Many heart attack patients are mystified by the number of tests they undergo. Understanding why these tests are important and how they contribute to a better outcome can help make them easier to endure.
Tests to help confirm that a heart attack did occur may be invasive, meaning they penetrate the body, or noninvasive. Four tests are usually routine for heart attack patients:
- Blood tests
For some heart attack patients, cardiac catheterization and coronary angiography also may be recommended. In addition, other imaging tests are available in many hospitals.
In the emergency room, an electrocardiogram (ECG) is useful for establishing that a heart attack is developing or has already occurred. In the CCU, electrocardiography is used to monitor patients for changes in heart rhythm. Heart attack patients are vulnerable to a second heart attack and other complications soon after the initial event. Changes in ECG readings may help to identify the onset of another heart attack.
Certain enzymes are released into the bloodstream by damaged heart muscle cells. Taking blood samples and analyzing them for enzyme content helps doctors determine the extent — and therefore the damage — of a heart attack. The most important enzyme is called troponin. Troponin lives within heart muscle cells. It appears in the blood stream only when cell walls are damaged or dying. Another important enzyme is called creatine kinase. Blood levels of this enzyme are usually elevated within a day after a heart attack.
Other blood tests include electrolyte levels in the blood, blood oxygen levels and analysis of your blood's ability to clot. A newer test, called brain natriuretic peptice (BNP), reflects how much "strain" is being put on the pumping portions of your heart.
Doctors use a chest X-ray to find out whether the heart is enlarged or fluid is accumulating in the patient's lungs as a result of the heart attack.
Coronary angiography is one of the most common heart tests. It involves injecting a contrast dye directly into the coronary arteries. X-rays of the heart, showing the dye filling the coronary arteries, then detect sites where they are narrowed or completely blocked.
Echocardiography uses ultrasound to create an image of your heart and major blood vessels. A device called a transducer is placed over your chest to transmit the ultrasound waves. The waves bounce off your heart and create a picture. The picture can provide valuable information about the health of your heart.
Here are some imaging tests doctors may use to study a heart attack patient:
Single photon emission computed tomography (SPECT) involves taking a series of pictures around the chest after a radioactive substance (thallium or technetium) is injected into the blood. Then computer graphics are used to create three-dimensional images of the heart. The technique can show lesions in the coronary arteries and the location of injured heart muscle.
Computerized axial tomographic scan (CT scan) is an imaging technique that provides cross-sectional images of the chest, including the heart and the great vessels. Sometimes a contrast dye is injected through a vein to enhance the image. CT gives detailed, three-dimensional pictures. When undergoing a CT scan, you will have to lie on a table that slides into the center of the machine. Other than lying still, you won't feel anything, though some people complain of a feeling of claustrophobia from being surrounded by the machine.
In general, a CT scan is useful in evaluating aortic disease (such as aortic dissection), cardiac masses and pericardial disease. Ultrafast CT, in particular, is useful to evaluate bypass graft surgery, congenital heart abnormalities, and quantify right and left ventricular muscle mass, chamber volumes, and systolic and diastolic function (such as cardiac output and ejection fraction). Ongoing research also suggests ultrafast CT may provide useful information about calcium deposits that signify blockages in the coronary arteries. However, this new form of CT scanning is still being investigated.
An even newer type of CT is called multislice CTA or CT angiography. These new scanners use more radiation and more "scanners" to produce rapid, high quality snapshots of the heart's arteries after contrast dye is injected into the patient's veins. They can take as many as 64 pictures (slices) at once, providing images that are nearly as good as coronary angiography. Which patients should undergo these scans is under research. Because of the increased amounts of radiation involved in the scan, they should probably not be used by patients who just want to see if they have evidence of atherosclerosis.
Cardiac positron emission tomography (PET) allows the study of various aspects of heart tissue function, including metabolic function and blood flow. PET is useful in research and has provided novel observations in various heart studies. Recent studies have suggested that PET is an important tool for diagnosing patients, describing disease and developing treatment strategy, especially in those patients with coronary artery disease. But because PET is expensive and requires specialized equipment, it's not used routinely.
Magnetic resonance imaging (MRI) uses magnetic fields and radio-waves to create an image. Computer-generated pictures can produce an image of the heart muscle, show damage from a heart attack, diagnose certain congenital heart defects and evaluate disease of larger blood vessels such as the aorta. It also can outline the affected part of the brain affected by stroke. Because the machine is essentially a magnet, certain patients can't be scanned, those with a pacemaker or other internal metal parts, for example.