Failure In Your Dog
Canine Dilated Cardiomyopathy (DCM)
Ron Hines DVM PhD
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Acute cardiomyopathy puts enormous emotional strain on pet owners. It is so hard to accept that veterinary medicine has no cures for illnesses like Congestive heart failure and that cherished time with the pet you love is now limited. Many owners can not accept that, and dealing with health issues like these is the hardest part of being a veterinarian. Many pet owners write to me in their grief. You can read how that affects me here.
About Your Pet's Heart :
This article deals with a type of heart failure that affects primarily large breeds of dogs. Doberman pinscher, Labrador retriever, deerhunds, boxers, irish wolfhounds and golden retrievers are some of the breeds that suffer from this condition. Only occasionally, cocker spaniels and other smaller breeds will develop the condition. Typically, the pets are 4-10 years old when signs first occur and the signs of distress come on quite suddenly. For the more common cause of heart failure in older dogs, see another article I have written.
The heart of all mammals is made up of four chambers. The upper left and right chambers are called the atria (atrium) and the lower left and right chambers are called the ventricles.
Blood flows from the veins of the body into the right atrium. It is stored there briefly as it is pumped on into the right ventricle. The right ventricle pumps blood into the lungs, where it receives oxygen. It then flows from the lungs into the left atrium where it is held briefly before going on to the left ventricle. The left ventricle contains the largest muscle of the heart so it can pump blood out through the arteries to all parts of the body.
When Your Pet's Heart Fails :
There are two types of cardiac failure or myopathy that occur in dogs. In one form called hypertrophic cardiomyopathy the walls of the chambers of the heart thicken, leading to a decrease in pumping efficiency. This form of cardiac failure is quite rare in dogs. In the second form of cardiomyopathy the chambers of the heart increase in size and the muscles that form the walls of the heart stretch thinner. This is called dilated cardiomyopathy. The eventual result is congestive heart failure (CHF) in our pets. Canine Dilative Cardiomyopathy (DCM) is only one of the causes of CHF (a much more common cause is failure of the pet's mitral valve). eVeterinarians believe that most cases of DCM are due to genetic defects that are passed on to dogs by their parents. In humans, 30-40% are. (ref)
It is rather common for a dog’s failing heart to enlarge and no longer pump sufficient blood throughout the body. The most common cause of this in our pets as they age is damage to the valves that control the flow of blood within the heart. Pets are usually over five years of age when the condition is first noticed.
For reasons we do not understand, the incidence of cardiomyopathy in doberman pinchers is greater than that in all other breeds combined. When it occurs in Boxers it is common for serious heart rhythm abnormalities to occur while enlargement of the heart stays minimal.
As the failing heart enlarges, the left side looses its ability to contract forcefully to pump blood through the body’s blood vessels. When this occurs, blood begins to pools in the right side of the heart, which supplies blood to the lungs for oxygenation and receives spent blood from the thorax and abdomen. Sometimes the damage is more apparent on the right side of the heart first, sometimes on the left. But, eventually, both sides are affected because one relies on the other. The dog’s heart works hard to compensate for these changes but eventually your pet can no longer perform the activities it once did. This stage of the disease is called congestive heart failure.
In congestive heart failure, the heart is no longer able to provide blood with adequate oxygen to supply the body. Without adequate oxygen, the body's cells become desperate and trigger a series of responses. Various hormones are released by several organs in an attempt to correct the problem. These hormones conserve and retain fluids in an effort to increase blood volume and the output of blood. For several months, these compensatory responses help the situation. However, increased fluid retention eventually becomes harmful. More and more fluid leaks out of the capillaries, causing increased gagging and coughing, and reduced stamina. Fluid in the lungs is called pulmonary edema, fluid below the skin is called peripheral or limb edema, and fluid in the abdomen is called ascites. Peripheral or limb edema is much less common in dogs than in people with congestive heart failure.
What Are The Signs of Heart Failure ?
Dogs in the later stages of congestive heart failure become much less active and tire easily. Their appetite usually falls of and they show signs of difficult respiration, panting and coughing while at rest. Their tummy enlarges and takes on a pear-shape as fluid accumulates in the liver and abdomen.
Electrocardiograms taken of these dogs are always abnormal. When I examine these dogs, the color of the membranes of the mouth are grayish rather than healthy pink and blood vessels on the surface are abnormally congested with blood. These dogs often have a condition called a jugular pulse in which the beating of the heart can be seen in the large jugular veins of the neck. The sounds of heartbeat that I hear through my stethoscope are always abnormal to some degree.
By the time dogs become symptomatic with cardiomyopathy and congestive heart failure, they rarely live beyond a year. Many will die in six months. The disease is known to run in families so families with this problem should not be bred.
Doberman pinchers develop abnormal electrocardiograms up to four years before they develop clinical signs of heart failure. Many of these dogs die suddenly without warning. Owners often think these dogs have been poisoned. Others develop the cough and fluid retention characteristic of the heart failure along with muscle wasting and difficulty getting about.
In Boxers abnormal heart rhythms are often picked up as an incidental finding on routine health exams when no signs of illness are present. Later, the Boxers may have sudden incidents of collapse, fainting and weakness due to this irregular heart beat.
Dilated cardiomyopathy or congestive heart failure develops over many months or even years. Its effects on blood flow also develops slowly. As heart function declines, the body is able to compensate for several weeks or months. However, at some point, the body's ability to compensate is no longer effective. At this point, dogs go into severe heart failure in what appears to be a matter of hours. Rapid, heavy breathing, blueish tongue, excessive drooling, or collapse may be the first signs that anything is wrong.
Why Did My Pet Get This Problem ?
Nothing you did caused this problem. The disease runs in blood lines so it was probably preordained that your pet was susceptible to the disease.
How Is Cardiomyopathy Diagnosed In My Pet ?
Heart failure is often suspected simply from the results of a veterinarian's physical examination of your pet. A stethoscope placed on the left side of the pets chest just behind the elbow allows the person listening to hear abnormal heart rhythms as well as abnormal sounds of blood whooshing through overly distended heart valves. Heart sounds in this condition tend to be muffled and the raspy noise of air passing through fluid-filled lungs is often audible.
To confirm suspicions, the veterinarian will obtain chest x-rays or a cardiac ultrasound image. Hearts in cardiac failure have a very distinctive globular shape. The normal, chiseled cardiac silhouette is replaced by a much larger, rounded heart shadow. Early in the disease the left side of the heart may be more enlarged than the right but with time both the left and right side of the heart enlarge. In boxers, rhythm irregularities may be present before x-rays show abnormal findings. The lungs of dogs in heart failure are abnormally dense due to fluid buildup within them.
Many veterinarians rely on electrocardiograms (EKG) to detect early heart abnormalities before x-ray diagnosis is possible. A fast, out-of-control fibrillation of the muscle of the atrium is present in seventy to eighty percent of giant dogs with cardiomyopathy. The portion of the paper tracing called the QRS complex lengthens and increases in height (amplitude) signifying left ventricular enlargement. Heart rate is faster than normal in the tracing and premature contractions of the ventricles give the tracing an abnormal rhythm.
Visualization of the heart in real time with an ultrasound also gives a good indication of the efficiency of the heart in pumping blood. It gives me the most accurate measure of the size of each heart chamber as well as some indication of the degree of heart enlargement as it is occurring in real time.
Blood serum chemistry and urine chemistry tests do not detect heart problems but they do let veterinarians know if problems in the liver or kidneys might affect the action of heart medications we will use.
Many cases of cardiomyopathy are accompanied by heart rhythm abnormalities. These are caused by disturbances in the electrical impulses that control heart rate and rhythm and they can be life threatening. It is a good idea to learn to check your dog’s pulse at its wrist to detect this abnormality at home. You may even choose to buy a nurse’s stethoscope for more accuracy.
What Are The Treatment That Are Available ?
Cardiomyopathy responds best to a cocktail of medications. One of the oldest drugs used to treat this condition is digitalis (Digoxin, Cardoxin, Lanoxin). This medication belongs to a group called positive inotropic agents which increase the concentration of calcium in heart muscle cells. This increases the force of cardiac contractions and usually slows heart rate Digoxin is a powerful drug with many side effects. It must be used in caution in dogs with kidney or liver problems. If loss of appetite, vomiting, diarrhea or lethargy occur I lower the dose. the level of the drug in your pet's body has to be monitored until just the right dose is found. No to dogs are the same. Digoxin is eliminated from your pet's body through the kidneys so dogs with kidney damage are less able to tolerate the drug. In these dogs the dose must be lowered or digitoxin should be used instead because it is metabolized and excreted through the liver.
Another helpful group of drugs for dogs in heart failure are diuretics. These drugs remove accumulation of fluids that occur in the lungs and abdomen of cardiac patients due to the sluggish flow of blood. The most common and best drug of this class is furosemide (Lasix). Dogs taking furosemide usually drink and urinate more frequently. While on this drug the dog should have its potassium level monitored and, if it is low, receive a potassium supplement. When furosemide is no longer sufficient, spironolactone (Spiractin, Spirotone, etc.) can be added.
Another important group of drugs used in treating dilated cardiomyopathy are blood vessel dilators called ACE inhibitors. These compounds decrease certain chemicals that tighten blood vessels so more blood flows smoothly through them allowing the heart to pump blood more efficiently. The most commonly used drug in this class is enalapril (Enacard, Vasotec, Lotensin, Prinavil, Zestril).. Since this drug can cause kidney problems, it is wise to have your pet's BUN and creatinine serum level checked two weeks after starting the medication and then every three or four months.
When side effects of enalapril occur, they are usually lack of appetite,
vomiting and an increase in toxic waste products due to decreased
blood flow through the kidney (azotemia).
Drugs used to treat heart beat abnormalities (ventricular arrhythmias) include mexiletine (Mexitil), procainamide or its long acting form, Procan SR. Unfortunately this drug and their sister compound, quinidine, often cause depression and lack of appetite. Mexiletine is often given along with atenolol .
Both Hills Prescription Diets (h/d) and Purina’s CNM (CV formula) make low sodium diets for use in dogs with heart disease. A recipe for a low sodium home-cooked diet is included in this series . They do not seem to have as much of a beneficial effect as they do in humans.
There have been scientific studies that indicate that a few cases of cardiac failure, particularly in boxers, are due to a deficiency in the amino acid L-carnitine. If tests show an abnormally low carnitine level, supplementing your pet's diet with this product could help. Because it is expensive, it is not usually given unless a deficiency can be proven. Another group of cocker spaniels have been found to develop heart failure when there are deficient in another amino acid, taurine. Since this amino acid is not toxic and inexpensive there is no harm in administrating it to heart patients.
In humans, Coenzyme Q supplementation has improved the strength of heart muscle contraction . We do not know if this compound helps dogs in cardiac failure.
What Is The Outlook For My Pet ?
Unfortunately, pets with this problem do not live long. Medication can prolong the lives of some pets for a while, but most pass on within the year. Big breeds with the severer form may only live a few weeks from the time you notice the problem. A few live as long as two years.
How Will I Know If The Medications Are Working ?
The most common reason pets with heart problems come to see veterinarians is because of breathing problems. These pets tend to breath faster than they should and they tend to be congested. One can have complicated tests performed to evaluate if the medications are doing their job, but monitoring your pet's breathing rate and freedom from congestion at home is just as accurate - perhaps more so. If the medications are working, your pet will breath slower and easier when it is at rest. If you want to confirm your decision about its progress based on its respiration, do so by having your vet run occasional proBNP tests to confirm their level is dropping or holding steady. You can read an article that confirms this here.
Can We Predict Which Dogs Will Develop This Disease Before It Occurs ?
There has been progress in finding genes that are associated with doberman pinchers developing cardiomyopathy later in life. (ref) The problem is that some dogs that carry these genes will never develop the disease (incomplete or variable penetrance) while others that appear free of those genes develop cardiomyopathy (DCM) all the same. If you have an interest in the availability of these tests, contact the Veterinary Genetics Department of North Carolina State University.