between the chambers of the heart. Beta blockers can also decrease blood pressure in cats with hypertension. 

• ACE inhibitors: medications such as benazepril are often prescribed to cats with HCM who have heart failure. It can reduce blood pressure. 

• Aspirin: used to thin the blood and prevent clotting in cats with HCM. It’s important that pet parents never give over-the-counter medications to their cats without a veterinarian's approval. 

• Warfarin: another blood-thinning medication that can help prevent blood clots 

• Furosemide or Lasix: a common medication prescribed for cats who have congestive heart failure due to HCM. 

• Spironolactone: another diuretic medication that is used in cats with HCM and heart failure to remove fluid buildup. Spironolactone is often used along with Lasix®. 

• Nitroglycerin ointment: can be applied inside the ears of cats to treat severe fluid buildup when administered along with Lasix. It can also improve blood flow to the body by relaxing the ventricles and arteries, so they are able to accommodate more blood. 

• Pimobendan: can help increase the function of the left atrium and left ventricle during the pumping phase of the heart cycle, when the heart is pushing blood from the left ventricle to the body. 

PerMD also states that in addition to medications, some cats may need routine pleurocentesis, that is a procedure that removes excess fluid from the lungs. Cats with severe, acute HCM and heart failure may need oxygen therapy in the hospital. Cats that suddenly develop heart failure may benefit from being put under anesthesia, intubated, and helped to breathe if respiratory failure occurs. Anxious cats may be given sedatives such as acepromazine to keep them calm, as stress can cause breathing difficulties and increase the risk of heart failure in cats with HCM. 

Prevention of HCM, Selective Breeding and why its Important.

You may be wondering, is HCM preventable? Well, Because HCM is generally a genetic condition it cannot be prevented, however early identification and management can help to manage and reduce the risk of complications along with improve the quality of life of a cat.

Now, selective breeding is crucial and plays such an important role in managing HCM in cats. This is especially important in breeds where genetic mutations are known to cause HCM. Breeders can reduce the prevelance of HCM in their lines by being up to date with DNA, genetic and health testing. Breeding cats that carry the genetic mutation should always be avoided. Breeders should be very strategic in choosing their breeding pairs.

Here at PurrCozi Kitties, we are extremely diligent in choosing our breeding cats. We genetically test each one of our breeding cats along with preforming an echo. Because HCM is common in most breeds we are extremely careful to choose our breeding cats from lines that have been genetically tested negative for HCM along with other diseases. We are more than happy to share this information with our kitty families and you can find this on our adult cat page!

If you are planning on bringing a new kitten into your family, always make sure to talk to your breeder about HCM and health testing. If a breeder does not have any health testing done that is a major red flag and you are potentially risking bringing home a kitten that has hidden genetic health issues.

If you are a breeder (or potential breeder) please be diligent in making sure that your cats have their genetic and regular health testing done and are negative for HCM along with other diseases your breed is prone to carrying. Breeding is a big responsibilty and it is so important to choose your breeding cats carefully to prevent heartache and expensive veternarian visits.

If you are someone who is reading this because you just recieved and HCM diagnosis, we want to be the first to tell you we are so sorry for this unexpected news about your kitty. We hope that this gives you a better understanding about HCM and what to look out for. Hugs and prayers for your sweetheart.

Thank you so much for taking the time to read this blog about HCM. We hope that it is extremely informative and helpful! Remember that PurrCozi Kitties are not veternarians and this information is just for education purposes only. If you suspect HCM in your kitty please discuss this with your veternarian.

Lots of Love,

The PurrCozi Crew <3