- EKG Fundamentals
- Reading EKGs
The standard 12-lead EKG consists of 6 precordial leads (V1-V6) and 3 limb leads. Yes, 6 + 3 does not equal 12, but we will get to that soon enough. For now, just focus on how to properly place the electrodes. Of note, there are often four electrodes placed, with the extra lead placed on the right leg to serve as a grounding wire.
To ensure accuracy, anatomical landmarks should be used when placing leads. When proper technique is not used, there is a tendency to misplace the leads superiorly, leading to changes in wave shape and amplitude.
V1 – fourth intercostal space at the right sternal border
V2 – fourth intercostal space at the left sternal border
V3 – midway between V2 and V4
V4 – fifth intercostal space in the midclavicular line
V5 – horizontal plane of V4 in the anterior axillary line (or between V4 and V6 if the anterior axillary line is unclear).
V6 – in the horizontal plane of V4 in the midaxillary line. *See V5 note
In women with large breasts, electrodes may be placed under or over the breast tissue.
There are three limb leads, one on each arm and one on the (traditionally left) leg. Previously, electrodes were placed on the wrist and ankles. This was a continuation of the original string galvanometer developed by Willem Einthoven, who had his patients dip their hands and feet in buckets filled with a salt water solution. However, the limbs are now viewed as simple electrical extensions that do not appreciably alter the EKG recording, so placement has been moved closer to the torso for ease of use. Currently, limb leads may be placed anywhere distal to the shoulders and hips.
The grounding wire has been included in this illustration.