Heart diseases in dogs

It is estimated that a little over 10% of all pets have some form of heart disease. There are many different reasons for the presence of heart disease – from genetics to poor diet, ageing, illness/infection and obesity – but what is common among all types of heart disease is that the condition does not simply go away on its own. It is usually progressive and, depending on how severe the symptoms are and when the dog is diagnosed with the disease, it can eventually lead to heart failure.

Types of heart disease

Heart disease can refer to any abnormality of the heart’s structure, electrical activity and function. The most common types of heart disease in dogs include those that affect the functioning of the heart valves (valvular degeneration), weaken the heart muscle (dilated cardiomyopathy), thicken the heart muscle (hypertrophic cardiomyopathy), and those in which the electrical activity of the heart is affected (arrhythmia).

Heart disease can be congenital – meaning dogs are born with a defect that results in the disease – or it can be acquired – meaning that it develops over time as a result of the side effects of infection, old age, (especially) if the dog is overweight or is not fed a complete and balanced diet.

The following are just some of the more common types of heart disease that affect dogs:

Valvular degeneration

Valvular degeneration occurs when the valves of the heart no longer function as they’re supposed to. The function of the valves is to open and close, allowing blood to flow through or stopping the flow, depending on where they are located. When they thicken, weaken and degenerate, the valves cannot open or close properly, which causes a leakage of blood and the enlargement of the heart.

Mitral valve disease or degenerative mitral valve disease is the valvular degeneration most often seen in dogs. It affects the two left heart chambers and can eventually lead to congestive heart failure. It can be diagnosed even before any symptoms show up, and will only present as a slight heart murmur. Once diagnosed, it can be managed through specific medications and the appropriate diet. It cannot be cured, which is why managing the condition is so important.

Mitral valve disease is a congenital disease for which the Cavalier King Charles spaniel is most commonly known. Almost all dogs of this breed will develop mitral valve disease and eventually succumb to heart failure.

Dilated cardiomyopathy (DCM)

If we break down the name, dilated (enlarged) cardio (heart) myo (muscle) pathy (disease) refers to a range of conditions that negatively affect the heart’s muscle, causing it to weaken and enlarge. The enlargement happens because the heart muscle (the walls of the heart) thins and weakens; the heart then cannot pump efficiently and it fails to pump all of the blood out of the heart, causing it to enlarge.

Dilated cardiomyopathy (DCM) is the most common heart disease diagnosed in large breed dogs, and second most common overall. It is progressive and often leads to congestive heart failure. If DCM is diagnosed early on, it can be managed with medication, allowing the affected dogs to live longer with fewer symptoms, but there is no cure. It is usually large and giant breed dogs who develop DCM – breeds like boxers, Great Danes, Doberman pinschers, St Bernards, Irish wolfhounds, some German shepherd dogs and some spaniels, especially those older than four years.

DCM is more common in certain breeds than others, but it is not always congenital and can be acquired due to other factors like diet and old age.

Pericardial disease

Also called pericardial effusion, this type of heart disease affects the thin sac around the heart called the pericardium. In healthy dogs, this sac contains a little fluid to assist the heart’s beating mechanism, while in pericardial effusion, the sac fills with fluid to the extent that it restricts the heart’s ability to fill with blood, which constrains its vital function.

Pericardial disease is usually a symptom or effect of hemangiosarcoma – cancer of the blood vessels near the heart – or inflammation of the heart, which causes scarring on the pericardium. When the cause of the scarring cannot be determined, the condition is called idiopathic pericardial effusion. Some dogs are even born with a pericardial sac that does not function properly, which risks normal heart function and causes heart disease.

This particular type of heart disease usually goes undetected until it causes a medical emergency. It requires the veterinarian to insert a long needle through the dog’s side and into the pericardium to drain the excess fluid that is restricting the heart’s function. The prognosis of pericardial effusion varies depending on the cause of the fluid build-up, and dogs can live for three months to three years with repeated treatments. There is no cure and the vet will encourage owners to consider the dog’s quality of life (with the possibility of sudden death) before consenting to ongoing treatments.

Heart arrhythmias

The heart’s beating function is controlled by an electrical current or pulse that stimulates the heart muscle and causes it to contract in a coordinated way. When there is an interruption in the electrical current or a disruption to the coordination, this causes arrhythmia. The different types of arrhythmias are defined by an increase or decrease of the heart rate (tachycardia or bradycardia, respectively), blockages, or a lack of coordination between the different parts of the heart (premature ventricular contractions and atrial fibrillation).

If a dog is diagnosed with an arrhythmia, there are various ways of treating or correcting it including medication or a pacemaker.

Congenital heart disease

Some heart diseases result from an abnormality in the dog’s heart development and are present at birth. Congenital heart problems account for around 4% of veterinary cardiology cases, so they are rare, but they can be devastating for the pet parents of the affected puppy. Congenital heart diseases are detected when the vet hears a heart murmur during the puppy’s checkup, but they require more extensive testing methods (such as ultrasound and electrocardiogram (ECG)) to make an accurate diagnosis.

When serious congenital heart diseases are detected in purebred puppies, it is critical that the breeders are notified so that they do not continue breeding with the parents of the sick puppies, and to provide data on the relevant  bloodlines.

Congenital heart diseases include:

  • Patent ductus arteriosus (PDA)

An open artery that should close after birth, but doesn’t. Can be corrected with surgery.

  • Pulmonic stenosis

An abnormally narrow heart valve that makes the right side of the heart work harder. Can be corrected with a catheter and balloon to open up the valve.

  • Subaortic stenosis

An abnormally narrow channel connecting the left ventricle to the aorta, which makes the left side of the heart work harder. Surgical treatment is difficult and often unsuccessful, while medication is used to slow the development of disease and heart failure.

  • Ventricular septal defect

This describes an abnormal connection between the heart’s two ventricles, which can result in an enlarged heart and more blood being pumped to the lungs. Depending on the size of the problem, the dog can live with VSD, or it can be treated with medication and a carefully managed diet. Surgical intervention depends on the severity of the progression of the disease.

Symptoms of heart disease

A dog with heart problems will experience symptoms such as:

  • shortness of breath
  • rapid breathing
  • coughing (especially after exercise)
  • round belly (abdominal swelling) from fluid build-up
  • fatigue
  • fainting
  • rapid weight loss

Some heart disease does not present any symptoms, but may first be suspected if the vet detects a heart murmur during a routine check-up. By the time symptoms show, the dog could already be nearing heart failure, which is why it’s important to get the dog checked by a vet if any of the above symptoms are present.

How are heart diseases diagnosed?

From the stethoscope to the electrocardiogram (ECG); the chest X-ray to a simple observation; from the echocardiogram (echo) to a blood pressure monitor – there are many diagnostic tools for identifying heart diseases, depending on which type of heart disease the vet suspects.

Can heart disease be treated?

Each type of heart disease is monitored and treated for the type and severity, as well as the impact it is having on the dog’s quality of life.

Dog heart diseases range in type and severity – with some not showing symptoms until well into the dog’s life, while others show symptoms in puppyhood and need serious treatment. The vast range of heart diseases means it’s vital that dog owners take their beloved dogs for their annual check-up to allow for regular screening; and that they pay attention to potential symptoms of heart disease and act quickly if they observe any troubling symptoms in their pets.

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