Acquire a 12-lead electrocardiogram with correct electrode placement, recognise common artefacts, and prepare the tracing for provider interpretation.

Which statement best describes the standard placement of the four limb electrodes for a resting 12-lead ECG in an adult patient who can lie supine?

• AOn the upper arms over the deltoids and on the upper anterior thighs near the inguinal crease.
• BOn the wrists and ankles, with the right leg lead serving as the neutral or ground reference.check_circle Correct
• COn both shoulders and both lower ribs along the mid-axillary lines to shorten cable runs.
• DOn the wrists and ankles, with the left leg lead acting as the neutral or ground reference.

Why A is wrong: Placing limb leads on the torso (Mason-Likar variant) is used for exercise testing, not a standard resting 12-lead, and it alters the frontal-plane axis and inferior-lead morphology compared with true limb placement.

Why B is correct: Standard resting 12-lead placement uses the distal limbs (wrists and ankles), with the right leg electrode acting as the driven reference. This gives Einthoven's triangle and the augmented vectors their classic frontal-plane geometry.

Why C is wrong: Torso placement on the trunk is not the resting standard and can shift the QRS axis and mimic inferior infarction; cable length is not a clinical justification for moving limb electrodes from the wrists and ankles.

Why D is wrong: The driven reference electrode is the right leg, not the left leg. The left leg electrode (LL) is an active recording electrode that contributes to leads II, III, and aVF, so misassigning it as ground would corrupt the inferior leads.