What is the proper placement of electrocardiogram (ECG) electrodes on a patient?

Proper ECG Electrode Placement

For diagnostic 12-lead ECGs, place limb electrodes on the arms and legs distal to the shoulders and hips (traditionally at wrists and ankles), and position precordial electrodes V1-V6 using precise anatomical landmarks with the patient supine. 1

Limb Electrode Placement

Standard Diagnostic ECG

• Place the four limb electrodes on the wrists and ankles with the patient in the supine position 1
• The American Heart Association recommends placement on the arms and legs distal to the shoulders and hips, though not necessarily at the exact wrists and ankles 1
• Electrode placement along the limbs significantly affects ECG voltages and durations, particularly in limb leads 1

Exercise/Treadmill Testing (Modified Placement)

• Use the Mason-Likar lead position to reduce motion artifact during exercise testing 2
• Place arm electrodes in the infraclavicular fossae medial to the deltoid insertions or over the outer clavicles 2
• Position the left leg electrode midway between the costal margin and iliac crest in the left anterior axillary line 2
• ECGs recorded with torso placement cannot be considered equivalent to standard ECGs and must not be used interchangeably for serial comparison 2, 3

Precordial Electrode Placement (V1-V6)

Precise Anatomical Positions

• V1: Fourth intercostal space at the right sternal border 1
• V2: Fourth intercostal space at the left sternal border 1
• V3: Midway between V2 and V4 1
• V4: Fifth intercostal space in the midclavicular line 1
• V5: In the horizontal plane at the anterior axillary line (same horizontal level as V4) 1
• V6: In the horizontal plane at the midaxillary line (same horizontal level as V4) 1

Critical Technical Points

• Position precordial electrodes with reference to underlying bony landmarks to avoid an erroneously vertical orientation 1, 4
• V5 and V6 should follow the horizontal plane of V4, not the fifth intercostal space, as the intercostal space course is variable 1
• Avoid using the "anterior axillary line" as a marker for V5, as its definition is vague 1

Skin Preparation

• Shave the electrode application areas, then rub with alcohol-saturated gauze 1
• After the skin dries, mark with a felt-tipped pen and rub with fine sandpaper or rough material 1
• Skin preparation by cleaning and gentle abrasion reduces noise and improves ECG quality 1
• These procedures should reduce skin resistance to 5000 Ω or less 1

Common Pitfalls and Their Consequences

Superior Misplacement of V1 and V2

• Placing V1 and V2 in the second or third intercostal space reduces initial R-wave amplitude by approximately 0.1 mV per interspace 1, 4
• This causes poor R-wave progression or erroneous signs of anterior infarction 1, 4
• Superior displacement often produces rSr' complexes with T-wave inversion resembling lead aVR 1
• Only 16% of cardiologists correctly identified V1 position in one study, compared to 90% of cardiac technicians 5

Inferior Misplacement of V5 and V6

• Placing V5 and V6 in the sixth intercostal space or lower alters amplitudes used for ventricular hypertrophy diagnosis 1, 4
• This can cause false-negative results for left ventricular hypertrophy 4

Torso Placement of Limb Electrodes

• Moving limb electrodes from extremities to torso causes rightward axis shifts and voltage changes 6
• Over half (13 of 25) of ECGs showing inferior infarct criteria with standard placement had those criteria erased with Mason-Likar positioning 6
• R wave amplitude increases >3 mm in inferior leads can cause disappearance of inferior infarcts 7
• Decreases >3 mm in leads I and aVL may cause false lateral infarcts 7

Special Populations

• In patients with obstructive pulmonary disease and low diaphragm position, V3 and V4 may record negative deflections that falsely simulate anterior infarction 1, 4
• In women with large breasts, place electrodes beneath the breast to reduce amplitude attenuation and favor reproducibility 1

Documentation Requirements

• Any ECG using modified electrode placement must be clearly labeled as such to prevent misinterpretation when compared to previous standard ECGs 2
• Record any modification of lead placement on the tracing 1

Quality Assurance

• Technicians and medical personnel should have periodic retraining in skin preparation, proper electrode positioning, and proper patient positioning 4
• Use silver plate or silver chloride crystal pellet electrodes, as they have the lowest offset voltage 1
• Ensure electrode gel remains moist 1