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PubMedDate not supplied

Automated external defibrillator (AED) utilization rates and reasons fire and police first responders did not apply AEDs.

OBJECTIVES: To determine the rate at which fire and police first responders (FRs) apply automated external defibrillators (AEDs) and to ascertain reasons for not applying them. METHODS: Twenty-one emergency medical services (EMS) systems whose FRs had been supplied with AEDs by a philanthropic foundation provided data for all out-of-hospital cardiac arrest (OHCA) patients. Data including the incidence of AED application and explanations for not applying AEDs were analyzed using descriptive statistics. RESULTS: A total of 2,456 OHCAs were reported. AED application information was available for 2,439 patients and revealed that FRs had not applied AEDs to 1,025 patients (42%). Fire FRs were more likely than police FRs to have applied AEDs (relative risk 1.87, 95% confidence interval 1.65-2.12). Reasons for not applying AEDs were listed for 664 (65%) of the OHCA patients to whom AEDs had not been applied. The predominant reason the FRs did not apply an AED was that the transporting ambulance defibrillator had already been applied (74%). However, when response times for FRs and the transporting ambulances were compared for these OHCA patients, it was found that the transporting ambulances arrived after the FRs 23% the time, simultaneously with the FRs 45% of the time, and before the FRs only 32% of the time. CONCLUSION: Fire and police FRs did not apply AEDs to a significant number of OHCA patients. Use of the transport ambulance defibrillator was the primary reason given for not applying the FR AED. Given low AED application rates by FRs, future studies are needed to determine the characteristics of communities in which equipping FRs with AEDs is the most beneficial deployment strategy, and how to increase AED application by FRs in communities with FR AED programs.

Adult↗
PubMedDate not supplied

Willingness of high school students to perform cardiopulmonary resuscitation and automated external defibrillation.

OBJECTIVE: To evaluate the willingness of high school students to perform cardiopulmonary resuscitation (CPR) and automated external defibrillation (AED). METHODS: A convenience sample of high school students was surveyed regarding how they would respond if they witnessed a cardiac arrest. Participants were first shown a video segment on the operation of an automated external defibrillator. They were then shown a series of video clips depicting six different cardiac arrest scenarios: motor vehicle collision (MVC) with facial bleeding, pediatric drowning, intravenous (IV) drug user, choking family member, victim of differing race, and victim with facial vomitus. Following each video, the subjects were asked how they would respond had they actually witnessed a similar event. RESULTS: With parental permission and institutional review board approval, 683 students participated, representing 6.8% of the total student body. Of these, 585 (86%) were trained in CPR and 142 (21%) in AED. One hundred six participants (16%) had witnessed a cardiac arrest prior to the survey. Of these, 24 (23%) had intervened in some way. Twenty (19%) had performed mouth-to-mouth resuscitation (MMR), 15 (14%) had performed chest compressions (CC), and one (0.9%) had performed AED. Across all six mock scenarios and all 683 respondents collectively (4,098 simulated cardiac arrest events), the respondents indicated they would be willing to perform AED 1,308 times (32%). In comparison, the respondents indicated they would be willing to perform MMR 1,768 times (43%) and CC 2,249 times (55%). More respondents were willing to intervene on behalf of a child or family member, while fewer were willing to act in the setting of blood, vomitus, or an IV drug user (p < 0.05). There was no association between willingness to intervene and prior experience with any of the interventions. Fear of infection, legal consequences, and fear of harming the patient were the most frequently cited reasons for not intervening. CONCLUSIONS: Among high school students, few are willing to perform automated external defibrillation. Willingness to perform MMR and CC appears to depend on the circumstances.

Adolescent↗
PubMedDate not supplied

Performance of police first responders in utilizing automated external defibrillation on victims of sudden cardiac arrest.

OBJECTIVE: Rates of resuscitation from cardiac arrest are directly tied to time to defibrillation. To maximize results, the first arriving care provider should be equipped and trained to defibrillate. This would include police in those systems where they serve this function; to date, no training program has been examined for effectiveness in this group. The purpose of this study was to evaluate a training program designed to train police first responders in the use of an automated external defibrillator (AED). METHODS: One hundred seventy police officers previously trained to the level of first responders underwent a four-hour course to teach incorporation of the AED in their practice. The evaluation of police performance was assessed by written tests prior to, immediately after, and six months post initial training. Actual field use was evaluated by using separate data collection forms filled out at the time of the resuscitation by both police and EMS providers. Each trip sheet was also reviewed. Cassette tapes from the AED were reviewed for continuous ECG tracings and audio recordings to validate and confirm the previous data. RESULTS: One hundred twenty-eight police cases were reviewed. The officers performed with few errors in AED operation, with the only problem areas being incorrect airway management and delay in performance of CPR to use the AED to reanalyze a nonshockable rhythm. These results were compared with those of the only two other studies examining the performance of first responders, which were EMTs and firefighters. The police results compared favorably with, and in some instances exceeded, those results. CONCLUSION: Police first responders trained in the use of AEDs performed at a level equivalent or superior to that in other reported studies. Future training strategies should stress proper integration of airway and CPR skills.

Automation↗
PubMed1987

Resuscitation-induced myocardial necrosis. Catecholamines and defibrillation.

Prolonged resuscitation in adults produces a recognizable pattern of myocardial injury characterized by contraction band necrosis, focal hemorrhage, and coagulation necrosis. To rule out the possibility of these changes being due to ischemia and underlying coronary artery disease, autopsies of 26 children admitted to Stanford from 1981 to 1983 were reviewed. Seventeen had attempted resuscitation with catecholamines and defibrillation; the remainder did not. Sections of myocardium were graded by two observers. For controls, brain-dead heart donors otherwise disease-free and essentially untreated with either defibrillation or beta-active catecholamines were used. Defibrillation alone and catecholamines alone each produced equal amounts of destruction, but using these together resulted in a statistically significant increase in tissue destruction. This suggests that the damaging effects of these agents are synergistic, not additive.

Adolescent↗
PubMed1992

Transcutaneous cardiac pacing in patients with automatic implantable cardioverter defibrillators and epicardial patch electrodes.

In patients with automatic implantable cardioverter defibrillators, insulation of the epicardial patch electrodes (patches) prevents externally applied current from passing through the electrode to the cardiac muscle so that external transthoracic and even internal defibrillation can be unsuccessful. Because emergency cardiac pacing may be required in such a case, a study was performed to evaluate whether, and at what threshold and electrode orientation, transcutaneous pacing is possible in patients with implanted patches. Thresholds for transcutaneous pacing were determined during general anesthesia in nine patients with patches sewn across the heart (anterior right and posterior left ventricles) either before or after surgery, or at both times (automatic implantable cardioverter defibrillator implantation/exchange with or without coronary artery bypass grafting). Because surgery per se can increase the pacing threshold, nine patients of similar body size and weight undergoing routine coronary artery bypass grafting also were evaluated and served as a control group. Pacing thresholds (stimulus duration: 50 ms) were determined during normothermia with a transportable transcutaneous pacer, and adult cutaneous electrodes were placed across the patients' chest in the standard anteroposterior and right-to-left orientations. In all patients with patch electrodes, antero-posterior pacing was possible at a mean threshold of 73 +/- 30 mA standard deviation (range: 40-140 mA). This threshold was not significantly different (Mann-Whitney test) from that in control patients before (57 +/- 20 mA; range: 30-90 mA) or after (94 +/- 24 mA; range: 40-120 mA) coronary artery-bypass grafting. The surgical procedure per se significantly increased the threshold (Wilcoxon test, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1989

Treatment of malignant ventricular arrhythmias with the automatic implantable cardioverter defibrillator.

Twenty-eight patients with malignant ventricular arrhythmias were treated with the automatic implantable cardioverter-defibrillator (AICD) in a 14-month period. Thirteen patients were resuscitated from a ventricular fibrillation (VF) episode. Fifteen patients presented with ventricular tachycardia (VT) refractory to medical therapy. The etiology was coronary artery disease in 23 of 28 patients (82%), dilated cardiomyopathy in 2 of 28 patients (7%), sarcoidosis in 2 of 28 patients, and 1 patient in 28 had lupus erythmatosis. The mean left ventricular ejection fraction was 29%. A total of 27 of 28 patients (96%) patients had inducible ventricular tachycardia using programmed stimulation. The patients considered for AICD implant failed a mean of 3.6 antiarrhythmic drugs. Rate counting and defibrillating leads were inserted through a lateral thoracotomy in 17 patients and a mediansternotomy incision in 11 patients in conjunction with another cardiac procedure in 10 patients. The generators were positioned in a subcutaneous pocket beneath the left costal margin. There were no operative deaths. The mean follow-up was 6.7 months (range 1 to 14) with no VT/VF deaths in patients with defibrillators. The study demonstrated that AICD is an effective device for prevention of sudden cardiac death.

Adult↗
PubMed2001

Update on external cardioversion and defibrillation.

External cardioversion is a technique used electively or emergently to terminate arrhythmias such as atrial fibrillation, ventricular tachycardia, and ventricular fibrillation. There have been several advances made to modern defibrillators, including an improvement in the efficacy of the delivered shock. Biphasic shock waveforms have been shown to be superior to monophasic shocks and these are being incorporated into modern units. This paper reviews several reports on biphasic defibrillation. In addition, initiatives to make defibrillators more accessible are also being tested. Although not a technological advance, this initiative may significantly improve the survival of victims of out of hospital cardiac arrests.

Arrhythmias, Cardiac↗
PubMed2000

Electrophysiology of ventricular fibrillation and defibrillation.

The survival rate from ventricular fibrillation is very high for short-duration fibrillation (<30 secs) but decreases to approximately 3% to 30% in out-of-hospital conditions. During short-duration fibrillation, action potentials occur rapidly with no intervening period of electrical diastole; a shock defibrillates by interacting with the fibrillation action potential to produce a uniformly long postshock extension of refractoriness. In contrast, during long-duration fibrillation, ischemia-induced degradation of cellular electrophysiology occurs, which causes intervening periods of electrical diastole between fibrillation action potentials and, thus, slowing of fibrillation frequency. A successful defibrillation shock must now not only prolong refractoriness when delivered during the action potential but must also excite cells during the periods of depolarized diastole. Biphasic waveforms enhance both effects by causing premature membrane repolarization with the first pulse, thereby allowing sodium channel recovery from inactivation so that the second pulse produces better-formed responses both during the cellular action potential and during the depolarized diastole. Therefore, biphasic waveforms remain superior to monophasic waveforms for treatment of long-duration fibrillation. Improved understanding of the ischemia-induced changes in cellular electrophysiology will suggest further improvements in both defibrillator waveforms and resuscitation techniques.

Animals↗
PubMed1990

A practical approach to teaching the automatic implantable cardioverter-defibrillator patient.

An implantable defibrillator is a surgically implanted device capable of continuously monitoring the patient's heart rhythm and automatically delivering a cardioverting or defibrillating shock to the heart. This article describes one approach to teaching the implanted defibrillator patient. Preoperative, postoperative, and discharge teaching goals and content are discussed. A case study illustrates the need for contact with the emergency medical system.

Arrhythmias, Cardiac↗
PubMed1995

Effect of isoproterenol on facilitation of electrical defibrillation by E-4031.

To determine whether isoproterenol could reverse enhancement of electrical defibrillation effectiveness by class III antiarrhythmic agents, we measured the internal defibrillation threshold (DFT) in 12 anesthetized dogs during infusion of (a) saline (baseline), (b) isoproterenol, (c) isoproterenol + E4031 (a new class III antiarrhythmic agent), and (d) E4031 alone. The isoproterenol infusion was adjusted so that heart rate (HR) was at least 30 beats/min greater than baseline. E4031 was given as a 40-micrograms/kg bolus at the beginning of the third stage of the study, followed by constant infusion at 2 micrograms/kg/min. Eight dogs completed the study. Although the energy-based DFT was not affected by isoproterenol (from 6.1 +/- 1.5 to 6.0 +/- 1.7 J), it was decreased to 3.7 +/- 1.6 J in the third stage by infusion of E4031 and isoproterenol (p < 0.01 vs. baseline and vs. isoproterenol). After the discontinuation of isoproterenol in the fourth stage, i.e., during infusion of E4031 alone, DFT was 3.4 +/- 1.6 J (p < 0.01 vs. baseline and vs. isoproterenol). Therefore, isoproterenol did not antagonize the effect of E4031 on the DFT, suggesting the possible clinical usefulness of class III agents for facilitating defibrillation even in the presence of augmented sympathetic activity.

Animals↗
PubMed1997

Hypertonic saline does not reverse the sodium channel blocking actions of lidocaine: evidence from electrophysiologic and defibrillation studies.

Studies have shown that increasing extracellular sodium concentration can partially reverse sodium channel blockade. However, there is conflicting in vitro evidence in this regard for lidocaine. The effects of lidocaine on cardiac electrophysiology and defibrillation were studied in a basal and hypernatremic state to determine reversibility of sodium channel blockade. Electrophysiologic studies measured right ventricular effective refractory period at 350 ms pacing cycle length and QRS interval, JT interval, and monophasic action potential duration during sinus rhythm and right ventricular pacing (350 ms cycle length) in 14 pentobarbital-anesthetized swine (25-30 kg). Defibrillation threshold (DFT) was measured by quantitating successful conversion of sustained ventricular fibrillation to normal sinus rhythm. Each pig was randomly assigned to a treatment group with three study phases; group 1 = baseline, lidocaine (20 mg/kg/h), and lidocaine plus placebo (D5W; n = 7); and group 2 = baseline, lidocaine, and lidocaine plus hypertonic saline (2-3 mM/kg/h; n = 7). In groups 1 and 2, lidocaine infused alone significantly (p < 0.01) increased DFT values from baseline (9.8 +/- 3.9 to 15.7 +/- 5.8 J and 8.9 +/- 2.9 to 14.7 +/- 5.4 J, respectively) and increased QRS duration from baseline during right ventricular pacing (89 +/- 6 to 109 +/- 10 ms; p < 0.01; and 87 +/- 6 to 103 +/- 12 ms; p < 0.01). Lidocaine alone reduced right ventricular action potential duration (APD) in groups 1 and 2 (214 +/- 18 to 206 +/- 20 ms; p < 0.10; and 228 +/- 8 to 212 +/- 8 ms; p < 0.05), respectively, and it reduced paced JT interval in both groups (194 +/- 20 to 184 +/- 18 ms; p < 0.10; and 200 +/- 12 to 183 +/- 16 ms; p < 0.05), respectively. When hypertonic saline was added to lidocaine, DFT and QRS duration values were unaffected (14.7 +/- 5.4 to 16.1 +/- 3.7 J and 103 +/- 12 to 100 +/- 11 ms, respectively). However, APD and JT intervals returned to basal values when hypertonic saline was added to lidocaine (212 +/- 8 to 225 +/- 13; p < 0.05; and 183 +/- 16 to 192 +/- 18; p < 0.05, respectively). When D5W was added in the control group, no changes occurred in DFT or electrophysiologic values. Lidocaine slowed ventricular conduction velocity and reduced APD. The administration of hypertonic saline to increase extracellular sodium concentrations failed to reverse the effect of lidocaine on conduction-velocity slowing or elevated DFT values. Hypertonic saline did reverse the effects of lidocaine on repolarization parameters. These data suggest that shortening of repolarization is not a mechanism by which lidocaine makes it more difficult to defibrillate the heart.

Action Potentials↗
PubMed2006

Difficulty of cardiac arrest rhythm identification does not correlate with length of chest compression pause before defibrillation.

OBJECTIVE: Performing high-quality cardiopulmonary resuscitation immediately before electrical defibrillation serves as an important predictor of shock success. Long preshock pauses in cardiopulmonary resuscitation frequently occur, as noted by recent clinical investigations. We sought to determine whether these long pauses were due to difficulties in identifying shockable rhythms or rather due to local factors during resuscitation attempts. DESIGN: Prospective in-hospital study of cardiac arrest resuscitation attempts coupled with a retrospective review of preshock pause rhythms by 12 trained providers. Reviewers scored rhythms by ease of identification using a discrete Likert scale from 1 (most difficult to identify) to 5 (easiest to identify). The resuscitation cohort was organized into preshock pause-duration quartiles for statistical analysis. Resident physicians were then surveyed regarding human factors affecting preshock pauses. RESULTS: A total of 118 preshock pauses from 45 resuscitation episodes were collected. When evaluated by quartiles of preshock pause duration, difficulty of rhythm identification did not correlate with increasing pause time. In fact, the opposite was found (longest preshock pause quartile of 23.8-60.2 secs vs. shortest pause quartile of 1.1-7.9 secs; rhythm difficulty scores, 3.2 vs. 3.0; p = .20). When 29 resident physicians who recently served on resuscitation teams were surveyed, 18 of 29 (62.1%) attributed long pauses to lack of time sense during resuscitation, and 16 of 29 (55.2%) thought that room crowding prevented rapid defibrillation. CONCLUSIONS: Long cardiopulmonary resuscitation pauses before defibrillation are likely due to human factors during the resuscitation and not due to inherent difficulties with rhythm identification. This preliminary work highlights the need for more research and training in the area of team performance and human factors during resuscitation.

Cardiopulmonary Resuscitation↗
PubMed2004

Waveforms for defibrillation and cardioversion: recent experimental and clinical studies.

PURPOSE OF REVIEW: The advent of biphasic waveforms for external defibrillation has generated extensive experimental and clinical investigation. At the same time, it has led to the development and clinical use of biphasic waveforms of several different designs. Finally, other types of waveforms, primarily triphasic, have entered experimental evaluation. RECENT FINDINGS: There is virtually universal agreement that biphasic waveforms, regardless of design, have greater efficacy in defibrillation of ventricular fibrillation and in cardioversion of atrial fibrillation when compared with monophasic waveforms. It remains unresolved, however, whether any specific biphasic waveform has greater clinical superiority than others. Likewise, it remains to be demonstrated whether any biphasic waveform is less injurious to myocardial function than another and whether injury, if it is incurred, is secondary to peak delivered current or to delivered energy. Biphasic truncated exponential waveforms are used by most manufacturers, whereas a rectilinear biphasic waveform and a pulsed waveform also are being used clinically. SUMMARY: Biphasic waveforms have supplanted monophasic waveforms for defibrillation and cardioversion. They include biphasic truncated exponential, rectilinear, and pulsed biphasic versions. At this time, there is no certain evidence of clinical superiority of one waveform over another in terms of either efficacy or myocardial injury.

Arrhythmias, Cardiac↗
PubMed1994

Refractory period prolongation by biphasic defibrillator waveforms is associated with enhanced sodium current in a computer model of the ventricular action potential.

Mechanisms through which biphasic waveforms lower defibrillation threshold are unknown. Previous work showed that low-intensity biphasic shocks (BS2), delivered during the refractory period of a control action potential (S1), produced significantly longer responses than monophasic shocks (MS2). To test the hypothesis that longer responses are due to hyperpolarization-induced excitation channel recovery during the first portion of the biphasic waveform, we used the Beeler-Reuter ventricular action potential computer model with the Drouhard-Roberge (BRDR) modification to study refractory period stimulation with MS2 (10 msec) and symmetrical BS2 (10 msec each pulse). At 1.5 times diastolic threshold, BS2 prolonged action potential duration when delivered 50 msec into the S1 refractory period, and produced a maximum BS2 versus MS2 response duration difference of 62 msec. Longer BS2 responses corresponded to enhanced BS2-induced sodium current compared to MS2. Maximum BS2 vs MS2 sodium current difference was 400 uA/cm2. These results show that, in a computer model of the ventricular action potential, hyperpolarization by the first phase of a biphasic waveform enhances S2 sodium current and prolongs duration of refractory-period responses. This effectively shortens the cellular refractory period. Prolonged refractory period responses, produced by biphasic defibrillator waveforms, may underlie enhanced defibrillating efficacy at low shock intensities.

Action Potentials↗
PubMed1995

Computational studies of transthoracic and transvenous defibrillation in a detailed 3-D human thorax model.

A method for constructing and solving detailed patient-specific 3-D finite element models of the human thorax is presented for use in defibrillation studies. The method utilizes the patient's own X-ray CT scan and a simplified meshing scheme to quickly and efficiently generate a model typically composed of approximately 400,000 elements. A parameter sensitivity study on one human thorax model to examine the effects of variation in assigned tissue resistivity values, level of anatomical detail included in the model, and number of CT slices used to produce the model is presented. Of the seven tissue types examined, the average left ventricular (LV) myocardial voltage gradient was most sensitive to the values of myocardial and blood resistivity. Incorrectly simplifying the model, for example modeling the heart as a homogeneous structure by ignoring the blood in the chambers, caused the average LV myocardial voltage gradient to increase by 12%. The sensitivity of the model to variations in electrode size and position was also examined. Small changes (< 2.0 cm) in electrode position caused average LV myocardial voltage gradient values to increase by up to 12%. We conclude that patient-specific 3-D finite element modeling of human thoracic electric fields is feasible and may reduce the empiric approach to insertion of implantable defibrillators and improve transthoracic defibrillation techniques.

Computer Simulation↗
PubMed1999

Analysis of defibrillation efficacy from myocardial voltage gradients with finite element modeling.

Increasing defibrillation efficacy by lowering the defibrillation threshold (DFT) is an important goal in positioning implantable cardioverter-defibrillator electrodes. Clinically, the DFT is difficult to estimate noninvasively. It has been suggested that the DFT relates to the myocardial voltage gradient distribution, but this relation has not been quantitatively demonstrated. We analyzed the relation between the experimentally measured DFT's and the simulated myocardial voltage gradients provided by finite element modeling. We performed a series of experiments in 11 pigs to measure the DFT's, and created and solved three-dimensional subject-specific finite element models to assess the correlation between the computed myocardial voltage gradient histograms and the DFT's. Our data show a statistically significant correlation between the DFT and the left ventricular voltage gradient distribution, with the septal region being more significant (correlation coefficient of 0.74) than other myocardial regions. The correlation between the DFT and the right ventricular and the atrial voltage gradient, on the other hand, is not significant.

Animals↗
PubMed2003

Measurement of thoracic current flow in pigs for the study of defibrillation and cardioversion.

Although defibrillation has been in clinical use for more than 50 years, the complete current flow distribution inside the body during a defibrillation procedure has never been directly measured. This is due to the lack of appropriate imaging technology to noninvasively monitor the current flow inside the body. The current density imaging (CDI) technique, using a magnetic resonance (MR) imager, provides a new approach to this problem [Scott et al. (1991)]. CDI measures the local magnetic field generated by the current and calculates the current density by computing its curl. In this study, CDI was used to measure current density at all points within a postmortem pig torso during an electrical current application through defibrillation electrodes. Furthermore, current flow information was visualized along the chest wall and within the chest cavity using streamline analysis. As expected, some of the highest current densities were observed in the chest wall. However, current density distribution varied significantly from one region to another, possibly reflecting underlying heterogeneous tissue conductivity and anisotropy. Moreover, the current flow analysis revealed many complex and unexpected current flow patterns that have never been observed before. This study has, for the first time, noninvasively measured the volume current measurement inside the pig torso.

Animals↗
PubMed1978

Reprogramming of implanted pacemaker following external defibrillation.

This report describes reprogramming of a pulse generator consequent to cardiac defibrillation. Analysis of the explanted pulse generator revealed normal function. We tested the electrical properties of several defibrillators and our studies suggest that erratic electrostatic discharges at the time of paddle application before defibrillation may create a signal sequence capable of reprogramming the particular pulse generator by activating either the reed switch or internal electronics.

Electric Countershock↗