How does an electric shock restart the heart?


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The first act of any doctor in a televised hospital show is the use of a DEFRIBILLATOR – a device that sends an electric shock to a patient’s heart. While it is not explicitly explained how (or even why) the technique is used, it is undoubtedly the most popular way to imitate a doctor. The technique of defibrillation is used in the real world, within permissible limits, and under a restricted range of situations.

Defibrillation is utilized to treat CARDIAC ARRHYTHMIA, a medical condition in which the heartbeat is irregular – either too fast or too slow. A defibrillator is said to send a stipulated dosage of electric current via its paddles to the heart to stabilize the heartbeat. A type of arrhythmia, called VENTRICULAR FIBRILLATION, is one of the special situations where defibrillators are used. Ventricular fibrillation is characterized by an error in the ventricles of the heart, which tremble instead of pumping. This condition can lead to a CARDIAC ARREST if left untreated.


Another medical condition in which defibrillation is used is a VENTRICULAR TACHYCARDIA.  It arises due to an electrical instability observed in the ventricles of the heart, which leads to a faster heartbeat rate. Since the two cases described above are severe, defibrillation is not employed for patients who are conscious and/or have a pulse. Improper usage of defibrillation is no less than a crime and can prove to be extremely fatal to the patient.


How is defibrillation performed?

Most forms of defibrillation require a trained professional to handle it. Since there is a passage of electric current through the machine, the utmost safety of the healthcare staff and the patient must be ensured. To get the paddles (electrodes) into contact with the patient’s body, a CONDUCTIVE gel is employed. An electrically conductive gel is one that lets electricity pass through its molecules. If the paddles of the defibrillator are directly in contact with the patient, the skin poses an electrical resistance. The use of this gel minimizes the resistance and thereby, reduces the chances of having a burn

shock to heart

The PADDLES of a defibrillator are electrodes with an insulating (plastic) handle which is held by a health professional. Newer types of defibrillators use self-adhesive pads that can directly be attached to the patient and do not require to be held. Often, the placement of the paddles is wrongly depicted in movies – there are two placements generally accepted for defibrillation. The type of placement is in conjecture with the type of arrhythmia. One electrode may be placed on the chest and the other on the back, while the other placement is one electrode above the heart and the other below.

Different types of defibrillators have been designed according to the situation the patient is in. There are internal defibrillators, that can be directly placed on the heart during open-heart surgery.  Another type of defibrillator is wearable as an external unit, which examines the heart condition of the patient and supplies an appropriate amount of electric shock.


How does defibrillation work?

Defibrillation is a crucial part of CARDIOPULMONARY RESUSCITATION (CPR), a procedure employed during emergencies to stabilize a patient until further treatments can be administered.

A defibrillator uses voltage in the moderate range of 200 – 1000 volts and the patient receives about 300 joules of electricity which is directed to the heart. The heart has a natural PACEMAKER, which governs the heart rate and prevents arrhythmias. When a person goes into cardiac arrest, the natural pacemaker property of the heart is suppressed and becomes redundant. The electric shock that is delivered to the heart impacts the cardiac muscles and makes it ineffective. As the rest of the heart loses control, the pacemaker gains control of the muscles and regulates the heart rate.

Although the mechanism behind defibrillation is still in its initial stages, it is extensively used in medicine because of the success rate. It may not be able to salvage a heart which is in cardiac arrest, it can be used to prevent someone from going into one. Hospitals have systems like an ELECTROCARDIOGRAM which can predict arrhythmia before it occurs and alerts the hospital staff.

One of the reasons for the mystery behind the principle of a defibrillator is due to its emergency usage, wherein the state of heart is observed for only a few seconds. However, mathematical models are being used to understand the physics behind the supply of electricity used to ‘restart’ a heart.

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