12-Lead EKG Electrode Placement
Updated October 27, 2026
EKG Acquisition is the biggest domain on the NHA CET exam: 44 of the 100 scored questions. Correct lead placement is at the center of it. A 12-lead EKG uses 10 electrodes: 6 on the chest and 4 on the limbs. Here’s where each goes, followed by free practice questions.
Chest (precordial) electrodes
| Electrode | Position |
|---|---|
| V1 | 4th intercostal space, right sternal border |
| V2 | 4th intercostal space, left sternal border |
| V3 | Midway between V2 and V4 |
| V4 | 5th intercostal space, left midclavicular line |
| V5 | Left anterior axillary line, at the same level as V4 |
| V6 | Left midaxillary line, at the same level as V4 and V5 |
To find the 4th intercostal space, feel for the angle of Louis (the ridge where the top of the sternum meets its body), which is level with the 2nd rib. The space below the 2nd rib is the 2nd intercostal space; count down two more spaces to the 4th.
Limb electrodes
| Electrode | Position |
|---|---|
| RA | Right arm or wrist |
| LA | Left arm or wrist |
| RL | Right leg or ankle (ground) |
| LL | Left leg or ankle |
Place limb electrodes on fleshy areas, avoiding bone, and in matching spots on each side.
Common problems
- Artifact from muscle tremor or movement: help the patient relax, keep them warm and still, and support the limbs.
- Wandering baseline: often from poor electrode contact or breathing. Clean and dry the skin and check the electrodes.
- 60-cycle (AC) interference: electrical interference from nearby devices. Unplug nearby equipment if possible and check that the cables aren’t crossing power cords.
- Reversed arm leads: lead I looks inverted. Check that RA and LA aren’t swapped.
Free 12-lead placement practice questions
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Where is V1 placed?Answer: AV1 goes in the 4th intercostal space at the right sternal border. V2 is in the same space at the left sternal border.
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Where is V4 placed?Answer: BV4 goes in the 5th intercostal space at the left midclavicular line. V5 and V6 are placed at the same level, further to the side.
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How many electrodes are used for a standard 12-lead EKG?Answer: BA 12-lead EKG uses 10 electrodes: 6 chest electrodes and 4 limb electrodes. The machine combines them to produce 12 views (leads) of the heart.
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Where is V3 placed?Answer: CV3 sits midway between V2 and V4, so V4 is usually placed before V3.
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A tracing shows a fuzzy, irregular baseline from a patient who is shivering. What should the technician do?Answer: DShivering causes somatic tremor artifact. Warm the patient, help them relax, support the limbs and make sure they're still, then repeat the tracing.
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Which landmark helps find the 2nd intercostal space?Answer: AThe angle of Louis, where the top of the sternum meets its body, is level with the 2nd rib. The 2nd intercostal space is just below it; count down from there to find the 4th.
Pass your EKG technician exam on the first try
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