Kinetics of defibrillation shock-induced response: design implications for the optimal defibrillation waveform

Abstract

The time constant of the membrane depends on the field, action potential phase and the shock polarity, but exceeds 1 msec. Therefore, we suggest using a slower shock leading edge, since the membrane cannot follow potentially damaging faster waveforms.

Mechanisms of superiority of ascending ramp waveforms: new insights into mechanisms of shock-induced vulnerability and defibrillation

“…Two factors are responsible for a smaller VEP and ٌ VEP of the DR waveform. First, our previous study (27) implicated that the cardiac tissue cannot follow the very sharp initial rise of an applied shock because of a slower cardiac cell transmembrane time constant. Thus only part of the total energy in a DR waveform is utilized to polarize the membrane.…”

Membrane Time Constant During Internal Defibrillation Strength Shocks in Intact Heart: Effects of Na+ and Ca2+ Channel Blockers

“…Briefly, the heart was continuously paced at a basic cycle length of 300 ms. Truncated exponential monophasic shocks of 8 ms duration and strengths of ±100, ±130, ±160, ±190, and ±200 V were delivered from a 150 μ F capacitor clinical defibrillator (HVS-02, Ventritex, Sunnyvale, CA, USA). The shocks were applied at 25%, 50%, and 75% of the APD 22,23. For each heart, the protocol was first carried out with no drug infusion (control) and then repeated with the addition of either lidocaine (15 μ M, n = 6) or nifedipine (2 μ M, n = 6).…”

“…Theoretical modeling has been commonly used to assess τ 19-21. There are limited reports of assessments of τ in cardiac tissue and whole heart preparations 11,22,23. However, no data on shock-induced changes in τ and in colocalized ΔVm in intact hearts under Na + and Ca 2+ channel blockers are available.…”

Development of Device Therapy for Ventricular Arrhythmias

“…61 Changes in shock waveforms are likely in the future, as kinetic studies suggest the fast leading edge of the truncated exponential waveforms currently delivered by implantable defibrillators are suboptimal with slower rising, more rounded waveforms being more physiological and thus more energy efficient. 56 …”

“…In spite of quantitative and theoretical models 55 being developed to predict the optimal defibrillation waveform, optimisation of the shock waveform parameters such as capacitor size, tilt or duration, polarity, relation between first and second phases and timing of delivery have been largely empirical due to the complexity of the kinetics of the cellular response. 56 Whatever the mechanism for this reduction, the biphasic waveform produces a fundamental physiological response as defibrillation energy reduction by up to 30% is universally observed across many species: calves, 57 isolated rabbit hearts, 58 dogs 59 and humans. 52,60 Furthermore, in contrast to our initial ovine studies, biphasic wave pulses defibrillated sheep hearts even though the threshold was high and post shock recovery was often eventful.…”