The first defibrillation of a human heart took place in 1947 in an operating theatre in Cleveland University Hospital, America, where an occurrence of ventricular fibrillation was
treated (with the thorax open) by applying a 60 Hz alternating current direct to the heart muscle. External defibrillation was carried out for the first time in the 1950’s using alternating current and electrodes placed on the thorax. This procedure was further improved with the use of direct current defibrillators. This method of applying current proved successful in the succeeding years and led to the development and first industrial
production of defibrillators.
The defibrillation pulse, initially of the monophasic type, was developed in the 1960’s.
This monophasic pulse has been used for external defibrillation in clinical practice for
more than thirty years. The procedure attempts to neutralise fibrillation in the ventricular myocardium by means of a one-dimensional electric shock of a relatively high energy level. The defibrillation pulse corresponds to the discharge curve of a capacitor, in which the flow of current is not controlled.
Even if the resuscitation rate can be described as satisfactory, the side effects, i. e. the irreversible damage to the heart tissue, is considerable. In addition, the monophasic pulse conceals an increased risk of triggering refibrillation. Developed in the 1990’s, the biphasic waveform, by contrast, is two-dimensional, i.e. the pulse consists of a positive and negative current pulse.
In order to defibrillate a heart muscle successfully, the biphasic impulse curve uses less energy than the corresponding monophasic shock. In consequence, damage to the heart occurs less often and is less severe. In principle, biphasic pulses of suitable magnitude are more effective than the monophasic type, given that the risk of refibrillation from the second phase of the shock is reduced. The biphasic pulse, initially used with implanted defibrillators, has also become established over a number of years for external defibrillators.