When the heart muscle of a dog or cat is affected by any disease, small animal veterinarians call the condition "cardiomyopathy." But diseases of this type tend to fall into one of three major categories, all of them considered "idiopathic" (meaning we don't understand what causes them).
This condition is characterized by the inability of the cardiac muscles to contract properly. Ultimately, that means that the amount of blood pumped by the heart is decreased, leading to poor circulation and secondary effects on the unaffected heart muscles. This is the most common cardiomyopathy in dogs and it's considered fairly widespread among certain breeds. (Cats can get this too, though it's generally caused by a nutritional deficiency in the amino acid, taurine. Because it's highly treatable, preventable and non-idiopathic, it will not be considered in this discussion.)
Canines who acquire this condition are usually large breed dogs and they generally do so during or after middle age. A strong genetic tendency is presumed for this disease.
This kind of heart muscle disease is the most common cardiac condition seen in cats (it's rare in dogs). The left ventricle of the heart is most often affected, growing to an abnormal size for unknown reasons. Consequently, the inner chamber of the heart gets squeezed to a small size, increasing the workload for the rest of the heart and limiting the outflow of blood.
Because certain breeds of cats are more often affected (some as young as 3 months and others as old as 17 years, but generally at middle age) a genetic basis for this disease has been assumed.
This disease of cats is poorly understood and less well-studied than the others. In these cases, the heart muscle begins "filling in," encroaching on the size of the heart's four chambers and thereby limiting blood output--usually severely. As it is relatively rare, this article will concentrate on the other idiopathic versions of this disease.
Symptoms and Identification
The symptoms of cardiomyopathy are notable in that they vary widely according to breed and species.
In cats, hypertrophic cardiomyopathy can be completely asymptomatic for an entire lifespan. Alternatively, it can lead to collapse or difficulty breathing (often the result of major changes to heart rhythm or congestive heart failure, respectively), life-threatening blood clots (usually leading to hind limb weakness or paralysis) and sudden death (for those who suffer sudden, devastating electrical disturbances to their heart rhythms).
In dogs, the dilated form of cardiomyopathy varies according to breed. For Boxers ("Boxer cardiomyopathy") and Dobermans, the disease is characterized by collapse and weakness up to 35% of the time and 20% of the time, respectively. Sudden death is also seen. These events are usually the result of changes in electrical conduction secondary to the stretching or compensation of the heart muscle. Still, some affected boxers may live long enough to suffer from congestive heart failure (usually from left-sided heart malfunction), for which coughing and difficulty breathing are the most typical signs.
For other breeds, sudden death and collapse are far less common. Right-sided heart failure with fluid build-up in the abdomen (ascites), weakness, exercise intolerance and fluid in the chest cavity (pleural effusion) are the most common signs.
Veterinarians can often identify these diseases before symptoms occur. A heart murmur is the common tip-off, though in some cases some animals won't develop one before succumbing.
Diagnosis is typically achieved with X-rays (demonstrating marked enlargement of the heart), EKGs (electrocardiograms, which may or may not show electrical disturbances in the heart) and most effectively, cardiac ultrasonography (echocardiograms) to elucidate the physical changes in the heart muscle.
In dogs, small breeds are only rarely affected. Among the medium and large breeds, the following have been found to be at a greater risk:
Treatment for cardiomyopathy usually rests on the idea of controlling the symptoms of congestive heart failure and cardiac enlargement while increasing the ability of the heart muscle to contract. Diuretics (like furosemide) for removing fluid, beta blockers for decreasing the work the heart has to do, and drugs like digoxin (to improve the strength of heart contractions) are usually employed. "ACE inhibitors" may also be indicated to reduce some of the hormonal changes we see in these cases. Special drugs to hedge against the electrical conduction issues may also be used.
For cats, reducing the possibility of clot formation has been advocated, but drugs to control this possibility have thus far proved ineffective. Work is underway to find solutions to this particular symptom in felines.
For pets with congestive heart failure, a new drug called pimobendin (Vetmedin) has been shown to be very effective, thereby increasing the survival times for many of these patients.
The cost of treatment is not insubstantial if you consider the high cost of a definitive diagnosis for these conditions. Initial and follow-up echocardiograms can be expensive (up to $500-$600), as are board-certified veterinary cardiologists (ideally suited to treat these conditions).
Drugs for cardiomyopathies are usually not terribly expensive, but the need for multiple drugs in some cases may nonetheless prove untenable for some pet owners.
Preventing cardiomyopathy is a hereditary concern. Therefore, preventing reproduction in any affected pet is considered critical. Screening dogs and cats from highly affected breeds prior to breeding is strongly recommended.
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