Theoretical predictions of the optimal monophasic and biphasic defibrillation waveshapes.

Abstract

The truncated decaying exponential waveshape has become the de facto standard for implantable cardiac defibrillators. However, the optimal defibrillation waveshape with respect to delivered energy remains unknown. To this end, this study has derived the theoretically optimal waveshapes for monophasic and biphasic defibrillation shocks as predicted from a lumped-component model of cardiac tissue in conjunction with the "charge-banking" and "charge-burping" hypotheses of defibrillation. These derivations predict that a truncated ascending exponential waveshape--with a shock time constant, tau s, always equal to the underlying tissue time constant, tau m--minimizes the delivered energy required for defibrillation. These predictions are qualitatively consistent with available experimental data. Thus, to the extent that "charge-banking" and "charge-burping" are assumed to be valid and accurate models of defibrillation, these derivations identify the theoretical "gold standards" of defibrillation waveshapes requiring minimum delivered energy.