Note: Also included on this page are: Signs of Heart Disease and Glossary of Terms.

Dilated Cardiomyopathy (DCM)

Dilated cardiomyopathy (DCM) is an acquired disease in which the heart muscle becomes dysfunctional over time. Defective transport of calcium ions within the heart muscle diminishes the cells' ability to contract. The heart muscle becomes thin and flabby. Quietly, over a period of several months, the thinning worsens, the heart chambers become dilated (enlarged), the electrical timing of the heart malfunctions and affected dogs begin to have visible trouble. Before long, the problems cascade into full-blown congestive heart failure and then death. Over the usual one- to two-year course of the disease, the heart deteriorates from a muscular, automated, fine-tuned pump to a bag of overstretched elastic
with misfiring electronics.

DCM has been recognized in a number of species, including dogs, cats and human beings. In cats, DCM is due primarily to a dietary deficiency of the amino acid taurine. In dogs, the cause of the disease is generally unknown but the disease itself is highly breed-specific, being observed most commonly in Doberman Pinschers, Boxers, Great Danes, Irish Wolfhounds, Saint Bernards, Cocker Spaniels, Golden Retrievers and German Shepherd Dogs. More than 90% of cases of canine DCM are confined to these eight breeds. The disease is likely genetic in origin, although this has not yet been proved and the mode of inheritance has yet to be documented. Middle-aged dogs are most often affected.

Symptoms
The signs of DCM often appear suddenly, as if the affected animal has become ill only within the last few days. In reality, the dogs by this time have already progressed through the early stages of the disease and are now in severe heart failure. The symptoms include dyspnea, ascites, weakness and exercise intolerance. Arrhythmias may also occur, consequently worsening heart failure and precipitating collapse or sudden death.

Diagnosis
Physical exam findings for DCM are not as distinct as for other heart problems. Dogs with DCM commonly have no heart murmur or only a soft murmur with or without a gallop. Thus, DCM should be suspected in any dog with signs or symptoms suggestive of heart disease. When veterinarians suspect cardiomyopathy based on age, breed and physical exam findings, they use chest x-rays, an electrocardiogram and an echocardiogram to confirm the diagnosis. X-rays are used to evaluate the heart for enlargement and the lungs and pulmonary vessels for backed up fluid. The electrocardiogram will record any arrhythmias and trace the relative sizes of different heart chambers as the electric impulses run through them. The echocardiogram or ultrasonic examination of the heart provides the definitive diagnosis. The veterinarian is able to examine the dog without invasive surgery and document that the muscular walls of the heart are thinned, that various chambers are dilated and that the strength of the heart muscle contraction is decreased.

Treatment
There is no cure for cardiomyopathy but treatment can slow the progression of clinical signs and improve the dog's quality of life.

Medication
Treatment consists of medications aimed at improving cardiac function, decreasing the heart's workload and controlling arrhythmias, if present. Prognosis depends on severity, rate of progression and response to treatment.

Heart failure often can be controlled by medication (diuretics, ACE inhibitors, digoxin). The use of diuretics aims to reduce retained fluids, thereby easing the load the heart must pump, digoxin helps the heart muscles contract more vigorously and ACE inhibitors reduce the resistance in peripheral blood vessels, allowing blood to flow more easily.

If the disease is very severe, however, an affected dog may not survive the initial hospitalization. Even if the illness is initially controlled, the long term prognosis is poor; for example, most affected Dobermans will die within one to six months. The prognosis in other breeds can be somewhat better, but in almost all cases, the disease is ultimately fatal. Exceptions to the rule are some Cocker Spaniels that are taurine-deficient and respond to the administration of taurine and carnitine (an amino acid required for energy production), some Boxers (and rarely other breeds) that may respond to carnitine and few dogs that are taurine-deficient and that may respond to taurine therapy.

New Developments in DCM
Evaluating Nutritional Factors
From Morris Animal Foundation "Animal News" 2002

Understanding the diet fed to our pets has become more important than ever. Taurine is an essential amino acid naturally produced by the dog. Just like a recipe, taurine is made up of multiple "ingredients." The sulfur amino acids methionine and cystine are critical to the production of taurine. Dogs can only produce adequate amounts of taurine when the correct levels of methionine and cystine are available in their diet.

Taurine deficiencies in cats and foxes have been associated with low plasma taurine concentrations and subsequent heart problems, specifically DCM. Sadly, similar signs have been observed in dogs fed commercial diets low in methionine and cystine, thus inhibiting the body's ability to produce taurine. This might be a good time to consult your veterinarian regarding your dog's diet. 

Dr. Quinton Rogers of the University of California-Davis' School of Veterinary Medicine says, "During the past few years, our clinic has seen an increasing number of dogs with low plasma taurine concentrations and clinical signs of cardiomyopathy. The common factor in all cases was their diet history."

As a result of this finding, Dr. Rogers and his colleagues have designed (and are about to complete) a one year study aimed at identifying an accurate diagnostic procedure for detecting taurine deficiency and determining a dose of taurine that can be used to treat diet-induced DCM in dogs. The study, titled "Muscle Taurine Concentration as an Indicator of Taurine Status" focuses on large and mixed breed dogs.

According to Dr. Rogers, the most common way to determine taurine status is by plasma or whole blood analysis. Plasma concentrations can vary with dietary intake, while whole blood taurine is less affected by feeding. Muscle tissue, however, remains unaltered for longer periods of time. Therefore, the investigating team hypothesizes that muscle concentrations of taurine will be a better indicator of a dog's taurine status than traditional evaluation methods. During the study, plasma, whole blood, urine and muscle tests will be compared as viable methods to determine taurine levels in the canine body. "Defining accurate diagnostic procedures will help to establish the severity of the disease, the necessity of treatment, and can be used as a tool to monitor the animal's response to therapy" said Dr. Rogers.

Beyond diagnosis, the team is focused on uncovering a dosage of taurine that will effectively treat dogs with DCM. In cats, administering taurine to those with DCM caused by low taurine concentrations has resulted in normalization of heart function. Dr. Rogers said, "This [problem] has the possibility of impacting a large portion of this country's canine population, their owners, and the veterinarians who care for these dogs. Identifying a sensitive diagnostic indicator of taurine status will enable veterinarians to identify and treat dogs with DCM resulting from this condition."

Feed Supplements for a Healthy Heart
From Dog Fancy Magazine

Holistic veterinarian Shawn Messonnier (www.petcarenaturally.com) suggests that dietary supplements can fuel a dog's body with the essential nutrients it may need for optimal recovery. For example, amino acids taurine and carnitine help regulate heart function by helping to produce energy and muscle tissue strength.

A healthy dog's body produces the nutrients naturally - taurine from vitamin B-6 and the amino acids methionine and cysteine; carnitine from lysine, methionine and vitamins C, B-1 and B-6 in the liver. Supplementation may not only help dogs with chronic valvular disease, the most common canine heart condition, but it can help DCM, apparently indicated by low taurine and carnitine blood levels.

Found in the nervous system and muscles, taurine is among the body's most abundant amino acids and the heart's most abundant free amino acid. It helps regulate the heartbeat, takes in calcium during periods of reduced oxygen levels, and protects the heart from calcium overload. Taurine supplementation has proven beneficial for American Cocker Spaniels, a breed predisposed to DCM with simultaneous taurine and possibly carnitine deficiencies. In a small study of dogs with low plasma-taurine levels, twice daily doses of taurine (500 mg) and L-carnitine (1,000 mg) resulted in an improvement for several patients.

A blood test can reveal a taurine deficiency. However, even with normal blood-taurine levels, the amount within heart-muscle cells can be inadequate.

Taurine is safe and has no side effects. However, maximum safe dosages of taurine supplements have not been determined for human children, pregnant or nursing women, or patients with liver or kidney disease; thus similar precautions are warranted in dogs.

Carnitine accumulates in both skeletal and cardiac muscles to transport long-chain fatty acids into muscle cells, where they convert into energy. Supplemental carnitine can improve cells' ability to produce energy and support treatments for various muscle diseases and heart conditions. Heart muscle tissue is particularly vulnerable to carnitine deficiency because it needs the energy.

It's important to note that blood levels do not correlate with levels in heart-muscle cells; therefore, researchers must biopsy heart muscle cells to determine carnitine deficiency. Most dogs with carnitine deficiencies and DCM suffer from a membrane transport defect that prevents adequate carnitine from moving from the blood to the heart-muscle cells. These dogs, paradoxically, commonly have high carnitine blood levels.

Carnitine supplementation appears safe, even taken with traditional medications. Avoid forms of carnitine known as D-carnitine or DL-carnitine, which in some cases have caused angina, muscle pain and loss of muscle function. Consult your veterinarian to determine a safe dosage.

Supplementation with taurine and carnitine will not hurt, and might benefit a dog with DCM. Dogs must have a compete cardiac examination before being given any supplemental treatments. 

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Treatment for Rapid Heart Beat

If your dog has an abnormally rapid heart beat, you should be aware that there is a new technique for diagnosing and treating it called an Electrophysiology Study and Radiofrequency Catheter Ablation. The procedure is unique in that it offers a cure for certain abnormal rhythms, rather than simply trying to decrease the number of episodes of rapid rhythms. All rhythm medications can be stopped after a successful ablation procedure. Dogs who have heart muscle disease and heart failure secondary to their rapid rhythm are typically able to be weaned off their heart failure medications over the first two months after successful ablation.

For more information, have your veterinarian contact Kathy N. Wright, DVM, Dipl.ACVIM (Cardiology and Internal Medicine) Assistant Professor (513) 636-4395 or her registered veterinary technician, Beth Bleas.

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Signs of Heart Disease

• Lack of energy
• Irregular and rapid breathing
• Decreased appetite and weight loss
• Coughing
• Weakness
• Fainting
• Abdominal Swelling

Glossary of Terms

ACE (Angiotensin Converting Enzyme) inhibitors
Drugs that include enalapril, enacard (approved by the FDA for use in dogs), captopril, lisionpril and benazepril. They are used to relax blood vessels, lower blood pressure, decrease sodium retention and help the heart pump blood more efficiently. 

Acquired Heart Disease
A cardiac condition that develops after birth (does not mean that the condition is transmissible from dog to dog; it simply means it was not present at birth)

Arrhythmia - Abnormal or irregular rhythms of the heart

Ascites - Fluid accumulation in the abdomen

Congenital Heart Disease - A cardiac condition present at birth

Congestive Heart Failure
A cardiac condition that most frequently causes edema (fluid in tissue) or effusion (accumulation of fluid in a body cavity) that results when the heart is unable to maintain an adequate circulation of blood. 

Diuretic
Any drug that promotes urination (to remove excess fluid from the body)

Digoxin
A drug that is administered to improve the performance of the heart
muscle

Dyspnea - Labored breathing; a common sign of heart disease

Electrocardiogram - Recording of heart's electrical activity

Gallops - Abnormal sounds caused by change in heart flow

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