A defibrillator is a medical device that delivers a controlled electrical shock to the heart. It corrects life-threatening abnormal heart rhythms by restoring the heart’s natural, organized electrical activity. This intervention is used in emergency medical care to improve survival during sudden cardiac events.
The Electrical Power of Defibrillation
While defibrillators involve voltage, the more significant measure in defibrillation is the energy delivered, which is quantified in Joules (J). Energy requirements vary by device type and patient. Biphasic defibrillators, which send current in two directions, are now common and typically deliver between 120 and 200 Joules for an initial shock. In contrast, older monophasic defibrillators, which deliver current in one direction, often require a higher energy level, typically 360 Joules.
The voltage itself can fluctuate based on the patient’s impedance, which is the resistance to electrical flow within the body. Despite voltage variations, the total energy delivered to the heart muscle remains the primary factor for successful defibrillation. This substantial energy is necessary to depolarize a large portion of the heart muscle simultaneously, allowing its electrical system to reset. The ability of biphasic waveforms to achieve similar success rates with less energy also contributes to fewer post-shock complications.
How Defibrillators Restore Heart Rhythm
Defibrillators address life-threatening heart rhythms like ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). In these conditions, the heart’s electrical activity becomes chaotic and disorganized, preventing effective blood pumping. This results in sudden cardiac arrest, where the brain and other organs are deprived of oxygen.
The controlled electrical shock momentarily halts all electrical activity in the heart. This temporary cessation allows the heart’s natural pacemaker to regain control and re-establish a normal, organized electrical rhythm. This process “reboots” the heart, allowing it to resume regular pumping. Early defibrillation is important because the chance of survival decreases significantly with each minute of delay.
Different Defibrillator Types and Safety
There are two primary types of external defibrillators: Automated External Defibrillators (AEDs) and manual defibrillators. AEDs are for general public use, providing voice prompts and automatically analyzing the heart’s rhythm to determine if a shock is needed. These devices are commonly found in public spaces and guide the user step-by-step through the rescue process.
Manual defibrillators, by contrast, are operated by trained medical professionals who manually interpret heart rhythms and select the appropriate energy levels for the shock. These devices offer more advanced capabilities and are typically used in clinical settings.
Regardless of type, safety precautions are universal when using a defibrillator. It is important to ensure the patient is on a dry surface and that no one is in contact with the patient during the shock delivery. Removing metal objects from the chest and ensuring direct skin contact for the pads are also important steps. Always call emergency services immediately in any cardiac emergency.