Updated April 19, 2015.
Diagnosing coronary artery disease (CAD) can be a challenge for both patients and their doctors, because there are so many people at risk for CAD and so many tests that can be used. Who should be tested, and which tests should they have?
What is CAD?
CAD is a chronic disease of the coronary arteries. In CAD, atherosclerosis causes the smooth, elastic lining of the arteries to become hardened, stiffened and swollen by "plaques," which are deposits of calcium, fats and abnormal inflammatory cells.
These plaques can protrude in to the channel of the artery, causing a partial blockage to blood flow, a condition that often causes angina. The plaques can also suddenly rupture, causing a blood clot to form acutely within the coronary artery that produces a sudden obstruction of blood flow. Most myocardial infarctions (heart attacks) are due to the acute rupture of a plaque.
CAD is a chronic, progressive disease that is usually present for many years before a person is aware that anything is wrong. All too often, the very first indication that there is a problem is when some irreversible event occurs, such as a myocardial infarction or cardiac arrest. This means that if you are at an increased risk for CAD, you should not wait for symptoms to develop before finding out whether you have a problem.
Diagnosing CAD
Identifying "Significant" Blockages
Traditionally, the diagnosis of CAD has relied on tests that look for evidence of "significant" blockages within the coronary arteries. (In general, cardiologists consider a "significant" blockage to be one that obstructs 70% or more of an artery's channel.)
Exercise testing (or stress testing) is often helpful in diagnosing partially blocked coronary arteries. Controlled stress testing can often bring out symptoms of angina and characteristic changes on the electrocardiogram (ECG) — findings which strongly suggest that blockages are present.
Read About Stress Testing
Performing a stress test in conjuction with either a thallium/Cardiolite study or an echocardiogram improves the ability to find partially blocked coronary arteries. Thallium and Cardiolite are radioactive substances that are injected in to a vein during exercise. These substances are carried to the heart muscle by the coronary arteries, thus allowing the heart to be imaged with a special camera. If one or more of the coronary arteries are partially blocked, the areas of heart muscle supplied by those arteries show up on the image as dark spots. The echocardiogram creates an image of the beating heart using sound waves. Any abnormal movement in the heart muscle seen on the echocardiogram during exercise suggests CAD.
Read about thallium/Cardiolite testing and echocardiograms
If stress testing strongly suggests that one or more blockages are present, patients generally are referred for cardiac catheterization. The purpose of the catheterization is to fully characterize the location and extent of all coronary artery blockages, usually for the purpose of angioplasty, stenting or bypass surgery.
Read About Cardiac Catheterization
Noninvasive tests are being developed that may some day replace the need for cardiac catheterization. These include the multislice CT scan and cardiac MRI. Unfortunately, neither of these approaches today can entirely replace the need for cardiac catheterization.
Identifying Plaques that Are Not Causing Significant Blockages
In recent years, cardiologists have recognized that both myocardial infarctions and unstable angina are caused by the rupture of the plaques in coronary arteries. It turns out that in many if not most cases, the plaques that end up rupturing would have been considered "nonsignificant" (i.e., not causing significant blockage) prior to their rupture. This is why we often hear of people who suffer a heart attack soon after being told they have no significant CAD. (This is what happened to TV journalist Tim Russert in 2008.)
Since any plaque can rupture, it is useful to know whether plaques are present — even small ones. People who have any amount of CAD should take steps to stabilize plaques and reduce the risk of plaque rupture. (Such measures often include risk factor management, lifestyle changes, statins and aspirin.)
Calcium scans are emerging as a useful way of detecting the presence of even small amounts of CAD. Calcium scans are a form of CT scanning that can quantify the amount of calcium deposits in the coronary arteries. Since calcium deposits generally occur in plaques, measuring the amount of calcium in the arteries yields an indication of whether CAD (and therefore plaques) is present as well as how extensive the CAD may be. By alerting you that you have at least enough CAD to produce "silent" plaques, the calcium scan can give you an opportunity to change your lifestyle, and perhaps take appropriate medications, while there's still time to do so.
Read More About Calcium Scans and Who Can Benefit from Them
Sources:
Gibbons, RJ, Balady, GJ, Timothy Bricker, J, et al. ACC/AHA 2002 guideline update for exercise testing: summary article. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). J Am Coll Cardiol 2002; 40:1531.
Califf, RM, Armstrong, PW, Carver, JR, et al. Task Force 5. Stratification of patients into high, medium and low risk subgroups for purposes of risk factor management. J Am Coll Cardiol 1996; 27:1007.
Source...