c. The standard ECG machine utilizes 12 "leads." These leads represent paths
of electrical activity and are designated as leads I, II, III, aVR, aVL, aVF, V1, V2, V3, V4,
V5, and V6. It is neither practical nor necessary to go into an explanation of leads in
this text. To do so would require extensive explanation of electrophysiological
principles. It will suffice to say that each lead senses and records the electrical
impulses from different positions related to the heart's surface. Since each lead takes a
different view of heart activity, it generates its own characteristic tracing. Wave
abnormalities that appear in the different leads indicate damage or defects in particular
portions of the heart muscle.
d. The ECG provides quite a bit of valuable information for the small amount of
effort involved in obtaining an ECG recording. It is a procedure that is completely
noninvasive and without risk to the patient. It is easily performed by anyone with the
proper training. The ECG provides information about the heart rate, rhythm, the
condition of the myocardium, the presence of ischemia or necrosis, conduction
abnormalities, the presence of certain drugs, and the effects of disturbed electrolytes.
e. Because it does provide so much valuable information, it is important that the
procedure be performed correctly. Correct procedure will vary depending upon the type
of equipment used in your facility. Be sure to read the local standard operating
procedures (SOP) and the manufacturer's instructions before attempting to use the
equipment. Another important factor in correct performance is proper placement of the
electrodes. Electrodes should be secured over a fleshy area, not over a bone, as bone
interferes with the electrical impulse readings. In order to obtain accurate readings the
patient may need to be shaved using a prep razor if the area where the electrodes are
to be placed. Location of the electrodes is standard for all designs of ECG equipment.
(1) Leg electrodes are best placed on the medial or lateral aspect of the calf
to avoid contact with bone.
(2) Arm electrodes are best placed on the inner aspect of the arm or
forearm, several inches above or below the antecubital space.
(3) Chest electrodes are placed as follows. Remember to place the
electrodes over the intercostal spaces, not over the ribs.
4th intercostal space at the right sternal border.
4th intercostal space at the left sternal border.
Halfway between V2 and V4.
5th intercostal space at the midclavicular line.