Understanding Optimal Electrode Placement

Optimizing Current Delivery

In sudden cardiac arrest (SCA), the heart stops beating in a productive manner and is unable to efficiently pump blood to the brain and other vital organs. Rescuers must shock the heart with enough current from an automated external defibrillator (AED) or manual defibrillator to interrupt the irregular activity and allow the heart to resume a normal cardiac rhythm.

Electrodes, commonly referred to as pads, adhere to a victim’s chest and connect to a defibrillator. The pad allows the AED to analyze a heart’s rhythm, and if necessary, conduct current to the heart.

Careful pad placement allows for the most direct and unobstructed path of transthoracic current (TTC). Improper pad placement and the presence of a variety of substances can create resistance to current flow, also called transthoracic impedance (TTI). This guide explains pad placement and other important considerations to keep in mind when defibrillating adult and pediatric SCA victims.

Positioning Pads on Adults

Both adult and pediatric electrodes come packaged with simple graphics showing placement that will optimize the delivery of current. Electrode placement may vary by manufacturer, so be sure to review your electrode's instructions before you find yourself in a rescue situation.

In general, however, the American Heart Association (AHA) recommends two basic ways to position pads when treating adult victims: anterior-lateral and anterior-posterior.¹ When pads are placed anterior-laterally, or front-side, one electrode is placed on the victim’s upper right torso above the right nipple, just below the clavicle, and the other (lateral) pad should align with the bottom portion of the pectoral muscle on a male patient or under the breast on a female patient.

Alternatively, rescuers may choose to place pads in an anterior-posterior position, or front-back. Place the posterior pad to the left of the spine just below the scapula at the heart level. Place the front pad over the cardiac apex between the midline of the chest and nipple on a male victim or under the breast on a female. Both arrangements allow the AED to analyze the victim’s heart and deliver a shock if necessary.

ZOLL^® Electrodes

When using the ZOLL defibrillator, rescuers should attach pads to victims as indicated on the packaging of the ZOLL electrodes:

1. Place one electrode to the right of the patient’s sternum (patient’s right), just below the clavicle.
2. Place the other electrode just below and to the left of the patient’s left nipple, along the anterior-axillary line.

Positioning Pads on a Child

Children suffering from sudden cardiac arrest are treated in the same fashion as adults, with one significant difference. Because children require less energy during defibrillation, the current delivered must be attenuated, or reduced, through the use of specially designed pediatric pads. For this reason, the AHA recommends that any child under 8 years of age should be defibrillated using pediatric pads.²

It is also important that electrodes don’t overlap or make contact during defibrillation. A child’s smaller physical size can make it a challenge to position both electrodes on the chest without any overlap. To ensure safe pediatric defibrillation, the best location for pads is the anterior-posterior (front-back) configuration.  One electrode is placed on the front (anterior) chest wall and the other on the center of the child’s back (posterior)

The American Heart Association (AHA) states anterior-lateral placement or anterior-posterior placement may be reasonable to defibrillate pediatric victims,² however ZOLL pediatric electrodes are designed to be used in anterior-posterior placement as shown in the images below. Attach the back pad center along the spine of the victim. Attach the front pad over the cardiac apex between the midline of the chest and nipple.

Pad size

In an emergency, EMS rescuers should always act as quickly as possible, using the electrodes provided with the defibrillator at hand. To ensure that your AED is properly outfitted with appropriately sized adult and pediatric electrodes, the American Heart Association offers some guidance:

• Larger electrodes have been shown to lower transthoracic impedance, so the AHA suggests using adult electrodes that are between 8–12 cm (3.14–4.72 inches)  in diameter.¹
• To achieve the best outcomes when defibrillating a child, pediatric electrodes should also be as large as possible, while still providing 3 cm (1.18 inches) of space between the edges of the pads.
• When defibrillating infants and small children under 8 years of age or weighing less than 25 kg (55 lb), the AHA recommends using pediatric electrodes. ²

Elements of Successful Defibrillation

In addition to appropriate pad size and position, there are other factors EMS and hospital clinicians need to consider when preparing to defibrillate a victim.

Above all, it is important to make sure that the pads are completely adhered to the victim’s skin. Air pockets or gaps between skin and the pads can lead to the possibility of arcing and burns. To avoid this, apply one edge of the pad securely to the patient. Roll the pad smoothly from the applied edge to the other, being careful not to trap any air pockets between the pad and the skin.

Items on a victim’s body can interfere with the delivered current and some elements can even create impedance, or resistance, to current. To ensure the best possible outcome, pay close attention to the following list and quickly prepare the victim prior to defibrillation:

Jewelry: Remove all of a victim’s metal jewelry, including nipple piercings and necklaces, that may come in contact with electrodes.¹

Chest hair: If the victim has excessive chest hair, rapidly shave it with the razor provided with the AED before you apply pads to ensure proper adhesion. Those who are at risk for or who have already experienced SCA are encouraged to regularly remove chest hair.³

Breast tissue: Significant breast tissue can contribute to impedance. To accommodate for this, the AHA recommends placing the electrode beneath the tissue, using one hand to elevate the breast tissue and the other to apply the pad.³

Moisture: Excessive moisture can interfere with adhesion and electricity conduction. Move the victim and the AED away from sources of water, remove any wet clothing, and dry the victim to the best of your ability before applying electrodes.

Adequate pressure: Pad placement depends on adequate pressure. Studies have recommended that at least 80 N of force be applied when adhering pads to a victim, so it’s best to press down as firmly as possible to ensure proper application.⁴

These guidelines should help you respond in the event of an SCA. For further information, always refer to your AED manual or the American Heart Association website.

¹Panchal AR, et al. Circulation. 2020;142:16:S366–S468.
²Topjian AA, et al. Circulation. 2020;142:16:S469–523.
³Jacobs I, et al. Circulation. 2010;122:16:S325–S337.
⁴Sado DM, et al. J R Soc Med. 2005;98:1:3–6.