This week I’d like to tackle one of the types of canine heart disease. It’s fairly common, with a few breeds particularly at risk. Before we dig in, though, I want to put up a couple of links that you might find interesting and helpful if you’re still feeling a little overwhelmed by the heart and its physiology.
This link leads to a really neat animation of the heart. It shows the flow of blood into the various chambers, the contraction of the chambers, and the flow of blood out of the chambers. Valves are shown opening and closing. There are also two graphs that show pressure in the various chambers during the contraction cycle and the EKG tracing as it relates to the various chambers.
This page is full of cardiology and respiratory cases. It’s pretty technical stuff, but it was too neat not to share. If you’ve got an interest in cardiology, it’s a great resource.
Now, onward to Canine Dilated Cardiomyopathy.
Dilated Cardiomyopathy (DCM) is a disease in which the muscle walls of the heart chambers become weak and gradually lose the strength in their contractions. When this happens, the pressure in the heart and the blood vessels of the body causes the chambers to stretch even further. The whole heart enlarges in the chest cavity. This is the exact opposite sort of change from what occurs in cats with HCM. When the heart chambers enlarge like this, the valves aren’t able to close completely, so blood flows backwards when the heart contracts. This makes a murmur occur in the heart, which we can hear through the stethoscope.
Just as with cats, the blood doesn’t flow the way it’s supposed to and pressures start to back up. In dogs with DCM, both the left and right side of the heart can fail simultaneously. Heart failure causes fluid to start building up in one or both of two places.
Dogs with DCM can have fluid build up in the abdomen because of the right sided failure. Fluid in the abdomen is called ascites. The abdomen will become distended/enlarged. Dogs may have trouble breathing because of the pressure on the diaphragm. I’ve had a few DCM patients vomit, too, or not want to eat.
DCM will also cause fluid leak into the lungs themselves because of left sided failure. This fluid buildup is called pulmonary edema. (It’s different than cats, which fill the chest cavity with fluid.) When fluid fills up the little spaces in the lungs that are supposed to have air in them, dogs can’t get oxygen into their blood. This causes very severe problems, and is often the cause of death in dogs with DCM. Dogs suffering from pulmonary edema will cough, breathe heavily, or even have their lips/tongue turn a bluish color.
The radiograph below shows a normal dog’s chest from the side. (Sorry about the gray labels – I don’t know why they weren’t in color like they should have been! ) Take note of the angle between the two lines labeled “spine” and “trachea.” Those lines should get closer together toward the front of the dog, where the arrowheads point. Notice also that the lungs are nice and dark, just like air should be on a radiograph. The branching white lines in there are blood vessels in the lungs.
The next radiograph shows a dog with DCM. Notice how big and round the heart looks. Also, notice the two lines for spine and trachea — they’re much closer to being parallel instead of coming together. This means that the heart has enlarged and has pushed the trachea up from underneath. The lung fields have lots of white fluffy looking stuff in them. That white fluffiness is fluid in the lungs themselves — pulmonary edema. The lungs are being flooded because of pressure backup in the heart and blood vessels in the lungs.
The next couple of radiographs show you a side and top-bottom view of a dogs’s chest that has DCM. The heart is HUGE and round. This dog does NOT have pulmonary edema, so the lungs still look pretty clear. No white fluffy stuff.
The breeds that are prone to this type of heart disease include Doberman Pinschers, Boxers, Irish Wolfhounds, Great danes, St. Bernards, and Cocker Spaniels.
Some of the signs that owners may notice are: not able to exercise like as much as before (exercise intolerance), coughing, weight loss, lethargy, abdominal distention, fainting, weakness, not eating, shock, and sudden death.
Radiographs of the chest can give an initial diagnosis, but an ultrasound of the heart is essential to see how much muscle function is left, and later to see if treatments are helping at all.
If DCM is discovered before it’s too severe, there are medications that can be given to help the heart contract better and to help prevent failure from building fluid up in the lungs/abdomen. Patients can also develop abnormalities in the way the heart contracts (arrhythmias) that are dangerous and sometimes difficult to manage.
Unfortunately, DCM is a progressive disease that we lose the fight with. The life expectancy is as little as 6 months or as long as 24 months. Dobermans tend to do worse and often live 6 months or less.
There’s some debate in the veterinary community about whether we have ways to detect DCM before it’s actual heart failure and the dog is in severe trouble. Different breeds go about DCM differently enough that one single method won’t catch all dogs of all breeds who have DCM. Anything from a 24-hour EKG to an annual ultrasound has been suggested, but it really comes down to two things: Will the screening help the patients live better quality lives for a longer period of time, and can the owner afford the diagnostics? Cost is obviously up to the owner. Whether we can help these patients remains uncertain. In some cases, we may not make any difference at all. In others, I believe we can help these patients have much better quality of life for the time they have remaining. No matter what, it’s well worth trying to treat as long as the patient can be returned to a reasonable quality of life.
Thanks for reading!