What are Defibrillators and How do they Work?

Defibrillators are life-saving medical devices that deliver a dose of electric shock to the heart during cardiac arrest. Cardiac arrest occurs when the heart's electrical system malfunctions, causing a disorderly heartbeat called ventricular fibrillation. During ventricular fibrillation, the heart quivers instead of beating effectively, causing blood flow to stop and death within minutes if not treated. Defibrillators are used to restore a normal heart rhythm during ventricular fibrillation through a process called defibrillation.

Types of Defibrillators

There are different types of defibrillators available depending on their intended use and portability. The main types are:

Automatic External Defibrillators (AEDs): AEDs are small, lightweight defibrillators designed for public use. They can be found in many public buildings like airports, sports arenas, etc. AEDs contain spoken instructions to guide bystanders through the defibrillation process without any training. They can determine if defibrillation is needed through built-in computers and electronics.

Implantable Cardioverter Defibrillators (ICDs): ICDs are implantable devices placed surgically below the skin in the chest area. They continuously monitor a person's heartbeat and deliver electric shocks if needed to restore normal rhythm. ICDs are primarily used for people at high risk of irregular heartbeats that could result in cardiac arrest.

Wearable Defibrillators: Also known as life vests, wearable defibrillators are lightweight, wearable devices intended for short-term use by patients awaiting an ICD implantation. They deliver shock therapy through adhesive patches worn on the chest.

Manual Defibrillators: Used in hospitals, ambulances, and other emergency response settings, manual defibrillators require a trained operator to analyze the heart rhythm and administer shocks as needed. They are more versatile than AEDs and can do additional functions like cardiac monitoring.

How Defibrillation Works

When the heart goes into ventricular fibrillation, its electrical activity becomes chaotic. Defibrillation aims to stop this chaotic activity through a controlled electric shock delivered by the defibrillator via adhesive pads or paddles placed on the chest.

Specifically, during defibrillation:

- The defibrillator analyzes the heart's rhythm through sensors on its pads. For shockable rhythms like ventricular fibrillation, it will charge automatically.

- At full charge, it delivers a controlled electric shock measured in joules through the pads and into the heart muscle.

- This electric shock depolarizes a critical mass of the heart muscle simultaneously, terminating the chaotic electrical activity.

- After shock delivery, the heart is given a chance to reestablish its natural pacemaker-driven rhythm on its own.

The shock essentially resets the heart, allowing its natural pacemaking system another chance to regain control of the heartbeat. Most often a single shock is enough, but occasionally multiple shocks may be needed.

Effectiveness of Defibrillation

Studies show that defibrillation is highly effective if administered promptly during ventricular fibrillation. For every minute that passes without defibrillation after cardiac arrest, a victim's chances of survival reduce by up to 10%. Yet with immediate defibrillation, survival rates can exceed 90% for witnessed collapses in public settings.

Even for unmonitored out-of-hospital cardiac arrests, early defibrillation through public-access AED programs has been associated with survival rates as high as 49-75%. Bystander CPR combined with early defibrillation within 3-5 minutes of collapse can produce survivals exceeding 50%.

Common Misconceptions about Defibrillation

While defibrillators are undoubtedly life-saving when used properly, there remain some common misconceptions that do more harm than good:

- Defibrillators are not for all cardiac arrests. They are only effective for shockable rhythms and will not work for rhythms like asystole that require CPR instead. Untrained responders are advised to start CPR and wait for an AED if one is available.

- Defibrillators do not cause harm if not needed. Their safety features prevent shock delivery for non-shockable rhythms. They analyze and will not charge up unnecessarily.

- A defibrillator shock is not painful for the victim, as they will be unconscious during cardiac arrest. The electric shock is a designed part of the lifesaving process.

- Early initiation of CPR and defibrillation maximize chances of survival. Waiting for paramedics or advanced care means losing the critical minutes needed to resuscitate someone in cardiac arrest. Early action saves lives.

Conclusion

In recent decades, widespread placement of defibrillators like AEDs in public areas along with CPR training for large numbers have revolutionized out-of-hospital cardiac resuscitation. Defibrillators can determine a shockable rhythm and deliver a lifesaving shock safely and effectively. With defibrillation and CPR available promptly in the first minutes after cardiac arrest, more lives can now be saved each year from cardiac emergencies previously deemed fatal. Continued education is still needed to address misperceptions that prevent optimal utilization of this technology when needed most urgently.