What is a Defibrillator?


Defibrillation is a procedure used to treat life threatening conditions that affect the rhythm of the heart such as cardiac arrhythmia, ventricular fibrillation and pulseless ventricular tachycardia.

The procedure involves the delivery of an electric shock to the heart which causes depolarisation of the heart muscles and re-establishes normal conduction of the heart’s electrical impulse. The machine used to deliver this therapeutic shock to the heart is called a defibrillator.

The different types of defibrillators used include external defibrillators, transvenous defibrillators and implanted defibrillators.

Defibrillation was first presented by Prevost and Batelli, two physiologists from University of Geneva, Switzerland in 1899. In animal studies, they observed that small electric shocks delivered to the heart could trigger ventricular fibrillation, while the delivery of large electrical charges could reverse the fibrillation.

In 1947, the procedure was used for the first time in a human patient. Claude Beck, Professor of surgery, at Case Western Reserve University treated a 14 year old boy undergoing a surgical procedure for a chest defect and managed to restore a normal sinus rhythm in the boy’s heart.

The early forms of defibrillator delivered a charge of between 300 and 1000 volts to the heart using “paddle” type electrodes. However, the units had major drawbacks such as the need for open-heart surgery, the transformers were large and difficult to transport, and post-mortem examination showed the technique was damaging to the heart muscles. Furthermore, the technique was often unsuccessful in actually reversing ventricular fibrillation.

In the 1950s, an alternative method of delivering an electric shock to the heart was pioneered by V.Eskin and colleague A. Klimov from the USSR. Rather than the paddle electrodes used in open heart surgery, the closed-chest device could apply a charge of over 1000 volts through nodes applied to the outside of the chest cage.

It was in 1959 that Bernard Lown and engineer Barouh Berkovits developed a way of delivering the charge using resistance to create a less strong sinusoidal wave that would last 5 milliseconds using paddle electrodes. The researchers also established the optimal timing regarding when shocks should be delivered, which enabled application of the technique in other cases of arrhythmias such as atrial fibrillation, atrial flutter and one form of tachycardia.

This technique was termed the Lown-Berkovits waveform and it became the standard defibrillation treatment to be used into the late 1980s. Thereafter, the biphasic truncated waveform (BTE) was adopted as an equally effective waveform that required less charge to achieve defibrillation. The unit was also lighter to transport. The BTE waveform in conjunction with automatic transthoracic impedance measurement, forms the basis of the modern defibrillator.

Today’s portable defibrillators were introduced in the early 1960s by Prof. Frank Pantridge in Belfast. Today, these tools form an essential part of the equipment found in an ambulance.

A further development was the implantable cardioverter-defibrillator (or ICD), which was developed at Sinai Hospital in Baltimore by a team of people that included Stephen Heilman, Alois Langer, Jack Lattuca, Morton Mower, Michel Mirowski, and Mir Imran at Sinai Hospital in Baltimore. The device was made by Intec Systems of Pittsburgh.

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