372
Chapter 12
(b)
V1
V2
V3 V4
V5
V6
(–)
Lead III
aVL
(a)
(+)
(+)
(–)
Ground
(+)
(+)
(+)
(–)
Lead II
(–)
(–)
(–)
Lead I
aVR
(+)
aVF
Figure 12–15
Placement of electrodes in electrocardiography. Each of the twelve leads uses a different combination of reference (negative pole) and
recording (positive pole) electrodes, thus providing different angles for “viewing” the electrical activity of the heart. (a) The standard limb
leads (I, II, and III) form a triangle between electrodes on the wrists and left leg (the right leg is a ground electrode). Augmented leads bisect
the angles of the triangle by combining two electrodes as reference. (For example, for lead aVL the right wrist and foot are combined as the
negative pole, thus creating a reference point along the line between them, pointing toward the recording electrode on the left wrist.)
(b) The precordial leads (V
1
–V
6
) are recording electrodes placed on the chest as shown, with the limb leads combined into a reference point at
the center of the heart.
Table 12–2
Electrocardiography Leads
Name of Lead
Electrode Placement
Standard Limb Leads
Lead I
Lead II
Lead III
Reference (–) Electrode
Right arm
Right arm
Left arm
Recording (+) Electrode
Left arm
Left leg
Left leg
Augmented Limb Leads
aVR
aVL
aVF
Left arm and left leg
Right arm and left leg
Right arm and left arm
Right arm
Left arm
Left leg
Precordial (Chest) Leads
V1
V2
V3
V4
V5
V6
Combined limb leads
"
"
"
"
"
"
"
"
"
"
"
"
"
"
"
4
th
intercostal space, right of sternum
4
th
intercostal space, left of sternum
5
th
intercostal space, left of sternum
5
th
intercostal space, centered on clavicle
5
th
intercostal space, left of V4
5
th
intercostal space, under left arm
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