Defibrillators are medical devices that deliver an electrical shock to the heart. They correct life-threatening electrical disturbances, saving lives during sudden cardiac arrest. They re-establish a regular heart rhythm, allowing the heart to effectively pump blood throughout the body.
Understanding Cardiac Arrest
Sudden cardiac arrest occurs when the heart stops beating effectively due to an electrical malfunction. This differs from a heart attack, a circulation problem where blood flow to a part of the heart is blocked. In cardiac arrest, the heart’s electrical signals become chaotic, preventing it from pumping blood to the brain and other organs.
The electrical issues leading to cardiac arrest treatable by defibrillators are ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). Ventricular fibrillation involves disorganized electrical activity that causes the heart’s lower chambers to quiver ineffectively instead of contracting. Pulseless ventricular tachycardia is a rapid, but organized, heart rhythm where the heart beats so quickly it cannot adequately fill with blood, resulting in no detectable pulse. Both conditions prevent the heart from pumping blood, leading to immediate loss of consciousness and collapse.
How Defibrillators Deliver Life-Saving Shocks
A defibrillator delivers a controlled electrical current to the heart. This shock momentarily stops all chaotic electrical activity. This allows the heart’s natural pacemaker to regain control and re-establish a normal, organized rhythm.
The shock depolarizes a large portion of the heart muscle, essentially resetting its electrical system. This process interrupts the disorganized electrical circuits that cause conditions like ventricular fibrillation. The electrical pulse alters heart muscle cells, allowing them to reset and resume a normal rhythm. Modern defibrillators often use biphasic waveforms, which can defibrillate with less energy and reduce skin burns compared to older monophasic waveforms.
Types of Defibrillators
Defibrillators are available in various forms, each designed for specific environments and users. Automated External Defibrillators (AEDs) are known for user-friendliness and public accessibility. These devices feature voice prompts and visual instructions, making them usable by individuals without extensive medical training. AEDs are commonly found in public spaces such as airports, schools, and gyms, and are designed to analyze heart rhythms and advise or deliver a shock automatically.
Manual defibrillators are used by trained medical professionals in hospitals and ambulances. Unlike AEDs, these devices require the operator to interpret the heart’s rhythm and manually select the appropriate energy level and timing for the shock. This allows for precise control over the defibrillation process in complex clinical situations.
Implantable Cardioverter-Defibrillators (ICDs) are small devices surgically placed inside the body, typically in the chest. These devices continuously monitor the heart’s rhythm and are programmed to automatically deliver electrical therapy, including shocks, if they detect life-threatening arrhythmias. ICDs are often recommended for individuals at high risk of sudden cardiac arrest, providing ongoing protection by intervening as needed.
Using an Automated External Defibrillator
If someone collapses and is unresponsive, an AED can be used. First, ensure emergency services are called. Turn on the AED and listen carefully to its voice prompts, as the device will guide you through each step.
Expose the person’s bare chest by removing or cutting clothing. If the chest is wet, quickly dry it. If there is excessive chest hair, it may need to be trimmed or shaved to ensure proper pad adhesion. Apply the adhesive pads to the person’s chest as shown in the diagrams, typically one below the right collarbone and the other on the lower left side of the chest. Plug the pad connector cable into the AED if it isn’t already connected.
After the pads are attached, the AED will analyze the heart’s rhythm. During analysis, ensure no one touches the person. If the AED determines a shock is needed, it will instruct you to press the shock button (for semi-automatic AEDs) or deliver the shock automatically (for fully automatic AEDs). Once the shock is delivered, or if no shock is advised, immediately resume cardiopulmonary resuscitation (CPR) for two minutes before the AED re-analyzes the rhythm. Continue following the AED’s prompts until emergency medical personnel arrive.