defibrillation

Defibrillation is a medical intervention that delivers a controlled electrical shock to the heart to restore a normal rhythm in life-threatening arrhythmias such as ventricular fibrillation and pulseless ventricular tachycardia. It can be delivered externally with defibrillators or internally via implantable devices such as an implantable cardioverter-defibrillator (ICD). In some hospital settings, synchronized shocks during certain tachyarrhythmias may also be used.

The mechanism of defibrillation involves depolarizing a large portion of the cardiac muscle at once, interrupting chaotic electrical activity and allowing the heart’s natural pacemaker and conduction system to reestablish an organized rhythm. Effectiveness depends on factors including the energy delivered, waveform (biphasic or monophasic), timing, and the underlying heart condition.

External defibrillation is performed with automated external defibrillators (AEDs) or manual defibrillators. AEDs analyze heart rhythm and advise a shock, guiding lay responders through CPR and defibrillation steps. Energy for external biphasic shocks commonly range from 150 to 200 joules, though devices may adjust based on context. Shocks are unsynchronized for cardiac arrest, whereas synchronized shocks are used for certain tachyarrhythmias in a controlled setting to avoid inducing ventricular fibrillation.

Internal defibrillation includes implanted devices such as ICDs, which continuously monitor heart rhythm and automatically deliver shocks when dangerous rhythms are detected. ICDs provide protection for individuals at high risk of sudden cardiac death, and some systems can also deliver pacing or anti-tachycardia therapies.

Training and safety: public access to AEDs, early CPR, and rapid defibrillation improve survival in cardiac arrest. Proper device use requires training, and safety considerations include scene assessment and avoiding shock delivery in unsafe or inappropriate conditions.