Dilated cardiomyopathy (DCM) refers to a primary disease of the left ventricular heart muscle. In this disease, the left ventricle is no longer able to contract properly and becomes dilated. DCM is generally considered to be a disease of large breed dogs such as the Doberman Pinscher, German Shepherd, Boxer, Great Dane and Irish Wolfhound. It is occasionally recognised in small breed dogs and cats.
In the Doberman Pinscher the disease is known to be inherited. Breeding from affected dogs is not recommended. In other breeds the disease is called ‘idiopathic’ which means the cause is unknown however, in many large breed dogs, a genetic component is suspected. Inherited or idiopathic DCM is considered a progressive disease. While there are treatment options available, cure is not possible.
There are some secondary causes of dilated cardiac disease with are treatable:
Taurine deficiency. Taurine is an amino acid (a building block of protein) that can be metabolized abnormally in some dogs and cats. Taurine is essential to the diet of cats and they will develop taurine deficiency and DCM if the diet is deficient. Most dogs are able to manufacture taurine internally but the occasional dog is unable to do this and can develop taurine deficiency while on a normal diet. If proven (with a blood test), this form of dilated cardiomyopathy is reversible with taurine supplementation.
Hypothyroidism. Thyroid hormone is essential for normal metabolism and cellular function of all cells of the body, including the heart. Occasionally, dogs with severe untreated hypothyroidism can develop what appears to be DCM but is reversible with thyroid supplementation.
Tachycardia induced cardiomyopathy (TICM). The heart starts to fail and develops what looks like DCM when the rate is greater than 180 beats/minute for 3-4 weeks. In this situation, treatment of the arrhythmia can result in reversal of the damage to the left ventricular heart muscle and improved function.
How is DCM diagnosed?
A soft heart murmur or irregular heartbeat (arrhythmia) in a large breed dog may be consistent with DCM. However, in the early stages of the disease, no signs or abnormalities on the physical exam may be noticed. More severe signs can include collapse or signs of congestive heart failure (lethargy and increased respiratory rate).
The only real way to diagnose DCM is to perform an echocardiogram (heart ultrasound). This gives the most accurate determination of the size of the heart chambers and their contractile function. Once diagnosed, the echocardiogram will be repeated periodically to monitor for progression of the disease.
ECG and Holter monitoring
It is very common for dogs with DCM to develop irregular heart beats (arrhythmias), which, if severe enough, can result in sudden death. Hence, a short in hospital ECG and occasionally a Holter monitor (24 hr ECG your dog wears at home) will be recommended in order to accurately diagnose and treat such arrhythmias.
If your pet is showing any respiratory signs (cough, laboured breathing) or fatigue, chest xrays will be recommend to look for evidence of congestive heart failure (pulmonary oedema).
If your dog develops congestive heart failure (pulmonary oedema), medications will be prescribed. Some of these can adversely affect the kidneys, especially at high doses. Blood work prior to starting medication and periodically during the course of the disease will be recommended.
There are genetic tests available to look for SOME causes of DCM specifically in the Doberman Pinscher and the Boxer dog. These tests are NOT transferable to other breeds. Genetic testing is primarily helpful to breeders when deciding wether to breed from a particular dog. Not all genetic markers of DCM have been identified. Thus, a negative test result does not guarantee that your dog won’t develop DCM. Conversely, some dogs with a positive genetic test result, do not go on to develop the disease.
If your dog is diagnosed with dilated cardiomyopathy, a drug called pimobendan will be prescribed. This is a safe drug, which improves cardiac contractility and may slow the progression of the disease. Once in congestive heart failure, triple therapy will be recommended (see the congestive heart failure handout).