"Advanced Fitness Assessment and Exercise Prescription" by Vivian H. Heyward, Ph.D. describes how the 12-lead electrocardiogram measures the heart's electrical activity during the cardiac cycle. Depolarisation and repolarization as a result of the heart contracting, signal an electrical impulse to tissues surrounding the heart. The 12-lead ECG is measured using 10 electrodes (V) and includes three limb leads, three augmented unipolar leads and six chest leads. According to the "Merck Manual Home Edition," the ECG provides information about the part of the heart that triggers each heartbeat, the nerve conduction pathways of the heart and the rate and rhythm of the heart." Proper placement of each electrode is critical for accurate results.
Identify the anatomical locations for electrode placement. To properly perform a 12-lead ECG test, locate the sternum, mid-clavicular line, anterior axillary line and mid-axillary line. A pen can be used to mark the spots for future placement.
Obtain the electrodes for the three limb leads. Place one on the right arm and one on the left on either the wrist or deltoid, and one on the left leg near the ankle or thigh. Obtain a ground electrode and place it on the right leg.
Position the six chest leads (V1 to V6) according to the proper anatomical location. Place V1 near the fourth intercostal space to the right of the sternum, V2 on the opposite side of the sternum and V1, and V3 at the midpoint of a straight line between V2 and V4, which goes on the fifth intercostal space along the mid-clavicular line. Place V5 horizontal to V4 on the anterior axillary line, and V6 should be horizontal to V4 and V5 on the mid-axillary line.
Make sure the patient is relaxed before performing a 12-lead ECG test on him. When performing an ECG on a resting patient, make sure she is lying on her back on an exam table. Hair should be removed from the electrode sites and cleansed with alcohol prior to placement of electrodes.
Avoid performing an ECG test near electrical cords, as they may interfere with proper readings.