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《心肺复苏指南》参考资料（英文版）Part 5：Electrical Therapies

Automated External Defibrillators Defibrillation Cardioversion, and Pacing his chapter presents guidelines for defibrillation with Delays to either start of CPR or defibrillation can reduce automated external defibrillators(AEDs) and manual survival from SCA. In the 1990s some predicted that CPR defibrillators, synchronized cardioversion, and pacing. AEDs could be rendered obsolete by the widespread development of may be used by lay rescuers

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Part 5: Electrical Therapies Automated External Defibrillators Defibrillation Cardioversion, and Pacing his chapter presents guidelines for defibrillation with Delays to either start of CPR or defibrillation can reduce automated external defibrillators(AEDs) and manual survival from SCA. In the 1990s some predicted that CPR defibrillators, synchronized cardioversion, and pacing. AEDs could be rendered obsolete by the widespread development of may be used by lay rescuers and healthcare providers as part community AED programs. Cobb noted, however, that as of basic life support. Manual defibrillation, cardioversion, more Seattle first responders were equipped with AEDs, and pacing are advanced life support therapies. survival rates from SCA unexpectedly fell. He attributed this decline to reduced emphasis on CPR, and there is growing Defibrillation Plus CPR: evidence to support this view. Part 4: Adult Basic Life a Critical Combination Support" summarizes the evidence on the importance of Early defibrillation is critical to survival from sudden cardiac effective chest compressions and minimizing interruptions in arrest(SCA)for several reasons: (I)the most frequent initial providing compressions. rhythm in witnessed SCA is ventricular fibrillation (VF),(2 the treatment for VF is electrical defibrillation, (3)the defibrillation were evaluated during the 2005 Consensus probability of successful defibrillation diminishes rapidly Conference. I The first question concerns whether CPR over time, and (4)VF tends to deteriorate to asystole within should be provided before defibrillation is attempted. The Several studies have documented the effects of time second question concerns the number of shocks to be deli defibrillation and the effects of bystander CPR on survival ered in a sequence before the rescuer resumes CPR. from SCA. For every minute that passes between collapse and Shock First Versus CPR First defibrillation, survival rates from witnessed VF SCA de- When any rescuer witnesses an out-of-hospital arrest and an crease 7% to 10% if no CPR is provided. When bystander AED is immediately available on-site, the rescuer should use CPR is provided, the decrease in survival rates is more the AED as soon as possible. Healthcare providers who treat gradual and averages 3% to 4% per minute from collapse to cardiac arrest in hospitals and other facilities with AEDs defibrillation. 2 CPR can doublel- or triple+ survival from on-site should provide immediate CPR and should use the itnessed sca at most intervals to defibrillation AED/defibrillator as soon as it is available. These recommen- If bystanders provide immediate CPR, many adults in VF dations are designed to support early CPR and early defibrin- can survive with intact neurologic function, especially if lation, particularly when an AED is available within moments defibrillation is performed within about 5 minutes after of the onset of sca SCA.5.6 CPR prolongs VF-9(ie, the window of time during When an out-of-hospital cardiac arrest is not witnessed by h defibrillation can occur) and provides a small amount EMS personnel, they may give about 5 cycles of CPR before f blood flow that may maintain some oxygen and substrate checking the ECG rhythm and attempting defibrillation delivery to the heart and brain. o Basic CPR alone, however, (Class IIb). One cycle of CPR consists of 30 compressions is unlikely to eliminate VF and restore a perfusing rhythm and 2 breaths. When compressions are delivered at a rate of New Recommendations to Integrate CPr and about 100 per minute, 5 cycles of CPR should take roughly 2 AED USe minutes (range: about 1h to 3 minutes ). This recommenda- To treat VF SCA, rescuers must be able to rapidly integrate tion regarding CPR prior to attempted defibrillation is sup- CPR with use of the AED. To give the victim the best chance ported by 2 clinical studies (LOE 25: LOE 36)of adult of survival, 3 actions must occur within the first moments of out-of-hospital VF SCA. In those studies when EMS call-to- a cardiac arrest:(1) activation of the emergency medical arrival intervals were 46 to 55 minutes or le services(EMS)system or emergency medical response sys- received 1/ to 3 minutes of CPR before defibrillation tem,(2)provision of CPR, and (3)operation of an AED showed an increased rate of initial resuscitation. survival to When 2 or more rescuers are present, activation of EMS and hospital discharge, 5.6 and 1-year survival when compared Imitaton of CPR can occur simultaneously. with those who received immediate defibrillation for VF SCA. One randomized study, 2 however, found no benefit to CPR before defibrillation for non-paramedic-witnessed SCA (Circulation. 2005: 112: IV-35-IV-46) EMS system medical directors may consider implement o 2005 American Heart Associa protocol that would allow EMS responders to provide abou This special supplement to Circulation is freely available http://www.circulationaha.org 5 cycles(about 2 minutes)of CPR before defibrillation of patients found by EMS personnel to be in VF, particularly DOI: 10.1161/CIRCULATIONAHA. 105.166554 when the EMs system call-to-response interval is >4 to 5

Part 5: Electrical Therapies Automated External Defibrillators, Defibrillation, Cardioversion, and Pacing This chapter presents guidelines for defibrillation with automated external defibrillators (AEDs) and manual defibrillators, synchronized cardioversion, and pacing. AEDs may be used by lay rescuers and healthcare providers as part of basic life support. Manual defibrillation, cardioversion, and pacing are advanced life support therapies. Defibrillation Plus CPR: A Critical Combination Early defibrillation is critical to survival from sudden cardiac arrest (SCA) for several reasons: (1) the most frequent initial rhythm in witnessed SCA is ventricular fibrillation (VF), (2) the treatment for VF is electrical defibrillation, (3) the probability of successful defibrillation diminishes rapidly over time, and (4) VF tends to deteriorate to asystole within a few minutes.1 Several studies have documented the effects of time to defibrillation and the effects of bystander CPR on survival from SCA. For every minute that passes between collapse and defibrillation, survival rates from witnessed VF SCA decrease 7% to 10% if no CPR is provided.1 When bystander CPR is provided, the decrease in survival rates is more gradual and averages 3% to 4% per minute from collapse to defibrillation.1,2 CPR can double1–3 or triple4 survival from witnessed SCA at most intervals to defibrillation. If bystanders provide immediate CPR, many adults in VF can survive with intact neurologic function, especially if defibrillation is performed within about 5 minutes after SCA.5,6 CPR prolongs VF7–9 (ie, the window of time during which defibrillation can occur) and provides a small amount of blood flow that may maintain some oxygen and substrate delivery to the heart and brain.10 Basic CPR alone, however, is unlikely to eliminate VF and restore a perfusing rhythm. New Recommendations to Integrate CPR and AED Use To treat VF SCA, rescuers must be able to rapidly integrate CPR with use of the AED. To give the victim the best chance of survival, 3 actions must occur within the first moments of a cardiac arrest: (1) activation of the emergency medical services (EMS) system or emergency medical response system, (2) provision of CPR, and (3) operation of an AED. When 2 or more rescuers are present, activation of EMS and initiation of CPR can occur simultaneously. Delays to either start of CPR or defibrillation can reduce survival from SCA. In the 1990s some predicted that CPR could be rendered obsolete by the widespread development of community AED programs. Cobb6 noted, however, that as more Seattle first responders were equipped with AEDs, survival rates from SCA unexpectedly fell. He attributed this decline to reduced emphasis on CPR, and there is growing evidence to support this view. Part 4: “Adult Basic Life Support” summarizes the evidence on the importance of effective chest compressions and minimizing interruptions in providing compressions. Two critical questions about integration of CPR with defibrillation were evaluated during the 2005 Consensus Conference.11 The first question concerns whether CPR should be provided before defibrillation is attempted. The second question concerns the number of shocks to be delivered in a sequence before the rescuer resumes CPR. Shock First Versus CPR First When any rescuer witnesses an out-of-hospital arrest and an AED is immediately available on-site, the rescuer should use the AED as soon as possible. Healthcare providers who treat cardiac arrest in hospitals and other facilities with AEDs on-site should provide immediate CPR and should use the AED/defibrillator as soon as it is available. These recommendations are designed to support early CPR and early defibrillation, particularly when an AED is available within moments of the onset of SCA. When an out-of-hospital cardiac arrest is not witnessed by EMS personnel, they may give about 5 cycles of CPR before checking the ECG rhythm and attempting defibrillation (Class IIb). One cycle of CPR consists of 30 compressions and 2 breaths. When compressions are delivered at a rate of about 100 per minute, 5 cycles of CPR should take roughly 2 minutes (range: about 11⁄2 to 3 minutes). This recommendation regarding CPR prior to attempted defibrillation is supported by 2 clinical studies (LOE 25; LOE 36) of adult out-of-hospital VF SCA. In those studies when EMS call-toarrival intervals were 46 to 55 minutes or longer, victims who received 11⁄2 to 3 minutes of CPR before defibrillation showed an increased rate of initial resuscitation, survival to hospital discharge,5,6 and 1-year survival5 when compared with those who received immediate defibrillation for VF SCA. One randomized study,12 however, found no benefit to CPR before defibrillation for non–paramedic-witnessed SCA. EMS system medical directors may consider implementing a protocol that would allow EMS responders to provide about 5 cycles (about 2 minutes) of CPR before defibrillation of patients found by EMS personnel to be in VF, particularly when the EMS system call-to-response interval is 4 to 5 (Circulation. 2005;112:IV-35-IV-46.) © 2005 American Heart Association. This special supplement to Circulation is freely available at http://www.circulationaha.org DOI: 10.1161/CIRCULATIONAHA.105.166554 IV-35

Circulation December 13. 2005 minutes. There is insufficient evidence to support or refute AEDs should give an initial shock of 360 J; if VF persists CPR before defibrillation for in-hospital cardiac arrest after the first shock, second and subsequent shocks of 360J hould be given. This single dose for monophasic shocks is I-Shock Protocol Versus 3-Shock Sequence At the time of the 2005 Consensus Conference, no published designed to simplify instructions to rescuers but is not a human or animal studies were found that compared a I-shock mandate to recall monophasic AEDs for reprogramming. If protocol with a 3-stacked shock protocol for treatment of VF the monophasic AED being used is programmed to deliver a cardiac arrest. In animal studies, however, frequent or long interruptions in precordial chest compressions for rhythm One study compared the effectiveness of 175 J versus 320 J monophasic waveform shocks for out-of-hospital VF cardiac analysis 3or rescue breathing 4 I5 were associated with post- arrest. 2s Approximately 61% of patients who received shocks resuscitation myocardial dysfunction and reduced survival rates. Secondary analyses of 2 randomized trials 6, 17 showed with either 175 J or 320 J monophasic damped sine waveform were defibrillated with the first shock, which was delivered an hat interruption in chest compressions is associated with a decreased probability of conversion of vF to another rhythm average of 10.6 minutes after the call to EMs. There was ne In 2 recent clinical observational studies (loe 4) of out-of- significant difference in the percentage of patients who devel- oped advanced atrioventricular (Av) block after I shock. AV hospitals and in-hospitall9 CPR by healthcare providers, block was more likely to develop after 2 or 3 shocks of 320 chest compressions were performed only 51%18 to 76% of than after 2 or 3 shocks of 175 J, but the block was transient and total CPr time In 2005 the rhythm analysis for a 3-shock sequence did not affect survival to hospital discharge. 28 Healthcare providers must practice efficient coordination performed by commercially available AEDs resulted in de- between CPR and defibrillation. When VF is present for more and delivery of the first post-shock compression. 13 This delay than a few minutes, the myocardium is depleted of oxygen and metabolic substrates. a brief period of chest compres- is difficult to justify in light of the first-shock effi sions can deliver oxygen and energy substrates, increasing the >90% reported by current biphasic defibrillators. 20-25 If I likelihood that a perfusing rhythm will return after defibrin- shock fails to eliminate VF, the incremental benefit of another lation (elimination of VF).29 Analyses of VF waveform shock is low, and resumption of CPR is likely to confer a characteristics predictive of shock success have documented greater value than another shock. This fact, combined with that the shorter the time between a chest compression and the data from animal studies documenting harmful effects delivery of a shock, the more likely the shock will be from interruptions to chest compressions, suggests that a successful. 29,30 Reduction in the interval from compression to I-shock scenario plus immediate CPR is reasonable shock delivery by even a few seconds can increase the When VF/pulseless ventricular tachycardia(VT)is present probability of shock success. 16 the rescuer should deliver i shock and should then immedi- The rescuer providing chest compressions should minimize ately resume CPR, beginning with chest compressions( Class interruptions in chest compressions for rhythm analysis and Ila). The rescuer should not delay resump of chest shock delivery and should be prepared to resume CPR, compressions to recheck the rhythm or pulse. After 5 cycles beginning with chest compressions, as soon as a shock is (about 2 minutes) of CPR, the AEd should then analyze the delivered. When 2 rescuers are present, the rescuer operating cardiac rhythm and deliver another shock if indicated(Class the AEd should be prepared to deliver a shock as soon as th IIb). If a nonshockable rhythm is detected, the AED shoul compressor removes his or her hands from the victims chest instruct the rescuer to resume CPR immediately, beginning and all rescuers are"clear" of contact with the victim. The with chest compressions(Class Ib). Concern that chest lone rescuer should practice coordination of CPR with effi- oppressions might provoke recurrent VF in the presence of cient AED operation a post-shock organized rhythm does not appear to be warranted Defibrillation Waveforms and Energy Levels AED voice prompts should not instruct the lay user to Defibrillation involves delivery of current through the chest reassess the patient at any time. AED manufacturers should and to the heart to depolarize myocardial cells and eliminate seek innovative methods to decrease the amount of time chest VF. The energy settings for defibrillators are designed to oppressions are withheld for AED operation. Training provide the lowest effective energy needed to terminate VF. materials for lay rescuers should emphasize the importance of Because defibrillation is an electrophysiologic event that continued CPR until basic or advanced life support personnel occurs in 300 to 500 milliseconds after shock delivery, the take over CPR or the victim begins to move term defibrillation(shock success) is typically defined as First-shock efficacy for monophasic shocks is lower than termination of VF for at least 5 seconds following the first-shock efficacy for biphasic shocks 17.26. 27 Although the shock, 31.32 VF frequently recurs after successful shocks, but optimal energy level for defibrillation using any of the this recurrence should not be equated with shock failure. 17.25 phasic or biphasic waveforms has not been determined, the typical definition of defibrillation a recommendation for higher initial energy when using a should not be confused with resuscitation outcomes such as monophasic waveform was weighed by expert consensus restoration of a perfusing rhythm, survival to hospital with consideration of the potential negative effects of a high sion, or survival to hospital discharge. 31.33 Although first-shock energy versus the negative effects of prolonged tation outcomes including survival may be affected by VF. The consensus was that rescuers using monophasic variables in addition to shock delivery, defibrillation pro-

minutes. There is insufficient evidence to support or refute CPR before defibrillation for in-hospital cardiac arrest. 1-Shock Protocol Versus 3-Shock Sequence At the time of the 2005 Consensus Conference, no published human or animal studies were found that compared a 1-shock protocol with a 3-stacked shock protocol for treatment of VF cardiac arrest. In animal studies, however, frequent or long interruptions in precordial chest compressions for rhythm analysis13 or rescue breathing14,15 were associated with postresuscitation myocardial dysfunction and reduced survival rates. Secondary analyses of 2 randomized trials16,17 showed that interruption in chest compressions is associated with a decreased probability of conversion of VF to another rhythm. In 2 recent clinical observational studies (LOE 4) of out-ofhospital18 and in-hospital19 CPR by healthcare providers, chest compressions were performed only 51%18 to 76%19 of total CPR time. In 2005 the rhythm analysis for a 3-shock sequence performed by commercially available AEDs resulted in delays of up to 37 seconds between delivery of the first shock and delivery of the first post-shock compression.13 This delay is difficult to justify in light of the first-shock efficacy of 90% reported by current biphasic defibrillators.20–25 If 1 shock fails to eliminate VF, the incremental benefit of another shock is low, and resumption of CPR is likely to confer a greater value than another shock. This fact, combined with the data from animal studies documenting harmful effects from interruptions to chest compressions, suggests that a 1-shock scenario plus immediate CPR is reasonable. When VF/pulseless ventricular tachycardia (VT) is present, the rescuer should deliver 1 shock and should then immediately resume CPR, beginning with chest compressions (Class IIa). The rescuer should not delay resumption of chest compressions to recheck the rhythm or pulse. After 5 cycles (about 2 minutes) of CPR, the AED should then analyze the cardiac rhythm and deliver another shock if indicated (Class IIb). If a nonshockable rhythm is detected, the AED should instruct the rescuer to resume CPR immediately, beginning with chest compressions (Class IIb). Concern that chest compressions might provoke recurrent VF in the presence of a post-shock organized rhythm does not appear to be warranted.25 AED voice prompts should not instruct the lay user to reassess the patient at any time. AED manufacturers should seek innovative methods to decrease the amount of time chest compressions are withheld for AED operation. Training materials for lay rescuers should emphasize the importance of continued CPR until basic or advanced life support personnel take over CPR or the victim begins to move. First-shock efficacy for monophasic shocks is lower than first-shock efficacy for biphasic shocks.17,26,27 Although the optimal energy level for defibrillation using any of the monophasic or biphasic waveforms has not been determined, a recommendation for higher initial energy when using a monophasic waveform was weighed by expert consensus with consideration of the potential negative effects of a high first-shock energy versus the negative effects of prolonged VF. The consensus was that rescuers using monophasic AEDs should give an initial shock of 360 J; if VF persists after the first shock, second and subsequent shocks of 360 J should be given. This single dose for monophasic shocks is designed to simplify instructions to rescuers but is not a mandate to recall monophasic AEDs for reprogramming. If the monophasic AED being used is programmed to deliver a different first or subsequent dose, that dose is acceptable. One study compared the effectiveness of 175 J versus 320 J monophasic waveform shocks for out-of-hospital VF cardiac arrest.28 Approximately 61% of patients who received shocks with either 175 J or 320 J monophasic damped sine waveform were defibrillated with the first shock, which was delivered an average of 10.6 minutes after the call to EMS. There was no significant difference in the percentage of patients who developed advanced atrioventricular (AV) block after 1 shock. AV block was more likely to develop after 2 or 3 shocks of 320 J than after 2 or 3 shocks of 175 J, but the block was transient and did not affect survival to hospital discharge.28 Healthcare providers must practice efficient coordination between CPR and defibrillation. When VF is present for more than a few minutes, the myocardium is depleted of oxygen and metabolic substrates. A brief period of chest compressions can deliver oxygen and energy substrates, increasing the likelihood that a perfusing rhythm will return after defibrillation (elimination of VF).29 Analyses of VF waveform characteristics predictive of shock success have documented that the shorter the time between a chest compression and delivery of a shock, the more likely the shock will be successful.29,30 Reduction in the interval from compression to shock delivery by even a few seconds can increase the probability of shock success.16 The rescuer providing chest compressions should minimize interruptions in chest compressions for rhythm analysis and shock delivery and should be prepared to resume CPR, beginning with chest compressions, as soon as a shock is delivered. When 2 rescuers are present, the rescuer operating the AED should be prepared to deliver a shock as soon as the compressor removes his or her hands from the victim’s chest and all rescuers are “clear” of contact with the victim. The lone rescuer should practice coordination of CPR with efficient AED operation. Defibrillation Waveforms and Energy Levels Defibrillation involves delivery of current through the chest and to the heart to depolarize myocardial cells and eliminate VF. The energy settings for defibrillators are designed to provide the lowest effective energy needed to terminate VF. Because defibrillation is an electrophysiologic event that occurs in 300 to 500 milliseconds after shock delivery, the term defibrillation (shock success) is typically defined as termination of VF for at least 5 seconds following the shock.31,32 VF frequently recurs after successful shocks, but this recurrence should not be equated with shock failure.17,25 Shock success using the typical definition of defibrillation should not be confused with resuscitation outcomes such as restoration of a perfusing rhythm, survival to hospital admission, or survival to hospital discharge.31,33 Although resuscitation outcomes including survival may be affected by many variables in addition to shock delivery, defibrillation proIV-36 Circulation December 13, 2005

Part 5: Electrical Therapies IV-37 grams must strive to improve patient survival, not just shock forms, other determinants of survival (eg, interval from collapse to CPR or defibrillation) are likely to supersede the Modern defibrillators are classified according to 2 types of impact of specific biphasic waveforms or energies waveforms: monophasic and biphasic. Monophasic wave- d Fixed and Escalating Energy forms are used in almost all AEDs and manual defibrillators Commercially available biphasic AEDs provide either fixed sold today. Energy levels vary by type of device. No specifi or escalating energy levels waveform (either monophasic or biphasic)is consistently Multiple prospective human clinical studies(LOE 2)2742 associated with a higher rate of return of spontaneou and retrospective,24 26. 38.43.44 studies have failed to identify circulation(ROSC)or rates of survival to hospital discharge an optimal biphasic energy level for first or subsequent after cardiac arrest shocks. Therefore, it is not possible to make a definitive recommendation for the selected energy for the first or Monophasic Waveform Defibrillators subsequent biphasic defibrillation attempt Monophasic waveforms deliver current of one polarity (ie, Biphasic defibrillators use one of two waveforms, and each direction of current flow ). Monophasic waveforms can be waveform has been shown to be effective in terminating VF further categorized by the rate at which the current pulse over a specific dose range. The ideal shock dose for a decreases to zero. The monophasic damped sinusoidal wave- biphasic device is one that falls within the range that has been form(MDS)returns to zero gradually, whereas the monopha- documented to be effective using that specific device. Current sic truncated exponential waveform (MTE) current is research confirms that it is reasonable to use selected energies abruptly returned to baseline(truncated) to zero current flow. of 150 J to 200 J with a biphasic truncated exponent Few monophasic waveform defibrillators are being manu- waveform or 120 J with a rectilinear biphasic waveform for factured but many are still in use. Most of these use MDs the initial shock For second and subsequent biphasic shocks waveforms. As noted above, no specific waveform(either use the same or higher energy( Class Ila). In this context monophasic or biphasic) is consistently associated with a "selected"refers to the energy dose selected by the operator greater incidence of RoSC or survival to hospital discharge (or programmed by the AED manufacturer). With the recti- rates after cardiac arrest than any other specific waveform. linear biphasic waveform de vice. Research indicates, however, that when doses equivalent to or energies usually differ; delivered energy is typically higher in lower than monophasic doses are used, biphasic waveform the usual range of impedance. For example, in a patient with shocks are safe and effective for termination of vF 80 n2 impedance, a selected energy of 120 J will deliver 150J Biphasic waveform Defibrillators None of the available evidence has shown superiority of Researchers have collected data from both out-of-hospi- either nonescalating or escalating energy biphasic waveform tal34-36 and in-hospital studies(electrophysiologic studies and defibrillation for termination of VF. Nonescalating and esca implantable cardioverter-defibrillator [ICD] testing and eval- lating energy biphasic waveform shocks can be used safely uation).37 Overall this research indicates that lower-energy and effectively to terminate short-duration and long-duration biphasic waveform shocks have equivalent or higher success VF(Class lla). The safety and efficacy data related to specific for termination of VF than either damped sinusoidal or biphasic waveforms, the most effective initial shock, and truncated exponential monophasic waveform shocks deliver- whether to use escalating sequences require additional studies ing escalating energy(200 J, 300 J, 360 J)with successive in both the in-hospital and out-of-hospital setting shocks. No direct comparison of the different biphasic wave- forms has been made Automated External Defibrillators The optimal energy for first-shock biphasic wa AEDs are sophisticated, reliable computerized devices that defibrillation yielding the highest termination rate for use voice and visual prompts to guide lay rescuers and health- t been determined. Several randomized (Loe 2) care providers to safely defibrillate VF SCA. 4 36.45 46 In recent observational studies (loe 5)26.38 have shown that defibril clinical trials, 18, 19 modified prototype AEDs recorded informa- lation with biphasic waveforms of relatively low energy tion about frequency and depth of chest compressions during (s200 J)is safe and has equivalent or higher efficacy for CPR. If such devices become commercially available, AEDs termination of VF than monophasic waveform shocks of may one day prompt rescuers to improve CPR performance equivalent or higher energy(Class Ila).32,39-41 Compensation for patient-to-patient differences in imped- Lay Rescuer AED Programs ance may be achieved by changes in duration and voltage of Since 1995 the American Heart Association(AHA)has shocks or by releasing the residual membrane charge(called recommended the development of lay rescuer AED program burping). Whether there is an optimal ratio of first-phase toto improve survival rates from out-of-hospital SCA. second-phase duration and leading-edge amplitude is unclear. These programs are also known as public defibrilla- It is unknown whether a waveform more effective for tion, or PAD, programs. The goal of these programs is immediate outcomes(defibrillation) and short-term outcomes shorten the time from onset of vF until CPR and shock (ROSC, survival to hospital admission) results in better delivery by ensuring that AEDs and trained lay rescuers are long-term outcomes(survival to hospital discharge, survival available in public areas where SCA is likely ur. To for I year). Given the high efficacy of all biphasic wave- maximize the effectiveness of these programs, the AHA has

grams must strive to improve patient survival, not just shock success. Modern defibrillators are classified according to 2 types of waveforms: monophasic and biphasic. Monophasic waveform defibrillators were introduced first, but biphasic waveforms are used in almost all AEDs and manual defibrillators sold today. Energy levels vary by type of device. No specific waveform (either monophasic or biphasic) is consistently associated with a higher rate of return of spontaneous circulation (ROSC) or rates of survival to hospital discharge after cardiac arrest. Monophasic Waveform Defibrillators Monophasic waveforms deliver current of one polarity (ie, direction of current flow). Monophasic waveforms can be further categorized by the rate at which the current pulse decreases to zero. The monophasic damped sinusoidal waveform (MDS) returns to zero gradually, whereas the monophasic truncated exponential waveform (MTE) current is abruptly returned to baseline (truncated) to zero current flow. Few monophasic waveform defibrillators are being manufactured but many are still in use. Most of these use MDS waveforms. As noted above, no specific waveform (either monophasic or biphasic) is consistently associated with a greater incidence of ROSC or survival to hospital discharge rates after cardiac arrest than any other specific waveform. Research indicates, however, that when doses equivalent to or lower than monophasic doses are used, biphasic waveform shocks are safe and effective for termination of VF. Biphasic Waveform Defibrillators Researchers have collected data from both out-of-hospital34–36 and in-hospital studies (electrophysiologic studies and implantable cardioverter-defibrillator [ICD] testing and evaluation).37 Overall this research indicates that lower-energy biphasic waveform shocks have equivalent or higher success for termination of VF than either damped sinusoidal or truncated exponential monophasic waveform shocks delivering escalating energy (200 J, 300 J, 360 J) with successive shocks. No direct comparison of the different biphasic waveforms has been made. The optimal energy for first-shock biphasic waveform defibrillation yielding the highest termination rate for VF has not been determined. Several randomized (LOE 2)17,24,27 and observational studies (LOE 5)26,38 have shown that defibrillation with biphasic waveforms of relatively low energy (200 J) is safe and has equivalent or higher efficacy for termination of VF than monophasic waveform shocks of equivalent or higher energy (Class IIa).32,39–41 Compensation for patient-to-patient differences in impedance may be achieved by changes in duration and voltage of shocks or by releasing the residual membrane charge (called burping). Whether there is an optimal ratio of first-phase to second-phase duration and leading-edge amplitude is unclear. It is unknown whether a waveform more effective for immediate outcomes (defibrillation) and short-term outcomes (ROSC, survival to hospital admission) results in better long-term outcomes (survival to hospital discharge, survival for 1 year). Given the high efficacy of all biphasic waveforms, other determinants of survival (eg, interval from collapse to CPR or defibrillation) are likely to supersede the impact of specific biphasic waveforms or energies. Fixed and Escalating Energy Commercially available biphasic AEDs provide either fixed or escalating energy levels. Multiple prospective human clinical studies (LOE 2)27,42 and retrospective17,24,26,38,43,44 studies have failed to identify an optimal biphasic energy level for first or subsequent shocks. Therefore, it is not possible to make a definitive recommendation for the selected energy for the first or subsequent biphasic defibrillation attempts. Biphasic defibrillators use one of two waveforms, and each waveform has been shown to be effective in terminating VF over a specific dose range. The ideal shock dose for a biphasic device is one that falls within the range that has been documented to be effective using that specific device. Current research confirms that it is reasonable to use selected energies of 150 J to 200 J with a biphasic truncated exponential waveform or 120 J with a rectilinear biphasic waveform for the initial shock. For second and subsequent biphasic shocks, use the same or higher energy (Class IIa). In this context “selected” refers to the energy dose selected by the operator (or programmed by the AED manufacturer). With the rectilinear biphasic waveform device, selected and delivered energies usually differ; delivered energy is typically higher in the usual range of impedance. For example, in a patient with 80 impedance, a selected energy of 120 J will deliver 150 J. None of the available evidence has shown superiority of either nonescalating or escalating energy biphasic waveform defibrillation for termination of VF. Nonescalating and escalating energy biphasic waveform shocks can be used safely and effectively to terminate short-duration and long-duration VF (Class IIa). The safety and efficacy data related to specific biphasic waveforms, the most effective initial shock, and whether to use escalating sequences require additional studies in both the in-hospital and out-of-hospital settings. Automated External Defibrillators AEDs are sophisticated, reliable computerized devices that use voice and visual prompts to guide lay rescuers and healthcare providers to safely defibrillate VF SCA.34,36,45,46 In recent clinical trials,18,19 modified prototype AEDs recorded information about frequency and depth of chest compressions during CPR. If such devices become commercially available, AEDs may one day prompt rescuers to improve CPR performance. Lay Rescuer AED Programs Since 1995 the American Heart Association (AHA) has recommended the development of lay rescuer AED programs to improve survival rates from out-of-hospital SCA.47–49 These programs are also known as public access defibrillation, or PAD, programs. The goal of these programs is to shorten the time from onset of VF until CPR and shock delivery by ensuring that AEDs and trained lay rescuers are available in public areas where SCA is likely to occur. To maximize the effectiveness of these programs, the AHA has Part 5: Electrical Therapies IV-37

IV-38 Circulation December 13, 2005 emphasized the importance of organization, planning, train- AEDs are of no value for arrest not caused by vF/pulseless ing, linking with the EMS system, and establishing a process VT, and they are not effective for treatment of nonshockable of continuous quality improvement. 50,51 rhythms that may develop after termination of VF. Nonper Studies of lay rescuer AED programs in airports52 and fusing rhythms are present in most patients after shock casinos53.54 and first-responder programs with police offi- delivery, 5. 26. 28.44 and CPR is required until a perfusing cers26,3436.44.55-57 have shown a survival rate of 41% to 74% rhythm returns. Therefore, the AEd rescuer should be trained from out-of-hospital witnessed VF SCA when immediate not only to recognize emergencies and use the AED but also bystander CPR is provided and defibrillation occurs within to support ventilation and circulation with CPR as needed. about 3 to 5 minutes of collapse. These high survival rates, The mere presence of an AEd does not ensure that it will however, are not attained in programs that fail to reduce time be used when SCA occurs Even in the NHLBI trial, in which to defibrillation, 58-60 almost 20 000 rescuers were trained to respond to SCA, lay In a large prospective randomized trial (LOE 1)6l funded rescuers attempted resuscitation before EMS arrival for only (NHLBI, and several aeD manufacturers, lay rescuer CPR was used for only 34% of the victims who experience o by the AHA, the National Heart, Lung, and Blood Institute half of the victims of witnessed SCA, and the on-site Al Aed programs in targeted public settings doubled the arrest at locations with AED programs. b These findings number of survivors from out-of-hospital VF SCA when ggest that lay rescuers need frequent practice to optimize compared with programs that provided early EMS call and response to emergencies early CPR. The programs included a planned response, lay ment processes of continuous quality improvement(Class ing elements are recommended for community lay rescuer routine inspections and postevent data(from AED recordings AED programs and responder reports) to evaluate the following 50,51 A planned and practiced response; typically this requires Performance of the emergency response plan, including oversight by a healthcare provider accurate time intervals for key interventions (such as Training of anticipated rescuers in CPR and use of the AED collapse to shock or no shock advisory to initiation of Link with the local EMS system CPR), and patient outcome Process of ongoing quality improvement Responder performance More information is available on the aha website: www AED function, including accuracy of the ECG rhythm Under the topic "Links on this site, analysis Battery status and function Lay rescuer AED programs will have the greatest potentia impact on survival from SCA if the programs are created locations where SCA is likely to occur. In the NHLBI trial, Automated Rhythm Analysis programs were established at sites with a history of at least I AEDs have microprocessors that analyze multiple features of out-of-hospital cardiac arrest every 2 years or where at least the surface ECG signal, including frequency, amplitude, and I out-of-hospital SCA was predicted during the study period some integration of frequency and amplitude, such as slope or (ie, sites having >250 adults over 50 years of age present for wave morphology. Filters check for QRS-like signals, radio >16hd).61 transmission, or 50-or 60-cycle interference as well as loose To be effective, AED programs should be integrated into electrodes and poor electrode contact. Some devices are an overall EMS strategy for treating patients in cardiac arrest. programmed to detect spontaneous movement by the patient CPR and AED use by public safety first responders(tradi or others. Prototype defibrillators were used in 2 recent witnessed cardiac arrest(eg, airports, casinos, sports facili- providea, mpt resaa9al tional and nontraditional) are recommended to increase sur- clinical trials evaluating quality of CPr in the out-of-hospital vival rates for SCA(Class I). AED programs in public and hospital settings, and they hold promise for future AEDs locations where there is a relatively high likelihood of that may the quality of CF ties)are recommended( Class I). Because the improvement in AEDs have been tested extensively, both in vitro against survival rates in aED programs is affected by the time to libraries of recorded cardiac rhythms and clinically in many CPR and to defibrillation, sites that deploy AEDs should field trials in adultsb3, 6 and children. os. 6 They are extremely establish a response plan, train likely responders in CPR and accurate in rhythm analysis. Although AEDs are not designed AED use, maintain equipment, and coordinate with local to deliver synchronized shocks(ie, cardioversion for VT with EMS systems pulses), AEDs will recommend a(nonsynchronized) shock Approximately 80% of out-of-hospital cardiac arrests oc- for monomorphic and polymorphic VTif the rate and r-wave cur in private or residential settings (LOE 4).62 Reviewers morphology exceed preset values found no studies that documented the effectiveness of home Electrode placement AED deployment, so there is no recommendation for or Rescuers should place AED electrode pads on the victim' against personal or home deployment of AEDs(Class bare chest in the conventional sternal-apical(anterolateral) position(Class Ia). The right(sternal)chest pad is placed on

emphasized the importance of organization, planning, training, linking with the EMS system, and establishing a process of continuous quality improvement.50,51 Studies of lay rescuer AED programs in airports52 and casinos53,54 and first-responder programs with police officers26,34,36,44,55–57 have shown a survival rate of 41% to 74% from out-of-hospital witnessed VF SCA when immediate bystander CPR is provided and defibrillation occurs within about 3 to 5 minutes of collapse. These high survival rates, however, are not attained in programs that fail to reduce time to defibrillation.58–60 In a large prospective randomized trial (LOE 1)61 funded by the AHA, the National Heart, Lung, and Blood Institute (NHLBI), and several AED manufacturers, lay rescuer CPR AED programs in targeted public settings doubled the number of survivors from out-of-hospital VF SCA when compared with programs that provided early EMS call and early CPR. The programs included a planned response, lay rescuer training, and frequent retraining/practice. The following elements are recommended for community lay rescuer AED programs50,51: ● A planned and practiced response; typically this requires oversight by a healthcare provider ● Training of anticipated rescuers in CPR and use of the AED ● Link with the local EMS system ● Process of ongoing quality improvement More information is available on the AHA website: www. americanheart.org/cpr. Under the topic “Links on this site,” select “Have a question?” and then select “AED.” Lay rescuer AED programs will have the greatest potential impact on survival from SCA if the programs are created in locations where SCA is likely to occur. In the NHLBI trial, programs were established at sites with a history of at least 1 out-of-hospital cardiac arrest every 2 years or where at least 1 out-of-hospital SCA was predicted during the study period (ie, sites having 250 adults over 50 years of age present for 16 h/d).61 To be effective, AED programs should be integrated into an overall EMS strategy for treating patients in cardiac arrest. CPR and AED use by public safety first responders (traditional and nontraditional) are recommended to increase survival rates for SCA (Class I). AED programs in public locations where there is a relatively high likelihood of witnessed cardiac arrest (eg, airports, casinos, sports facilities) are recommended (Class I). Because the improvement in survival rates in AED programs is affected by the time to CPR and to defibrillation, sites that deploy AEDs should establish a response plan, train likely responders in CPR and AED use, maintain equipment, and coordinate with local EMS systems.50,51 Approximately 80% of out-of-hospital cardiac arrests occur in private or residential settings (LOE 4).62 Reviewers found no studies that documented the effectiveness of home AED deployment, so there is no recommendation for or against personal or home deployment of AEDs (Class Indeterminate). AEDs are of no value for arrest not caused by VF/pulseless VT, and they are not effective for treatment of nonshockable rhythms that may develop after termination of VF. Nonperfusing rhythms are present in most patients after shock delivery,25,26,28,44 and CPR is required until a perfusing rhythm returns. Therefore, the AED rescuer should be trained not only to recognize emergencies and use the AED but also to support ventilation and circulation with CPR as needed. The mere presence of an AED does not ensure that it will be used when SCA occurs. Even in the NHLBI trial, in which almost 20 000 rescuers were trained to respond to SCA, lay rescuers attempted resuscitation before EMS arrival for only half of the victims of witnessed SCA, and the on-site AED was used for only 34% of the victims who experienced an arrest at locations with AED programs.61 These findings suggest that lay rescuers need frequent practice to optimize response to emergencies. It is reasonable for lay rescuer AED programs to implement processes of continuous quality improvement (Class IIa). These quality improvement efforts should use both routine inspections and postevent data (from AED recordings and responder reports) to evaluate the following50,51: ● Performance of the emergency response plan, including accurate time intervals for key interventions (such as collapse to shock or no shock advisory to initiation of CPR), and patient outcome ● Responder performance ● AED function, including accuracy of the ECG rhythm analysis ● Battery status and function ● Electrode pad function and readiness, including expiration date Automated Rhythm Analysis AEDs have microprocessors that analyze multiple features of the surface ECG signal, including frequency, amplitude, and some integration of frequency and amplitude, such as slope or wave morphology. Filters check for QRS-like signals, radio transmission, or 50- or 60-cycle interference as well as loose electrodes and poor electrode contact. Some devices are programmed to detect spontaneous movement by the patient or others. Prototype defibrillators were used in 2 recent clinical trials evaluating quality of CPR in the out-of-hospital and hospital settings, and they hold promise for future AEDs that may prompt rescuers to improve the quality of CPR provided.18,19 AEDs have been tested extensively, both in vitro against libraries of recorded cardiac rhythms and clinically in many field trials in adults63,64 and children.65,66 They are extremely accurate in rhythm analysis. Although AEDs are not designed to deliver synchronized shocks (ie, cardioversion for VT with pulses), AEDs will recommend a (nonsynchronized) shock for monomorphic and polymorphic VT if the rate and R-wave morphology exceed preset values. Electrode Placement Rescuers should place AED electrode pads on the victim’s bare chest in the conventional sternal-apical (anterolateral) position (Class IIa). The right (sternal) chest pad is placed on IV-38 Circulation December 13, 2005

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