Please remember, if you need assistance or have any questions, call us on 0330 223 6336 or drop us an email at sales@defibworld.org
- Published:12 February 2025
Defibrillation is often portrayed in movies as a dramatic, last-ditch effort to bring someone back to life. A person collapses, a heroic rescuer shouts “Clear!” and a powerful shock jolts their body. Within seconds, their eyes flutter open, and they miraculously return to normal. That’s not how it works.
Defibrillation is a complex, life-saving procedure that resets the heart’s electrical system. While it’s an essential tool in treating sudden cardiac arrest (SCA), the actual process is far more scientific and precise than Hollywood suggests. To truly appreciate the importance of a defibrillator, we need to break down exactly what happens to the body during a defibrillation shock and why it works.
Understanding the Electrical System of the Heart
The human heart isn’t just a pump; it’s a finely tuned electrical machine. At its core, the heart relies on a coordinated electrical impulse to keep it beating in a normal, rhythmic fashion. This impulse originates in the sinoatrial (SA) node, often referred to as the body’s natural pacemaker. From there, electrical signals travel through the heart muscle, triggering contraction and allowing blood to be pumped throughout the body.
However, when sudden cardiac arrest occurs, the electrical system of the heart malfunctions. Instead of coordinated beats, the heart enters ventricular fibrillation (VF), a chaotic, disorganised state where it quivers instead of pumping blood effectively. Without immediate intervention, brain damage and death can occur within minutes. This is where a defibrillator comes in.
- 12 February 2025
What a Defibrillator Actually Does
Contrary to popular belief, a defibrillator does not restart a stopped heart. Instead, it delivers a controlled electrical shock that stuns the heart muscle, stopping the chaotic fibrillation and allowing the natural pacemaker to regain control. Think of it like rebooting a frozen computer by shutting it down momentarily, it has the chance to start back up correctly.
When defibrillation occurs, here’s what happens inside the body:
The Shock is Delivered
- A defibrillator, whether a semi-automatic or fully automatic AED, delivers an electrical current through electrode pads placed on the chest.
- This energy is measured in joules (J), with typical shocks ranging from 150J to 360J, depending on the device and patient needs.
- The electrical current passes through the chest and heart, depolarising a critical mass of heart cells.
The Heart Cells Are “Reset”
- Heart cells, known as myocytes, function through an exchange of sodium, potassium, and calcium ions.
- The shock forces all cardiac cells to depolarise simultaneously, temporarily silencing any erratic electrical activity.
- The goal is to eliminate the abnormal electrical circuits causing ventricular fibrillation or ventricular tachycardia (VT).
The Body’s Natural Pacemaker Takes Over
- Once the heart’s chaotic activity has been stopped, the SA node (natural pacemaker) has a chance to regain control.
- If successful, the heart resumes its normal sinus rhythm, restoring proper circulation.
If the first shock doesn’t work, additional shocks may be needed. Some defibrillators automatically escalate energy levels in subsequent shocks to increase the chances of success.
How the Body Reacts to Defibrillation
Defibrillation is not a gentle process, and the body responds in several ways:
- Muscle Contractions: The jolt of electricity can cause sudden, involuntary muscle spasms, sometimes lifting the patient slightly off the ground. This is due to the rapid depolarisation of nerve and muscle fibres.
- Skin Burns: In rare cases, high-energy shocks can cause mild skin burns where the electrode pads make contact.
- Brief Unconsciousness: If the patient regains a normal rhythm, they may remain disoriented or unconscious for a short period due to the lack of oxygen to the brain before resuscitation.
However, if defibrillation is successful and performed quickly, a patient’s chances of survival increase dramatically, up to 74%, when an AED is used within the first few minutes.
Why Timing is Critical
One of the biggest misconceptions about defibrillation is that it’s an all-powerful fix. The truth is, time is everything.
- Within 1 minute of cardiac arrest, survival chances are over 90%.
- After 5 minutes, survival rates drop to 50%.
- After 10 minutes, survival is unlikely unless CPR and defibrillation are performed.
This is why having publicly accessible defibrillators in places like offices, schools, and sports facilities is absolutely crucial. Every second counts.
When a Defibrillator Won’t Work
Not every person in cardiac arrest can be saved by a defibrillator. It’s important to understand when an AED won’t deliver a shock:
- Asystole (Flatline): If there is no electrical activity in the heart at all, an AED will not advise a shock. Instead, CPR is the only option to circulate blood until professional help arrives.
- Normal Heart Rhythms: If a person collapses but has a pulse or normal heart rhythm, the AED will not deliver a shock, as it only responds to specific life-threatening rhythms.
Defibrillators and the Future of Cardiac Care
Defibrillator technology has advanced significantly over the years. Smart AEDs can now provide real-time CPR feedback, voice instructions, and automatic adjustments in shock delivery. Some models can even transmit heart rhythm data to emergency responders, allowing for better treatment upon arrival. As more businesses, schools, and communities install defibrillators, cardiac arrest survival rates will continue to improve.
Understanding what happens to the body during defibrillation is crucial, not just for medical professionals but for anyone who might need to use a defibrillator in an emergency. These devices don’t restart the heart but rather reset its rhythm, giving it a fighting chance to resume normal function.
The key takeaway? Immediate defibrillation saves lives. Whether in a construction site, office, school, or public space, having access to a defibrillator can mean the difference between life and death.
For more information on defibrillators, including the best models for different environments, visit:
- Defibrillators
- Semi-Automatic Defibrillators
- Fully Automatic Defibrillators
- Defibrillators for Schools
- Defibrillators for Community Use
By staying informed and prepared, you can be the reason someone survives a cardiac emergency.
Category: Cardiac Health Awareness
Information on cardiac arrest, the bystander effect, and related topics.