CAD Screening Test

1 What are Coronary Artery Disease (CAD) Screening Tests?

Coronary artery disease (CAD) occurs when atherosclerotic plaque (hardening of the arteries) builds up in the wall of the arteries that supply blood and oxygen to the heart muscles.

This plaque is primarily made of cholesterol but plaque accumulation can be accelerated by smoking, high blood pressure, elevated cholesterol, and diabetes.

Symptoms of CAD include:

  • chest pain (angina pectoris) from inadequate blood flow to the heart
  • heart attack (acute myocardial infarction), from the sudden total blockage of a coronary artery
  • sudden death, due to a fatal rhythm disturbance

Each patient should discuss with the doctor about the risk factors, which include a family history of CAD at relatively young ages, smoking, high blood pressure, elevated cholesterol and diabetes, and need for the screening test.

The common initial screening tests for CAD are:

  • electrocardiogram (EKG)
  • exercise cardiac stress testing (ECST)
  • radionuclide stress test
  • stress echocardiography
  • pharmacologic stress test

The electrocardiogram (ECG or EKG) is a noninvasive test which reflects underlying heart conditions by measuring the electrical activity of the heart. It is the first and the simplest test used to look for any CAD signs.

On the ECG (EKG) can be measured or detected: evidence of increased thickness (hypertrophy) of the heart muscle, evidence of acutely impaired blood flow to the heart muscle, evidence of damage to the various parts of the heart muscle, the underlying rate and rhythm mechanism of the heart, the orientation of the heart (how it is placed) in the chest cavity and patterns of abnormal electric activity that may predispose the patient to abnormal.

The exercise stress test (also called stress test, exercise electrocardiogram, treadmill test, graded exercise test, or stress ECG) is a test which provides information about how the heart responds to exertion. It is usually performed on a treadmill or a stationary bike at increasing levels of difficulty, while electrocardiogram, heart rate, and blood pressure of the patient are monitored.

The test is used to: determine the likelihood of having coronary heart disease and the need for further evaluation, determine if there is adequate blood flow to your heart during increasing levels of activity, evaluate the effectiveness of your heart medications to control angina and ischemia, check the effectiveness of procedures done to improve blood flow within the heart vessels in people with coronary heart disease, identify abnormal heart rhythms and help patient develop a safe exercise program.

If the ECST does not clarify the diagnosis, additional tests like radionuclide isotope injection and ultrasound of the heart (stress echocardiography) during the stress test are often used to clarify the condition.

Radionuclide stress test is a procedure during which an injection of a radioactive isotope (typically thallium or cardiolite) is injected into the patient's vein after which an image of the patient's heart becomes visible with a special camera.

One set of images is taken at the resting condition and one set immediately following exercise and then are compared. If a blockage in a coronary artery results in diminished blood flow to a part of the cardiac muscle, this region of the heart will appear as a relative "cold spot" on the nuclear scan during exercise, because this region cannot be seen while the patient is at rest.

Stress echocardiography combines echocardiography (ultrasound imaging of the heart muscle) with exercise stress testing (ECST).

The sound waves of ultrasound are used to produce images of the heart at rest and at the peak of exercise so if a segment of the left ventricle does not receive optimal blood flow during exercise, that segment will demonstrate reduced contractions of heart muscle relative to the rest of the heart on the exercise echocardiogram.

This procedure can be used to exclude the presence of significant CAD in patients suspected of having a "false-positive" ECST.

A pharmacologic stress test is a stress test performed with a drug for a people who are unable to exercise. Dobutamine increases the heart rate and strength of the contractions of the heart muscle and simultaneously, echocardiography or radionuclide imaging is performed.

Also, a medicine called adenosine can be used in combination with radionuclide isotope imaging to provide a very accurate test for the detection of significant CAD. Regadenoson (Lexiscan), a newer agent, is also often used as it seems to be better tolerated.

Another noninvasive test for CAD is CT scanning – electron-beam computerized tomography (EBCT) which is designed to measure calcium deposits in the coronary arteries.

The test can identify calcium in blockages as mild as 10%-20% so the initial therapy as cholesterol lowering and cessation of smoking, adjunctive use of aspirin and certain vitamins can be started but this therapy is also advised in all patients with risk factors for CAD, regardless of the results of any noninvasive tests.

Calcification is a function of age so in younger patients (men under 50, women under 60) the calcium score is less helpful when low.

CT angiography (ultrafast CT) also can be used as a noninvasive test for CAD because there is no catheter involved but still involves dye exposure and radiation, and is less precise than a coronary angiogram but it is still a rather new modality, and its role is still being defined.

The most accurate method of defining CAD is coronary angiogram – a procedure that uses X-ray imaging to see heart's blood vessels and to identify the exact location and severity of coronary artery disease (CAD).

During the procedure, a doctor, with small catheter inserted into an artery, with the assistance of a fluoroscope and a small amount of radiographic contrast (solution containing iodine, which is easily visualized with X-ray images) injected into each coronary artery, can see images (angiogram) which accurately reveal the extent and severity of all coronary artery blockages.

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