The diagnosis often is first suspected when symptoms compatible with DCM are present in a large or giant purebred dog or cocker spaniel. Physical examination abnormalities frequently include the presence of an extra heart sound called a gallop rhythm, or a soft heart murmur. Arrhythmias can be detected while listening to the heart with a stethoscope and while feeling for the pulse or heartbeat. Abnormal lung sounds are heard in dogs with left-sided heart failure, while distention or pulsation in the jugular veins, liver enlargement, or abdominal fluid accumulation may be present in dogs with right-sided heart failure. In addition, laboratory results may indicate mild changes in serum protein concentrations, sodium and potassium levels, liver enzymes, and mild increases in serum urea nitrogen and creatinine levels, or kidney values.
Although they will not always reveal major changes, chest x-rays should always be evaluated in patients suspected of having heart disease. Heart enlargement and blood vessel changes consistent with heart failure may be seen, and fluid accumulation in or around the lungs can be identified if heart failure has developed.
The most definitive diagnostic test for DCM is the echocardiogram, an ultrasound evaluation of the heart. Heart chamber dilation and enlargement, reduced heart muscle wall thickness, and decreased heart muscle wall movement are the hallmarks of DCM. In addition, mild heart valve abnormalities may be seen. Doppler echocardiography may be used to assess the severity of valvular abnormalities based on changes in blood flow through the heart.
The electrocardiogram may identify abnormal rhythms or changes in the normal tracings. The most common rhythm disturbance occurring with DCM is atrial fibrillation, a condition characterized by a tremendous increase in the rate of contraction of the atria, the uppermost chambers of the heart, coinciding with an increased rate of contraction of the ventricles, the lower and larger chambers of the heart. Other rhythm disturbances, including premature ventricular beats, may be detected.
