Heart Disease: Congestive Heart Failure

What is congestive heart failure?

When the heart fails to pump sufficient blood around the body it tries to compensate by changing the rate and sometimes the strength of contractions. This sometimes improves the situation and symptoms virtually disappear. However without treatment the condition will slowly get worse. Pooling of blood in the organs and tissues of the body leads to signs of congestion. The animal will be said to have ‘decompensated’ and to have developed congestive heart failure.

Clinical signs vary depending on whether the dog has left or right sided heart failure. This usually involves failure of the valves of the heart although sometimes the muscle can be involved.

What is the difference in the signs?

With right sided heart failure there is a poor venous return to the heart. In other words, when the heart contracts instead of the right ventricle pushing the blood through the lungs for oxygenation some returns to the right atrium and thus blood is unable to be cleared from the systemic circulation which consequently becomes congested. Accumulations of fluid occur in the abdomen interfering with the function of the organs in these areas. The abdomen may become enlarged due to fluid and this is called ascites, or dropsy. Sometimes fluid also leaks from the thin walled veins and swelling may appear in the limbs in severe cases (this is called peripheral oedema). Fluid may also accumulate in the chest cavity (pulmonary effusion).

With left sided heart failure, when the heart pumps, instead of the left ventricle pushing the blood into the systemic circulation, some leaks throught the mitral valve back into the left atrium and and then backs up into the the lungs. This  causes fluid to seep out into the lung tissue. This fluid build up in the lungs is known as pulmonary oedema. This causes coughing and breathing difficulties. Left sided heart failure is the most common form of congestive heart failure.

"Accumulations of fluid occur in the abdomen and/or the chest cavity, interfering with the function of the organs in these areas. The abdomen may become enlarged due to fluid and this is called ascites, or dropsy."

What causes congestive heart failure in dogs?

There are many causes. The two most common causes are mitral valve insufficiency and dilated cardiomyopathy (for further information see handouts Heart disease 1 and Heart disease 2). Other causes include irregularities of rhythm and narrowing of some of the major blood vessels.

Do dogs have heart attacks?

In humans, a heart attack is more strictly myocardial infarction (MI). This is death of the cells of an area of the heart muscle (myocardium). This is usually due to oxygen deprivation caused by obstruction to the coronary vessels. It is not a common disease in dogs but it can occur. Unexpected and sudden death in dogs diagnosed with any form of heart disease is possible.  

What signs should I expect?

CHF usually results in coughing, exercise intolerance, general lethargy, weakness and often weight loss although the dog may develop a big abdomen due to the ascites or dropsy. The normal pink colour of the mucous membranes (for example inside the lips or under the eyelids), may become pale or even a bluish colour.

How is the condition diagnosed?

As with any heart problem, diagnosis involves what is known as a ‘full work-up’. This includes blood and urine tests to establish that there is not a problem in other organs, particularly the liver and kidneys. Auscultation which is listening to the heart with a stethoscope, will detect abnormalities of the valves (murmur) and also irregular rhythms. Radiography which will give an indication of changes in the heart size or shape as well as the state of the lungs; and ultrasound examinations which allow us to examine the heart in motion and, if necessary, take measurements which gives a very accurate diagnosis of heart function. An electrocardiogram (ECG) is used to assess the electrical activity of the heart and abnormalities of heart rhythm.

Are these tests likely to be expensive?

Unfortunately a full work up can cost several hundred dollars but, depending on the condition, and its severity, sometimes only selected tests are necessary.

Is it not possible to treat my dog without these tests since surely it is better to spend the money on treatment?

Accurate diagnosis gives us a much better guide to the type and extent of treatment necessary. Today there are a wide selection of drugs that can be used to treat congestive heart failure and treatment regimes have to be tailored for each animal.

Correct treatment, although not curative, may stabilize the dog and many animals are able to live a normal life often for months or years. If you would like to discuss this further, please do not hesitate to contact us.