In this lecture we will discuss canine dilated (DCM) and arrhythmogenic cardiomyopathy (ARVC). We will pay particular attention
to breed specific findings.
Canine Dilated Cardiomyopathy - DCM
Strictly speaking, dilated cardiomyopathy (DCM) is defined as an idiopathic functional abnormality of the myocardium causing
systolic dysfunction and/or arrhythmias. Definitive breed predispositions exist. Even though the disease is referred to as
DCM in each breed, there are important clinical and pathological differences between the breeds mentioned. Although Boxer
dogs can get dilated cardiomyopathy, most Boxers develop Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC), a very different
Dilated cardiomyopathy is an adult onset disease, with the exception of the Portuguese Water Dog in which it is diagnosed
between two and thirty-two weeks.
There appear to be two stages of DCM, an asymptomatic stage, referred to as occult, which may be detected by careful screening,
and a stage at which symptoms appear, referred to as overt. There is some preliminary evidence that early recognition of the
occult stage may slow progression of the disease therefore, being aware of early signs may be beneficial to patient management.
Clinical signs may include coughing, dyspnea, tachypnea, syncope and occasionally, ascites.
A soft systolic murmur consistent with mitral valve regurgitation and/or a gallop rhythm (S3) may be ausculted at the left
A tachyarrhythmia of sinus, supraventricular or ventricular origin may be noted. In some cases, a murmur or an arrhythmia
may be the first signs of the occult form of the disease and should not be overlooked. Since primary valvular disease is relatively
uncommon in large breed dogs, and the detection of DCM before the development of congestive heart failure (CHF) may be beneficial
in the long-term management of the case, identification of a new murmur, gallop or tachyarrhythmia in suspect breeds should
be considered a "red flag" and may warrant a thorough cardiac work-up. Although canine DCM is predominantly a left ventricular
disease, biventricular involvement and heart failure with jugular venous distension and ascites is frequently noted, particularly
in the giant breeds.
Many dogs with DCM have normal electrocardiograms but atrial and/or ventricular enlargement patterns (R > 3.5 mV Lead II for
the left ventricle) may be noted. Sinus tachycardia, atrial fibrillation or ventricular arrhythmias are common. In some cases,
ventricular tachyarrhythmias can develop before any ventricular dilation or systolic dysfunction. Routine Holter monitoring
may help detect these.
Dilated cardiomyopathy is a progressive myocardial disease. If the disease is diagnosed in the early stages, radiographic
findings may be subtle. Therefore, depending on the stage of the disease, thoracic radiographs may be within normal limits
or may indicate atrial and ventricular enlargement (typically left) with or without pulmonary venous distension and pulmonary
edema. In some cases, biatrial and biventricular enlargement may be noted.
Echocardiography is the diagnostic test of choice for diagnosing canine DCM and is also an important test for occult disease.
Echocardiographic findings in the patient with overt disease should include left and sometimes right atrial and ventricular
dilation and decreased contractility as characterized by shortening fraction (FS%). Typically the decrease in contractility
is quite severe with decreased fractional shortening % (< 20%).
A differential diagnosis for DCM is severe atrioventricular (AV) valve disease since severe ventricular dilation and systolic
dysfunction may be occasionally observed in these cases. Consideration of the breed of dog may be helpful in differentiating
between DCM and AV valve disease since it is uncommon for many of the large breed dogs to develop significant primary valve
disease. An exception to this may be the cocker spaniel, a breed that has a high incidence of primary valve disease, and also
is at increased risk of DCM.
Prohormone BNP is released when the ventricles are dilated, hypertrophic or subjected to increased wall tension. Levels of
BNP (Idexx) have been shown be increased in dogs with congestive heart failure and can be used to help diagnose, or exclude
a diagnosis of heart failure in dogs that presented for cough or dyspnea. At this point it has not yet been shown to be sensitive
enough for detection of early disease.
It is clear that several breeds appear to be over represented and some breeds seem to have unique characteristics of the disease
that may suggest that this is unique disease for their breed. A familial form of DCM has now been identified in several breeds
and is suspected in others. Occasionally, atypical breeds of dogs develop DCM. The etiology of the disease in these cases
is unknown and external factors that can insult the myocardium including infectious organisms or nutritional imbalances should