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Dog: Heart Failure

General information

Other common/scientific names: congestive heart failure, cardiomyopathy

The heart is a muscular organ responsible for pumping oxygenated blood to the body and receiving unoxygenated blood back from the body. It is divided into two halves-the left side and the right side. The left side of the heart is the larger, more muscular side receiving oxygen rich blood from the lungs and pumping it throughout the body. The right side of the heart is smaller and receives oxygen depleted blood from the body delivering it to the lungs where the carbon dioxide is exchanged for oxygen.

Both sides of the heart have two chambers - the upper atrium and the lower ventricle. One-way valves between the atrium and ventricle regulate the flow of blood. Blood is received into the right atrium from the body and flows through the tricuspid valve into the right ventricle. The valve prevents backflow into the atrium. From the right ventricle, blood enters the pulmonary artery through the pulmonary valve and travels to the lungs. The left atrium receives the oxygenated blood from the lungs which flows through the mitral valve into the left ventricle. The left ventricle then pumps the blood through the aortic valve into the aorta which carries it to the body.

Heart failure results when the heart muscle is unable to pump blood out to the body (left-sided heart failure) or it is unable to pump blood to the lungs (right-sided heart failure). In the early stages of heart failure, the dog’s body will compensate for the lower output by constricting blood vessels, increasing the heart rate and retaining water and sodium. These three changes help to increase the blood pressure and maintain circulation. However, these changes eventually lead to an accumulation of fluid in the tissues and the body. In the case of decreased output on the left side, fluid will accumulate in the lungs. If the right side of the heart is affected, fluid will accumulate in the abdomen.

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Abb. H2IOPNFF: Schematic illustration of the four chambers of the heart and bloodflow pattern.

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Abb. GGUHWA9V: Schematic illustration of the heart and pulmonary circulation.

Causes

Heart failure occurs in older dogs as a result of cardiac or systemic disease. Heart failure usually occurs in young dogs as a result of a congenital (present at birth) heart defect. This article will focus mainly on heart failure in older dogs.

  • Diseases of the Heart Valves. This is a common cause of heart failure in dogs. When the valves are unable to close and form a tight seal, blood leaks back into the atrium, causing decreased blood output. There are two main diseases of the valves:
    • Valvular Heart Disease (VHD, endocardiosis, valvular regurgitation). VHD is a progressive disease in which the valves of the heart become thickened and nodular, unable to close completely. The cause of this degeneration is unknown but it is more commonly seen in small breed dogs such as Miniature Poodles, Cocker Spaniels, Miniature Schnauzer and Dachshunds. This disease accounts for approximately 75% of heart failure in dogs. The mitral valve is most commonly affected resulting in left-sided heart failure.
    • Endocarditis. Endocarditis is a serious infection of the valves of the heart that causes small growths to form on the valves affecting their ability to function. It is most commonly caused by a bacterial infection. Periodontal disease, immunosuppressive drugs or any procedure causing a bacterial infection in the blood are potential causes. The mitral valve is most commonly affected resulting in left-sided heart failure.
  • Diseases of the Heart Muscle (Cardiomyopathy). There are two forms of heart muscle disease in dogs. Both types result in an enlarged heart and a decrease in the heart’s ability to contract and pump blood. Cardiomyopathies commonly start in the left side of the heart but usually progress to the right side.
    • Dilated Cardiomyopathy (DCM). DCM is the most common form in dogs. The muscles of the heart begin to weaken and in an effort to compensate for ineffective pumping, the chambers of the heart become dilated or enlarged. This is most commonly seen in Dobermans, Great Danes and Boxers and is thought to be inherited. DCM can also result from a nutritional deficiency of the amino acid, taurine. Other causes of DCM include canine parvovirus, chemotherapy, hypothyroidism, heartworm disease and other infections.
    • Hypertrophic Cardiomyopathy (HCM). HCM is uncommon in dogs. It results when the chambers of the heart thicken, leading to a decrease in pumping efficiency. Some causes are unknown but chronic high blood pressure from systemic disease has been implicated.
  • Heartworm Disease. Adult heartworms live in a dog’s right side of the heart and pulmonary artery, greatly hampering the ability of the right side of the heart to receive blood and pump it to the lungs. In severe infections, dogs will show signs of right-sided heart failure and dilated cardiomyopathy leading to heart failure.
  • Pericardial Disease. The pericardium is the lining that surrounds the heart. When excess fluid collects between this lining and the heart muscle, the heart loses its ability to pump blood normally. Causes of excess pericardial fluid include inflammation, infection, bleeding, tumors or trauma.

Cardinal symptom

  • Coughing
  • Exercise Intolerance

Symptoms

Clinical signs of heart failure will depend on the cause and which side of the heart is affected. Many times, heart disease progresses to include both sides of the heart and a combination of clinical signs are seen. Typically, with left-sided involvement, fluid backs up into the lungs resulting in pulmonary edema and coughing at night. Right-sided heart failure results in fluid accumulation in the abdomen (ascites) and limbs and an enlarged liver. Shortness of breath, difficulty breathing, fatigue, fainting and weight loss are other signs commonly seen.

Diagnosis

Heart failure is diagnosed by the clinical signs and physical examination with careful auscultation (listening) of the heart and lungs with a stethoscope. A murmur is detected with many cases of heart disease, especially with valvular disease. Murmurs can be either left-sided or right-sided which helps determine the cause. Pulmonary edema or fluid can be heard as moist crackles. Other diagnostic tests include:

  • Bloodwork to assess blood parameters, inflammation and organ function is necessary for diagnosis, prognosis and treatment.
  • Radiography of the chest will help determine the size and shape of the heart. Radiographs will also reveal fluid in the lungs.
  • An electrocardiogram (ECG) is used to detect an arrhythmia (irregular heart rhythm) and identify heart enlargement.
  • Echocardiogram is an ultrasound of the heart used to assess chamber size, cardiac output, valve function, blood flow direction and blood flow velocity. An echocardiogram is usually performed by a veterinarian specializing in cardiology.
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Abb. GG3QD36A: Echocardiogram.
This is a photograph of a dog undergoing an ultrasound examination of its heart.

Treatment

The goal in treating heart failure is to improve heart function, prevent fluid accumulation and prevent further deterioration of the heart muscle. Heart failure is rarely curable. Medications commonly used to treat heart failure include:

  • Diuretics increase urination which prevents and removes fluid from the lungs and abdomen.
  • Vasodilators which dilate blood vessels and lower the workload on the heart. These include ACE inhibitors and inodilators.
  • Positive inotropic medications to help the heart muscle contract more efficiently.
  • Cough suppressants are used when a cough is due to an enlarged heart pressing on the airways.
  • Diets low in sodium or salt to help reduce blood pressure.
  • Overweight dogs should be placed on a calorie restricted diet. Weight loss will also reduce the workload of the heart.

Prognosis

The prognosis for dogs with heart failure will depend on the cause, the severity of clinical signs and their response to treatment. Many dogs respond well to medication and can live a symptom free life. However, heart failure will require life-long medications and a commitment from the owner to maintain regular veterinary visits.

Prevention

Heartworm disease can be easily prevented by monthly administration of preventative medication. Keeping your dog vaccinated for parvovirus and preventing periodontal disease can avoid these systemic diseases which can lead to heart failure. Avoiding table scraps will help maintain your dog at a healthy weight and prevent increased sodium intake.

Update version: 12/13/2012, © Copyright by www.enpevet.de
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