Threshold of Time-Varying Magnetic Fields Affecting Cardiac Activity

Abstract

The safety issue of time-varying magnetic fields on cardiac activity was experimentally investigated. Strong pulsed magnetic fields were applied to several canine hearts from the outside body with differnt stimulating coils. The effect of the magnetic field was the induction of premature contraction (pc) immediately after the magnetic field. The threshold strength S induducing pc was determined as a function of the duration D when S was the peak electric field at the heart and D was the one-cycle period of the damped sinusoidal pulse. The threshold is expresed by the equation S=Srh/{1-exp(-D/k)} where Srh is the rheobase of 30V/m and k is the time constant of 2ms.