In honor of National Heart Month, we’re going to talk about one of the more common feline heart diseases, hypertrophic cardiomyopathy or HCM to help you better understand the symptoms, how it’s diagnosed and most importantly how it can be treated. We’re very fortunate in Northern Virginia to have numerous CVCA (cardiac specialists for pets) offices. At Just Cats Clinic, we work closely with our local CVCA office to ensure your cat has the best care possible whether they suffer from something more severe like HCM or a mild heart murmur. For more information about veterinary cardiology, visit CVCA: Cardiac Care for Pets

What is hypertrophic cardiomyopathy?
In general terms, feline heart diseases can be divided into two categories: congenital and adult onset. As the name suggests, congenital diseases result from heart defects present from birth. Though those illnesses might manifest themselves during the cat’s youth, the diseases often remain hidden for years. Adult onset heart disease, on the other hand, is generally caused by damage to a feline’s heart suffered at some time in the course of its life. It might also occur as a result of a genetic condition that worsens as the kitty gets older. For example, cats with hyperthyroidism or high blood pressure sometimes develop heart problems alongside those illnesses.

The most common type of adult onset heart disease is the aforementioned HCM. Cats who suffer from this affliction have left ventricles that are thicker and more heavily muscled than normal. As a result, their hearts gradually lose the ability to pump sufficient amounts of blood into the aorta. If this important cardiac function is impaired enough, the kitty affected can have heart failure.

What causes hypertrophic cardiomyopathy?
Why certain cats get HCM is very often unclear, but genetic mutations are one common cause. Certain purebreds have been shown to be at greater risk of developing HCM. For example, a recent study found that as many as 33% of Maine Coons have a genetic abnormality relating to HCM. A similarly high incidence of HCM appears in Persians, and a less serious form of the disease occurs in American and British shorthairs.

HCM occurs most frequently in middle-aged cats (five to seven years old). It tends to show up earlier in Maine Coons, though, often appearing between the ages of two and four. Even Maine Coons as young as three months old have been diagnosed with HCM. The disease generally affects male kitties more frequently than their female counterparts.

How is hypertrophic cardiomyopathy diagnosed?
 Unfortunately, cats with HCM do not typically show any clinical signs until the disease is advanced. Unlike dogs, felines rarely respond to heart ailments by coughing. Kitties with HCM do often become exercise intolerant, but that can be difficult to notice because of their generally sedentary natures.

So what should concerned cat parents look for? The most common (relatively) early symptoms of HCM in cats include the following:

  • A loss of appetite and/or sudden weight loss
  • Sudden weight gain
  • Lethargy
  • Difficulty breathing and/or making “crackling” breathing sounds
  • Abnormal heart sounds, such as muffled beats, a galloping rhythm or murmurs

If you notice any of these symptoms, please make an appointment with your veterinarian immediately. The earlier you catch HCM, the better your chances of managing the disease will be. Once HCM’s more serious symptoms manifest, your kitty’s blood flow has been seriously disrupted, which can turn fatal if not treated. If things have progressed to that point, here is what to look for:

  • A bluish discoloration of the foot pads and nailbeds because of the lack of oxygen flowing to the legs
  • A sudden paralysis of the hind legs due to a blood clot in the aorta
  • Collapse
  • Sudden heart failure

How is hypertrophic cardiomyopathy diagnosed?
If you suspect that your kitty has HCM, the first step is to talk to your primary veterinarian about whether you need a referral to a veterinary cardiologist – like CVCA in our area. At that point, the cardiologist will start by conducting an electrocardiogram or EKG. That will track the electrical currents passing through your cat’s heart muscles and help your veterinarian determine whether there are any abnormal rhythms in the heartbeat.

Further testing will still be necessary to definitively diagnose HCM. Your vet will need to perform a radiograph (x-ray) and/or an echocardiograph (ultrasound) to examine the walls of your cat’s heart for signs that the left ventricle wall has thickened. He or she will then also have to rule out hyperthyroidism and hypertension. As mentioned above, the symptoms of those diseases aggravate underlying heart conditions. This means that they essentially mimic HCM and can lead to incorrect diagnoses if not ruled out. For the former, your vet will test for abnormally high levels of thyroid hormones. For the latter, he or she will check your kitty’s blood pressure.

How is hypertrophic cardiomyopathy treated?
Unfortunately, HCM is not corrected surgically. Instead, treating a cat with HCM requires long-term management of the disease and its symptoms. As with other diseases of this nature, early detection greatly expands the options available to you.

If you catch the disease early enough, your veterinarian might recommend one of or a combination of several of the following medications to minimize the effects of HCM:

  • Diltiazem, which slows the heart rate, normalizes irregular heartbeats and might reduce the thickening of the left ventricle’s walls
  • Beta blockers, which also slow the heart rate and normalize irregular heartbeats, but which also minimize blockages of the blood flow
  • Ace inhibitors, which improve blood flow through the ventricle
  • Nitroglycerin ointment, which also improves blood flow by dilating the ventricle and associated arteries
  • Aspirin, which decreases the risk of blood clots
  • Warfarin, which also prevents blood clotting
  • Furosemide, which is a diuretic that removes excess fluid that builds up in the body
  • Spironolactone, which is also a diuretic

If your vet prescribes any of these medicines, it is imperative that you follow the accompanying instructions to the letter. These are strong drugs and failure to give them at the times and in the doses indicated can have undesired consequences.

If the HCM has progressed to the point of causing congestive heart failure, some of the abovementioned medications might also be prescribed, but additional measures will also be necessary. For starters, your cat will need to be hospitalized so that it receives fulltime care and monitoring. Your kitty will be housed in a quiet and stress-free environment and will receive oxygen therapy if it is having difficulty breathing. The poor blood flow might bring your cat’s body temperature down, so the veterinary hospital staff will probably wrap it in blankets to keep it warm.

Once your feline friend is feeling well enough to come home, you will need to monitor it very closely during its recovery. Watch out for the symptoms mentioned above, especially for any difficulty breathing, lethargy, weakness, a lack of appetite or paralysis of the hind limbs. It will also be critical that you keep your cat’s blood pressure as stable as possible, so as not to put any undue stress on its left ventricle. This means creating a safe and calm space away from children, dogs and other cats if they are sources of stress for your cat. Make sure that your feline friend’s body weight stays at an appropriate level, adjusting the calorie content of its diet as needed. Your cat will also potentially need more of the amino acid taurine.

Follow ups and rechecks with your veterinarian and cardiologist will be necessary for life and how often you’ll need to go will vary based on your particular cat’s condition. As a minimum, your cat should be evaluated every six months to ensure there isn’t further damage to the heart muscles.