An Automated External Defibrillator (AED) is a portable, sophisticated device used by the public to treat Sudden Cardiac Arrest (SCA). The device uses adhesive electrode pads placed on the chest to analyze the heart’s electrical activity. If the AED detects a life-threatening rhythm, it delivers a controlled electrical impulse to help the heart re-establish an effective pumping rhythm.
The Electrical Problem the AED Addresses
Sudden Cardiac Arrest is fundamentally an electrical malfunction, which is distinct from a heart attack. In SCA, the heart’s electrical system fails, causing the heart muscle to stop beating effectively. The most common electrical chaos the AED targets is Ventricular Fibrillation (VF). During VF, the heart’s lower chambers, the ventricles, do not contract in a coordinated manner. Instead, the muscle fibers twitch rapidly and chaotically. This disorganized electrical activity means the heart cannot pump blood, causing the person to collapse immediately. Another rhythm the AED treats is Pulseless Ventricular Tachycardia (VT), where the heart beats far too quickly for the chambers to fill. These two rhythms are collectively known as the “shockable” rhythms because they can be reset by an electrical shock.
Resetting the System: The Defibrillation Mechanism
The electrical shock delivered by the AED is a carefully measured, high-energy pulse designed to affect every heart muscle cell simultaneously. This process is called depolarization, and its purpose is to create a moment of complete electrical silence. The shock acts like a massive reset button for the heart’s electrical circuitry, rather than “jump-starting” a heart that has flatlined. By depolarizing the entire myocardium at once, the shock terminates the chaotic electrical activity of ventricular fibrillation. This momentary cessation of all electrical signaling creates a brief, temporary period of asystole, or a flatline. This electrical reset allows the heart’s own natural pacemaker, the Sinoatrial (SA) node, the opportunity to regain control. The SA node, located in the upper right chamber of the heart, then attempts to initiate a normal, coordinated electrical impulse. If successful, this restores a functional, rhythmic beat known as a sinus rhythm. Modern AEDs use biphasic waveforms, which alternate the direction of the electrical current during the shock. This advanced technology achieves successful defibrillation with lower energy levels, minimizing potential damage to the heart muscle and surrounding tissue.
Immediate Systemic Reactions Beyond the Heart
The powerful electrical current delivered by the AED travels through all tissues between the electrode pads, causing immediate and visible systemic effects. The most noticeable reaction is the strong, involuntary contraction of the skeletal muscles in the chest and arms, often resulting in a forceful jerking of the torso. This is the body’s natural response to the sudden passage of a high-energy electrical field. The skin beneath the electrode pads may show temporary redness or minor burns due to the heat generated by the electricity overcoming the skin’s natural resistance. However, a significant portion of post-shock redness is often a reaction to the conductive gel on the pads. Since the patient is unconscious during Sudden Cardiac Arrest, they do not feel the pain of the shock itself. Following a successful defibrillation that restores a pulse, a patient may experience a brief period of confusion or disorientation. This temporary state is a combination of the shock’s impact and the brain’s recovery after a period of poor blood flow during the cardiac arrest event.