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A brief discussion on feline heart disease
What is Heart Disease?
Heart disease is a broad term used to describe a wide variety of heart conditions. It includes everything from anatomical defects to parasitic infections. Heart disease can be classified in many ways. If the animal was born with the condition it is termed “congenital”. It can be described by cause, ie. due to an infection, genetics, injury or aging. Status and duration of disease can also be used. Has the animal had the condition for a long time? It may be called “chronic”. Is the condition localized to a particular part of the heart? You find terms like left-heart failure, atrial or ventricular septal defects. The words “heart failure” of course describe the end of heart disease. You might have heard people say “we all die of heart failure.” When the heart stops beating and cannot be restarted, it is game over. Asystole is perhaps one of the scariest terms in medical terminology. While all mammalian hearts follow the same anatomical “pattern” if you will, there are some differences in how certain conditions may manifest. Today, I will be discussing some heart conditions as they appear in cats as opposed to other animals and a general overview of heart diseases.
Anatomy of the Heart
In order to discuss heart diseases I would be remiss if I left out the basic anatomy of the heart itself. The heart is a muscular organ located roughly left-center in an animals chest, more specifically in an area known as the mediastinum (the space between the two lungs). The heart itself is roughly heart-shaped with the atria containing base of the heart located cranially (towards the head), and ventricle containing apex of the heart positioned ventrally (towards the belly). The left and right sides of the heart are separated by an interatrial (between the atria) and interventricular (between the ventricles) septum. Simplified, the atria receive blood from the body and the ventricles pump the blood to the body. The atria and ventricles are separated by unidirectional atrioventricular valves. Atria are thinner than ventricles as they only need to pump the blood directly below them.
Blood flows through the heart from right to left. The right atrium receives deoxygenated venous blood returning from the body and pumps it through the tricuspid valve to the right ventricle. The right ventricle which pumps blood through the pulmonary valve into the pulmonary artery where it travels to the lungs to pick up more oxygen and drop off CO2. After conducting its business in the lungs the blood flows into the left atrium from the pulmonary vein and is shunted through the mitral valve into the left ventricle. The left ventricle contracts and forces the blood through the aortic valve which delivers the newly oxygenated blood to the arteries that will carry it to all the major bodily systems. All of this is completed in the time it takes for a single “lub-dub”. It is also worth mentioning that the right and left sides of the heart contract simultaneously, the “lub” sound is made by both atria contracting and the “dub” by both ventricles. This ensures there is never a pause or break in blood flow. An interesting fact about the heart is that it is autorhythmic. This means the heart muscle is capable of beating autonomously from the rest of the body from before you’re born till the day you die. It’s also why in horror movies, a ripped out heart may still be beating for a few seconds while the villain holds it and laughs maniacally. However, the heart does need some intervention to keep a regular rhythm which is where electricity comes in.
The contractions of the atria and ventricles are controlled through a complex series of electrical impulses generated by the pacemaker, or in fancy terms, the sinoatrial node (SA node), a cluster of specialized heart cells. Without getting into the chemical science of how it generates an electrical impulse, the SA node fires a pulse from its spot in the right atrium that travels through the atria causing contraction until it hits the atrioventricular node (AV node in the atrioventricular septum. At the AV node there is a split second pause whilst the atria empty before the impulse shoots through a series of fibers called the bundle of His in the interventricular septum and to the Purkinjie fibers which direct the impulse up the ventricles causing contraction and ejection of blood from the heart.
Now that you know the basic anatomy of the heart. It is time to discuss what happens when things go terribly, horribly, wrong.
Types of Heart Conditions
The Merck Veterinary Manual breaks down heart conditions into roughly 6 lovely categories. These consist of:
Valvular diseases which occur from improper closings of the valves of the heart which results in improper blood flow and a “murmur”.
Myocardial diseases which cause a failing of the pump through various failings in its ability to relax or contract.
Arrythmias which loosely describes an abnormal heart rhythm. Animals with arrythmias have hearts that beat too fast, too slow, or just whenever they seem to feel like throwing in a couple extra or long lasting beats. An arrythmia can be reasonably harmless or severely disrupting to function. For instance, one of my cats has a fast heart-beat (tachycardia) that has never caused him issues in the last 12 years he’s lived while another has hypertrophic cardiomyopathy and his heart sounds roughly like a high school marching band without a conductor as it struggles to carry a tune. Remember when I mentioned the two sides of the heart are supposed to beat simultaneously? Yeah… about that.
Then there are vascular diseases in which the heart is not so much a problem as the vessels of the body. Vascular diseases incorporate conditions like hypo- or hypertension and may result from diagnosable conditions like hyperthyroidism or kidney failure.
Cardiac shunts occur when communication is lacking between the right and left sides of the heart. Often this may be due to a congenital malformation resulting in a hole in various parts of the heart. This can again be minor or severe. Some cats may be born with a small septal defect (hole between the left and right sides) that they simply grow out of as they age. This might appear as a heart murmur in a kitten that simply vanishes as they become an adult. But these conditions are always worth monitoring as if blood is sloshing between the two atria or two ventricles, guess where it isn’t going? The heart has to work that much harder to pump blood to the body and can become enlarged, it is also possible that the blood merely over circulates the lungs which can lead to the lungs becoming fluid saturated and impairs gas exchange.
Parasitism. This is one you might not typically associate with heart disease, but is relevant nonetheless and particularly so in animals. Humans are not the natural hosts of heart-worm which is why you nearly never hear of someone going into heart failure due to Dirofilaria immitis, the parasitic worm resembling spaghetti. Grossed out yet? Heart worm, left untreated matures in the blood and adult worms grow until they block the chambers of the heart, blood vessels, and basically cause a wriggling disgusting mess that must be surgically removed. Luckily it is easily prevented through regular anti-parasitic medications. Should an animal need surgical removal of heart worms, however; understand that it will suffer permeant heart damage and the outlook for survival doesn’t beget happy feelings. Heartworm is carried largely by mosquitos, which is why, especially in areas of high prevalence, it is worth spending the extra dough over the summer months for preventative medications. While most common in dogs, be aware that cats can get it too.
Heart Diseases of Cats
It is important to note that this is by no means a comprehensive list. That being said, here are some forms of heart disease in cats which I find most interesting.
Hypertrophic Cardiomyopathy (HCM)
Hypertrophic cardiomyopathy is one of the most common forms of heart disease in cats and is characterized by a thickening of the left-ventricular wall. This thickened heart muscle prevents proper relaxation of the ventricle. It is primarily caused by a defect within the muscle cells themselves and can be inherited. Breeds like ragdolls and Maine coons can be predisposed through a myosin binding protein mutation, in other cats it can be idiopathic. While many cats go undiagnosed, severe cases can quickly become life threatening. Congestive heart-failure is associated with end-stage of this disease. In terms of outlook, a cat can have anywhere from a few months to a few years after becoming symptomatic. They can develop pulmonary effusion, which essentially means that fluid fills the lungs and makes it very difficult for the animal to breath. HCM is typically treated with a diuretic called furosemide aka. Lasix, which eases fluid on the lungs, as well as ACE inhibitors which help dilate blood vessels through lessening of angiotensin II. Other drugs such as blood thinners may also be included. While the outlook is grim for severe HCM, some cats do considerably outlive their initial prognosis. In my personal experience as an owner of a cat with end-stage HCM, supplemental oxygen in addition to medications is extremely helpful. Tanked oxygen can be prescribed by a veterinarian and masks can be purchased for at home use. When needed, I usually administer oxygen to my cat using a conical shaped mask which fits snuggly over his mouth and nose at around 8-10 L/min, for 15 minutes. Check his heart rate and respiratory rate, and continue 15 minutes on 2-3 minutes off until the episode passes. As always though, check with your veterinarian for their recommendations. If you do wish to give your cat oxygen it is extremely important to do so by prescription for medical grade gas, and that you receive proper instruction on how to administer. There are other ways to administer oxygen such as with an oxygen tent. Either way, for my cat an O2 tank was the best $30 monthly subscription service I ever shelled out for.
Dilated Cardiomyopathy
Dilated cardiomyopathy is essentially the opposite to HCM. It is characterized by a thinning/stretching of the muscle and dilation of the ventricles. Luckily for most cats on professionally formulated diets it is almost eliminated thanks to the inclusion of Taurine. Cats diagnosed with DCM are often treated for taurine deficiency, however; in cases where taurine is not deficient and or it is warranted, inotropes like Digoxin may be used to improve systolic dysfunction. Systolic heart failure occurs when there is poor ejection of blood from the heart, in this case thanks to a thinning and weakened ventricular wall. Other drugs like furosemide and ACE inhibitors are also helpful in treating DCM. Similar to HCM the outlook for a diagnosed cat can vary. However, in cases caused by taurine deficiency, when caught early the disease is curable through taurine supplementation. DCM is one of the reasons why people should avoid playing with vegetarian feline diets, home-cooked diets, or alternative diets. If you do choose such a diet for your pet, it is vital that you and your vet communicate to ensure the food is properly balanced and that the animal is receiving adequate amounts of taurine.
Congenital Heart Disease
Congenital malformations are a rarer form of disease in cats as most cardiac patients acquire disease later in life. Less than 10% of feline cardiac patients have congenital conditions (Feline Cardiology 2011). Congenital conditions in cats usually take the form of ventral septal defects such as a cardiac shunt, or mitral and or tricuspid valve malformations. There are many different types valve malformations. Sometimes the leaflets may be too thick or fail to separate from the heart wall in utero, other times there may be issues with the papillary muscles. Valve malformations usually result in improper closing of the valve and regurgitation of blood. This means that rather than fully draining into the ventricles the blood may move back into the atria and will not circulate properly. Depending on severity these conditions can lead to death.
Whatever the case, congenital issues generally require an echocardiogram for specific diagnostics as it is very difficult to tell the exact malformation with radiology, or by murmur. The book, Feline Cardiology, also states that most cases are asymptomatic and do not require treatment. That being said, severe abnormalities may require surgical repair. It is worth noting that heart surgery in cats is very challenging as depending on the condition the surgeon may need to place on bypass, an organ that is roughly the size of a walnut or even smaller in a kitten.
Blocks
Simply put a “block” refers to erroneous electrical conduction within the heart. There are many different kinds of blocks. AV blocks occur when there is a prevention of electrical conduction from atria to ventricles through the atrioventricular node. A first degree block is considered mild and the cat won’t generally show any ill-effect, there is still some transmission of impulse from atria to ventricles. A third-degree block is the most severe form of block where the impulse doesn’t pass from atria to ventricles at all. The cat may or may not show symptoms like fainting or problems performing exercise if the ventricles maintain a high enough escape rate. Some cases of third degree block may require a pacemaker to be placed. Feline cardiology 2011 recommends a human pediatric pacemaker be used. Whether a pacemaker is the correct choice will depend on your veterinarian’s recommendations, your budget, and the underlying conditions that caused the block if any. For some animals if prognosis from a cardiomyopathy was already poor, it may be kinder and more cost-effective to consider euthanasia in a cat that is suffering.
Symptoms/Signs of Heart Problems in Cats
Syncope: an animal with heart issues may experience weakness or syncope. Syncope is more or less a fancy term for fainting. This can be the result of arrythmias, low oxygen saturation, as well as sudden drops in blood pressure and many other conditions. If your cat is fainting your vet may want to consider testing for heart conditions.
Cyanosis: Cyanosis is a bluish or purplish tint to the skin. It is caused generally by poor circulation and low blood oxygen. Cats with cyanosis may also have cool or cold extremities noticeable by feeling the ears or paw pads. It may be hard to notice cyanosis through fur. If you are concerned you may wish to check the mucous membranes of the gums, or the inside of the ears where there is less fur.
Exercise intolerance: You may notice your cat gets tired easily after playing or moving around, or is simply moving sluggishly when it does. It may also refrain from exercise, sleeping more often, and gaining weight. While weight gain could also be a sign that the animal is being overfed, unexplainable gains in weight or lethargy should be taken up with your veterinarian.
Difficulty breathing, coughing, wheezing: Some forms of heart disease cause shortness of breath. This may or may not have to do with fluid accumulation on the lungs. You may notice your cat panting, breathing with its mouth open, sides heaving up and down, or additional coughing. If you notice these symptoms you should be calling your veterinarian. Especially if it is accompanied by signs of discomfort like crying, pacing, or hiding. One way to check if your cat’s circulation is acceptable is to check capillary refill time. This can be done by briefly pressing a finger against the animals gum and counting the seconds it takes to return to normal coloration. If the time it takes for the mucous membrane to go from white to pink is longer than 2-3 seconds it is a medical emergency. Similarly, if your animals gums appear pale and or cyanotic, it likely isn’t getting enough oxygen. Always call your vet if you are concerned and never share human medications with an animal unless your veterinarian explicitly instructs you to do so.
Closing remarks
Thank you very much for reading. I hope you found this article informative. If you have any feedback, or questions please let me know in the comments. This article is not meant to supplement or serve as veterinary advice. I list the resources used to write this article below. Let me know what topics you’d like to hear about in the future!
References:
Aiello, Susan, and Asa Mays. “Circulatory System.” The Merck Veterinary Manual, 11th ed., Merck & Co., in Cooperation with Merial Limited, Whitehouse Station, NJ, NJ, 2016, pp. 4–145.
Colville, Thomas, and Joanna M Bassert. “14 The Cardiovascular System.” Clinical Anatomy and Physiology for Veterinary Technicians, 3rd ed., Elsevier, 2016, pp. 338–359.
Côté Etienne, et al. Feline Cardiology. Wiley-Blackwell, 2011.
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