Boxers are a very popular breed in the UK but sadly, as with many dog breeds, they are known for certain health problems. For them the focus is often on their heart. The heart is an incredibly intricate organ with many parts that can go wrong and when they do, the results can be catastrophic. So what is it about Boxer’s hearts that predispose them to issues and can we do anything about it?
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How the heart works
The heart is basically a large muscle divided into 4 chambers (2 atria and 2 ventricles) with a dividing wall between the right and left sides (septum), and a series of valves. There are valves between each atria/ventricle pair (mitral valve on the left and tricuspid valve on the right) and at the exit to each ventricle (aortic valve on the left and pulmonic valve on the right). The heart works through electrical fibres in the walls which stimulate rhythmical contractions of each chamber to pump blood either out to the lungs or around the body.
What can go wrong?
There are many different forms of ‘heart disease’ which can affect how the heart functions. In the case of Boxer dogs, the conditions they are most prone to are Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC), otherwise known as Boxer Cardiomyopathy; Pulmonic or Aortic stenosis and Dilated Cardiomyopathy (DCM).
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)
What is it?
This disease is characterised by replacement of the normal heart tissue with fatty or fibrous tissue. Over time, this will upset the normal electrical activity of the heart. It can lead to arrhythmias, or an irregular heartbeat. This irregularity means the heart is unable to function efficiently enough to pump blood and oxygen around the body to meet demand.
Symptoms
The most common symptom seen with this condition is fainting, or syncope. Unfortunately, sometimes the first sign that a dog has ARVC is sudden death. In other situations, the changes in the heart can cause heart failure and lead to symptoms such as a cough, breathlessness and exercise intolerance.
Causes
ARVC is a genetic condition, hence the frequency with which it’s seen in the Boxer population. There is testing available to determine if a dog carries the particular genetic mutation which is to blame for ARVC. But being a carrier doesn’t necessarily mean the dog will go on to develop the condition; it is estimated that over 40% of Boxer dogs do carry it.
Diagnosis and treatment
Once diagnosed, by way of an ECG and an echocardiogram, treatment is aimed at controlling the arrhythmia with medications in order to reduce the chance of collapse.
Pulmonic and/or Aortic stenosis
What is it?
Both of these conditions involve a narrowing of the pulmonic and aortic valves respectively. The pulmonic valve controls the flow of blood out of the right side of the heart and towards the lungs. A narrowing at this location means a higher pressure in the right ventricle is needed to push the blood through, which can overload the right side of the heart. The aortic valve controls the flow of blood out of the left side of the heart and towards the rest of the body. A narrowing at this location means a higher pressure is needed in the left ventricle to push the blood through, which can overload the left side of the heart.
Causes
The cause of both conditions is usually due to a developmental defect of the valve, sometimes involving fusion of the valve leaflets (“flaps”). Most cases are picked up in puppyhood.
Symptoms
In both cases, symptoms can include a murmur over the affected valve, signs of heart failure and arrhythmias.
Diagnosis and treatment
Diagnosis is by echocardiography and although the symptoms can be controlled with medication, ultimately, surgery is often needed.
Dilated cardiomyopathy (DCM)
What is it?
DCM is disease of large breed dogs, Boxers included. DCM occurs when the muscle in the walls of the heart degenerates, causing it to thin and stretch. These changes mean that the heart is unable to beat efficiently and therefore will eventually lead to signs of heart failure.
Causes
As well as the suspected genetic component to DCM, more recently there have also been potential causal links made to certain diets, specifically grain-free diets. Infections and other diseases such as thyroid disease have also been implicated.
Symptoms
The symptoms are similar to the other conditions mentioned, as often, the signs are subtle until the animal begins to develop heart failure. General fatigue, breathlessness, coughing, collapse and exercise intolerance are all common.
Diagnosis and treatment
DCM is fairly easily diagnosed on echocardiography and treatment again revolves around managing the symptoms of heart failure, treating any arrhythmias and relieving any excess strain on the heart.
What is the prognosis?
As vets, we see common things commonly. We will regularly see and diagnose cases of heart disease in dogs, in many different breeds. Boxers are known to have a high incidence of heart disease but bear in mind, not all these cases are symptomatic and many won’t ever require any treatment or have any impact on the dog’s quality of life. For those that do, the earlier it is detected, potentially the better the outcome. Annual checks, often at the time of vaccination, are recommended, but if you notice any of the symptoms mentioned in this article, it is worth seeking veterinary attention sooner.
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