An automated external defibrillator (AED) is a portable medical device designed to assist individuals experiencing sudden cardiac arrest. This condition occurs when the heart unexpectedly stops beating effectively. AEDs are user-friendly, making them accessible for use by the general public in emergency situations. They are often found in public places like airports, schools, and community centers, and can be used by laypeople with minimal training.
The Shockable Rhythms
An AED is programmed to deliver an electrical shock for two life-threatening heart rhythms: ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). In VF, the heart’s ventricles quiver chaotically due to erratic electrical activity, preventing effective blood pumping. Pulseless VT involves a very rapid, ineffective heart rate from the ventricles, meaning the heart cannot pump enough blood to generate a pulse. In both VF and pulseless VT, the heart’s ability to circulate blood is severely compromised or absent. Immediate intervention is necessary as lack of blood flow to the brain and other organs causes rapid cell death.
Why a Shock is Necessary
Defibrillation, the delivery of an electrical shock by an AED, is necessary because ventricular fibrillation and pulseless ventricular tachycardia are primarily electrical problems within the heart. The heart’s electrical activity becomes so disorganized or rapid that it loses its coordinated pumping action. The AED’s shock momentarily halts all electrical activity. This brief pause allows the heart’s natural pacemaker, typically the sinoatrial node, a chance to reset and resume a normal, effective rhythm. This electrical reset is the only way to correct these arrhythmias and restore effective blood circulation.
AED Response to Other Rhythms
When an AED analyzes a heart rhythm and determines it is not ventricular fibrillation or pulseless ventricular tachycardia, it will advise “no shock.” This occurs in rhythms like asystole, a “flat line” with no electrical activity to reset. Similarly, in pulseless electrical activity (PEA), organized electrical activity exists, but the heart muscle does not effectively contract or pump blood. In these non-shockable situations, an electrical shock would be ineffective because there is no activity to reorganize or the present activity does not lead to mechanical pumping.
For these rhythms, effective cardiopulmonary resuscitation (CPR) is the primary intervention. The AED will prompt the rescuer to continue CPR, focusing on chest compressions to maintain blood flow until advanced medical help arrives.