Congestive Heart Failure (CHF) is the most common heart condition in dogs. It is usually diagnosed in ageing pets. When the heart is no longer able to pump out the volume of blood it receives, fluid starts to accumulate in the body – in particular in and around the lungs and in the abdomen – causing congestion of the circulatory system and various organs. While inherited heart anomalies occur in a number of dog breeds, they are much less common than CHF.
Basic heart facts
The heart is a hollow, muscular organ with four chambers – the left atrium and ventricle, and the right atrium and ventricle. Between each atrium and ventricle is a one-way valve. Blood returning from general circulation via the veins (oxygen-depleted venous blood) enters the right atrium, moves through the tricuspid valve into the right ventricle and from here it is pumped straight to the lungs to be oxygenated. The oxygen-rich blood returns from the lungs to the left atrium, travels through the mitral valve into the left ventricle and from here it is pushed throughout the body via the arterial system.
What causes congestive heart failure?
There are many causes of CHF in dogs. The two most common are mitral valve insufficiency (MVI) and dilated cardiomyopathy (DCM). Depending on which side of the heart is affected, symptoms will help determine if the pet has left-sided or right-sided congestive heart failure – left-sided congestive heart failure is by far the most common heart condition in dogs.
If left untreated, heart failure can progress to involve both sides of the heart.
- Mitral valve insufficiency (MVI)
It’s estimated up to 80% of CHF in dogs is caused by mitral valve insufficiency. The mitral valve is the valve between the left atrium and the left ventricle. Normally the heart pumps blood from the left ventricle out into general circulation. If the mitral valve becomes weak and starts to leak, some blood will find its way back up into the left atrium causing a back-up of fluid in the lungs (pulmonary oedema).
- Dilated cardiomyopathy (DCM)
Cardiomyopathy is a term describing degeneration of the heart muscle. There is no known cause for the most commonly-diagnosed cases of DCM. Seen more frequently in larger breeds of dogs (whereas MVI occurs more in small dogs), DCM results in weaker heart contractions and poor pumping ability. As the disease progresses, the heart chambers become larger, the heart muscle thinner, and blood leaks back through the valves into the atria causing a build-up of fluid and congestive heart failure.
On the left, normal thickness of the muscle walls of left and right ventricles. Compare this with the diagram on the right of dilated cardiomyopathy (DCM), showing dilatation and enlargement of both atrial and ventricular chambers and thinning of the ventricular walls. Note the DCM heart has also increased in overall size compared to the normal heart on the left. Image courtesy www.bichonhealth.org.
Clinical signs of CHF vary depending on whether the dog has left or right-sided heart failure, but the most common signs relate directly to the accumulation of excess fluid – that is, decreased stamina, coughing and difficulty breathing.
The pulmonary oedema (fluid in the lungs) from left-sided heart failure causes a persistent moist cough and rapid, difficult breathing, often most noticeable when the pet is at rest or during exercise.
In right-sided CHF, fluid accumulates in the abdomen leading to a swollen belly, and fluid in the thoracic cavity around the lungs causes a gagging cough. Most CHF patients, regardless of whether they have left or right-sided failure, will become weak, have less energy, are disinclined to exercise and may have a poor appetite.
When our vets are presented with a dog showing signs typical of CHF, their first step is to listen to the heart and chest with a stethoscope. This identifies any heart murmurs, irregularities in the heart beat and ‘crackling’ caused by fluid in and around the lungs. Heart murmurs are caused by the turbulence created when blood leaks back through the weakened mitral valve into the left atrium.
Chest x-rays are an important next step. Because the heart has to work harder to push blood around the body, the heart enlarges as it tries to cope and the abnormal size and shape of the heart is easy to demonstrate on x-ray. X-rays can also show changes in lungs when pulmonary oedema is present.
Blood and urine tests will assess the liver and kidney, organs that are often impaired in CHF (fluid can also back up into the liver). Other diagnostic tests include electrocardiogram (ECG) and ultrasound examinations, and testing for heartworm is essential if the pet has spent time in areas where heartworm is prevalent.
It’s important to understand that treating congestive heart failure is all about managing the condition. CHF can’t be cured, but with the correct diagnosis, an individual treatment plan can be developed for pets with congestive heart failure that will ease their symptoms and improve their quality of life.
The aim of any CHF therapy is to ease the clinical signs, decrease the work load on the heart and, at the same time, help the heart ventricular muscle pump more efficiently to increase the amount of blood being pumped to the lungs and the rest of the body. The excess fluid needs to be cleared from the lungs in particular, and from other affected organs.
This requires a careful balance of medications and the sooner a management and treatment plan is instituted, the better the long term prognosis.
Modifying your pet’s diet and limiting the amount of dietary salt is a critical component of management. At CVH we have excellent prescription diets for pets with CHF.
CVH vets treat a significant number of dogs with CHF and, with the assistance of their owners who monitor symptoms to enable us to carefully balance medications, congestive heart failure patients can live for many years with a good quality of life. Regular communication between vets and owners is critical as often simple changes in medication can make a real difference to the pet’s comfort and longevity.