Where Should AED Pads Be Placed in Anterolateral Placement?

In anterolateral placement, one AED pad goes on the upper right chest, just below the collarbone and to the right of the breastbone, while the second pad goes on the left side of the torso, roughly below the armpit and below the level of the left nipple or breast. This sounds straightforward, but research consistently shows that even trained professionals get it wrong more often than you’d expect, and the diagrams printed on AED pads themselves are part of the problem.

The Two Pad Positions, Step by Step

The anterolateral configuration is what most AED instruction manuals and resuscitation courses teach as the default. The right-side pad (sometimes called the sternal pad) sits on the upper right chest. Specifically, it should be placed to the right of the sternum, below the clavicle. Think of it as a hand’s width below the right collarbone, centered between the sternum and the right shoulder. The left-side pad (sometimes called the apical pad) goes on the lower left side of the chest. Operating guides for commonly available defibrillators describe this as the area between the anterior axillary line and the midaxillary line on the left side, which in plain terms means the side of the ribcage roughly aligned with the armpit, not the front of the chest.¹

The goal is to position the two pads so that the electrical current they deliver passes through as much of the heart muscle as possible. The heart sits slightly left of center in the chest, angled so that its base points toward the right shoulder and its apex points toward the left hip. By placing one pad high and right and the other low and left, the shock vector runs diagonally through the bulk of the cardiac tissue. If either pad drifts too far from its intended landmark, less current reaches the heart, and the shock is less likely to convert a lethal rhythm back to something organized.

Why So Many People Place Them Wrong

A study of Advanced Life Support instructors, the people who teach others how to use defibrillators, found that only about one in five placed the sternal and apical pads correctly on a manikin. The sternal pad was misplaced 82% of the time, usually too high (toward the neck) and too far toward the shoulder. The apical pad was wrong 80% of the time, split between being placed too high, too low, too far forward on the chest, or too far back toward the spine.¹ If trained instructors miss the mark this often, untrained bystanders face an even steeper challenge.

Lay rescuers actually do better than you might assume, at least in simulation. In one study, about 79% of lay participants correctly placed the upper pad and about 79% got the lower pad right. First responders were slightly better with the upper pad (about 89% correct) but similar on the lower pad (about 78%). When placement was wrong, the most common mistake for both pads was placing them too low on the torso.² The discrepancy between instructors and laypersons in these studies likely reflects differences in what “correct” was measured against and how strictly the target zones were defined, but the theme is the same: the apical pad drifts, and it usually drifts in a direction that reduces current flow through the heart.

The Diagrams on AED Pads Are Not Helping

Part of the problem is that the pictorial instructions printed on or packaged with AED pads are surprisingly poor at guiding placement. A study that tested how well people could position pads using only the manufacturer’s diagrams found that every diagram currently on the market failed to achieve accurate placement. Depending on which brand was used, as few as 8% of participants placed both pads within an acceptable range of the recommended position.³ The apical pad was the most frequent casualty, typically ending up too far forward on the front of the chest rather than wrapping toward the side.

A separate analysis of AED pad diagrams concluded that all current instructional illustrations fail to produce accurate pad placement, and called for a redesigned diagram as a matter of urgency.⁴ When researchers designed an alternative diagram that specifically showed a lateral view of where the apical pad should sit on the side of the chest, the proportion of people who got both pads close to the target jumped to 64%.³ The takeaway for anyone using an AED: the diagram on the packaging is a rough guide at best. Think “side of the ribcage, below the armpit” for the left pad rather than “front of the chest below the heart.”

Placement on Women

Breast tissue complicates apical pad placement for a simple physical reason: breast tissue has higher electrical impedance than the underlying chest wall. A study in the Journal of the American College of Cardiology found that placing the apical defibrillation electrode directly on top of the breast increased transthoracic impedance, reducing the current that actually reaches the heart. The researchers recommended placing the apical pad lateral to or underneath the breast.⁵

In practical terms, this means you should lift or move the left breast out of the way and place the pad on the chest wall beneath it, or position the pad further toward the side so it sits lateral to the breast rather than on top of it. The sternal pad on the upper right chest is generally unaffected, since it sits above breast tissue in most women. Reluctance to touch a woman’s chest is one of the documented reasons bystanders hesitate to use AEDs on female cardiac arrest victims, but the evidence is clear that a pad placed over breast tissue delivers a weaker shock. Moving the breast is not optional if you want the defibrillator to work as designed.

Placement on Larger Patients

Obesity adds a similar challenge. Excess adipose tissue on the chest wall increases the distance between the pad surface and the heart, and fat is a poor conductor of electricity. For obese patients, defibrillator operating guides describe the same anterolateral landmarks: the right pad goes over the right upper chest to the right of the sternum, and the left pad goes between the anterior and midaxillary lines on the left side.¹ The key practical issue is making sure the pads adhere firmly, since loose contact also raises impedance. In very large patients, clinicians sometimes switch to an anteroposterior configuration, where one pad goes on the center of the chest and the other on the back between the shoulder blades, because this can provide a more direct path through the heart with less tissue in the way.

Pad size also matters for heavier patients. A study examining defibrillation success with different electrode sizes found that larger pads (12 cm diameter) succeeded in terminating ventricular fibrillation with a single 200-joule shock about 82% of the time, compared with only 31% for smaller pads (8 cm diameter). Larger pads lowered transthoracic impedance substantially.⁶ Most modern adult AED pads are already in the larger size range, but if you have a choice, bigger pads with full contact are better than smaller ones with partial adhesion.

When the Heart Is on the Wrong Side

About 1 in 10,000 people have dextrocardia, a condition where the heart is oriented to the right side of the chest rather than the left. You would logically expect that the standard anterolateral pad positions would be ineffective for these patients, since the left-sided apical pad would be pointing current at empty space rather than cardiac tissue. One proposed approach is to mirror the placement: put the apical pad on the right side and the sternal pad on the left.⁷

However, a published case report documented successful defibrillation of a dextrocardia patient using the conventional, non-mirrored anterolateral paddle positions, which suggests that exact positioning may be less critical than commonly assumed.⁸ The likely explanation is that current still passes through enough cardiac tissue in the standard configuration to terminate fibrillation, even when the heart is flipped. This is reassuring for emergency situations: if you don’t know about a patient’s dextrocardia (and you almost certainly won’t), standard placement still has a reasonable chance of working. That said, if the first shock fails and you do know or suspect dextrocardia, mirroring the pads is a sensible next step.

Anterolateral Versus Anteroposterior

Anterolateral is the default placement taught in most courses, but it’s not the only option. Current American Heart Association guidelines state that four different pad configurations, including anterolateral and anteroposterior, have equivalent shock success rates for terminating both atrial and ventricular arrhythmias.⁹ Shock success in this context means stopping fibrillation for at least five seconds, which is the immediate electrical goal.¹⁰

But shock success and patient survival aren’t the same thing. A large observational study of out-of-hospital cardiac arrests found that patients with initial anteroposterior pad placement had roughly 2.6 times the adjusted odds of achieving return of spontaneous circulation at any point compared to those with anterolateral placement. When it came to longer-term outcomes like surviving to hospital discharge, the anteroposterior group trended better but the differences didn’t reach statistical significance.¹¹ This is an observational finding, not a randomized trial, so it’s possible that paramedics who chose anteroposterior placement were making that choice in patients they assessed differently. Still, it has sparked genuine interest in whether anteroposterior positioning should be considered more routinely.

Why might anteroposterior work better for restoring circulation? The back pad sits directly behind the heart, creating a more direct front-to-back current path through the left ventricle. In anterolateral placement, the current path runs more diagonally and may pass through less ventricular tissue. Neither configuration is wrong, and in a bystander scenario with a public-access AED, anterolateral remains the standard because it’s simpler for untrained rescuers: the patient stays on their back and both pads go on the front.

Changing the Vector When Shocks Keep Failing

When ventricular fibrillation persists after multiple standard shocks, one of the first things paramedics and emergency physicians consider is changing the pad position to alter the direction of current flow through the heart. A landmark randomized trial published in the New England Journal of Medicine tested two alternatives against standard repeated shocks for refractory ventricular fibrillation. One strategy was vector change, where the pads were moved from anterolateral to anteroposterior position. The other was dual sequential external defibrillation (DSED), which used two sets of pads in both positions simultaneously, delivering two rapid shocks in sequence. Survival to hospital discharge was roughly twice as high in the vector-change group and about 2.3 times as high in the DSED group compared with standard care.¹²

A follow-up analysis examining the same strategies found that both DSED and vector change reduced the time patients spent in ventricular fibrillation and increased the likelihood of both return of spontaneous circulation and survival to discharge compared with standard repeated shocks.¹³ In the DSED approach, one set of pads is placed in the standard anterolateral position and a second set is placed in the anteroposterior position, so the two electrical vectors cross through the heart from different angles.¹⁴

This has practical implications for how early pad positioning decisions get made. A simulation study found that applying anteroposterior pads after mechanical chest compressions have already been started causes significant interruptions to compressions and takes considerably longer than placing them beforehand. The researchers recommended that if anteroposterior pads might be needed, they should be placed before or at the same time as starting a mechanical compression device, not after.⁹ For a bystander using a public AED, this level of planning isn’t relevant. But for paramedics arriving on scene, thinking ahead about whether dual pads might be needed can save crucial seconds later.

Pediatric Placement Differences

Children’s smaller chest size changes the practical rules. For infants and small children, the two anterolateral pads may be large enough that they overlap or touch each other if placed in the standard adult positions. When that happens, the recommendation is to switch to anteroposterior placement: one pad on the center of the chest and one on the center of the back. Most pediatric AED pads are designed with smaller dimensions to reduce this problem, and many AEDs have a pediatric mode or separate pediatric pads that deliver a lower energy dose. For children roughly 8 years old and older, or weighing more than about 25 kilograms, standard adult pads and the normal anterolateral landmarks generally apply. The key rule is that the two pads should never touch or overlap, since this creates a short circuit where the current travels across the skin surface between pads rather than through the chest.

Common Mistakes and How to Avoid Them

The evidence across multiple studies points to a few recurring errors worth knowing about:

Apical pad too far forward: This is the single most common mistake. People place the left pad on the front of the chest, roughly over the nipple or the area where they imagine the heart to be. It needs to be further toward the side, closer to the armpit line.
Sternal pad too high: Placing the right pad up near the neck or on the collarbone itself, rather than just below the collarbone. The pad should be on the chest wall, not the shoulder.
Both pads too low: In simulation studies with laypersons, placing pads too low was the most frequent error for both positions. The sternal pad ends up over the lower ribs, and the apical pad ends up on the abdomen.
Pads on top of breast tissue: As noted above, this raises impedance and reduces current delivery. Lift or displace the breast and place the pad on the chest wall beneath or lateral to it.
Poor skin contact: A hairy chest, sweat, or medication patches under a pad all reduce contact quality. If time permits, quickly dry the skin and remove any patches before applying pads. Some AED kits include a razor for chest hair.

None of these errors mean you shouldn’t use an AED. An imperfectly placed pad still delivers current through the chest, and a suboptimal shock is vastly better than no shock at all. Cardiac arrest survival drops by roughly 7 to 10 percent with every minute that passes without defibrillation, so speed matters more than precision. Place the pads as well as you can, follow the AED’s voice prompts, and let the device analyze and shock. If the rhythm doesn’t convert, repositioning the pads slightly between shocks is a reasonable step, but never at the cost of delaying compressions or the next shock cycle.