F308
Heart Disease

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patent ductus arteriosus | aortic stenosis | pulmonic stenosis | mitral valve insufficiency | infective endocarditis | cardiomyopathy 


Introduction: The heart is an extremely complex organ upon which the life of any animal depends from minute to minute. It is responsible for providing the power to circulate blood throughout the body. In a large dog, the heart normally pumps approximately 300 liters of blood per hour! Heart problems are relatively common in canine patients seen at veterinary hospitals. Most dogs with heart problems are 7 years and older. Some heart diseases, however, are more common in younger dogs. Heart disease in dogs can be very complicated and must be treated on an individual basis. Therefore, this section will give only a brief overview of some of the more common heart disorders seen in dogs. The intent of this material is to give the pet owner a better understanding of the clinical signs, diagnosis, and treatment for many of the problems associated with the canine heart.

Common Terms:

  1. Cardiac - Adjective referring to the heart.
  2. Artery - A blood vessel carrying blood away from the heart.
  3. Vein - A blood vessel carrying blood toward the heart.
  4. Capillary - Tiny vessel from which oxygen and nutrients dissolve out of the blood stream and into the surrounding tissue. Capillaries are present everywhere in the body and are the connection between arteries and veins.
  5. Atrium - Upper chambers in the heart. Dogs have two atria, right and left.
  6. Ventricle - Lower chambers in the heart. Dogs have two ventricles, right and left.
  7. Valve - "Doorways" into and out of the ventricles. Each ventricle has two valves, one for inflow and one for outflow. Subsequently, each canine heart has four valves. The valves which allow blood to flow into the ventricles open during the first phase of a heartbeat and close during the second phase. The valves which allow blood to flow out of the ventricles function in the opposite manner, closing during the first phase of the heartbeat and opening during the second phase. The four canine heart valves are described as follows:

The "lub-DUB, lub-DUB" sound heard when listening to the heart with a stethoscope is actually the noise made when the valves shut and create turbulence in the blood. The pulmonic and aortic valves close on the "lub" portion of the sound, while the right and left atrioventricular valves close on the "DUB" portion of the sound.

  1. Aorta - The largest artery in the body. The aorta carries blood from the left ventricle down through the chest and into the abdomen. Arteries branch off the aorta carrying blood to all parts of the body.
  2. Pulmonic artery - The major vessel which carries blood from the right ventricle into the lungs to receive oxygen. The pulmonic artery and its branches are the only arteries in the body that normally carry blood which is low in oxygen content.
  3. Vena cava - The largest veins in the body. All veins eventually empty into one of these two veins. One carries blood from the head and upper body into the heart, and the other carries blood from the lower body. Both empty into the right atrium.
  4. Pulmonic veins - Veins which drain blood from the lungs back into the heart. The pulmonic veins empty into the left atrium and are the only veins in the body which carry blood high in oxygen content.
  5. Systole - Contraction or pumping phase of the heartbeat. During systole, the heart contracts and empties its chambers, pumping blood into the body.
  6. Diastole - Resting or filling phase of the heartbeat that occurs in between heartbeats. During this brief resting phase, the heart fills with blood.
  7. Murmur - An abnormal heart sound heard with a stethoscope. Murmurs may be caused by turbulent blood flowing through a defect in the heart or through a faulty valve that is not closing when it should.
  8. Arrhythmia - An abnormality in the electrical activity of the heart. Some types of arrhythmias can be life-threatening emergencies.
  9. Edema - Fluid buildup in the tissues. Edema may be due to various causes; heart defects are one of the more serious causes in which edema may severely affect the health of the animal.

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Heart Disease

A large variety of problems can lead to heart disease. Deaths stemming from a heart disorder are usually due to either the development of a fatal arrhythmia or to congestive heart failure and its various complications. All heart problems can be placed into one of two categories: congenital or acquired. A few of the more common heart diseases will be addressed as follows:

Congenital - These are defects present at birth. Congenital cardiac defects are among the most common birth defects that occur in puppies.

This is probably due to the complicated process of cardiac development in the unborn fetus.

  1. Patent Ductus Arteriosus (PDA) - This is a shunt or duct, normally present in unborn puppies, which allows blood to pass from the right side of the heart to the left. This shunt (ductus arteriosus) is located just above the heart and is a connection between the two main arteries leading away from the heart, the pulmonic artery and the aorta. The ductus arteriosus allows blood to bypass the undeveloped lungs and enter directly into the aorta. The ductus arteriosus normally closes within hours to days after a puppy is born and starts to breathe on its own. If the ductus arteriosus fails to close, blood is still shunted through, although the direction usually reverses itself and shunt blood from the aorta into the pulmonary artery. This is called a Left-to-Right Shunting PDA. This condition results in overload to the left side of the heart, and more than 50% of affected puppies will succumb to heart failure within a year without surgical treatment.

    Breeds most commonly affected with PDA include Bichon Frise, Chihuahua, Cocker Spaniel, Collie, English Springer Spaniel, German Shepherd, Keeshond, Labrador Retriever, Maltese, Poodle, Pomeranian, Shetland Sheepdog, and Yorkshire Terrier. Females seem to be at greater risk.
  1. Clinical Signs: Most dogs with a PDA experience signs that include failure to gain weight and thrive, difficulty breathing, and coughing. Most commonly, the condition is detected initially by a veterinarian listening with a stethoscope to an apparently healthy puppyís heart.
  2. Diagnosis: The murmur caused by a PDA is unique, notorious for having a continuous or "washing machine" sound. An ultrasound of the heart, or echocardiogram, is necessary to view the shunt. An electrocardiogram (ECG or EKG) is also important to determine if the condition is causing any abnormalities in the heartís electrical rhythm.
  3. Treatment: Surgery is strongly recommended for all puppies under 2 years of age that have a PDA. In dogs over 2 years of age, a cardiologist should be consulted. Surgery consists of passing suture (stitch) material around the open ductus and tying it closed. While the procedure may sound simple, it does carry serious risks and must be performed by a skilled surgeon. Prognosis with surgery is generally excellent.
  1. Aortic Stenosis - This defect consists of a ring of thickened tissue around or near the aortic valve where blood flows from the left ventricle into the aorta and rest of the body. This ring of tissue makes it very difficult for the heart to pump blood out into the aorta. Blood pressure builds up in the left ventricle, and the heart begins to overwork itself to perform its normal function.

    Golden Retrievers seem to be the breed most commonly affected. Other affected breeds include Boxer, Bull Terrier, German Shepherd, German Shorthair Pointer, Great Dane, Newfoundland, Rottweiler, and Samoyed.
  1. Clinical Signs: Abnormal signs are usually absent in puppies, but this does not make the disease any less serious. A dog may die suddenly and without warning before its owner is even aware anything is wrong. Fainting spells (syncope) may also occur. As with PDA, these murmurs are often first noticed during a veterinarianís examination of a puppy.
  2. Diagnosis: The diagnosis is made by echocardiology (ultrasound of the heart), through which the thickened tissue ring can be seen and blood pressures inside the heart may be calculated. Chest radiographs and ECG studies may also be helpful.
  3. Treatment: Treatment includes various medications to help reduce stress on the heart muscle. Some surgical techniques are available, but are difficult to perform, costly, and as a result, are seldom performed. Aortic stenosis is a difficult disease to treat, and the prognosis, even with treatment, is not generally good. Any dog of the above listed breeds with any family history of aortic stenosis should not be bred.
  1. Pulmonic Stenosis - This is usually a defective pulmonic valve. This condition, which is present at birth, includes any defect in the heart which makes it difficult for blood to exit the right ventricle and enter the pulmonary artery and lungs. Because of the defect, blood pressure increases in the right side of the heart and in the vessels that empty blood from the body back to the heart.

    Breeds commonly affected include Basset Hound, Beagle, Boxer, Chihuahua, Chow Chow, Cocker Spaniel, English Bulldog, Labrador Retriever, Mastiff, Newfoundland, Samoyed, Schnauzer, and terrier breeds.
  1. Clinical Signs: Some mild to moderately affected individuals may live normally without problems. Severely affected dogs may develop signs of heart failure, arrhythmias, and fainting spells, especially when excited or exercising. Sudden death, without warning, may occur. A murmur will usually be detected by a trained professional using a stethoscope.
  2. Diagnosis: The diagnosis of pulmonic stenosis is best made through the use of echocardiography. Chest X-rays and ECG studies may also be helpful.
  3. Treatment: For mild-moderate cases, treatment may not be necessary. For moderate-severe cases, medication to alleviate congestive heart failure and/or arrhythmias, as well as some surgical techniques, are available. A cardiologist should be consulted, especially if considering surgery. Affected dogs should not be bred.
  1. Other Congenital Heart Defects: These include atrial and ventricular septal defects, mitral and tricuspid valve dysplasia, cor triatriatum dexter, and Tetralogy of Fallot. Each of these conditions usually occur in specific genetic lines and can lead to failure of the heart muscle in diseased individuals. Professional advice should be sought when dealing with any congenital defect of the heart.

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Acquired Disorders: These are disorders which are not present at birth, but rather develop at some point later in life.

  1. Mitral Valve Insufficiency - This condition is the most common heart disorder seen in dogs. One study reported that 75% of 16 year-old dogs have this disorder. Chronic deterioration of the left atrioventricular valve (mitral valve) may occur as a result of infection of the valve leaflets or may be idiopathic (no known cause). As the valve deteriorates, it begins to allow blood to seep through during its closed phase. Over time, as the valve continues to fail, the seepage becomes more and more significant. Blood that crosses the leaky valve during the contraction of the ventricles ends up in the left atrium instead of in the aorta. Extra volumes of blood, present in the left atrium as a result of the failing valve, cause enlargement of the chamber and back up of blood into the lungís blood vessels. Eventually, fluid begins to leak out of the distended vessels in the lungs. This fluid, known as pulmonary edema, fills the lung airspaces and results in a cough.

    Small chords known as chordae tendineae connect the valve leaflets to the heart muscle. These chords prevent the leaflets of the valve from being forced open backwards during the powerful contraction of the heart. When the valve leaflets begin to deteriorate, the attachment of these chords to the leaflets may also deteriorate. Occasionally, a dog with minor symptoms of mitral valve insufficiency may experience a sudden decline or even sudden death. This is often due to rupture of one or more of these chords. This would, in effect, suddenly turn the small trickle of blood through the leaky valve into a "large river." The body has a tremendous capacity to compensate for certain problems over time. If the same "large river" had slowly developed over months to years, the animal may still be going strong, with minor symptoms. An acute (sudden) problem, resulting from a ruptured chordae tendineae, usually results in sudden weakness and heart failure. Development of arrhyt
    hmias may also result in sudden onset of illness
    and/or death.

    All breeds can be affected by mitral valve insufficiency, although it seems to be more common in the small and toy breeds. Males may be more at risk than females. This problem is very common in the Cavalier King Charles Spaniel, and starts to affect these dogs at a much younger age. Mitral valve insufficiency is usually first detected after 5 years of age, and problems associated with the disease are usually not manifested until several years later.

    Early detection is helpful; however, treatment is usually not started until symptoms begin. The disease is usually first suspected when a veterinarian hears a heart murmur in a middle-aged or older dog. In other cases, the owners may notice a minor cough during parts of the day, but until the cough becomes severe, many do not seek medical help. Valuable time will thus be lost in slowing the progression of the disease. This is one of many reasons why routine examinations are essential to a petís health.
  1. Clinical Signs: These are usually related to chronic, left-sided heart failure. A cough is the most common early symptom. The cough is usually a dry, hacking cough and may occur with more frequency at night or with exercise. Inability to exercise, fainting spells during times of excitement or exertion, increased respiratory rate, difficulty breathing, restlessness at night, and changes in sleeping positions may also be noted.
  2. Diagnosis: The disease is usually first suspected when a veterinarian hears a heart murmur in a middle-aged or older dog. Crackling noises in the lungs (pulmonary edema) may also be heard with a stethoscope. Chest radiographs are very useful and may show enlargement of the left atrium, elevation of the trachea/bronchi, and edema in the lungs. A presumptive (preliminary) diagnosis of mitral valve insufficiency can often be made on the basis of physical examination findings and chest X-rays. Echocardiography is required for a definitive, or certain diagnosis. ECG monitoring is recommended to detect any abnormalities in the heartís electrical activity.
  3. Treatment: Treatment should be initiated when symptoms first begin. A wide variety of medications exist which can be used to help dogs with mitral valve insufficiency. Each medication has a different goal or purpose; some may help reduce the work load on the heart, while others may help strengthen the heartís ability to contract. One goal of high importance is slowing the progression of heart failure. This is probably the most important factor in extending the life-span of a patient suffering from mitral valve insufficiency. Owners of dogs with this condition should consult a veterinarian regarding this particular ailment and its treatment.
  1. Infective Endocarditis - Infective endocarditis is the infection of the heart muscle, valves, or supporting structures of the heart. Bacteria are usually responsible for the infection, although fungal infections can also occur. The bacteria must first enter the bloodstream and be carried to the heart. Because the bloodstream carries bacteria to all parts of the body, organs other than the heart (particularly the kidneys and the spleen) may also be affected. The source of bacteria entering the bloodstream differs from individual to individual; however, the most common sources include the mouth, digestive tract, skin, and urinary tract. Dogs with bad teeth, urinary tract infections, ear/skin infections, or indiscriminate eating behavior (will eat anything, including garbage) are more at risk.

    The heart valves and supporting structures seem to be the more common sites of infection within the heart, possibly due to their constant exposure to turbulent blood. Any of the four heart valves may be affected. Valves on the left side of the heart (aortic and mitral valves) are affected more than the valves on the right side of the heart.

    German Shepherds and Boxers seem to be more at risk, although any dog may have this disease.
  1. Clinical Signs: Heart murmurs (especially a new heart murmur never previously heard), fever, and sometimes lameness are found in dogs with infective endocarditis. Other clinical signs will vary and depend upon where in the heart the infection has occurred and what other organ systems are involved.
  2. Diagnosis: Blood cultures are an important part of making the diagnosis of infective endocarditis. This diagnostic test requires that blood samples be taken and sent to a diagnostic laboratory for culture. The culture results may take up to 3 weeks to be finalized; therefore, treatment is usually started before a final test result can be obtained. If bacteria are found circulating in the bloodstream, and recent heart problems are present, a definitive (positive) diagnosis of infective endocarditis can be made. If the actual bacterial colony is large enough, it may be viewed with echocardiography, thus making cardiac ultrasound a useful diagnostic tool. Radiographs (X-rays) of the heart, CBC, blood (serum) chemistry panel, and ECG are other recommended tests to aid in diagnosis. See Section D for additional information on the above tests.
  3. Treatment: Therapy for infective endocarditis focuses on antibiotics and heart stabilization. Based on their general success in helping patients with this condition, antibiotics are chosen in the beginning before blood culture results can be finalized. After obtaining blood culture results, a veterinarian will select antibiotics based on the culture and sensitivity data (please see Culture and Sensitivity page D135). Treatment for damage done to the heart itself is based on severity, structures affected, and need.
  4. Prevention: Maintaining a healthy pet is critical in preventing this disease. While nothing will guarantee 100% prevention, providing basic pet hygiene is perhaps the most important part an owner can take in avoiding this ailment. Brushing a dogís teeth regularly and providing annual dental cleaning under the care of a veterinarian are central in pet hygiene. Keeping a close watch for skin and ear infections, anal gland impactions, urine abnormalities, and strictly monitoring diet are also important components of pet hygiene. Each of these areas is given special attention in other sections of this manual.
  1. Cardiomyopathy - This is a disease of unknown origin affecting the heart muscle. There are several forms of cardiomyopathy in dogs. The most common of these is termed Dilated Cardiomyopathy (DCM). This discussion will concentrate on this variation, because others are seen only occasionally. As stated in the name of the disease, the heart muscle begins to dilate and weaken. Because the heart muscle weakens, it is unable to generate sufficient pressures during contraction to properly pump blood out of the heart. The heart failure which develops is known as systolic failure. Death occurs from congestive heart failure or development of fatal arrhythmias.

    While this disease seems to be increasing in spaniels, it is primarily seen in large and giant purebred dogs. Deerhounds, wolf hounds, Doberman Pinschers, Great Danes, Boxers, and St. Bernards top the list, although any large or giant breed may be affected. Males seem to be more prone to DCM than females; some reports state that as many as 70% of DCM cases are male. Most affected animals are diagnosed when they are between 4 and 10 years of age.
  1. Clinical Signs: Anorexia, lethargy, development of a cough, weakness, abdominal distention, fainting episodes, and weight loss are common clinical signs.
  2. Diagnosis: Heart murmurs are present in approximately half of the affected dogs. These heart murmurs and other abnormal heart sounds may be heard with a stethoscope. Some animals may also have an increased heart rate. However, it is important to realize that even a dog with a severe case of DCM may have a "normal-sounding" heart. In most cases, a definitive (precise) diagnosis is made with echocardiography. Radiography of the heart provides sufficient evidence in some cases to make the diagnosis, but will not give sufficient evidence as to the degree of heart failure. Because dangerous arrhythmias may develop, ECG testing and evaluation are also important in dogs with DCM.
  3. Treatment: Medication for heart failure and the development of arrhythmias is the only way to manage this disease in dogs. Quality of life may be improved and life-span may be increased, but the disease is considered incurable and the prognosis is grave. Death usually occurs within 2 years.
  1. Other Diseases - Myocardial infarction (MI), or "heart attacks," are commonly blamed for sudden death in dogs. True MI in dogs, however, is relatively rare. In MI, an object known as an embolus lodges itself into one of the coronary arteries and deprives the heart muscle, fed by that artery, of its blood supply. When deprived of its blood supply and oxygen, the heart muscle will die. If only a small section of muscle is affected, the heart attack is considered minor. A massive heart attack is usually caused by blockage of a major artery or many arteries, and results in the death of a large portion of the heart. The embolus is usually in the form of a blood clot, but can also be a fragment of dislodged tissue, a foreign object, or an air bubble. Embolus damage in dogs can also affect other organs such as the lungs or the kidneys.
This is an electrocardiogram (ECG or EKG) machine. This machine is used to determine if a heart condition is causing any abnormalities in the heartís electrical rhythm. It is used to help diagnose specific arrhythmias of the heart.

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