What is Defibrillator?
[[File:Defibrillator Monitor.jpg|thumb|right|An external defibrillator.]] A '''defibrillator''' is a machine that can help when [[ventricular fibrillation]] happens in the [[heart]] of a human. A defibrillator is a life saving device. Fibrillation happens when many different cells in the heart begin to act as pacemaker cells. This means that many thousands of cells tell the heart to beat, all at different times and with no rhythm. This confusion causes the heart to become unable to move blood around the body. This causes [[cardiac arrest]] and death. A defibrillator sends a high [[energy]] pulse from the top-right of the heart to the bottom-middle of the heart. This causes the whole heart to stop all activity. The heart's natural [[pacemaker]] then can try and restart normal beating. Defibrillation does not always work. == Types of defibrillators == === Internal defibrillators === Implantable cardioverter-defibrillators (ICD) are defibrillators that are designed to help patients from inside their body. They are put inside people that are at high-risk of going into [[cardiac arrest]] and monitor a person's heart rate, rhythm, and waveform. By comparing the activity in the different chambers of the heart, an icd can detect [[cardiac arrhythmia]]s and treat them quickly. === External defibrillators === External defibrillators are often used in [[hospital]]s and [[ambulance]]s. They are now also being used outside of medical environments more as [[automated external defibrillator]]s (see below) become safer and cheaper. There are many different types of external defibrillators, and progress in cardiac research has led to big improvements in the underlying technology. ==== Biphasic defibrillation ==== Until the 1990s, external defibrillators relied on monophasic (''one phase'') shock waves. Electrical pulses are quickly sent from one electrode to the other in one direction. Biphasic (''two phases'') defibrillation, however, changes the direction of the pulses. It completes one cycle in approximately 10 [[Millise