Dog - Heart Disease - Dilated Cardiomyopathy

What is dilated cardiomyopathy?

Cardiomyopathy is degeneration of the heart muscle so that the heart, which is basically the pumping machine of the body, progressively weakens and finally 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. This is described as dilated cardiomyopathy.

How common is the condition?

Dilated cardiomyopathy is the most common cause of heart failure in the medium and large breeds of dogs including Boxers, Dobermanns, German Shepherd dogs, Great Danes etc. Occasionally breeds such as Spaniels, (both Cocker and English) can be affected. Small breeds are rarely affected with this particular heart condition.

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.

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. Auscultation (listening with a stethoscope) is carried out first. 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 involved.
2. Laboratory tests involving 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. Radiographs. Chest x-rays 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 x-ray.
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 confirm any abnormalities of rhythm that we may have heard on auscultation.
5. Ultrasound examination (echocardiogram or ultrasonography). 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 and compared with the normal. Ultrasound equipment is now widely available in veterinary practice.

It is the combination of all these tests that gives us our best evaluation of the dog and its heart function. However to carry out a full cardiac evaluation may prove to be quite expensive.

What is the treatment?

A collection of drugs can be used to treat dilated cardiomyopathy. Initially stabilisation depends upon the use of:

1. Diuretics. These are drugs that stimulate the kidneys to remove excess fluid from the body. Frusemide is most common although there are other drugs used in certain circumstances.
2. Digitalis glycosides. These drugs improve heart function in several ways. Mainly they are used to slow the heart rate and strengthen each contraction of the heart so the blood is pumped more effectively.
3. In addition various other drugs are used, particularly enzyme blockers or so-called ACE (angiotensin converting enzyme) inhibitors. They work by reducing blood pressure and the risk of imminent heart failure. They do this by preventing the conversion of certain enzymes which have an adverse effect on the heart. Today they are one of the most powerful and commonly used groups of drugs for certain forms of heart disease, including DCM, which involve the need to decrease blood pressure.
4. Vasodilators. These drugs dilate the arteries and/or veins of the body so that the heart does not have to generate so much pressure and work so hard in order to pump the blood around the body. They are used as effective long term treatment to stabilise the patient with DCM.
5. Bronchodilators. These drugs help a lung that has been affected by a fluid build up due to the failing heart and help breathing.

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 they feel better they want to continue as before. Therefore if you have a very active or excitable dog it is important that you exercise much greater control. 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 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.