What is congestive heart failure?
Congestive heart failure (CHF) refers to the heart's inability to pump adequate blood to the body. There are many causes of CHF in dogs. The two most common causes are as follows:
- mitral valve insufficiency (MVI). MVI is a leaky mitral valve, which is the valve between the left atrium and the left ventricle.
- dilated cardiomyopathy (DCM).
For further information about these specific causes, see the handouts "Dilated Cardiomyopathy in Dogs" and "Mitral Valve Disease in Dogs".
Clinical signs of CHF vary depending on whether the dog has left- or right-sided heart failure.
What is the difference between right-sided and left-sided CHF?
Right-sided congestive heart failure (RS-CHF) causes blood to back up in the vessels that are returning to the heart..In other words, when the heart contracts or pumps, instead of the right ventricle pushing the blood through the lungs for oxygenation, some blood leaks backwards through the tricuspid valve (the valve between the right atrium and right ventricle) and into the right atrium. This blood backs up into the systemic circulation (the main circulation of the body) and becomes congested. When blood vessels become congested, it increases pressure on the vessel walls and, to relieve the pressure, fluid from the blood leaks out of the vessels and into the surrounding area.
In right-sided heart failure, blood accumulates in the vessels of the abdomen, interfering with the function of organs in these areas. The abdomen may fill with fluid, a condition called ascites. Fluid may also leak from veins in the limbs, causing swelling known as peripheral edema.
In left-sided congestive heart failure (LS-CHF), when the heart contracts or pumps, instead of the left ventricle pushing the blood into the systemic circulation, some blood leaks through the mitral valve back into the left atrium, and then it backs up into the vessels of the lungs. Fluid then seeps into the lung tissue, resulting in pulmonary edema. This condition causes coughing, difficulty breathing, and decreased energy due to a reduced ability to absorb oxygen. LS-CHF is the most common form of congestive heart failure. The classic signs of heart failure, coughing and fluid in the chest, are most commonly caused by LS-CHF.
Is CHF due mainly to heart valve disease?
CHF is most caused by valvular insufficiency (inability of the valve to work properly). It is estimated that 80% of CHF cases in dogs are caused by MVI. However, there are many other causes, such as disease of the heart muscle (cardiomyopathy), irregularities of rhythm, and narrowing of some of the major blood vessels. Initially, MVI results in left-sided congestive heart failure.
If left untreated, the heart failure may progress to involve both sides of the heart.
What clinical signs should I expect?
The most common clinical sign of CHF is persistent coughing accompanied by difficulty breathing. This is due mainly to pulmonary edema or the accumulation of fluid in the lungs. Many dogs with CHF will tire out more easily, have reduced stamina, and do not engage in playing or walking as they once did. Other signs associated with heart failure include coughing when at rest or sleeping, an increased resting respiratory rate or excessive panting, persistent loss of appetite, a swollen belly, and pale or bluish gums. The dog will develop generalized weight loss and muscle wasting due to the effects of CHF on other body systems. If any of these signs develop in a pet with a heart murmur, notify your veterinarian immediately.
Do dogs have heart attacks?
In humans, a heart attack usually refers to myocardial infarction (MI). Myocardial infarction is death of the cells in an area of the heart muscle or myocardium. Cell death is usually due to oxygen deprivation caused by obstruction of the coronary blood vessels that supply blood to the heart muscles. Heart attacks are rare in dogs, but unexpected and sudden death in dogs diagnosed with any form of heart disease is possible.
Is there a way to detect CHF early?
Although CHF can sometimes present acutely, there are often subtle changes that may be observed before more severe signs occur. Your veterinarian may recommend you monitor your pet’s resting respiratory rate (RRR). This is a measure of the number of breaths they take when they are sleeping or resting quietly. By doing this several times over a week, you will learn your pet’s average RRR and, by continuing to check it as often as your veterinarian recommends, you can identify changes in your pet’s need for oxygen. A significant increase, even within normal range for an average dog, should be reported to your veterinarian; they may recommend additional testing to detect early CHF.
How is CHF diagnosed?
As with any heart problem, diagnosis involves several tests.
- Auscultation or listening to the heart with a stethoscope is the first step in diagnosing heart disease. Heart murmurs are detected by auscultation; the murmur's location and intensity help determine its significance. The heart rhythm is assessed and, if there are concerns, the veterinarian may simultaneously palpate or feel the pulse to determine its strength and rhythm. Finally, the lungs are assessed, looking for evidence of changes associated with heart failure. Your veterinarian may also observe the veins in your dog’s neck to see if they are distended with and without pressure on their abdomen.
- Chest X-rays are taken to evaluate the size and shape of the heart and look for lung changes such as the presence of fluid.
- Blood and urine tests are performed to give an indication of any other disorders in the body. Liver and kidney function are often impaired in patients with heart disease.
- An electrocardiogram (ECG) measures the electrical activity of the heart and allows accurate determination of both heart rate and rhythm. Any persistent abnormal rhythms (arrhythmias or dysrhythmias) can be detected and evaluated.
- Ultrasound examination (echocardiogram) uses ultrasound waves to evaluate the heart. The size and thickness of each heart chamber can be evaluated, and the effectiveness of the heart’s contractions can be directly observed. Measurements can be taken to evaluate the heart’s pumping efficiency.
Can't you treat my dog without these tests?
Accurate diagnosis gives your veterinarian a much better guide to the type and extent of treatment necessary. Today, there is a wide selection of heart medications that can be used to treat congestive heart failure and the treatment regime must be tailored for each patient. Without these tests, your veterinarian is unable to determine the optimal treatment for your pet and may inadvertently cause more harm than good. With proper treatment, many dogs can live a normal life for many months to years.
