Dilated Cardiomyopathy in Dogs
Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS
Table of Contents
Cardiomyopathy is the term for any condition affecting the muscular walls of the heart. The most common cardiomyopathy seen in dogs is called dilated cardiomyopathy, known as DCM. The heart contains four chambers; two atria at the top, and two ventricles at the bottom. Deoxygenated blood from the body flows into the right atrium, before passing to the right ventricle which pumps it towards the lungs. Oxygenated blood from the lungs enters the left atrium, before passing to the left ventricle which pumps it to the body. In DCM, the ventricles stretch and become enlarged. This reduces the capacity and the efficiency of the heart.
DCM is significantly more common in large breeds of dog, such as Dobermans and Irish Wolfhounds. We do not fully understand why certain breeds are more affected than others, but in several breeds there is evidence of a genetic component to the condition. DCM is most common in middle-aged or older dogs.
In early or mild cases of DCM, the heart is still pushing enough oxygenated blood around the body, so there are no visible symptoms. In some patients, dilation of the ventricles leads to widening of the mitral valve, allowing the valve to leak. This can cause turbulent blood flow, which may be heard as a heart murmur when listening to the heart with a stethoscope. However, in many cases of DCM, there is no audible murmur.
As the heart stretches, the electrical impulses that control contraction can become distorted. This causes an abnormal heart beat, known as an arrhythmia. The most common arrhythmia seen due to DCM is known as atrial fibrillation. The heart will be beating extremely fast, and the beats will sound abnormal when auscultated with a stethoscope. Atrial fibrillation causes dogs to be lethargic and struggle to exercise, and can cause collapse.
Over time, changes in the heart due to DCM reduce its ability to function normally. Many dogs will cope with this gradual change, and still may not have symptoms even on examination. Eventually, the heart deteriorates to a point known as congestive heart failure (CHF). This means the enlargement of the ventricles is preventing the heart from pushing sufficient blood around the body. This causes fluid to back-up into the lungs (known as pulmonary oedema) which affects the breathing. Symptoms include reduced ability to exercise, faster or laboured breathing, and sometimes collapse.
Both atrial fibrillation and CHF have symptoms that lead to a high index of suspicion on examination, but neither can be diagnosed on clinical exam alone, and neither are solely seen in DCM.
A definitive diagnosis of DCM is only made using an ultrasound scan of the heart, known as echocardiography (commonly called an “echo”). An echo allows us to see the chambers of the heart, assess how they are filling and contracting, and even directly observe turbulent blood flow. Measurements are recorded, allowing comparison with future scans to monitor progression of disease.
If an arrhythmia is heard or suspected, an electrocardiogram (ECG) will be advised. This records a trace of the heart's electrical activity and allows different arrhythmias to be identified. Occasionally, an intermittent arrhythmia is suspected, so a continuous ECG recording may be recommended, lasting anywhere from 24 hours to 7 days. This is known as a Holter monitor, and is usually performed by vets with a particular interest or training in cardiology.
Dogs who are diagnosed with DCM, but have no clinical signs of congestive heart failure, are known as having pre-clinical or occult DCM. It is recommended to start daily treatment with a drug called Pimobendan. This helps the heart to pump effectively, and may delay the development of CHF. Repeat assessment, usually a check-up and repeat heart scan, are recommended every 3-6 months to monitor progression of the disease.
Dogs experiencing atrial fibrillation will require medication to manage this, and regular check-ups, as well as management of the DCM. Dogs who present very unwell or collapsed may require a short stay in the clinic until the arrhythmia is under control.
Dogs who are diagnosed with congestive heart failure will always need treatment. Diuretics are given to relieve fluid build-up in the lungs. Depending how unwell the dog is, this may be given orally at home or may be administered by injection in the practice. Other medications may also be prescribed, based on the individual findings in your dog. Some dogs will benefit from a short period of hospitalisation for more intensive care than can be provided as an out-patient. A repeat echo may be required for a current assessment of the heart and its response to the medication, and chest x-rays may be recommended to assess the lungs. The majority of cases will respond to treatment, but will need to continue taking oral medication for the rest of their life.
Sadly, there is no cure for DCM, and the condition is considered progressive. This means that it will continue to get worse, and the majority of dogs with DCM will eventually develop CHF. Every dog will progress differently, however, and some can remain stable with pre-clinical DCM for months or even years. Once dogs do enter CHF, the typical survival is 9-12 months from diagnosis.
A small number of dogs with DCM can experience sudden death, despite seeming outwardly stable. This is often due to the combination of DCM and atrial fibrillation, and very rarely can happen in dogs without a prior diagnosis. There is no way of predicting which cases this will affect, so dogs should be allowed to enjoy life to the best of their abilities. It is important to continue any medication prescribed for the rest of the dog’s life, and speak to your vet directly if you have any concerns.
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Last review date: 13th February 2024
Next review date: 13th February 2026