The search for novel defibrillation methodologies focuses on minimizing deposition of energy to the heart, as this is an indicator for side effects including pain and tissue death. In this work, we investigate the effect of reducing the duration of the applied shocks from low milliseconds to the nanosecond range.
300 ns defibrillation was observed and confirmed to require lower energy than monophasic shocks by almost an order of magnitude with no tissue damage. Additionally, the safety factor, the ratio of median effective doses for electroporative damage and defibrillation, was similar for both durations. To predict how defibrillation shocks of any duration affect the heart, the stimulation strength-duration curve from 200 ns to 10 ms was determined.
To investigate whether high frequency trains of nanosecond shocks (MHz compression) are capable of reducing the electric field and energy of defibrillation, they were compared with a single shock of the same duration. The average voltage for the pulse trains was slightly lower than for long shocks, but the energy almost doubled.
Finally, to understand how shocks even shorter than 300 ns perform, we attempted to determine the defibrillation threshold of 60 ns shocks. Both the estimated electric field and energy were markedly higher than for 300 ns. We also investigated the stimulation threshold of 60 ns shocks followed by a negative phase of varying amplitude and showed that the negative phase reduces the ability of the shocks to stimulate.
In conclusion, this work contributes to the understanding of how nanosecond shocks interact with cardiac tissues. It shows that 300 ns defibrillation is effective and similarly safe as 10 ms shocks, while requiring almost an order of magnitude less energy. The stimulation strength duration curve for cardiac tissue follows the same trend, with lower than expected thresholds for nanosecond shocks. However, low voltage MHz compressed nanosecond shocks are similarly effective as long shocks of the same duration, indicating that the greater efficacy of nanosecond defibrillation is linked to the effects of high voltage. Finally, investigations in 60 ns shocks show defibrillation and stimulation are possible, and that bipolar cancellation occurs in cardiac tissue
