Defibrillator Working Principle


The heart can accomplish the vital task of pumping blood until the heart muscle fibers are coordinated. Defibrillation is a technique to restore the fibers to their normal, coordinated functioning. A defibrillator is used to administer a therapeutic dose of electric energy to the damaged heart. Defibrillators are machines that shock or pulse an electric current into the heart to get it to beat, usually again. They are used to prevent or treat an irregular heartbeat that beats too slowly or too quickly, called arrhythmia. Defibrillators can also restart a suddenly stopped heart.

What is Defibrillator?

A medical device that gives the heart a regulated electric shock to control the heart’s muscular action. Defibrillators can either be external, transvenous or implanted, depending on the device being utilized. Depending on this, fibrillation is divided into two types: atrial fibrillation, which affects the atrial muscles, and ventricular fibrillation, which affects the ventricles.

Purpose of Defibrillator

Defibrillation is used to stop the heart from going into cardiac arrest, which is life-threatening fibrillation. As soon as it is determined that the patient is undergoing a cardiac emergency, has no pulse, and is not responding, it should be carried out.


Brief History Of Defibrillator

The following is the year-wise brief history of the defibrillator.

  1. 1899, The first demonstration: The first use of an early defibrillator model was demonstrated in 1899 by two physiologists from the University of Geneva in Switzerland, Jean-Louis Prevost and Frederic Batelli. They demonstrated how a mild electrical shock might cause dogs to have irregular heartbeats and how a tremendous shock could make them resume their normal rhythm.
  2. 1933, The Hyman Otor: A method for directly injecting medications into the heart to restore its function was devised sometime around 1899. C. Henry Hyman, an electrical engineer, and Dr. Albert Hyman, a cardiologist, collaborated in 1933 to create a different strategy. Their technique required passing an insulated wire through a hollow needle inserted into the chest. The wire struck the heart with an electrical jolt. Their creation was known as the “Hyman Otor.”
  3. 1930: Another electrical engineer, William Kouwenhoven, created the first version of what we now know as an external defibrillator. While attending the Johns Hopkins University School of Engineering, he researched the electrical impulses in the human heart. Later, he created an external device that gave seats that had lost beat a “jump start.”
  4. 1947: The first tests on human patients: Kouwenhoven first tried out his invention on dogs. It took 17 years after its creation before it was tried on a human.
  5. The 1950s, Closed-chest defibrillation: Before the 1950s, the only way to restart a heart with defibrillation was to open the chest and shock the patient’s heart directly. The 1950s saw a change in that. Dr. V. Eskin created and tested a closed-chest defibrillator device that delivered more than 1,000 volts to the surface of the chest during that decade in the USSR (in what is today Kyrgyzstan) (before that, voltages supplied by the defibrillator ranged from 300 to 1,000 volts). Usually, the shocks lasted between 100 and 150 milliseconds.
  6. 1958, “Reanimation Research” and the reversal of death: Some of the most significant advancements in defibrillator technology occurred in the USSR during the 1930s and 1950s.
  7. In the 1950s and 1960s, Portable AEDs were developed: It is possible that the USSR invented the first portable defibrillator in 1959. In the 1960s, in Belfast, Ireland Professor Frank Pantridge created a portable replica for use in the West.
  8. 1980, Implantable AED devices: Although the AED may appear to be a recent invention, it took more than 120 years of research and development to make this incredible gadget.


 Defibrillator Working Principle

While waiting for a defibrillator to be ready for use, you should keep performing CardioPulmonary Resuscitation (CPR). Make sure no one is touching the individual who is about to receive the shock before you deliver it (or their bed). An automated external defibrillator (AED) can assess your heart’s rhythm to determine whether a shock is necessary. An AED charges itself and gives verbal usage instructions.
The following is what a first responder or healthcare professional will do:

  • On your chest, place two defibrillator paddles or sticky pads attached to the device. Below your right shoulder and your left nipple, respectively, are two paddles or pads.
  • The conductive substance is already present in the pads to prevent burning. However, your healthcare provider will need to apply conducting material to your chest before utilizing paddles.
  • Push a button on the machine to provide the shock for sticky pads. Push the button on each handheld paddle at the same time.
    A defibrillator temporarily paralyzes your cardiac muscle so your heart can generate an electrical impulse that initiates a regular beat. Defibrillation essentially resets your heart.

After using a Defibrillator, what happens?

  • For a second time, for two minutes, your first responder or provider will perform CPR. After that, they’ll feel for a pulse and see if your heart rhythm has returned to normal. They will perform further CPR and administer another electrical shock if necessary. They’ll also give you drugs (epinephrine or amiodarone) to attempt and rectify the irregular rhythm if defibrillation didn’t work the first time.
  • Your healthcare provider may need to lower your body temperature to between 32 and 36 degrees Celsius (89.6 to 96.8 degrees Fahrenheit) to protect and support the recovery of your brain function if your blood is pumping, but you are still unresponsive. Your healthcare professional might do cardiac catheterization after your condition is stable.


Types of Defibrillator

There are essentially two types of defibrillators in use:

  • AC Defibrillator:

The earliest and most basic type is an AC defibrillator. The design of an AC defibrillator allows suitable values for internal and exterior defibrillation. In AC defibrillation, electrodes deliver a shock with a 50 Hz a.c frequency to the chest for 0.25 to 1 second. Countershock is a technique that involves giving an electric shock to the heart to resynchronize it. Until the patient reacts to the treatment, defibrillation is continued. A step-up transformer with primary and secondary windings and two switches makes up an AC defibrillator. Switches and fuses supply a.c. to the transformer’s primary winding. The timing circuit is coupled with a button that controls when the patient will get a shock from the defibrillator. The timing circuit comprises a monostable multivibrator and a basic resistive and capacitor network. A foot switch or a push button switch is used to activate it. Along the secondary winding, various tapping options are available. They are attached to the electrodes that shock the patient’s heart with electricity.

Voltage values between 250 V and 750 V are used for AC external defibrillation. The secondary coil should be disconnected from the ground for safety purposes to prevent shock. The voltage applied for internal fibrillation ranges from 60 V to 250 V. For external defibrillation, high currents cause the cardiac muscles to contract uniformly and simultaneously. However, this causes heart muscles to contract violently and causes the skin under electrodes to burn. Additionally, it causes ventricular fibrillation to halt and causes atrial fibrillation.

  • DC Defibrillator:

A DC defibrillator produces a regular heartbeat and no negative effects. Ventricular fibrillation is prevented when a high-energy shock is delivered through a discharging capacitor directly in contact with the patient’s heart or chest. The autotransformer T1 is the main of the high voltage transformer T2 in a DC defibrillator. The output voltage from T2 is rectified using a diode rectifier. It is attached to a high voltage over vacuum switch. The switch is linked to the capacitor’s end at position A. The capacitor charges to a voltage when connected in this manner. The electrode’s handle has a foot switch that shocks the patient. The high voltage switch now switches to position B, causing the capacitor to discharge through electrodes to the heart. An inductor L is inserted into one of the electrodes, which leads to a slow discharge rate from the capacitor. This L produces a counter voltage that lowers the discharge value of the capacitor.

Additional Defibrillator Types

There are additional defibrillator types besides these two. Following is a list of some of them:

AEDs: AEDs (Automated external defibrillators) are portable, life-saving medical devices used to treat persons suffering from sudden cardiac arrest, in which the heart stops beating abruptly and unexpectedly.
AED Working: A portable, battery-powered AED that examines the heart’s rhythm and shocks it to get it back to normal can be carried around easily. The tool is applied to support persons experiencing cardiac arrest. Electrodes are sticky pads with sensors affixed to the chest of a person experiencing cardiac arrest. The electrodes in the person’s AED communicate cardiac rhythm data to a computer. The computer analyses the cardiac rhythm to determine whether an electric shock is required. The electrodes administer the shock if necessary.

ICDs: A tiny battery-operated device known as an implanted cardioverter-defibrillator (ICD) is inserted into the chest to identify and treat abnormal heartbeats (arrhythmias). When necessary, an ICD administers electric shocks to the heart to help it return to a normal rhythm. If you have a heart rhythm disorder (arrhythmia) with a dangerously rapid heartbeat that prevents your heart from pumping enough blood to the rest of your body, such as ventricular tachycardia or ventricular fibrillation, or if you are at high risk for developing one, typically due to a weak heart muscle, you may require an ICD. A pacemaker, an implantable device that can stop dangerously slow heartbeats, differs from an ICD.

ICDs Working: ICDs are placed surgically in the stomach or chest region, where the device may detect arrhythmias. Arrhythmias can stop your heart from beating or prevent blood from flowing from your heart to the rest of your body. To get your cardiac rhythm back to normal, the ICD shocks you. An ICD can provide a high-energy shock to stop irregular or fast heartbeat or a low-energy shock from speeding up or slowing down an abnormal heart rate. The gadget may switch to high-energy shocks for defibrillation if low-energy shocks fail to restore your normal cardiac rhythm. While pacemakers only produce weak electrical shocks, ICDs also deliver electrical shocks. ICDs have a generator attached to cables that monitor your heartbeat and administer an electric shock as necessary. Some ICDs contain wires that are positioned in one or more heart chambers. Others rest on the heart to monitor its beat rather than having wires enter the heart chambers. The ICD can also record the heart’s electrical activity and cardiac rhythms. Your healthcare professional can adjust the device’s programming with the help of the recordings to improve how well it corrects irregular heartbeats. The system is set up to react to the kind of arrhythmia you are most likely to experience.

WCDs: Patients at risk of sudden cardiac death are prescribed a wearable cardioverter defibrillator (WCD or “LifeVest”) (SCD). Clothing, an electrode belt, and a monitor make up the device. The wearable defibrillator is worn below clothing, next to the patient’s skin, instead of some defibrillator devices implanted beneath the skin.

WCDs Working: Sensors on WCDs are skin attached. They are wired to a device that monitors your heartbeat and administers shocks as necessary. The WCD can administer low- and high-energy shocks, like an ICD. The apparatus is a vest you wear underneath your clothes with a belt. The device is adjusted by your provider to fit you. It is set up to recognize a particular heart rhythm.

When an arrhythmia happens, the sensors warn the user. You can turn off the alert to avoid a shock if it is unnecessary. If you do not react, the machine will shock your heart to restore its proper beat. Usually, this takes place within a minute. Throughout an episode, the gadget can administer further shocks. The sensors need to be changed after each episode. Your doctors can receive a record of the activity of your heart from the device.


Components of Defibrillator

The elements used to analyze the rhythm and, if necessary, deliver an electric shock are listed below.

Batteries: Batteries are one of the most crucial components of the AED system and essentially serve as containers for chemical reactions. Lead and nickel-cadmium batteries were first utilized, but they are quickly replacing non-rechargeable lithium batteries, which are smaller and have a longer maintenance-free life (up to five years). Defibrillators must be stored in climate-controlled conditions since excessive temperatures harm the batteries. Additionally, batteries contain highly dangerous and corrosive materials, so they must be disposed of in the proper containers.
Capacitor: High voltage circuits use energy from a capacitor that can store up to 7 kV of electricity to generate the electrical shock that is given to the patient. This technology is capable of delivering 30 to 400 joules of energy.
Electrodes: The defibrillator’s electrodes are what the device uses to administer energy to the patient’s heart and gather data for rhythm analysis. Several kinds of electrodes are available, including self-adhesive disposable electrodes, internal paddles, and hand-held electrodes. Disposable electrodes are typically preferred in emergencies because they hasten shock delivery and enhance the defibrillation method.
Electrical circuit: AEDs are highly advanced, microprocessor-based devices that evaluate the frequency, amplitude, slope, and pattern shape of the surface ECG signal, among other characteristics. It has several filters for loose electrodes, poor contact, QRS signals, radio transmission, and other interferences. The ability to monitor patient movement is built into some devices.
Controls: An AED often has a power button, a screen trained rescuers can use to examine the patient’s cardiac rhythm, and a discharge button. A charge button and an energy select control are also found on defibrillators that can be operated manually. Specific controls for internal paddles or disposable electrodes are available on some defibrillators.



 Safety Measures after Defibrillators are Implanted

1. Mobile gadgets such as cell phones: Talking on the phone is safe but keep them at least 6 inches (15 centimeters) away from your body.
2. Security apparatus: You will get a card stating that you have a defibrillator after surgery. Because the ICD may activate airport security alarms, show your card to airport staff.
3. Magnet: Keep magnets at least 6 inches (15 centimeters) away from the ICD site, as interests may influence them.
4. Wireless chargers and headphones. A magnetic material included in headphones may cause defibrillators to malfunction. Keep wireless chargers and headphones at least 6 inches (15 centimeters) away from your body.


1. An infection around the implant.
2. The potentially fatal condition of heart-related bleeding.
3. Regurgitation, or blood spilling through the heart valve where the ICD lead is inserted.


1. They are used to prevent or treat an irregular heartbeat that is too slow or too rapid, known as an arrhythmia.
2. If a defibrillator is utilized for the right arrhythmia and within 10 minutes of the irregular rhythm beginning, it can save your life.

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