dilatedcardiomyopathy

This work was originally published by Veterinary Information Network, Inc. (VIN)
and is republished with VIN's permission.

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Dilated Cardiomyopathy (DCM) in Dogs

http://animalpetdoctor.homestead.com

Affected Animals
The dogs most frequently diagnosed with DCM are large and giant purebred dogs, including Scottish deerhounds, Doberman pinschers, boxers, Saint Bernards, Afghan hounds, Newfoundlands, and old English sheepdogs. Recently, both English and American cocker spaniels have been diagnosed more frequently with DCM than other small breed dogs. Most dogs with DCM are older, as the prevalence of DCM increases with age. Male dogs are affected more commonly than female dogs for most breeds.

Overview
The term cardiomyopathy literally means "sick heart muscle". Dilated cardiomyopathy, or DCM, occurs when the heart muscle is thin, weak, and does not contract properly. DCM most commonly affects large or giant purebred dogs, but it also can be seen in smaller breeds such as cocker spaniels, and in mixed breed dogs. The condition can lead to congestive heart failure, in which fluid accumulates in the lungs, the chest or abdominal cavities, or under the skin. Because of reduced blood flow to the rest of the body, DCM also can result in weakness, fainting, and exercise intolerance. Abnormal heart rhythms, or arrhythmias, frequently accompany DCM, and can complicate the treatment of dogs with this disease.

In rare cases, supplementation with substances such as l-carnitine or taurine may dramatically reduce signs in individual patients, but for most dogs, the main goals of treatment are to lessen signs due to congestive heart failure and to attempt to improve the heart's ability to pump blood. The long-term outlook for dogs with DCM is usually quite poor, and most dogs with DCM eventually die from the disease. Despite the poor long-term outlook, however, many dogs with DCM can benefit from medical treatment that helps control symptoms.

Clinical Signs
Signs may be consistent with right heart failure, left heart failure, or both. Right heart failure signs can include abdominal distention due to ascites, jugular venous engorgement or pulsation, hepatomegaly, pleural effusion, edema, pericardial effusion, and weight gain due to fluid retention. Left heart failure signs can include cough due to pulmonary edema, shortness of breath, tachypnea, and dyspnea. Some signs can be seen with right or left sided heart failure, including fatigue and weakness, exertional dyspnea, gallop rhythm, pallor, increased capillary refill time, cyanosis, cool extremities, and weight loss.

Symptoms
Dogs with dilated cardiomyopathy can show symptoms due to right-sided congestive heart failure including abdominal enlargement; distention of the veins in the neck or other parts of the body; and fluid accumulation in the abdomen or chest, in the sac around the heart or underneath the skin, especially in the legs and on the underside of the body. This fluid retention can lead to weight gain. Other dogs will show evidence of lung problems due to left-sided congestive heart failure, including shortness of breath, rapid, shallow breathing, difficulty resting comfortably at night, and coughing.

It is also common for dogs with DCM to show signs of both right and left heart failure. These signs can include weakness and exercise intolerance, and difficulty breathing with increased activity. Weight loss is common in dogs with DCM that do not retain fluid. Some animals exhibit signs due to reduced blood flow to tissues, including pale mucous membranes, bluish color to the mucous membranes, and cold feet and legs. Fainting may occur if abnormal heart rhythms are present, or if the heart's output is severely reduced.

Description
Heart failure occurs when the blood returning to the heart from the rest of the body cannot be pumped out fast enough to meet the demands of body tissues. Heart muscle disease is one of the potential causes of heart failure. Dilated cardiomyopathy is a condition characterized by a variety of changes in the heart muscle that result in pump failure. As the name implies, the heart chambers are usually dilated or enlarged, and the heart muscle itself is usually thin and weak, contracting with much less vigor than normal. The term cardiomyopathy literally means "sick heart muscle."

The primary abnormality occurring with DCM is impaired function of the ventricles due to decreased strength of the heart muscle. The left ventricle pumps blood from the lungs to the rest of the body, and the right ventricle pumps blood from the rest of the body to the lungs. When the heart muscle fails, pressures can increase and ultimately lead to left- or right-sided heart congestive heart failure. Reduced output from the heart may result in signs such as weakness, exercise intolerance, fainting, and shock. Heart valve insufficiencies, abnormal heart rhythms or arrhythmias, and the results of the body's compensatory responses to reduced heart muscle performance can compound the problems seen with DCM. Ventricular arrhythmias can often lead to sudden death, especially in boxers and Doberman pinschers. The development of an atrial arrhythmia called atrial fibrillation can have important short-term and long-term consequences for dogs with DCM. This arrhythmia can be seen in all breeds of dogs.

Medications are used to treat the consequences of heart muscle failure, to attempt to improve the heart muscle's ability to contract, and to normalize or improve rhythm disturbances. Drugs used to accomplish these goals include diuretics, digoxin, and angiotensin converting enzyme inhibitors. Supplementation with substances such as taurine or l-carnitine may be helpful for some dogs with DCM.

Diagnosis
The diagnosis often is first suspected when symptoms compatible with DCM are present in a large or giant purebred dog or cocker spaniel. Physical examination abnormalities frequently include the presence of an extra heart sound called a gallop rhythm, or a soft heart murmur. Arrhythmias can be detected while listening to the heart with a stethoscope and while feeling for the pulse or heartbeat. Abnormal lung sounds are heard in dogs with left-sided heart failure, while distention or pulsation in the jugular veins, liver enlargement, or abdominal fluid accumulation may be present in dogs with right-sided heart failure. In addition, laboratory results may indicate mild changes in serum protein concentrations, sodium and potassium levels, liver enzymes, and mild increases in serum urea nitrogen and creatinine levels, or kidney values.

Although they will not always reveal major changes, chest x-rays should always be evaluated in patients suspected of having heart disease. Heart enlargement and blood vessel changes consistent with heart failure may be seen, and fluid accumulation in or around the lungs can be identified if heart failure has developed.

The most definitive diagnostic test for DCM is the echocardiogram, an ultrasound evaluation of the heart. Heart chamber dilation and enlargement, reduced heart muscle wall thickness, and decreased heart muscle wall movement are the hallmarks of DCM. In addition, mild heart valve abnormalities may be seen. Doppler echocardiography may be used to assess the severity of valvular abnormalities based on changes in blood flow through the heart.

The electrocardiogram may identify abnormal rhythms or changes in the normal tracings. The most common rhythm disturbance occurring with DCM is atrial fibrillation, a condition characterized by a tremendous increase in the rate of contraction of the atria, the uppermost chambers of the heart, coinciding with an increased rate of contraction of the ventricles, the lower and larger chambers of the heart. Other rhythm disturbances, including premature ventricular beats, may be detected.

Prognosis
Currently, DCM is almost always fatal. Most dogs die within six to 24 months after being diagnosed. Severely ill dogs often do not survive the first two days in the hospital. Doberman pinschers may have a worse prognosis compared to other breeds. However, the response to treatment will vary for any individual dog. Treatment should always be attempted before rendering a prognosis. As with almost any disease, dogs diagnosed with DCM before serious complications have developed may be able to live longer with treatment.

Transmission or Cause
There appears to be a strong association between breed and DCM. Infectious diseases, including Lyme disease, bartonellosis, and trypanosomiasis, have been reported in association with DCM and are usually accompanied by other symptoms.

Treatment
DCM generally is not curable, and spontaneous recovery is unlikely. The primary goals of treatment are to lessen clinical signs of heart failure and to prolong survival. Treatment of an individual dog is dictated by the severity of its signs at the time of diagnosis, and the presence or absence of changes such as congestive heart failure and arrhythmias. The primary drug to reduce fluid accumulation secondary to congestive heart failure is furosemide, marketed as Lasix. It can be used to treat acute, life-threatening fluid accumulation or to control and prevent congestive abnormalities in chronic settings.

Digoxin is used for several reasons in the treatment of DCM. It may help increase the heart's ability to contract and slow down the ventricular response rate in dogs with atrial fibrillation. Digoxin also blunts some of the neurological and hormonal responses to heart failure that lead to worsening of the condition. Drugs such as dobutamine, amrinone, and milrinone may be used to increase the heart muscle's ability to contract, but they are indicated primarily for short-term emergency situations.

Recently, the use of drugs called angiotensin converting enzyme, or ACE, inhibitors has been shown to benefit dogs with DCM by reducing the signs due to heart failure and improving exercise tolerance. ACE-inhibitors have many effects, including blood vessel dilation, which reduces the resistance the heart has to pump against. The drug also remodels the diseased heart muscle. Other types of blood vessel dilators can be used in the short-term or long-term treatment of DCM to reduce the load that the heart has to pump against to get blood to flow.

Other drugs control heart rhythm disturbances. Digoxin is commonly used in dogs with atrial fibrillation. Other anti-arrhythmic drugs, including procainamide, marketed as Procan, and mexiletine, marketed as Mexitil, are used for dogs with ventricular arrhythmias due to DCM.

L-carnitine is a compound that plays an important role in fatty acid metabolism and in neutralizing potential toxins in cells. Carnitine deficiency in the heart muscle has been shown to be potentially reversible in at least one family of boxers with DCM. Although the diagnosis of heart muscle carnitine deficiency is difficult, and the appropriateness of supplementation with l-carnitine for all dogs with DCM is unknown, such supplementation is not known to be harmful. L-carnitine supplementation can be considered for all dogs with DCM.

Another substance that may play a role in the treatment of DCM, particularly in cocker spaniels, is taurine. Taurine deficiency was found to be the most important factor associated with DCM in cats in the 1980's, and correction of cat food formulations to eliminate taurine deficiency resulted in the almost complete elimination of DCM as a major heart muscle disease in cats. However, the exact role of taurine in the treatment of DCM in dogs remains undetermined. Other substances, such as coenzyme Q-10, may also play a role in the treatment of this disease.

Prevention
Affected dogs should not be bred. Early screening of dogs of breeds that have a high incidence of DCM may help identify important changes prior to the onset of signs. This can help prevent the breeding of dogs that could pass DCM on to their offspring.

Reprinted with kind permission from Roger Ross DVM,

http://animalpetdoctor.homestead.com

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Hypertrophic Cardiomyopathy

Authored by: Dr. Robert Prošek

http://www.VeterinaryPartner.com

What Is Hypertrophic Cardiomyopathy?
Hypertrophic cardiomyopathy (HCM) is the most common acquired heart diseases in cats but very rare in dogs. HCM is a primary heart muscle disease where the muscular walls of the ventricles become abnormally thickened (hypertrophied.) The name hypertrophic cardiomyopathy literally means “thick heart muscle disease” (Figure 1 below). This thickening has several consequences (see below). HCM is diagnosed once other secondary causes of left ventricular wall thickening (hypertrophy), such as hyperthyroidism, systemic hypertension, aortic stenosis and others have been ruled out.

Like the similar disease in humans, HCM is often familial in cats, thought to be inherited in an autosomal dominant manner. A specific mutation has been identified in Maine Coon cats and a genetic test exists to identify affected cats. While many purebred cats (such as American shorthairs, oriental breeds and Persians) are predisposed to the disease, the domestic short hair (regular house cat) is the type most commonly diagnosed with HCM. Cats are usually middle aged to older; however, the disease can be diagnosed at any age, often less than 5 years in purebred cats. In humans, HCM is also familial and several different genetic mutations have been identified as being able to cause the disease. To date, no viral or nutritional causes of HCM have been identified in humans or cats.

What Are the Consequences of the Thickened Left Ventricle?
Unlike thickening of the walls in response to a physical stress (e.g. weight lifting, or running marathons) where the thickening occurs to deal with the extra workload placed on the heart, the thickening with HCM is not normal. The degree to which the muscle walls thicken ultimately determines the clinical severity of the disease – some cats (and people) have mild disease, others have severe disease.

As HCM develops and progresses, the structure and function of the heart is altered in several ways. The hallmark problem with HCM lies in the inability of the left ventricle to relax appropriately. The thickened left ventricular walls become less flexible which prevents the left ventricle from relaxing or stretching sufficiently to fill with blood from the left atrium. This abnormal relaxation and inability to stretch may ultimately result in a build-up of blood “upstream” of the left ventricle – namely the left atrium and the pulmonary circulation. As the blood backs up, fluid is forced from the pulmonary capillaries into the lungs and chest cavity causing pulmonary edema and pleural effusion, respectively (commonly called “congestive heart failure,” or CHF).

In some cats, the thickening leads to arrhythmias and can result in sudden death (akin to what is seen in young basketball players that suddenly die on the court). It is difficult to predict which cats are likely to do

Other cats can suffer from feline aortic thromboembolism (FATE) – a blood clot in the aorta that causes blockage of blood flow to the back legs (most commonly), leading to sudden paralysis, severe pain, and often, death.


On the left is a graphic representation of a normal left ventricle and on the right is an enlarged (concentric hypertrophy) left ventricle as noted in hypertrophic cardiomyopathy.

How is HCM Diagnosed?
The clinical signs of HCM are variable. To some degree, the clinical signs depend on the severity – mild disease doesn’t cause obvious problems, but severe disease often does. Additionally, cats are masters at masking problems until they become severe, so cats with severe HCM may appear completely normal or have only subtle signs that go unnoticed (i.e., mildly increased respiratory rate) or they may be very nonspecific to heart disease (i.e., decreased appetite). On the other hand, an owner may notice signs such as respiratory distress secondary to congestive heart failure or leg paralysis secondary to a thromboembolic (blood clot) event. In addition, your veterinarian can clue in on signs when he or she listens to your cat’s chest during their physical exam. An increased heart rate, heart murmur, and/or gallop rhythm (extra heart sound) may be appreciated as the disease advances.

A common feature of HCM is termed systolic anterior motion (SAM) of the mitral valve. This abnormal motion of the mitral valve partially obstructs the outflow of blood from the left ventricle into the aorta, resulting in a heart murmur which can be heard by your veterinarian with a stethoscope during your pet’s physical examination. However, it is important to note that not all murmurs in cats are due to SAM. Additional diagnostic tests are required to confirm both the presence of SAM and of HCM.

An echocardiogram (ultrasound of the heart) with color flow Doppler imaging offers the best means to diagnose HCM. Echocardiography allows a veterinarian to observe the physical structure and dynamic function of the heart. Fortunately, the test is non-invasive and poses essentially no risk to the cat. Electrocardiograms and radiographs provide additional useful information and are often used to assist a veterinarian in diagnosing HCM, but cannot be used alone to diagnose the disease. Since very subtle structural and functional changes can occur within the heart in the early stages of HCM, it is strongly recommended that a veterinary cardiologist be consulted for diagnosis as well as subsequent management of the disease.

As previously mentioned, additional tests might be needed to rule out underlying diseases such as systemic hypertension or hyperthyroidism which may cause similar hypertrophy of the left ventricle as HCM. If no other causes are found, the diagnosis of HCM is made.

In Maine Coon cats, a blood test is now available to determine if the pet has the genetic mutation associated with this condition. The test does not work for other cats with HCM. You can request this test from your veterinarian.

How is HCM Treated?
Currently, there is no cure for HCM. The changes occurring to the heart muscle are irreversible. However, if your pet’s left ventricular hypertrophy is secondary to some other underlying heart disease, such as hyperthyroidism, treatment of the primary disease may result in some or complete resolution of the heart condition.

As previously mentioned, hypertrophy of the heart muscle affects the ability of the left ventricle to relax properly, and therefore, function appropriately. While veterinarians may prescribe one or more medications to try to improve the heart’s relaxing ability, it is important to recognize that no drugs have been shown to be effective in achieving this. Thus, attempts to reduce the risk of heart failure and to help the heart function efficiently are largely theoretical and may ultimately be of no value.

Some treatment options that may be prescribed include:
Drugs that are thought to alter relaxation of heart muscle, or slow down the heart rate to allow a longer time for the heart to fill, or both. No proof exists that either of these approaches actually benefits cats with HCM. It is quite acceptable to not treat cats with HCM prior to the onset of CHF – when information becomes available showing a benefit of any treatment, guidelines may change.

Drugs to treat congestive heart failure (diuretics and ACE inhibitors). These medications are not specific for HCM, but are used in cats with heart failure secondary to any heart condition. With severe fluid build up in the chest cavity, the veterinarian may physically remove the fluid with a catheter to help the cat breathe.

Drugs that are thought to reduce the risk of clot formation, or clot recurrence. A medication that reduces the ability of the blood to clot may be prescribed if the patient is felt to be at risk for blood clot formation or currently has a blood clot in one of its arteries or heart chambers. The use of certain drugs for this purpose must be closely monitored to insure the patient is not placed at risk for hemorrhage. Treatment does not guarantee that a blood clot will not form, nor is it designed to break down previously formed clots. There are no studies showing that any of these medications actually do what they’re claimed to do. Currently a study is underway examining the effect of one type of anti-clotting drug on survival of cats that have had a thromboembolic episode.

As an owner of a cat with HCM, you should be very sensitive to changes in your pet's condition and should not hesitate to seek veterinary advice. Your veterinarian may show you how to monitor your cat's respiratory rate as an increased rate may be a sign that congestive heart failure is developing or worsening. Cats with congestive heart failure do not cough like dogs or people, but often exhibit open mouth breathing and panting. A cat that is having difficulty breathing from heart failure or has loss of function of hindlimbs or front limbs, requires veterinary care as quickly as possible. In the acute setting, these problems may need specific treatments (oxygen therapy, injectable medications, anticoagulation medications, or pain medications) that can only be offered by a veterinarian.

What Is the Prognosis?
The prognosis of a cat with HCM is highly variable. Some cats may develop only mild hypertrophy and suffer little compromise of heart function, while others progress to more severe disease. HCM may worsen quickly over a period of months, or it may progress slowly over several years. Its severity may not change for many years and then suddenly worsen. Some cats with HCM die very suddenly even though they had no clinical signs of heart disease.

A cat with mild to moderate disease may enjoy an essentially normal life for a number of years. However, the prognosis is much more guarded once the cat has more severe disease. The risk of developing congestive heart failure is proportional to disease severity, which is often classified by measuring wall thicknesses and left atrial size. Although congestive heart failure can be treated medically, severe heart failure may become difficult to manage over time as the disease progresses. The prognosis for a cat with heart failure, unfortunately, is guarded to poor. On average, survival for cats with HCM and heart failure is 12-18 months after diagnosis.

Thromboembolism is a severe uncommon complicating condition in HCM. It can cause acute pain and various clinical signs such as loss of function of the hindlimbs (most commonly, although other organs or limbs can be affected). Although treatment to break down or remove the clot is available, the high treatment costs of the procedure, death during administration of the drugs and high recurrence rate of thromboembolism dissuades most from attempting this type of therapy. With supportive care, about 40-50% of patients with thromboembolic disease will break down clots on their own and regain limb function over time. However, despite the best medical efforts to prevent their reoccurrence, a cat that has survived a thromboembolic event has a significant risk of developing another over the following weeks to months.

How Can I Participate in Clinical Trials of HCM?
Currently, there is a clinical trial examining the efficacy of anti-clotting medications in the prevention of recurrence of aortic thromboembolism (FATE). If your pet has suffered such an episode, your veterinarian can help you enroll your pet in this trial by visiting the study website at http://www.vin.com/fatcat/.

Copyright 1991 - 2007, Veterinary Information Network, Inc.
This work was originally published by Veterinary Information Network, Inc. (VIN)
and is republished with VIN's permission.

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Canine Cardiomyopathy

What is cardiomyopathy?

Dilated Cardiomyopathy

Dilated Cardiomyopathy (DCM) in Dogs

Hypertrophic Cardiomyopathy