Defibrillation waveforms

Improved defibrillator waveforms have been developed and been advocated during the years from [1] multiple pulse sine waveform to [2] simple capacitor discharge waveform to [3] damped sine (RLC) waveform, to [4] monophasic truncated exponential decay waveform, to [5] a pair of truncated exponential waveforms, to [6] paired, biphasic truncated exponential decay waveforms. It is evident that the... 

The inductor is used in a defibrillation circuit to modify the discharge waveform of the device so as to prolong the effective delivery of current to the myocardium. 

Cardioversion or defibrillation is the electrical termination of arrhythmias using field stimulation. Unlike pacing, in which cardiac excitation is initiated in and propagates from a small region of tissue near the electrode, cardioversion must arrest electrical activity by simultaneous stimulation of most of the heart. In practice, this means establishing a critical field across a critical mass of cardiac tissue. This requires a compromise between the electrical response of the tissue and the electrical capabilities of the device. The electrical response of cardiac cells is complex, but stimulation mostly depends on the first-order properties of the membrane [6]. Theoretical and experimental studies have shown that the optimum voltage waveform for stimulation of cardiac tissue is a waveform with a characteristic rise time comparable to the cell membrane time constant [7,8]. 

S. R. Shorofsky, E. Rashba, W. Havel, P. Belk, P. Degroot, C. Swerdlow, and M. R. Gold. Improved defibrillation efficacy with an ascending ramp waveform in humans. Heart Rhythm, 2(4) 388-394,... 

A DC or pulse current polarizes the electrode, and from the electrolytic basic experiment described in Section 2.2 it is also clear that faradaic current flow changes the chemical environment at the electrode surface. Current carrying electrodes are used in such different applications as nerve stimulation, pacemaker catheter stimulation and defibrillation with 50 A passing for some milliseconds. Often a square wave pulse is used as stimulation waveform (e.g., pacemaker), and the necessary overvoltage is of great interest (see Section 9.1). In such applications a clear distinction must be made between tissue nonlinearity (Section 8.4.3) and electrode nonlinearity (this section). Nonlinearity network theory is treated in Section 7.9.3. 

Defibrillators are also made as implanted types, using intracardial catheter electrodes. To reduce energy consumption, new waveforms have been taken into use the exponential truncated waveform. It may be monophasic or biphasic. The idea of the hiphasic waveform is that the second pulse shall cancel the net charge caused by the first pulse and thereby reduce the chance of refibrillation. 

Shepard RK, DeGroot PJ, Pacifico A, Wood MA, Ellenbogen KA. Prospective randomized comparison of 65%/65% versus 42%/42% tilt biphasic waveform on defibrillation thresholds in humans. J Interv Card Electrophysiol 2003 8 221-5. 

Sweeney MO, Natale A, Volosin KJ, Swerdlow CD, Baker JH, Degroot P. Prospective randomized comparison of 50%I50% versus 65%/65% tilt biphasic waveform on defibrillation in humans. Pacing Clin Electrophysiol 2001 24 60-5. 

Zhang Y, Boddicker KA, Davies LR, Jones JL, Kerber RE. Surgical open-chest ventricular defibrillation triphasic waveforms are superior to biphasic waveforms. Pacing Clin Electrophysiol 2004 27 941-8. 

Jung J, Hahn SJ, Heisel A, Buob A, Schubert BD, Siaplaouras S. Defibrillation efficacy and pain perception of two biphasic waveforms for internal cardioversion of atrial fibrillation. J Cardiovasc Electrophysiol 2003 14 837-40. 

Schwartzman D, Callans DJ, Gottlieb CD, Heo J, and Marchlinski FE. Early postoperative rise in defibrillation threshold in patients with nonthoracotomy defibrillation lead systems attenuation with biphasic shock waveforms. J Cardiovasc Electrophysiol 1996 7 483-493. 

In a published clinical trial, the SCOPE waveform was shown to be more efficacious than a leading competitor s defibrillator, (Walsh era/, Am J Cardiol 2004 94 378-380)... 

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