Heart Muscle Diseases
Diseases of the heart muscle are less common than disorders of the valves. Dilated cardiomyopathy is, however, the second most common from of canine heart disease. Hypertrophic cardiomyopathy, although a common condition in cats and people, is rare in dogs; so, too, is myocarditis. The risk of heart diseases is inherited, particularly in certain breeds. It can be reduced by breeding from dogs whose families are free of disease.
Forms of Heart Muscle Diseases
Dilated Cardiomiopathy
This condition, also called DCM, affects relatively young dogs, usually under 7 years old, and sometimes as young as 2 years of age. In Cocker spaniels it may be associated with hypothyroidism, a condition in which a dog's own immune system attacks the thyroid gland, resulting in diminished thyroid hormone production. DCM may also be associated with immune system in the Doberman Pinscher. The breeds most commonly affected include the Boxer, Doberman Pinscher, Irish Wolfhound (all high-risk), and also the Afghan Hound, Great Dane, Old English Sheepdog, and St. Bernard. The condition now is also being diagnosed in smaller breeds, including Cocker spaniels and Dalmatians. DCM affects more males and females.
Signs and Diagnosis
Affected dogs are lethargic, tire easily from routine exercise, and often go off their food and lose weight. They may have a cough, especially at night. Congestive heart failure develops; as a result, fluid accumulates in the lungs and/or in the belly, causing the abdomen to swell. Both Boxers and Dobermans may die suddenly without showing any previous signs of illness.
An ECG will show changes in the heart's rhythmic contraction, while a chest X-ray will reveal that that the heart has become enlarged and expanded. Echocardiography will confirm that the heart wall is thin and the heart chambers are enlarged.
Treatment of Dilated Cardiomiopathy
The dog is given treatment for congestive heart failure. Diuretic drugs such as spironolactone or furosemide diminish the buildup of fluid in the lungs and abdomen, while ACE inhibitors and a new drug, pimobendan (Vetmedin), improve the heart function and circulation. There is nutritional logic in supplementing the diet with taurine and L-carnitine, although the benefit of these nutrients is still being studied. The long-term outlook for an affected dog is rather poor, although the use of pimobendan has increased survival time threefold in Doberman Pinchers.
Hypertrophic Cardiomiopathy
In this condition, the heart wall becomes thickened. It usually affects the ventricles (the lower chambers of the heart). As the muscle thickens, it reduces the space inside the heart for blood. The most common sigh is reduced exercise tolerance.
Diagnosis and Treatment
Hypertrophic cardiomyopathy is diagnosed by echocardiography. Treatment with the calcium channel blocker drug diltiazem appears to prolong life expectancy. strenuous exercise should be avoided.
Myocarditis
This rare inflammation of the heart muscle has many possible causes. When canine parvovirus infection first occurred, the virus caused a fatal form of myocarditis in puppies, but this cause is now extremely rare. Other causes of myocarditis include canine distemper virus; Lyme disease; other viral and bacterial infections; and trauma.
Diagnosis and Treatment
Clinical signs of myocarditis include lethargy, fainting and heart rhythm disturbances. The treatment for this condition is similar to that for congestive heart failure.
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