Sudden cardiac arrest associated with ventricular fibrillation

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1 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 Thomas Schneider, MD; Patrick R. Martens, MD; Hans Paschen, MD; Markku Kuisma, MD; Benno Wolcke, MD; Bradford E. Gliner, MS; James K. Russell, PhD; W. Douglas Weaver, MD; Leo Bossaert, MD; Douglas Chamberlain, MD; for the Optimized Response to Cardiac Arrest (ORCA) Investigators Background In the present study, we compared an automatic external defibrillator () that delivers 150-J biphasic shocks with traditional high-energy (200- to 360-J) monophasic s. Methods and Results s were prospectively randomized according to defibrillation waveform on a daily basis in 4 emergency medical services systems. Defibrillation efficacy, survival to hospital admission and discharge, return of spontaneous circulation, and neurological status at discharge (cerebral performance category) were compared. Of 338 patients with out-of-hospital cardiac arrest, 115 had a cardiac etiology, presented with ventricular fibrillation, and were shocked with an. The time from the emergency call to the first shock was (mean SD) minutes. Conclusions The 150-J biphasic waveform defibrillated at higher rates, resulting in more patients who achieved a return of spontaneous circulation. Although survival rates to hospital admission and discharge did not differ, discharged patients who had been resuscitated with biphasic shocks were more likely to have good cerebral performance. (Circulation. 2000;102: ) Key Words: defibrillation resuscitation heart arrest heart-arrest device Sudden cardiac arrest associated with ventricular fibrillation (VF) remains a leading cause of unexpected death in the Western world. 1,2 Rapid-response programs 3,4 with automatic external defibrillators (s) used as part of the chain of survival 5 have achieved marked improvements in survival rates in selected localities. The European Resuscitation Council, the American Heart Association, and the International Liaison Committee on Resuscitation have advocated the widespread dissemination of s. 6 8 The success of widespread lifesaving programs depends on the development of therapeutic technology suitable for mass deployment with infrequent individual use. This will require great strides in defibrillator cost, size, and unattended reliability. Traditional monophasic defibrillators deliver high and escalating energies, from 200 to 360 J. These waveforms and energy levels place fundamental limitations on device cost, weight, and volume reduction. 9 Biphasic waveforms have replaced monophasic waveforms for implantable defibrillators because of proved advantages in energy requirements, size, and weight The incorporation of low-energy impedance-compensating biphasic truncated exponential (ICBTE) waveforms into external defibrillators facilitates effective and automated application of the therapy to the general patient population. The safety and efficacy of these waveforms have been demonstrated under controlled laboratory and inhospital conditions, and evidence that the use of lower energies and biphasic waveforms offers further benefit by reducing postshock myocardial dysfunction is mounting Prospective, clinical studies to date have been conducted under highly controlled in-hospital conditions. Out-ofhospital cardiac arrest victims have more varied and longer arrest times. Data from out-of-hospital studies are needed to investigate the new role of low-energy biphasic waveforms in sudden cardiac arrest. 24 Observational studies on patients with out-of-hospital cardiac arrest have previously demonstrated that a 150-J ICBTE terminated long-duration VF at high rates We now present the results of the first prospective, randomized trial that compared a 150-J ICBTE with traditional, energyescalating monophasic s. The objective of this multicenter trial was to assess the effectiveness of the s for victims of cardiac arrest in the out-of-hospital setting. Received March 3, 2000; revision received May 15, 2000; accepted May 16, From Johannes Gutenberg-Universitaet (T.S., B.W.), Mainz, Germany; St Jan Hospital (P.R.M.), Brugge, Belgium; Feuerwehr Hamburg (H.P.), Hamburg, Germany; Helsinki City EMS (M.K.), Helsinki, Finland; Agilent Technologies Heartstream Operation (B.E.G., J.K.R.), Seattle, Wash; Henry Ford Hospital (W.D.W.), Detroit, Mich; University Hospital (L.B.), Antwerp, Belgium; and University of Wales College of Medicine (D.C.), Cardiff, UK. Correspondence to Benno Wolcke, MD, Clinic of Anaesthesiology, The Johannes Gutenberg-University Medical School, Langenbeckstr 1, D Mainz, Germany. wolcke@mail.uni-mainz.de 2000 American Heart Association, Inc. Circulation is available at

2 Schneider et al Biphasic and Monophasic Resuscitation 1781 TABLE 1. Description of EMS Systems Mainz, Germany Brugge, Belgium Hamburg, Germany Helsinki, Finland Population served million Training level, 1st tier Paramedic, 2000 h EMT, 130 h Paramedic, 2000 h EMT, 1200 h Training level, 2nd tier Anesthesiology residents, 3 y clinical experience, 80 h emergency training Emergency physicians, assisted by emergency department nurses Physicians, mainly anesthesiologist, 80 h of specialized training Paramedics, 2200 h of training EMS 1st tier vehicles, participating/total EMS 2nd tier vehicles, participating/total 5/5 emergency ambulances 0/1 fast-response vehicle, 1/1 MICU 6/7 emergency ambulances 4/61 emergency ambulances 6/7 ambulances, 0/8 fire engines 2/2 MICUs, 0/1 helicopter 0/4 fast-response vehicles, 3/6 MICUs, 0/2 helicopters ALS indicates advanced life support; EMT, emergency medical technician; MICU, mobile intensive care unit (physician staffed). 0/3 ALS units, 0/1 MICU Methods Enrollment On approval by each local ethics committee, all patients who weighed 36 kg, who had a known or suspected cardiac arrest, and who were attended by the emergency medical services (EMS) system during the study period were included. All devices used in the study were CE (European Community) marked and commercially available in Europe, so informed consent was not required under the circumstances of this study. Arrests witnessed by EMS personnel were excluded because the response time from collapse was not representative of out-of-hospital arrest. Patients with do-notresuscitate instructions, patients whose arrest resulted from a noncardiac cause such as trauma or drowning, and patients who were not treated with s were also excluded. Protocol Patients were prospectively enrolled in 4 EMS systems (Table 1). First responders, whether first or second tier, used either 150-J ICBTE s or 200- to 360-J monophasic s on victims of sudden collapse when defibrillator application was indicated. All consecutive incidents were included in the study in each area until the study was completed. Shocks were delivered with self-adhesive defibrillation pads recommended by the respective equipment manufacturers. Physicians also carried manual defibrillators as backup and to address other electrotherapy and monitoring needs (eg, synchronized cardioversion, external pacing). If the responder suspected that the patient was in cardiac arrest, then the randomly preselected was immediately turned on. The patient was then positioned for cardiopulmonary resuscitation (CPR) and use. CPR was typically performed while the defibrillation pads were being attached to the patient. A sequence (200, 200, and 360 J for monophasic or 150,150, and 150 J for biphasic) of up to 3 defibrillation shocks was then delivered. If 3 consecutive shocks failed to defibrillate or if the did not advise that a shock be delivered, the local protocols according to European Resuscitation Council guidelines were followed. 28,29 Randomization A daily schedule of randomly selected types was distributed on a quarterly basis. At the change of crew shifts in the morning, the carrying case of the selected type was tagged, clearly indicating which had to be used for the entire day. If the was being used in a mission at the designated time, then randomization was delayed until immediately after that mission was completed and the was returned. Descriptions The biphasic s (ForeRunner ; Agilent Technologies Heartstream Operation) delivered 150-J impedance-compensated biphasic waveforms from a 100- F capacitor. This waveform adjusts the duration of each phase in response to patient impedance measured during each shock, providing the desired total waveform duration, tilt, and energy delivery ,25 Monophasic waveforms were delivered by s designed to conform to the defibrillation waveform requirements of AAMI/ANSI Standard DF The monophasic s delivered either monophasic truncated exponential (MTE) or monophasic damped sine (MDS) defibrillation waveforms, depending on the device model in use at each investigational site. MTE s included Heartstart 3000 and Heartstart 911 (Laerdal Medical Corporation). MDS s included Heartstart 2000 (Laerdal Medical Corporation) and LifePak 200 (Physio-Control). End Points The primary end point of the study was the percentage of patients with VF as the initial monitored rhythm who were defibrillated in the first series of 3 shocks. Secondary end points included defibrillation with 2 shocks, first-shock defibrillation, and survival to hospital admission and discharge. Other predetermined observations included return of spontaneous circulation (ROSC), response times, and neurological status at discharge. Sample Size The sample size was based on historical data from the investigators, which suggested that 70% of monophasic-waveform patients would be defibrillated within 3 shocks. The detection of a 22% increase or a 28% decrease in the primary end point with 80% power and a significance level of 0.05 would therefore require 48 patients per arm. With the estimation that VF would be the initial monitored rhythm in 40% of the sudden cardiac arrest victims, 31 a total enrollment of 240 was anticipated. Data Collection ECG and shock data were obtained from the recording systems within the s. Patient data were collected from the incident reports and follow-up reports. Neurological status was scored according to the Glasgow-Pittsburgh Cerebral Performance Category (CPC) and Overall Performance Category (OPC) by study investigators at each site at patient discharge from the hospital. 32 Rhythm Definitions Postshock ECGs were classified by the investigator at each site and reviewed by an independent Data and Safety Monitoring Board (DSMB). VF was defined as a disorganized rhythm with a median peak-to-peak amplitude of 100 V. Any rhythm with an amplitude of 100 V was defined as asystole. An episode of VF was required to persist 5 seconds before transition to a non-vf rhythm. The subsequent recurrence of VF was considered a new episode. Defibrillation was defined as the termination of VF for 5 seconds, without regard to hemodynamic factors. 33 By definition, rhythms that occurred after successful shocks included supraventricular and paced rhythms, ventricular standstill (asystole), bradycardia, and idioventricular rhythms. Non-VF ventricular tachyarrhythmias

3 1782 Circulation October 10, 2000 TABLE 2. Enrollment Data for Cardiac Arrest Patients Who Presented With VF and Were Treated With an Biphasic Monophasic P Patients Age, mean SD y (range) (30 87) (37 94) 0.89 Sex, n (%) 0.83 Female 13 /54 (24) 13 /59 (22) Male 41 /54 (76) 46 /59 (78) Not reported 0 2 Weight, mean SD kg (range) (55 150) (45 150) 0.79 Primary structural heart disease,* n (%) 0.74 Coronary artery disease 36/41 (88) 37/39 (95) Primary electrical disease 3/41 (7) 3/39 (8) Idiopathic dilated cardiomyopathy 1/41 (2) 1/39 (3) Hypertrophic cardiomyopathy 0/41 (0) 0/39 (0) Other 1/41 (2) 1/39 (3) Not reported Cause of cardiac arrest, n (%) 0.97 Primary cardiac arrest 18/39 (46) 18/36 (50) Proved acute myocardial infarction 20/39 (51) 17/36 (47) Other 1/39 (3) 1/36 (3) Not reported Location, n (%) 0.08 Home 35 (65) 33 (54) Public place 19 (35) 23 (38) Workplace 0 (0) 5 (8) Cardiac arrest witnessed by bystander, n (%) 48 (89) 53 (87) 0.74 Lay person 45 (83) 48 (79) Medical professional 3 (6) 5 (8) Bystander CPR, n (%) 25 (46) 26 (43) 0.69 Lay person 17 (31) 15 (25) Medical professional 5 (9) 10 (16) Both lay and medical 3 (6) 1 (2) Duration of bystander CPR, median (25th, 75th percentile) All patients 0 (0, 6.1) 0 (0, 7.1) 0.99 Bystander CPR patients only 6.3 (5.3, 9.3) 8.2 (6.7, 10.8) 0.07 Responder, n (%) 0.59 Paramedic 45 (83) 53 (87) Physician 9 (17) 8 (13) used, n ForeRunner, 54 Heartstart 3000, 47 LifePak 200, 7 Heartstart 2000, 6 Heartstart 911, 1 *The categories are not mutually exclusive. were defined as successful defibrillation rhythms if they selfterminated within 30 seconds from shock delivery. Data and Safety Monitoring Each case report form was sent independently from the centers to the independent DSMB. Members of the DSMB (D.C., L.B., W.D.W.) reviewed all case reports to ensure patient safety and integrity of the data and selected source data (eg, original ECGs) as deemed necessary to resolve apparent discrepancies, by judgment of the chairman (D.C.). The DSMB conducted a separate analysis of the major study end points. The data were formally analyzed after the accumulation of the first 10% of the data and each successive 25% thereafter, based on the equivalent group sequential test for the primary hypothesis. The board reviewed each case at the conclusion of the study. Discrepancies were discussed until an agreement was reached on all cases.

4 Schneider et al Biphasic and Monophasic Resuscitation 1783 TABLE 3. Resuscitation of VF Patients With s On Treatment Intention to Treat Monophasic Biphasic Monophasic Biphasic P (95% CI) P (95% CI) Defibrillation efficacy, n (%) 1 Shock 36/61 (59) 52/54 (96) (24 to 51) 44/67 (66) 44/48 (92) (12 to 40) 2 Shocks 39/61 (64) 52/54 (96) (19 to 45) 47/67 (70) 44/48 (92) (8 to 35) 3 Shocks 42/61 (69) 53/54 (98) (17 to 41) 49/67 (73) 46/48 (96) (11 to 35) Patients defibrillated,* n 49/58 (84) 54/54 (100) (6 to 23) 57/65 (88) 46/47 (98) 0.05 (1 to 19) (%) ROSC, n (%) 33/61 (54) 41/54 (76) 0.01 (5 to 39) 35/67 (52) 39/48 (81) (13 to 45) Survival to hospital 31/61 (51) 33/54 (61) 0.27 ( 8 to 28) 31/67 (46) 33/48 (69) 0.02 (5 to 40) admission, n (%) Survival to hospital discharge, n (%) 19/61 (31) 15/54 (28) 0.69 ( 20 to 13) 18/67 (27) 16/48 (33) 0.45 ( 11 to 24) *Final defibrillation status was not available for 3 patients treated with backup defibrillators. Statistical Analysis Continuous variables are expressed as mean SD and compared with the use of t tests. Ordinal variables (discharge destination, CPC, OPC) were compared by the Kruskal-Wallis rank sums test. Discharge destination was assigned a rank of 1 for home, 2 for rehabilitation facility, and 3 for extended care facility. Proportions were compared by log-likelihood ratio 2 tests and include 95% CIs of differences. Tests were 2-tailed and were computed with the JMP software application developed by the SAS Institute. A P value of 0.05 was considered statistically significant. Results Enrollment The site in Mainz, Germany, enrolled 197 patients starting from December 1996; the site in Brugge, Belgium, enrolled 69 patients starting from September 1997; the site at Hamburg, Germany, enrolled 37 patients starting from November 1997; and the site at Helsinki, Finland, enrolled 35 patients starting from July By the conclusion of the study in December 1998, a total of 338 patients had been enrolled. Of the 338 patients, 246 had an arrest of cardiac etiology that was not witnessed by EMS personnel and were randomized to an. There were no statistical differences between the monophasic and biphasic patients in terms of age, sex, weight, primary structural heart diseases, cause or location of arrest, bystanders who witnessed the arrest or performed CPR, or the type of responder. Similarly, these factors were not statistically different when only the 115 patients who presented with VF as their initial monitored rhythm were considered (Table 2). The patients who presented with VF are the subjects of interest for this study of efficacy. All analyses and discussions from this point on focus exclusively on these patients. TABLE 4. Outcomes of Patients Resuscitated With s and Discharged From Hospital On Treatment Intention to Treat Monophasic Biphasic P Monophasic Biphasic P Destination of discharge, n (%) Home or prearrest residence 9/19 (47) 10/15 (67) 9/18 (50) 10/16 (63) Rehabilitation facility 6/19 (32) 4/15 (27) 5/18 (28) 5/16 (31) Extended care facility 4/19 (21) 1/15 (7) 4/18 (22) 1/16 (6) Cerebral performance category at time of discharge, n (%) Good 10/19 (53) 13/15 (87) 9/18 (50) 14/16 (88) Moderate 4/19 (21) 1/15 (7) 4/18 (22) 1/16 (6) Severe 1/19 (5) 1/15 (7) 1/18 (6) 1/16 (6) Coma 4/19 (21) 0/15 (0) 4/18 (22) 0/16 (0) Overall performance category at time of discharge, n (%) Good 4/19 (21) 5/15 (33) 4/18 (22) 5/16 (31) Moderate 9/19 (47) 9/15 (60) 8/18 (44) 10/16 (63) Severe 2/19 (11) 1/15 (7) 2/18 (11) 1/16 (6) Coma 4/19 (21) 0/15 (0) 4/18 (22) 0/16 (0)

5 1784 Circulation October 10, 2000 Figure 1. Prehospital defibrillation and resuscitation efficacy for 115 patients who presented with VF. (A) On-treatment analysis. (B) Intention-totreat analysis. Response Time The time from the emergency call to the first shock was minutes overall and did not differ between treatments: for monophasic versus for biphasic (P 0.51). Resuscitation of VF Patients The defibrillation efficacy of the 150-J biphasic waveform was superior to that of the 200- to 360-J monophasic waveforms (Table 3, Figure 1). Four patients in the monophasic group were not treated with the due to lowamplitude VF not being detected by the. For the primary end point of defibrillation within the first shock series, 53 of 54 (98%) VF patients were defibrillated with 150-J biphasic shocks compared with 42 of 61 (69%) patients defibrillated with 200- to 360-J monophasic shocks (P ). More patients were defibrillated with the initial biphasic shock than with the initial monophasic shock (96% compared with 59%, P ), and ultimately all patients treated with biphasic s were defibrillated while under EMS care, whereas this was not true for those treated with monophasic s or a combination of monophasic s and backup manual monophasic defibrillators (100% compared with 84%, P 0.003). A higher percentage of patients (76%) achieved ROSC after 150-J biphasic-waveform defibrillation compared with higher-energy monophasic-waveform defibrillation (54%) (Figure 1, P 0.01). Rates of survival to hospital admission and to hospital discharge did not differ between the treatments. Outcomes of Discharged Patients Destination of discharge did not differ between the treatments (Figure 2). CPC at hospital discharge favored patients treated with 150-J biphasic shocks (Figure 2). Among survivors to hospital discharge, 87% of patients resuscitated with 150-J

6 Schneider et al Biphasic and Monophasic Resuscitation 1785 Figure 2. Destination and neurological and functional status at hospital discharge for 34 patients with VF who were discharged alive. (A) On-treatment analysis. (B) Intention-to-treat analysis. biphasic shocks had good cerebral status compared with only 53% after resuscitation with higher-energy monophasic shocks (P 0.04, 95% CI 6% to 62%). OPC did not differ between the treatments (Figure 2). Discussion Improved Defibrillation Efficacy The high defibrillation efficacy of the particular 150-J impedance-compensating biphasic waveform observed in the present study is consistent with previous reports but strengthens the finding by providing randomized data from out-ofhospital emergency care. 26,27 The concurrent controls substantiate the magnitude of the improvement in defibrillation efficacy obtained with this biphasic waveform compared with conventional escalating-energy monophasic-waveform methods. In addition to the improved defibrillation rates of individual biphasic shocks or shock sequences, it is noted that all patients who received treatment with 150-J biphasic shocks were eventually defibrillated during the resuscitation attempt and without resort to backup manual defibrillators, which was not true for the higher-energy monophasic waveforms. Dynamic control of waveform parameters via impedance compensation with a 150-J biphasic shock provides consistently high defibrillation rates without the need for escalating energies. This finding is key to encouraging the further evolution of small, low cost, and widely available technology with dynamic waveform control techniques. Impact on Patient Survival Despite a statistically significant increase in ROSC after defibrillation with 150-J biphasic shocks, no differences in survival to admission to or discharge from hospital were

7 1786 Circulation October 10, 2000 established. The present study was statistically powered to show differences in defibrillation efficacy, not in patient survival. Our objective was to assess the relative performances of the s. The determination of statistical differences in short- or long-term patient survival would require a prohibitively large study to mitigate the uncontrolled variables associated with EMS system influences and postresuscitation treatment. Impact on Patient Outcome Although the rate of survival to discharge from hospital did not differ between treatments, among patients who survived to be discharged, those treated with the biphasic waveform were more likely to be in good condition (eg, to have a CPC of good ) than were those treated with monophasic waveforms. Discharge destinations and OPCs were consistent with these findings in favoring biphasic patients, although the differences were not statistically significant. Improved neurological status has previously been associated with shorter overall resuscitation times in the treatment of sudden cardiac arrest victims 34 but not with defibrillation energy or waveform. It is our hypothesis that the superior neurological status observed at hospital discharge after resuscitation with 150-J biphasic defibrillation shocks is associated with shorter time to ROSC and resultant better postresuscitation cardiac output during the critical interval immediately after severe ischemic compromise. This hypothesis is supported by the significantly higher rate of ROSC obtained with the biphasic waveform. Furthermore, studies in animals have demonstrated that both defibrillation waveform and energy dose affect postresuscitation myocardial function In these studies, both stroke volume and ejection fraction were significantly depressed for many hours after high-energy monophasic shocks to a much greater degree than after 150-J biphasic shocks. Increasing the number of neurologically intact survivors from out-ofhospital sudden cardiac arrest may directly depend on reducing the compromise of cardiac output associated with highenergy defibrillation. Study Limitations Randomization of treatment was conducted on the basis of date rather than on the basis of patient and responders were not blinded to the type. The s were all commercially available devices, with each of the 5 models differing in its user interface, analysis algorithm, and therapy waveform. The EMS personnel were familiar with the monophasic devices at the outset of the study, whereas the biphasic devices were newly introduced. These choices were made due to practical and ethical considerations. The urgency of immediate intervention precluded concealment. Training, budget, and regulatory constraints precluded the development and use of novel devices solely for the purposes of the study. Our method is, however, superior to the alternative day technique used in other recent resuscitation trials. 35,36 In designing our nonblinded study, we considered that unintended randomization errors might favor one mode of defibrillation or the other. Bias in selection of the type of defibrillator used would then be difficult to disprove. It was for this reason that an intention-to-treat analysis was included in the protocol and in this report. The control s used in the present study deployed either MTE (79%) or MDS (21%) shocks, reflecting the distribution of types in service at the time of the study. There is some evidence that MTE waveforms have lower defibrillation rates than MDS waveforms. 37 Thus, the observed defibrillation efficacy of the control group may depend in part on the distribution of monophasic types. However, a subset analysis that compared the efficacy of each waveform substantiates the benefits of the biphasic waveform over each of the monophasic waveforms (P. Martens, MD, unpublished data, 2000), as does a comparison of this biphasic with only MDS s in a similar smaller study (K.-G. Kanz, unpublished data, 1999). In summary, the results of the present study show that an appropriately dosed low-energy impedance-compensating biphasic-waveform strategy results in superior defibrillation performance in comparison with escalating, high-energy monophasic shocks in out-of hospital cardiac arrest. Moreover, the 150-J biphasic-waveform results in a higher rate of ROSC and better neurological status at the time of hospital discharge. Acknowledgments This work was supported by a grant from Agilent Technologies Heartstream Operation. B. Gliner and Dr Russell were employees of and Dr Weaver was an advisor to Heartstream during the study. Prof Chamberlain s Honorary Chair in Cardiff is supported (expenses only) by a grant from the Laerdal Foundation. Appendix Investigators and participating institutions are given in the order of the number of patients enrolled: Thomas Schneider, MD; Benno Wolcke, MD; Gerhard Tauscher, Study Coordinator; Heinke Teichmann, Clinic of Anaesthesiology, The Johannes Gutenberg-University Medical School, Mainz, Germany; Patrick R. Martens, MD; Francis Cooman, MD; Martin De Meyer, RN, Emergency Medical Department, St Jan Hospital, Brugge, Belgium; Luc Charles, Project Coordinator, Fire Brigade, Brugge, Belgium; Hans-Richard Paschen, MD, EMS Medical Director, Hamburg Fire Brigade, Hamburg, Germany; and Markku Kuisma, MD, Janne Aaltonen, MD, Jouni Pousi, RN, Helsinki City EMS, Helsinki, Finland. References 1. Emergency Cardiac Care Committee and Subcommittees, American Heart Association. Guidelines for cardiopulmonary resuscitation and emergency cardiac care, part I: introduction. JAMA. 1992;268: Myerburg RJ, Kessler KM, Castellanos A. Sudden cardiac death: structure, function, and time-dependence of risk. Circulation 1992; 85(suppl I):I-2 I White RD. External defibrillation: the need for uniformity in analyzing and reporting results. Ann Emerg Med. 1998;32: Eisenberg MS, Horwood BT, Cummins RO, et al. Cardiac arrest and resuscitation: a tale of 29 cities. Ann Emerg Med. 1990;19: Cummins RO, Ornato JP, Thies WH, et al. Improving survival from sudden cardiac arrest: the chain of survival concept: a statement for health professionals from the Advanced Cardiac Life Support Subcommittee and the Emergency Cardiac Care Committee, American Heart Association. Circulation. 1991;83: Weisfeldt ML, Kerber RE, McGoldrick RP, et al. American Heart Association Report on the Public Access Defibrillation Conference, December 8 10, 1994: Automatic External Defibrillation Task Force. Circulation. 1995;92:

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Early out-of-hospital experience with an impedancecompensating low-energy biphasic waveform automatic external defibrillator. J Intervent Cardiol Electrophysiol. 1997;1: Handley AJ, Bahr J, Baskett P, et al. The 1998 European Resuscitation Council guidelines for adult single rescuer basic life support: a statement from the Working Group on Basic Life Support, and approved by the Executive Committee. Resuscitation. 1998;37: Robertson C, Steen P, Adgey J, et al. The 1998 European Resuscitation Council guidelines for adult advanced life support: a statement from the Working Group on Advanced Life Support, and approved by the Executive Committee. Resuscitation. 1998;37: Association for the Advancement of Medical Instrumentation. Cardiac Defibrillator Devices: ANSI/AAMI DF Arlington, Va: Association for the Advancement of Medical Instrumentation; Schneider T, Mauer D, Diehl P, et al. Early defibrillation by emergency physicians or emergency medical technicians? 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A comparison of standard cardiopulmonary resuscitation and active compression-decompression resuscitation for out-of-hospital cardiac arrest: French Active Compression- Decompression Cardiopulmonary Resuscitation Study Group. N Engl J Med. 1999;341: Gueugniaud PY, Mols P, Goldstein P, et al. A comparison of repeated high doses and repeated standard doses of epinephrine for cardiac arrest outside the hospital: European Epinephrine Study Group. N Engl J Med. 1998;339: Behr JC, Hartley LL, York DK, et al. Truncated exponential versus damped sinusoidal waveform shocks for transthoracic defibrillation. Am J Cardiol. 1996;78: