Defibrillators are electronic devices which send electric shocks to the heart to stop a rapid, irregular heartbeat and restore a normal heart rhythm. Defibrillators can be classified into two main types: internal defibrillators (also known as pacemakers) and automated external defibrillators (AED).
Pacemakers are installed within the chest cavity and connected to the heart via wiring. When an abnormal heartbeat is detected, the device sends a small electric shock to the heart. These devices are sometimes referred to as implantable cardioverter-defibrillators (ICD).
AEDs are small computerized devices which attach to a patient's chest via electrodes. Through the electrodes, the device analyzes the detected heartbeat and delivers a large electric current if the detected rhythm is chaotic or otherwise abnormal. AEDs may feature integral technology such as multi-channel displays, LCD screens, guided instruction, and built-in self-test capabilities.
A pacemaker (left) and a portable AED. (Not to scale.)
Image credit: NPR | Dan Woog