The electrocardiograph and ECG preparation

The Electrocardiograph

The lead wires may have a snap or a clip (also called an alligator clip; patient end adaptor) that attaches to the electrode. The lead wires merge into the patient cable that takes the electrical impulses to the electrocardiograph (ECG machine). In the machine, the impulses pass through an amplifier, which magnifies the impulses. A digital converter changes the analog signal into a digital signal. The digital signal can be printed off on special ECG paper, which is discussed in the next section.

Features

The features of ECG machines can vary greatly. The two types of ECG devices in ambulatory healthcare facilities include the box model and computer-based models. The box model ECG machine usually has an LCD screen. The computer-based ECG may have a touch screen and stress testing features. The software can be preloaded onto its own computer, or the facility can purchase software to be added to any laptop computer. These additional features are commonly seen in both types of ECG devices:

• Interpretive software: Assists providers with reading the tracing
• Bluetooth or Wi-Fi capacity: Allows the ECG to be sent to providers and printers and to be uploaded into an electronic health record (EHR)
• Thermal printers
• Spirometer

Settings and calibration

ECG machines have settings that can be useful for obtaining a tracing. Many machines have filters to block disturbances. Filters can help to create a clearer tracing. Refer to the operators’ manual when changing settings. Table 26.2 presents common settings. It is important to indicate on the tracing if any of the default settings were changed. Changes to the default settings will affect how the provider measures and interprets the tracing.

Most ECG machines automatically complete a self-test when the machine is turned on. Typically, the self-test examines the battery and the memory. Like many machines used in the healthcare setting, the ECG machine needs to be calibrated daily or per the facility’s policy. The calibration results should be documented on the log flow sheet.

When ECG machines are calibrated, the sensitivity (also called gain) should be checked. The machines usually print a calibration marking either at the beginning or the end of the tracing. This marking is called the standardization mark. If the machine is set at 10 mm/mV, the standardization mark will be an upward rectangle that is 10 small boxes tall. If the gain is doubled, then the standardization mark also will be doubled in size.

Maintenance

After the ECG is obtained and the patient has left, the medical assistant must clean the room and the electrocardiograph. Maintenance of the machine includes these steps:

• Clean the lead wires as indicated in the users’ guide. The lead wires are not disposable.
• Handle the lead wires and patient cable with care. They should be stored in a loose coil. Tight coils or bending of the wires and cable can result in breakage of the fine wires inside the unit. This will cause artifacts on the ECG and requires replacement of the cable.
• Clean the tracing stylus and the machine casing as indicated in the users’ guide.

ECG procedure

The medical assistant must prepare the patient prior to the ECG procedure, apply the electrodes and lead wires, and coach the patient just before taking the ECG tracing. Providing coaching prior to the procedure helps to decrease the patient’s anxiety.

Patient preparation

Learning Objective: Describe how the medical assistant should prepare the patient for the ECG procedure.

Before the procedure begins, it is always important for the medical assistant to coach the patient on the procedure and the preparation required. The medical assistant should prepare the patient for an ECG by explaining these points:

• Ten electrodes and wires are placed on the body.
• The machine will take 12 pictures of the electrical activity of the heart.
• The procedure is painless.
• The patient must be still and not talk during the time the pictures are being made (during the actual tracing).
• The patient should not use a cell phone or other electronic device during the procedure.
• The provider will need to look at the ECG pictures, and then the patient will be notified of the results. (Remember, the medical assistant cannot tell the patient if it is normal or abnormal.)

The patient needs to remove all clothing above the waist and wear a gown that opens in the front. Cloth gowns or paper capes can be used. An electrode must be placed on each lower leg, so tights or pantyhose also must be removed. Socks and pants can be moved to allow application of the electrodes, so they can usually stay on.

The patient should be in the supine position on the exam table. A pillow can be placed under the patient’s head. The patient’s legs and arms need to be supported on the table. It is important for the patient to be relaxed and comfortable during the procedure. If the patient has chest pain or problems breathing, the head of the exam table may be elevated. Any change of position from the supine position must be noted on the ECG tracing. Any position change can create a change on the leads (pictures). The provider needs to be aware of it when reading the tracing.

Before placing the electrodes on the skin, it is important to prepare the skin. This helps the electrodes adhere and minimizes artifacts, thus producing an accurate tracing. There are several techniques used to prepare the skin:

• Wipe the area with an alcohol pad to clean it. This helps remove sweat and lotion that may prevent the electrodes from adhering to the skin.
• Use a razor to shave chest hair. Obtain the patient’s verbal consent before shaving the chest.
• Gently abrade the skin using a gauze sponge, special gel, or special fine sandpaper tape

Applying electrodes and lead wires

Apply electrodes to both arms and legs. The electrodes on the lower legs should be placed on the inner side, just above the ankles. If tab electrodes are used, have the tabs on the leg electrodes point toward the center of the person. All the other tabs can be facing the feet.

The placement of the arm electrodes may vary depending on the ECG machine and manufacturer. For instance, many Schiller ECG machines indicate that the electrodes should be placed just above the wrists. Other machines indicate placement on the upper arms. Check the users’ guide for correct placement of the arm electrodes.

Electrode and lead wire placement

Electrode	Lead Wire Abbreviation & Color	Placement
Right arm	RA (white)	Just above the wrist or upper arm (per user guide)
Left arm	LA (black)	Just above the wrist or upper arm
Right leg	RL (green)	Inner lower leg, just above the ankle
Left leg	LL (red)	Inner lower leg, just above the ankle
Chest V1	V1 (red)	4th intercostal space (ICS), right sternal edge
Chest V2	V2 (yellow)	4th ICS, left sternal edge
Chest V3	V3 (green)	Midway between V2 and V4
Chest V4	V4 (blue)	5th ICS, midclavicular line
Chest V5	V5 (orange)	Same horizontal plane as V4, left anterior axillary line or midpoint between V4 & V6
Chest V6	V6 (purple)	Same horizontal plane as V4, midaxillary line

The lead wires are typically color coded and include an abbreviation on each wire. Colors may vary from manufacturer to manufacturer. It is important to know and to use the abbreviations. One of the most common errors is to mix up the right and left limb lead wires. This can cause abnormal leads (pictures) and result in additional patient workup before the mistake is discovered. It is important to always double-check the placement of the lead wires.

In some cases, the electrodes may need to be placed in alternative locations, such as with the following:

• Dextrocardia: Place the chest electrodes on the right side of the chest using the same intercostal spacing and landmarks. Switch the right and left limb lead wires (e.g., LA would be attached to the right arm electrode).
• Amputated limb: Place the electrode on the remaining part of the limb. Place the electrode on the opposite limb in the same location.
• Casted limb: Place the electrode above the cast on the limb. Place the electrode on the opposite limb in the same location.
• New surgical incision or wound: Place the electrodes near the correct area but not on the incision or wound.

It is important to note on the ECG tracing any electrode placement deviation from the normal location. The provider reading the tracing needs to take the placement into consideration.