Heart Disease: Dilated Cardiomyopathy

What is dilated cardiomyopathy?

Cardiomyopathy is degeneration of the heart muscle so that the heart, which is basically a muscle pump progressively fails.

As a result of this degeneration the muscle becomes thinner, particularly the thick muscle wall of the left ventricle whose contraction pumps blood around the body. The pressure of the blood inside the heart then allows this thin wall to stretch resulting in a much larger left ventricle and this is then described as dilated cardiomopathy.

How common is the condition?

Dilated cardiomyopathy is the most common cause of heart failure in the large breeds of dogs. These include Boxers, Dobermanns, and Great Danes. Occasionally medium sized breeds such as Cocker Spaniels, English Springer Spaniels and Miniature Schnauzers are also affected. Small breeds are only affected occasionally.

My dog suddenly seemed to get very slow and the vet says he’s got Dilated Cardiomyopathy (DCM). Can this happen so quickly?

Dilated cardiomyopathy may have a very sudden onset. Some dogs may go into severe heart failure in only a few hours. Rapid heavy breathing, a blue tongue, excessive drooling or collapse may be the first signs.

"Dilated cardiomyopathy may have a very sudden onset. Some dogs may go into severe heart failure in only a few hours."

How is the condition diagnosed?

Before a diagnosis of dilated cardiomyopathy is made, several tests are used that assess different aspects of heart function.

1.  Cardiac auscultation, which is listening to the heart with a stethoscope. This allows us to identify murmurs due to the improper closure of heart valves, their location and their intensity. In addition we can pick up abnormal heart rhythms, (arrhythmias and dysrythmias) and the stethoscope also allows us to pick up lung sounds. This aids our understanding of what is happening within the chest since with many heart conditions the lungs are also affected.

2.  Laboratory tests involve both blood and urine.  These do not give direct information about heart function but they allow us to appreciate other disorders in the body that may affect heart function and influence our treatment of the heart problem.

3.  Radiography. Chest radiographs allow us to examine the lungs and also the size and shape of the heart. Dilated cardiomyopathy usually causes very obvious enlargement of the heart, particularly the left side which is very apparent on radiograph.

4.  Electrocardiogram (ECG). This is an assessment based on the electrical activity of the heart. It allows us to accurately determine heart rate and to pin point any abnormalities of rhythm that we may have picked up on auscultation. Sometimes a heart monitor will need to be worn for 24hrs to identify intermittent cardiac events.

5.  Ultrasound examination (echocardiogram). This gives the most accurate determination of the size of each heart chamber and actually permits measurement of the thickness of the heart walls. This can be seen on the monitor and the contractions of the heart can be watched and evaluated. Certain measurements can be taken which allow the actual strength of the heart’s contraction to be measured which we can compare with the normal animal. Ultrasound equipment is now widely available in veterinary practice. 

It is the combination of all these tests that give us our best evaluation of the dog and its heart function.

What is the treatment?

There is no cure for DCM however a number of drugs are used to control the symptoms and improve quality of life.

Treatment is aimed at improving the pump function of the heart, eliminating pulmonary congestion if present and controlling the heart rate and cardiac arrhymias if present.  

Today we have a wide range of heart medications available which your vet will individualize to the treatment to your pet. It is not uncommon for dogs to require an increased number of medications as the  disease progresses.

As a result of all these tests and treatment, is there any guarantee that my dog will live much longer?

This question cannot be answered with certainty. Dogs are not people and as soon as your pet feels better he will want to continue his normal life style. Therefore if he was normally a very active or excitable dog it is important that you exercise much greater control. The results of the tests at least lead us to a positive diagnosis. The response that occurs to the drugs within the first few days gives a good indication of how much success we are likely to have.

If response does not occur within a few hours to days the prognosis is not good. Dogs that stabilise quickly often live for a period of months but long term prognosis always has to be guarded.