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Electrocardiogram (ECG) (cont.)

What Happens During an ECG?

The ECG is a relatively simple test to perform. It is non-invasive and does not hurt. Patches are placed on the skin to detect electrical impulses that the heart generates. These impulses are recorded by an ECG machine. Four patches are placed on the limbs. One is placed on each shoulder or upper arm and one on each leg. These are called the limb leads. There are six patches that are placed on the chest wall beginning just to the right of the breast bone. Patches are placed in the shape of a semi-circle ending near the left axilla (underarm). These are called the chest leads. These patches are connected to an ECG machine that records the tracings and prints them onto paper.

Newer machines also have video screens that help the technician, nurse, or doctor decide whether the quality of the tracing is adequate or whether the test should be repeated. ECG machines are also equipped with computer programs that can help interpret the ECG, although they are not completely accurate.

In certain situations, the physician may want to “look” at the heart from different angles after the initial ECG is done. The chest leads may then be placed across the right chest wall or on the back.

The skin should be clean and dry to prevent electrical interference to get an acceptable tracing for interpretation. Sometimes that means shaving chest hair or aggressively toweling off the skin. Shivering or tremors can interfere with the tracing and cause interference that affects the quality of the ECG tracing. Usually, the patient has to hold still for 5-10 seconds without moving to get an accurate ECG.

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