When someone with a pacemaker needs an AED, place the pads at least four fingers’ width away from the implanted device. The standard pad positions still apply, but you may need to shift one pad slightly to keep that distance. The most important thing is to not delay defibrillation: a pacemaker is never a reason to withhold a shock during cardiac arrest.
How to Spot a Pacemaker
Pacemakers and implantable cardioverter-defibrillators (ICDs) are typically placed just under the skin below the collarbone, most often on the left side. You’ll see a small rectangular or oval bulge about the size of a matchbox, usually with a visible surgical scar over it. In a cardiac arrest situation, when you expose the person’s chest to apply AED pads, this bump is usually easy to feel even if it’s harder to see.
The Four-Finger Rule
The core guidance is straightforward: place your AED pad at least four finger-widths away from the implanted device. In standard AED use, the upper pad goes on the right side of the chest below the collarbone, and the lower pad goes on the left side of the chest below the armpit. Since most pacemakers sit under the left collarbone, the upper right pad is rarely an issue. It’s the lower left pad that sometimes needs adjusting.
If the pacemaker is on the left side and the lower pad would overlap or sit too close, simply shift the pad down or to the side until you have that four-finger gap. Don’t overthink exact positioning. AED pads are forgiving as long as one is on the upper chest and the other is on the lower left side, with the heart between them.
If the pacemaker happens to be on the right side (less common but not rare), you’d apply the same logic to the upper pad, moving it further from the device while keeping it on the upper chest.
Why Distance From the Device Matters
Placing a pad directly over a pacemaker or ICD creates two problems. First, the hard metal casing of the device can prevent the electrical current from reaching the heart muscle effectively. The shock essentially gets absorbed or deflected by the device housing instead of traveling through the cardiac tissue where it’s needed.
Second, the energy from an external defibrillator can damage the pacemaker’s internal circuitry. Research published in resuscitation science has documented that external defibrillation can impair multiple pacemaker functions, including its ability to pace the heart and sense cardiac rhythms correctly. After any external shock, the device needs to be re-evaluated by a cardiologist to check whether its pacing and sensing thresholds have shifted. But that’s a problem for later. During cardiac arrest, delivering the shock is what saves a life.
Pad Positions That Work
The American Heart Association’s 2020 guidelines confirm that several pad configurations are comparably effective for treating dangerous heart rhythms. These include:
- Anterior-lateral: One pad on the upper right chest, one on the lower left side. This is the standard position printed on most AED pad packaging.
- Anterior-posterior: One pad on the center of the chest (over the breastbone), one on the back between the shoulder blades.
- Anterior-left infrascapular: One pad on the front of the chest, one under the left shoulder blade.
For someone with a pacemaker under the left collarbone, the anterior-posterior option can be especially useful. Placing one pad on the front of the chest and one on the back keeps both pads well clear of the device while still sending current through the heart. If you’re unable to position the standard anterior-lateral pads with enough clearance from the device, switching to front-and-back placement solves the problem neatly.
What to Do Step by Step
Start CPR immediately if the person is unresponsive and not breathing normally. Send someone to grab the nearest AED. When you open the AED and expose the person’s chest, look and feel for a device bulge near either collarbone. If you find one, mentally note its location.
Peel the pads and check the diagram on them. Place the first pad (upper right chest) as shown. For the second pad, check the distance from the pacemaker. If you can fit four fingers between the edge of the device and the edge of the pad, you’re fine. If not, slide the pad further down or toward the side until you have enough clearance. Then follow the AED’s voice prompts as usual.
The entire process should add only a few seconds to your AED setup. Speed matters enormously in cardiac arrest. Every minute without defibrillation reduces the chance of survival by roughly 7 to 10 percent. A slightly imperfect pad position that gets a shock delivered quickly is far better than a perfect position that takes an extra minute to figure out.
After the Shock
Continue CPR between shocks as the AED directs. If the person regains a pulse or starts breathing, place them in the recovery position and leave the pads attached. When paramedics arrive, tell them the person has an implanted cardiac device. This information is critical because the pacemaker or ICD will need to be interrogated at the hospital to assess whether the external shock caused any programming changes or lead damage. In many cases the device continues to function normally, but verification is always necessary.