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Abstract
Cardiac arrest, as a result of ventricular fibrillation or pulseless ventricular tachycardia, is a common phenomenon, and the only treatment available is defibrillation. Currently, defibrillators deliver either a monophasic or biphasic shock, depending on the device used. In 2005, the American Heart Association published new cardiac arrest management guidelines, which included directions about energy selection for both types of defibrillators. These guidelines created a platform to address misconceptions that exist in the practice setting with regard to the use of biphasic defibrillators. The purpose of this literature review was to highlight the issues related to the practical use of biphasic energy, including optimal energy selection and safety.
Ventricular fibrillation (VF) and pulseless ventricular tachycardia (PVT) are the arrest rhythms for 20% to 38% of adult cardiac arrests.1 The only treatment available to terminate these rhythms is defibrillation.2-4 Ventricular fibrillation and PVT involve a state of unorganized electrical activity within the myocardium. The unorganized activity results in a multitude of electrical impulses that are ineffective for generating a coordinated myocardial contraction that will sustain life. The goal of defibrillation is to stun the myocardium, stopping all electrical activity within the myocardium to allow for one of the organized pacemakers to initiate an organized rhythm.5 Physiologically, the objective is to alter the transmembrane potential so that fibrillation is halted, and no new fibrillation is induced, thus allowing the sinus node to dominate electrical activity.6 The return of an organized rhythm, ideally, should result in a myocardial contraction that would in turn create a level of cardiac output sufficient to perfuse the organs and sustain life. Sufficient output takes some time to occur; therefore, the current recommendation is to continue cardiopulmonary resuscitation for 2 minutes after defibrillation.7
The American Heart Association (AHA) published new cardiac arrest management guidelines, which included energy selection for defibrillation for both monophasic and biphasic defibrillators. The publication of these guidelines has created a platform to address misconceptions that exist in the practice setting with regard to the use of biphasic defibrillators. The purpose of this literature review was to highlight the issues related to the practical use of biphasic energy, including optimal energy selection and safety.
Background and History
Defibrillation was pioneered for internal use by Claude Beck in the 1940s and Paul Zoll in 1956 for external defibrillation.8 Originally, defibrillators delivered monophasic energy or energy that flowed from one paddle to the other in a single direction. However, in the last decade, biphasic defibrillators have been developed. These defibrillators deliver energy bidirectionally, toward 1 paddle and then returning. Biphasic waveforms have a higher rate of first-shock efficacy in the context of the termination of atrial fibrillation, VF, and PVT.3,9-12 Biphasic delivery requires less energy than monophasic delivery to achieve conversion of a ventricular dysrhythmia,13 making it theoretically safer.13-15 However, survival to 30 days after hospital discharge does not differ according to the energy form used.3,10,16
Despite the widespread use of biphasic defibrillators, several questions have yet to be resolved with regard to their use. The following literature review highlights the state of knowledge as it relates to the practical use of biphasic defibrillation, identifies outstanding issues, and clarifies the underpinnings of the current AHA guidelines.
State of Technological Innovation
Before beginning this discussion in earnest, it may be helpful to briefly review the terminologies relevant to the procedure of defibrillation. Joules (J) refers to a unit of energy, the desired current. In contrast, voltage refers to the force required to deliver the prescribed joules. Biphasic external defibrillators have the ability to self-adjust, after measuring impedance, to ensure the patient is receiving the desired current. Impedance refers to a measure of opposition to electric current. Patients with high impedance will require more voltage to ensure the delivery of the charge. Conditions that are associated with high impedance include dry skin, chronic obstructive pulmonary disease, a hairy chest, improper pad placement, and ventilatory phase.17
Research has demonstrated that biphasic waveforms improve defibrillation efficacy via 2 distinct mechanisms: the reduction of shock-induced myocardial dysfunction and the reduction of the defibrillation threshold.15,18,19 There are 2 types of biphasic waveforms currently approved for use in external defibrillation: biphasic truncated exponential (BTE), which may be used with a "low-energy protocol" or "high-energy protocol," and rectilinear biphasic (RLB) currently used with a low-energy protocol. The clinical difference between the low and high-energy protocols relates to the amount of energy available to the provider. Low-energy defibrillators have a maximum setting of 200 J. In contrast, high-energy defibrillators have a maximum setting of 360 J. The difference between the waveforms has not yet been proven to be clinically relevant in relation to outcomes such as 30-day mortality.10,20
Several international manufacturers research and develop defibrillators including Zoll, Medtronic, and Philips Medical Systems. The BTE waveform was developed for use in external defibrillators by both Philips Medical Systems (formerly Hewlett Packard and Agilent/Philips) and Medtronic Physio-control (LIFEPAK). Philips defibrillators use the low-energy protocol, whereas the manufacturers of LIFEPAK offer a range of energy that can accommodate both the low- and high-energy protocol. In contrast with other manufacturers, Zoll defibrillators use the RLB waveform and use the low-energy protocol.21
Manufacturers of biphasic defibrillators claim to have a unique technology for the measurement of transthoracic impedance, which ensures that patients are treated with the desired amount of current. Each manufacturer argues the relative advantages of the patented waveforms used in their devices. However, there is no research documenting a superior waveform. Independent research shows equivalent performance between BTE and RLB, across similar energy levels.21,22
Unfortunately for practitioners using these devices, not only do the waveforms differ, but the energy selection protocols recommended by the various manufacturers also differ. Therefore, the practitioner choosing the appropriate energy selection for the termination of VF or PVT requires information about (a) the waveform utilized within the device and (b) whether the manufacturers subscribe to a fixed-joules protocol (eg, 200, 200, 200 J) or an escalating-joules protocol (eg, 200, 300, 360 J). Practitioners need also be aware that a single, standardized approach to defibrillation does not exist.20 Anecdotally, it is the experience of the authors of this article, both of whom are emergency nurse educators, Advanced Cardiac Life Support instructors, and practicing emergency nurses, that users are often unaware of these considerations when using the devices.
The current Advanced Cardiac Life Support guidelines arose from the International Consensus Conference on Cardiopulmonary Resuscitation and Emergency in 2005. In reference to energy selection for biphasic defibrillators, the guidelines provide the following statement:
If a biphasic defibrillator is available, providers should use the dose at which that defibrillator has been shown to be effective for terminating VF [according to the manufacturer's guidelines] (typically a selected energy of 120-200 J). If the provider is unaware of the effective dose range of the device, the rescuer may use a dose of 200 J for the first shock and an equal or higher shock dose for the second and subsequent shocks.10
This statement reflects the ongoing debate in the healthcare literature regarding optimum energy selection for VF and PVT. Lacking comprehensive evidence supporting the efficacy of one approach over another, the AHA guidelines provide a consensus statement rather than a recommendation. Clinicians are referred to the particular manufacturer for directions regarding joule selection. Unfortunately, the manufacturers offer defibrillator-specific recommendations, but always defer to the medical providers for the final decision, therefore leaving a clinician with little concrete direction.
In clinical practice, users are commonly perplexed about the energy selection for biphasic external defibrillators, particularly if the users of the defibrillators practice in more than a single site and the equipment differs between those sites. There is clearly a knowledge deficit in clinical practice with regard to this topic,20 and energy selection for biphasic defibrillators remains a topic of heated debate.23
Biphasic External Defibrillation: Outstanding Issues
Readers may now be left with many questions. Do I need to know the waveform used by a particular defibrillator? Do I need to know whether the defibrillator use a low- or high-energy protocol? Whether the device should be used with a fixed- or escalating-energy protocol? And most importantly, if the guidelines are applied as a "one-size-fits-all" recommendation and 360 J is selected, will harm be done? Questions about efficacy and safety are the focus of the remainder of this article.
With regard to efficacy, researchers continue to advance our knowledge about optimal biphasic energy use. There is currently no research documenting a superior waveform. Independent research shows equivalent performance between BTE and RLB, across similar energy levels.21
When comparing the efficacy of low- and high-energy protocols for the termination of VF and PVT, the evidence is sometimes contradictory. For example, Stiell et al,16 in a randomized controlled trial, studied the outcomes of 221 out-of-hospital cardiac arrests. They randomized patients to receive 1 of 2 defibrillation protocols: 3 stacked, fixed defibrillations with 150 J of biphasic energy (150, 150, 150J) or 3 stacked, escalating defibrillations (200, 300, 360 J). The authors reported no significant difference for the first-shock (150 or 200 J) success rate between the 2 groups. However, if a patient required multiple defibrillations, conversion rates were significantly higher when the escalating shock protocol was used (36.6% vs 24.7%; P = .027; confidence interval, 1.2-24.4).
In contrast, White et al17 studied transthoracic impedance and outcomes when patients in VF or PVT were defibrillated, concluding that nonescalating, biphasic energy at 150 J was as effective as an escalating-energy protocol. Rapid defibrillation, rather than escalation of energy settings, was the key to successful resuscitation. As summarized by the AHA,10 the optimal energy selection for first-shock biphasic defibrillation yielding the highest termination rate for VF and PVT has not yet been established. None of the available evidence has illustrated the superiority of escalating or nonescalating energy for the termination of VF.
Offering another point of view, the International Liaison Committee on Resuscitation and the AHA within the current practice guidelines10 pointed out that given the high efficacy of all biphasic waveforms, other factors may be more strongly implicated in survival. For example, the interval between cardiac arrest and the commencement of active resuscitation efforts likely supersedes the impact of a specific waveform or energy level selected.
With regard to safety, slightly more information is known. Walcott et al19 argued that although defibrillation with a large magnitude shock will result in temporary or permanent damage to the heart, the converse is also true. Shocks of small magnitude will not cause damage but will fail to convert the rhythm and restore circulation. The optimum charge remains unknown. Given the fact that individuals differ in terms of size, shape, and bone density, pad placement varies, and the root cause of dysrrhythmias varies, the authors pointed out that a one-size-fits-all approach to energy selection in defibrillation is unwise. In addition, only a fraction of the energy delivered reaches the myocardial cells, regardless of the charge used.19 For example, Lerman and Deale24 found that only 4% of the current delivered to the chest wall reached the heart, with the remaining energy shunted around the heart to the muscles of the chest wall. Walcott et al19 concluded that the damage threshold is well above any shock size delivered in the clinical setting.
Summary and Conclusions
After a comprehensive review of the healthcare literature, the following conclusions are possible:
1. Biphasic external defibrillators use 1 of 2 wave forms. Each has been proven to be effective for the conversion of VF or PVT to a perfusing rhythm. No waveform has proven to be consistently associated with a higher rate of return of spontaneous circulation or rate of survival to hospital discharge in cardiac arrest.10,20
2. Energy level recommendations vary by manufacturer. The optimal first-shock biphasic waveform yielding the highest termination rate for VF and PVT has yet to be determined,10 and therefore, it is not possible to make a specific recommendation for the first shock, pending the results of additional studies.
3. In the context of the 2005 AHA guidelines, the 200-J default energy level for biphasic defibrillators is not a firm recommendation. Two hundred joules is a consensus, rather than a recommended dose. It was selected as it falls within the reported range of doses effective for initial and subsequent biphasic shocks. Two hundred joules can be provided by every biphasic manual machine available in 2005, regardless of manufacturer. In addition, this consensus resulted after an extensive review of the available research to date. For those facilities with monophasic defibrillators, the recommendation is 360 J for all shocks.
In this article, it has been noted that there is an absence of consistent direction for the use of biphasic external defibrillators in the clinical setting, arising from differing manufacturer recommendations and a dearth of clinical research providing data regarding the optimal doses of energy. Given this situation, concerns about safety and efficacy in the clinical setting have been reviewed. According to published research, with the maximum settings available for energy selection in combination with safe defibrillation technique, there is little chance that patients will be harmed. Several issues require additional study including the safety and efficacy data related to the use of particular waveforms, the most appropriate energy selection for initial and subsequent shocks, and whether escalating joules improve outcomes.10,25
Acknowledgment
The authors thank Dr Alec Ritchie for his review and comments on an earlier draft of this article.
REFERENCES
1. American Heart Association Statistics Committee. Heart disease and stroke statistics, 2007 Update. Circulation. 2007;115:1-105. [Context Link]
2. Gliner BE, Jorgenson DB, Poole JE, et al. Treatment of out-of-hospital cardiac arrest with a low-energy impedance-compensating biphasic waveform automatic external defibrillator. Biomed Instrum Technol. 1998;32:631-644. [Context Link]
3. Schneider T, Martens PR, Paschen H, et al. Multicenter, randomized, controlled trial of 150-J biphasic shocks compared with 200 to 360-J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims. Circulation. 2000;102:1780-1787. [Context Link]
4. Zepf B. Long-term follow-up after rapid defibrillation. Am Fam Physician. 2004;69:1-2. [Context Link]
5. Wesley AK. Improving the hemodynamics of CPR. http://www.emsresponder.com . Accessed August 20, 2007. [Context Link]
6. Ideker RE, Chattipakorn N, Walcott GP, Fast VG. Electrophysiology of defibrillation. In: Santini M, ed. Sudden Death: Non-Pharmacological Treatment. Casalcchio, Italy: Arianna Edtrice; 2003:95-118. [Context Link]
7. American Heart Association. Management of cardiac arrest. Circulation. 2005b;112:IV58-IV66. [Context Link]
8. Furman S. Early history of cardiac pacing and defibrillation. Indian Pacing Electrophysiol J. 2002;2:2-3. [Context Link]
9. Amato-Vealey E, Colonies PA. Demystifying biphasic defibrillation. Nursing. 2005;35(8)6-11. [Context Link]
10. American Heart Association. Electrical therapies: automated external defibrillators, defibrillation, cardioversion, and pacing. Circulation. 2005a;112:35-46. [Context Link]
11. Higgins SL, Herre JM, Epstein AE, et al. A comparison of biphasic and monophasic shocks for external defibrillation. Prehosp Emerg Care. 2000;4:305-313. [Context Link]
12. Van Alem AP, Chapman FW, Lank P, Hart AAM, Koster RW. A prospective, randomized and blinded comparison of first shock success of monophasic and biphasic waveforms in out-of-hospital cardiac arrest. Resuscitation. 2003;58:17-24. [Context Link]
13. 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. [Context Link]
14. Faddy SC, Powell J, Craig JC. Biphasic and monophasic shocks for transthoracic defibrillation: a meta analysis of randomized controlled trials. Resuscitation. 2003;58:9-16. [Context Link]
15. Page RL, Kerber RE, Russell JK, et al. Biphasic versus monophasic shock waveform for conversion of atrial fibrillation. J Am Coll Cardiol. 2002;39:1956-1963. [Context Link]
16. Stiell IG, Walker RG, Nesbitt LP, et al. BIPHASIC trial: a randomized comparison of fixed lower versus escalating higher energy levels for defibrillation in out-of-hospital cardiac arrest. Circulation. 2007;115:1511-1517. [Context Link]
17. White RD, Blackwell TH, Russell JK, Snyder DE, Jorgenson DB. Transthoracic impedance does not affect defibrillation, resuscitation or survival in patients with out-of-hospital cardiac arrest treated with a non-escalating biphasic waveform defibrillator. Resuscitation. 2005;64:63-69. [Context Link]
18. Vikas CJ, Wheelan K. Successful cardioversion of atrial fibrillation using 360-joules biphasic shock. Am J Cardiol. 2002;90:331-332. [Context Link]
19. Walcott GP, Killingsworth CR, Ideker RE. Do clinically relevant transthoracic defibrillation energies cause myocardial damage and dysfunction? Resuscitation. 2003;59:59-70. [Context Link]
20. Jacobs IG, Tibballs J, Morley PT, et al. Energy levels for biphasic defibrillation. EMJA. 2003;179:451. [Context Link]
21. Kim ML, Kim SG, Park DS, et al. Comparison of rectilinear biphasic waveform energy versus truncated exponential biphasic waveform energy for transthoracic cardioversion of atrial fibrillation. Am J Cardiol. 2004;94:1438-1440. [Context Link]
22. Neal S, Ngarmukos T, Lessard D, Rosenthal L. Comparison of the efficacy and safety of two biphasic defibrillator waveforms for the conversions of atrial fibrillation to sinus rhythm. Am J Cardiol. 2003;92:810-814. [Context Link]
23. Adgey AAJ, Spence MS, Walsh SJ. Theory and practice of defibrillation: (2) defibrillation for ventricular fibrillation. Heart. 2005;91:118-125. [Context Link]
24. Lerman BB, Deale OC. Intrathoracic current flow during transthoracic defibrillation in dogs. Circ Res. 1990;67:1405-1419. [Context Link]
25. Gazmuri RJ, Nolan JP, Nadkarni VM, et al. Scientific knowledge gaps and clinical research priorities for cardiopulmonary resuscitation and emergency cardio vascular care identified during the 2005 International Consensus Conference on ECC and CPR science with treatment recommendations. Resuscitation. 2007;75:400-411. [Context Link]