12-Lead EKG Placement
Where all ten electrodes go, the right-sided and posterior placements, how to clear artifacts and how to read the paper. Then test yourself with EKG technician questions.
100 NHA CET-style questions in 100 minutes, with electrode placement, artifacts and rhythm questions explained for every answer.
Or try a free EKG Acquisition drillIn a five-electrode telemetry system, where is the right arm (RA) electrode usually placed?
Chest (precordial) electrodes
Find the angle of Louis (the ridge where the manubrium meets the sternum). The 2nd intercostal space is just beside it; count down from there. Place V1, V2 and V4 first, then V3 midway between V2 and V4, then V5 and V6 level with V4.
| Lead | Electrode site |
|---|---|
| V1 | 4th intercostal space, just right of the sternum |
| V2 | 4th intercostal space, just left of the sternum |
| V3 | Midway between V2 and V4 |
| V4 | 5th intercostal space, left midclavicular line |
| V5 | Left anterior axillary line, level with V4 |
| V6 | Left midaxillary line, level with V4 and V5 |
Limb electrodes
For a diagnostic 12-lead, place the four limb electrodes on the limbs, on fleshy areas away from bone, at matching levels on each side. Moving them onto the torso is a monitoring setup and changes the tracing. For an amputee, place the electrode on the remaining part of the limb and match the other side.
- RA
Right arm (wrist or upper arm)
- LA
Left arm, at the same level as RA
- RL
Right leg: the ground (reference) electrode
- LL
Left leg, at the same level as RL
If lead I shows an inverted P wave, QRS and T wave, the arm electrodes are usually reversed. Check them before you record again.
See if you can place them under time pressure
100 NHA CET-style questions in 100 minutes, with electrode placement, artifacts and rhythm questions explained for every answer.
Or try a free EKG Acquisition drillRight-sided and posterior leads
- Right-sided EKG: the chest leads are mirrored on the right chest. V4R sits in the 5th intercostal space at the right midclavicular line.
- Posterior EKG: V7, V8 and V9 sit level with V6, at the left posterior axillary line (V7), at the tip of the left scapula (V8) and just left of the spine (V9).
- Label the tracing with the leads you moved, so nobody reads it as a standard 12-lead.
Artifacts and how to fix them
| Artifact | What it looks like | Common causes | Fix |
|---|---|---|---|
| Somatic tremor (muscle artifact) | Jittery, irregular spikes over the baseline | Shivering, tense muscles, talking, tremor | Warm and reassure the patient, support the limbs, ask the patient to relax and stay still |
| Wandering baseline | The baseline drifts up and down | Breathing movement, lotion or oil on the skin, loose or dried electrodes | Clean and dry the skin, use fresh electrodes, move limb electrodes off the chest wall |
| AC (60-cycle) interference | A thick, regular fuzz across the tracing | Nearby electrical equipment, poor grounding, lead wires lying across power cords | Unplug nearby devices you can, straighten the lead wires, check the machine is grounded |
| Interrupted baseline | Sections of the tracing drop out | A loose electrode or a broken lead wire | Reattach the electrode and check the cable for damage |
EKG paper and heart rate
- Standard paper speed
- 25 mm per second
- Standard gain
- 10 mm tall for 1 mV
- One small box
- 1 mm: 0.04 seconds wide, 0.1 mV tall
- One large box
- 5 mm: 0.20 seconds wide, 0.5 mV tall
- Five large boxes
- 1 second
- 1500 method (regular rhythms): 1500 ÷ small boxes between two R waves. 20 small boxes = 75 beats per minute.
- 300 method (regular rhythms): 300 ÷ large boxes between two R waves. 4 large boxes = 75 beats per minute.
- 6-second method (any rhythm, including irregular): count the QRS complexes in 6 seconds (30 large boxes) and multiply by 10.
Lead placement questions
How many electrodes does a 12-lead EKG use?
Ten: four limb electrodes (RA, LA, RL, LL) and six chest electrodes (V1 to V6). The machine combines them into twelve views of the heart: I, II, III, aVR, aVL, aVF and V1 to V6.
Where does V1 go?
In the 4th intercostal space just to the right of the sternum. V2 sits in the same space just to the left. Find the angle of Louis, slide to the 2nd intercostal space beside it and count down to the 4th.
Where do V4, V5 and V6 go?
V4 goes in the 5th intercostal space at the left midclavicular line. V5 and V6 sit level with V4, at the anterior axillary line and the midaxillary line. Place V4 before V3, since V3 sits midway between V2 and V4.
What does it mean if lead I is upside down?
A lead I with an inverted P wave, QRS and T wave usually means the arm electrodes are reversed. Check that RA is on the right arm and LA on the left, then repeat the tracing.
Where do the electrodes go for a right-sided or posterior EKG?
A right-sided EKG mirrors the chest leads on the right side: V4R sits in the 5th intercostal space at the right midclavicular line. Posterior leads V7, V8 and V9 sit level with V6 at the left posterior axillary line, at the tip of the scapula and beside the spine.
How is lead placement tested on the CET exam?
Electrode placement, special placements and artifact troubleshooting belong to EKG Acquisition, the largest CET domain at 44 of the 100 scored questions.
Ready for the EKG exam?
100 NHA CET-style questions in 100 minutes, with electrode placement, artifacts and rhythm questions explained for every answer.
Or try a free EKG Acquisition drillKeep practicing
Exam weights from NHA CET test plan (2017 job analysis). Electrode sites follow the standard 12-lead placement taught in EKG technician programs.
Original independent practice. Not affiliated with or endorsed by the National Healthcareer Association (NHA). CET is a certification of the National Healthcareer Association.