Optimal Truncation of Defibrillation Pulses

Irnich, Werner

doi:10.1111/j.1540-8159.1995.tb04662.x

Cited by 67 publications

(61 citation statements)

References 11 publications

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“…This is the first time that the validity of the "rheobase condition" that we postulated since 1990 (13) is verified by two sets of differently shaped pulses. "Rheobase condition" means that all portions of a pulse below rheobase do not positively contribute to electrostimulation; in defibrillation they even may have refibrillating qualities (16). We believe this finding to be so important for what we call the "Fundamental Law of Electrostimulation" that this experiment and its result deserve the designation "experimentum crucis" of electro-and magnetostimulation (17).…”

Section: Discussionmentioning

confidence: 99%

Stimulation threshold comparison of time‐varying magnetic pulses with different waveforms

Irnich¹,

Hebrank²

2008

Magnetic Resonance Imaging

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Purpose: To clarify whether sinusoidal pulses possess lower thresholds than rectangular ones at perception threshold, a statement often made that contradicts the theory of stimulation. Materials and Methods:The results of a nerve stimulation study with 65 volunteers and with trapezoidal and sinusoidal gradient pulses were used to apply the combination of the electric field, induced in the tissue of the human body, with the "Fundamental Law of Electrostimulation." This law claims that the waveshape of a pulse is not essential as long as the amplitude of the pulse does not decrease below rheobase (rheobase condition). Results:If the rheobase condition is applied to sinusoidal waveforms and the pulse duration and amplitude is corrected accordingly, both trapezoidal and sinusoidal gradient pulses have identical threshold amplitudes as a function of pulse duration. Conclusion:The "Fundamental Law of Electrostimulation," including the "rheobase condition," proved to be a good basis for describing magnetic field stimulation (magnetostimulation) and that application of it to magnetostimulation is suitable as the basis for describing magnetic field stimulation with various waveforms. For nonrectangular pulses, pulse durations and pulse amplitudes must be corrected according to the "rheobase condition." The exponential Blair Equation is less suited to be applied in magnetostimulation. NATIONAL AND INTERNATIONAL BODIES have discussed possible hazards due to gradient switching in magnetic resonance imaging (MRI) systems and have formulated limiting exposure levels of magnetic fields (1). KeyHowever, there is still interest in understanding the process of stimulation in human subjects exposed to timevarying magnetic fields as they are used in MRI. The need to avoid painful peripheral nerve stimulation (PNS) or, even worse, cardiac stimulation, due to rapidly switched magnetic fields sets an upper limit on the magnetic field gradient strengths that can be employed in fast MRI. It is generally recognized that in whole-body imaging the ygradient coil causes PNS at the lowest rates of gradient change (2,3). A search of the literature of which electric fields can stimulate the heart revealed that the rheobase field strength of the heart for single monophasic stimuli is Ϸ60 V/m (4), and thus, 10 times higher than the lowest assumed threshold for 20 m diameter nerves with 6.2 V/m (5). Due to the fact that cardiac magnetostimulation has not yet been reported in humans and is not expected with the hardware currently available, the following considerations are focused on PNS, the first sensations that appear in whole-body MRI.Since publication of our first article on electrostimulation by time-varying magnetic fields (4), it is mostly accepted in the MRI literature that it is the electric field and not the current density that is responsible for magnetostimulation and that there is a hyperbolic relationship between pulse duration and the electric field characterized by the terms rheobase and chronaxie as they were introduced by Lapicq...

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Section: Discussionmentioning

confidence: 99%

Stimulation threshold comparison of time‐varying magnetic pulses with different waveforms

Irnich¹,

Hebrank²

2008

Magnetic Resonance Imaging

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“…6,12 In one study the time constant was calculated to be Ϸ8 ms. 6 Therefore, pulse 1 tilts of 65% as used in many clinical devices may be too high, 6,12 possibly because of refibrillation caused by lowvoltage shock tails compared with lower tilts. 7,13 However, simple replacement of a phase-1 tilt of 65% by a fixed phase-1 tilt of 42% to 50% may not always be advantageous. On the basis of mathematical models, the optimal phase-1 tilt increases with decreasing time constant for monophasic as well as for biphasic shocks.…”

Section: Discussionmentioning

confidence: 99%

“…3 The phase duration of defibrillation shocks is an important factor influencing the DFT. 6,7 Because the time constant (time that is required to deliver 68% of the stored energy) is directly related to the capacitor following the equation ϭRϫC (Rϭresistance), shocks delivered from smaller capacitors need less time to deliver the same amount of energy than shocks from larger capacitors. We hypothesized that DFTs for 70-F capacitors may have a minimum at other pulse widths and tilts than for larger capacitors and investigated the relation between phase duration of biphasic shocks and the defibrillation energy requirement for 70-F capacitors.…”

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confidence: 99%

Influence of Phase Duration of Biphasic Waveforms on Defibrillation Energy Requirements With a 70-μF Capacitance

et al. 1998

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Background-Phase duration of biphasic shocks may be an important determinant of defibrillation success. The purpose of this study was to investigate the effect of changing phase duration of biphasic pulses delivered by 70-F capacitors on defibrillation energy requirements. This may be clinically relevant for the optimization of implantable cardioverterdefibrillator design and programming. Methods and Results-Defibrillation thresholds (DFTs) were determined for 13 waveforms in 13 pigs by application of a 70-F capacitance and a transvenous/submuscular lead system. In part I, phase-1 duration varied, preserving a phase-1/phase-2 duration ratio of 60%/40%. The phase-1 durations were 1, 2, 3, 4, 5, and 6 ms. The DFT was lowest (22.9Ϯ7 J) for phase 1ϭ3 ms compared with phase 1ϭ1 ms (36.4Ϯ7.5 J), 2 ms (25Ϯ6.5 J), 4 ms (25Ϯ7.6 J), 5 ms (30.7Ϯ7.3 J), or 6 ms (32.9Ϯ8.1 J) (PϽ.001). In part II, phase-1 duration was 3 ms but phase-2 duration varied: 0.7, 1.3, 2, 2.7, 3.3, 4, and 6 ms. Significant DFT minima were found at phase 2ϭ2 ms (22.5Ϯ4.2 J) and phase 2ϭ4 ms (22.5Ϯ4.2 J) compared with phase 2ϭ0.7 ms (31.7Ϯ9.3 J), phase 2ϭ3.3 ms (26.7Ϯ6.1 J), or phase 2ϭ6 ms (28.3Ϯ6.8 J) (PϽ.05). Conclusions-The strength-duration curve of biphasic defibrillation shocks demonstrates a single optimum for phase-1 duration. In contrast, two optima with minimal energy requirements were found for phase-2 duration. Optimization of both phases of low-capacitance biphasic shocks may reduce energy requirements for defibrillation. (Circulation. 1998;97:2073-2078.)

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“…The decaying tail is suggested to be profibrillatory. 22 Therefore, for a given duration of the PIAD waveform, all of the pulse width remains above the threshold voltage (minimum peak voltage to achieve successful cardioversion), maintaining a good success rate.…”

Section: Efficacy Of the Piadmentioning

confidence: 99%

Novel Passive Implantable Atrial Defibrillator Using Transcutaneous Radiofrequency Energy Transmission Successfully Cardioverts Atrial Fibrillation

Manoharan

Evans²,

Kidwai³

et al. 2003

Circulation

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Background-Conventional methods for cardioversion of atrial fibrillation (AF) to sinus rhythm have numerous difficulties. A novel method for cardioversion using the passive implantable atrial defibrillator (PIAD) was tested in acute animal models. This device does not have a battery or a capacitor to store energy and is activated by transferring RF energy across the skin from an external transmitter to the subcutaneously implanted defibrillator. On activation, a novel monophasic shock waveform with 5% tilt is delivered to the heart via 2 intracardiac defibrillation leads. Methods and Results-Cardioversion attempts with the device were assessed in 2 phases: a feasibility and efficacy study and randomized comparison against standard waveforms. Defibrillation leads were placed transvenously into the distal coronary sinus and the right atrial appendage. These were connected to the subcutaneously implanted PIAD. Sustained AF was induced by rapid atrial pacing. The transmitter coil was placed on the skin overlying the defibrillator, and defibrillation synchronized to the R wave was attempted. The method was found to be efficacious at very low voltage and energy, with 100% cardioversion success observed for 10-ms 100-V shocks (mean energy, 1.54Ϯ0.02 J). The PIAD waveform had a higher cardioversion success rate than a truncated, 70% tilt monophasic exponential pulse (100 V, 100% versus 78.0Ϯ7.57%; Pϭ0.001). There were no postshock complications. Conclusions-Considering these animal results, this method is promising for cardioverting AF in symptomatic patients.

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Optimal Truncation of Defibrillation Pulses

Cited by 67 publications

References 11 publications

Stimulation threshold comparison of time‐varying magnetic pulses with different waveforms

Stimulation threshold comparison of time‐varying magnetic pulses with different waveforms

Influence of Phase Duration of Biphasic Waveforms on Defibrillation Energy Requirements With a 70-μF Capacitance

Novel Passive Implantable Atrial Defibrillator Using Transcutaneous Radiofrequency Energy Transmission Successfully Cardioverts Atrial Fibrillation

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