Use of the automatic external defibrillator in the management of out-of-hospital cardiac arrest

Impact of community-wide deployment of biphasic waveform automated external defibrillators on out-of-hospital cardiac arrest in Taipei

OBJECTIVES

To determine the impact and outcome of out-of-hospital cardiac arrests (OHCA) while using automated external defibrillators (AED) with biphasic waveforms and its effectiveness when using the Utstein Style community-wide in Taipei.

MATERIAL AND METHODS

A one-year study was conducted to collect OHCA patients with AED utilization prospectively in Taipei City. All events and variables were recorded in the Utstein Style. Electrocardiography and voice records recovered from AED data cards were analysed. The endpoints were survival outcomes.

RESULTS

Of 653 OHCA patients with AED utilization, only 80 (12.6%) patients with 635 true arrests presented with ventricular fibrillation or tachycardia (VF/VT) as the initial rhythm. The interval between call-to-shock was 5 min longer than call-to-EMS arrival (9.3 min versus 4.0 min). Fourteen (25%) of the 55 witnessed VF/VT arrests survived to home discharge. Ninety-seven percent of shockable rhythms were successfully terminated with less than three shocks. For all OHCA patients, initial rhythm of VF/VT (OR 3.4; 95% CI = 1.2-9.4), witnessed status (OR 4.7; 95% CI = 1.3-16.6), and presence of organised rhythm irrespective of pulse during prehospital resuscitation (OR 9.2; 95% CI = 3.2-26.8) demonstrated an independent association with survival to home discharge. For VF/VT arrests, witnessed status, shorter call-to-shock time, high successful rate of the first shock, fewer averaged number of shocks delivered for each patient, and presence of an organised rhythm during prehospital resuscitation showed a likelihood to predict to predict discharged survival in univariate analysis.

CONCLUSIONS

Low frequency of VF arrests is unique to certain eastern populations but without a reduction of AED shock efficacy with biphasic waveform. Besides initial VF and witnessed status, a prehospital post-shock organized rhythm irrespective of pulse appears to be correlated to survival. Certain circumstances in a congested metropolitan city consume time to deliver shocks even after EMS arrival, and might require bystander or public access defibrillation.

Automated external defibrillators: safety and efficacy in children and adolescents

Although children do not suffer from ventricular fibrillation (VF) as frequently as adults, it does occur in 10% to 20% of pediatric cardiac arrests. The technology is available to recognize and treat ventricular fibrillation in children as quickly as we can for adults. This article discusses the evidence to support automated external defibrillator use in young children. As this technology gains increased acceptance, resuscitation rates and outcomes for VF in children should approach those that are seen in adults.

Preliminary in-hospital experience with a fully automatic external cardioverter-defibrillator

BACKGROUND

Ventricular fibrillation (VF) and ventricular tachycardia (VT) are frequently present as initial rhythms during in-hospital cardiac arrest. Although ample evidence exists to support the need for rapid defibrillation, the response to in-hospital cardiac arrest remains without major advances in recent years. The delay between the arrhythmic event and intervention is still a challenge for clinical practice.

OBJECTIVE

To analyze the performance and safety of in-hospital use of a programmable, fully automatic external cardioverter-defibrillator (AECD).

METHODS

We conducted a prospective study at the Emergency Department of a university hospital. A total of 55 patients considered to be at risk of sustained VT/VF were included. Patients underwent monitoring of their cardiac rhythm by the AECD. Upon detection of a ventricular tachyarrhythmia, the AECD was programmed to automatically deliver shock therapy.

RESULTS

We recorded 19 episodes of VT/VF in 3 patients. The median time between the beginning of the arrhythmia and the first defibrillation was 33.4 s (21-65 s). One episode of spontaneous reversion of VT was documented 20 s after its origin and shock therapy was aborted. The defibrillation success was 94.4% (17/18) for the first shock and 100% (1/1) for the second shock. No case of inappropriate shock discharge was registered during the study period.

CONCLUSION

The AECD has the feasibility to combine long-term monitoring with automatic defibrillation safely and effectively. It presents the possibility of providing rapid identification of, and response to, in-hospital ventricular tachyarrhythmias.

Clinical review: Devices and drugs for cardiopulmonary resuscitation -- opportunities and restraints

The science and technology of CPR is only just emerging from its infancy. However, substantial improvements are anticipated, including the ability of lay rescuers to identify cardiac arrest promptly, the availability of additional measurements, and expanded intelligence provided by expanded AEDs with which to more effectively prompt the rescuer through the resuscitation procedure. Most important in our view is the ability to maintain uninterrupted precordial compression. Better timing and better waveforms for defibrillation are emerging. The recognition of the importance of postresuscitation myocardial dysfunction and the selection of better vasopressor agents to minimize the adverse inotropic and chronotropic actions of adrenergic drugs are also likely to improve outcomes of CPR.

Preparedness for cardiopulmonary resuscitation in primary care

OBJECTIVE

To evaluate preparedness for resuscitation of patients in cardiac arrest in primary care.

DESIGN

Questionnaire study sent to every health centre in Finland (n = 277).

SETTING

Primary care.

MAIN OUTCOME MEASURES

Resuscitation training frequency and prevalence of automated external defibrillators and nurse-performed early defibrillation.

RESULTS

One-hundred-and-forty-one health centres (51%) responded to the survey. Fifty-nine percent had appointed one person to be in charge of resuscitation training. The nurses in these health centres were trained to defibrillate (p < 0.001), physicians had advanced life support training (p < 0.001) and the first defibrillation was likely to be performed by a nurse on the ward (p < 0.01) more often. In 87% of health centres, it was not customary to defibrillate before the physician arrived beside the patient. Forty-four percent of the health centres used only manual defibrillators, 26% used automated external defibrillators and 30% used both. Only 18% of respondents considered resuscitation training in their health centre to be sufficient and systematic.

CONCLUSION

Resuscitation training appears insufficient and non-systematic in most health centres in Finland. Automated external defibrillators are not in common use. In health centres with an appointed person in charge of resuscitation training, the training is more often regular.

A comparison of first-responder automated external defibrillator (AED) application rates and characteristics of AED training

OBJECTIVE

To determine whether there were associations between the characteristics of first-responder automated external defibrillator (AED) training and AED application rates.

METHODS

This multicenter retrospective cohort study analyzed data from ten emergency medical services systems where first responders were trained and equipped with AEDs. Data were provided for all out-of-hospital cardiac arrests (OHCAs) occurring over two years, including whether the first-responder AED was applied (pads attached to patient). Systems were surveyed to determine the characteristics of their initial and continuing AED training. Data were analyzed using odds ratios (ORs) with 95% confidence intervals (95% CIs).

RESULTS

Overall, the first-responder AED was applied to 53% of 2,181 OHCAs. First responders applied AEDs to 60% of OHCAs when a national AED training curriculum was used and to 49% of OHCAs when a locally created curriculum was used (OR=1.58; 95% CI=1.32-1.88). First responders applied AEDs to 61% of OHCAs when they were trained to the level of Certified First Responder or higher and to 28% of OHCAs when they were trained only in cardiopulmonary resuscitation (OR=3.97; 95% CI=3.20-4.93). First responders applied AEDs to 66% of OHCAs when they each had an opportunity to apply the AED during continuing training and to 17% of OHCAs when they did not have this opportunity (OR=9.04; 95% CI=7.15-11.42). First responders applied AEDs to 59% of OHCAs when they had not received continuing training within one year of their initial training and to 42% of OHCAs when they had received continuing training in the first year (OR=2.00; 95% CI=1.67-2.40).

CONCLUSION

Use of a national AED training curriculum, training to the level of Certified First Responder or higher, and the ability for each first responder to apply the AED during continuing training were associated with higher AED application rates. Continuing training within the first year did not appear to be as important as actually using the AED during the training.

Skill acquisition and retention in automated external defibrillator (AED) use and CPR by lay responders: a prospective study

This prospective study evaluated the acquisition and retention of skills in cardio-pulmonary resuscitation (CPR) and the use of the automated external defibrillator (AED) by lay volunteers involved in the Department of Health, England National Defibrillator Programme. One hundred and twelve trainees were tested immediately before and after and initial 4-h class; 76 were similarly reassessed at refresher training 6 months later. A standardised test scenario that required assessment of the casualty, CPR and the use of on AED was evaluated using recording manikin data and video recordings. Before training only 44% of subjects delivered a shock. Afterwards, all did so and the average delay to first shock was reduced by 57 s. All trainees placed the defibrillator electrodes in an "acceptable" position after training, but very few did so in the recommended "ideal" position. After refresher training 80% of subjects used the correct sequence for CPR and shock delivery, yet a third failed to perform adequate safety checks before all shocks. The trainees self-assessed AED competence score was 86 (scale 0-100) after the initial class and their confidence that they would act in a real emergency was rated at a similar level. Initial training improved performance of all CPR skills, although all except compression rate had deteriorated after 6 months. The proportion of subjects able to correctly perform most CPR skill was higher following refresher training that after the initial class. Although this course was judged to be effective in teaching delivery of counter-shocks, the need was identified for more emphasis on positioning of electrodes, pre-shock safety checks, airway opening, ventilation volume, checking for signs of a circulation, hand positioning, and depth and rate of chest compressions.

Results of the introduction of an automated external defibrillation programme for non-medical personnel in Galicia

OBJECTIVES

To describe the plan and development of a programme for the introduction of automated external defibrillation for non medical personnel and to report the results of the first 10 months of activity in a community which is predominently rural, such as Galicia.

METHODS

The plan for introduction of the project included aspects of logistics, training and control. We studied cardiac arrests, that were treated in basic life support ambulances (BLS-A) equipped with automated external defibrillators (AEDs), from 1st March to 31st December 2001.

RESULTS

Our community benefits from pioneering legislation in Spain. During the 10 months of study, 28 AEDs were in service, mostly in urban areas. In all cases, a thorough control of the quality of the service in which AEDs was used was carried out. 12% of the patients, who were victims of sudden cardiac death (SCD) and were found in ventricular fibrillation (VF), survived and were discharged from hospital. However, the percentage of patients found in VF is only around 26%. This is due to long assistance intervals (from the call to the arrival on site), and an important delay from the moment when circulatory collapse takes place until the emergency service 061 is called, more than 5 min in half the cases.

CONCLUSIONS

The programme followed for the introduction of AEDs in Galicia was adapted to the socio-demographic characteristics of the population. The prehospital emergency assistance model was developed, executed and controlled by the Public Emergency Health Foundation of Galicia 061 (PEHF-061). The overall results of our first 10 months experience with the automated external defibrillation programme were as to be expected. In general, they are comparable to other published reports; however, ways of shortening the times from the point of collapse to defibrillation must be found, mainly by training the population and through the extension of automated external defibrillation provision to other first responders.

Optimal defibrillation response intervals for maximum out-of-hospital cardiac arrest survival rates

STUDY OBJECTIVE

Many centers optimize their emergency medical services (EMS) systems to achieve a target defibrillation response interval of "call received by dispatch" to "arrival at scene by responder with defibrillator" in 8 minutes or less for at least 90% of cardiac arrest cases. The objective of this study was to analyze survival as a function of time to test the evidence for this standard.

METHODS

This prospective cohort study included all adult, cardiac etiology, out-of-hospital cardiac arrest cases from phases I and II of the Ontario Prehospital Advanced Life Support (OPALS) study. Patients in the 21 Ontario study communities received a basic life support level of care with defibrillation by ambulance and firefighters but no advanced life support. Survival was plotted as a function of the defibrillation response interval. The equation of the curve, generated by means of logistic regression, was used to estimate survival at various defibrillation response interval cutoff points.

RESULTS

From January 1, 1991, to December 31, 1997, there were 392 (4.2%) survivors overall among the 9,273 patients treated. The defibrillation response interval mean was 6.2 minutes, and the 90th percentile was 9.3 minutes. There was a steep decrease in the first 5 minutes of the survival curve, beyond which the slope gradually leveled off. Controlling for known covariates, the decrement in the odds of survival with increasing response interval was 0.77 per minute (95% confidence interval 0.74 to 0.83). The survival function predicts, for successive 90th percentile cutoff points, both survival rates and additional lives saved per year in the OPALS communities compared with the 8-minute standard: 9 minutes (4.6%; -18 lives), 8 minutes (5.9%; 0 lives), 7 minutes (7.5%; 23 lives), 6 minutes (9.5%; 51 lives), and 5 minutes (12.0%; 86 lives).

CONCLUSION

The 8-minute target established in many communities is not supported by our data as the optimal EMS defibrillation response interval for cardiac arrest. EMS system leaders should consider the effect of decreasing the 90th percentile defibrillation response interval to less than 8 minutes.

Racial disparity in cardiac procedures and mortality among long-term survivors of cardiac arrest

BACKGROUND

It is unknown whether white and black Medicare beneficiaries have different rates of cardiac procedure utilization or long-term survival after cardiac arrest.

METHODS AND RESULTS

A total of 5948 elderly Medicare beneficiaries (5429 white and 519 black) were identified who survived to hospital discharge between 1990 and 1999 after admission for cardiac arrest. Demographic, socioeconomic, and clinical information about these patients was obtained from Medicare administrative files, the US census, and the American Hospital Association's annual institutional survey. A Cox proportional hazard model that included demographic and clinical predictors indicated a hazard ratio for mortality of 1.30 (95% CI 1.09 to 1.55) for blacks aged 66 to 74 years compared with whites of the same age. The addition of cardiac procedures to this model lowered the hazard ratio for blacks to 1.23 (95% CI 1.03 to 1.46). In analyses stratified by race, implantable cardioverter-defibrillators (ICDs) had a mortality hazard ratio of 0.53 (95% CI 0.45 to 0.62) for white patients and 0.50 (95% CI 0.27 to 0.91) for black patients. Logistic regression models that compared procedure rates between races indicated odds ratios for blacks aged 66 to 74 years of 0.58 (95% CI 0.36 to 0.94) to receive an ICD and 0.50 (95% CI 0.34 to 0.75) to receive either revascularization or an ICD.

CONCLUSIONS

There is racial disparity in long-term mortality among elderly cardiac arrest survivors. Both black and white patients benefited from ICD implantation, but blacks were less likely to undergo this potentially life-saving procedure. Lower rates of cardiac procedures may explain in part the lower survival rates among black patients.

The potential role for automatic external defibrillators in palliative care units

Cardiopulmonary resuscitation (CPR) has received frequent attention by professionals and the public in recent times. Concerns regarding the potential harms for little chance of success have caused palliative care units (PCUs) doubts about initiating CPR. However, there appears to be a moral responsibility to offer CPR to some, carefully selected, patients. Automatic external defibrillators (AEDs) have been shown to significantly increase chances of survival following CPR and are simple to use, even for non-professionals. It is argued that AEDs may increase the moral imperative on PCUs to offer CPR to certain patients and provide the basis for a necessary debate on where the border between appropriate active treatment and a disturbance to the aim of a peaceful death rests.

The automated external defibrillator: critical link in the chain of survival

Sudden death due to ventricular fibrillation (VF) is the leading cause of death in the United States. Early defibrillation is the most important determinant of survival and is the key element in cardiopulmonary resuscitation. Obstacles to rapid defibrillation by trained emergency personnel persist, but the development of the automated external defibrillator (AED) promises to realize the goal of widespread early defibrillation and translate to an improved chance for survival for the cardiac arrest victim. Technological advancements have made the AED safe, easy to use, accurate, and effective in terminating VF. Use of the AED by trained nontraditional first responders (e.g., firefighters, police officers, flight crews) has improved survival rates in a variety of settings and forms the basis for public-access defibrillation.

Age and sex analyses of out-of-hospital cardiac arrest in Osaka, Japan

OBJECTIVE

To determine effective interventional targets for out-of-hospital cardiac arrests by analyzing the distribution characteristics of arrest patients according to age and sex with special emphasis on ventricular fibrillation (VF).

METHODS

All patients who suffered out-of-hospital cardiac arrest in Osaka Prefecture, Japan during 2 years, were prospectively recorded based on the Utstein style. The number and the incidence rate of cases of arrest, witnessed arrest, and witnessed VF were evaluated according to age and sex. The percentage of resuscitation attempts in arrest cases was also calculated.

RESULTS

We recorded 10139 consecutive out-of-hospital cardiac arrest cases. Resuscitation was attempted in 97.0% of 10139 and showed no significant differences by age and sex. The incidence rate of cardiac arrests increased exponentially with age. Men showed a significantly higher incidence rate of out-of-hospital arrests than women in every age group. Most of the witnessed VF cases showed cardiac a aetiology and were predominantly observed in men in their 50s, 60s and 70s. The incidence rates of witnessed VF were also greater in them.

CONCLUSION

Our study provides evidence that there are significant age and sex related epidemiological differences in cardiac arrests and we need to understand them better. Strategies that focus on high yielded patients, those in witnessed VF, should be pursued. These efforts should be expected to yield sex and age related differences in survivors.

A survey of first-responder firefighters' attitudes, opinions, and concerns about their automated external defibrillator program

OBJECTIVE

To identify barriers to first-responder automated external defibrillator (AED) use by determining firefighter attitudes, opinions, and concerns about their AED program.

METHODS

An anonymous survey was mailed to all firefighters in a municipal department that had had first-responder defibrillation for more than two years. A follow-up survey was mailed to all nonrespondents. The survey requested firefighter demographics, comfort and experience with AED, definition of DOA (dead on arrival), and opinion of the program.

RESULTS

Of 749 firefighters surveyed, 686 responded (92%). The respondents had an average of 12 +/- 8 years of experience; 66% felt very comfortable using the AED and 3% felt very uncomfortable. The respondents had applied an AED to a patient a median of 2 times (range 0-30); 24% had never applied an AED. Eighty-three percent reported they had been on the scene of an out-of-hospital cardiac arrest when their AED was not used for at least one patient. Predominant reasons for not applying an AED included the ambulance arrived "soon enough" (72%), the ambulance arrived first (63%), the patient was DOA (61%), and the patient had a do-not-resuscitate (DNR) order (32%). Eighty-one percent of the respondents correctly listed at least one clinical finding that defines DOA. Ninety-nine percent felt they should continue the AED program. The respondents gave numerous suggestions for improving the program, including being able to visualize the rhythm, increasing their level of care, and improved AED training.

CONCLUSIONS

Municipal first response firefighters view their AED program favorably despite infrequently applying an AED. The appropriateness of withholding defibrillation because a secondary response unit will arrive "soon enough" should be reviewed. The definition of DOA should be reviewed to ensure that viable patients are not denied defibrillation.

Treatment of cardiac arrest with automatic external defibrillators: impact on outcome

Sudden cardiac death is the leading cause of death in the US and most developed nations. Ventricular fibrillation (VF) is the most common initial rhythm in survivors of cardiac arrest. The most important factor in determining survival from VF is the time from collapse to administration of the first defibrillation shock. Automatic external defibrillators (AEDs) have been developed and widely deployed in an attempt to reduce the time to defibrillation. Data on early defibrillation using AEDs has led to a number of public access defibrillator placements in the US and ongoing studies of public access AED use. The safety of lay person AED use is clear. Clearly some concentrated captive populations (e.g. airports, airplanes) may benefit from public access AEDs. Therefore, widespread AED education as a means of increasing public acceptance of lay person AED use must be a priority. As technology evolves costs will decline, however, the current economic reality requires careful consideration of the cost effectiveness of specific AED placement.

Opportunities to prevent sudden out-of-hospital death due to coronary heart disease in a community

BACKGROUND

Intervening successfully to reduce the burden of sudden out-of-hospital death due to coronary heart disease (OHCD) requires knowledge of where these deaths occur and whether they are observed by bystanders.

METHODS

To establish the proportion of OHCDs that were witnessed and where they occurred, we reviewed the coroner's notes and medical records of a previously-described sample of OHCD cases among residents of Olmsted County, Minnesota. This cohort (n=113) consisted of a 10% random sample of all Olmsted County residents who died out-of-hospital between 1981 and 1994 and whose deaths were attributed to coronary heart disease.

RESULTS

Excluding deaths in nursing homes (n=27), 71 (83%) of the deaths occurred in private homes and 15 (17%) occurred in public places. The event was not witnessed in 59% of deaths occurring in private homes and in 20% of deaths occurring in public places. The presence or absence of a bystander could not be established for 10% of deaths in private homes and 7% of deaths in public areas.

CONCLUSIONS

A significant proportion of OHCDs occur in private homes and are not witnessed. Prevention of unwitnessed deaths will require programs that result in primary prevention and/or calls to first responders at the time of impending cardiac arrest.

Automated external defibrillator arrhythmia detection in a model of cardiac arrest due to commotio cordis

INTRODUCTION

Cardiac arrest due to chest wall blows (commotio cordis) has been reported with increasing frequency in children, and only about 15% of victims survive. Automated external defibrillators (AEDs) have been shown to be life saving in adults with cardiac arrest, but data on their use in children are limited. In a swine model of commotio cordis designed to be most relevant to young children, we assessed the efficacy of a commercially available AED for recognition and termination of ventricular fibrillation.

METHODS AND RESULTS

Ventricular fibrillation was produced in anesthetized juvenile swine by precordial impact from a baseball under controlled conditions. Animals were randomized to defibrillation after 1, 2, 4, or 6 minutes of ventricular fibrillation. Twenty-six swine underwent 50 ventricular fibrillation inductions. Sensitivity of the AED for recognition of ventricular fibrillation was 98%, and specificity for nonshockable episodes was 100%. All episodes of ventricular fibrillation were successfully terminated by the AED.

CONCLUSION

In this experimental model of commotio cordis, the AED proved to be highly sensitive and specific for recognition of ventricular fibrillation and effective in terminating the arrhythmia and restoring sinus rhythm. These findings suggest that early defibrillation with the AED could save young lives on the athletic field.

Public access defibrillation

Very early defibrillation, within the first few minutes of VF cardiac arrest, results in significantly improved survival rates [1,10-12,34]. Most EMS systems cannot consistently provide defibrillation within the first few minutes following cardiac arrest. Defibrillation within the first few minutes following collapse is potentially achievable through the use of AEDs and PAD [9-14,62]. The delivery of defibrillation with AEDs has been made more efficient through the use of impedance-compensated defibrillation, larger pad sizes, and biphasic waveforms [34]. The technology is simple and easy to use. Preliminary cost-effectiveness analysis indicates that PAD and first-responder defibrillation are economically as attractive as other interventions in cardiac arrest [44]. Effective PAD requires significant investment in time, energy, informed planning, and rigorous quality improvement; however, the benefits are enormous. Reported VF survival rates can approach 50% or higher [11,12,62]. PAD provides the potential opportunity to transform cardiac arrest into a survivable event for most victims by making the community the ultimate coronary care unit.

New concepts in transthoracic defibrillation

The transition of biphasic waveforms from ICDs to external defibrillators constitutes a significant technological advances for transthoracic defibrillation. Impedance compensation has enabled the delivery of defibrillating current adapted to each patient and each shock in the same patient. Optimally designed biphasic waveforms have been shown clinically to have greater efficacy in the termination of VF when compared with monophasic waveforms, and because peak current delivery is less, these waveforms are likely to be less injurious to myocardial function. Advances in the understanding of the mechanisms of fibrillation and defibrillation have identified the electrophysiologic events that initiate and sustain VF and the effects of defibrillation shocks on those events. Definition of the role of VEP and postshock excitation has clarified the mechanisms by which shocks can either fail or succeed. The ability of the second phase of optimal biphasic waveform shocks to exploit recruited sodium channels in negatively polarized areas and thus induce rapid propagation of postshock excitation assures uniform depolarization and prevention of re-entry. This appears to be the major mechanism of greater efficacy of biphasic waveforms. It seems certain that continuing investigation of virtual electrodes will enhance our understanding of defibrillation and optimal waveforms. At the same time, much more needs to be known regarding translation of these experimental observations to mechanisms of defibrillation in human hearts with long-standing underlying structural heart disease, which often arises of multiple factors. This represents a major challenge in defibrillation research.

Prehospital ACLS--does it work?

Cardiac disease is the most common cause of death in the United States, and sudden cardiac arrest frequently claims the lives of men and women during their most productive years. It is believed that much better survival rates can be achieved for victims of cardiac arrest through optimizing the "chain of survival" as described by the American Heart Association. The relative and incremental benefit of full prehospital ACLS over basic life support and defibrillation is unproven, however. This is an important issue in this era of cost containment. Some of the ongoing studies including the OPALS study may clarify the cost effectiveness and relative efficacy of rapid defibrillation and full ACLS programs for victims of prehospital cardiac arrest [6].

Defibrillation threshold and cardiac responses using an external biphasic defibrillator with pediatric and adult adhesive patches in pediatric-sized piglets

Before recommendations for using an automatic external defibrillator on pediatric patients can be made, a protocol for the energy of a biphasic waveform energy dosing needs to be determined that will allow ventricular defibrillation of 8 year olds while causing only a minimal amount of cardiac damage to infants. Pediatric- and adult-sized electrode patches were alternately applied to 10 isoflurane-anesthetized piglets weighing 3.8-20.1 kg to approximate the body weights of newborns to children < 8 years old. The defibrillation threshold (DFT) was determined for biphasic truncated exponential waveform shocks. Additional shocks, varying from the DFT to 360 Joules (J), were delivered during sinus rhythm or following 30 s of ventricular fibrillation (VF). The DFT was 2.4+/-0.81 and 2.1+/-0.65 J/kg for pediatric and adult patches, respectively (P = N.S.). The change in left ventricular (LV) dP/dt from baseline as a function of shock strength was significantly different at 1 and 10 s after shocks of increasing energy that were delivered in sinus rhythm, and 1, 10, 20, and 30 s after defibrillation shocks. There was no significant difference in LV dP/dt with increasing shock energy at 60 s with either patch size. The time to return of sinus rhythm, ST-segment deviation, and cardiac output were also not significantly different from baseline 60 s following shocks of up to 360 J delivered during sinus rhythm or VF with either patch. The same amount of energy delivered with a biphasic external defibrillator successfully defibrillated VF whether adult or pediatric patches were used. Cardiac rhythm and hemodynamic variables were unaltered at 60 s after shocks delivered at energies of up to 360 J. These data suggest that there is a substantial safety margin above a DFT strength shock for this biphasic waveform in piglets.

Potential impact of public access defibrillators on survival after out of hospital cardiopulmonary arrest: retrospective cohort study

OBJECTIVE

To estimate the potential impact of public access defibrillators on overall survival after out of hospital cardiac arrest.

DESIGN

Retrospective cohort study using data from an electronic register. A statistical model was used to estimate the effect on survival of placing public access defibrillators at suitable or possibly suitable sites.

SETTING

Scottish Ambulance Service.

SUBJECTS

Records of all out of hospital cardiac arrests due to heart disease in Scotland in 1991-8.

MAIN OUTCOME MEASURES

Observed and predicted survival to discharge from hospital.

RESULTS

Of 15 189 arrests, 12 004 (79.0%) occurred in sites not suitable for the location of public access defibrillators, 453 (3.0%) in sites where they may be suitable, and 2732 (18.0%) in suitable sites. Defibrillation was given in 67.9% of arrests that occurred in possibly suitable sites for locating defibrillators and in 72.9% of arrests that occurred in suitable sites. Compared with an actual overall survival of 744 (5.0%), the predicted survival with public access defibrillators ranged from 942 (6.3%) to 959 (6.5%), depending on the assumptions made regarding defibrillator coverage.

CONCLUSIONS

The predicted increase in survival from targeted provision of public access defibrillators is less than the increase achievable through expansion of first responder defibrillation to non-ambulance personnel, such as police or firefighters, or of bystander cardiopulmonary resuscitation. Additional resources for wide scale coverage of public access defibrillators are probably not justified by the marginal improvement in survival.

Automated external defibrillation as part BLS: implications for education and practice

The latest Adult Basic Life Support (BLS) guidelines support the inclusion of the use of the automated external defibrillator (AED), as part of basic life support (BLS). Emphasis on the provision of early defibrillation as part of BLS acknowledges the importance of this manoeuvre in the successful termination of ventricular fibrillation. The ramifications of such changes for both first responders and organisations implementing the guidelines should not be underestimated. Issues relating to resourcing, content and duration of training and retraining, auditing and evaluation require further exploration. To consider these issues now seems particularly pertinent, given the recent launch of the UK Government's paper on public health, 'Saving Lives-Our Healthier Nation' which seeks to deploy AEDs in busy public places for use by trained members of the lay public. Additionally, defibrillation has been identified as one of the key competencies that all trained nurses and other health care providers should be able to undertake. This paper will consider the background to the current guideline changes, analyse the wider implications of translating the recommendations into practice, and offer possible solutions to address the issues raised. Whilst the analysis is particularly pertinent to the United Kingdom, many of the issues raised have international importance.

Tripling survival from sudden cardiac arrest via early defibrillation without traditional education in cardiopulmonary resuscitation

BACKGROUND

Early defibrillation is the most important intervention affecting survival from sudden cardiac arrest (SCA). To improve public access to early defibrillation, we established Piacenza Progetto Vita (PPV), the first system of out-of-hospital early defibrillation by first-responder volunteers.

METHODS AND RESULTS

The system serves a population of 173 114 residents in the Piacenza region of Italy. Equipment for the system comprises 39 semiautomatic external biphasic defibrillators (AEDs): 12 placed in high-risk locations, 12 in lay-staffed ambulances, and 15 in police cars; 1285 lay volunteers trained in use of the AED, without traditional education in cardiac pulmonary resuscitation, responded to all cases of suspected SCA, in coordination with the Emergency Medical System (EMS). During the first 22 months, 354 SCA occurred (72+/-12 years, 73% witnessed). The PPV volunteers treated 143 SCA cases (40.4%), with an EMS call-to-arrival time of 4.8+/-1.2 minutes (versus 6.2+/-2.3 minutes for EMS, P=0.05). Overall survival rate to hospital discharge was tripled from 3.3% (7 of 211) for EMS intervention to 10.5% (15 of 143) for PPV intervention (P=0.006). The survival rate for witnessed SCA was tripled by PPV: 15.5% versus 4.3% in the EMS-treated group (P=0.002). A "shockable" rhythm was present in 23.8% (34 of 143) of the PPV patients versus 15.6% (33 of 211) of the EMS patients (P=0.055). The survival rate from shockable dysrhythmias was higher for PPV versus EMS: 44.1% (15 of 34) versus 21.2% (7 of 33), P=0.046. The neurologically intact survival rate was higher in PPV-treated versus EMS-treated patients: 8.4% (12 of 143) versus 2.4% (5 of 211), P=0.009.

CONCLUSIONS

Broad dissemination of AEDs for use by nonmedical volunteers enabled early defibrillation and tripled the survival rate for out-of-hospital SCA.

Law Enforcement Agency Defibrillation (LEA-D): proceedings of the National Center for Early Defibrillation Police AED Issues Forum

Why does LEA-D intervention seem to work in some systems but not others? Panelists agreed that some factors that delay rapid access to treatment, such as long travel distances in rural areas, may represent insurmountable barriers. Other factors, however, may be addressed more readily. These include: absence of a medical response culture, discomfort with the role of medical intervention, insecurity with the use of medical devices, a lack of proactive medical direction, infrequent refresher training, and dependence on EMS intervention. Panelists agreed that successful LEA-D programs possess ten key attributes (Table 6). In the end, the goal remains "early" defibrillation, not "police" defibrillation. It does not matter whether the rescuer wears a blue uniform--or any uniform, for that matter--so long as the defibrillator reaches the victim quickly. If LEA personnel routinely arrive at medical emergencies after other emergency responders or after 8 minutes have elapsed from the time of collapse, an LEA-D program will be unlikely to provide added value. Similarly, if police frequently arrive first, but the department is unwilling or unable to cultivate the attributes of successful LEA-D programs, efforts to improve survival may not be realized. In most communities, however, LEA-D programs have tremendous lifesaving potential and are well worth the investment of time and resources. Law enforcement agencies considering adoption of AED programs should review the frequency with which police arrive first at medical emergencies and LEA response intervals to determine whether AED programs might help improve survival in their communities. It is time for law enforcement agency defibrillation to become the rule, not the exception.

Eight minutes or less: does the ambulance response time guideline impact trauma patient outcome?

Emergency Medical Services (EMS) agencies are increasingly being held to an ambulance response time (RT) criterion of responding to a medical emergency within 8 min for at least 90% of calls. This recommendation resulted from one study of outcome after nontraumatic cardiac arrest and has never been studied for any other emergency. This retrospective study evaluates the effect of exceeding the 8 min RT guideline on patient survival for victims of traumatic injury treated by an urban paramedic ambulance EMS system and transported to a single Level I trauma center. Of 3576 patients identified by the hospital trauma registry, 3490 (97.6%) had complete records available. Patients were grouped according to ambulance RT: < or = 8 min (n = 2450) or > 8 min (n = 1040). After controlling for other significant predictors, there was no difference in survival after traumatic injury when the 8 min ambulance RT criteria was exceeded (mortality odds ratio 0.81, 95% CI 0.43-1.52). There was also no significant difference in survival when patients were stratified by injury severity score group. Exceeding the ambulance industry response time criterion of 8 min does not affect patient survival after traumatic injury.

Automated external defibrillators and first responders: a satisfaction survey

PRIMARY OBJECTIVE

Automated external defibrillators (AEDs) are used with increasing frequency in the United States by first responders (FR) such as police officers (PO) or firefighters (FF). However, FR satisfaction with use of AEDs has not been investigated. We hypothesized that FR satisfaction is comparable with that of paramedics (PA) and that, among those who have defibrillated with AEDs, those who have restored a pulse before PA arrival have a higher level of satisfaction than those who have not restored a pulse.

MATERIALS AND METHODS

A 21-item questionnaire with closed answers was sent to FR and PA in four communities. Each answer was scored 0, 1 or 2. A score between 10 and 16 correlated with the highest satisfaction level.

RESULTS

276 out of 311 questionnaires were returned (89%). Two hundred and eleven respondents (35 PA, 70 FF and 106 PO) had used an AED and 99 FF and PO had restored a pulse before PA arrival. The satisfaction level of PO, FF and PA was high as demonstrated by the scores: 13.26, 13.07 and 13.39, respectively. Use of AED and pulse restoration resulted in higher scores than those of groups who had been trained only and who had not restored a pulse.

CONCLUSION

FR demonstrated a high level of satisfaction with using AEDs, and also had a favorable attitude toward implementation of AED use. Restoration of a pulse was clearly a factor responsible for a higher satisfaction. This positive attitude should encourage further implementation of early defibrillation programs in non-medical first responder settings.

Update in pediatric resuscitation

This article updates research concerning the resuscitation of a pediatric patient. The topics discussed include the state of pediatric life support, the current guidelines, the management of those guidelines, and coping with death.

Biphasic waveform external defibrillation thresholds for spontaneous ventricular fibrillation secondary to acute ischemia

OBJECTIVES

The goal of this study was to determine if the defibrillation threshold (DFT) after spontaneous ventricular fibrillation (VF) secondary to acute ischemia differs from the DFT for electrically induced VF in the absence of ischemia in anesthetized, closed-chest dogs and pigs.

BACKGROUND

The efficacy of external defibrillators has been tested mainly in animals and humans using E-VF, yet external defibrillators are often used in patients to halt S-VF.

METHODS

Protocol 1: biphasic truncated exponential (BTE) waveform shocks were delivered through electrodes placed in an anterior-anterior (A-A) position (left and right lateral thorax) in nine dogs. After measuring the E-VF DFT, acute ischemia was induced with an angioplasty balloon in either the left anterior descending or left circumflex coronary artery, and the S-VF DFT was determined. Protocol 2: in a group of 12 pigs, the E-VF DFT and S-VF DFT were determined for electrodes in the A-A position and in the anterior-posterior position (A-P). Protocol 3: the E-VF DFT was determined in seven pigs. Then up to three shocks 1.5x the E-VF DFT were delivered to S-VF. If defibrillation did not occur, a step-up protocol was used until defibrillation occurred.

RESULTS

Protocol 1: the DFT for E-VF was 65 +/- 28 J (mean +/- SD) compared with 226 +/- 97 J for S-VF, p < 0.05. Protocol 2: the DFT was 152 +/- 58 J for E-VF and 315 +/- 123 J for S-VF for A-A electrodes. The DFT was 100 +/- 43 J for E-VF and 206 +/- 114 J for S-VF for A-P electrodes. Protocol 3: 11/37 shocks of strength 1.5x E-VF DFT (182 +/- 40 J) stopped the arrhythmia. The episodes of S-VF not halted by these shocks required energy levels of up to 400 J for defibrillation.

CONCLUSIONS

External defibrillation of S-VF induced by acute ischemia requires significantly more energy than VF induced by 60-Hz current in the absence of ischemia. A safety margin >1.5x the DFT for electrically induced VF may be necessary in BTE external defibrillators to defibrillate S-VF.

Highlights of latest American College of Cardiology and American Heart Association Guidelines for Management of Patients with Acute Myocardial Infarction

The recently published American College of Cardiology/American Heart Association Guidelines for the Management of Patients with Acute Myocardial Infarction stress 3 major points: (1) the prehospital phase from the onset of symptoms to definitive therapy in the emergency department must be shortened by 50% in order to reduce further the estimated 30% mortality rate for all patients in the community who suffer an acute myocardial infarction; (2) a more widespread use of thrombolytic agents is warranted because of the demonstrated, extremely time-dependent benefit to survivorship: the sooner it is given, the better the outcome; and (3) the administration of aspirin (160-325 mg) daily for an indefinite period is perhaps the most important therapy for a patient with acute myocardial infarction. Long-term therapy with lipid-lowering Statin drugs and angiotensin-converting enzyme inhibitor agents are gaining increasing evidence-based data to support their perpetual use as well.

Automated external defibrillation in the occupational setting

ACOEM supports ongoing efforts to enhance emergency response to medical emergencies in the occupational environment. The development of training and use of AEDs is a reasonable and appropriate aspect of such programs for managing sudden cardiac arrest, an important cause of morbidity and mortality among working age adults. The implementation of such an AED program, which should be a component of a more general worksite emergency response plan, requires clearly defined medical direction and medical control.

Cardiac arrest and monitoring

Initial assessment to determine pulselessness, monitoring the status of the patient, and the effectiveness of resuscitation efforts are integral parts of cardiopulmonary resuscitation. This article focuses on aspects of monitoring during cardiopulmonary resuscitation: electrocardiography and assessment of the adequacy of chest compressions.

Out-of-hospital defibrillation with automated external defibrillators: postshock analysis should be delayed

STUDY OBJECTIVE

The American Heart Association protocols for use of automated external defibrillators (AEDs) recommend that a rhythm analysis be done immediately after each defibrillation attempt. However, shock is often followed by electrical silence or marginally organized electrical activity before ventricular fibrillation (VF) or ventricular tachycardia (VT) recurs. The optimal timing of postshock analysis for identification of recurrent VF/VT is unknown. This study examines the time to recurrence of VF/VT after a defibrillation attempt with AED.

METHODS

Over an 18-month period, all tapes from patients with out-of-hospital cardiac arrest who received shocks at least once with an AED were screened for recurrent VF/VT. All cases come from a single emergency medical services system providing basic life support, defibrillation with AED, and intubation with an esophageal-tracheal twin-lumen airway device (Combitube) for a population of 633,511 individuals. Pediatric and traumatic cases were excluded. When VF/VT recurred within 3 minutes of the defibrillation attempt, rhythm strips were printed and included in the study. Two cardiology fellows, blinded to the study objectives, measured the time from defibrillation to recurrent VF/VT for each strip.

RESULTS

Over the study period, 222 tapes from 96 patients met the inclusion criteria. Only 44 (20%) occurrences of VF/VT had recurred within 6 seconds of defibrillation, 162 (73%) at 60 seconds, and 200 (90%) at 90 seconds.

CONCLUSION

Eighty percent of VF/VT recurred more than 6 seconds after defibrillation and were missed when using current American Heart Association AED protocols. Subsequent analysis should be postponed until at least 30 seconds after defibrillation. Performing 30 seconds of chest compressions after defibrillation before subsequent AED rhythm analysis would increase AED identification of VF/VT to 52%.

Effect of reducing ambulance response times on deaths from out of hospital cardiac arrest: cohort study

OBJECTIVES

To determine the association between ambulance response time and survival from out of hospital cardiopulmonary arrest and to estimate the effect of reducing response times.

DESIGN

Cohort study.

SETTING

Scottish Ambulance Service.

SUBJECTS

All out of hospital cardiopulmonary arrests due to cardiac disease attended by the Scottish Ambulance Service during May 1991 to March 1998.

MAIN OUTCOME MEASURES

Survival rate to hospital discharge and potential improvement from reducing response times.

RESULTS

Of 13 822 arrests not witnessed by ambulance crews but attended by them within 15 minutes, complete data were available for 10 554 (76%). Of these patients, 653 (6%) survived to hospital discharge. After other significant covariates were adjusted for, shorter response time was significantly associated with increased probability of receiving defibrillation and survival to discharge among those defibrillated. Reducing the 90th centile for response time to 8 minutes increased the predicted survival to 8%, and reducing it to 5 minutes increased survival to 10-11% (depending on the model used).

CONCLUSIONS

Reducing ambulance response times to 5 minutes could almost double the survival rate for cardiac arrests not witnessed by ambulance crews.

Technologic advances and program initiatives in public access defibrillation using automated external defibrillators

Widespread provision of early defibrillation following cardiac arrest holds major promise for improved survival from ventricular fibrillation. The critical element in predicting a successful outcome is the rapidity with which defibrillation is achieved. A worldwide awareness of this potential and its advocacy by such organizations as the American Heart Association have been pivotal in the evolution of initiatives to make defibrillation more widely and more rapidly available. The feasibility of this initiative, known as public access defibrillation, is in large measure a direct consequence of major technologic advances in automated external defibrillators (AEDs). New low-energy waveforms with biphasic morphology have been shown to be more effective in terminating ventricular fibrillation and may do so with less myocardial injury. Placement of AEDs in a variety of nontraditional settings such as police cars, aircraft and airport terminals, and gambling casinos has been shown to yield an impressive number of survivors of cardiac arrest in ventricular fibrillation. Questions yet to be answered center on the appropriate disposition of AEDs in public access defibrillation settings, training and retraining issues, device maintenance, and collection of accurate data to document benefit and to identify areas of needed improvement or expansion of AED availability.

Optimal Response to Cardiac Arrest study: defibrillation waveform effects

INTRODUCTION

Advances in early defibrillation access, key to the "Chain of Survival", will depend on innovations in defibrillation waveforms, because of their impact on device size and weight. This study compared standard monophasic waveform automatic external defibrillators (AEDs) to an innovative biphasic waveform AED.

MATERIAL AND METHODS

Impedance-compensated biphasic truncated exponential (ICBTE) and either monophasic truncated exponential (MTE) or monophasic damped sine (MDS) AEDs were prospectively, randomly assigned by date in four emergency medical services. The study design compared ICBTE with MTE and MDS combined. This subset analysis distinguishes between the two classes of monophasic waveform, MTE and MDS, and compares their performance to each other and to the biphasic waveform, contingent on significant overall effects (ICBTE vs. MTE vs. MDS). Primary endpoint: Defibrillation efficacy with < or =3 shocks. Secondary endpoints: shock efficacy with < or =1 shock, < or =2 shocks, and survival to hospital admission and discharge. Observations included return of spontaneous circulation (ROSC), refibrillation, and time to first shock and to first successful shock.

RESULTS

Of 338 out-of-hospital cardiac arrests, 115 had a cardiac aetiology, presented with ventricular fibrillation, and were shocked by an AED. Defibrillation efficacy for the first "stack" of up to 3 shocks, for up to 2 shocks and for the first shock alone was superior for the ICBTE waveform than for either the MTE or the MDS waveform, while there was no difference between the efficacy of MTE and MDS. Time from the beginning of analysis by the AED to the first shock and to the first successful shock was also superior for the ICBTE devices compared to either the MTE or the MDS devices, while again there was no difference between the MTE and MDS devices. More ICBTE patients achieved ROSC pre-hospital than did MTE patients. While the rates of ROSC were identical for MTE and MDS patients, the difference between ICBTE and MDS was not significant. Rates of refibrillation and survival to hospital admission and discharge did not differ among the three populations.

CONCLUSIONS

ICBTE was superior to MTE and MDS in defibrillation efficacy and speed and to MTE in ROSC. MTE and MDS did not differ in efficacy. There were no differences among the waveforms in refibrillation or survival.

Results from the first 12 months of a fire first-responder program in Australia

STUDY OBJECTIVE

We aimed to reduce response times and time to defibrillation for out-of-hospital cardiac arrest patients through fire first-responders equipped with automatic external defibrillators (AEDs). The fire first-responders were added as an extra tier to the existing two-tired ambulance response.

METHODS

This prospective controlled trial set in Melbourne, Australia, consisted of a control area (277 km2, population density 2343/km2-ambulance only dispatch) and a pilot area (171 km2, population density 2290/km2-ambulance and fire first-responder dispatch). The main outcome measures were time to emergency medical service (EMS) arrival at scene for all cardiac arrest patients and time to defibrillation for cardiac arrest patients presenting in ventricular fibrillation (VF). The study participants were patients who suffered a cardiac arrest of presumed cardiac aetiology for which a priority 0 emergency response was activated. A total of 268 patients were located in the control area and 161 in the pilot (intervention) area.

RESULTS

The mean response time to arrival at scene was reduced by 1.60 (95% CI 1.21, 1.99) min, P < 0.001. A large reduction in prolonged responses (> or = 10 min) to cardiac arrests was also observed in the pilot area (2%) compared with the control area (18%), chi = 23.19, P < 0.001. Mean time to defibrillation was reduced by 1.43 (95% CI 0.11, 2.98) min, P = 0.068.

CONCLUSION

The results from this study suggest that fire officers can be successfully trained in the use of AEDs and can integrate well into a medical response role. The combined response of ambulance and fire personnel significantly reduced the response interval and reduced time to defibrillation. This suggests that in appropriate situations other agencies could be considered for involvement in co-ordinated first-responder programs.

Current status of the implantable cardioverter-defibrillator

Clinical trials have established the superiority of the implantable cardioverter-defibrillator (ICD) over antiarrhythmic drug therapy in survivors of sudden cardiac death and in high-risk patients with coronary artery disease. The ICD has evolved to overcome the limitation of earlier devices that required thoracotomy for implantation and were fraught with inappropriate shock delivery. Current ICDs are implanted in a similar manner to cardiac pacemakers and incorporate sophisticated rhythm-discrimination algorithms to prevent inappropriate therapy. Managing the patient with an ICD requires an understanding of the multiprogrammable features of modern devices. Drug interactions and potential sources of electromagnetic interference may adversely affect ICD function. Driving restrictions may be necessary under certain conditions. The cost-effectiveness of ICD therapy appears favorable, given the marked survival benefit seen in randomized trials relative to antiarrhythmic drug treatment. The growing number of ICD recipients necessitates an understanding of the specialized features of the modern ICD and the role of device therapy in clinical practice.

Geographical distribution of cardiac arrest in Nottinghamshire

BACKGROUND

to analyse the incidence of out-of-hospital cardiac arrest in Nottinghamshire; to ascertain its geographical distribution; and to determine whether the geography of coronary heart disease mortality and out-of-hospital cardiac arrest are the same.

METHODS AND RESULTS

population based, retrospective study in the County of Nottinghamshire with a total population of 993,914 in an area of 2183 km2 divided into 191 electoral areas. In the 4 years from 1 January, 1991 to 31 December, 1994, 1634 patients sustained a cardiac arrest attributed to a cardiac cause (International Classification of Diseases codes 390-414 and 420-429) and were attended by the Nottinghamshire Ambulance Service. The overall crude mean incidence rate of community cardiac arrest per electoral area was 40.2 per 100,000 population (range 0-121.2). Thirteen electoral areas, relatively deprived according to the Townsend score, had a significantly greater than expected incidence rate of cardiac arrest (median of 75.6/100,000 per electoral area; interquartile range (IQR) 65.3, 83.8). Twelve relatively affluent electoral areas had a significantly lower than expected incidence rate (median of 18.5/100,000 per area (IQR 13.0, 28.7). After adjusting for deprivation index, there were no differences in coronary heart disease (CHD) mortality and community cardiac arrest in urban and rural electoral areas. Apart from response times by ambulance crews, the events that follow the cardiac arrest such as bystander resuscitation, ventricular fibrillation found as the presenting rhythm and survival were similar in all electoral areas.

CONCLUSIONS

increasing level of deprivation is associated with areas of increased incidence of out-of-hospital cardiac arrest in Nottinghamshire, and the effect is apparently different from that on CHD mortality. There is scope for reducing incidence rates of community cardiac arrest and to introduce strategies to improve survival in areas identified as having high rates of community cardiac arrest.

Multicenter study of principles-based waveforms for external defibrillation

STUDY OBJECTIVE

The efficacy of a shock waveform for external defibrillation depends on the waveform characteristics. Recently, design principles based on cardiac electrophysiology have been developed to determine optimal waveform characteristics. The objective of this clinical trial was to evaluate the efficacy of principles-based monophasic and biphasic waveforms for external defibrillation.

METHODS

A prospective, randomized, blinded, multicenter study of 118 patients undergoing electrophysiologic testing or receiving an implantable defibrillator was conducted. Ventricular fibrillation was induced, and defibrillation was attempted in each patient with a biphasic and a monophasic waveform. Patients were randomly placed into 2 groups: group 1 received shocks of escalating energy, and group 2 received only high-energy shocks.

RESULTS

The biphasic waveform achieved a first-shock success rate of 100% in group 1 (95% confidence interval [CI] 95.1% to 100%) and group 2 (95% CI 94.6% to 100%), with average delivered energies of 201+/-17 J and 295+/-28 J, respectively. The monophasic waveform demonstrated a 96.7% (95% CI 89.1% to 100%) first-shock success rate and average delivered energy of 215+/-12 J for group 1 and a 98.2% (95% CI 91.7% to 100%) first-shock success rate and average delivered energy of 352+/-13 J for group 2.

CONCLUSION

Using principles of electrophysiology, it is possible to design both biphasic and monophasic waveforms for external defibrillation that achieve a high first-shock efficacy.

Clinical characteristics of unexplained sudden cardiac death in Korea

In Western countries, sudden cardiac death (SCD) is closely related to coronary artery disease, but in Korea the clinical characteristics of SCD are not well determined. Over a 4-year period (June 1995 to May 1999), 186 cases of SCD, ranging in age from 16 to 75 years, were admitted to the Chonnam National University Hospital. In 82 (44.1%) of these, neither symptoms nor evidence of structural heart disease was found and so their clinical characteristics were investigated. There were 66 (80.5%) men and 16 (19.5%) women (male/female ratio = 4.1:1). The mean age was 50 +/- 14 years: 19 (23.2%) were in their 40s, 21 (25.6%) in their 50s, and 17 (20.7%) in their 60s. The time of circulatory collapse witnessed in 68 cases of SCD showed 2 peaks: between midnight and 03.00h (n=16, 23.5%) and between 09.00h and midday (n=15, 22.1%). Unexplained SCD occurred at home in 48 (64.9%) cases and on the street in 12 (16.2%); it occurred during normal daily routine activity in 23 (39.6%) and during sleep in 15 (25.9%). Thirty-three patients (40.2%) experienced various prodromal symptoms, including chest discomfort (n=13, 15.9%) and dyspnea (n=8, 9.8%). The electrocardiogram taken on arrival recorded asystole in 65 (79.3%) and ventricular fibrillation in 17 (20.7%). Idiopathic ventricular fibrillation was diagnosed in 14 (10 men, 4 women; 45 +/- 11 years) of 21 patients who recovered spontaneous circulation. Five (6.1%) patients were discharged alive, and an implantable cardioverter-defibrillator was implanted in 2. Unexplained SCD is common in Korea and develops predominantly in middle-aged males around midnight or in the late morning usually with no prodromal symptoms (59.8%). Idiopathic ventricular fibrillation is thought to be one of the important causes.

Use of automated external defibrillators by a U.S. airline

BACKGROUND

Passengers who have ventricular fibrillation aboard commercial aircraft rarely survive, owing to the delay in obtaining emergency care and defibrillation.

METHODS

In 1997, a major U.S. airline began equipping its aircraft with automated external defibrillators. Flight attendants were trained in the use of the defibrillator and applied the device when passengers had a lack of consciousness, pulse, or respiration. The automated external defibrillator was also used as a monitor for other medical emergencies, generally at the direction of a passenger who was a physician. The electrocardiogram that was obtained during each use of the device was analyzed by two arrhythmia specialists for appropriateness of use. We analyzed data on all 200 instances in which the defibrillators were used between June 1, 1997, and July 15, 1999.

RESULTS

Automated external defibrillators were used for 200 patients (191 on the aircraft and 9 in the terminal), including 99 with documented loss of consciousness. Electrocardiographic data were available for 185 patients. The administration of shock was advised in all 14 patients who had electrocardiographically documented ventricular fibrillation, and no shock was advised in the remaining patients (sensitivity and specificity of the defibrillator in identifying ventricular fibrillation, 100 percent). The first shock successfully defibrillated the heart in 13 patients (defibrillation was withheld in 1 case at the family's request). The rate of survival to discharge from the hospital after shock with the automated external defibrillator was 40 percent. A total of 36 patients either died or were resuscitated after cardiac arrest. No complications arose from use of the automated external defibrillator as a monitor in conscious passengers.

CONCLUSIONS

The use of the automated external defibrillator aboard commercial aircraft is effective, with an excellent rate of survival to discharge from the hospital after conversion of ventricular fibrillation. There are not likely to be complications when the device is used as a monitor in the absence of ventricular fibrillation.

Circadian variation in witnessed out of hospital cardiac arrest

OBJECTIVES

To examine the effect on circadian variation of out of hospital cardiac arrest according to the underlying aetiology and presenting rhythm of arrest, and to explore strategies that might help to improve survival outcome using circadian variation.

DESIGN

Population based retrospective study.

SETTING

County of Nottinghamshire with a total population of 993 914 and an area of 2183 km(2).

SUBJECTS

Between 1 January 1991 and 3 December 1994, all witnessed cardiac arrests attended by the Nottinghamshire Ambulance Service, of which 1196 patients had a cardiac cause for their arrest (ICD, 9th revision, codes 390-414 and 420-429) and 339 had a non-cardiac cause.

RESULTS

The circadian variation of the cardiac cases was not significantly different from that of non-cardiac cases (p = 0.587), even when adjusted for age, sex, or presenting rhythm of arrest. For cardiac cases, the circadian variation of those who presented with ventricular fibrillation was significantly different from those presenting with a rhythm other than ventricular fibrillation (p = 0.005), but was similar to the circadian variation of bystander cardiopulmonary resuscitation (p = 0.306) and survivors (p = 0.542). Ambulance response time was also found to have a circadian variation.

CONCLUSIONS

There is a common circadian variation of out of hospital cardiac arrest, irrespective of underlying aetiology, where the presenting rhythm is other than ventricular fibrillation. This is different from the circadian variation of cases of cardiac aetiology presenting with ventricular fibrillation. The circadian variation of ventricular fibrillation, and consequently survival, may be affected by the availability of bystander cardiopulmonary resuscitation and the speed of ambulance response.