Dilated Cardiomyopathy In Dogs: Signs, Diagnosis, & Treatment

The heart has four chambers. the upper chambers are called the atria (singular: atrium), and the lower chambers are called the ventricles. In addition to the upper and lower chambers, the heart is also considered to have a right and a left side.

Blood flows from the body into the right atrium. it is stored there for a few seconds and then pumped into the right ventricle.

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The right ventricle pumps blood into the lungs, where it receives oxygen. It flows from the lungs into the left atrium; it is held here for a few seconds before going into the left ventricle. The left ventricle contains the largest muscle of the heart so the blood can be pumped out to all parts of the body.

dilated cardiomyopathy (dcm) is a disease in which the heart muscle (myocardium) becomes much thinner than normal. in particular, the thick muscular wall of the left ventricle is affected. the pressure of the blood inside the heart causes this thinned wall to begin to stretch, resulting in a much larger left ventricular chamber. The three characteristics of dilated cardiomyopathy are a heart wall that is much thinner than normal, a chamber that is much larger than normal, and decreased contractility of the heart wall.

prevalence

Primary dilated cardiomyopathy is the most common cause of heart failure in large breed dogs. small breeds are only occasionally affected. the most commonly affected breeds are Boxers, Doberman Pinschers, and Great Danes. Occasionally, medium-sized breeds, especially English Cocker Spaniels and Springer Spaniels, develop this condition.

causes/transmission

In some cases, CMD develops as a result of chemical toxicity, nutritional deficiency, or an inflammatory condition in the heart. Doxorubicin, a drug commonly used in chemotherapy, can induce CMD after repeated administration. Nutritional deficiencies of carnitine and taurine have been linked to DCM, although this cause is rare. Some noncardiac conditions, such as pancreatitis and electrical shock, have occasionally been found to cause CMD. unfortunately, however, for most dogs, the cause is unknown. this is called primary or idiopathic mcd.

clinical signs

When the heart begins to fail, it cannot supply adequate oxygen to all of the body’s tissues. this sets in motion a series of compensatory events. various organs release various hormones in an attempt to correct the problem. these hormones conserve fluid in an effort to increase blood volume and the heart’s production of blood and oxygen. for several months, these compensatory responses help the situation. however, increased fluid retention eventually becomes harmful.

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Perhaps the most damaging event occurs when this excess fluid leaks from the pulmonary capillaries into the air spaces (alveoli) of the lung; this is called pulmonary edema. Notable symptoms include weakness, coughing or gagging, fainting or collapse, and an obvious intolerance to exercise.

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Fluid can also accumulate in the abdominal cavity and body tissues. congestive heart failure is a common cause of these signs. dilated cardiomyopathy can have a very sudden onset. some dogs go into severe heart failure in what seems like a matter of hours. rapid and heavy breathing, blue tongue, excessive drooling, or collapsing may be early signs.

diagnosis

There are several tests used to look at different aspects of the structure and function of the heart.

1. Auscultation: A stethoscope is used to identify murmurs, their location, intensity, and any abnormal heart rhythms (arrhythmias). it also allows us to hear sounds inside the lungs.

2. blood and urine tests: these allow us to understand other disorders in the body that can affect heart function and the treatment of heart disease.

3. thoracic x-rays (chest x-rays): These give us the best view of the lungs and a view of the size and shape of the heart. In most cases, dilated cardiomyopathy causes the heart to enlarge. these changes are often very apparent on x-rays.

4. electrocardiogram (ecg): is an evaluation of the electrical activity of the heart. allows us to accurately determine the heart rate and more accurately identify any arrhythmias that may be present.

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5. ultrasound test (sonogram, echocardiogram): This test uses sound waves that bounce off structures in the heart. gives the most accurate determination of the size of each chamber of the heart and allows the thickness of the heart’s walls to be measured. Certain measurements can be taken that allow the actual force of the heart’s contraction to be measured as a number and compared to the normal animal.

The combination of all of these tests gives us our best assessment of the dog and its heart function.

therapy

There is little data demonstrating the efficacy of therapy for dilated cardiomyopathy in dogs until after the onset of congestive heart failure. human studies have indicated that beta-blocker therapy such as carvedilol and metoprolol should provide benefit. enalapril or other angiotensin-converting enzyme inhibitors (ACEIs) may also be helpful. proper nutrition, including taurine, is also beneficial.

If the dog has sudden onset of heart failure, prompt administration of appropriate medication is essential for survival.

Congestive heart failure therapy for a dog with DCM may include:

1. an oil: block some of the hormonal changes that accompany congestive heart failure. Some of these changes include higher blood pressure, saving fluids and salt, and constriction of blood vessels. this is generally a lifelong therapy. Kidney function can rarely be affected, so regular blood tests are important. 2. diuretics: act on the kidney so that the dog produces more urine. diuretics can be both an emergency and a long-term therapy. 3. pimobendan: This is a new therapy that dilates blood vessels and increases the heart’s ability to contract. it has markedly better survival than other drugs used to increase contractility, perhaps due to its dilating effects. 4. Digoxin: This medication slightly increases contractility and may also help slow some abnormal heart rhythms that may be associated with CMD. digoxin has a very narrow therapeutic range (toxic and therapeutic doses are similar) and does not greatly increase contractility. It has fallen somewhat out of favor as the main therapy for CMD.

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forecast

Prognosis varies greatly depending on test results and relative responsiveness to medical treatment. however, while the long-term prognosis remains fair to poor, most dogs that stabilize quickly will live for 6 to 12 months.

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