DILATED CARDIOMYOPATHY

CAUSE

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• Canine dilated cardiomyopathy (DCM) is a primary disease of cardiac muscle that results in a decreased ability of the heart to generate pressure to pump blood through the vascular system.

• The definitive cause of canine DCM is the subject of debate, although a number of factors including nutritional, infectious, and genetic predisposition have been implicated. 

• Breeds predisposed to DCM include the Doberman Pinscher, the Great Dane, the Boxer, and the Cocker Spaniel.

• Dietary carnitine deficiency may play a role in some cases of Boxer DCM, and taurine responsive DCM has been identified in Cocker Spaniels.

• Doxorubicin, an anti cancer drug has been found to be associated with DCM in dogs.

• Parvo-virus in puppies of 2 to 4 weeks of age can also cause DCM

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CLINICAL SIGNS

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•  DCM is characterized by dilation of the ventricles with ventricular wall thinning. 

• The ability of the heart to serve as a pump is diminished.

• Clinical signs of DCM occur secondary to-

  • Decreased delivery of oxygenated blood to the body - lethargy, weakness, weight loss, collapse

  • Congestion of blood in the lungs- coughing, increased respiratory rate and/or effort, abdominal distention

• Cardiac dilation, decreased oxygen supply, and increased oxygen demand secondary to elevated heart rate and ventricular wall stress may predispose to the development of cardiac arrhythmias arising in either the atria (atrial fibrillation, supraventricular tachycardia) or in the ventricles (ventricular premature complexes, ventricular tachycardia).

• Arrhythmias may predispose affected dogs to sudden death.

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DIAGNOSIS

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• DCM is diagnosed by-

  • Echocardiography, which demonstrates the chamber dilation and indices of decreased pump function characteristic of the disease.

  • Thoracic radiography is useful to evaluate the heart, pulmonary (lung) tissue and vessels, and may show evidence of chamber enlargement and fluid accumulation in the lungs (pulmonary edema) or around the lungs (pleural effusion).

  • Electrocardiography may be used to characterize heart rhythm and to rule out arrhythmias; and in some cases, a 24 hour electrocardiogram (Holter monitor) may be recommended to more accurately characterize cardiac rhythm.

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TREATMENT

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• Treatment goals of DCM-

  • Improving systolic (pump) function of the heart - Pimobendan lowers the pressure in the arteries and veins and improves the heart muscle strength, thereby increasing blood flow to the body.

  • Decreasing the blood pressure to reduce the resistance to blood flowing out of the heart - Angiotensin converting enzyme inhibitor (ACE inhibitors), such as benazepril or enalapril

  • Eliminating pulmonary congestion if present - Furosemide and spironolactone

  • Controlling heart rate - Cardiac glycosides (Digoxin) slow the heart rate and strengthen heart contractions, so the blood is pumped more effectively. Digoxin use has mostly been replaced by pimobendan, except for cases with a specific arrhythmia called atrial fibrillation.

  • Controlling cardiac arrhythmias - If arrhythmias are not controlled with the above medications, antiarrhythmic drugs may be added in cautiously. Two main classes are beta-blockers (such as atenolol, sotalol, carvedilol) and calcium-channel blockers (such as diltiazem).

  • Specific treatment in cases of infectious/nutritional DCM - Taurine, Carnitine supplementation 

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PROGNOSIS

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• Canine DCM can be a devastating disease, and the prognosis for dogs with DCM is variable depending upon breed and status at presentation.

• The prognosis for Doberman Pinschers with DCM, for example, is less favorable than in other breeds, while DCM in Cocker Spaniels may be relatively slowly progressive.

• Patients that present in congestive heart failure generally have a worse prognosis than those that are not in congestive heart failure at presentation.

• Irrespective of this, medical therapy may provide significant improvement in lifespan and quality of life in affected dogs.

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