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Acquired Heart and Blood Vessel Disorders in Dogs

By Davin Borde, DVM, DACVIM, Staff Cardiologist, Veterinary Heart Institute ; Clay A. Calvert, DVM, DACVIM, Professor, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia ; Benjamin J. Darien, DVM, MS, DACVIM, Associate Professor of Internal Medicine, School of Veterinary Medicine, University of Wisconsin ; Jorge Guerrero, DVM, PhD, DEVPC (Ret), Adjunct Professor of Parasitology, Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania ; Michelle Wall, DVM, DACVIM

Also see professional content regarding acquired heart and blood vessel disorders.

Dogs can have a variety of cardiovascular diseases. The most common ones are discussed below.

Degenerative Valve Disease

Degenerative valve disease is the most common heart disease in dogs and accounts for about 75% of cardiovascular disease in this species. This disease is characterized by thickening of the heart valves. It most commonly affects the mitral or tricuspid valve. The disease is age- and breed-related. The cause is unknown, but, in Cavalier King Charles Spaniels (which are prone to this disease), it is believed to be inherited. It is more common in older, small-breed dogs. Male dogs are also more likely to develop it than female dogs.

Failure of the valve to close properly results in turbulent blood flow. Blood is regurgitated into the atrium, leading to an increase in pressure. If the mitral valve is affected, the result is elevated blood pressure in the capillaries of the lungs and, ultimately, fluid in the lungs. If the tri-cuspid valve is affected, elevated blood pressure in the body’s veins occurs, and accumulation of fluid in the abdomen may develop. Further damage to the heart can occur due to the continued high-speed flow of blood back into the atrium and also to the body’s attempts to compensate for the decreased blood flow. Over time, these compensatory mechanisms become harmful rather than beneficial.

In dogs, there are no signs during the early stages of the disease, although a heart murmur can be heard. As the disease progresses, affected dogs may be unwilling to move or exercise, have difficulty breathing, and develop a cough. Fainting may also occur due to decreased blood flow or arrhythmia. Sudden death is rare, but may occur.

A veterinarian can often diagnose degenerative valve disease based on physical examination findings and appropriate imaging procedures, which may include chest x-rays and echocardiography (ultrasonography). Arrhythmias may develop as the disease progresses and can be detected with electrocardiography.

Treatment in small-breed dogs should begin when signs start to appear or when fluid in the lungs is found on chest x-rays. Optimal treatment should be planned by your veterinarian for each stage of disease.

Treatment for early signs of congestive heart failure includes ACE inhibitors (see Drugs Used to Treat Heart and Blood Vessel Disorders : Angiotensin-converting Enzyme (ACE) Inhibitors) to reduce adverse hormonal effects caused by activation of the certain hormones, and to reduce mitral regurgitation and signs of fluid in the lungs. Control of fluid in the lungs is also accomplished by use of diuretics. Arrhythmias can be controlled with the use of medications to improve heart function and reduce signs of congestive heart failure. Other drugs or therapy (such as administration of oxygen) may be added as needed. Affected dogs can live for years with appropriate treatment.

Disorders of the Heart Muscle (Cardiomyopathy)

Cardiomyopathy is the name for any disease that mostly affects the heart muscle. The cardiomyopathies of animals are diseases with no known cause that are not the result of any generalized or primary heart disease. Several types of cardiomyopathy occur in animals; however, dilated cardiomyopathy is the only type commonly seen in dogs. Cardiomyopathy can also occur as a result of other diseases. In these cases, they are usually called secondary myocardial diseases.

Dilated Cardiomyopathy

Dilated cardiomyopathy is an acquired disease that causes the progressive loss of the heart muscle’s ability to contract. The cause is not known. It has a very long early phase in dogs, during which no signs are detectable. Signs then become evident for a relatively short period of time.

Dilated cardiomyopathy is one of the most common acquired heart diseases of dogs, only surpassed by degenerative valve disease and, in some parts of the world, heartworm disease. The disease is typically seen in middle-aged dogs. More males are affected than females. It most commonly affects large-breed dogs, with a few exceptions such as American Cocker Spaniels, Springer Spaniels, and English Cocker Spaniels. Some large-breed dogs that are particularly at risk include Doberman Pinschers, Boxers, Great Danes, German Shepherds, Irish Wolfhounds, Scottish Deerhounds, Newfoundland Retrievers, Saint Bernards, and Labrador Retrievers.

The signs of dilated cardiomyopathy may vary by breed, but include episodes of weakness or collapse, fainting, difficulty breathing, coughing, unwillingness to move, and accumulation of fluid in the chest or abdomen.

A low-grade murmur may be heard during a veterinary examination; sometimes a third heart sound or gallop heart sound is also present. Femoral pulses (in the thigh) may be weak, and an arrhythmia may be noted. Chest x-rays are helpful in showing enlargement of the heart and, if present, fluid in the lungs. Many veterinarians consider echocardiography (ultrasonography) the ideal test to diagnose dilated cardiomyopathy. Electrocardiograms may show arrhythmias or enlargement of the left atrium and ventricle.

The objectives of treatment are to control the congestion and fluid accumulation (diuretics are often prescribed), improve the ability of the heart to contract, and reduce adverse effects of hormonal changes.

Some cardiomyopathies result from a lack of a particular amino acid or enzyme and can be treated by reversing the lack. For example, myocardial failure due to the lack of an amino acid called taurine occurs in some breeds, particularly American Cocker Spaniels, Golden Retrievers, and Dalmatians, and possibly Welsh Corgis, Tibetan Terriers, and other breeds. In many of these breeds, blood tests can confirm a diagnosis of taurine deficiency. Response to taurine supplementation (which may take 2 to 4 weeks) can be dramatic, many times eliminating the need for other heart medications. Carnitine-responsive cardiomyopathy has been reported in Boxers and Doberman Pinschers; however, supplementation with L-carnitine may be cost prohibitive. Administration of fish oil may reduce the severity of weight and muscle loss in dogs with dilated cardiomyopathy. Your veterinarian will recommend a treatment program that meets your pet’s needs.

Congestive heart failure, which may be severe, often occurs and should be treated appropriately (see Heart Failure in Dogs). As fluid in the lungs resolves, your veterinarian is likely to prescribe medications to improve the ability of your pet’s heart to function. Antiarrhythmic treatment is frequently indicated, especially for Doberman Pinschers and Boxers with severe arrhythmias.

Dogs that are taurine or carnitine responsive have a fair to good outlook once signs of congestive heart failure lessen. The outlook is poor in most Doberman Pinschers. About 65% die within 8 weeks of diagnosis of heart failure. The outlook in other breeds is better but remains guarded—75% die within 6 months of diagnosis. Dogs with severe heart failure, particularly left-sided congestive heart failure, have a worse outlook than those with milder signs or signs of right-sided congestive heart failure.

Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is a condition in which the walls of the left ventricle thicken and become stiff as a result of a heart muscle disorder. This can lead to decreased blood flow and volume, accumulation of fluid in the chest and lungs, and the formation of blood clots. Hypertrophic cardiomyopathy is rare in dogs. Signs may include those of heart failure (coughing, difficulty breathing), collapse, and paralysis of the back legs; sometimes no signs are noted. Treatment should include medication to relieve signs of congestive heart failure, restore heart muscle function, and prevent blood clots.

Myocarditis

Myocarditis is a local or widespread inflammation of the heart muscle with degeneration or death of the heart muscle cells. There are numerous causes, including viruses (for example, canine parvovirus), bacteria (for example, Borrelia burgdorferi, which causes Lyme disease), and protozoa (for example, Trypanosoma cruzi, which causes Chagas’ disease). Deficiencies of minerals such as iron, selenium, or copper can also result in degeneration of the heart muscle. Deficiencies of vitamin E or selenium may cause death of the heart muscle. Certain antibiotics and plant toxins (poisons) can also cause myocarditis.

Signs include the typical signs of congestive heart failure, including heart murmurs and arrhythmias. Your veterinarian may request echocardiography (ultrasonography) and certain blood tests for diagnosis.

Treatment is directed at improving the ability of the heart to contract, relieving congestion, and controlling the narrowing of blood vessels (which can increase blood pressure). Your veterinarian will prescribe the most appropriate medication or drug combination for your pet.

Other Causes of Heart Muscle Failure

A form of cardiomyopathy called atrial standstill destroys the muscle wall of the atrium. In some dogs it affects the muscle wall of the ventricle as well. Eventually, heart muscle failure occurs. The condition has been reported in English Springer Spaniels, Old English Sheepdogs, Shih Tzus, German Shorthaired Pointers, and mixed-breed dogs.

Signs are similar to those of dilated cardiomyopathy (see Acquired Heart and Blood Vessel Disorders in Dogs : Dilated Cardiomyopathy), with right or left heart failure being noted. Treatment is similar to that provided for other heart muscle failure disorders, but it may not be effective. Pacemaker implantation may improve heart rate and blood flow.

Endocardial fibroelastosis is a disease of unknown cause that leads to thickening of the thin membranous lining of the left atrium, left ventricle, and mitral valve. It is a rare cause of heart muscle failure in young dogs. Affected animals are usually less than 6 months of age and have signs of left-sided heart failure. Breeds affected by this disease include Labrador Retrievers, Great Danes, English Bulldogs, Springer Spaniels, Boxers, and Pit Bull Terriers. Signs, treatment, and outlook are similar to those for dilated cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy is a rare cause of heart muscle failure in dogs. It is restricted primarily to the right side of the heart, but may also involve the left ventricle. It is characterized by a fibrous and fatty muscle of the right ventricle causing progressive heart muscle failure. Difficulty breathing, increased breathing rate, fainting, and nonspecific signs such as loss of appetite and lethargy may be seen. Treatment is similar to that for dilated cardiomyopathy.

Duchenne’s cardiomyopathy is an inherited disorder associated with the X chromosome. It has been reported in dogs, particularly Golden Retrievers. A similar disease called X-linked muscular dystrophy has been reported in Irish Terriers, Samoyeds, and Rottweilers. These diseases may affect heart muscle as well as nerve and muscle tissue elsewhere in the body. Tissue changes usually develop by 6 to 7 months of age and decrease in size over the next 2 years. In patients that survive, heart muscle failure may develop.

Infective Endocarditis

The endocardium is the thin membrane that lines the heart cavity. Infection of the endocardium typically involves one of the heart valves, although endocarditis of the cavity’s wall may occur. Infection is caused by bacteria carried in the blood. The infection gradually destroys the valve and keeps it from working properly. In dogs, the aortic and mitral valves are most commonly affected. Middle-aged dogs and large breeds are most likely to develop endocarditis. Males are more commonly affected than females.

Bacteria released from the infected valves enter the circulation and can infect other organs. Therefore, infective endocarditis can produce a wide range of signs from various body systems, including primary cardiovascular effects or signs related to the nervous, digestive, urinary, or reproductive systems, or joints. Fever that comes and goes, lameness that shifts from one leg to another, weight loss, and lethargy are seen in many cases. If a right-sided valve is affected, fluid may accumulate in the abdomen, and a large pulse in the jugular vein may be present. Blood and pus in the urine may also be noted. A heart murmur is present in most cases; the exact type depends on the valve involved.

Bacteria most often found in affected pets include Streptococcus, Staphylococcus, and Klebsiella species, and Escherichia coli. Other bacteria or fungi may be involved. Various blood samples may be needed for diagnosis and to monitor the effects of the infection. X-rays may show enlargement of a heart chamber; however, echocardiography (ultrasonography) is the diagnostic test of choice for most veterinarians, because blood tests are positive in only 50 to 90% of dogs. Electrocardiography (recording electrical activity of the heart) may show arrhythmias.

Treatment and Prevention

Treatment is directed at controlling signs of congestive heart failure, resolving any significant arrhythmias, killing the bacteria that started the infection, and eliminating the spread of infection. Controlling heart failure requires the use of diuretics, ACE inhibitors, and, in some cases, digoxin. The outlook is poor in most dogs. Those that respond to treatment will likely require longterm heart medications and frequent reevaluations. Your veterinarian will prescribe a drug treatment program that is appropriate for your pet.

Considering the poor outlook for this infection, prevention is vital. When animals with a heart disease that could lead to infective endocarditis (for example, subaortic stenosis, patent ductus arteriosus, ventricular septal defect, cyanotic congenital heart disease) are to undergo procedures with a potential to introduce bacteria into the blood—such as dental scaling or tooth extractions—the preventive use of a broad-spectrum antibiotic may be appropriate. Your veterinarian will evaluate both the condition of the animal’s heart and the risk of bacterial infection before prescribing any antibiotic.

Pericardial Disease

The pericardium is the membrane surrounding the heart. When fluid builds up in the pericardium, the pressure is increased. The increased pressure compresses the heart, interfering with its ability to pump blood. This condition is called cardiac tamponade. The compression significantly affects blood circulation and causes swollen jugular veins and accumulation of fluid in the abdomen. In addition, too little oxygen reaches the body’s tissues. In an attempt to increase the oxygen supply, the animal’s breathing rate goes up.

This condition is uncommon compared with other acquired cardiovascular diseases; however, it does occur in dogs. Golden Retrievers, Great Danes, and Great Pyrenees are among the most commonly affected breeds. Overall, most cases involve middle-aged, mostly male, large- and giant-breed dogs. Cancer is the most common cause of fluid in the membrane surrounding the heart in dogs. Tumors in the right atrium are the most frequently seen cardiac tumor, followed by heart base tumors. Less common causes of this accumulation of fluid in dogs are infections, trauma, chamber rupture, and congestive heart failure.

Signs may include unwillingness to move or exercise, loss of appetite, listlessness, and an accumulation of fluid in the abdomen. The severity of the signs depends on the rate of fluid accumulation in the sac surrounding the heart. A veterinarian may notice a swollen jugular vein and muffled heart sounds during examination of the dog. X-rays may show an enlarged heart. In most cases, an electrocardiogram is normal or just shows an increased heart rate. Echocardiography (ultrasonography) examination is the most sensitive and specific test for the detection of cardiac tamponade.

Animals with cardiac tamponade require urgent treatment. The best way to rapidly reduce fluid in the sac surrounding the heart is pericardiocentesis. This procedure involves inserting a needle into the sac to withdraw the fluid. Pericardiocentesis is relatively easy to perform and serious complications are rare. Broad-spectrum antibiotics and intravenous fluids may be given immediately before and after pericardiocentesis. If the fluid returns, the procedure may be repeated.

Heart base tumors are usually benign in dogs, and if the fluid in the sac surrounding the heart is due to a heart base tumor, surgical removal of part of the pericardium is commonly performed. Many dogs survive with no signs up to 2 years following surgery.

High Blood Pressure (Hypertension)

Systemic hypertension is an increase in the body’s blood pressure. There are 2 major types of systemic hypertension. Essential (primary) hypertension is of unknown cause. This type of hypertension is common in humans, but is rare in dogs. Secondary hypertension results from a specific underlying disease. In dogs, the most common cause of hypertension is kidney disease. An increase in adrenal gland hormones (hyperadrenocorticism), diabetes mellitus, and pheochromocytoma (a type of pituitary gland tumor) are other causes of high blood pressure in dogs.

Dogs with extremely high blood pressure may have no signs that are visible to the owner. Blood tests may help with diagnosis of the cause of high blood pressure. Treatment should be started in dogs with sustained and severe high blood pressure, or in dogs with sustained high blood pressure and a documented underlying cause such as kidney failure.

Pulmonary hypertension is elevation of blood pressure in the lungs. Possible causes include increased thickness of blood (for example, an abnormal increase in red blood cells) and increased pulmonary blood flow (caused by, for example, a ventricular septal defect, patent ductus arteriosus, or an atrial septal defect). Other causes include abnormalities of the blood vessels in the lungs, which may be caused by heartworm disease, narrowing of the arteries within the lungs, or blood clots within the lungs. Primary pulmonary hypertension is rare in dogs. Signs are similar to those seen in right-sided congestive heart failure, such as accumulation of fluid in the lungs or abdomen. A swollen and pulsating jugular vein may be noted. Doppler echocardiography (ultrasonography) is the most likely method of confirming the diagnosis. Treatment is usually not effective, and the outlook is poor. The best chance for a successful outcome is the identification and treatment of the underlying disease.

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Also see professional content regarding acquired heart and blood vessel disorders.