Hypertrophic cardiomyopathy almost always involves stiffening and thickening of the walls of the left ventricle. To diagnose this disease, other potential causes of left ventricular thickening and rigidity must first be ruled out. This is called making a diagnosis on the basis of exclusion. The other conditions that can cause ventricular stiffness include hyperthyroidism, subaortic stenosis (SAS), acromegaly and systemic hypertension (high blood pressure). The best way to identify physical abnormalities in one or more heart chambers is through a technique known as echocardiography. An echocardiogram basically is an ultrasound examination of the heart and surrounding tissues. It is completely painless and noninvasive. However, mild to moderate sedation usually is necessary during the procedure, because the animal must lie still to ensure accurate results. In addition to ventricular thickening, an echocardiogram can also disclose outflow obstruction, abnormal blood turbulence, blood pooling (stagnation) and mitral valve regurgitation – all abnormalities that may be present in dogs with hypertrophic cardiomyopathy.
Auscultation of the heart (listening to heart sounds through a stethoscope) may reveal heart murmurs or other abnormal heart sounds in affected animals. An electrocardiogram (ECG) can also be helpful in the diagnosis of HCM. An ECG measures the rhythm, rate and electrical activity of the heart. The results of a urinalysis and routine blood work (a complete blood count and serum biochemistry profile) usually are unremarkable if the dog’s only medical condition is hypertrophic cardimyopathy. Blood work to assess functional thyroid hormone levels (called a thyroid panel), together with measurement of systemic blood pressure, both are important to rule out other potential causes of ventricular thickening. Thoracic radiographs (chest X-rays) may or may not be helpful. Sometimes they can be useful to disclose whether the left atrium has enlarged from the backflow and pooling of blood from the left ventricle.
Some of the medications used to treat heart disease in domestic animals can have adverse side effects on the kidneys, liver or other organs. Regular monitoring of renal (kidney) function is important if affected animals are being treated for heart disease. Usually, this only involves a simple blood test and is relatively inexpensive.