Heart Disease (cont.)

How is heart disease diagnosed?

The diagnosis of heart disease begins with obtaining a history that the potential for coronary artery disease exists. Risk factors need to be assessed, and then testing may be required to confirm the presence of heart disease.
Heart disease tests
Not every patient with chest pain needs heart catheterization (the most invasive test). Instead, the healthcare provider will try to choose the testing modality that will best provide the diagnosis, and if coronary artery disease is present, decide what impairment, if any, is present.

Electrocardiogram (ECG or EKG)

The heart is an electrical pump, and the electrical impulses it generates can be detected on the surface of the skin. Normal muscle conducts electricity in a reproducible fashion. Muscle that has decreased blood supply conducts electricity poorly. Muscle that has lost its blood supply and has been replaced with scar tissue cannot conduct electricity. The electrocardiogram (EKG) is a noninvasive test used to reflect underlying heart conditions by measuring the electrical activity of the heart.
Some people have "abnormal" EKGs at baseline but this may be normal for them. It is important that an electrocardiogram be compared to previous tracings. If a patient has a baseline abnormal EKG, they should carry a copy with them for reference if they ever need another EKG.

Stress testing

If the baseline EKG is relatively normal, then monitoring the EKG tracing while the patient exercises may uncover electrical changes that may indicate the presence of coronary artery disease. There are a variety of testing protocols used to determine whether the exercise intensity is high enough to prove that the heart is normal.
Some patients are unable to exercise on a treadmill test, but they can still undergo cardiac stress testing by using intravenous medication that causes the heart to work harder.
Stress testing is done under the supervision of medical personnel because of the potential of provoking angina, shortness of breath, abnormal heart rhythms, and heart attack.

Echocardiography

Used with or without exercise, echocardiography can assess how the heart works. Using sound waves to generate an image, a cardiologist can evaluate many aspects of the heart. Echocardiograms can examine the structure of the heart including the thickness of the heart muscle, the septum (the tissues that separate the four heart chambers from each other) and the pericardial sac (the outside lining of the heart).
The test can indirectly assess blood flow to parts of the heart muscle. If there is decreased blood flow, then segments of the heart wall may not beat as strongly as adjacent heart muscle. These wall motion abnormalities signal the potential for coronary artery disease.
The echocardiogram can also assess the efficiency of the heart by measuring ejection fraction. Normally when the heart beats, it pushes more than 60% of the blood in the ventricle out to the body. Many diseases of the heart, including coronary artery disease, can decrease this percentage (the ejection fraction).

Perfusion studies

Radioactive chemicals like thallium or technetium can be injected into a vein and their uptake measured in heart muscle cells. Abnormally decreased uptake can signify decreased blood flow to parts of the heart because of coronary artery narrowing. This test may be used when the patient's baseline EKG is not normal and is less reliable when used to monitor a stress test.

Computerized tomography

The latest generation of CT scanners can take detailed images of blood vessels and may be used as an adjunct to determine whether coronary artery disease is present. In some institutions, the heart CT is used as a negative predictor. That means that the test is done to prove that the coronary arteries are normal rather than to prove that the disease is present.

Heart catheterization or coronary angiography

This test is the gold standard for the diagnosis of coronary artery disease. A cardiologist inserts and then threads a small tube through the groin or arm into the coronary arteries, where dye is injected to directly visualize the arteries on an x-ray. This test defines the anatomy of the coronary arteries.
CT coronary angiogram is a fairly new test to diagnose coronary artery disease. During this procedure, intravenous dye containing iodine is injected into the patient and CT scanning is performed to image the coronary arteries.