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Posts Tagged ‘Heart disease’

The mitral or left atrioventricular valve is one of four one-way valves in the heart. It controls blood flow from the left atrium, where oxygenated blood coming from the lungs collects, to the left ventricle where arterial blood is pumped out into the body. When the left ventricle contracts the mitral valve closes thus preventing blood from going back into the atrium. With a slight delay the aortic valve, the outlet valve from the left ventricle, opens and blood is pumped out into the arterial system.

Two kinds of mitral valve disease occur. Stenosis or narrowing of the valve results in interference with the blood’s ability to flow into the left ventricle. Insufficiency is the inability for the valve to close properly, and allows blood to be pumped back through the valve into the left atrium. Either condition can result in the valve not closing properly resulting in blood leaking, regurgitating, or flowing back into the left atrium. When this happens a murmur can usually be detected.

Mitral valve disease can be the result of a birth defect, or acquired as the result of bacterial or viral infections, some types of cancer that affect the heart muscle or just as a result of the aging process, particularly in smaller breeds of dogs. When the mitral valve does not function properly the ability of the left atrium to empty is compromised and the larger than normal volume of blood in the left atrium causes the pressure in that chamber to increase. As a result blood flow out of the lungs is compromised. Depending upon the severity of the lesion the outcome can be congestive heart failure characterized by pulmonary edema, the collection of fluid in the lungs.

Congenital mitral valve stenosis is more commonly found in Newfoundland and bull terrier breeds but can occur in any breed including mixed-breeds. Acquired mitral valve disease, particularly age associated degenerative valve disease, can occur in any breed of dog but appears to happen more frequently in the smaller breeds and is endemic in King Charles spaniels. Mitral valve disease in the King Charles spaniel has been shown to be a polygenetic disease that can afflict over fifty percent of all individuals of this breed by the time they are five years old. By age ten any of these dogs that survive almost always demonstrate signs of the condition.

Depending upon the severity and progression of the valve disease many dogs will have no clinical signs in the early stages. We usually notice that as the dog gets older it seems to lose energy. Your veterinarian will usually detect a murmur, the result of the blood regurgitating through the diseased valve. This results in turbulent flow and can be detected before any clinical signs are noticed. The loudness of the murmur is not always associated with the severity of disease. A small area of leaking can result in a very turbulent and noisy jet while a large area might not create enough turbulence to create a loud murmur. If the disease progresses the dog may exhibit exercise intolerance, coughing, trouble breathing, increased rate of respiration, weakness and collapse with exercise.

The diagnosis is usually made by auscultation, use of the stethoscope. If the dog is showing clinical signs of congestive heart failure your veterinarian, or the veterinary cardiologist to whom you have been referred, may need to take X-rays, an electrocardiogram, an ultra-sound exam or even catheterize the animal to determine the severity of the disease, the prognosis and the level of treatment required.

Treatment for this condition is palliative, designed to control the symptoms and delay the progression of the disease. Medical treatment cannot cure the problem. Because the valve usually degenerates slowly the treatment can change over time. A variety of drugs are used depending on the stage and progression of disease. These include diuretics, vasodilators, positive inotropic drugs (drugs that increase the force of contraction of the heart muscle) like digitalis, and other agents that may prove beneficial in certain individuals. In humans if the patient is showing signs of heart failure as a result of mitral valve disease the treatment of choice is open-heart surgery and heart valve replacement with a prosthetic valve. This is possible to do in dogs, and available in some very specialized institutions, but it is expensive and usually not an option to be considered.

This disease can also occur in cats and almost any other species of animals but is most commonly identified in dogs. The problem is reasonably easy for your veterinarian to detect and another good reason for regular physical exams.

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Cardio” obviously pertains to the heart, “myo” pertains to muscle and “pathy” signifies pathology or abnormality. Therefore, cardiomyopathy is pathology or abnormality of the heart muscle. We describe two kinds of cardiomyopathy; hypertrophic and dilated. Both types occur because of genetic mutations in one or more of the various proteins that comprise the heart muscle.

A study published in 1993 in the American Journal of Cardiology compared lesions found in 38 humans, 51 cats and 10 dogs that died of spontaneous hypertrophic cardiomyopathy. The authors of the paper discovered almost identical changes in all of the subjects.

Hypertrophic cardiomyopathy results in an increase in the volume of the heart muscle. As the muscle, usually that of the left ventricle, the chamber of the heart responsible for pumping blood out into the body, is forced to work harder it becomes thicker. As this happens the muscle also becomes stiffer, less compliant, and the result is that the ventricle is less able to relax and fill with blood during the resting phase between beats, called diastole. Eventually the left ventricle cannot fill enough to pump enough blood to meet the metabolic demands of the body and the resulting condition is “heart failure”. These same changes can also occur in the right ventricle, the heart chamber responsible for pumping blood to the lungs. Sometimes both chambers are afflicted. The results are left heart failure, right heart failure or total heart failure. Hypertrophic cardiomyopathy seems to be particularly prevalent in Maine Coon, Maine Coon crossbreds and Ragdoll cats.

The other type of cardiomyopathy, dilated, is the yang of hypertrophic’s yin. The myocardium dilates and becomes thinner rather than thicker. This condition is also most often a genetic defect and thought to be an autoimmune disease as are Lou Gehrig’s disease, Cohn’s disease, lupus, and many others. The myocardium stretches and becomes weaker over time. Eventually the affected heart chamber(s) stretch to the point where the beating muscle looses strength. When it contracts it can no longer expel enough blood and heart failure occurs. Again, either the left, right or both ventricles can be affected. Large breeds of dogs, especially Irish Wolfhounds and Doberman Pinschers, seem to be the most afflicted by this condition but it has been found in German Shepherds, Boxers, and English Cocker Spaniels, mixed breeds and occasionally other breeds. For unknown reasons dilated cardiomyopathy kills males 2-3 times more commonly than it does females.

Genetic lesions resulting in myocardial changes closely resembling cardiomyopathy have been reported in Polled Hereford cattle, mustached tamarinds (monkeys) and pygmy sperm whales. Cardiomyopathies can also develop as the result of persistent rapid heart rate, high blood pressure, either systemic or pulmonary, diseases of the outflow valves of either the right or left ventricles (aortic or pulmonary valves), following treatment with certain chemotherapeutic agents, following obstruction of the coronary arteries, and after exposure to a host of toxic substances.

If your pet shows signs of lethargy, labored breathing, decreased levels of activity and tiring easily take it to your veterinarian for a checkup. The earlier a heart condition is caught the more successful the treatment and/or management is.

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