Heart Murmur Grades Don’t Always Reflect the Degree of Disease

It is recommend that an echocardiogram be performed in an animal with a heart murmur before anesthesia, if possible. Although listening to the heart for abnormal heart sounds such as murmurs or gallops is an important way to look for heart disease, this only gives you an indication that the animal may have underlying heart disease. It doesn’t necessarily tell you which type of heart disease or how severe it is.

Based on the type of abnormal heart sound, the location and the breed of animal, your veterinarian can often make an educated guess as to what type of heart disease your pet has based on what’s most likely, but this is still not definitive.

Heart murmurs in dogs are typically graded on a scale of 1 through 6, with 1 being the quietest and 6 being the loudest.

In smaller breeds of dogs, the most common cause of a heart murmur is a leak in a heart valve, referred to as chronic valvular disease. With this type of disease, the loudness of the heart murmur typically does correlate to the severity of the disease, though there are rare exceptions to this.

Larger breeds of dogs, however, can commonly get other types of heart disease — such as dilated cardiomyopathy (DCM), a disease that causes the heart muscle to weaken — or even have cancerous tumors grow in the heart. With these diseases, you can have a very quiet murmur and still have severe disease.

The fact that Buddy has a grade 2 heart murmur doesn’t really give us any indication of how serious his heart disease is. He could have very mild disease, where anesthesia wouldn’t be a problem; or he could have more significant disease, where anesthesia may be more worrisome.

An echocardiogram is an ultrasound, or a sonogram of the heart. Much like a sonogram would be performed to look at a fetus, the echocardiogram allows us to visualize the heart, assess the size of the different chambers, evaluate how well the heart is contracting, determine where the blood is flowing within the heart and evaluate the thickness of the heart walls. It even allows us to estimate the pressures inside the heart and inside the lungs.

Using this information, we can diagnose the cause of the abnormal heart sound, how severe the disease is, and what types of risks will be encountered with anesthesia. In many cases, the cardiologist can even provide your veterinarian with specific recommendations for types of medications and fluids to be used during anesthesia that would be safest for the type of heart disease your pet has.

Specifically with dental disease,  treating a pet with certain types of heart disease with antibiotics before the procedure may be recommended to decrease the risk of infections in the heart.

Ask the Vets is a weekly column published by The Record. This question was answered by Dr. Jennifer Mulz of Oradell Animal Hospital in Paramus, N.J.