If the cause of a patient's chest pain is uncertain but believed to be a blockage in a coronary artery, the attending physician may order one of several tests. Which of these tests is performed depends on several factors, such as the degree to which coronary artery disease is suspected, the status of overall health, the ability of a patient to walk on a treadmill, and the results of the initial evaluation, including the electrocardiogram.
Cardiac Exercise Stress Test (Treadmill Test)—During a cardiac exercise test on a treadmill, the patient is connected to a monitor that continuously displays the electrocardiogram. The speed and uphill gradient of the treadmill increases every 3 minutes. As the test progresses, the patient's heart must work harder, which increases its need for oxygen and causes the heart rate and blood pressure to rise. In patients with one or more blockages in the coronary arteries, an insufficient amount of oxygen is delivered to parts of the heart as oxygen demand increases. This can result in the development of chest pains and/or certain diagnostic changes on the electrocardiogram.
The cardiac stress test is imperfect: A "positive" test does not definitively diagnose the presence of coronary artery disease, nor does a "negative" test absolutely rule it out. Positive or negative findings only indicate the likelihood that blockages are or are not present.
Nuclear Imaging Studies—A cardiac stress test typically is performed in a hospital nuclear medicine department. It involves injecting a minute amount of a radioactive substance into the patient's bloodstream. The two most commonly used nuclear substances are thallium and sestamibi. The radioactive substance flows to the heart, accumulating in healthy parts of the heart. Pictures are then taken to display where the substance has concentrated in the heart. This is done by scanning the patient's chest during a period of stress and again during a period when the heart is not being stressed. The stress is produced by having a patient walk on a treadmill or by injecting certain substances into the bloodstream that affect the blood flow within the heart. Pictures of the heart obtained during and after stress are then compared. It can be then determined if parts of the heart are receiving insufficient blood flow during stress. Such a finding suggests a significant blockage in one or more of the coronary arteries.
Cardiac Stress Studies or "Dobutamine" Echo Studies—During a cardiac stress study, sound waves are used to take pictures of the heart before and during periods of physical stress. As with nuclear imaging studies, stress can be induced by exercising on a treadmill or by infusion of a chemical. The chemical usually used in echo testing is dobutamine, an agent that causes the heart to beat more vigorously and, to some extent, faster. The pictures obtained before and during stress show how well different parts of the heart are contracting. By comparing how well different areas of the heart contract at baseline and with stress, areas receiving inadequate blood flow due to blockages in the coronary arteries can be identified.
Cardiac Catheterization—In cardiac catheterization, a straw-like tube is inserted in an artery in the patient's groin. Differently shaped catheters are inserted through this tube and threaded up into the heart. An iodine-based dye is injected through the catheter into the coronary arteries, and pictures of the coronary arteries are obtained. These pictures can show partial or total blockages in the coronary arteries.