Tests to Diagnose Heart Disease

Many tests are available to diagnose possible heart disease. The choice of which tests to perform depends on your symptoms, risk factors, and history of heart problems. The types of tests used to diagnose heart disease include:

• Cardiac Catheterization or Coronary Angiography
• Chest X-Ray
• Computed Tomography (CT) Scan
• Echo-cardiogram
• Electrocardiogram
• Exercise Stress Test
• Event Monitor
• Holter Monitor (Ambulatory Electrocardiogram)
• Magnetic Resonance Imaging (MRI)
• Magnetic Resonance Angiography (MRA)
• Multigated Graft Acquisition (MUGA) Scan
• Positron Emission Tomography (PET) Scan
• Signal-Averaged Electrocardiogram (SAECG)
• Single Photon Emission Computed Tomography (SPECT) Scan
• Radioisotope (Cardiolite or thallium) Stress Test.

Cardiac Catheterization or Coronary Angiography

Angiography is the process of taking pictures of the inside of the heart or blood vessels. The picture itself is called an angiogram. The angiogram allows your doctor to check the inside of a blood vessel to see if it is narrowed or blocked.

A special dye that shows up in an x-ray is injected into a blood vessel through a needle or a small tube called a catheter. As the dye flows in the blood vessel, an x-ray machine rapidly takes a series of pictures. Sometimes the pictures are taken so fast that they form a movie of the progress of the dye. Cardiac catheterization and the injection of dye into the arteries is the best way to study the coronary arteries.

Chest X-Ray

X-rays are a form of electromagnetic energy, or radiation. X-rays are able to penetrate body tissues. They are used to create pictures of body structures on film. An x-ray of your chest can show:

• if the heart is enlarged or normal
• signs of heart failure and fluid overload
• pneumonia or a collapsed lung
• tumors in the lung that could mean cancer.

Computed Tomography (CT) Scan

Cardiac electron beam computed tomography, sometimes called ultra-fast CT, is a computer-assisted x-ray scan of the heart. It can show how much calcium is in the coronary arteries of the heart. Normal coronary arteries have very little or no calcium in them. Atherosclerosis gradually clogs the arteries and causes heart attacks. It attracts and concentrates calcium in the blood vessels. The more calcium there is in the arteries, the higher the risk of a heart attack.

After you are positioned in an x-ray scanner, a series of x-ray pictures are taken rapidly. The whole test is painless and takes only a few minutes.

Echocardiogram

An echocardiogram makes pictures by bouncing high-frequency (ultrasound) waves off your heart. The sound waves are produced by a device usually placed on your chest. The echoes of the sound waves, translated by a computer and recorded on videotape, provide a picture of your heart as it beats. The heart valves, heart chambers, blood vessels, and the heart muscle itself can be carefully measured and examined. A special part of the echocardiogram called the color Doppler signal shows blood flow through your heart. Ultrasound pictures of the heart are better than x-rays for outlining details of the heart.

If your doctor orders a transesophageal echocardiogram, a very small transducer on the end of a tube will be passed down your throat. Transesophageal means the sound waves are directed through the esophagus (the tube that carries food from the throat to the stomach) to the heart. Because the probe is much nearer your heart when it is inside you instead of outside on your chest, the pictures of the heart structures are much clearer.

Electrocardiogram

An electrocardiogram (ECG or EKG) is a recording of the electrical activity of the heart. (Each heartbeat starts with an electrical impulse that causes the heart to squeeze.) For this test small, sticky electrode patches are placed on your chest, wrists, and ankles. These patches are connected to a machine that records the electrical activity of your heart. The recording is printed on paper for your doctor to interpret.

The ECG gives information about the electrical health of the heart while the echocardiogram shows the structural health of the heart and its valves.

Exercise Stress Test

The most common cause of heart disease is narrowing of the coronary arteries. This narrowing occurs when cholesterol and other substances build up inside the artery. Many people with narrowing of the coronary arteries have no symptoms when they are at rest. The exercise test helps to detect narrowing of the arteries.

You will be asked not to eat for about 2 hours before the test. Small, sticky metal disks or suction cups are placed on your back and chest for the electrocardiogram. Blood pressure and the electrocardiogram are recorded while you are resting. You then start a slow walk on the treadmill. The speed and the upward slope of the treadmill will be increased about every 3 minutes. The electrocardiogram and blood pressure continue to be recorded while you exercise on the treadmill and just after the test.

Event Monitor and Holter Monitor (Ambulatory Electrocardiograms)

Ambulatory electrocardiographic monitoring (AEM) is used to record a continuous electrocardiogram for a certain period. You take an event recorder home and turn it on when you have symptoms of irregular heartbeats. You keep the recorder for up to a month.

Holter monitors record the electrical activity of your heart on a tape cassette for 24 to 48 hours. Holter monitors have been around for 30 years.

AEM is mostly used for two purposes:

• to observe and record heart rhythm and any abnormality that might occur
• to look for times when the heart muscle is not getting enough blood flow through the coronary arteries.

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) produces very detailed pictures of body tissues and organs.

You lie on a special table inside the opening of the MRI unit. Radio waves in a strong magnetic field create 2-D or 3-D images that may be viewed from any direction. MRI images are very sharp and detailed, and so are able to detect even tiny changes from the normal pattern.

Magnetic Resonance Angiography (MRA)

MR angiography (MRA) is an MRI study of the blood vessels. It uses MR technology to detect, diagnose, and aid the treatment of heart disorders, stroke, and blood vessel diseases. The procedure is painless, and the magnetic field is not known to cause tissue damage of any kind.

Multigated Graft Acquisition (MUGA) Scan

MUGA scans provide information about the heart’s pumping function. They measure the amount of blood that is pumped with each heartbeat, and the flow of blood into the pumping chamber. MUGA scans are also used to check the chamber of the heart that pumps blood to the lungs and to diagnose heart wall problems.

An injection of a radioactive chemical temporarily highlights your red blood cells. A gamma camera linked to a computer follows the blood moving through the heart. Information from several hundred heartbeats are collected and analyzed.

Positron Emission Tomography (PET) Scan

PET measures chemical changes that occur before signs of disease can be seen on CT and MRI images.

PET scans use a small amount of a radioactive chemical that is attached to a substance that is used by heart cells. Substances such as glucose, water, ammonia, and drugs may be used. The radioactive substance is injected into a vein. The PET scan shows how different parts of the heart use the substance.

Signal-Averaged Electrocardiogram (SAECG)

The signal-averaged electrocardiogram (SAECG) is a special type of electrocardiogram (ECG or EKG) that records very low electrical power signals of the heart. The test requires a special ECG machine that includes a computer. A regular ECG is taken, for at least 15 to 20 minutes. About 1,000 heartbeats in a row are needed to average the low power signals. A computer lays the signals on top of an average ECG signal and quickly analyzes the results when enough heartbeats have been collected.

Radioisotope Stress Test

A radioisotope stress test shows how well blood flows to the heart muscle. A radioisotope is a radioactive substance such as Cardiolite or thallium. This test is usually done along with an exercise stress test on a treadmill or bicycle. Sometimes the stress is provided by medicine instead of by exercise.

When you nearly reach your maximum level of exercise, a small amount of radioisotope is injected into your bloodstream. You then lie down on a special table under a gamma camera that can detect the radioisotope and make pictures. The radioisotope moves from the blood into the cells of the heart muscle. If a part of the heart muscle doesn’t receive a normal blood supply during exercise, the cells in that part of the heart will have less of the radioisotope.

Another series of pictures is made when your heart has not been stressed by exercise. Comparing these pictures to the ones done after exercise gives important information about how your heart is doing.