Congestive heart failure occurs when the heart fails to pump enough blood, causing a fluid backup (congestion).
The four chambers of the heart contain two pumps. The left side of the heart takes oxygenated blood from the lungs and pumps it to the tissues. The right side of the heart takes blood from the venous system and pumps it to the lungs for oxygenation. If the left pump fails, fluid backs up in the lungs, resulting in pulmonary edema. If the right side fails, fluid backs up in the venous system and leaks into the body cavities. Fluid in the chest cavity is called pleural effusion, and fluid in the abdominal cavity is called ascites.
Risk factors and detection
The causes of congestive heart failure include:
Myocardial failure. These disorders of the heart muscle include dilated cardiomyopathy, infection or inflammation of the heart muscle, and drug toxicity (from the drug doxorubicin, for example).
Pressure overload. These disorders require the heart to pump against abnormally high pressure, causing it to fail. They include high blood pressure, heartworm infection, and abnormal narrowing (stenosis) of the heart valves.
Volume overload. These disorders require the heart to pump too much blood to meet the tissues' metabolic demands. They include congenital heart and valve defects, impaired heart valve functioning, anemia, and hyperthyroidism.
Impaired filling of the heart chambers. These disorders prevent the heart chambers from filling, and include hypertrophic cardiomyopathy; restrictive cardiomyopathy; and pericardial disease, a disease involving the protective sac-like structure surrounding the heart.
Congestive heart failure can affect any age and breed of dog. However, older (10- to 12-year-old) small-breed dogs are more susceptible to mitral valve insufficiency, a common cause of heart failure. In this condition, the valve between the heart's two left chambers doesn't work properly, allowing blood to seep backward.
Large-breed dogs are at increased risk for dilated cardiomyopathy, an abnormality of the heart muscle. Outdoor dogs and those not receiving a heartworm preventive are at high risk for heartworm infection. Any condition that increases the heart's workload, such as hyperthyroidism, anemia, high blood pressure, lung disease, and obesity, raises the risk of congestive heart failure.
Signs of congestive heart failure include:
- a moist cough, especially at night
- rapid or labored breathing
- inability to exercise
- a blue tint to the gums
- a distended abdomen
- lethargy
- unexplained weight loss.
If you notice signs of congestive heart failure in your dog, see your veterinarian immediately. Your doctor will perform a complete physical examination and may use blood tests, X-rays, ultrasound (echocardiography), and an electrocardiogram (ECG) to determine the cause and severity of the problem.
Prevention and treatment
Although you can't always prevent congestive heart failure, you can minimize the risk by exercising your dog, feeding him a balanced diet, helping him maintain a healthy weight, and administering heartworm preventive. Routine examinations will help your veterinarian detect and treat heart problems in their early stages.
If your dog develops congestive heart failure, your veterinarian will tailor a treatment program to meet your dog's needs. Treatment may include a diet change and administration of diuretics, positive inotropic drugs, or vasodilators. Switching to a salt-restricted food will reduce fluid retention and reduce the heart's workload. Your veterinarian can recommend one of these therapeutic diets or recipes for low-salt food you can prepare at home.
Diuretics cause the kidneys to remove excess fluids from the body, reducing the heart's workload and decreasing congestion. The most commonly used diuretic is furosemide. If furosemide alone doesn't work, your veterinarian may add other diuretics, such as spironolactone and chlorothiazide.
Positive inotropic drugs make the heart pump more effectively, usually by increasing the heart muscle contraction. The most commonly used positive inotrope is digoxin. Because the therapeutic dose is only slightly lower than the toxic dose, veterinarians must closely monitor patients taking this medication. Other positive inotropes are dopamine and dobutamine.
Vasodilators relax the muscles of the blood vessels, reducing the pressure against which the heart must pump. Examples of vasodilators are enalapril, captopril, hydralazine, prazosin, and nitroglycerin.
Depending on the nature of the heart disease, other treatments may include oxygen therapy, bronchodilators, antiarrhythmia medications, taurine supplementation, potassium supplementation, and anticlotting medications. If your dog has fluid in his chest cavity, your veterinarian may drain the fluid to ease the breathing and make your dog more comfortable.
Veterinarians can't cure many cases of congestive heart failure, but with proper medical management your dog can lead a good-quality life.
