If you swap the AED electrode positions (placing the right clavicle pad under the left armpit and vice versa), the shock will still be delivered, but the vector of the electrical current through the heart will be altered. The standard placement is optimized to direct the current across the ventricles for maximal defibrillation effectiveness. Switching the pads could lead to a less efficient shock, possibly reducing the chances of successful defibrillation. However, in an emergency, it's better to apply the pads and deliver a shock rather than delay treatment.

The standard AED (Automated External Defibrillator) pad placement is:

• One pad under the right clavicle
• One pad on the left side of the chest, mid-axillary line, just below the armpit

This configuration creates an electrical vector across the heart that maximises the chance of successful defibrillation. Pads are labelled and shaped to guide correct placement.

So what happens if AED pads are placed in reverse?

If the pads are swapped, the direction of the electrical current will reverse, but in most adult cases, this doesn't significantly impair the effectiveness of the shock. The current will still pass through the heart, which is the critical factor. Shock effectiveness is primarily about the vector through the myocardium, not which pad is labelled "right" or "left". Modern AEDs are designed to work even if placement is slightly off — they're built for layperson use, often in chaotic situations. Reversed pad placement may matter more in paediatrics or if pads are placed too far off target. If time allows, always correct the placement for optimal results.

What is the "vector of current" in defibrillation?

The vector refers to the path the electrical current takes through the chest, ideally passing through the heart's ventricles — particularly the left ventricle, which is the main pumping chamber. With correct AED pad placement (right upper chest + left side of chest), the vector goes: From upper right chest → diagonally through the heart → to the left lower chest This maximises current delivery through the myocardium, particularly the ventricular mass, which is crucial for terminating arrhythmias like ventricular fibrillation (VF).

What happens if you reverse the pads?

The current vector reverses direction, but the heart is still within that path. So, effectiveness may slightly decrease, but it won't nullify the shock. In most adult bodies, the ventricular mass is central enough that reversed pads still create a usable current path through the heart. Studies and simulation data suggest minimal impact on defibrillation success in emergency situations.

Bottom line: The vector matters, but not so rigidly that reversing pads renders a shock ineffective — it's more about getting current through the heart, not the exact direction of flow.

Real-world AED use. In an emergency:

• Shock quickly. Time is more critical than perfect pad positioning.
• AEDs are intelligently designed to deliver effective shocks even with some variation in pad placement.

But in ideal conditions (like in a hospital or training scenario), correct placement ensures the most efficient current vector and the highest chance of success.

In summary:

Swapping pads likely won’t prevent the AED from working, but correct placement is always preferred to ensure the best chance of defibrillation success.

the electrical vector in the heart is directed from the right shoulder to the left leg. so in a monophasic defibrillator, this matters as the current travels in one direction. but in a biphasic defibrillator, this does not matter much as current travels in both directions but still as the first current passes in the direction of sternal to apex its better to give it in the sternum apex labelled way.