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PubMed2003

Defibrillation causes immediate cardiac dilation in humans.

UNLABELLED: Defibrillation Causes Dilation. INTRODUCTION: Prior studies in isolated heart tissue have shown both excitation and deexcitation to be the primary mechanism of defibrillation. This article presents the first evidence in man of deexcitation immediately following defibrillation by tracking the heart's mechanical response. METHODS AND RESULTS: The geometric changes of the ventricular chambers were measured before and after defibrillation in seven human subjects receiving an implantable cardioverter defibrillator (ICD). The ICD was used to produce approximately three episodes of ventricular fibrillation and defibrillation in each subject. Twenty-two two-dimensional echocardiographic images of the right ventricle (RV) and 11 images of the left ventricle (LV) were recorded and analyzed at 30 frames per second. Just over 2 seconds of each episode were digitized, beginning half a second before the defibrillation shock. Individual frames were analyzed to yield cross-sectional, ventricular chamber area as a function of time. Immediately following defibrillation, ventricular chambers dilated with significant fractional area increase (RV: 1.58 +/- 0.25, LV: 1.10 +/- 0.06), with peak dilation at 194 +/- 114 msec. CONCLUSION: Defibrillation causes a rapid increase in ventricular chamber area due to relaxation of the myocardium, suggesting that defibrillation synchronizes the cardiac cells to the deexcited state in man.

Aged↗
PubMed1994

Advances in implantable cardioverter-defibrillator therapy.

The use of implantable defibrillation systems in patients with cardiac arrest has resulted in lower mortality than expected from studies of similar patients not receiving defibrillators. Nonthoracotomy lead systems have led to a decrease in operative mortality and lowered the cost of defibrillator implantation, but these systems have a higher energy requirement for defibrillation than do epicardial ones. The recent introduction of single-lead systems and bipolar defibrillation pulses has simplified nonthoracotomy defibrillator implantation and improved defibrillation efficiency. A prototype unipolar, single-lead pectoral implant defibrillation system is described that may significantly improve the reliability, safety, and cost effectiveness of nonthoracotomy defibrillators. This and other improved nonthoracotomy systems may expand the indications for defibrillator implantation to prophylactic use in high-risk patients who have not yet experienced life-threatening ventricular arrhythmias.

Defibrillators, Implantable↗
PubMed1996

Relative efficacy of different tilts with biphasic defibrillation in humans.

OBJECTIVE: The goal of this study was to assess if tilt bears any impact on defibrillation efficacy of biphasic shocks. BACKGROUND: Although it has been shown that biphasic waveform may increase the defibrillation efficacy, this pulsing method has not been as extensively studied in patients, and information regarding the effect of different tilts is lacking. METHODS: This study consisted of two similar but distinct protocols including 33 patients undergoing transvenous defibrillator implant. In 17 patients (Part I) defibrillation threshold was obtained delivering biphasic waveforms with 50%, 65%, and 80% tilt in random fashion. Similarly, in 16 patients (Part II) testing of biphasic waveform with 40%, 50%, and 65% tilt was performed in random order. The electrode system used consisted of two transvenous leads and a subcutaneous patch in all 33 patients. RESULTS: In Part I, tilt of 50% demonstrated a defibrillation threshold significantly lower than 65% tilt (7.5 +/- 4.3 J vs 9.7 +/- 5.0 J; P = 0.04) and 80% tilt (7.5 +/- 4.3 J vs 11.7 +/- 5.9 J; P < 0.01). Similarly, 65% tilt provided a lower defibrillation threshold than 80% tilt (9.7 +/- 5.0 J vs 11.7 +/- 5.9 J; P = 0.02). In Part II, no significant difference was observed in terms of defibrillation threshold between 40% tilt and the two tilts of 50% and 65%. However, as in Part I, 50% tilt provided a significant reduction of the energy to defibrillate as compared to 65% tilt (6.3 +/- 3.6 J vs 9.0 +/- 4.8 J; P < 0.01). The 50% tilt resulted in better defibrillation efficacy than 65% tilt independent of the lead system used for testing (Medtronic Transvene and CPI Endotak-C). CONCLUSIONS: Biphasic shocks with 50% tilt required less energy for defibrillation than 40%, 65%, and 80% tilts. However, in the clinical setting a programmable tilt may be preferable to account for some patient-to-patient variability.

Adult↗
PubMed1997

The effect of electrode size on transvenous defibrillation energy requirements: a prospective evaluation.

Recent technological advances have resulted in high success rates for implantation of nonthoracotomy defibrillation lead systems. Further decreases in defibrillator size, facilitating pectoral placement, will depend in part on lowering defibrillation energy requirements. The purpose of this study was to determine if endocardial defibrillation energy requirements are influenced by electrode size. Thirteen adult mongrel dogs were studied under general anesthesia. A 9 Fr integrated bipolar pace/sense/defibrillation electrode (cathode) was positioned transvenously at the RV apex. The second defibrillation electrode (anode) was positioned at the junction of the RA and SVC. Two diameters of the proximal electrode, 7 Fr and 11 Fr, were sequentially tested in random order in each animal. The DFT for each electrode was determined using a 50-V up-down method. Energy, leading edge voltage, and current, current distribution, and total resistance were measured. The mean defibrillation voltage threshold with the 11 Fr proximal electrode was significantly less than with the 7 Fr proximal electrode (551.1 +/- 76.5 V vs 588.5 +/- 54.6 V, P < 0.01). Similarly, the mean DFT with the 11 Fr electrode was less than with the 7 Fr electrode (20.7 +/- 5.7 J vs 23.3 +/- 4.4 J, P < 0.01). Lower DFTs were found using the larger electrode in 11 of the 13 animals studied. However, there was no difference in defibrillation lead impedance between the two electrode systems. Endocardial defibrillation energy requirements may be lowered with a larger diameter proximal electrode. The mechanism by which this occurs may be due to a more even distribution of current gradients with the larger electrode. Determination of the optimal electrode size requires evaluation in humans, as this may allow further reduction in defibrillation energy requirements and defibrillator size.

Animals↗
PubMed1997

Simulated internal defibrillation in humans using an anatomically realistic three-dimensional finite element model of the thorax.

INTRODUCTION: Determination of the optimal electrode configuration during implantable cardioverter defibrillator (ICD) implantation remains largely an empirical process. This study investigated the feasibility of using a finite element model of the thorax to predict clinical defibrillation metrics for internal defibrillation in humans. Computed defibrillation metrics from simulations of three common electrode configurations with a monophasic waveform were compared to pooled metrics for similar electrode and waveform configurations reported in humans. METHODS AND RESULTS: A three-dimensional finite element model was constructed from CT cross-sections of a human thorax. Myocardial current density distributions for three electrode configurations (epicardial patches, right ventricular [RV] coil/superior vena cava [SVC] coil, RV coil/SVC coil/subcutaneous patch) and a truncated monophasic pulse with a 65% tilt were simulated. Assuming an inexcitability threshold of 25 mA/cm2 (10 V/cm) and a 75% critical mass criterion for successful defibrillation, defibrillation metrics (interelectrode impedance, defibrillation threshold current, voltage, and energy) were calculated for each electrode simulation. Values of these metrics were within 1 SD of sample-size weighted means for the corresponding metrics determined for similar electrode configurations and waveforms reported in human clinical studies. Simulated myocardial current density distributions suggest that variations in current distribution and uniformity partially explain differences in defibrillation energy requirements between electrode configurations. CONCLUSION: Anatomically realistic three-dimensional finite element modeling can closely simulate internal defibrillation in humans. This may prove useful for characterizing patient-specific factors that influence clinically relevant properties of current density distributions and defibrillation energy requirements of various ICD electrode configurations.

Adult↗
PubMed1993

Influence of implantable cardioverter-defibrillators on the long-term prognosis of survivors of out-of-hospital cardiac arrest.

BACKGROUND: Survivors of out-of-hospital cardiac arrest not associated with acute myocardial infarction are at high risk for recurrent cardiac arrest and sudden cardiac death. The impact of the implantable cardioverter-defibrillator on long-term prognosis in these patients is uncertain. METHODS AND RESULTS: Three hundred thirty-one survivors of out-of-hospital cardiac arrest (age, 56 +/- 13.7 years) underwent electrophysiologically guided therapy. Implantable defibrillators were placed in 150 patients (45.3%), and 181 patients (54.7%) received pharmacological and/or surgical therapy alone. Left ventricular ejection fraction was 35.2 +/- 16.6% in defibrillator recipients and 45.3 +/- 18.2% in nondefibrillator patients. Median patient follow-up was 24 months in the defibrillator group and 46 months in the nondefibrillator group. In a proportional hazards model, the independent predictors of total cardiac mortality were left ventricular ejection fraction of less than 0.40 (relative risk, 4.55; 95% confidence interval, 2.44 to 8.33; P = .0001), absence of an implantable defibrillator (relative risk, 2.70; confidence interval, 1.41 to 5.00; P = .017), and persistence of inducible sustained ventricular tachycardia (relative risk, 1.84; 95% confidence interval, 0.97 to 3.49; P = .045). The 1- and 5-year probabilities of survival free of cardiac mortality in patients with left ventricular ejection fraction of less than 0.40 were 94.3% and 69.6% with a defibrillator and 82.1% and 45.3% without a defibrillator, respectively. For patients with left ventricular ejection fraction of 0.40 or more, the 1- and 5-year probabilities of survival free of cardiac mortality were 97.7% and 94.6% with a defibrillator and 95.4% and 86.9% without a defibrillator, respectively. CONCLUSIONS: In survivors of out-of-hospital cardiac arrest, the implantable defibrillator is associated with a reduction in cardiac mortality, particularly in patients with impaired left ventricular function.

Anti-Arrhythmia Agents↗
PubMed1994

Upper limit of vulnerability reliably predicts the defibrillation threshold in humans.

BACKGROUND: The upper limit of vulnerability is the stimulus strength above which electrical stimulation cannot induce ventricular fibrillation even when the stimulus occurs during the vulnerable period of the cardiac cycle. The purpose of this study was to test the hypothesis that the upper limit of vulnerability can accurately predict the defibrillation threshold in patients undergoing implantable cardioverter-defibrillator (ICD) implantation using nonthoracotomy lead systems. METHODS AND RESULTS: We studied 77 patients at the time of ICD implantation. Multiple endocardial-endocardial and endocardial-subcutaneous shock pathways were used. Two different protocols were used to test the upper limit of vulnerability. In protocol 1 (n = 17), the upper limit of vulnerability was tested with two shocks on the peak or the up-slope of the T wave of paced rhythm. The shocks were given randomly either at the peak and 20 milliseconds before the peak of T wave (n = 7) or at 20 and 40 milliseconds before the peak of T wave (n = 10). In protocol 2 (n = 60), the upper limit of vulnerability was tested with three shocks delivered at 0, 20, and 40 milliseconds before the peak of the T wave. The weakest shock that failed to induce ventricular fibrillation by a 5-J step-down or step-up method was defined as the upper limit of vulnerability. The defibrillation threshold was also determined by a 5-J step-down or step-up method. In protocol 1, the upper limit of vulnerability (9 +/- 6 J) was significantly lower than the defibrillation threshold (13 +/- 7 J) with a correlation coefficient of .87 and P < .001. In protocol 2, the upper limit of vulnerability (13 +/- 6 J) was not significantly different from the defibrillation threshold (13 +/- 6 J) with a correlation coefficient of .85 and P < .001. In 45 of the 60 patients, the upper limit of vulnerability was < or = 15 J; all had a defibrillation threshold of < or = 20 J. In 51 of the 60 patients, the upper limit of vulnerability was within 5 J of the defibrillation threshold. The upper limit of vulnerability overestimated the defibrillation threshold by > 10 J in 8 patients and underestimated the defibrillation threshold by > 10 J in only 1 patient. The overestimation and underestimation occurred only in patients with the upper limit of vulnerability > 15 J. CONCLUSIONS: When tested with three shocks on and before the peak of the T wave, the upper limit of vulnerability accurately predicted the defibrillation threshold in patients undergoing ICD implantation using nonthoracotomy lead systems. This method required either one or no episodes of ventricular fibrillation in most patients.

Aged↗
PubMed2000

[Atrial defibrillator].

Atrial fibrillation (AF) is a frequent and costly health care problem representing the most common arrhythmia resulting in hospital admission. Total mortality and cardiovascular mortality are significantly increased in patients with AF compared to controls. In addition to symptoms of palpitations, patients with AF have an increased risk of stroke and may also develop decreased exercise tolerance and left ventricular dysfunction. All of these problems may be reversed with restoration and maintenance of sinus rhythm. External electrical cardioversion has been a remarkably effective and safe method for termination of this arrhythmia. Originally described by Lown et al. in 1963, it has been a well accepted mode of acute therapy. However, this technique requires general anesthesia or heavy sedation. Internal atrial defibrillation has been evaluated as an alternative approach to the external technique for over 2 decades. Recent studies have shown that low-energy internal atrial defibrillation using biphasic shocks is an effective and safe means in restoring sinus rhythm in patients with AF and should be considered especially in patients in whom external cardioversion attempts have failed. Implantable Atrial Defibrillator: Recently, a stand alone IAD, the Metrix System (models 3000 and 3020), has entered clinical investigation. Atrial defibrillation is accomplished by a shock delivered between electrodes in the right atrium and the coronary sinus. The right atrium lead has an active fixation in the right atrium. The coronary sinus lead has a natural spiral configuration for retention in the coronary sinus, and can be straightened with a stylet. Both leads are 7 French in diameter and the defibrillation coils are each 6 cm in length. The electrodes may be placed using separate leads, or very soon by using a single bipolar lead. A separate bipolar right ventricular lead is used for R wave synchronization and post shock pacing. The Metrix defibrillator can be used to induce AF by using R wave synchronous shocks and can store intracardiac electrograms (EGMs) for up to 2 minutes from the most recent 6 AF episodes. The device can be programmed into one of the following operating modes: fully automatic, patient activated, monitor mode, bradycardia pacing only, and off. As AF is not life-threatening, in the automatic mode the device is only intermittently active in detecting and treating AF, and this "sleep wake-up" cycle interval is programmable. The device employs extensive processing both for detection and R wave synchronization. In April 1996, the phase I Metrix multicenter clinical trial was started. As of May 1997, a total of 51 Metrix systems had been implanted as part of the phase I multicenter clinical trial. Preliminary data suggest that both defibrillation thresholds and electrograms are stable over time (implant to 3 months). Detection accuracy has been excellent (100% specificity, 92.3% sensitivity) and there have been no errors of R wave selection for synchronization. No proarrhythmias have resulted from over 3700 shocks delivered. The device is effective in electrically converting 96% of the spontaneous episodes of AF. In 27% of episodes several shocks were required because of early recurrence of AF. In 5 patients, the atrial defibrillator was removed: 2 infections, 1 cardiac tamponade, 1 permanent loss of telemetry, 1 patient required His-Bundle ablation because of frequent episodes of drug refractory AF with rapid ventricular response. Initial clinical experience under controlled conditions with the Metrix system suggests that the implantable atrial defibrillator may offer a therapeutic alternative for a subgroup of patients with drug refractory, symptomatic, long lasting, and infrequent episodes of AF. Further efforts must be undertaken to reduce the patient discomfort associated with internal atrial defibrillation in an attempt to make this new therapy acceptable to a larger patient population with AF. (ABSTRACT TRUNCATED)

Algorithms↗
PubMed1995

[Implantable cardioverter/defibrillators with endocardial electrode systems: long-term stability of the defibrillator's effectiveness].

The vast majority of cardioverter/defibrillator implantations is performed with non-thoracotomy lead systems. The temporal stability of defibrillation energy requirements is well established for epicardial defibrillation lead systems, but not for non-thoracotomy lead systems. The defibrillation energy requirements were reevaluated in 30 patients, 13 months after implantation of a cardioverter/defibrillator with a non-thoracotomy lead system. The study patients group consisted of 4 females and 26 males; mean age 60.1 +/- 10.5 years; mean left ventricular ejection fraction was 32.2 +/- 6.2%. Coronary artery disease was the underlying heart disease in 12 patients, dilated cardiomyopathy in 15 patients, and artificial valve replacement in 3 patients. There was no clinical progression in the underlying heart disease between defibrillator implantation and control measurements; left ventricular ejection fraction was unchanged (32.2 +/- 6.2 vs. 32.3 +/- 6.4%); no changes occurred regarding patients' clinical status. In 27/30 patients the defibrillation threshold at defibrillator implantation could be reconfirmed at control measurements. The mean defibrillation energy/requirements at implantation (14.4 +/- 4.8 Joules) were unchanged compared to control measurements (14.8 +/- 4.6 Joules). A temporal stability of defibrillation energy requirements could be established for the monophasic (n = 15; 18.0 +/- 4 vs. 18.1 +/- 3.4 Joules) as well as for the biphasic waveform (n = 15; 11.1 +/- 3.4 vs. 11.5 +/- 2.9 Joules). The results of intraoperative defibrillation thresholds measurements are predictive for chronic defibrillation energy requirements in patients with non-thoracotomy lead systems.

Aged↗
PubMed1996

Implantable cardioverter-defibrillator: present and future indications.

Indications for of automatic cardioverter-defibrillators of automatic in patients with ventricular tachyarrhythmias have changed since the publications of first guidelines in 1991. Less invasive surgical approaches reduced the perioperative mortality. Tiered therapy devices improved the quality of life by reducing appropriate and inappropriate shocks. A low annual incidence of sudden death with implantable cardioverter defibrillators and frustrating results with antiarrhythmic drugs caused an extension of implantable cardioverter-defibrillator indications. Despite the absence of prospective studies implantable cardioverter-defibrillators have become a first line treatment for patients with ventricular tachyarrhythmias which are not due to acute myocardial infarction. In cardiac arrest survivors implantable cardioverter-defibrillator therapy has become the gold standard due to the low annual incidence of sudden death seen in implantable cardioverter-defibrillator patients. The results of ongoing prospective studies comparing implantable cardioverter-defibrillator therapy to antiarrhythmic drugs have to be awaited and will influence tomorrow's indications for implantable cardioverter-defibrillator therapy in patients with documented ventricular tachyarrhythmias. Additionally, studies evaluating prophylactic implantable cardioverter-defibrillator implantations in patients at high risk for ventricular tachyarrhythmias might expand indications for implantable cardioverter-defibrillator therapy.

Cardiac Pacing, Artificial↗
PubMed1997

Automated external defibrillators: design considerations.

Biphasic defibrillation waveforms are now the standard of care in clinical use for defibrillation with implantable cardioverter-defibrillators (ICDs), due to the superior performance demonstrated over that of comparable monophasic waveforms. To better understand these significantly different outcomes, ICD research has developed cardiac cell response models to defibrillation. Waveform design criteria have been derived from these first principles and have been applied to monophasic and biphasic waveforms to optimize their parameters. These principles-based design criteria have produced significant improvements over the current art of waveforms. Monophasic defibrillation waveforms remain the standard of care in clinical use for transthoracic defibrillation. Waveform design has not yet been influenced by the important gains made in ICD research. The limitations of present transthoracic waveforms may be due in part to a lack of application of these design principles to determine optimal waveform characteristics. To overcome these limitations, design principles based on cell response have recently been developed for external defibrillation waveforms. The transthoracic model incorporates elements into a cell response model that extends it to external defibrillation. External waveform design principles demonstrate reductions in capacitance, voltage, duration, and delivered energy. Therefore, design principles based on cardiac electrophysiology may provide a means to significantly reduce the energy required for safe and efficacious external defibrillation. Footnotes, formulae, and figures augment this presentation in order to clarify the defibrillation waveform theory.

Animals↗
PubMed1990

Epicardial activation times after defibrillation in open-chest dogs using unipolar DC-coupled activation recordings.

The widespread clinical application of implantable electrical defibrillation devices has engendered considerable interest into the mechanism of action of such devices. In addition, better means of rapid detection of postshock efficacy have been sought. The authors performed this study to test the following hypotheses: (1) postshock epicardial activation times may be used to differentiate successful from unsuccessful defibrillation attempts; and (2) successful defibrillation can be characterized by whether two or more activation wavefronts are simultaneously present on the epicardium after a defibrillation attempt. Unipolar Ag/AgCl sintered electrodes were directly coupled from 120 recording sites that covered both right and left ventricular surfaces. This technique was applied to 203 defibrillation attempts in 6 open-chest dogs during electrically induced ventricular fibrillation. There were 139 successful and 64 unsuccessful defibrillation attempts. The difference between the first and second post-shock activation times was significantly different between the successful and unsuccessful attempts. This difference was secondary to the activation time delay of the second post-shock activation cycle relative to the first post-shock activation cycle. When the first-to-second post-shock time delay was greater than 140 ms, the defibrillation attempt was found to be uniformly successful. In no case of successful defibrillation accompanied by total termination of ventricular fibrillation were more than two wavefronts simultaneously present on the heart after shock. In contrast, successful defibrillation accompanied by transient residual fibrillating activity or unsuccessful defibrillation attempts were observed to present with either two simultaneous activation wavefronts or an activation wavefront in temporal isolation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Effects of ventricular fibrillation and defibrillation on pacing threshold in the anesthetized dog.

The effects of transthoracic and internal defibrillation on the bipolar ventricular pacing threshold in 20 anesthetized dogs were examined. Ventricular pacing was accomplished with a computer-controlled, constant voltage pacemaker that permitted rapid determination of pacing threshold. Defibrillation at various energy levels was administered during ventricular pacing and after ventricular fibrillation of 5, 15, 30, 45, 60 or 120 s duration in the 20 dogs. Defibrillation during pacing or within 15 s after initiation of ventricular fibrillation did not significantly increase threshold, regardless of defibrillation energy or mode of delivery. Defibrillation after ventricular fibrillation lasting greater than or equal to 30 s increased (p less than 0.05) threshold determined 6 s after defibrillation. The increase in threshold (in volts) determined 6 s after defibrillation was an exponential function of fibrillation duration (30 s = 0.30 +/- 0.09 V; 45 s = 0.53 +/- 0.13 V; 60 s = 2.24 +/- 1.05 V), but was independent of defibrillation energy or mode of delivery. Threshold returned to control values 15 to 30 s after defibrillation. Cardiopulmonary bypass to maintain coronary perfusion prevented the increase in pacing threshold even after ventricular fibrillation of up to 2 min duration. Pacing threshold is not increased by transthoracic or internal defibrillation, but is increased by ventricular fibrillation of sufficient duration to create substantial myocardial hypoxemia.

Anesthesia↗
PubMed2003

Do clinically relevant transthoracic defibrillation energies cause myocardial damage and dysfunction?

Sufficiently strong defibrillation shocks will cause temporary or permanent damage to the heart. Weak defibrillation shocks do not cause any damage to the heart but also do not defibrillate. A relevant and practical question is what range of shock energies is most likely to defibrillate while not causing damage to the heart. This question is most difficult to answer in the pre-hospital defibrillation setting where the patients' size and shape vary, placement of the defibrillation patches vary, and the etiology of their arrhythmia varies. Unlike internal defibrillators, which are tested at implantation, efficacy of an external defibrillator is determined only once, when it is most needed. This review discusses shock damage and dysfunction caused by monophasic waveforms as well as biphasic waveforms. Evidence is presented suggesting that for perfused hearts, the threshold for damage is well above any shock size delivered clinically. For non-perfused hearts, both in humans and animals, evidence is presented that monophasic shocks of up to 5 J/kg do not cause any more cardiac damage/dysfunction than that associated with smaller shocks and that much of this damage is caused by the ischemic period itself rather than the shock. Although many patients can be defibrillated with 150 J (2.2 J/kg) biphasic shocks, some patients may require biphasic shocks up to 360 J (5 J/kg) to be defibrillated. Studies still need to be performed comparing the efficacy and damaging effects of 360 J biphasic shocks to 150 J biphasic shocks. Until those studies are completed, it seems reasonable to use the same 360 J (5 J/kg) energy limit for biphasic shocks as for monophasic shocks.

Animals↗
PubMed2003

EMS defibrillation-first policy may not improve outcome in out-of-hospital cardiac arrest.

OBJECTIVE: Early defibrillation using automated external defibrillators (AEDs) has been advocated to improve survival in witnessed out-of-hospital cardiac arrest (OHCA) due to pulseless ventricular tachycardia (VT) and ventricular fibrillation (VF). However, when VT/VF is untreated and prolonged for more than a few minutes, defibrillation using AEDs may fail. METHODS: This retrospective study reviewed the charts from local emergency medical service (EMS) between the years 1993 to 2001 to evaluate the value of the AED after its introduction into our EMS. All witnessed OHCA due to VT/VF were analysed; cases of collapse witnessed by EMS were excluded. The primary endpoint was defined as survival to hospital discharge and at 1-year follow-up, and the secondary endpoint as survival without major neurological deficit. A total of 76 patients were treated for witnessed VT/VF before the implementation of the AED and 92 patients after its implementation. RESULTS: Before the introduction of paramedic AED defibrillation, physician defibrillation was performed at 15.6 min (+/-5.5, S.D.). After the introduction of AED defibrillation, paramedic defibrillation was performed at 5.7 min (+/-2.4, S.D.); the mean response interval from the call to defibrillation was shortened significantly (P<0.001). At the same time, survival to hospital discharge decreased from 23.7% (18/76 patients) to 14.1% (13/92) (P=0.112) and at 1-year follow-up from 17.1% (13/76) to 9.8% (9/92) (P=0.161). Favourable neurological outcome at 1-year follow-up also decreased from 14.5% (11/76) to 8.7% (8/92) (P=0.239). CONCLUSION: Implementation of the AED did not improve survival or a favourable neurological outcome in patients with OHCA due to VF/VT. However, with 5.7 min time to defibrillation, our EMS did not meet the criteria for early defibrillation. For prolonged periods of VT/VF, initial basic life support (BLS) may be superior to immediate AED. If response times of <4 min cannot be attained by the emergency systems, reconsidering of resuscitation algorithms seems to be advisable.

Algorithms↗
PubMed2002

Public use of automated external defibrillators.

BACKGROUND: Automated external defibrillators save lives when they are used by designated personnel in certain public settings. We performed a two-year prospective study at three Chicago airports to assess whether random bystanders witnessing out-of-hospital cardiac arrests would retrieve and successfully use automated external defibrillators. METHODS: Defibrillators were installed a brisk 60-to-90-second walk apart throughout passenger terminals at O'Hare, Midway, and Meigs Field airports, which together serve more than 100 million passengers per year. The use of defibrillators was promoted by public-service videos in waiting areas, pamphlets, and reports in the media. We assessed the time from notification of the dispatchers to defibrillation, survival rate at 72 hours and at one year among persons with cardiac arrest, their neurologic status, and the characteristics of rescuers. RESULTS: Over a two-year period, 21 persons had nontraumatic cardiac arrest, 18 of whom had ventricular fibrillation. With two exceptions, defibrillator operators were good Samaritans, acting voluntarily. In the case of four patients with ventricular fibrillation, defibrillators were neither nearby nor used within five minutes, and none of these patients survived. Three others remained in fibrillation and eventually died, despite the rapid use of a defibrillator (within five minutes). Eleven patients with ventricular fibrillation were successfully resuscitated, including eight who regained consciousness before hospital admission. No shock was delivered in four cases of suspected cardiac arrest, and the device correctly indicated that the problem was not due to ventricular fibrillation. The rescuers of 6 of the 11 successfully resuscitated patients had no training or experience in the use of automated defibrillators, although 3 had medical degrees. Ten of the 18 patients with ventricular fibrillation were alive and neurologically intact at one year. CONCLUSIONS: Automated external defibrillators deployed in readily accessible, well-marked public areas in Chicago airports were used effectively to assist patients with cardiac arrest. In the cases of survivors, most of the users had no duty to act and no prior training in the use of these devices.

Aged↗
PubMed2003

Specificity and sensitivity of automated external defibrillator rhythm analysis in infants and children.

STUDY OBJECTIVES: The rhythm detection algorithms of automated external defibrillators have been derived from adult rhythms, and their ability to discriminate between shockable and nonshockable rhythms in children is largely unknown. This study evaluates the performance of 1 automated external defibrillator algorithm in infants and children and evaluates algorithm performance with anterior-posterior versus sternal-apex lead placement. METHODS: We enrolled pediatric patients in a critical care unit, an electrophysiology laboratory, and a cardiac operating room. A monitor-defibrillator recorded ECGs by means of standard defibrillation-monitor pads. Selected 15-second rhythm samples were played into a LIFEPAK 500 automated external defibrillator, and the automated external defibrillator "shock/no shock" decision was documented. To determine sensitivity and specificity, the automated external defibrillator decision was compared with the "shockable" versus "nonshockable" rhythm classification provided by 3 expert clinicians who were blinded to the automated external defibrillator decision. RESULTS: We recorded 1,561 rhythm samples from 203 pediatric patients (median age 11 months; range, day of birth to 7 years). The automated external defibrillator recommended a shock for 72 of 73 rhythm samples classified as coarse ventricular fibrillation by expert review (sensitivity 99%; 95% confidence interval [CI] 93% to 100%); and correctly reached a "no shock advised" decision for 1,465 of 1,472 rhythm samples classified as nonshockable by experts (specificity 99.5%). Specificity was 99.1% (95% CI 97.8% to 99.8%) with the sternal-apex lead and 99.4% (95% CI 98.1% to 99.9%) with the anterior-posterior lead. CONCLUSION: This automated external defibrillator algorithm has high specificity and sensitivity when used in infants and children with either sternal-apex or anterior-posterior lead placement.

Age Factors↗
PubMed2003

Interruption of cardiopulmonary resuscitation with the use of the automated external defibrillator in out-of-hospital cardiac arrest.

STUDY OBJECTIVE: The protocol for the use of the automated external defibrillator calls for a period of "hands-off" time, during which no cardiopulmonary resuscitation (CPR) can be performed. We assessed the actual interruption time of CPR during the use of the automated external defibrillator in patients in out-of-hospital cardiac arrest. METHODS: This study included 184 patients experiencing out-of-hospital cardiac arrest in which an automated external defibrillator was applied by first responders. ECG and voice recordings from the automated external defibrillator were downloaded and analyzed. Start and end times of CPR were recorded, as were intervals measured from the recordings concerning the programmed interruption time and the interruption time related to performance. RESULTS: The automated external defibrillators were connected for a median time of 4 minutes 47 seconds (range 31 to 1,404 seconds). CPR was performed during 45%+/-15% (mean+/-SD) of the connected time or until return of spontaneous circulation. During the automated external defibrillator connection time in the 96 patients with a shockable rhythm, CPR was performed 36%+/-20% of the time. Programmed interruption of CPR took 40%+/-15% of the automated external defibrillator connection time, and no CPR was performed related to performance during 23%+/-15% of the time. A palpable pulse was never present immediately after a shock, and return of spontaneous circulation was observed in 3 of 184 patients before arrival of the ambulance. Ultimately, return of spontaneous circulation occurred in 87 of 184 patients. CONCLUSION: First responders using automated external defibrillator voice prompts provide CPR less than half the time that the automated external defibrillator is connected to the patient. Technical improvements in automated external defibrillator rhythm analysis, more efficient resuscitation algorithms, and first-responder education could increase CPR delivery and, perhaps, improve outcome.

Adolescent↗