Canine Dilated Cardiomyopathy (DCM): Causes, Symptoms, Diagnosis & Treatment

When your dog has dilated cardiomyopathy (DCM), his heart can no longer maintain enough pressure to properly pump blood through his vascular system to the rest of his body. It’s a very dangerous—often fatal—disease among medium and large sized dogs. In fact, it’s the most common cause of heart failure in certain large breed dogs.

Before we get into the more complex details about DCM, let’s break it down into simpler terms. 

• Cardiac (or cardio) means relating to the heart. 
• Myopathy refers to diseases that affect skeletal muscles. 
• Cardiomyopathy means degeneration of the heart muscles. 

When this happens, the heart muscle wall—primarily the thick muscle wall of the left ventricle—becomes thinner and stretches under the pressure of blood flow, which causes the heart to become enlarged. This condition is called dilated cardiomyopathy (DCM).

What Causes Canine Dilated Cardiomyopathy?

The definitive cause of canine dilated cardiomyopathy is up for debate, however, nutritional, infectious, and genetic predisposition could be key factors. 

Small dogs rarely develop DCM, and it’s more common in males than females. Canine dilated cardiomyopathy is typically seen in large and giant breeds, such as Doberman Pinschers, Great Danes, Saint Bernards and Irish Wolfhounds (among others). 

According to the FDA, dilated cardiomyopathy is also seen in Cocker Spaniels associated with taurine deficiency. “We suspect that cases are underreported because animals are typically treated symptomatically, and diagnostic testing and treatment can be complex and costly to owners.”

When it comes to genetic forms of DCM, mid- to senior-aged male large and giant breed dogs are often affected.

In terms of dietary or nutritional causes of DCM, dry dog food formulas greatly outweighed wet, moist, and raw foods. Read Canine Dilated Cardiomyopathy Complaints Submitted to FDA-CVM Through April 30, 2019 for a specific breakdown of DCM reports submitted to the FDA.

Symptoms of Canine Dilated Cardiomyopathy

When your dog’s heart is struggling to pump blood through the vascular system, several problems arise, each causing different symptoms, such as:

• Decreased delivery of oxygenated blood to the body causes lethargy, weakness, weight loss, and may even cause your dog to collapse.
• Congestion of blood in the lungs causes coughing, increased respiratory rate and/or effort (panting or difficulty breathing), abdominal distention, or both.
• Decreased oxygen supply and increased oxygen demand (secondary to increased heart rate and ventricular wall stress) may cause cardiac arrhythmias in either the atria (presenting as atrial fibrillation or supraventricular tachycardia) or in the ventricles (ventricular premature complexes or ventricular tachycardia). 

An arrhythmia is an irregular heart beat—too fast, too slow, or with an irregular rhythm.

Tachycardia is the medical term for a heart rate over 100 beats per minute.

Watch out for these potential signs of DCM:

• Rapid breathing (more than 30-35 breaths per minute) while resting or sleeping

• Difficulty breathing

• Restless sleeping (moving around and repositioning frequently)

• Coughing or gagging

• Weakness or lethargy

• Collapse or fainting

• Decreased appetite and/or weight loss

• Distended belly

• Depressed mood, lack of interest in play

Some dogs develop severe congestive heart failure (CHF) in just a few hours, while others may not show signs right away. DCM may develop slowly over time, so it’s extremely important to see your vet for annual checkups. 

How is Canine Dilated Cardiomyopathy Diagnosed?

Your veterinarian will perform several tests to assess various aspects of your dog’s heart function. In addition to a standard checkup, including listening to the heart with a stethoscope, checking for belly distention, and reviewing your dog’s general behaviour, more in-depth diagnostic tests may be performed.

Blood and urine samples are taken to test liver and kidney function, which can often be impaired by DCM. Your vet may also be looking for ProBNP, a specific protein level in the blood that changes when heart disease is present.

Echocardiography (ultrasound) allows your vet to see the heart wall dilation (thinning and enlargement) as well as its ability (or lack thereof) to pump blood through the ventricular system. 

Thoracic radiography (X-rays) may also be used to evaluate pulmonary (lung) tissue and vessels. Your vet will use this to look for signs of fluid in the lungs (pulmonary edema) or around the lungs (pleural effusion). 

Electrocardiography (ECG) may be used to check your dog’s heart rhythm. Sometimes, a 24-hour electrocardiogram (Holter monitor) may be used to more accurately measure cardiac rhythm and diagnose arrhythmias.

What is the Treatment for Canine DCM?

Treatment for dogs with dilated cardiomyopathy depends on the issues associated with the disease, but typically aims to improve the heart’s ability to pump, open up the blood vessels to reduce stress put on the ventricular system, eliminate lung congestion, and regulate heart rate or cardiac arrhythmias.

Let’s look at some of the issues and treatment options:

• Diuretics (such as furosemide or spironolactone) may stimulate the kidneys to remove excess fluid from the body.
• ACE (angiotensin converting enzyme) inhibitors (such as Enalapril and benazepril) may lower blood pressure. These drugs have vasodilators, which open up the arteries or veins, allowing the heart to pump blood to the rest of the body more efficiently.
• Pimobendan may lower arterial and vein pressure to strengthen the heart muscle and increase blood flow to the rest of the body.
• Bronchodilators (such as theophylline or aminophylline) may make it easier for your dog to breathe.
• Cardiac glycosides (such as digoxin) may slow the heart rate and strengthen heart contractions allowing blood to pump more efficiently. Your veterinarian will likely perform regular blood tests and ECG analyses to watch for potentially toxic side effects of these drugs.
• Antiarrhythmic drugs (such as beta-blockers: atenolol, sotalol, carvedilol; calcium channel blockers: diltiazem; or others: procainamide, mexiletine, amiodarone) may be used cautiously if the above-mentioned drugs fail to control arrhythmias. 

Canine dilated cardiomyopathy can be a potentially fatal disease. The prognosis for dogs with DCM depends on the breed and stage of the disease, but there are treatments available that could significantly improve and prolong your dog’s quality of life.

If your dog is showing signs of dilated cardiomyopathy, such as decreased energy, difficulty breathing, lethargy, coughing, collapse, weight loss, decreased appetite, or distended belly, contact your veterinarian immediately. If your regular vet is not available, seek emergency veterinary care.