Dilated Cardiomyopathy (DCM) in Dogs – In-Depth

How does the normal heart work?

The heart is the organ responsible for pumping blood to and from all tissues of the body.  The heart is divided into right and left sides.  The job of the right side is to pump oxygen-deficient blood returning from the body through the lungs, where it is re- oxygenated and the carbon dioxide waste that the body produces is removed.  After the blood passes through the lungs, it enters the left side of the heart where it is pumped out to the body though the aorta and other arteries. The picture below illustrates the pathway that blood takes as it moves through the heart. The structures shown in red contain blood that has lots of oxygen. The structures shown in blue contain blood that has very little oxygen and high levels of carbon dioxide. 

cdv1Blue arrows represent deoxygenated blood flowing through the right side of the heart to the lungs, and red arrows represent oxygenated blood leaving the lungs through the left side of the heart.  RA = right atrium, RV = right ventricle, TV = tricuspid valve, PA = pulmonary artery, PV = pulmonary vein, LA = left atrium, MV = mitral valve, LV = left ventricle.

Each side of the heart has two chambers: an upper atrium and a lower ventricle. Between the atrium and ventricle on each side lies a valve – the tricuspid on the right and the mitral on the left – that regulates blood flow into the lower ventricular chambers. As the heart pumps (squeezes), these valves act as one-way gates, allowing blood to flow from the atrium above to the ventricle below and preventing blood from flowing backwards into the atrium when the ventricle squeezes.  From the ventricles, blood is then forced to flow out into the lungs through the pulmonary artery (on the right) or out to the body through the aorta (on the left) through a second series of one-way valves (the pulmonic valve on the right and the aortic valve on the left). The number of heartbeats per minute (heart rate) and the types of heartbeats are controlled by the electrical system in the heart. Normal heartbeats start in the right atrium but in sick hearts, heartbeats can start from any chamber.

 

What is dilated cardiomyopathy (DCM)?

DCM is a disease that causes the heart muscle cells (myocardium) to become weak and frequently causes abnormal heart beats (arrhythmias) to occur. Both of these problems can cause the heart to lose its ability contract or pump blood effectively out to the body. DCM can affect one or both sides of the heart, but typically it affects the left chambers, especially the left ventricle. DCM eventually leads to two main types of problems that can occur alone or together. First, because the heart muscle is weak and does not pump blood effectively, blood backs up in the heart chambers and causes them to enlarge or dilate. In some dogs that have DCM, when the heart is significantly dilated the mitral (and/or tricuspid) valves can leak and cause a heart murmur that your veterinarian can hear with a stethoscope.  Secondly, the abnormal heartbeats can occur intermittently throughout the day and night, and can reduce the amount of blood pumped to the body. This can lead to weakness or fainting, or even sudden death.  In cases where the heart chamber size and pumping function are still normal but abnormal heartbeats are present, DCM is often referred to as the arrhythmogenic form of DCM.  In some dogs that have DCM, your veterinarian may hear abnormal heartbeats or abnormal heart sounds with a stethoscope, but many dogs with DCM do not have heart murmurs, abnormal heartbeats or abnormal heart sounds.

 

Who gets DCM?

Dilated Cardiomyopathy (DCM) is a relatively common heart disease, accounting for about 10% of all heart disease in dogs. Large and giant breeds are most commonly affected.  DCM is very rare in smaller breed dogs (under 30 lbs. or 13.6 kg) and cats The risk of getting DCM increases as dogs get older, and rarely occurs in dogs that are under 4 years old. Certain breeds have a higher risk of developing DCM, especially Doberman Pinschers.

General risk factors are:

  • Dogs older than 4 years
  • Large or giant breed over 30 lbs. or 13.6 kg
  • High risk breeds:
    • Doberman Pinschers (have about a 60% chance of developing DCM at some point during their lives)
    • Cocker spaniels
    • Boxer dogs (may get the arrhythmogenic form of DCM -[chamber size and pump function is normal but abnormal heart beats are present] as young as 1 year of age)
    • Great Danes

 

What causes DCM?

There are many theories as to the cause of DCM, but the true cause has not been identified, and is often referred to as “idiopathic” for that reason. It is believed that there may be an inherited genetic component, but specific genetic evidence for the majority of DCM cases is lacking.

DCM may be related to a nutritional deficiency in taurine in some dogs but this is a very rare cause of DCM. Taurine is an amino acid required for the development and function of the heart muscle cells, so some dogs (especially Cocker spaniels) may develop DCM if they eat taurine-deficient diets or if they cannot absorb taurine normally from the food they eat.

Note: the majority of cases of DCM that are supplemented with taurine will NOT improve, but if your pet is diagnosed with DCM, ask your veterinarian if your pet might benefit from taurine supplementation.

L-carnitine is another amino acid that is required for the heart muscle cells to produce energy and pump normally. A nutritional deficiency in L-carnitine can also lead to the development of DCM some dogs (especially some Boxers and Cocker spaniels), but the role of L-carnitine deficiency in most dogs with DCM is unknown.

Note: the majority of cases of DCM that are supplemented with L-carnitine will NOT improve, but if your pet is diagnosed with DCM, ask your veterinarian if your pet might benefit from L-carnitine supplementation.

 

What happens to my dog when it gets DCM?

There are two main forms of dilated cardiomyopathy in dogs. The first causes the heart muscles to get weak, which causes blood to back-up into the heart chambers and the heart chambers to enlarge or dilate. The second form causes abnormal heartbeats to occur. Dogs with DCM can have one form at a time or suffer from both forms at the same time. Early in the course of the disease, dogs with DCM feel and act normally, and the only evidence that they have DCM may be the fact that your veterinarian heard a heart murmur, abnormal heartbeat(s) or an abnormal heart sound.  In some cases, DCM may be diagnosed through a screening test, such as an echocardiogram or Holter recorder, which is sometimes recommended for high risk breeds such as Dobermans or Boxers. At this stage, DCM is typically called asymptomatic, preclinical or occult (Stage B). The majority of dogs with asymptomatic DCM will develop clinical signs 6-24 months after they are diagnosed with asymptomatic DCM. In general, the dogs with the biggest (most dilated) hearts, and the dogs with the most abnormal heartbeats are the most likely to develop clinical signs. In some cases, the first sign that a dog has DCM could be that they die suddenly. Problems or clinical signs occur when the pressures in the dilated heart chambers cause fluid to leak out of the blood vessels into the lungs (called pulmonary edema) and sometimes the belly (ascites), or when there are a lot of abnormal heartbeats.  Once a dog develops clinical signs it is considered to have symptomatic DCM. The buildup of fluid in the symptomatic stage is called congestive heart failure (Stage C).

 

What are the clinical signs of symptomatic DCM?

Note: these clues represent clinical signs that may occur in dogs with DCM but can also occur with other diseases. If you know your dog has DCM you should always watch for them, and if they do develop, you should contact your veterinarian. Not every dog will develop all of these, but many dogs will have more than one.

  • Rapid breathing when resting or sleeping (more than 30-35 breaths per minute)
    • Note: for details on how and why to evaluate this in your dog see the section on evaluating home breathing rates below
  • Increased effort associated with breathing
  • Restless sleeping; moving around a lot and changing positions
  • Coughing or gagging
  • Weakness
  • Reduced ability to exercise
  • Collapse or fainting
  • Decreased appetite
  • Weight loss
  • Distended belly
  • Depressed attitude or quiet and not interactive
  • Sudden death

 

How can my veterinarian determine if my dog has DCM?

Because the majority of dogs with asymptomatic DCM are normal, and often have no abnormalities that can be detected by your veterinarian with a stethoscope, they frequently are not diagnosed with DCM until they are symptomatic. In some high risk breeds, such as the Boxer and Doberman Pinscher, your veterinarian may recommend annual screening tests to determine if DCM is present even if your dog appears healthy.

 

What are the screening tests that my veterinarian may recommend for high-risk breeds?

  • Echocardiogram: an ultrasound of the heart
  • Holter recorder: a 24 hour electrocardiogram (ECG) that your dog wears home to detect abnormal heart beats
  • ECG: 3 minute evaluation that is done in the hospital to detect abnormal heart beats
  • NT-proBNP: a blood test to evaluate the pressure in the heart might be used in Dobermans to help determine if your Doberman should have an echocardiogram
  • Genetic tests: might be used in combination with other screening tests. It is important to know that a positive genetic test does not mean that your dog has DCM or will get it, and a negative test does not mean they can’t get DCM. These tests are often used by breeders to help plan breeding programs.

 

What tests might be recommended by my veterinarian once my dog has DCM?

If your dog is asymptomatic (no clinical signs of DCM are present) and your veterinarian detects a murmur, abnormal heart beats or an abnormal heart sound with a stethoscope, they will recommend tests to help them determine is DCM is present and to determine if your dog should start taking any heart medications. Tests are also done to see if there are any other problems that may cause complications if they have DCM, like high blood pressure or kidney disease.

Dogs with one or more of the clinical signs listed above could have heart failure and require medications. Your veterinarian will recommend tests to help determine the cause of the clinical signs and help them select the appropriate medications. These tests may include:

  • Chest radiographs (x-rays): to see if there is any pulmonary edema (fluid in the lungs backed up from the heart) and to evaluate the heart size.
  • Echocardiogram: ultrasound of the heart to be sure of the diagnosis and evaluate the size and function of the heart.
  • ECG: to identify abnormal heart beats.
  • Holter recorder: 24 hour ECG that the dog wears home to help evaluate abnormal heart beats.
  • Blood tests to evaluate kidney and liver function.
  • Urine test to evaluate kidney function.
  • Thyroid blood test.
  • Blood pressure test.
  • NTproBNP to evaluate the pressure in the heart.

Genetic testing is available for the Boxer and Doberman but does not replace other important tests and cannot diagnose DCM.

Referral to a veterinary cardiologist may be suggested in some cases.

 

How is DCM treated?

The treatment of DCM depends on the stage of the disease and the individual dog’s problems.

Asymptomatic DCM

  • There are 3 medications that are commonly used to treat asymptomatic DCM:
    • Pimobendan (Vetmedin)
    • An angiotensin-converting enzyme inhibitor (enalpril or benzepril)
    • An antiarrhythmic (sotalol).

These medications can be used alone or together, and in some cases other medications may also be prescribed. The goal of these medications is to slow down the progression of the disease and help your dog stay asymptomatic and live longer.

Symptomatic DCM (heart failure and or abnormal heart beats)

Medications will be prescribed if your dog has clinical signs and the test results have led to a diagnosis of heart failure with or without a large number of abnormal heart beats. These medications will be continued forever, although the doses and frequency may change over time. Sometimes additional medications are required, while others are sometimes stopped.  In addition, your dog may need to stay in the hospital for a few days while adjusting to the medications.

Common medications used to treat heart failure and abnormal heart beats due to DCM:

  • Furosemide, also known as Lasix®
  • Pimobendan  (Vetmedin®)
  • Angiotensin converting enzyme inhibitor (ACEI), such as benazepril or enalapril 
  • Spironolactone
  • Sotalol-for abnormal heart beats
  • Mexilitine-for abnormal heart beats
  • Diltiazem- for abnormal heart beats

Additional medications are frequently used depending on the individual dog.

Note: some medications and herbal supplements can have adverse interactions with heart medications. Be sure to discuss any new or currently used medications with the veterinarian that prescribes your dog’s heart medication before giving them to your dog.

 

Are there any side effects of any of these medications?

Common side-effects of medication used to treat heart failure and/or abnormal heart beats due to DCM:

  • Drinking large amounts of water more frequently: it is critical that dogs on medications like furosemide have free choice access to water at all times.
  • Urinating larger amounts more frequently: dogs always need to urinate within 1-2 hours after receiving furosemide. To prevent accidents in the house, use a ‘doggy door’, or be sure to not give the furosemide pills within 2 hours of bedtime or leaving the house for an extended period of time.
  • Reduced appetite or not eating normal amounts of food: if this happens to your dog, talk to your veterinarian, as it is important that your dog not lose weight.

 

What kind of follow-up will my dog need now that it has DCM?

If your dog has asymptomatic DCM (Stage B): your veterinarian will recommend recheck appointments every 3-6 months depending on how advanced the disease is. If and when a medication is started, you may need to return in 10-14 days for a follow up to make sure everything is going well. This may include a blood test to check the kidney and liver, a check of your dog’s blood pressure, and a recheck of the abnormal heart beats.

If you notice any of the clinical signs listed above at any time, you should not wait for the next recheck appointment, but rather call your veterinarian and make an urgent/emergency appointment.

If your dog cannot breathe, rest or sleep comfortably, or if he collapses or faints, take your dog to the nearest emergency facility as soon as possible.

One of the best ways to help your veterinarian determine when to start or adjust your dog’s heart medication is to observe and record the home resting/sleeping breathing rate of your dog (see below).

If your dog has symptomatic DCM (heart failure and or abnormal heart beats): Your veterinarian will recommend a recheck appointment every 2-4 months. If and when a new medication is started, you may need to return in 10-14 days for follow up to make sure everything is going well. This can include a blood test to check the kidneys and liver, and a check of your dog’s blood pressure.

If you notice any of the clinical signs listed above at any time, you should not wait for the next recheck appointment, but rather call your veterinarian and make an urgent/emergency appointment.

If your dog cannot breathe, rest or sleep comfortably, or if he collapses or faints, you should take your dog to the nearest emergency facility as soon as possible.

One of the best ways to help your veterinarian determine when to start or adjust your dogs heart medication(s) is to observe and record the home resting/sleeping breathing rate of your dog (see #10 below).

 

Why should I evaluate my dogs resting/sleeping breathing rate at home?

Increases in your dog’s breathing rate while resting quietly or sleeping is a very important clinical sign that your dog may be developing heart failure and needs to see your veterinarian.  This is an early clue that heart failure is developing, and your observations can help limit how sick your dog becomes, reduce the chances that your dog will ever have to stay overnight in the hospital, and help reduce the costs associated with heart failure treatment.

 

What is a normal resting/sleeping breathing rate in a dog?

In general, normal dogs, and dogs with asymptomatic heart disease and heart failure that is well controlled on medications, have a breathing rate between 15-30 breaths every minute when they are resting calmly or sleeping. Lower rates are even possible and are no cause for concern provided, your dog is otherwise acting normally. It is considered normal for breathing rates to be much higher than this when dogs are hot, stressed, active or panting. Resting/sleeping breathing rates that are consistently greater than 30 breaths per minute are increased and considered abnormal. Since for some dogs, rates lower than 30 breaths per minute can be considered increased and abnormal by your veterinarian, you should ask your veterinarian what rate is considered increased and abnormal for your dog.

 

What should I do if the resting/sleeping breathing rate is increased in my dog?

The first thing to do is to count the breathing rate a few times over the next couple of hours to ensure it is a consistent finding. If the breathing rate is consistently increased then you need to contact your veterinarian as soon as possible. Typically your veterinarian will recommend a recheck appointment in the next day or two so medications can be adjusted.

If the resting/sleeping breathing rate is increased and other clinical signs as outlined below are observed, then the situation may represent an emergency. In this case, especially if it is after hours, you may need to go to a veterinary emergency center.

Clinical signs that may be associated with heart disease or heart failure:

  • Fast breathing when resting or sleeping (more than 30 breaths per minute)
  • Increased effort associated with breathing
  • Restlessness, agitation and difficulty finding a comfortable position to sleep
  • A change in how your dog sleeps (e.g. if your pet normally sleeps on his back or on his side, or curled up in a ball, and now sleeps sitting up or in a sphinx position).
  • Coughing or gagging
  • Weakness
  • Reduced ability to exercise
  • Collapse or fainting
  • Decreased appetite
  • Weight loss
  • Distended abdomen
  • Depressed attitude or quiet and not interactive

 

How do I count my dog’s resting/sleeping breathing rate?

When your dog is sleeping (or resting quietly if he won’t sleep), watch your dog’s chest; it moves in and out as your dog breathes. One breath is counted when the chest has moved in and out once. Use your watch or phone to time 30 seconds and count how many breaths occur during a 30 second period.  Next, multiply the number of breaths that you counted by 2 to get the number of breaths in 60 seconds or 1 minute.  Alternatively, you can count the total number of breaths that occur during in 60 seconds, and then there is no need to multiply.  Keep a record, such as in a diary or on a calendar, of the breathing rates you count. There are some free smartphone applications that can help you keep track of your dog’s home breathing rate. Search ‘your dog’s heart resting respiration rate’.

 

How often should I count my dog’s resting/sleeping breathing rate?

Typically, your veterinarian will have you count the breathing rate once per day for a week when you are learning so that you become comfortable performing this exercise.  This way you and your veterinarian can also learn what your dog’s normal resting/sleeping breathing rate is.

 

How often do I need to check my dog’s breathing rate if he doesn’t have any clinical signs of heart disease?

Home breathing rates do not need to be evaluated in all dogs with asymptomatic heart disease. Your veterinarian will tell you if and when it is time to start monitoring the home breathing rate in your dog. In general, it is most important to start in dogs with advanced asymptomatic heart disease that have a high risk of developing heart failure within the next year. In this case, breathing rates are typically recorded once or twice per week, although your veterinarian may ask you to monitor it more frequently.

 

How often do I need to check my dog’s breathing rate if he has heart failure?

Home breathing rate should be evaluated at least once per day in all dogs that have heart failure and are now receiving medications, such as furosemide.

 

Can special diets help dogs with DCM live longer?

Some pet food manufacturers have developed heart-specific diets.  Some of these diets are severely restricted in salt and some are moderately restricted in salt.  The diets that are severely restricted in salt should never be used in asymptomatic dogs with DCM. They may be used in dogs with heart failure as long as the dog will eat them.  The heart-specific diets that are moderately restricted in salt (or any diet that is moderately restricted in salt, such as most senior diets) can be used in asymptomatic dogs with DCM. While these diets are unlikely to be harmful if used as outlined above, they have not been shown to have any benefit, so it is unlikely that your veterinarian will recommend that you change your dog’s diet if he is otherwise healthy.

It is often beneficial to limit treats that are high in sodium for dogs that have heart disease, especially those in heart failure.

 

Are there any dietary supplements that may help dogs with DCM live longer?

Supplements are unlikely to be harmful if used as outlined by a veterinarian who is familiar with all the medications your dog is receiving and the type and severity of heart disease your dog is suffering from.  In most cases there is no proof that your dog needs to take any supplements if he is on a high quality commercial dog food diet.  The most common supplement recommended in dogs with DCM is omega 3 fatty acids, and in some cases taurine and or L-carnitine (see above). You should discuss any supplements your dog receives, or any new ones you wish to start, with your veterinarian.

 

What about exercise for my dog with DCM?

In general, dogs with both asymptomatic and symptomatic DCM should be allowed to exercise at their normal level if they want to, but the duration of sustained strenuous activities such as ball retrieval, swimming, Frisbee etc. should be limited, especially in really hot or cold weather. Some exercise is good for you and your dog and part of what helps your dog enjoy life.

 

Are there any research studies trying to learn how to treat DCM more effectively?

Some researchers (Dr. Amara Estrada at the University of Florida Veterinary School) are evaluating stem cell treatment in Dobermans. In the future, gene therapy may also be available for some dogs. Heart transplantation is not an option in dogs.

 

How long will my dog live now that he has DCM?

Asymptomatic DCM

It is difficult to say how an individual dog’s condition will progress, and it is for this reason that your veterinarian recommends tests and recheck appointments. On average, the majority of dogs with asymptomatic DCM can live for 1-3 years before they develop any clinical signs of heart failure. A few will die suddenly, and while this can happen at any time, it is most common in dogs that have a lot of abnormal heartbeats (it is not painful).

Symptomatic DCM

Once your dog develops clinical signs of DCM, medications can typically eliminate or reduce the severity of the clinical signs, but the disease will still progress and eventually the medications will not work as well. In some cases your dog will seem to be doing very well but die suddenly (this is most common in the dogs that have a lot of abnormal heartbeats and is not painful). Sometimes, new medications can be added, or the doses of your dog’s current medications adjusted, but eventually this will not maintain your dog’s quality of life. Your veterinarian will help you recognize when and if this is the case for your dog, but in general, with the appropriate medications and recheck appointments, many dogs with heart failure due to DCM live for more than 6-12 months.

This client information sheet is based on material written by: Sonya G. Gordon DVM, DVSc, DACVIM Cardiology

© Copyright 2017 LifeLearn Inc. Used and/or modified with permission under license.

Location Hours
Monday7:30am – 7:30pm
Tuesday7:30am – 7:30pm
Wednesday7:30am – 7:30pm
Thursday7:30am – 7:30pm
Friday7:30am – 7:30pm
Saturday8:00am – 4:00pm
Sunday5:00pm – 6:00pm

The telephone number at the Emergency Veterinary Clinic is 905-495-9907.