Tests for angina and heart attack

If you have chest pain that may be caused by a heart attack, your doctor will ask about your symptoms and will usually evaluate you with electrocardiography and cardiac enzyme blood tests.
Electrocardiogram
Your heart has its own electrical system that controls the rate and rhythm of your heartbeat. Electrocardiography (EKG or ECG) is a simple, non-invasive test that records the activity of this electrical system. The ECG machine then displays the electrical signals as "spikes," or waves on a graph.
If your heart is healthy, your ECG will show the electrical signals in a normal, consistent pattern. If your heart is starved for oxygen, it won't conduct electricity the way it normally does. This problem shows up as changes on the ECG.
When you have angina, the ECG becomes normal again when your chest pain goes away because your heart is getting oxygen again. With a heart attack, the ECG is not likely to return to normal. Instead, the ECG may begin showing new changes over time that represent the permanent injury to your heart that the heart attack has caused.
What do my ECG results mean?
Ischemia is said to be present when your heart is not getting enough oxygen. When this occurs, your heart may not function normally, and its electrical system doesn't conduct the electrical signal properly. Ischemia produces an abnormal ECG reading called ST segment depression. This abnormal reading usually resolves after blood flow to your heart improves. If you have chest pain and your ECG reveals ST segment elevation, it may mean that one of your coronary arteries is blocked.
An ECG can help diagnose a heart attack (myocardial infarction). A heart attack is diagnosed when two of the following three conditions are present:
Symptoms consistent with ischemia or myocardial infarction
ECG changes consistent with myocardial infarction
Elevated cardiac enzymes
About half of the ECGs done at the time someone arrives at the hospital do not yet show evidence of a heart attack. For this reason, it is important to monitor your ECG results over time. You will likely have to stay in the hospital for several hours for repeat ECG testing until your doctor is more confident about whether you have had a heart attack.
What other tests can help determine the difference between angina and a heart attack?
Because some heart attacks do not cause typical symptoms, and the initial ECG is often not conclusive, testing levels of cardiac enzymes is also very important.
What are cardiac enzymes?
If your heart muscle goes without oxygen for a long enough period of time, the muscle cells are injured and later may die. When this happens, cells of the heart release proteins (enzymes) into the bloodstream.
These enzymes can be detected with simple blood tests. Blood tests exist that can measure several different cardiac enzymes. Some of the enzymes can be detected within hours after a heart attack begins, making it very important to get these blood tests as soon as possible to determine if you are having a heart attack. Other enzymes may remain in your blood for several days, which makes it possible to diagnose a heart attack several days after it has happened.


Author:	Douglas Dana Robin Parks, MS	Last Updated August 15, 2007
Medical Review:	Anne C. Poinier, MD - Internal Medicine Caroline S. Rhoads, MD - Internal Medicine Stephen Fort, MD, MRCP, FRCPC - Interventional Cardiology
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