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Heart disease in dogs and cats

October 16, 2022 at 4:00 a.m.

Our dogs and cats can experience several forms of heart disease. The cause for heart disease can be either congenital (a defect the animal was born with), or acquired (develops over time). This article will focus on the most common forms of acquired heart disease: valvular disease and cardiomyopathy.

Valvular heart disease is the most common form of heart disease I see in practice. Most often, this form of heart disease occurs in senior pets, but can be diagnosed in animals of any age. Valvular disease is usually acquired, meaning the animal was not born with a defect, rather the defect developed over time. To understand this form of heart disease better, an explanation of the heart valves' normal function will be helpful. The heart is divided into four chambers: the left atrium, left ventricle, right atrium, and right ventricle. Valves are present within these chambers to make sure blood flows in the proper direction. As the heart pumps, valves open to allow blood to flow out of their chamber, then seal tightly to keep the blood from returning in a backward direction.

With age or with certain forms of infection or exposure, heart valves can weaken. Instead of sealing tightly, they are flimsy or floppy. This allows some blood to flow backward and remain in the chamber it should have left. The result is that the affected heart chamber now has to hold the new blood that was just pumped in and the old blood that flowed back into it. The chamber will stretch or enlarge to accommodate the extra blood. As it stretches, the muscle wall weakens. The chamber is not able to squeeze (pump) as strongly. So now, it holds additional blood and has difficulty emptying. This process causes a swishing sound, or murmur, that your veterinarian will hear during your pet's exam.

The severity of valvular disease is determined by the "grade" of the murmur, the progression of symptoms, etc. If a heart murmur is found on exam, your veterinarian will recommend additional testing, such as X-rays, EKG readings, blood pressure measurement, and/or ultrasound of the heart. This helps to identify which valve is affected, to better stage the severity of disease, and determine which, if any, medications are needed at the time. Animals can live normal lives with a heart murmur, but it is possible for them to develop Congestive Heart Failure over time. Keeping up with vet visits, testing and treatment recommendations will help to prolong the health of the heart for as long as possible.

Cardiomyopathy is present in two main forms in animals -- dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM). The dilated form (DCM) is known to be prominent among certain breeds of dog (Boxers, Doberman pinschers, Great Danes, Cocker Spaniels, and others). With DCM, there is a weakening in the muscle wall of the ventricle chamber of the heart. The result is the inability of the ventricle to squeeze when the heart pumps, which means it cannot push enough blood out of the heart to the body. The body's response comes from the kidney to retain water to increase the blood volume. The increase in blood volume causes the ventricle to stretch to hold the additional load. Heart failure can develop over time, and this disease can be fatal. DCM can be inherited, or can be associated with diet or nutritional deficiency. Symptoms include fast heart rate, fainting or collapse, coughing, etc. Testing as listed above will be recommended if your veterinarian suspects DCM.

hypertrophic cardiomyopathy (HCM) is most often seen in cats. HCM can arise from genetic mutations, and can be inherited. The problem occurring in this disease is a thickening of the muscle wall within the ventricle chamber of the heart. As the muscle thickens, the heart chamber cannot relax properly in between pumps of the heart. Without relaxing, it cannot accept blood trying to enter from the atrium to the affected ventricle. This causes a traffic jam for the blood. Blood builds up instead of flowing through the circulatory system, blood vessels stretch to hold the extra blood, and the stretched-out vessels leak fluid that accumulates in and around the lungs, causing congestive heart failure. Cats affected by HCM may or may not show any noticeable symptoms until it becomes obvious they are experiencing heart failure. Increased respiratory rate or difficulty breathing is the most common reason cats are brought in to the vet's office when affected by HCM. A somewhat strange consequence of HCM is the development of blood clots that can cause paralysis of the back legs. This happens suddenly and can be very painful and distressing to the cat.

At this time, there are medications used to help a cat with HCM, but there is no cure for the disease. The changes to the heart and thickening of the muscle cannot be reversed, but we may be able to help prolong the current function of the heart. The prognosis varies from cat to cat, depending upon the severity of the disease and the cat's response to medications. Testing is similar to that mentioned above. In addition, we will also test for Hyperthyroidism, another cause for thickening of the ventricle.

The common occurrence of the many different types of heart disease in animals makes it so important for them to receive regular examinations. In the early stages of disease, we are not likely to see symptoms at home. Unfortunately, by the time many pet owners realize their little buddy is sick, irreversible damage may have occurred. With timely diagnosis and proper treatment, we can help the heart to function longer, and even reduce symptoms in many cases.

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