Understanding Defibrillators in Cardiac Emergencies
When someone collapses and appears unresponsive, knowing how to respond can be life-saving. An automated external defibrillator (AED) is a portable electronic device used in sudden cardiac arrest. It delivers a controlled electrical shock to the heart, aiming to restore a normal, effective rhythm. These devices guide rescuers with audio and visual prompts.
How a Defibrillator Functions
A defibrillator does not “start” a heart that has completely ceased electrical activity, often referred to as a “flatline” or asystole. Instead, its function is similar to rebooting a computer. The device works by delivering an electrical current to the heart, causing a brief pause in chaotic electrical activity. This pause allows the heart’s natural pacemaker to potentially reset and resume a regular, effective pumping rhythm.
The purpose of defibrillation is to correct specific life-threatening electrical disturbances in the heart. It targets rhythms like ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT). In these conditions, the heart’s electrical signals are disorganized or excessively rapid, preventing it from effectively pumping blood.
Understanding Heart Rhythms and Defibrillation
The question of whether to use a defibrillator when there is no pulse often arises from a misunderstanding of heart rhythms. A person can have no pulse but still exhibit electrical activity that a defibrillator can address. This includes ventricular fibrillation, where the heart quivers chaotically instead of beating, and pulseless ventricular tachycardia, where the heart beats too fast to effectively pump blood.
These are considered “shockable rhythms” because the electrical shock can interrupt the chaotic activity, allowing the heart to reset. Conversely, conditions like asystole, where there is no electrical activity, or pulseless electrical activity (PEA), where there is organized electrical activity but no mechanical pumping action, are “non-shockable rhythms.” A defibrillator is designed to stop chaotic electrical activity, not to create it from scratch, which is why it will not deliver a shock for these rhythms.
The Role of CPR and AEDs
Cardiopulmonary resuscitation (CPR) is the immediate first step for someone unresponsive, not breathing normally, or without a pulse. CPR involves chest compressions to manually circulate blood and oxygen to the brain and vital organs. The AED works in conjunction with CPR, not as a replacement.
Once attached, the AED analyzes the heart’s electrical rhythm to determine if a shockable rhythm is present. If it detects ventricular fibrillation or pulseless ventricular tachycardia, it will advise and deliver a shock. Continuous, high-quality chest compressions help maintain blood flow until the AED is ready or professional medical help arrives.
When a Defibrillator Won’t Deliver a Shock
Even when a person has no pulse, an AED might indicate “no shock advised.” This occurs if the underlying heart rhythm is asystole or pulseless electrical activity (PEA). In these scenarios, the AED is not malfunctioning; it is correctly identifying that an electrical shock would not be beneficial for these specific rhythms.
When an AED advises “no shock,” the most appropriate action is to continue high-quality CPR without interruption. The AED pads should remain attached, as the heart rhythm can change over time. Ongoing CPR helps to supply oxygenated blood to the brain and heart until emergency medical services arrive, providing the best possible chance for survival.