Using an AED is designed to be straightforward, but certain situations require extra steps before you deliver a shock. Implanted devices, medication patches, excessive chest hair, children, and pregnancy all call for specific adjustments. Knowing these ahead of time can save critical seconds during an emergency.
Implanted Pacemakers and Defibrillators
Some people have a pacemaker or implanted defibrillator visible as a small, hard lump under the skin of the upper chest, usually just below the collarbone. If you spot one, place the AED pads at least 8 centimeters (about 3 inches) away from the device. Placing a pad directly over the implant can interfere with the shock’s path through the heart and potentially damage the device.
The standard pad position (one on the upper right chest, one on the lower left side) usually works fine as long as you keep that distance. If the implant is in the way of the default position, use an alternative placement such as one pad on the front of the chest and one on the back. Most importantly, don’t let the presence of an implanted device delay you. Adjusting pad placement should take only a few seconds, not minutes.
Medication Patches on the Chest
Transdermal patches for nitroglycerin, nicotine, pain medication, or hormone therapy are common, and they create a real problem if an AED pad is placed directly over one. The electrical current can heat the patch’s adhesive or medication, causing skin burns. It can also block the shock from reaching the heart effectively.
Before applying the pads, quickly scan the person’s chest for any patches. If you find one in the path of a pad, peel it off, wipe the area with a cloth or your hand to remove residue, then place the pad. Wear gloves if available, since some medications (especially nitroglycerin) can absorb through your skin and cause a sudden drop in your own blood pressure.
Excessive Chest Hair
AED pads need firm, direct contact with the skin to work. Thick chest hair traps air under the pads, which dramatically increases the electrical resistance between the pad and the heart. In one study, hairy-chested subjects had average resistance of 162 ohms compared to 103 ohms in subjects without significant chest hair. After shaving, resistance dropped right back to 105 ohms, essentially the same as a bare chest.
That difference matters because higher resistance means less of the shock actually reaches the heart. Many AED kits include a disposable razor for exactly this reason. If the AED gives a “check pads” warning or fails to analyze properly, try pressing the pads down firmly first. If that doesn’t work, rip the pads off quickly (this can pull out enough hair to improve contact), then apply a fresh set. Shaving the two pad areas is the most reliable fix if you have a razor and a few extra seconds.
Using an AED on Children
AEDs can be used on children and infants, but the shock dose needs to be smaller. The American Heart Association recommends using pediatric pads or a pediatric dose setting for children under 8 years old. Pediatric pads reduce the energy delivered to a level appropriate for a smaller body.
Some AEDs have a switch or a special key that activates a child mode, while others come with separate smaller pads. If you don’t have pediatric pads or a child setting available, use the adult pads. An adult shock dose is not ideal for a small child, but cardiac arrest without any shock is worse. On very small children, the two pads may not both fit on the front of the chest without touching each other. In that case, place one pad on the center of the chest and the other on the center of the back.
Pregnancy
An AED is safe to use during pregnancy at any stage. The electrical energy delivered to the mother’s chest passes minimal current to the fetus, and the standard shock protocol requires no modification for pregnant patients. The same pad positions apply: one on the upper right chest, one on the lower left side. For the left pad, place it under the breast tissue rather than on top of it, which becomes more important as breast size increases during pregnancy.
If the person is connected to a fetal monitor, leave it in place. Defibrillation is unlikely to cause arcing to the monitor’s electrodes, and removing it wastes time. The priority is restoring a normal heart rhythm in the mother, which is also the single most important thing for the fetus.
Wet Skin and Metal Surfaces
Water conducts electricity, so a soaking wet chest can cause the shock to travel across the skin surface instead of through the heart. If the person is lying in a shallow puddle, you don’t need to move them, but you should towel off the chest quickly before applying pads. If they’re submerged or lying in deep standing water, move them to a dry surface first for your own safety.
Metal surfaces like steel decks, industrial grating, or aluminum bleachers are safe to defibrillate on. The electrical path follows the pads through the chest, not down through the floor. Just make sure nobody is touching the person when the shock is delivered, which is the standard precaution regardless of the surface. Keep the edges of the pads from directly contacting the metal surface beneath the person.
Clothing, Jewelry, and Bras
All clothing needs to come off the chest before pad placement. AED pads must stick directly to bare skin. The American Heart Association guidelines specify removing all clothing and jewelry from the chest before attaching pads.
Underwire bras have long been a source of concern, but recent research suggests the actual risk is lower than many people assume. In an animal study that delivered 126 shocks with AED pads in direct contact with exposed bra underwire, researchers observed no arcing, no burns to the skin, and no redirection of current. That said, a bra still physically prevents proper pad contact with the skin, so it needs to come off regardless. The concern about metal causing sparks or burns appears to be largely theoretical, but good pad-to-skin contact is non-negotiable for the shock to work.
Body piercings that fall directly under a pad can be left in place if removing them would take significant time. The small amount of metal in a piercing is unlikely to cause problems, but if a piercing is easy to remove and sits right where a pad needs to go, taking it out is a reasonable precaution.
The Overriding Principle
Every one of these considerations matters, but none of them should cause a long delay. Cardiac arrest survival drops roughly 10% for every minute without defibrillation. Spending 10 to 15 seconds wiping off a chest, removing a patch, or adjusting pad placement around a pacemaker is worthwhile. Spending two minutes searching for a razor or debating whether to remove a piercing is not. The AED itself will guide you through the process, analyze the rhythm, and only deliver a shock if one is needed. Your job is to get the pads on bare skin, in roughly the right position, as quickly as possible.