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PubMedDate not supplied

Impact of prompt defibrillation on cardiac arrest at a major international airport.

OBJECTIVE: To describe the impact of a rapidly deployable, automated external defibrillator (AED)-equipped first-responder service at Boston's Logan International Airport on the rate of survival to hospital discharge after cardiac arrest. METHODS: A prospective observational outcome study was undertaken for cardiac arrests taking place on the airport grounds from January 1, 1995, to December 31, 1999. Patients were included if they were unresponsive, they had no palpable pulse and no spontaneous respirations, an AED was turned on, and the cardiac arrest took place on airport grounds. Airport fire rescue and emergency medical services (EMS) personnel submitted resuscitation records and AED memory modules for each cardiac arrest. Each author independently reviewed all cardiac arrest reports and code summaries to ensure accuracy and data integrity. Relevant dispatch and response times were determined from airport fire rescue and EMS dispatch records. Patient outcome was determined from hospital patient records. Descriptive statistics were calculated. RESULTS: The airport fire rescue crew responded to 53 cardiac arrests. Of those, 38 met inclusion criteria. In 36 of 38 cases (94.7%), the airport fire rescue crew was first to apply the defibrillator, and the first to deliver a shock in 28 of 32 cases (87.5%) where a shock was delivered. The median response time for the airport fire rescue crew was 2 minutes, with a mode of 1 minute. The EMS response times were 5:29 (95% CI 4:37-6:19) for basic life support crews and 8:07 (95% CI 7:17-8:57) for advanced life support crews. All patients who survived to hospital admission (n = 15) and hospital discharge (n = 8) received their first shock by the airport fire rescue crew. Eight patients (21.1%) survived to hospital discharge. In five of the eight survivors to hospital discharge, defibrillation by the airport crew alone achieved a return of spontaneous circulation. CONCLUSIONS: A rapidly deployable first-responder service permits early defibrillation minutes before arrival of EMS personnel. This rapid response positively impacts the return of spontaneous circulation and survival to hospital discharge after cardiac arrest.

Aged↗
PubMedDate not supplied

Automated external defibrillators appropriately recognize ventricular fibrillation in electromagnetic fields.

OBJECTIVES: Automated external defibrillators (AEDs) are increasingly available in industrial settings, but many industries have high electromagnetic fields (EMFs), which can interfere with the function of electronic devices. This study evaluated the performance of several AEDs when exposed to high EMFs. METHODS: Three commercially available AEDs were evaluated in the setting of a public utility coal-fired electrical generation plant. Each AED was placed in three areas of high EMF ranging from 310 to 1,600 milligauss. A signal generator, used to simulate various cardiac rhythms, was connected to the AEDs. Rhythms simulated were ventricular fibrillation, asystole, and normal sinus rhythm. Each of the AED's interpretations of various rhythms were evaluated in the different EMF settings. RESULTS: Rhythms of ventricular fibrillation, asystole, and normal sinus rhythm were correctly recognized by each AED in each of the three areas of high EMF. Each AED appropriately recommended defibrillation when presented with ventricular fibrillation. No misinterpretations or inappropriate defibrillations were observed. CONCLUSION: Electromagnetic fields generated by an electrical power plant did not interfere with three commercial AEDs' abilities to correctly interpret simulated rhythms and recommend appropriate defibrillation.

Cardiopulmonary Resuscitation↗
PubMedDate not supplied

The safe use of automated external defibrillators in a wet environment.

UNLABELLED: There has been concern regarding potential shock hazards for rescuers or bystanders when a defibrillator is used in a wet environment and the recommended safety procedure, moving the patient to a dry area, is not followed. OBJECTIVE: To measure the electrical potentials associated with the use of an automated external defibrillator (AED) in a realistically modeled wet environment. METHODS: A raw processed turkey was used as a patient surrogate. The turkey was placed on a cement floor while pool water was applied to the surrounding area. To simulate a rescuer or bystander in the vicinity of a patient, a custom sense probe was constructed. Defibrillation shocks were delivered to the turkey and the probe was used to measure the voltage an operator/bystander would receive at different points surrounding the surrogate. The test was repeated with salt water. RESULTS: The maximum voltage occurred approximately 15 cm from the simulated patient and measured 14 V peak (current 14 mA peak) in the case of pool water, and 30 V peak (current 30 mA peak) in the case of salt water. CONCLUSIONS: Thirty volts may result in some minor sensation by the operator or bystander, but is considered unlikely to be hazardous under these circumstances. The maximum currents were lower than allowed by safety standards. Although defibrillation in a wet environment is not recommended practice, our simulation of a patient and a rescuer/bystander in a wet environment did not show significant risk should circumstances demand it.

Animals↗
PubMedDate not supplied

Biphasic truncated exponential waveform defibrillation.

This paper presents data from studies that have compared the efficacies of biphasic truncated exponential (BTE) and monophasic damped sine (MDS) waveform defibrillation in patients with out-of-hospital cardiac arrest and in in-hospital defibrillation. When a shock is delivered, rhythms evolve rapidly in a variety of directions and take different courses, even over a short time. When defibrillation is defined as termination of ventricular fibrillation at 5 seconds postshock, whether to an organized rhythm or asystole, low-energy BTE shocks appear to be more effective than high-energy MDS shocks in out-of-hospital arrest. For future research, the terms associated with defibrillation should be standardized and used uniformly by all investi-gators. In particular, there should be an agreed-upon definition of shock efficacy.

Adolescent↗
PubMed1992

Should semi-automatic defibrillators be used by emergency medical technicians in Belgium? The Belgian Cerebral Resuscitation Study Group.

Early external defibrillation is the single most effective intervention in patients with out-of-hospital cardiac arrest. Literature data indicate that instructing emergency medical technicians (EMTs) to use defibrillators is beneficial, provided the local emergency medical system is well organized. We tried to estimate the potential benefit of early defibrillation in some centres in Belgium by retrospectively analyzing the data from the Belgian Cardio-Pulmonary-Cerebral Resuscitation Registry collected between 1983 and 1987 in Belgian centres with a Mobile Intensive Care Unit (MICU). The data show that 2310 out of 3371 patients (69%) were first attended by the EMTs; on subsequent arrival of the MICU-teams, 584 of these 2310 patients i.e. 17% of the whole study population, presented with ventricular fibrillation. Analysis of estimated time factors in these 2310 patients revealed that the median time interval between collapse and start of resuscitation by EMTs was 8 min; the median time interval between collapse and start of MICU-resuscitation attempts was 16 min. The duration of EMT-resuscitation before MICU-arrival was probably more than 5 min and 10 min in 58% and 23% of the cases respectively. It is concluded that EMTs can be expected to reach a substantial number of ventricular fibrillation victims within a few minutes after the collapse and many minutes before arrival of the MICU. Therefore, training of EMTs in the use of semi-automatic defibrillators seems worthwhile in MICU-served regions in Belgium.

Belgium↗
PubMed1987

Effects of early defibrillation of out-of-hospital cardiac arrest patients by ambulance personnel.

During the year of this study, the specially trained ambulance personnel initiated cardiopulmonary resuscitation in 307 out of hospital cardiac arrest patients. All arrests, regardless of aetiology, age or other circumstances, were studied. The mean age for the arrest patients was 66 years. The majority of arrests occurred in elderly patients at home. Although as many as 70% of the arrests were witnessed, cardiopulmonary resuscitation had been initiated in only 15% of patients before the arrival of the ambulance. One hundred and forty patients had rapid ventricular tachycardia or ventricular fibrillation when the ambulance arrived (mean delay of 7.8 +/- 3.7 min). The effects of defibrillation could be fully evaluated in 135 patients. QRS complexes, with a rate between 20 and 110 min-1, were seen after defibrillation in 94 patients, persistent asystole in 26 patients and persistent ventricular fibrillation, despite one or more 360 J DC shocks, in 15 patients. Nineteen of the 94 patients who had a return of QRS complexes also had a return of pulse shortly after defibrillation without further advanced life support measures, while another six patients had a return of pulse after further life support therapy. Six of the 32 ventricular fibrillation patients (19%) reached within 4 min and three of the 63 ventricular fibrillation patients (5%) reached between 4-8 min survived. An estimated 4.2 lives per 100,000 inhabitants a year were saved when early defibrillation was used as the only addition to the basic life support provided by the present ambulance service.

Adolescent↗
PubMed2001

Public access defibrillation: a shocking idea?

Currently, survival from out-of-hospital cardiac arrest in the United Kingdom is poor. Ambulance response standards require that an ambulance reach 75 per cent of cardiac arrests within 8 min. But a short time to defibrillation from the onset of collapse is a key predictor of outcome from out-of-hospital cardiac arrest. The Department of Health has recently implemented a lay responder defibrillation programme, with the aim of shortening this time interval for victims in public places. This initiative utilizes automated external defibrillators (AEDs), which provide written and recorded voice prompts to minimize training requirements and errors in use. Lay responder AED programmes with very short response times have reported survival to discharge rates of up to 53 per cent for patients presenting in ventricular fibrillation (VF). This compares well with the results of a meta-analysis that reported a survival rate of only 6.4 per cent for traditional defibrillator-equipped ambulance systems. The annual incidence of out-of-hospital cardiac arrest in England is 123 per 100,000 population. Approximately half of these present in VF, and could benefit from an AED programme. But only 16 per cent of cardiac arrests occur in a public place. It has been calculated that there are approximately 5,000 instances of VF in public places each year in England. If half of these patients can be reached and administered a first shock within 4 min of their collapse, an additional 400 victims may survive each year. Given the current investment by the DoH of 2 million pounds, this suggests a cost per life saved of approximately 505 pounds over a 10 year period.

Community Participation↗
PubMedDate not supplied

Influence of pH and hypoxia on the success of defibrillation.

Clinical impressions about the problem of defibrillation during states of acid-base imbalance and hypoxia have been influenced by studies involving the effect of these derangements on the ventricular fibrillation threshold. Based on body weight, energy requirements for defibrillation in normal dogs were compared to requirements in dogs subjected to commonly encountered acid-base disturbances and severe hypoxemia. No significant differences were found. Seventy-five percent of all animals in the study were electrically converted with low-to-moderate levels of energy. The incidence of spontaneous resumption of circulation following defibrillation was lowest in animals subjected to metabolic acidosis and hypoxia. The results suggest that pH and blood gas alterations, previously shown to influence the normal ventricular fibrillation threshold, do not significantly affect the normal defibrillation threshold.

Acid-Base Imbalance↗
PubMed1983

Efficacy and safety of defibrillation with rectangular waves of 2- to 20-milliseconds duration.

The effect of suprathreshold defibrillator shocks on cardiac function was compared in 8 isolated, perfused, contracting canine hearts using 4 durations of rectangular electrical waveforms. Defibrillation threshold was first determined for each duration; then overdose shocks of 3, 4.5, 6, and 9 times threshold current density were delivered. Left ventricular isovolumic systolic pressure decreased immediately after the shocks in proportion to the overdose shock strength. The mean defibrillation current density thresholds for the 2-, 5-, 10-, and 20-msec durations were 101, 63, 47, and 39 mA/cm2, respectively. The corresponding energy density thresholds were 4.6, 3.5, 4.4, and 6.4 mJ/cm3, respectively. The safety factor for defibrillation was defined as the current overdose ratio (delivered current density/threshold current density) required to produce a 50% decrease in isovolumic systolic pressure immediately after the shock. This dose was determined by interpolation of the curve for depression versus overdose of shock strength. The mean current safety factors for the 2-, 5-, 10-, and 20-msec durations were 3.9, 5.1, 5.4, and 5.2, respectively. The corresponding mean energy safety factors were 15, 25, 28, and 27. The margin of safety for functional depression of the heart was significantly less (p less than 0.05) for the 2 msec rectangular wave then for the 5-, 10-, and 20-msec rectangular waves.

Animals↗
PubMed2002

Expanding automatic external defibrillators to include automated detection of cardiac, respiratory, and cardiorespiratory arrest.

The new Guidelines of the American Heart Association state that lay rescuers can no longer rely on the manual pulse check to confirm cardiac arrest in an unresponsive patient. We were therefore prompted to develop a method for automated determination of the presence or absence of cardiac contraction and breathing. The technique was designed to be incorporated into conventional automated external defibrillators and to work in conjunction with the information derived from rhythm analyses by the automated defibrillator. Using conventional electrocardiographic sensing and defibrillation electrodes, the transthoracic impedance was measured by passing a constant amplitude alternating current of 5 mA through the thorax at a frequency of 35 kHz. In five anesthetized male domestic swine, we observed pulses that were coincident with cardiac contraction documented by esophageal echocardiography. In addition, we observed larger signals of lower frequency that were time related to ventilation and documented by capnography. Both signals disappeared after inducing ventricular fibrillation. The impedance measurement identified respiratory arrest in anesthetized animals and primary cardiac arrest after ventricular fibrillation was induced. The cardiac arrest detector is therefore likely to augment the current information provided by automated defibrillators and to allow for more precise verbal prompting of lay rescuers.

Animals↗
PubMed1996

A more effective approach to in-hospital defibrillation.

Survival rates from in-hospital cardiac arrests are low and have not improved since the 1960s. Increased emphasis on early defibrillation has significantly improved prehospital survival rates in recent years, but the organization of resuscitation efforts in hospitals has not changed. Nurses throughout the hospital should be trained and authorized to defibrillate on their own initiative, using defibrillators that are already close at hand. The basic procedure is not difficult, and an aggressive protocol using blind defibrillation could further simplify training and maximize survival. Working together, nurses can overcome psychologic and emotional barriers to these changes and improve their patients' odds of survival.

Electric Countershock↗
PubMed1992

Defibrillation energy requirements during moricizine and moricizine-lidocaine therapy.

Defibrillation energy requirements may be altered by antiarrhythmic agents. We investigated the effects of moricizine on the defibrillation threshold (DFT) in 18 pentobarbital-anesthetized pigs. The animals were randomized, in a blinded fashion, to moricizine or control (0.9% saline) treatment groups. Each group underwent three treatment phases: baseline, drug infusion (moricizine or saline), and drug infusion combined with lidocaine. Moricizine (2 mg/kg loading dose, 1.5 mg/kg/h infusion) and lidocaine (5 mg/kg loading dose, 4 mg/kg/h infusion) were dosed to achieve therapeutic concentrations. After 5 s of induced ventricular fibrillation, defibrillation was performed using a cardiac defibrillator interfaced with two epicardial electrode patches. DFTs were determined at baseline, during the drug phase, and during the combination of lidocaine with moricizine or saline. DFT values in the animals randomized to the control group were 15.2 +/- 4.2, 14.0 +/- 3.3, and 17.8 +/- 8.7 J at baseline, saline infusion, and saline combined with lidocaine, respectively. No significant differences were observed among the treatment phases. DFT values in the animals randomized to moricizine group were 12.1 +/- 2.8, 13.8 +/- 5.2, and 22.9 +/- 7.1 J at baseline, moricizine infusion, and moricizine combined with lidocaine, respectively. The DFT values during the lidocaine-moricizine combination treatment phase were significantly greater than baseline and moricizine alone (p < 0.002). The mean change in the DFT from baseline to moricizine (14% increase) was significantly different than the mean change in the DFT from baseline to saline (8% decrease) (p = 0.03). Lidocaine added to moricizine increased the DFT by 84%, which was significantly different from the 27% increase in the DFT when lidocaine was added to saline (p = 0.02). We conclude that moricizine minimally increases the DFT, but the combination of moricizine with lidocaine results in a synergistic rise in the DFT that may have detrimental clinical implications.

Animals↗
PubMed2005

Future shock: automatic external defibrillators.

PURPOSE OF REVIEW: This review provides a practical overview of the performance capabilities of automatic external defibrillators (AEDs), and of advances in technology and dissemination programmes for these devices. RECENT FINDINGS: Arrhythmia analysis by AEDs is extremely reliable in most settings (sensitivity 81-100%, specificity 99.9-97.6%). Accurate detection of arrhythmias has also been demonstrated in children, leading the US Food and Drug Administration to approve the use of several AEDs in children aged 8 years or younger. Factors that potentially may reduce the quality of arrhythmia detection are the presence of wide complex supraventricular tachycardia and location of an arrythmic event near to high-power lines. AED use by professional basic life support providers resulted in increased survival in the prehospital setting. However, provision of AEDs to nonmedical rescue services did not result in universal improvement in patient outcome. Public access defibrillation programmes have led to higher rates of survival from cardiac arrest. The role of AEDs in hospitals has yet to be elucidated, although in-hospital mortality from ventricular arrhythmias has been shown to decrease following AED deployment. SUMMARY: Given the correct setting, AEDs can ensure that defibrillation is not limited by lack of medical knowledge or difficulties in decision making. However, event-related variables and operator-related factors, that are yet to be determined, can significantly affect the efficacy of automatic external defibrillation.

Journal Article↗
PubMed1993

Effects of paddle placement and size on defibrillation current distribution: a three-dimensional finite element model.

A realistic three-dimensional finite element model of the conductive anatomy of a canine thorax was constructed for use in the study of transthoracic electrical defibrillation. The model was constructed from a series of 21 cross-sectional CT scans of a 14.5 kg beagle, each separated by 0.82 cm. The electrical conductive properties of 8 distinct tissues were incorporated, including the anisotropic properties of skeletal muscle. Current density distributions were obtained for six paddle pairings and two paddle sizes. A quantitative basis for comparing the resulting distributions was formulated. Our results suggest that placing one or both of the paddles near the heart delivers a higher fraction of current to the heart. However, such paddle placements also produce a less uniform myocardial current density distribution and thus have a higher potential for causing damage. We found that some paddle positions can produce myocardial current densities close to the threshold for damage in successful defibrillations. Results obtained for 8 and 12 cm paddles indicate that 12 cm paddles may offer modest advantages over 8 cm paddles in clinical defibrillation. Comparison of our results to available in vivo experimental data confirm the validity of the finite element method for examining continuum field variables pertinent to electrical defibrillation.

Animals↗
PubMed1995

Optimization of cardiac defibrillation by three-dimensional finite element modeling of the human thorax.

The goal of this study was to determine the optimal electrode placement and size to minimize myocardial damage during defibrillation while rendering refractory a critical mass of cardiac tissue of 100%. For this purpose, we developed a 3-D finite element model with 55,388 nodes, 50,913 hexahedral elements, and simulated 16 different organs and tissues, as well as the properties of the electrolyte. The model used a nonuniform mesh with an average spatial resolution of 0.8 cm in all three dimensions. To validate this model, we measured the voltage across 3-cm2 Ag-AgCl electrodes when currents of 5 mA at 50 kHz were injected into a human subject's thorax through the same electrodes. For the same electrode placements and sizes and the same injected current, the finite element analysis produced results in good agreement with the experimental data. For the optimization of defibrillation, we tested 12 different electrode placements and seven different electrode sizes. The finite element analyses showed that the anterior-posterior electrode placement and an electrode size of about 90 cm2 offered the least chance of potential myocardial damage and required a shock energy of less than 350 J for 5-ms defibrillation pulses to achieve 100% critical mass. For comparison, the average cross-sectional area of the heart is approximately 48 cm2, about half of the optimal area. A second best electrode placement was with the defibrillation electrodes on the midaxillary lines under the armpits. Although this placement had higher chances of producing cardiac damage, it required less shock energy to achieve 100% critical mass.

Computer Simulation↗
PubMed1995

A three-dimensional finite element model of human transthoracic defibrillation: paddle placement and size.

A detailed 3-D finite element model of the conductive anatomy of the human thorax has been constructed to quantitatively assess the current density distribution produced in the heart and thorax during transthoracic defibrillation. The model is based on a series of cross-sectional CT scans and incorporates isotropic conductivities for eight tissues and an approximation of the anisotropic conductivity of skeletal muscle. Current density distributions were determined and compared for four paddle pairs and two paddle sizes. Our results show that the myocardial current density distributions resulting from a defibrillation shock were fairly uniform for the paddle pairs and sizes examined in this study. Specific details of the spatial distribution of the current density magnitudes in the heart were found to depend on paddle placement and size. When the minimum current necessary to defibrillate was delivered, the maximum myocardial current density produced with any of the paddle sizes and positions examined was less than four times the minimum current density necessary to render a myocyte in a fibrillating heart inexcitable, and less than 40% of the damage threshold. These results suggest that common clinically used defibrillation paddle positions have a safety margin as large as 2.5 for current and approximately 6 for energy.

Adult↗
PubMed1999

Anode/cathode make and break phenomena in a model of defibrillation.

The goal of this simulation study is to examine, in a sheet of myocardium, the contribution of anode and cathode break phenomena in terminating a spiral wave reentry by the defibrillation shock. The tissue is represented as a homogeneous bidomain with unequal anisotropy ratios. Two case studies are presented in this article: tissue that can electroporate at high levels of transmembrane potential, and model tissue that does not support electroporation. In both cases, the spiral wave is initiated via cross-field stimulation of the bidomain sheet. The extracellular defibrillation shock is delivered via two small electrodes located at opposite tissue boundaries. Modifications in the active membrane kinetics enable the delivery of high-strength defibrillation shocks. Numerical solutions are obtained using an efficient semi-implicit predictor-corrector scheme that allows one to execute the simulations within reasonable time. The simulation results demonstrate that anode and/or cathode break excitations contribute significantly to the activity during and after the shock. For a successful defibrillation shock, the virtual electrodes and the break excitations restrict the spiral wave and render the tissue refractory so it cannot further maintain the reentry. The results also indicate that electroporation alters the anode/cathode break phenomena, the major impact being on the timing of the cathode-break excitations. Thus, electroporation results in different patterns of transmembrane potential distribution after the shock. This difference in patterns may or may not result in change of the outcome of the shock.

Action Potentials↗
PubMed2001

Frequency domain algorithm for quantifying atrial fibrillation organization to increase defibrillation efficacy.

We hypothesized that frequency domain analysis of an interatrial atrial fibrillation (AF) electrogram would show a correlation of the variance of the signal and the amplitude of harmonic peaks with the periodicity and morphology (organization) of the AF signal and defibrillation efficacy. We sought to develop an algorithm that would provide a high-resolution measurement of the changes in the spatiotemporal organization of AF. AF was initiated with burst atrial pacing in ten dogs. The atrial defibrillation threshold (ADFT50) was determined, and defibrillation was repeated at the ADFT50. Bipolar electrograms from the shocking electrodes were acquired immediately preshock, digitally filtered, and a FFT was performed. The organization index (OI) was calculated as the ratio of the area under the first four harmonic peaks to the total area of the spectrum. For a 4-s window, the mean OI was 0.505 +/- 0.087 for successful shocks, versus 0.352 +/- 0.068 for unsuccessful shocks (p < 0.001). Receiver operator characteristic (ROC) curve analysis was used to determine the optimal sampling window for predicting successful shocks. The area of the ROC curve was 0.8 for a 1-s window, and improved to 0.9 for a 4-s window. We conclude that the spectrum of an AF signal contains information relating to its organization, and can be used in predicting a successful defibrillation.

Algorithms↗