- AC Defibrillator Definition: An AC defibrillator is defined as the oldest and simplest type of defibrillator that uses a 50 Hz AC shock to resynchronize the heart.
- Countershock: Countershock is the procedure of applying an electric shock to the chest to restart the heart.
- DC Defibrillator Definition: A DC defibrillator is defined as a device that delivers a high-energy shock via a discharging capacitor to normalize the heartbeat, with fewer side effects than AC defibrillators.
- Voltage Levels: AC defibrillators use voltage values ranging from 250 V to 750 V for external defibrillation and 60 V to 250 V for internal defibrillation.
- Safety and Side Effects: DC defibrillators are preferred because they do not cause the side effects associated with AC defibrillators, such as skin burns and atrium fibrillation.
Two types of defibrillators are showing below.
- AC defibrillators
- DC defibrillators
AC Defibrillators
An AC defibrillator is defined as the oldest and simplest type of defibrillator. It is designed to provide appropriate voltage values for both internal and external defibrillation. In AC defibrillation, a 50 Hz AC shock is applied to the chest for 0.25 to 1 second using electrodes. This process of using an electric shock to resynchronize the heart is called Countershock.
Defibrillation continues until the patient responds to the treatment. An AC defibrillator includes a step-up transformer with primary and secondary windings, and two switches. The AC supply is provided through switches and a fuse to the transformer’s primary winding. The timing circuit, connected to a switch, presets the time for delivering the shock.
The timing circuit is formed by a resistive and simple capacitor network or a monostable multivibrator. It is triggered by a foot switch or push button. Various taps along the secondary winding connect to the electrodes, delivering the shock to the patient’s heart. For AC external defibrillation, voltage ranges between 250 V and 750 V.
For safety, the secondary coil should be isolated from the ground to prevent shock. For internal defibrillation, voltages between 60 V and 250 V are used. Large currents ensure uniform heart muscle contraction during external defibrillation. However, this can cause skin burns under the electrodes and violent heart muscle contractions, leading to atrium fibrillation and stopping ventricular fibrillation.
DC Defibrillators
DC defibrillator does not produce side effects and produces normal heartbeat. Ventricular fibrillation is avoided when high-energy shock is passed through discharging capacitor that is exposed to heart or chest of the patient. DC defibrillator consists of auto transformer T1 that acts as primary of the high voltage transformer T2.
A diode rectifier rectifies the output voltage from T2. It is connected to vacuum type-high voltage over switch. At position A, switch is connected to one end of the capacitor. When connected in this position capacitor charges to a voltage. A foot switch present on the handle of the electrode is used to deliver shock to the patient.
Now the high voltage switch changes it position to B that makes the capacitor to discharge to the heart through electrodes. To slow down the discharge from the capacitor an inductor L is placed in one of the electrode lead. This L induces a counter voltage that reduces the capacitor discharge value.
