Defibrillator (AED, ICD): devices for treating life‑threatening heart rhythms

How it works

The basic goal of defibrillation is to depolarize a critical mass of heart muscle nearly simultaneously so the heart's natural pacemaker can regain coordinated control. The device charges an internal capacitor and releases a brief, high‑current pulse through electrodes placed on the chest. Modern systems use waveforms (commonly biphasic) that improve effectiveness and reduce the energy required compared with earlier designs. The delivered pulse is a form of electrical energy tailored to interrupt disordered rhythms without causing prolonged damage.

Types and components

Defibrillators come in several forms and share common components such as a power source, a charging circuit, electrodes (pads or paddles), and control electronics. Major categories include:

• Automated external defibrillators (AEDs) — portable, user‑friendly units with voice prompts and built‑in rhythm analysis so lay rescuers can treat victims quickly.
• Manual defibrillators — used by trained clinicians who interpret the rhythm and select the energy and timing for shocks.
• Implantable cardioverter‑defibrillators (ICDs) — surgically placed devices that continuously monitor the heart and deliver internal shocks when dangerous rhythms are detected.

When and how it is used

Defibrillation is indicated for specific shockable arrhythmias, most notably ventricular fibrillation and pulseless ventricular tachycardia. In emergency care, it is integrated with basic and advanced life support measures: high‑quality cardiopulmonary resuscitation (CPR) maintains some circulation until a shock can be delivered, and post‑shock care supports recovery. For AED use, rescuers follow on‑screen and audible instructions; when using manual devices, clinicians synchronize shocks for certain rhythms or select unsynchronized shocks for fibrillation.

History and significance

Defibrillators evolved through the 20th century as electrical and biomedical engineering advanced. Early devices were large and required expert operation; later innovations made them faster, safer, and widely accessible. Public access to AEDs in airports, schools, and workplaces has become an important public health measure because rapid defibrillation markedly improves survival from sudden cardiac arrest when combined with bystander CPR.

Limitations and safety

Defibrillation does not guarantee restoration of a normal rhythm and is not appropriate for all cardiac arrests (for example, asystole or pulseless electrical activity are generally non‑shockable). Safety precautions include ensuring no one touches the patient during shock delivery and avoiding conductive surfaces. Successful outcomes depend on prompt recognition, rapid access to a defibrillator, effective CPR, and advanced medical care afterward. For further technical or clinical details see authoritative resources at ventricular fibrillation information and equipment guidance at energy and waveform references.