An Automated External Defibrillator (AED) is a portable device used to treat sudden cardiac arrest by delivering an electrical shock to the heart. The shock, known as defibrillation, can stop an abnormal heart rhythm, such as ventricular fibrillation, allowing the heart’s natural pacemaker to potentially resume a normal rhythm. The adhesive pads, or electrodes, are the interface between the AED and the victim’s body, enabling the device to analyze the heart’s electrical activity and deliver the shock. Understanding the correct use and placement of these pads is fundamental to improving the chances of survival.
The Standard Number and Function of AED Pads
The standard number of adhesive pads placed on a victim’s chest is two, which is a universal practice across nearly all defibrillator models. These two pads are required to establish a complete electrical circuit, ensuring the therapeutic current passes directly through the heart muscle. One pad functions as the positive electrode, and the other acts as the negative electrode, creating a pathway for the electrical energy.
This two-pad system is designed to depolarize the heart muscle simultaneously, effectively stunning the chaotic electrical activity of a shockable rhythm. For the circuit to be effective, the pads must have excellent contact with the skin, which is why they are coated with a conductive adhesive gel. Proper adhesion and skin preparation, including drying the skin and removing excessive chest hair if necessary, maximize the effectiveness of the delivered shock and minimize the risk of skin burns. The AED uses the pads to continuously monitor the heart’s rhythm.
Essential Pad Placement Techniques
The exact positioning of the two pads dictates the path the electrical current takes through the chest to reach the heart. The goal is to “bracket” the heart tissue within the electrical pathway to maximize successful defibrillation. The most common method for adults is the anterior-lateral placement.
Anterior-Lateral Placement
In this standard technique, one pad is positioned high on the victim’s right side, below the collarbone and to the right of the breastbone. The second pad is placed on the lower left side of the chest, situated on the lower rib cage. This configuration ensures the heart lies directly between the two electrodes.
Anterior-Posterior Placement
An alternative is the anterior-posterior placement, involving one pad on the center of the chest and the other on the back between the shoulder blades. This placement is used when the standard configuration is not possible or when the victim has an implanted medical device like a pacemaker.
Addressing Specialized Pad Types
While the number of pads remains two, a significant difference exists between adult and pediatric electrodes based on the victim’s size and age. Pediatric pads are necessary for children typically under eight years old or weighing less than 55 pounds (25 kilograms). These pads are smaller to prevent them from touching or overlapping on a child’s chest, which could cause a dangerous electrical short circuit.
Pediatric pads incorporate an attenuator, which acts as a resistor. This mechanism reduces the energy level of the electrical shock delivered by the AED to a safer dose for a child’s heart. For instance, an adult shock might be around 150 to 200 Joules, while a pediatric shock is often attenuated to approximately 50 Joules. Furthermore, for infants, the pads are often placed in the anterior-posterior configuration to ensure effective current delivery through the smaller body mass.