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 post￾resuscitation 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-of￾hospital18 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 de￾lays 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 immedi￾ately 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 devel￾oped 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 compres￾sions can deliver oxygen and energy substrates, increasing the likelihood that a perfusing rhythm will return after defibril￾lation (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 effi￾cient 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 admis￾sion, or survival to hospital discharge.31,33 Although resusci￾tation outcomes including survival may be affected by many variables in addition to shock delivery, defibrillation pro￾IV-36 Circulation December 13, 2005