Dilated Cardiomyopathy in Dogs, Symptoms and Treatment

Dilated cardiomyopathy (DCM) is a disease that affects the heart's systolic function (a dysfunction in its ability to contract), which may or may not come with arrhythmias. This condition affects dogs fairly often, especially males and larger breeds.

This condition accounts for more than half of heart disease cases seen in veterinary practice, and it's also fatal if not caught in time, so it's worth knowing about. Below, we'll explain what it involves, which dogs are at higher risk, how it can be diagnosed, and, above all, treated.

What is dilated cardiomyopathy?

This heart disease is characterized by enlargement of the heart's chambers and thinning of the ventricle walls. Remember that a dog's heart, like a human's, is divided into four chambers: two atria and two ventricles.

Any problem affecting the heart impacts how it functions, which affects proper blood circulation throughout the body. This results in what's known as heart failure.

Which dogs get dilated cardiomyopathy?

Dilated cardiomyopathy is a heart disease that can affect any dog, but it's true that some are more prone to it than others. In fact, this cardiomyopathy is the most common cause of heart failure in large and giant breeds. Toy or small breeds, on the other hand, don't usually develop this cardiomyopathy.

Some breeds are more predisposed to it, such as the Boxer, Pinscher, Cocker Spaniel, and Doberman. In two of these commonly affected breeds, 2 genes have been linked to this disease, thanks to various studies carried out to date. In Boxers, a mutation has been identified called "striatin," and in Dobermans, another mutation in the pyruvate dehydrogenase kinase 4 (PDK4) gene.

What's more, in this last breed, there's a second mutation involved, also present in humans who develop this same condition, known as the "titin" mutation, which results in excessive stretching of the heart's microfibers, preventing the muscle from doing its job properly.

Other breeds in the risk group would include the German Shepherd, Great Dane, Saint Bernard, or Schnauzer. What's more, males are affected more often. Symptoms usually appear between five and six years old, though onset age varies and depends on the individual dog and breed. Interestingly, for example, Portuguese Water Dogs commonly develop the disease at a very young age, known as the "juvenile form," described only in this breed.

Why does dilated cardiomyopathy occur?

This is a primary disease of uncertain cause, meaning in most cases the reason it develops is unknown. It's then said to be idiopathic; however, the leading hypothesis points to a genetic origin. In other cases, before it develops, the dog suffers from myocarditis, which is inflammation of the myocardium, the heart's muscle tissue.

Dilated cardiomyopathy has also been linked to hypothyroidism, a disease in which the thyroid gland doesn't produce enough thyroid hormone, and a genetic predisposition has been established in large and giant breed dogs.

Recently, it's been discovered that nutritional deficiencies in taurine and carnitine are linked to this condition, mainly in Cocker Spaniels and Newfoundlands. It can also be drug-induced, such as by doxorubicin, used in chemotherapy, and sustained high heart rates (tachycardia-induced cardiomyopathy) can also result in this disease.

Lastly, it appears that grain-free diets high in legumes such as peas, lentils, or both may be linked to a higher risk of this disease, though this is still being studied.

Symptoms of dilated cardiomyopathy

Any dog can develop this condition, but if they belong to one of the risk groups mentioned, the likelihood of this diagnosis is higher.

This disease develops progressively and includes an initial stage called the "preclinical phase," where the disease is present but there are no observable clinical signs, and a "clinical phase," where the pet does show symptoms.

The clinical signs that should alert us are the following:

• Rapid weight loss, visible within a few weeks.
• Lethargy, with a significant drop in activity.
• Tiring easily.
• Increased breathing rate (tachypnea).
• Frequent coughing, especially at night, which may be accompanied by bloody phlegm.
• Abdominal swelling known as ascites.
• General weakness.
• Collapse, and even sudden death in the most severe cases.

How is dilated cardiomyopathy diagnosed?

If our dog shows any of these symptoms, the vet can run several tests aimed at assessing the heart's condition. These are:

1. Electrocardiogram (ECG), which gives information on the heart's electrical activity. Arrhythmias — disruptions in heart rhythm — are commonly detected.
2. X-ray, which can show the heart's enlarged size.
3. Echocardiogram, an ultrasound of the heart that lets the vet assess the heart both functionally — seeing how it beats and pumps — and structurally, where a more rounded heart with a dilated left ventricle will be seen.
4. In cases where these tests come back negative, a Holter monitor is recommended (24-hour ECG monitoring) to identify any arrhythmias that weren't otherwise detected.

All of these tests provide very important information that lets the professional study each case in detail. The most appropriate treatment depends on this, and it will vary based on severity. It's recommended to run these tests yearly from 3 years of age onward in predisposed breeds mentioned above.

Treatment for dilated cardiomyopathy

This disease affects the heart and disrupts its rhythm, so treatment focuses on improving its function as much as possible and preventing arrhythmias, through the use of positive inotropes, which help increase contractile force, and vasodilators, which ease the heart's workload. Fluid buildup in the abdomen or lungs also needs to be prevented, which is achieved with diuretics. All of this should follow the dosing set by the vet.

It's also recommended to switch to a low-salt diet and restrict physical activity. On this last point, moderate exercise is beneficial, but only as long as the dog shows no symptoms. Of course, if coughing, tiredness, or breathing difficulty appears during any activity, it should be stopped.

Prognosis

Cardiomyopathy is a disease that has no cure but is treatable. This means that with the right treatment, we can improve our dog's wellbeing and help extend their life expectancy. That said, close veterinary follow-up through regular clinic visits is essential.

Either way, the prognosis depends on multiple factors, so generally speaking, and in the long term, it can be considered guarded. While asymptomatic dogs can live for years, once symptoms develop, average life expectancy is 9-12 months. Sudden death is always a possibility, and owners should be made aware of this.