MATTHEW W. MILLER, DVM, MS, DIPLOMATE ACVIM (CARDIOLOGY)
THERESA W. FOSSUM, DVM, MS, PHD, DIPLOMATE ACVS
As most dog owners are aware there have been reports of boutique, exotic grain free (BEG) diets being associated with dilated cardiomyopathy (DCM) in dogs. Vegetarian, vegan and home-cooked diets also have been linked with DCM.
What is dilated cardiomyopathy?
DCM is a primary condition of the heart muscle where the pumping ability of the is reduced. It cannot effectively pump blood to the lungs or body resulting in either congestion (backup of blood in the lungs or abdomen) or decreased delivery of oxygenated blood to the body, or both. Congestion may cause the dog to cough, breathe more rapidly and with more effort, and/or develop an enlarged, fluid-filled abdomen. Inability to pump enough oxygenated blood to the systemic circulation may cause the dog to collapse, appear weak or lethargic, and/or lose weight. Some dogs show all these signs. As the disease progresses, dangerous arrhythmias may occur and lead to sudden death.
DCM is most commonly seen in certain large breed dogs (e.g., Doberman Pinschers, Great Danes, Boxers, and Irish Wolfhounds) and in some breeds it has been proven to have a hereditary component. A genetic mutation has been identified in Boxers and Dobermans and this can be screened for by your veterinarian. Other breeds that may have a high incidence of DCM include Bulldogs, Golden Retrievers and Saint Bernards. Some smaller breeds are also affected by DCM (Cocker Spaniels, Portuguese Water dogs), and cats are occasionally diagnosed with the condition as well. It most commonly occurs in middle-aged to older dogs and is slightly more common in males than females.
What causes DCM?
The cause of DCM is not entirely understood but genetics, diet, nutritional deficiencies (e.g., taurine deficiency), toxins, and an association with other diseases (e.g., myocarditis, hypothyroidism, muscular dystrophy) have been implicated. A grain-free, legume-rich diet has increasingly been suspected as being a cause in some dogs. Even though an association between BEG diets and DCM has not been definitively proven and further research is needed, we have seen atypical breeds develop DCM when on BEG diets. Changing the diet has resulted in the cardiac function of some of these dogs returning to normal.
Boxers can get a specific type of cardiomyopathy called arrhythmogenic right ventricular cardiomyopathy (ARVC). It is associated with a genetic mutation in a gene called striatin. Most of these dogs have normally functioning heart muscle, but they develop ventricular arrhythmias which may cause them to faint or die suddenly. A portion of these dogs develop DCM.
What should I do if I suspect that my dog has DCM?
In its early phases, your dog may not show clinical signs thus, if your dog is a breed at high-risk for DCM or you suspect that he/she may have DCM, early screening is recommended. Your dog should be examined by your veterinarian if it is showing signs of heart failure. In addition to a complete physical examination, your veterinarian will examine your dog’s pulses, listen to the heart for any murmurs, and take X-rays to determine if the heart is enlarged and if fluid is present within the lungs (pulmonary edema) or within the thoracic cavity (pleural effusion). If your veterinarian is concerned that your dog may have DCM, they may refer you to a veterinary cardiologist for further examination such as an echocardiogram. In some cases, the cardiologist may request that your dog have continuous (24-hour) monitoring for arrhythmias (known as Holter monitoring). They will want to rule out other causes of heart disease such as cancer, fluid within the pericardiac sac (pericardial effusion), and congestive heart failure associated with valvular disease. In addition to the aforementioned tests your veterinarian may wish to measure certain cardiac biomarkers, including NT-pro BNP and cardiac troponin I, in the blood.
If the DCM is thought to be diet-related, your veterinarian will recommend that you change your dog’s diet to one made by a well-established manufacturer. Simply adding grains to the existing diet is not recommended.
How is DCM treated?
Early screening and detection of DCM are the important aspects of prolonging the lives of affected dogs. Your dog may be administered a drug that increases contractility of the heart such as pimobendan. If signs of congestive heart failure are present diuretics such as furosemide and spironolactone and an angiotensin-converting enzyme (ACE) inhibitor such as enalapril or benazepril may be given. Additional therapies may depend on the underlying cause if one is found. For example, taurine and L-carnitine deficiencies may be suspected or proven on blood tests and supplementation will be recommended.
What is prognosis if my dog is diagnosed with DCM?
The prognosis depends on the status of the dog at presentation and the breed; and while the long-term prognosis is generally not great, some dogs will live for several years post-diagnosis. Doberman Pinschers have a worse prognosis than most other breeds and dogs presenting with congestive heart failure typically do worse than dogs that are not in heart failure at presentation, If the cause is associated with diet, some dogs have complete reversal of their signs and the heart muscle gradually starts to function normally when the diet is changed and/or appropriate supplements are given.