Diagnosis of Canine Cardiac Disease

2. Diagnosis of Canine Cardiac Disease

Congenital and acquired cardiac diseases often lead to similar compensatory responses and neuroendocrine activation. Due to the similarities in response of the heart, systemic and pulmonary vasculature and the neuroendocrine systems, several common historical findings and clinical signs result from most of the canine cardiovascular diseases.

Clinical Signs

Common historical complaints include cough, shortness of breath, and syncope (Table 2). Cardiac disease can be quite advanced when the owner is first able to detect clinical abnormality, however many cardiac diseases can be detected by the attending veterinarian well in advance of the development of clinical signs.

Most congenital cardiac diseases are accompanied by a loud cardiac murmur. The most common form of cardiovascular disease in the dog, CVD, typically has a cardiac murmur that can be readily identified well before outward clinical signs of cardiovascular disease are evident. The abnormalities that are most commonly identified on physical examination from dogs with cardiovascular disease are listed in Table 3.

Diagnostic Tests

Once cardiovascular disease is established as a differential diagnosis, a battery of routine tests are often performed to confirm cardiovascular disease, establish the severity of disease, and permit an informed decision to be made regarding treatment.

An electrocardiogram should be performed in all dogs with evidence of cardiac arrhythmia, including those with arrhythmia noted on cardiac auscultation and those with femoral arterial pulse deficits, bradycardia, tachycardia, or a history of syncope, seizure, or collapse.

Thoracic radiographs are indicated to establish whether CHF is present and to help determine the degree of cardiac enlargement, the size of the pulmonary vessels, and the size of the caudal vena cava. Thoracic radiographs are the best diagnostic test to exclude respiratory diseases as either the cause or a contributor to the animal's clinical signs. For many cardiovascular diseases, echocardiography is the key diagnostic test to establish the exact cause of the disease. Echocardiography also facilitates the evaluation of cardiac chamber enlargement and permits quantitative evaluation of cardiac chamber size, wall thickness, and myocardial and valve function (Figure 1).

Figure 1. Echocardiography indicating dilated cardiomyopathy in a boxer. Right parasternal long axis view showing the dilatation of the left atrium (LA) and left ventricule (LV). (© Bussadori).

In dogs with congenital disease, echocardiography is used to confirm the type of defect, establish the severity of the defect, and is an invaluable aid in offering therapeutic and prognostic advice. Echocardiography is a key tool for the diagnosis and management of cardiac disease and should be offered in all cases where serious cardiovascular disease is a differential diagnosis.

Many additional tests are useful in the diagnosis and management of dogs with cardiac disease.

• Heartworm (Dirofilaria immitis) antigen testing should be carried out in dogs from endemic areas.
• A complete blood count and biochemistry profile should be carried out to search for concurrent diseases and establish baseline values prior to therapy. Alterations in blood urea nitrogen, creatinine, and the serum electrolytes sodium, potassium, chloride and magnesium can develop following the initiation of various cardiac medications, and knowledge of these alterations is useful in selecting or altering the diet.
• Plasma and whole blood taurine levels may be indicated in dogs with evidence of reduced systolic function on echocardiography, especially in certain breeds of dogs (e.g., Cocker Spaniel, Golden Retriever, Newfoundland) and in dogs consuming certain diets (see below).
• Measurement of systemic blood pressure is useful to exclude systemic hypertension as a contributing factor to the cardiovascular disease. In addition, when hypotension develops following initiation of pharmacologic therapy, a baseline blood pressure measurement can be used for comparison.
• A variety of additional specialized cardiovascular tests, such as Holter monitor recorders, event monitor recorders, computed tomography, phonocardiography, and cardiac catheterization are available for specific clinical settings.

Dilated cardiomyopathy may be associated with taurine deficiency in certain breeds, such as the Golden Retriever, the Newfoundland and the Cocker Spaniel. (© Hermeline and © Bouveron).