Dr. Anna Dunton-Gallagher
OFF THE LEASH
Valentine’s Day may be over now, but that just means all the candy is on super sale. While we stock up on truffles and caramels in heart-shaped boxes at 70 percent off, let’s think a little bit more about our animals’ hearts. I will go over a couple of common diseases that you can think about while you eat chocolates.
Our pets do not get “heart attacks” like people do, but many of them have heart disease that affects the quality and length of their life. Pets can have heart disease for many years before owners even know. Since our pets cannot tell us that they have mild chest pains, disease is found either on physical exam or when symptoms get so severe that they impact life. Heart disease develops not from diet, but from genetic factors and simple wear and tear. Though we would likely see some of the same problems in pets that people have if we didn’t control their diet, luckily even our overweight pets get a fairly balanced diet. Some pets are even born with heart disease. I’ll talk about the most common types in cats and dogs, and signs to look for that may help them be diagnosed sooner.
Chronic valvular disease
Many heart changes in dogs are detected first as heart murmurs, which is a good reason to have a yearly exam. We hear murmurs whenever the blood flow in the heart is changed. Instead of a steady whoosh-whoosh, we can hear the turbulent blood flow which interrupts this smooth beating cycle. The most common cause of heart failure in dogs is chronic valvular disease. In this, the valves between the sections of the heart start to wear out. They start to thicken and change so that they no longer meet in the middle. Instead of being a “watertight” seal, blood leaks through the gaps in these valves.
This blood creates little whirlpools of blood flow. If you think of a fast moving river, the water flows until it hits a point that creates some turbulence. Just like rocks will start to erode and change when water hits them continuously, the muscle starts to change where the blood hits it. The edge of the heart will start to enlarge to accommodate the extra flow. This is especially common in small-breed, pure-bred dogs, but can happen in any dog. Therefore, we see the valves get shorter and thicker while the heart muscle changes where the blood jet hits it.
Dogs also get something called dilated cardiomyopathy. In this disease, the walls of the heart become thin and the heart distends so it is larger than normal. You can think of a balloon that has been stretched a lot. The walls aren’t as strong, so every time the heart beats it contracts less than it should. Because of this, more blood stays in the heart and less is circulated to the body. We then see a shortage of oxygen to the brain and a backup of fluid in the lungs. This can present as exercise intolerance, coughing, or a distended abdomen. This is seen more commonly in large-breed dogs and usually happens over time, though Great Danes and Dobermans are more likely to have this as a congenital (born with it) problem.
We can also see dilated cardiomyopathy secondary to other changes. This happens as the heart responds to extra blood by “stretching” out. Dilated cardiomyopathy that is genetic and happens in young dogs is more difficult to treat, while when caught as an older-age secondary change, the earlier we see it the more effective our therapy can be.
Hypertrophic cardiomyopathy (or HCM) is the cat version of older-age changes. As sometimes happens, our cats like to do things exactly opposite of the dogs. This means that instead of the heart walls becoming thin, they become very thick. This leaves less space inside the heart for blood, and the heart walls do not contract effectively. This type of heart failure is often related to hyperthyroidism, but can also occur by itself. Unlike heart changes in dogs, this is not heard as easily with a stethoscope in most cases. Because of the way the heart beats, cats with HCM are more likely to develop clots which travel throughout their bodies. These can cause problems in the lungs, brain, abdominal organs or often cause hind-limb paralysis.
When we diagnose HCM secondary to hyperthyroidism, we can stop the changes by treating the thyroid. The earlier we control the thyroid the less of a chance it has to create heart changes. Because it isn’t always heard on physical exam until later stages, this is one reason that thyroid hormone is checked in routine feline wellness bloodwork.
The common thing to all types of heart disease is that the heart cannot function as well. Whether the heart can’t beat as well or isn’t holding as much blood volume, we start to see changes in our pets.
Heart disease can result in many different signs. Animals can become weak, less tolerant of exercise, and even collapse or “pass out” for a moment. You may also see a bloated abdomen. Since the heart also pumps blood to the lungs to become oxygenated before sending it to the body, fluid can build up in the lungs from ineffective pumping. Signs of this include coughing, panting and struggling to catch their breath after simple activity.
If a murmur is heard in a pet, usually the next step is to take chest x-rays. It is ideal to get a cardiac ultrasound (or echo) on them. This lets us see the thickness of the heart walls at every point, the function of the valves, and how the blood flows through the different parts of the heart. In this manner, we can more easily pinpoint the exact area of compromise and treat accordingly.
There are other rare heart disorders that pets can acquire or be born with. When pets are in utero, their hearts have holes in the walls because they don’t pump their own blood (the mother does this for them). Sometimes these holes can fail to close at birth. There are other very rare defects that can happen, but in general those animals do not survive the birthing process. If they do, these are usually heard as murmurs at an early veterinary visit. Many of these can be surgically or medically managed to some degree.
All types of heart failure can be treated with varying success. The earlier they are detected, the better chance there is of helping to prolong the animal’s life. There are medicines that help the heart beat faster, slower or stronger. There are also medications that help regulate blood pressure changes and fluid changes that might be associated with heart failure. Anytime you notice coughing, exercise intolerance, weight or appetite changes, it is important to get an exam. It is also important to make sure we are checking cats’ thyroid levels and blood pressures as they start to reach older age. The earlier we find heart disease the better, and you are an important piece in that puzzle, since you are the ones who see your pet every day.