Modelling transthoracic defibrillation waveforms

Recent investigations connected with implantable defibrillators yielded new data on heart electrophysiology, resulting in reassessment of existing and advancing of new types of electrical impulses. Different electrical equivalent circuits were proposed for modelling intracardiac and transthoracic defibrillation pulse waveforms, comprising generator, electrode interface and tissue resistances. We attempted modelling of the transmembrane voltage Vm time course, induced by different applied voltage Vs waveforms, taking into account only the shapes and the relative Vs and Vm amplitudes. The excitable cell membrane impedance Zm was modelled with higher resistance and lower capacitance, so that a shunting effect on the generator and tissue resistances was avoided. The result was a very simple equivalent circuit. We proposed criteria for efficient defibrillation pulse waveforms yielding a straightforward approach to model existing and new pulses and to assess their efficiency.