Anatomical Landmarks and Electrode Placement Sites — EKG Technician

Objective. Students will locate all 10 standard electrode placement sites on a live volunteer or manikin using palpation of anatomical landmarks without reference aids.

Why Electrode Placement Accuracy Matters

A 12-lead EKG records electrical activity from 10 electrodes placed at precise locations on the body. Each electrode captures a unique electrical perspective of the heart. Even a small placement error — moving an electrode one intercostal space too high or too low — can shift the waveform enough to mimic disease, mask a true abnormality, or cause a physician to order unnecessary tests. Because the EKG Technician is solely responsible for acquisition quality, getting placement right every single time is a core patient-safety responsibility and a central competency tested on the NHA CET exam.

The Ten Electrodes at a Glance

A standard 12-lead EKG uses four limb electrodes and six chest (precordial) electrodes. Together they produce 12 views of the heart from two electrode sets.

Four limb electrodes: right arm (RA), left arm (LA), right leg (RL), left leg (LL)
Six chest electrodes: V1, V2, V3, V4, V5, V6

Locating the Limb Electrodes

Limb electrodes are placed on the fleshy, non-bony portions of the limbs, away from major muscle masses that can introduce artifact.

RA: Inner surface of the right forearm, between the wrist and elbow.
LA: Inner surface of the left forearm, between the wrist and elbow.
RL: Inner surface of the right lower leg, between the ankle and knee.
LL: Inner surface of the left lower leg, between the ankle and knee.

For patients who have amputations, electrodes are placed on the residual limb stump or redirected to the torso according to facility protocol — always document any deviation.

Finding the Sternal Angle: Your Starting Landmark

All precordial placements depend on finding one key bony landmark: the sternal angle (angle of Louis). This is the horizontal ridge where the manubrium meets the body of the sternum. You can feel it as a distinct step or bump when you run your finger down the center of the chest from the neck.

Step-by-step palpation:

1. Place your fingertip at the suprasternal notch (the dip at the top of the sternum).

2. Slide downward a short distance until you feel a horizontal ridge — that is the sternal angle.

3. Move your finger laterally to the right. The rib that joins the sternum at this angle is the 2nd rib.

4. The space below the 2nd rib is the 2nd intercostal space (ICS).

5. Count downward: 3rd rib, 3rd ICS, 4th rib, 4th ICS.

Counting intercostal spaces correctly is the single most important skill for accurate V1 and V2 placement.

Precordial Electrode Placement Sites

V1

Fourth intercostal space, right sternal border. After counting to the 4th ICS on the right side, place the electrode immediately beside the sternum.

V2

Fourth intercostal space, left sternal border. Directly across from V1 on the left side of the sternum.

V3

Between V2 and V4. Place V4 first, then position V3 midway between V2 and V4.

V4

Fifth intercostal space, midclavicular line (MCL). The midclavicular line is a vertical line running through the midpoint of the clavicle downward. Count to the 5th ICS and mark where it intersects the MCL.

V5

Anterior axillary line, at the same horizontal level as V4. The anterior axillary line runs vertically from the front fold of the axilla (armpit). Do not move up or down — keep it level with V4.

V6

Midaxillary line, at the same horizontal level as V4 and V5. The midaxillary line runs from the middle of the axilla straight downward. Again, keep it level with V4.

Key rule: V4, V5, and V6 must all sit on the same horizontal plane. Drifting upward or downward breaks the lateral lead picture.

Safety and Patient Comfort Considerations

Expose only what is necessary. Use a drape or sheet to maintain patient dignity. Explain each step before touching the patient.
Skin preparation matters. Dry, clean, intact skin ensures good electrode contact. If the site is oily, gently clean with an alcohol wipe and allow to dry. If the site is very hairy, clip (do not shave roughly) only the electrode footprint.
Never place electrodes over open wounds, rashes, or pacemaker generator sites without supervisor guidance.
Document any deviation from standard placement (obesity, breast tissue, surgical scars, amputations) in the patient record so the reading clinician can interpret accordingly.
Breast tissue: For female patients, V4 and V5 are placed under the breast at the correct anatomical level, not on top of breast tissue. Breast tissue can attenuate (reduce) the signal.
Standard color coding (AHA convention in the US): RA = white, LA = black, RL = green, LL = red, V1–V6 = brown/red with subscript numbers. Always verify your department's lead wire labeling.

Practicing the Timed Drill

Being able to locate all 10 sites in under three minutes without reference aids is the practical standard expected in a clinical environment. Practice the sequence: establish the sternal angle → count to 4th ICS → place V1 and V2 → find MCL and place V4 → interpolate V3 → find anterior axillary line and place V5 → find midaxillary line and place V6 → apply four limb electrodes. Repeating this sequence builds the muscle memory and palpation confidence you need for the lab competency check and for daily clinical practice.

Key terms8

Sternal angle (angle of Louis)The palpable horizontal ridge where the manubrium meets the body of the sternum; used as the primary bony landmark to identify the 2nd rib and begin counting intercostal spaces.

Intercostal space (ICS)The gap between two adjacent ribs; numbered by the rib immediately above it (e.g., the 4th ICS lies below the 4th rib).

Midclavicular line (MCL)An imaginary vertical line drawn downward from the midpoint of the clavicle; the reference line for placing electrode V4.

Anterior axillary lineAn imaginary vertical line running downward from the anterior fold of the axilla (armpit); the reference line for placing electrode V5.

Midaxillary lineAn imaginary vertical line running downward from the midpoint of the axilla; the reference line for placing electrode V6.

Precordial electrodesThe six chest electrodes (V1–V6) that record electrical activity from a horizontal plane across the heart.

Limb electrodesThe four electrodes placed on the arms and legs (RA, LA, RL, LL) that produce the six frontal-plane leads of the 12-lead EKG.

Electrode misplacementPositioning an electrode at an incorrect anatomical site, which can alter waveform morphology and lead to misinterpretation of cardiac activity.

In class: Instructor demonstrates palpation of the sternal angle, intercostal spaces, midclavicular line, anterior axillary line, and midaxillary line while students follow along on their own torsos. · Students take turns placing color-coded sticker dots on a partner to mark V1 through V6 and the four limb sites, then compare placements against an overlay reference sheet. · Complete a timed landmark drill in which each student locates and verbally identifies all 10 sites on a manikin in under three minutes without assistance.
Materials: Manikin or student volunteers, color-coded sticker dots, anatomical landmark reference overlay, measuring tape, NHA CET exam content outline
Check: Instructor observes and records placement accuracy on a standardized checklist; all 10 sites must be within accepted clinical tolerance (V1–V2 correct intercostal space; limb sites on correct limb segment) to pass at 100% required sites correct.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.