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 hasgrams must strive to improve patient survival, not just shock success. Modern defibrillators are classified according to 2 types of waveforms: monophasic and biphasic. Monophasic wave￾form defibrillators were introduced first, but biphasic wave￾forms 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 wave￾form (MDS) returns to zero gradually, whereas the monopha￾sic truncated exponential waveform (MTE) current is abruptly returned to baseline (truncated) to zero current flow. Few monophasic waveform defibrillators are being manu￾factured 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-hospi￾tal34–36 and in-hospital studies (electrophysiologic studies and implantable cardioverter-defibrillator [ICD] testing and eval￾uation).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 deliver￾ing escalating energy (200 J, 300 J, 360 J) with successive shocks. No direct comparison of the different biphasic wave￾forms 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 defibril￾lation 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 imped￾ance 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 wave￾forms, 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 recti￾linear 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 esca￾lating 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 health￾care providers to safely defibrillate VF SCA.34,36,45,46 In recent clinical trials,18,19 modified prototype AEDs recorded informa￾tion 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 defibrilla￾tion, 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