What Types of Diagnostic Tests Are Used to Evaluate the Cardiovascular System?
Auscultation of the heart. Auscultation is listening to the heart through a stethoscope. The valves of the heart make certain sounds as they close, which can be heard through the stethoscope. Diseased valves usually produce abnormal sounds, called murmurs. Arrhythmias may also sometimes be detected on auscultation.
Palpation of pulses. Pulses are caused by blood traveling through arteries after contraction of the left ventricle. They represent the beat of the heart and provide information on the regularity and strength of the beat.
Evaluation of mucous membrane color and capillary refill time. The color of the gums of the mouth and the time it takes for color to return after pressure is applied to the gums both provide information on the circulation of blood to the body tissues. If oxygen levels are low in the blood, then the gums appear blue or cyanotic. If the blood is anemic, the gums may appear pale. If carbon monoxide levels are high in the blood, the gums are usually very bright red. If the gums take more than two seconds to have their color return (prolonged capillary refill time), then circulation to the tissues is poor.
Electrocardiogram (ECG). This is the graphic recording of electrical currents generated by the heart to study the action of heart muscle. The electrocardiogram can be performed awake in most dogs. It provides information on the size of the heart chambers, the regularity and speed of the heartbeat, and defines the type of any arrhythmia present.
Thoracic radiography. Chest X-rays allow the silhouette of the heart to be examined. They provide information on the size and contour of the heart, the size of the chambers of the heart, and the blood vessels around the heart. Chest X-rays also provide important information about the lungs, which are often affected by heart disease.
Echocardiography. Echocardiography is an ultrasound study of the heart. The position and motion of the heart, heart valves and chambers of the heart are measured by the echo obtained from ultrasonic waves. The dynamics of blood flow within and around the heart can also be studied with a form of echocardiography, called Doppler color flow ultrasonography. Echocardiography is also helpful to detect pericardial effusion (fluid around the heart), tumors of the heart, and thrombi within the heart. Heartworms are also sometimes detected on echocardiography.
Certain laboratory tests. Laboratory tests are often performed to assess various functions of the body and circulatory system. A complete blood count, biochemistry organ profile, and urinalysis may detect abnormalities such as anemia, kidney disease, and chemical imbalances. Blood may be submitted for heartworm tests. The measurement of oxygen and carbon dioxide (also known as blood gas analysis) may be performed in blood samples from both arteries and veins. Tests for certain infectious diseases may also be indicated. If bacterial infections of the blood stream are suspected, then samples of blood may be taken for culture.
Cardiac catheterization and angiocardiography. With this procedure a catheter is inserted into a vein or artery and guided into the interior of the heart. A dye is injected into the catheter that shows up white on X-rays. A video X-ray is acquired as the dye travels through the different chambers and vessels of the heart. Cardiac catheterization with angiocardiography is uncommonly performed in the dog, and has been replaced in large part by echocardiography. It is most often used to detect certain congenital heart defects.
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