How is electrocardiography (ECG) performed?

Updated: Mar 11, 2019
  • Author: Tarek Ajam, MD, MS; Chief Editor: Terrence X O'Brien, MD, MS, FACC  more...
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After preparation of the patient, apply the electrocardiographic (ECG) leads in the manner outlined below.

It is recommended that the standard limb leads are placed one on each limb distal to the shoulders and hips, but they do not necessarily need to be as far distal as the wrists and ankles. [16] Next, apply the precordial leads, taking care to be as precise as possible in their positioning.

Lead V1 is placed at the fourth intercostal space at the right sternal border. [16] Lead V2 is placed at the left sternal border directly across from lead V1, also in the fourth intercostal space. Lead V4 is placed in the fifth intercostal space at the mid clavicular line, and then lead V3 can be placed midway between leads V2 and V4. Lead V6 is placed in the horizontal plane of V4 at the mid-axillary line, and then lead V5 is placed in the same horizontal plane as that of lead V4 in the anterior axillary line or midway between leads V4 and V6 when the anterior axillary line is not readily discernible.

Note that precordial electrode placement in women with large breasts can be problematic due to obfuscation of bony landmarks. Therefore, it is recommended that the electrodes be placed beneath, rather than overlying, the breast. [16]

The importance of proper lead placement cannot be stressed enough. Furthermore, properly trained ECG technologists have been noted to be more likely to properly place the leads than are nurses or physicians, including cardiologists. [17] Improper placement of the leads can yield a tracing that gives the appearance of disease where none is present or vice versa. [18]

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