What is it?
DCM, or Dilated Cardiomyopathy, is a form of heart disease characterised by an enlarged but weakened heart muscle. It is most commonly seen in certain breeds, but may also be due to dietary deficiencies. In many cases, DCM leads to abnormal heart rhythms (arrhythmias).
What causes it?
In most cases, it is due to genetic disease, but a taurine-deficient diet can also be a cause. In either case, the heart muscle becomes weaker, resulting in decreased pumping effectiveness. As the muscle becomes weaker, the heart swells up like a balloon, resulting in an enlarged heart with very thin walls (which of course reduces the pumping power even further). The enlargement of the chambers of the heart and thinning of the muscular walls increases the risk of arrhythmias as the "communications system" inside the heart becomes less effective. Eventually, it will inevitably lead to heart failure.
What dogs are at risk?
Any dog with a taurine-poor diet (nowadays, this is usually confined to dogs fed a poorly designed home-cooked diet). The more common genetic form is seen primarily in Dobermans, Boxers, Deerhounds, Irish Wolfhounds, Great Danes and other giant breeds, although it is also recognised occasionally in Cocker Spaniels and Portuguese Water Dogs.
What are the symptoms?
Most dogs in the early stages of the disease (the "preclinical phase") show no symptoms. However, this will progress over time to include reduced exercise tolerance, weakness, depression, weak pulses and sometimes a highly irregular or chaotic heart rhythm (atrial fibrillation). Eventually, congestive heart failure will develop with breathlessness, coughing, blue gums, swelling of the abdomen and (sometimes) extremities, collapse and ultimately death. In some dogs (especially Boxers), sudden death may occur without warning. Unfortunately, the disease is always progressive and always fatal - without treatment, death usually occurs in 6-24 months after diagnosis.
How is it diagnosed?
Initially, signs of heart disease in a dog of a susceptible breed are highly suspicious; X-rays can identify an enlarged heart but not the exact cause. A confirmed diagnosis therefore relies on echocardiography - an heart scan using ultrasound. With this technique, the swollen, weak heart is clearly visible. In some cases, an ECG may also be useful to categorise the arrhythmia, allowing the vets to determine the best treatment.
How can it be treated or managed?
The mainstay of treatment is to increase the pumping strength of the heart; and to manage the abnormal heartbeat. The most commonly used drug is pimobendan, which makes the heart muscle work harder, increasing the heart's efficiency. If atrial fibrillation is occurring, the drug digoxin may be used instead, or beta-blockers to slow down the abnormal heart rate. If the dog has gone into congestive heart failure, diuretics ("water tablets") such as frusemide, and ACE inhibitors such as benazepril will help to mitigate the symptoms. Dietary management may also be useful - particularly a low-sodium high taurine and high carnitine diet (as in most commercial cardiac foods). Good medical management will not stop the progression of the disease, but it will slow it down, and make the dog more comfortable.
Can it be prevented?
The dietary form can (by feeding a proper, healthy diet with added taurine), but the genetic form cannot, sadly, be prevented.