Annals of Emergency Medicine
Volume 37, Issue 1 , Pages 59-61, January 2001

Defibrillation waveforms☆

Department of Medicine, UCLA School of Medicine Department of Emergency Medicine, Harbor-UCLA Medical Center

Article Outline

Abstract 

[Niemann JT. Defibrillation waveforms. Ann Emerg Med. January 2001;37:59-60.]

 

See related article, p. 5 .

In the past decade, transthoracic defibrillation using biphasic waveforms, although not a new concept, has received considerable attention.1 This renewed interest has been driven not only by the continuing dismal rate of survival from out-of-hospital cardiac arrest caused by ventricular fibrillation (VF), but also by what can be interpreted as a mandate for public access defibrillation.2 For the latter to be successful, defibrillators for lay public use need to be small, inexpensive, require little maintenance, and user-friendly. The smaller capacitor required for a biphasic, low-energy waveform helped meet these criteria.3 However, there are probably as many defibrillation waveforms as there are defibrillator manufacturers, and “the guys in the white belts” who populate the display booths at medical meetings will gladly tell you why their waveform is the best.

In simple terms, a defibrillation waveform describes the delivery of energy, or current, as a factor of time and is classified by the type of circuit used for its generation. A monophasic waveform has a single positive phase that returns to zero voltage either gradually (damped sinusoidal waveform) or rapidly (truncated exponential waveform), and current flows in only one direction between defibrillation electrodes. Limited comparisons in animal models and the clinical setting demonstrate that the monophasic dampened sine waveform performed better than the truncated exponential waveform.4, 5

In contrast, although the first phase of a biphasic waveform is positive, the second phase is negative, reflecting a reversal of current flow between anode and cathode. Biphasic waveforms may also be either damped sine or truncated trapezoidal. A biphasic waveform, the shape and characteristics of which vary from manufacturer to manufacturer, is currently the preferred waveform for endocardial defibrillation using implantable cardioverter-defibrillators (ICDs). This preference is because of the lower defibrillation threshold observed with this waveform as well as the smaller capacitor required.

Any defibrillation waveform would theoretically be more effective if the circuit could compensate or adjust for an individual patient. The most important variable in this regard would be transthoracic resistance or impedance. Impedance-compensating waveforms—waveforms that change in duration, voltage, or both—in response to patient impedance, would clearly have an advantage over those with fixed dose-duration characteristics.

When a new defibrillation waveform is developed, it is usually first studied in the electrophysiology laboratory in a select group of patients at risk for malignant ventricular arrhythmias and VF.6, 7, 8, 9 After extremely brief episodes (<30 seconds) of VF that are induced with electrical stimulation, “defibrillation efficacy” is determined. The typical trial usually involves an evaluation of a new waveform and an old waveform. Large trials are designed with the power and precision to evaluate equivalence with respect to first shock success. As such, new technology is always compared with old technology so new technology will usually appear “better” because it is or because the worst of old technology was selected for comparison. For example, comparing an impedance-compensated, low-energy biphasic defibrillation waveform with a commercially available monophasic truncated trapezoidal waveform with less than optimal waveform characteristics has been done and the results were predictable.10

In this issue of Annals , Bain et al11 present their findings when “principle-based” optimized biphasic and monophasic truncated trapezoidal defibrillation waveforms are compared after brief VF. The principle-based concept refers to impedance compensation. No clear difference or benefit of one over the other is obvious. The design of the study precluded an evaluation of whether an escalating energy dose after an unsuccessful first shock is necessary. In summary, Bain et al show that an old waveform can be made better assuming the patient populations were comparable.

Although an important first step in the evaluation process, the electrophysiology laboratory is unfortunately not the real world where emergency physicians practice. Whether new, improved, or modified defibrillation waveforms will affect the outcome of out-of-hospital cardiac arrest caused by prolonged VF remains to be determined. Fixed-dose, low-energy shocks may or may not have limitations when compared with the escalating doses currently recommended. However, even more problematic is the lack of a consistent definition of “successful defibrillation.”12 After 30 seconds or less of electrically induced VF, defibrillation would be expected to result in a sinus tachycardia with return of normal circulation. This definition of successful defibrillation in the electrophysiology laboratory is practical for the laboratory but not the out-of-hospital setting. Until such time as well-designed clinical trials are undertaken, the best defibrillation waveform remains the one that’s available in the shortest amount of time.

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References 

  1. Gurvich NL, Makarychev VA. Defibrillation of the heart with biphasic electric impulsation. Kardiologiia. 1967;7:109–112
  2. Nichol G, Hallstrom AP, Kerber R, et al.  American Heart Association Report on the Second Public Access Defibrillation Conference, April 17-19, 1997. Circulation. 1998;97:1309–1314
  3. Cummins RO, Hazinski MF, Kerber RE, et al.  Low-energy biphasic waveform defibrillation: evidence-based review applied to emergency cardiovascular care guidelines. Circulation. 1998;97:1654–1667
  4. Behr JC, Hartley LL, York DK, et al.  Truncated exponential versus damped sinusoidal waveform shocks for transthoracic defibrillation. Am J Cardiol. 1996;78:1242–1245
  5. Walker RG, Taylor JW, Schmitt PW, et al.  Comparison of a biphasic truncated exponential waveform to two standard monophasic waveforms for external defibrillation [abstract]. J Am Coll Cardiol. 2000;35(Suppl):400A
  6. Bardy GH, Marchlinski FE, Sharma AD, et al.  Multicenter comparison of truncated biphasic shocks and standard damped since wave monophasic shocks for transthoracic ventricular defibrillation. Circulation. 1996;94:2507–2514
  7. Greene HL, DiMarco JP, Kudenchuk PJ, et al.  Comparison of monophasic and biphasic defibrillating pulse waveforms for transthoracic cardioversion. Am J Cardiol. 1995;75:1135–1139
  8. Higgins SL, Herre JL, Epstein AE, et al.  A comparison of monophasic and biphasic shocks for external defibrillation. Prehosp Emerg Care. 2000;4:305–313
  9. Mittal S, Ayati S, Stein KM, et al.  Comparison of a novel rectilinear biphasic waveform with a damped sine wave monophasic waveform for transthoracic ventricular defibrillation. J Am Coll Cardiol. 1999;34:1595–1601
  10. Schneider T, Martens P, Paschen H, et al.  Multicenter, randomized, controlled trial of 150J biphasic shocks compared with 200-360J monophasic shocks in resuscitation of out-of-hospital cardiac arrest victims. Circulation. 2000;102:1780–1787
  11. Bain AC, Swerdlow CD, Love CJ, et al.  Multicenter study of principles-based waveforms for external defibrillation. Ann Emerg Med. 2001;37:5–12
  12. White RD. External defibrillation: The need for uniformity in analyzing and reporting results. Ann Emerg Med. 1998;32:234–236

☆ Reprints not available from the author. Address for correspondence: James T. Niemann, MD, Department of Emergency Medicine, Harbor-UCLA Medical Center, 1000 West Carson Street, Torrance, CA 90509; 310-222-3500, fax 310-782-1763; E-mail jniemann@emedharbor.edu.

PII: S0196-0644(01)02234-X

doi:10.1067/mem.2001.112886

Refers to article:

  • Multicenter study of principles-based waveforms for external defibrillation

    Allison C. Bain, Charles D. Swerdlow, Charles J. Love, Kenneth A. Ellenbogen, Thomas F. Deering, James E. Brewer, Ralph S. Augostini, Patrick J. Tchou
    Annals of Emergency Medicine January 2001 (Vol. 37, Issue 1, Pages 5-12)

Annals of Emergency Medicine
Volume 37, Issue 1 , Pages 59-61, January 2001

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