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

Functional Outcomes: One Year after a Cardiac Arrest

Objective. The study aim was to characterize the time-course of recovery in impairments, activity limitations, participation restrictions, disability, and quality of life during the first year after cardiac arrest. Secondarily, the study described the associations between the instruments used to measure each of these domains. Methods. Measures of global disability (Cerebral Performance Category, CPC, Modified Rankin Scale, mRS), quality of life, activity limitations, participation restrictions, and affective and cognitive impairments were administered to 29 participants 1, 6, and 12 months after cardiac arrest. Results. Global measures of disability indicated recovery between one month and one year after cardiac arrest (mean CPC: 2.1 versus 1.69,  P < 0.05; mean mRS: 2.55 versus 1.83, P < 0.05). While global measures of disability were moderately associated with participation, they were poorly associated with other measures. The cohort endorsed depressive symptomatology throughout the year but did not have detectable cognitive impairment. Conclusions. Recovery from cardiac arrest is multifaceted and recovery continues for months depending upon the measures being used. Measures of global disability, reintegration into the community, and quality of life yield different information. Future clinical trials should include a combination of measures to yield the most complete representation of recovery after cardiac arrest.

An algorithm used for ventricular fibrillation detection without interrupting chest compression

Ventricular fibrillation (VF) is the primary arrhythmic event in the majority of patients suffering from sudden cardiac arrest. Attention has been focused on this particular rhythm since it is recognized that prompt therapy, especially electrical defibrillation, may lead to a successful outcome. However, current versions of automated external defibrillators (AEDs) mandate repetitive interruptions of chest compression for rhythm analyses since artifacts produced by chest compression during cardiopulmonary resuscitation (CPR) preclude reliable electrocardiographic (ECG) rhythm analysis. Yet, repetitive interruptions in chest compression are detrimental to the success of defibrillation. The capability for rhythm analysis without requiring "hands-off" intervals will allow for more effective resuscitation. In this paper, a novel continuous-wavelet-transformation-based morphology consistency evaluation algorithm was developed for the detection of disorganized VF from organized sinus rhythm (SR) without interrupting the ongoing chest compression. The performance of this method was evaluated on both uncorrupted and corrupted ECG signals recorded from AEDs obtained from out-of-hospital victims of cardiac arrest. A total of 232 patients and 31,092 episodes of either VF or SR were accessed, in which 8195 episodes were corrupted by artifacts produced by chest compressions. We also compared the performance of this method with three other established algorithms, including VF filter, spectrum analysis, and complexity measurement. Even though there was a modest decrease in specificity and accuracy when chest compression artifact was present, the performance of this method was still superior to other reported methods for VF detection during uninterrupted CPR.

In a swine model, chest compressions cause ventricular capture and, by means of a long-short sequence, ventricular fibrillation

BACKGROUND

During resuscitation, fibrillation often recurs. In swine, we studied refibrillation after long-duration ventricular fibrillation, investigating an association with chest compressions (CCs).

METHODS AND RESULTS

In protocol A, 47 episodes of long-duration ventricular fibrillation lasting at least 2.5 minutes were induced in 8 animals. After defibrillation, CCs were required for 35 episodes and delivered with a pneumatic device (Lucas cardiopulmonary resuscitation). In 9 episodes, refibrillation occurred within 2 seconds of CC initiation (group 1) and in 26 episodes, CCs were delivered without refibrillation (group 2). From the ECG and intracardiac electrodes, the RR interval preceding CCs, the shortest cycle length during the first 2 CCs (short), and the preceding cycle length (long) were measured. A similar study was conducted in 3 more animals without intracardiac catheters (protocol B). In protocol A, the mean RR before CC was 665+/-292 ms in group 1 and 769+/-316 in group 2. CCs stimulated ventricular beats in all 35 episodes. The short and long intervals were shorter in group 1 (215+/-31 and 552+/-210 ms) than in group 2 (402+/-153 and 699+/-147 ms) (P=0.009 and P=0.04, respectively). The prematurity index (short/RR) was lower in group 1 than in group 2 (0.35+/-0.09 vs 0.58+/-0.21; P<0.01). A short interval <231 ms predicted refibrillation with 88% sensitivity and 91% specificity. In protocol B, CCs were required in 11 episodes, causing ventricular stimulation in all of them and ventricular fibrillation within the first 2 CCs in 3.

CONCLUSIONS

Under some conditions, CC during resuscitation can stimulate the ventricles and initiate ventricular fibrillation by a long-short sequence.

Electrocardiogram waveforms for monitoring effectiveness of chest compression during cardiopulmonary resuscitation

BACKGROUND

Newer guidelines address the importance of effective chest compressions, citing evidence that this primary intervention is usually suboptimally performed during cardiopulmonary resuscitation. We therefore sought a readily available option for monitoring the effectiveness of chest compressions, specifically using the electrocardiogram.

METHODS AND RESULTS

Ventricular fibrillation was induced by coronary artery occlusion and untreated for 5 mins. Male domestic pigs weighing 40 +/- 2 kg were randomized to optimal or suboptimal chest compressions after onset of ventricular fibrillation. Optimal depth of mechanical compression in six animals was defined as a decrease of 25% in anterior posterior diameter of the chest during compression. Suboptimal compression, also in six animals, was defined as a decrease of 17.5% in anterior posterior diameter. For each group, the chest compressions were maintained at a rate of 100 per min. After 3 mins of chest compression, defibrillation was attempted with a 150-J biphasic shock. All animals had return of spontaneous circulation after optimal compressions. This contrasted with suboptimal compressions, after which none of the animals had return of spontaneous circulation. Amplitude spectrum area values, representing the electrocardiographic amplitude frequency spectral area computed from conventional precordial leads, like coronary perfusion pressure and end tidal PCO2, were predictive of outcomes.

CONCLUSION

The effectiveness of chest compressions was reflected in the amplitude spectrum area values. Accordingly, the amplitude spectrum area predictor may be incorporated in current automated external defibrillators to monitor and prompt the effectiveness of chest compression during cardiopulmonary resuscitation.

Automated detection of ventricular fibrillation to guide cardiopulmonary resuscitation

Sudden death due to ventricular fibrillation (VF) is a catastrophic event, especially in out-of-hospital settings. Prompt detection of VF and preparedness to intervene with cardiopulmonary resuscitation (CPR) and especially the delivery of an electrical shock is potentially lifesaving. The reliability and accuracy of automated VF detection by current versions of automated external defibrillators (AEDs) require interruption of CPR because the ECG signal, which is the source of rhythm detection, is corrupted by chest compressions. Significantly better outcomes have been reported if effective chest compression precedes electrical defibrillation and especially if interruptions are minimized. We therefore sought a method by which VF detection could proceed without interrupting chest compressions. A VF detection algorithm was therefore derived based on a method by which continuous wavelet transform is used, together with measurement of morphologic consistency. This method was intended to distinguish between disorganized and organized rhythms. The Fourier-transform-based amplitude spectrum analysis was then used to detect the likelihood that VF was the rhythm prompting the delivery of an electrical shock. The algorithm was validated on 33,095 electrocardiographic segments, including 8840 segments corrupted by compression artifacts from 232 patients after out-of-hospital cardiac arrest. Nine thousand one hundred eighty-seven of 10,042 VF segments and 20,884 of 23,053 non-VF segments were correctly classified, with a sensitivity of 91.5% and a specificity of 90.6%. Although the proposed algorithm has a lesser predictive value for VF detection than the uncorrupted ECGs in clinical settings, it has the major potential for automated rhythm identification to guide defibrillation without repetitive interruptions of CPR.

Long-term survival after successful inhospital cardiac arrest resuscitation

BACKGROUND

Little is known about long-term outcomes of patients who survive inhospital cardiac arrest.

METHODS

We examined long-term survival after inhospital cardiac arrest and whether procedural changes that improved survival to discharge impacted long-term survival. Consecutive inhospital arrests in the Atlanta Veterans Affairs Medical Center (Atlanta, GA) from 1995 to 2004 (n = 732) were retrospectively analyzed. Data regarding the arrest was obtained, including age, left ventricular ejection fraction, medications, and comorbidities, presenting rhythm, location of arrest, code duration, and outcomes. Long-term mortality data was obtained based on chart and Social Security Death Index reviews. Further data was gathered on internal cardioverter-defibrillator presence and use in survivors.

RESULTS

Overall, 49 subjects (6.6%) survived to discharge. Univariate analysis found that ventricular tachycardia/ventricular fibrillation and the use of beta-blockers, angiotensin-converting enzyme inhibitors, and antiarrhythmics at the time of arrest were associated with increased survival, whereas advancing age and comorbidities were associated with a higher risk of mortality. Multivariate analysis determined that age, rhythm, and comorbidities independently affected survival. Implementation of a resuscitation program previously documented to improve survival to discharge did not translate to durable long-term survival. Three-year survival rate after discharge was only 41%. Alternatively, subjects with internal cardioverter-defibrillator showed a 36% improvement in 3-year survival rate to 77% (P = .001).

CONCLUSIONS

Subjects with inhospital cardiac arrest have poor long-term prognoses. A strategy that improved inhospital survival did not alter long-term mortality rate. Thus, survival to discharge may not be a sufficient end point for future resuscitation trials.

[First responder defibrillation in the USA, Europe and Germany--prerequisites, experiences, perspectives]

Sudden out-of-hospital cardiac arrest is a leading cause of death and only 5-8% of patients survive such event. Defibrillation is the mose effective treatment and should performed within 5 minutes; however, its effectiveness diminishes with each passing minute. "Early defibrillation" is the use of automated external defibrillators (AEDs) by trained public-safety personnal ("first responder"), whereas "public access" defibrillation describes AED use by persons who have no specific AED training. Several studies in the US and in Europe show that first responder defibrillation will increase the number of survivors of out-of-hospital cardiac arrest compared to paramedics. This is caused by a shorter "call-to-arrival-time" in first responders compared to paramedics. In Europe, programs for the use of automated external defibrillators exist only occasionally. Reasons for this are the lack of open-mindedness, logistic and legal problems. In Germany, there are only few AED programs with promising results. At the present time, placement of automated external defibrillators in public places frequented by a large number of susceptible people will increase overall survival. However, placement of AEDs in all public places is still debatable and further studies are necessary to estimate the potential impact of publicc access defibrillators.

Evolution of a community-wide early defibrillation programme

BACKGROUND

In November 1990, a 2-year trial period was initiated in which police officers in the city of Rochester, Minnesota, were trained in the operation of automated external defibrillators (AEDs). Following the trial, the program was expanded as the city grew in population and area. In 1998 firefighters also were equipped with AEDs, bringing to a total 18 AEDs with police and fire personnel, in addition to paramedic capability.

METHODS

From November 1990 to December 2003, all adult patients with atraumatic cardiac arrest with ventricular fibrillation (VF) as the presenting rhythm were included for analysis. Call-to-shock time intervals, restoration of spontaneous circulation after defibrillation shocks only (without need for vasoactive or inotropic drug administration), and neurologically intact survival (overall performance category (OPC) 1 or 2) were study end-points.

RESULTS

One hundred and ninety-three patients presented in VF. Of these, 80 (41%) were discharged neurologically intact. Of the 159 VF patients whose arrest was bystander-witnessed 73 (46%) were discharged. Survival from non-VF arrest was very low (5%). Assessment of VF survivors demonstrated a quality of life, adjusted for age, gender, and disease, similar to that of the general population.

CONCLUSIONS

These data demonstrate that a relatively high survival can be obtained in a city of this size and area employing a non-tiered community-wide approach within the emergency medical services (EMS) system.

Outcomes after ventricular fibrillation out-of-hospital cardiac arrest: expanding the chain of survival

Coronary heart disease is the most common cause of death in the United States, with ventricular fibrillation (VF) the most common initial rhythm when cardiac disease causes arrest. Survival after VF out-of-hospital cardiac arrest (OHCA) depends on a sequence of events called the chain of survival, which Includes rapid access to emergency medical services, cardiopulmonary resuscitation, defibrillation, and advanced care. Because of widespread implementation of defibrillation programs, more patients survive VF OHCAs, making subsequent care of these patients important. Early hospitalization must focus on potential neurologic injury and therapy targeted at the underlying cardiac disease and antiarrhythmic therapy for long-term secondary prevention of sudden death. Attention to certain cohorts who are at high risk despite their underlying disease, such as women and elderly patients, is necessary. These cohorts may have the greatest response to short-term and long-term therapies for cardiac rehabilitation. With these approaches, long-term survival and quality of life after VF OHCA are favorable. Broadening the focus of the chain of survival to include in-hospital and long-term care will further improve favorable outcomes achieved in an early defibrillation program.

Sex differences in outcome after ventricular fibrillation in out-of-hospital cardiac arrest

INTRODUCTION

Previous studies have shown that early defibrillation programs improve survival after an out-of-hospital cardiac arrest (OHCA). Reports also suggest that women fare worse than men do after cardiovascular events, but there is no population-based study of sex differences after an OHCA with early defibrillation. We, therefore, compared the short- and long-term survival and quality-of-life (QOL) in women and men after an OHCA.

METHODS

All patients with a ventricular fibrillation (VF) OHCA who received early defibrillation in Olmstead County, Minnesota between November 1990 and December 2000 were included. Using medical records and the cardiac arrest database, the short- and long-term survival and QOL based on a SF-36 survey of each sex were compared. Adjusted QOL scores were obtained by using age- and sex-specific norms from a sample of the general U.S. population; an adjusted score of 50 (normalized mean) was considered normal.

RESULTS

Thirty-seven female and 163 male patients presented with a VF OHCA and early defibrillation. Survival to hospital admission was significantly better for women than men [30 female survivors to admission (81%), 112 male (69%), p = 0.04]. Paradoxically, survival to discharge among those admitted was worse for women [13 female survivors to discharge (43%), 66 male (61%), p = 0.04]. The average length of follow-up was 4.8+/-3.0 years. The 5-year expected survival was 83% in women and 78% in men (p = 0.48). There was no difference in call-to-shock time (6+/-2, 6+/-2 min, p = 0.6) or whether the arrest was witnessed (86, 82%, p = 0.64). There was no statistical difference between women and men in age (64+/-17, 65+/-14 years), ejection fraction (40+/-17, 40+/-18%), diabetes (17, 29%, p = 0.16), hypertension (23, 28%, p = 0.58) or known CAD (27, 48%, p = 0.06). Adjusted QOL scores were similar between women and men in terms of pain (52+/-9, 52+/-10) vitality (47+/-11, 40+/-9), general health (49+/-9, 44+/-7), social function (51+/-10, 51+/-8), and mental health (50+/-10, 49+/-6).

CONCLUSION

Women are more likely to survive to hospital admission following an OHCA. However, admitted women less likely to survive their hospital stay. Long-term survival and QOL are equally favorable in both sexes.

Safety aspects for public access defibrillation using automated external defibrillators near high-voltage power lines

BACKGROUND

Automated external defibrillators (AEDs) must combine easy operability and high-quality diagnosis even under unfavorable conditions. This study determined the influence of electromagnetic interference caused by high-voltage power lines with 16.7-Hz alternating current on the quality of AEDs' rhythm analysis.

METHODS

Two AEDs frequently used in Austria were tested near high-voltage power lines (15 kV or 110 kV, alternating current with 16.7 Hz). The defibrillation electrodes were attached either to a proband with true sinus rhythm or to a resuscitation dummy with generated sinus rhythm, ventricular fibrillation, ventricular tachycardia or asystole.

RESULTS

Electromagnetic interference was much more prominent in a human's than in a dummy's electrocardiogram and depended on the position of the electrodes and cables in relation to the power line. Near high-voltage power lines the AEDs showed a significant operational fault. One AED interpreted the interference as a motion artifact, even when underlying rhythms were clearly detectable. The other AED interpreted 16.7-Hz oscillation as ventricular fibrillation with consequent shock advice when no underlying rhythm was detected.

CONCLUSION

The tested AEDs neither filter nor recognize a technical interference of 16.7 Hz caused by 15-kV power lines above railway tracks or 110-kV overland power lines, as run by railway companies in Austria, Germany, Norway, Sweden and Switzerland. These failures in AEDs' algorithms for rhythm analysis may cause substantial harm to patients undergoing public access defibrillation. The proper function of AEDs needs to be reconsidered to guarantee patients' safety near high-voltage power lines.

Impact of age on long-term survival and quality of life following out-of-hospital cardiac arrest*

OBJECTIVE

Early defibrillation programs have improved long-term outcomes following out-of-hospital cardiac arrest from ventricular fibrillation. Although long-term collective quality of life and survival are favorable, there are subsets of these patients who may be predisposed to worse outcomes. In particular, elderly patients may present with more comorbid medical conditions affecting their outcome. However, the impact of age on mortality rate and quality of life after rapid defibrillation is unknown.

DESIGN

Observational study.

SETTING

Hospital.

SUBJECTS

All patients with an out-of-hospital cardiac arrest between November 1990 and January 2001 who received rapid defibrillation for ventricular fibrillation in Olmsted County, Minnesota. All patients received treatment at one hospital.

INTERVENTIONS

Long-term outcome and quality of life were followed. Survival was estimated using the Kaplan-Meier method. The quality of life was established by an SF-36 survey.

MEASUREMENTS AND MAIN RESULTS

Two hundred patients presented in ventricular fibrillation out-of-hospital cardiac arrest; of these, 138 (69%) survived to hospital admission, seven (4%) died in the emergency department, and 79 (39%) were discharged neurologically intact. The average age was 62+/-16 yrs, with 51% (n = 40) of the population > or =65. The average length of follow-up was 4.8+/-3.0 yrs. The 5-yr survival in patients <65 was 94% (confidence interval, 86-100%) and 66% (confidence interval, 52-84%) in patients > or =65 (p <.001). The observed survival in the younger group was not different from that expected in a U.S. age- and gender-matched population. However, in the older group, the expected survival was significantly lower compared with an age- and gender-matched U.S. population (p =.01) but similar to an age-, gender-, and disease-matched cohort of patients from Olmsted County not experiencing an arrest. In both age-dependent cohort populations, the quality of life scores crossed the norm in all categories with exception of vitality in patients >65 yrs old (42.6+/-7.2). In direct comparison between the two patient groups, the older cohort reported lower levels of physical functioning (p =.002), role-emotional score (p =.03), and role-physical score (p =.007). Other SF-36 scores were not different between the groups. Sixty-five percent of patients <65 yrs returned to work compared with 56% of older patients.

CONCLUSIONS

The survival rate for ventricular fibrillation out-of-hospital cardiac arrest is significantly improved by the presence of a rapid defibrillation program. In patients <65 yrs old, long-term survival is equal to that of normal individuals and quality of life is similar to the general population. The survival, although high, in older patients is less than that in age-matched healthy controls, and physical and emotional quality of life scores are decreased.

[Transthoracic defibrillation. Physiologic and pathophysiologic principles and their role in the outcome of resuscitation]

As one major link in the chain of survival, early transthoracic (external) cardiac defibrillation is aimed at the termination of ventricular flutter and ventricular fibrillation. Most important to the success of defibrillation is the passage of a defined amount of current through a critical mass of heart muscle. Different transthoracic resistances reduce the effective density of the current within the heart. As for other therapeutic intervention procedures, recommendations for the optimal strength of current to be applied to the fibrillating heart need to be evaluated and defined for therapeutical defibrillation too. Unnecessarily high current density causes damage to the heart and should be prevented. By using biphasic waveforms in contrast to monophasic impulses, the amount of current can be reduced but the same or even higher efficacy is attained. Therefore possible myocardial damage might be clearly reduced. Even with individually altered thoracic impedance effective conversion of cardiac rhythm can be achieved by device-controlled compensation and biphasic waveforms. According to their different mechanisms or origin (electrically induced or spontaneously caused by organic heart disease) the probability of successful conversion of the cardiac rhythm by one single electrical impulse varies. The optimum point in time for defibrillation during resuscitation needs to be redefined. In order to improve comparability, further studies should use standardized definitions for successful defibrillation relating to the resulting cardiac rhythm.

Long-term subjective memory function in ventricular fibrillation out-of-hospital cardiac arrest survivors resuscitated by early defibrillation

BACKGROUND

Brain injury after a cardiac arrest remains a major cause of morbidity. Programs focusing on early defibrillation have yielded improved survival of patients after hospital discharge following ventricular fibrillation (VF) out-of-hospital cardiac arrest (OHCA). Early defibrillation that promptly restores a circulating rhythm should decrease the hypoxic period and subsequent organ injury. Therefore this study was designed to determine if long-term memory complaints persist in VF OHCA survivors resuscitated in an early defibrillation program when compared with a healthy control population not experiencing cardiac arrest.

METHODS

All patients with an OHCA between November 1990 and January 2001 who received defibrillation by emergency medical services personnel in Olmsted County, MN, USA, were included. The memory function questionnaire (MFQ), a 64-item, 7-point Likert-scaled instrument to evaluate the perception of everyday memory functioning was sent to all survivors. The MFQ comprises four scales: general frequency of forgetting (rates general forgetting), retrospective functioning (compares current memory with past ability), seriousness of forgetting (rates how memory impairment impacts daily life), and mnemonics usage (measures adaptation). The MFQ is scaled so that high scores reflect less severe memory complaints. The comparison population comprised members of the Mayo Older Americans Normative Studies (MOANS) cohort. Quality of life was ascertained with a short form (SF)-36 survey.

RESULTS

Seventy-nine of the 200 VF OHCA patients (40%) were discharged. Twenty-two patients have died since dismissal, with an overall average length of follow-up of 4.9+/-3.0 years. Thirty-eight (67%) of the survivors completed the MFQ. Compared with the normal, there was a significant decrease in the general frequency of forgetting score of 144.2+/-37.4 versus 168.1+/-27.3 ( P<0.001) and the seriousness of forgetting score of 84.8 +/-26.7 versus 95.2+/-19.7 (P=0.004). The retrospective function-scale scores were not significantly different ( 18.4+/-6.8 versus 18.7+/- 5.0 (P=0.74). Younger patients (lesser than 65 years of age) reported an increase in general forgetting and the seriousness of forgetting compared with older survivors. A comparison with SF-36 scores suggested an association between general forgetting and decreased vitality (P=0.03) and the seriousness of forgetting with a decreased general health (P=0.005), mental health (P=0.009), physical functioning ( P=0.02 ), and vitality ( P=0.05).

CONCLUSION

In a cohort of VF OHCA patients, survivors report more memory complaints in comparison with a general healthy older population. There were more long-term-memory complaints in younger patients. Patients with higher long-term quality-of-life score have fewer memory complaints.

Long-term outcomes of out-of-hospital cardiac arrest after successful early defibrillation

BACKGROUND

Mortality after out-of-hospital cardiac arrest from ventricular fibrillation is high. Programs focusing on early defibrillation have improved the rate of survival to hospital discharge. We conducted a population-based analysis of the long-term outcome and quality of life of survivors.

METHODS

All patients who had an out-of-hospital cardiac arrest between November 1990 and January 2001 who received early defibrillation for ventricular fibrillation in Olmsted County, Minnesota, were included. The survival rate was compared with that of an age-, sex-, and disease-matched (2:1) control population of residents who had not had an out-of-hospital cardiac arrest and with that of age- and sex-matched controls from the general U.S. population. The quality of life was assessed with use of the Medical Outcomes Study 36-item Short-Form General Health Survey (SF-36) and compared with U.S. population norms.

RESULTS

Of 200 patients who presented with an out-of-hospital cardiac arrest with ventricular fibrillation, 145 (72 percent) survived to hospital admission (7 died in the emergency department) and 79 (40 percent) were neurologically intact (good overall capability or moderate overall disability) at discharge. The mean (+/-SD) length of follow-up was 4.8+/-3.0 years. Nineteen patients died after discharge from the hospital. The expected five-year survival rate (79 percent) was identical to that among age-, sex-, and disease-matched controls (P=0.68) but lower than that among the age- and sex-matched U.S. population (86 percent, P=0.02). Fifty patients completed SF-36 surveys at the end of follow-up, and the majority had a nearly normal quality of life, with the exception of reduced vitality.

CONCLUSIONS

Long-term survival among patients who have undergone rapid defibrillation after out-of-hospital cardiac arrest is similar to that among age-, sex-, and disease-matched patients who did not have out-of-hospital cardiac arrest. The quality of life among the majority of survivors is similar to that of the general population.

Automated external defibrillation in cardiac surgery

Revision open heart surgery may be impeded by a dense network of pericardial adhesions rendering cardiac mobilization laborious or incomplete, and internal defibrillation impossible. External defibrillation, the current alternative to internal defibrillation, may result in myocardial stunning secondary to the delivery of escalating, monophasic, high-energy shocks. Automated external defibrillation, by delivering consecutive, non-escalating, impedance-compensated, low-energy, biphasic electric shocks to the myocardium, may provide a more effective and safer option whilst reducing the risk of myocardial stunning.

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.

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.

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.