A shocking past: a walk through generations of defibrillation development

Using Nanosecond Shocks for Cardiac Defibrillation

The purpose of this review article is to summarize our current understanding of the efficacy and safety of cardiac defibrillation with nanosecond shocks. Experiments in isolated hearts, using optical mapping of the electrical activity, have demonstrated that nanosecond shocks can defibrillate with lower energies than conventional millisecond shocks. Single defibrillation strength nanosecond shocks do not cause obvious damage, but repeated stimulation leads to deterioration of the hearts. In isolated myocytes, nanosecond pulses can also stimulate at lower energies than at longer pulses and cause less electroporation (propidium uptake). The mechanism is likely electroporation of the plasma membrane. Repeated stimulation leads to distorted calcium gradients.

Excitation and injury of adult ventricular cardiomyocytes by nano- to millisecond electric shocks

Intense electric shocks of nanosecond (ns) duration can become a new modality for more efficient but safer defibrillation. We extended strength-duration curves for excitation of cardiomyocytes down to 200 ns, and compared electroporative damage by proportionally more intense shocks of different duration. Enzymatically isolated murine, rabbit, and swine adult ventricular cardiomyocytes (VCM) were loaded with a Ca²⁺ indicator Fluo-4 or Fluo-5N and subjected to shocks of increasing amplitude until a Ca²⁺ transient was optically detected. Then, the voltage was increased 5-fold, and the electric cell injury was quantified by the uptake of a membrane permeability marker dye, propidium iodide. We established that: (1) Stimuli down to 200-ns duration can elicit Ca²⁺ transients, although repeated ns shocks often evoke abnormal responses, (2) Stimulation thresholds expectedly increase as the shock duration decreases, similarly for VCMs from different species, (3) Stimulation threshold energy is minimal for the shortest shocks, (4) VCM orientation with respect to the electric field does not affect the threshold for ns shocks, and (5) The shortest shocks cause the least electroporation injury. These findings support further exploration of ns defibrillation, although abnormal response patterns to repetitive ns stimuli are of a concern and require mechanistic analysis.

Low-energy defibrillation research using a rabbit ventricular model: optimizing the potential gradient distribution using multiple epicardial electrodes

Cardiac potential gradient distribution directly affects defibrillation efficacy, and the electrode configuration that ensures optimal distribution is yet to be determined. In this study, a rabbit ventricular finite element conductor model containing blood perfusion in ventricular cavities was developed. The electric field was solved on the model by using 95% myocardial volume potential gradient higher than 5 V/cm as the successful defibrillation threshold (DFT). Multiple epicardial electrodes (MEE) protocols and a SCAN protocol were used to identify the optimum defibrillation method. Results showed that when using the SCAN protocol, DFT energy reduced to 4.3% that of the control group which had the traditional implantable cardioverter defibrillator current path. Rapidly switching scanning stimuli generated using MEE pairs is a promising low-energy defibrillation method. For multiple electrodes defibrillation, the distribution of the electrode pairs determine the defibrillation efficacy, and the counteraction effect has negative effect on defibrillation. These findings can provide suggestions for clinical applications.

Low-energy defibrillation with multi-electrodes stimulation: A simulation study

The objective of this study is to explore the possible ways to reduce defibrillation energy and further reveal the mechanism of electric defibrillation. A bidomain simulation study was performed on a rabbit whole-ventricle electrophysiological model and the feasibility of the defibrillation strategy with multi-electrodes stimulation was verified. Simulation results indicate that the new approach is effective in low-energy defibrillation.