Is the Electric Current from an AED Dangerous? | Wellbeing

Dr. Nguyen Hoang Nguyen | Coordinator - "Fast First Aid - Saving Lives" Project Wellbeing Health Education Organization

1. The Mechanism and Power of the AED

The primary function of an AED is to analyze the heart's electrical activity to assess the specific life-threatening arrhythmias affecting a victim of Sudden Cardiac Arrest (SCA). Based on this real-time analysis, the device advises the rescuer on the next appropriate step, whether it is to continue Cardiopulmonary Resuscitation (CPR) or to deliver a shock. To facilitate this, the AED utilizes two electrode pads placed strategically on the victim's body: one on the upper right side of the chest (below the collarbone) and the other on the lower left rib cage, corresponding to the base and apex of the heart.

The electrical current discharged by an AED is substantial, typically characterized by an intensity of approximately 20 Amperes, a voltage ranging from 750V to 800V, and an energy level of 150 to 200 Joules. This immense energy travels from the right electrode to the left electrode in a fraction of a second (approximately 0.1 seconds).

Most modern devices utilize a Biphasic waveform (current flowing in two directions), which offers significant advantages over the older Monophasic waveform. Biphasic technology requires less energy to be effective, thereby causing less trauma to the victim's heart tissue and consuming less battery power. Clinically, the first-shock success rate for Biphasic AEDs is approximately 90%, compared to just 60% for Monophasic devices.

2. Assessing the Risks for Victims and Rescuers

For the victim, the procedure is considered safe because the current is directed specifically through the heart via the pads for an extremely brief duration, preventing damage to other organs. A minor side effect may occur in victims with excessive chest hair, where the hair can be singed, or the skin slightly burned due to poor contact. Therefore, rescuers should quickly shave the chest area if necessary to ensure proper adhesion and minimize skin damage.

However, this action must be performed rapidly to avoid prolonging the interruption of chest compressions. Minimizing "hands-off" time is crucial; research indicates that pausing chest compressions for just 13 seconds can reduce blood flow to the coronary arteries (which nourish the heart) by up to 40%.

Conversely, for the rescuer, the risk is significant if safety protocols are ignored. While the shock is lifesaving for the victim, the rescuer must remember they are dealing with a current of up to 20 Amperes. To put this in perspective, a current of just 9mA (0.009A) can cause muscle contractions, 80mA can induce ventricular fibrillation, and 3A can cause severe brain damage or loss of consciousness. Therefore, it is absolutely imperative that no one touches the victim while the AED is delivering the shock.

Rescuers must verbally announce "Clear!" and visually verify that the surrounding area is safe before pressing the shock button. Furthermore, contact should also be avoided while the machine is analyzing the heart rhythm, not due to electrical danger, but because movement can interfere with the device's diagnostic accuracy.