Clinical features and findings

It is typical to see dilatation of all cardiac chambers in dogs with dilated cardiomyopathy (DCM), although left atrial and ventricular enlargement may predominate. The ventricular wall thickness appears decreased compared with the lumen size. Papillary muscles often look flattened and atrophic; endocardial thickening may be noted. The atrioventricular (AV) valves generally have only mild to moderate, if any, degenerative changes. Histopathologic findings include scattered areas of myocardial necrosis, degeneration and fibrosis, especially in the left ventricle.

The presence of narrowed (attenuated) myocardial cells with a wavy appearance is reported to be a common finding (Tidholm and colleagues, 1998). Such abnormal cells have also been noted in some Newfoundlands thought to be predisposed to DCM but without any clinical or echocardiographic evidence of the disease (Tidholm and colleagues, 2000). Inflammatory cell infiltrates and myocardial hypertrophy are inconsistent features.

Idiopathic DCM is most common in large and giant breeds of dogs, including Great Danes, Doberman Pinschers, Saint Bernards, Scottish Deerhounds, Irish Wolfhounds, Boxers, Newfoundlands, Afghan Hounds, and Dalmatians. Among smaller breeds, English and American Cocker Spaniels, English Bulldogs, and others are affected, but the disease is rare in dogs weighing less than 25 lbs.
The prevalence of DCM increases with age, although most dogs presenting with heart failure are 4 to 10 years old. Most reports indicate that more male than female dogs are affected. Others suggest no gender predilection in Boxers and Doberman Pinschers once dogs with occult didease are included in the analysis. The nature of the cardiomyopathy in Boxers and Dobermans appears to be somewhat different from that in other large and giant breeds.

Clinical signs mat develop rapidly, especially in sedentary dogs in which ordinarily early signs may not be noticed until the disease is advanced. Presenting complaints include any or all of the following: weakness, lethargy, tachypnea or dyspnea, exercise intolerance, cough (sometimes described as ”gagging”, anorexia, abdominal distention (ascites), and syncope.

Loss of muscle mass (cardiac cachexia). accentuated along the dorsal midline, may be severe. Conversely, subclinical DCM is now being recognized more frequently, especially through the use of echocardiography. Some giant-breed dogs with mild-to-moderate left ventricular dysfunction are relatively asymptomatic, even in the presence of atrial fibrillation.