Dr. Anna Dunton-Gallagher
OFF THE LEASH
February is just a day away, and this month brings a lot of topics to write about. February is pet dental health month. While dental health is always important, this is a great time to emphasize it. February brings thoughts of hearts at Valentine’s Day. As a normal vet, hearts lead me to think about both heart disease and heartworm disease. Since it is (human) American Heart Month (proving that human doctors also have their share of weirdness) I will start with hearts. Pets rarely get heart attacks in the way that humans do, but their hearts undergo changes that can lead to issues. Most commonly, heart issues begin with a murmur that is found on physical exam. However, sometimes heart issues can present without a pet ever having had a murmur before. Additionally, some murmurs cause no harm and aren’t a worry unless they progress.
We have found several heart issues on routine physical exam; the rate, rhythm, synchronicity and extra noises all alert us to problems. We often look at an x-ray of the chest to measure the size of the heart, look at vessels and the surrounding lung. The next step is an ultrasound of the heart, or an Echo.
Echocardiograms let us look at the thickness of the heart wall, the volume of each chamber, the input and output from the heart, the sac surrounding the heart, the valves and the velocity that the blood flows. All of these parameters not only help us confirm a diagnosis, but also figure out an accurate treatment plan.
Dogs get something called dilated cardiomyopathy. This is especially common in Dobermans and Great Danes, though can be found throughout dogs. 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.
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. Cats can also get DCM, though theirs is almost always secondary to a nutrient deficiency. This is why any non-commercial cat food needs to be carefully monitored for levels of taurine.
Hypertrophic cardiomyopathy (or HCM) is the cat version of older age changes. As often happens, our cats like to do things very different from 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. In some cats this is a congenital disease, which means that they are born with abnormal heart muscles. These then worsen with time until they start to cause issues.
When we diagnose HCM secondary to hyperthyroidism, we can stop the changes in the heart 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.
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 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.
The one common thing to all types of heart disease is that the earlier we can treat the changes, the better your pet’s life will be. We can sometimes slow the progression of the disease down, and can always improve their quality of life by helping alleviate the symptoms.