Like their human companions, animals can suffer from heart disease.
The most common type of heart disease we see in dogs involves degeneration of the valves of the heart.
It is more common in some breeds, for example, cavalier King Charles spaniels, dachshunds and miniature and toy poodles.
The heart disease I see in practice tends to involve the mitral valve, which regulates flow to the left side of the heart, but sometimes involves the tricuspid valve, which regulates flow to the right side of the heart.
Over time, dogs with degenerative valve disease develop thickened, nodular heart valves that no longer form a proper seal when they close, allowing blood to leak.
This changes the dynamics of blood flow, causing a sound called a “heart murmur”.
Not all heart murmurs indicate disease.
They may occur in young animals (a juvenile murmur), but disappear as they grow up.
Or they can be due to other causes, such as a very fast heart rate with excitement or fear.
These “innocent” heart murmurs are not associated with clinical signs.
Heart murmurs are graded on a scale from one to six, reflecting how loud the murmur sounds when listened to via a stethoscope.
Grade 1 murmurs are challenging to hear, whereas grade 6 murmurs are very loud.
In the early stages of degenerative valve disease, the heart compensates for the leaking by working harder.
The heart may increase in size.
This can lead to a cough as the enlarged heart pushes up against the trachea or windpipe.
In the later stages, the heart can no longer compensate.
This leads to an accumulation of fluid in the lungs, which can lead to a soft cough.
Fluid may also build up in the abdomen, causing an enlarged belly.
This is known as heart failure, and it is life-threatening.
Signs of heart disease include fatigue, reduced willingness to exercise, weakness, a decreased appetite, laboured breathing, coughing and sometimes fainting which can look a bit like a seizure or fit.
The sign that owners seem to notice most is coughing.
It can be challenging to determine if a cough is due to heart disease or respiratory disease.
Some older dogs suffer from both.
Therefore it is important that dogs presenting with a cough have chest x-rays.
These give your veterinarian a good look at the size and shape of the heart and its associated vessels, as well as the lungs and airways.
Blood tests can be helpful in evaluating the systemic health of a dog, and in looking for hormonal markers of heart disease.
An echocardiogram, which is an ultrasound examination of the heart, provides a detailed view of the heart valves, chambers and vessels, and can be useful in staging heart disease.
We are fortunate that there are very effective medications available to manage heart disease, usually given in the form of tablets or liquids.
These can help the heart pump more effectively, and reduce accumulation of fluid in the body.
Dogs treated for heart disease should have more frequent check ups (every three to six months or more frequently as needed).
Repeat diagnostic tests may be performed to monitor progression of the disease and to guide therapy.
Owners can also monitor their dog’s sleeping respiratory rate, or the number of times the chest rises and falls, over a one-minute period.
The sleeping respiratory rate should be less than 30.
REFERENCE: Keene, B.W.; Atkins, C.E.; Bonagura, J.D.; Fox, P.R.; Hggstrm, J.; Fuentes, V.L.; Oyama, M.A.; Rush, J.E.; Stepien, R.; Uechi, M. Acvim consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. Journal of veterinary internal medicine 2019, 33, 1127-1140.
Dr Anne Quain BVSc (Hons), MANZCVS (Animal Welfare), Dip ECAWBM (AWSEL) is a lecturer at the Sydney School of Veterinary Science and a practising veterinarian.