Any dog suspected of having heart problems or other systemic disease will be given a thorough physical examination by the attending veterinarian, who will also take a history from the dog’s owner. Dogs with subaortic stenosis (SAS) usually have normal results on a urinalysis and on routine blood work, including a complete blood count (CBC) and a serum biochemistry profile. The next step in gathering the initial data base usually is thoracic radiographs (chest X-rays), which may or may not show an enlarged cardiac silhouette. In severe cases, the left side of the heart may be noticeably enlarged on the chest films. An electrocardiogram (ECG) can be performed and may or may not disclose signs of SAS based on thickening of the left ventricular wall.
More advanced testing includes echocardiography, which basically is an ultrasound of the heart. Also sometimes simply called an “echo,” this is a recording of the position and motion of the heart walls and internal structures by the echo obtained from beams of ultrasonic waves directed through the chest wall. An echocardiogram is usually diagnostic of SAS, especially when what is called a “Doppler study” is performed. Doppler echocardiography effectively measures the speed (velocity) and direction of blood flow through the various heart chambers.
Contrast radiography can be used to identify the thickening of the left ventricular wall, the narrowing of the aorta as it leaves the left ventricle through the left atrioventricular (AV) valve and the dilation (widening) of the aorta from high blood pressure further down the line. This process is known as angiocardiography. Cardiac catheterization can also be performed to determine the pressure differences across the left AV valve and compare them to normal. However, these last two techniques are almost never used diagnostically in veterinary medicine. They are invasive, require that the dog be put under general anesthesia and do not reliably provide more beneficial diagnostic information than echocardiography.
Echocardiography is currently considered to be the gold standard for diagnosing SAS.