What is Dilated Cardiomyopathy in Dogs?
Dilated Cardiomyopathy in dogs is a disease of the heart in predominantly large and giant breed dogs, although it can occasionally be seen in smaller breeds.
Also known as DCM, Dilated Cardiomyopathy is a progressive disease of the muscles that make up the heart (myocytes) that weaken and cause poor contractility, eventually dilating the heart chambers and causing an enlarged heart. The heart begins to beat with less force, and the blood isn’t pumped effectively, leading to signs of congestive heart failure in dogs.
The exact cause is not always clear in dogs with dilated cardiomyopathy, but certain breeds appear to have a genetic predisposition to DCM.
In this article, we will discuss predisposed breeds, diagnosing and treating DCM, and what prognosis you can expect if your dog has dilated cardiomyopathy.
Prevalence of DCM and Predisposed Dog Breeds
The prevalence of DCM in the general population of dogs is between 0.5-1.1%. It represents 11% of all cardiac conditions in dogs. Pure-bred dogs are more likely to develop dilated cardiomyopathy than mixed-breed dogs.
Typically the dogs affected are middle-aged (four-eight years old), and males are affected twice as much as female dogs.
Large breed dogs are more susceptible than small breed dogs to DCM. Of the large breeds predisposed, the most affected are the Scottish Deerhound, the Doberman, and the Irish Wolfhound. Other commonly affected species include the Great Dane, the Boxer, and the St Bernard.
Knowing that there are breeds more predisposed, we can determine an inheritable cause of DCM, but the exact genetic cause is unknown. Some drugs, such as doxorubicin (a chemotherapy agent), can sometimes cause DCM in dogs.
Other causes of DCM have been found, including a juvenile form in a population of Portuguese Water Dogs and Toy Manchester Terriers. Another possible cause is infections with parvovirus and Chagas Disease. There is also suspicion of low taurine levels in food being a cause of DCM, but this has not been confirmed.
Signs and Symptoms of Dilated Cardiomyopathy in Dogs
Dilated Cardiomyopathy can be present for a long time without apparent signs of disease. Specific signs of DCM are not usually seen. Instead, signs of congestive heart failure (a sequel of the disease) are often what arouses suspicion of something being wrong with your dog’s heart.
Common signs of congestive heart failure include weakness, collapse, difficulty breathing, increased breathing rate, exercise intolerance, distension of the abdomen (pot-bellied appearance, also called ascites), and coughing. As the disease progresses, your dog may experience inappetence and lose weight as they develop a condition called cardiac cachexia.
Typically DCM will cause left-sided heart failure meaning the left side of the heart is failing first, so the signs are usually focused around the lungs (coughing, difficulty breathing). However, as the disease progresses, the right side of the heart can fail, causing signs affecting the abdomen (ascites).
Sudden death is possible when an irregular rhythm in dogs’ hearts with DCM can stop adequate blood flow to the brain.
Although it may seem sudden when signs of heart disease develop, the condition has likely been present for many years, just not obviously so.
How Does a Vet Diagnose DCM?
When your veterinarian consults with you and your dog, certain things may trigger suspicion of heart disease.
As described above, certain breeds are predisposed to dilated cardiomyopathy, and your veterinarian will know this. This means that when you arrive for your consultation, they will already be considering this disease.
The disease is more prevalent in certain aged and sized dogs, so this will be considered on presentation.
A history including the signs and symptoms described above will also be considered potentially caused by heart disease. Although signs such as weakness are not specific, they will be added to a list of problems which will help narrow down possible causes.
Knowing the history of your dog’s parents may also help since the condition is genetically linked. Diet will likely also be questioned due to current concerns around possible links (described below).
Other important history will be collected, such as previous health concerns, vaccination status, and travel history.
When your veterinarian examines your animal, they will be checking certain things that can indicate heart disease.
The general demeanor of a dog can give a lot of clues. If a dog has a poor condition, is having trouble breathing, or is coughing, these can all indicate the possibility of heart disease.
Gum color can change with heart failure depending on severity. A typical healthy pink can become pale or, in severe cases, even go blue.
Auscultation of the chest is very valuable as the heart can be checked for any unusual sounds (heart murmur in dogs) or irregularities of the rhythm. The lungs can also be auscultated, and muffled lung sounds are common in left-sided congestive heart failure.
Feeling pulses of dogs with congestive heart failure can help with diagnosis. They can sometimes feel weak.
Palpating the abdomen can help diagnose ascites (fluid) through the process of ballottement.
Tests can be used to not only diagnose heart disease in a dog with signs but also in dogs without signs which can be incredibly useful.
This is where an ultrasound machine is used to look at the heart; characteristic signs of DCM include a dilated, poorly contracting heart. An echocardiogram is the only definitive test to confirm dilated cardiomyopathy.
These are used to examine the heart and lungs. It can be difficult to 100% confirm dilated cardiomyopathy on x-ray, but signs include an enlarged heart. Congestive heart failure can be suspected where signs of fluid are seen in the lungs or the abdomen, especially if these coincide with an abnormal-looking heart.
An electrocardiogram is used to monitor the electrical current in the heart, and abnormalities can help diagnose DCM and guide treatment. A Holter Monitor may be recommended, and this is a portable ECG that a dog will wear for 24 hours to give a full day’s reading of the ECG, allowing for diagnosing problems that may only occur infrequently.
These tests can be performed in certain breeds, e.g., Dobermans, where the gene responsible for DCM is known and can be screened for, this is especially useful in breeding. This usually involves using a swab to sample the inside of the cheek.
Blood tests checking the BNP levels can be used to confirm heart disease. This is not specific for DCM but can be a helpful check to perform.
Available Treatment Options in Dilated Cardiomyopathy in Dogs
Unfortunately, prevention of DCM is complicated, although there have been many medical protocols and nutritional supplements proposed. There is no cure for DCM once it has developed.
If there is a genetic test available, it is recommended that any breeding dogs are checked for the presence of the DCM gene prior to breeding. Other preventives include vaccinating against parvovirus and making sure to feed a good quality dog food to prevent deficiencies.
Once a diagnosis of DCM has been made, the disease will continue to progress, but there are options available to help delay the progression. In dogs where a diagnosable cause is found, e.g., taurine deficiency, fixing this can help slow/halt the progression and potentially reverse signs.
In dogs where dilated cardiomyopathy has been diagnosed before the onset of signs, medications can be administered to help slow the development of signs (i.e., congestive heart failure).
Once a dog develops congestive heart failure, the treatment focuses on helping the heart contract usually and removing the excess fluid that builds up in the chest and abdomen. Doses of medications are often increased as the disease progresses, and new drugs may need to be added to help keep your pet stable.
A List of Commonly Prescribed Medications:
Pimobendan– is a relatively new drug that can be used in subclinical (asymptomatic) and clinical (symptomatic) cases of DCM. Pimobendan helps lower the pressure in the veins and arteries and increases the contractility of the heart muscle. This is an essential drug in the treatment of DCM.
Angiotensin-converting enzyme (ACE) inhibitors- such as enalapril or benazepril, can be used in subclinical and clinical cases. ACE inhibitors work by lowering blood pressure and reducing the resistance to blood flowing out of the heart.
Diuretics such as furosemide or spironolactone stimulate the kidneys to remove excess fluid from the body, which is crucial in dogs with congestive heart failure.
Cardiac glycosides help to improve heart function by slowing the heart rate and strengthening heart contractions. Digoxin is the most commonly used cardiac glycoside but can become toxic quickly, so it needs to be used carefully.
Vasodilators dilate the arteries or veins in the body, depending on the one that is used. This helps give the heart a break by meaning it doesn’t have to pump as hard to supply blood to the body. ACE-inhibitors work to dilate blood vessels, so they are commonly used for this purpose.
Bronchodilators help to make breathing easier for dogs; examples include theophylline and aminophylline.
Antiarrhythmic drugs are used in dogs where an arrhythmia is found (an irregularity in the heart rhythm). The two main classes are beta-blockers and calcium channel blockers.
Other beneficial treatments include supplementing with taurine and carnitine as well as putting your dog on cardiac food.
The Lifespan of a Dog After DCM
There are unfortunately no guarantees with any animal’s lifespan, particularly those with heart disease. We can say that for dogs with DCM detected early and treated adequately, the prognosis is better without treatment. Response to treatment can also be a good indicator of prognosis where dogs don’t respond well they are less likely to “bounce back.”
Unfortunately, the prognosis for patients with DCM is poor. The individual prognosis varies between dog breeds and how early the disease is detected.
Most commonly, dogs with DCM will pass away from the development of congestive heart failure, whereby fluid in the lungs makes it difficult to breathe. Any dog with DCM is at risk for sudden death due to a lethal arrhythmia. This can be very distressing for owners, so it’s essential that you are aware this could happen.
The lifespan can be variable and breed-dependent. Irish Wolfhounds may survive for years, while Dobermans can succumb much faster. Luckily with advances in medicine and the development of pimobendan, a Doberman who would have previously survived <60 days can now be expected to survive six-eight months with treatment. The average survival after the onset of congestive heart failure is eight-ten months with therapy for other breeds.
The FDA and a Potential Dietary Link to DCM
In 2018 the FDA launched an investigation into a possible link between dilated cardiomyopathy and diets labeled as “grain-free,” often using peas, lentils, and potatoes in large quantities. The cases of DCM that were seen were not linked to breeds predisposed to the disease.
Nothing concrete has been found at this stage, and the FDA has no clear evidence of any link. The FDA has requested owners and veterinarians to submit information from any dog that develops DCM and is fed a “grain-free” diet.
The situation is developing, and more evidence may be found in the future. There is a clear spike in cases of DCM in the last few years, but unfortunately, as of now, the cause is unclear.
Dilated cardiomyopathy is a severe condition in large and giant breed dogs, particularly affecting Irish Wolfhounds and Dobermans. There are some known genetic causes, but a lot of what leads to the development of DCM in a dog remains unclear.
As an owner, you may begin to suspect heart disease if you notice a range of signs, including exercise intolerance and increase breathing rate. When you take your dog to a veterinarian, they will suspect heart disease from signalment, history, and physical exam and may recommend some tests.
Echocardiography is the only definitive test to confirm DCM. It can be used in dogs before developing obvious signs (subclinical) to diagnose the disease and allow for treatment to start early.
There are many medications available to help with DCM, and congestive heart failure occurs as the disease progresses, an essential drug in the treatment of DCM is pimobendan.
Unfortunately, the prognosis for a dog with DCM is poor and usually less than a year, even with treatment. Still, the good news is that the lifespan expected continues to improve with modern medicines and more research.
Currently, the FDA is investigating a link between “grain-free” diets and DCM, but no clear relationship has been discovered.