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PubMed1999

Marked reduction in atrial defibrillation thresholds with repeated internal cardioversion.

OBJECTIVES: This study was performed to assess the atrial defibrillation threshold in patients with recurrent atrial fibrillation (AF) using repeated internal cardioversion. BACKGROUND: Previous studies in patients with chronic AF undergoing internal cardioversion have shown this method to be effective and safe. However, current energy requirements might preclude patients with longer-lasting AF from being eligible for an implantable atrial defibrillator. METHODS: Internal shocks were delivered via defibrillation electrodes placed in the right atrium (cathode) and the coronary sinus (anode) or the right atrium (cathode) and the left pulmonary artery. After cardioversion, patients were orally treated with sotalol (mean 189 +/- 63 mg/day). Eighty consecutive patients with chronic AF (mean duration 291 +/- 237 days) underwent internal cardioversion, and sinus rhythm was restored in 74 patients. Eighteen patients underwent repeated internal cardioversion using the same electrode position and shock configuration after recurrence of AF (mean duration 34 +/- 25 days). RESULTS: In these 18 patients, the overall mean defibrillation threshold was 6.67 +/- 3.09 J for the first cardioversion and 3.83 +/- 2.62 J for the second (p = 0.003). Mean lead impedance was 55.6 +/- 5.1 ohms and 57.1 +/- 3.7 ohms, respectively (not significant). For sedation, 6.7 +/- 2.9 mg and 3.9 +/- 2.2 mg midazolam were administered intravenously (p = 0.003), and the pain score (0 = not felt, 10 = intolerable) was 5.1 +/- 1.9 and 2.7 +/- 1.8 (p = 0.001). Uni- and multivariate analyses revealed only the duration of AF before cardioversion to be of relevance, lasting 175 +/- 113 days before the first and 34 +/- 25 days before the second cardioversion in these 18 patients (p = 0.002). CONCLUSIONS: If the duration of AF is reduced, a significant reduction in defibrillation energy requirements for internal cardioversion ensues. This might extend the group of patients eligible for an implantable atrial defibrillator despite relatively high initial defibrillation thresholds.

Adult↗
PubMed1998

Changes in human coronary sinus blood flow and myocardial metabolism induced by ventricular fibrillation and defibrillation.

BACKGROUND: During implantation of cardioverter-defibrillators, repeated inductions of ventricular fibrillation and defibrillation are performed. Little is known about the myocardial metabolism associated with ventricular fibrillation and defibrillation in humans. METHODS: Sixteen patients scheduled for transvenous cardioverter-defibrillator implantation were included in the study. In 10 of the patients, blood samples were taken simultaneously in the coronary sinus and radial artery and analyzed for PO2, PCO2, standard bicarbonate, pH, lactate, alanine, glucose, and glycerol. Oxygen saturation, base excess, and oxygen content were calculated. The patients were studied before, shortly after, and 2 and 5 minutes after successful defibrillation. In six of the patients, coronary sinus blood flow was registered continuously. RESULTS: The coronary sinus blood flow declined from a basal value of 93 +/- 16 mL/min to 35 +/- 6 mL/min 14 +/- 2 seconds after induction of ventricular fibrillation. Following termination of ventricular fibrillation, coronary sinus blood flow increased to a peak value of 227 +/- 75 mL/min. Oxygen saturation, PO2, and oxygen content in the coronary sinus increased by approximately 25% shortly after each episode of ventricular fibrillation and defibrillation. The coronary sinus lactate increased and the arterio-coronary sinus lactate difference decreased shortly after each of the four episodes, but was normalized within 2 minutes. CONCLUSIONS: Repeated threshold tests during defibrillator implantation did not cause any long-lasting or cumulative metabolic effects, indicating that the described technique, with a 5-minute recovery period in between episodes, is safe as regards myocardial metabolism.

Adult↗
PubMed1997

Early out-of-hospital experience with an impedance-compensating low-energy biphasic waveform automatic external defibrillator.

Impedance-compensating low-energy biphasic truncated exponential (BTE) waveforms are effective in transthoracic defibrillation of short-duration ventricular fibrillation (VF). However, the BTE waveform has not been examined in out-of-hospital cardiac arrest (OHCA) with patients in prolonged VF often associated with myocardial ischemia. The objective of this study was to evaluate the BTE waveform automatic external defibrillator (AED) in the out-of-hospital setting with long-duration VF. AEDs incorporating a 150-J BTE waveform were placed in 12 police squad cars and 4 paramedic-staffed advanced life support ambulances. AEDs were applied to arrested patients by first-arriving personnel, whether police or paramedics. Data were obtained from PC Data Cards within the AED. Defibrillation was defined as at least transient termination of VF. Ten patients, 64 +/- 14 years, were treated for VF with BTE shocks. Another 8 patients were in nonshockable rhythms and the AEDs, appropriately, did not advise a shock. Five of the 10 VF arrests were witnessed with a 911 call-to-shock time of 6.6 +/- 1.7 minutes. VF detection and defibrillation occurred in all 10 patients. Spontaneous circulation was restored in 3 of 5 witnessed arrest patients and 1 survived to discharge home. Fifty-one VF episodes were converted with 62 shocks. Presenting VF amplitude and rate were 0.43 +/- 0.22 (0.13-0.86) mV and 232 +/- 62 (122-353) beats/min, respectively, and defibrillation was achieved with the first shock in 7 of 10 patients. Including transient conversions, defibrillation occurred in 42 of 51 VF episodes (82%) with one BTE shock. Shock impedance was 85 +/- 10 (39-138) ohms. Delivered energy and peak voltage were 152 +/- 2 J and 1754 +/- 4 V, respectively. The average number of shocks per VF episode was 1.2 +/- 0.5 (1-3). More than one shock was needed in only 9 episodes; none required > 3 shocks to defibrillate. Impedance-compensating low-energy BTE waveforms terminated VF in OHCA patients with a conversion rate exceeding that of higher energy monophasic waveforms. VF was terminated in all patients, including those with high impedance.

Adult↗
PubMed2001

Reentry site during fibrillation induction in relation to defibrillation efficacy for different shock waveforms.

INTRODUCTION: Unsuccessful defibrillation shocks may reinitiate fibrillation by causing postshock reentry. METHODS AND RESULTS: To better understand why some waveforms are more efficacious for defibrillation, reentry was induced in six dogs with 1-, 2-, 4-, 8-, and 16-msec monophasic and 1/1- (both phases 1 msec) 2/2-, 4/4-, and 8/8-msec biphasic shocks. Reentry was initiated by 141+/-15 V shocks delivered from a defibrillator with a 150-microF capacitance during the vulnerable period of paced rhythm (183+/-12 msec after the last pacing stimulus). The shock potential gradient field was orthogonal to the dispersion of refractoriness. Activation was mapped with 121 electrodes covering 4 x 4 cm of the right ventricular epicardium, and potential gradient and degree of recovery of excitability were estimated at the sites of reentry. Defibrillation thresholds (DFTs) were estimated by an up-down protocol for the same nine waveforms in eight dogs internally and in nine other dogs externally. DFT voltages for the different waveforms were positively correlated with the magnitude of shock potential gradient and negatively correlated with the recovery interval at the site at which reentry was induced by the waveform during paced rhythm for both internal (DFT = 1719 + 64.5VV - 11.1RI; R2 = 0.93) and external defibrillation (DFT = 3445 + 150VV - 22RI; R2 = 0.93). CONCLUSION: The defibrillation waveforms with the lowest DFTs were those that induced reentry at sites of low shock potential gradient, indicating efficacious stimulation of myocardium. Additionally, the site of reentry induced by waveforms with the lowest DFTs was in myocardium that was more highly recovered just before the shock, perhaps because this high degree of recovery seldom occurs during defibrillation due to the rapid activation rate during fibrillation.

Animals↗
PubMed2001

Atrial defibrillation threshold in humans minutes after atrial fibrillation induction; "A stitch in time saves nine".

AIMS: To assess the effects of atrial fibrillation duration on the defibrillation threshold in atrial fibrillation patients seconds or minutes after initiation of the arrhythmia. METHODS AND RESULTS: Nineteen patients with recurrent symptomatic atrial fibrillation were evaluated. After programmed induction of atrial fibrillation, the defibrillation threshold was assessed after two sequential periods of arrhythmia in the same patient: an "ultrashort" period of 30 s duration and a "short" period, which lasted 10 min. After the specified period, internal cardioversion was attempted using a balloon-guided catheter that allows the delivery of biphasic shocks between one electrode array placed in the left pulmonary artery and a proximal electrode array on the lateral right atrial wall. The defibrillation threshold was assessed with energy steps of 0.5 J with a starting level of 0.5 J. Mean time from induction to successful defibrillation was 92+/-30 s after the "ultrashort" period of atrial fibrillation and 910+/-86 s after the short period. The defibrillation threshold was significantly greater after 10 min of atrial fibrillation than after 30 s of arrhythmia (2.32+/-0.61 J vs 1.31+/-0.66 J, P<0.001). Clinical data were not found to affect the defibrillation threshold. CONCLUSIONS: Prolongation of atrial fibrillation over minutes in patients with paroxysmal arrhythmia increases the energy requirements for successful defibrillation.

Aged↗
PubMed1998

Internal atrial defibrillation - a new treatment of postoperative atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) commonly occurs following open heart surgery and may delay hospital discharge. Transthoracic electrical cardioversion is used when medical treatment is ineffective or associated with side effects. Traditionally general anesthesia is required. The aim of this multicenter study was to examine the feasibility and efficacy of low-energy atrial defibrillation using temporary epicardial defibrillation wire electrodes. METHODS: Epicardial stainless-steel defibrillation wire electrodes were sutured onto the left and right atrium during open heart surgery in 238 patients (age 64+/-9 years; 180 males). In case of postoperative AF R-wave synchronous low-energy shocks (0.6-10.8J) were applied to achieve cardioversion without anesthesia. RESULTS: Implantation of the electrodes added 4.3+/-2.8 minutes to the operating time. During the hospital stay AF occurred in 47 patients (20%) at 2.1+/-1.3 days postoperatively. Fifty-one episodes of AF occurring in 44 patients were treated by atrial defibrillation. Primary success rate of cardioversion was 33/51 (65%). Early recurrence of AF (within 60 seconds after defibrillation) developed in 15 patients. Seven of these 15 patients were successfully defibrillated later on. Overall success rate was 40/51 (78%). The mean energy of successful shocks was 5.8+/-2.7 J. A mean of 2.3+/-1.7 shocks were applied per patient. The shocks were well tolerated by the patients in the absence of anesthesia. No complications were observed with shock application or with lead extraction. CONCLUSION: Atrial defibrillation using temporary epicardial wire electrodes can be performed safely and effectively in patients following cardiac surgery. The shock energy required to restore sinus rhythm is low.

Atrial Fibrillation↗
PubMed2001

Successful defibrillation in the prone position.

Early defibrillation provides the greatest chance of survival after ventricular fibrillation. Conventional cardiopulmonary resuscitation and defibrillation requires the patient to be in the supine position. Electrical treatment of arrhythmias such as atrial fibrillation by means of a defibrillator back paddle in patients receiving prone ventilation in intensive care has been described. We report a case in which electrical defibrillation was successfully performed in the prone position in a patient undergoing complex spinal surgery. We suggest that, if defibrillation were required in ventilated patients positioned prone, defibrillation should be attempted in the prone position, as turning the patient supine would consume valuable minutes and reduce the chances of successful defibrillation.

Adult↗
PubMed1991

Comparison of biphasic and monophasic defibrillation waveforms in an isolated rabbit heart preparation.

STUDY OBJECTIVE: The aims were to develop a Langendorff rabbit heart model and to compare monophasic and biphasic defibrillation pulses. DESIGN: Hearts were perfused with a Krebs-Henseleit solution and two 1.4 cm2 Pt-Ir mesh patch electrodes were sutured onto the ventricles. A 5 ms monophasic or 10 ms biphasic pulse, with randomly selected voltages of 30, 50, 70, 90, 110, or 130 V, defibrillated the heart after 10 s of fibrillation. SUBJECTS: 11 adult male New Zealand white rabbits weighing 2.8(0.27) kg, were used for the studies. MEASUREMENTS AND MAIN RESULTS: A total of 72 fibrillation and defibrillation sequences were conducted in each preparation. The results were fitted to a sigmoidal dose-response curve by logistic regression analysis. Voltage and energy values from the fitted data at 50% and 80% success (V50, V80, E50, E80) indicated a significantly lower (p less than 0.05) defibrillation threshold voltage and energy for the biphasic waveform [V50 = 48 (SD19) V, V80 = 87(27) V, E50 = 0.15(0.12) J, E80 = 0.48(0.29) J] compared with the monophasic waveform [V50 = 79(20) V, V80 = 110(20) V, E50 = 0.27(0.12) J, E80 = 0.5(0.12) J]. There was no observed difference in defibrillation success rate between the first and second halves of any study. CONCLUSIONS: The Langendorff rabbit heart model is suitable for assessing electrical fibrillation and defibrillation mechanisms. Defibrillation can be achieved with a lower energy when using a biphasic rather than a monophasic pulse.

Animals↗
PubMed2002

Fixed-energy biphasic waveform defibrillation in a pediatric model of cardiac arrest and resuscitation.

OBJECTIVE: For adults, 150-J fixed-energy, impedance-compensating biphasic truncated exponential (ICBTE) shocks are now effectively used in automated defibrillators. However, the high energy levels delivered by adult automated defibrillators preclude their use for pediatric patients. Accordingly, we investigated a method by which adult automated defibrillators may be adapted to deliver a 50-J ICBTE shock for pediatric defibrillation. DESIGN: Prospective, randomized study. SETTING: A university-affiliated research institution. SUBJECT: Domestic piglets. INTERVENTIONS: We initially investigated four groups of anesthetized mechanically ventilated piglets weighing 3.8, 7.5, 15, and 25 kg. Ventricular fibrillation was induced with an AC current delivered to the right ventricular endocardium. After 7 mins of untreated ventricular fibrillation, a conventional manual defibrillator was used to deliver up to three 50-J ICBTE shocks. If ventricular fibrillation was not reversed, a 1-min interval of precordial compression preceded a second sequence of up to three shocks. The protocol was repeated until spontaneous circulation was restored, or for a total of 15 mins. In a second set of experiments, we evaluated a 150-J biphasic adult automated defibrillator that was operated in conjunction with energy-reducing electrodes such as to deliver 50-J shocks. The same resuscitation protocol was then exercised on piglets weighing 3.7, 13.5, and 24.2 kg. MEASUREMENTS AND MAIN RESULTS: All animals were successfully resuscitated. Postresuscitation hemodynamic and myocardial function quickly returned to baseline values in both experimental groups, and all animals survived. CONCLUSION: An adaptation of a 150-J biphasic adult automated defibrillator in which energy-reducing electrodes delivered 50-J shocks successfully resuscitated animals ranging from 3.7 to 25 kg without compromise of postresuscitation myocardial function or survival.

Analysis of Variance↗
PubMed1994

Barium decreases defibrillation energy requirements.

Certain antiarrhythmic drugs that inhibit myocardial repolarizing currents decrease defibrillation energy, but the effect of blocking particular currents on defibrillation is not well understood. We therefore investigated the effect of barium, a relatively selective blocker of inwardly rectifying potassium current (Ik1) on voltage and energy requirements for defibrillation in an open-chest dog model. Defibrillation energy and voltage requirements were assessed by delivering monophasic shocks through epicardial electrode patches at varying voltages to construct a dose-dependent curve of energy and voltage versus success in defibrillation. The energy and voltage for 50% success in defibrillation (E50 and V50, respectively) were determined by logistic regression. Monophasic action potential duration at 90% repolarization (MAPD90) was measured with a contact electrode, and ventricular refractory period (VERP) was measured. After baseline measurements were obtained of E50, V50, MAPD90, and VERP, saline (control) (n = 6) or barium (1.1 mg/kg/min for 5 min followed by 0.25 mg/kg/min) (n = 11) was administered. Defibrillation voltage and energy requirements and electrophysiologic measures were repeated after 30 and 120 min of barium or saline infusion. In control animals, there was no significant change with time in V50 (2.0 +/- 12.4 and -0.2 +/- 16.0% at 30 and 120 min, respectively), VERP (+3 +/- 5 and -2 +/- 3% at 30 and 120 min, respectively) or MAPD90 (+1 +/- 4 and -2 +/- 6, at 30 and 120 min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1994

Epicardial administration of ibutilide from polyurethane matrices: effects on defibrillation threshold and electrophysiologic parameters.

Polymer-drug composites known as controlled-release systems have been used effectively to prevent and treat ventricular arrhythmias in experimental studies. We wished to determine if such systems could be useful in reducing ventricular defibrillation energy requirements in an acute canine model without producing undesirable electrophysiologic effects. Ibutilide-polyurethane monolithic controlled-release matrices were formulated with ibutilide fumarate and a polyether polyurethane. In vitro drug-release characteristics of the drug matrices were determined. Two formulations were investigated: (a) 20% ibutilide by weight in polyether polyurethane, and (b) 4% ibutilide/16% dimethyl tartrate in polyurethane. Based on in vitro release studies, 20% ibutilide matrices (25 mg) would provide a 25-kg dog with a dose of 25 micrograms/kg ibutilide in a 2-h acute experimental period, and 4% ibutilide matrices were estimated to provide 3.5 micrograms/kg. We used each of these types of matrices in acute open-chest dog studies to assess electrophysiologic effects and the influence of epicardial controlled-release ibutilide, as compared with intravenous (i.v.) administration, on defibrillation energy thresholds (DFTs), using epicardial defibrillation electrodes. In monophasic defibrillation waveform studies, 20% matrices significantly decreased DFT as compared with a predrug control period [2.54 +/- 0.59 (mean +/- SEM) vs. 7.23 +/- 1.73 J, respectively, p = 0.038]. Administration of the same dose i.v. did not cause significant reduction in energy requirement. With a biphasic defibrillation waveform, 4% ibutilide matrices significantly decreased DFT as compared with control (2.53 +/- 0.34 vs. 3.42 +/- 0.46 J, respectively, p = 0.003). Administration of an equivalent i.v. dose did not cause a significant reduction in biphasic energy requirement. Both types of controlled-release systems significantly prolonged refractoriness and conduction times of ventricular extrastimuli as compared with vehicle. No proarrhythmia events were observed. Epicardial polymeric controlled-release ibutilide significantly prolonged ventricular refractoriness and conduction and thus may enhance antiarrhythmia activity. In addition, controlled-release ibutilide formulations significantly decreased DFT requirements. Thus, ibutilide-polymeric controlled-release matrix systems may be useful in conjunction with implantable defibrillators in preventing ventricular arrhythmias and reducing defibrillation energy requirements.

Animals↗
PubMed1984

The potential use of automatic defibrillators in the home for management of cardiac arrest.

Ventricular fibrillation, an abnormal cardiac rhythm, occurs in at least two-thirds of the 400,000 people who die out of the hospital from sudden cardiac arrest. This rhythm can be treated successfully by electric countershock, a procedure known as defibrillation. The survival rate following such cardiac arrest is directly related to the rapidity of response; the shorter the time from collapse to defibrillation, the more patients will survive. There are two basic options to shorten the time from collapse to defibrillatory shock. The first is to upgrade the emergency medical system. The second is to provide spouses and family members of potential cardiac arrest patients with automatic home defibrillators. This article considers the effectiveness of the second option, home defibrillation, compared with that of an equally costly upgrade in existing emergency medical service systems. The comparisons depend on the existing level of emergency medical service system, the cost of the home defibrillator, and the rate at which a home defibrillator would be used appropriately. The comparisons suggest that in many circumstances home defibrillation is an appropriate option to be considered.

Costs and Cost Analysis↗
PubMed2003

Optimal timing for electrical defibrillation after prolonged untreated ventricular fibrillation.

OBJECTIVE: It currently is recommended that electrical shocks be delivered immediately on recognition of ventricular fibrillation. However, decreased effectiveness of this approach has been reported after prolonged intervals of untreated ventricular fibrillation. We investigated the optimal strategy for successful defibrillation after prolonged untreated ventricular fibrillation by using a rat model of ventricular fibrillation and closed-chest resuscitation. DESIGN: Controlled, randomized, laboratory study. SETTING: Research laboratory at a VA hospital. SUBJECTS: Seventy pentobarbital anesthetized Sprague-Dawley rats. INTERVENTIONS: After 10 mins of untreated ventricular fibrillation, four groups of rats were randomized to receive electrical shocks (which we designated as "experimental shocks") immediately before or at 2, 4, or 6 mins of chest compression. Unsuccessfully defibrillated rats received additional shocks (which we designated as "rescue shocks") after 8 mins of chest compression. MEASUREMENTS AND MAIN RESULTS: The number of rats that restored spontaneous circulation after the experimental shocks increased with increasing duration of the predefibrillatory interval of chest compression (0 of 8, 0 of 8, 2 of 8, and 7 of 8, respectively, p <.005). Two additional groups then were randomized to receive repetitive experimental shocks at 2, 4, and 6 mins or a single attempt at 6 mins of chest compression. Although a comparable number of rats restored spontaneous circulation in each group, rats subjected to repetitive defibrillation attempts had more intense postresuscitation ectopic activity and worse survival. Two final groups were used to investigate whether inhibition of the sarcolemmal sodium-hydrogen exchanger isoform-1 (NHE-1) could facilitate return of spontaneous circulation during repetitive defibrillation attempts. Although spontaneous circulation was restored earlier in more rats subjected to NHE-1 inhibition, the differences were statistically insignificant. NHE-1 inhibition, however, replicated previously reported resuscitation and postresuscitation benefits. The optimal predefibrillation interval of chest compression was approximately 6 mins, and this coincided with partial return of the amplitude and frequency characteristics of the ventricular fibrillation waveform to those present immediately after induction of ventricular fibrillation. CONCLUSIONS: Improved outcome after prolonged untreated ventricular fibrillation may result from strategies that provide chest compression before attempting defibrillation and avoid early and repetitive defibrillation attempts. The amplitude and frequency characteristics of the ventricular fibrillation waveform could help identify the optimal timing for attempting electrical defibrillation.

Animals↗
PubMed2004

Human factors impact successful lay person automated external defibrillator use during simulated cardiac arrest.

OBJECTIVE: With the dissemination of automated external defibrillators in the community, there is increasing lay person use, along with less formal automated external defibrillator training and retraining. Therefore, the "ease of use" factors related to the human-device interface may be vital for successful use. We sought to determine whether human factor differences would result in differences in parameters of successful or safe use by lay persons in the setting of simulated cardiac arrest. METHODS: We measured parameters of successful and safe use with two automated external defibrillator devices among two groups of volunteers, those trained with a brief video tape and those without any training (completely naive). Both devices (the Philips FR2 or the HS1) are used in public access defibrillator settings. Volunteers entered a mock cardiac arrest scenario after randomization to either the naive (untrained) group or to a video-trained group. RESULTS: Both the FR2 and HS1 were found to be completely safe when used by video-trained and by naive groups of participants, with no adverse events observed (total, n = 256). For both devices, video-trained participants demonstrated high rates of successful defibrillation in the simulated testing (86% for FR2 and 89% for HS1). With the FR2, video-trained participants were significantly more successful compared with naive, untrained participants (86% vs. 48% successful use; p < .001). However, for the HS1, there was no significant difference in success rates for the video-trained vs. naive, untrained groups (89% vs. 87%; p = .79). CONCLUSIONS: Both devices are safe with either video-trained or naive users. The successful use of each device is high when participants view the training videotape designed for the device. An important difference in successful use was observed for naive users where the HS1 showed improved successful use compared with the FR2. Because defibrillation in the community may increasingly be attempted by lay persons whose training is remote or who have not been trained at all, the "naive" scenario may be increasingly relevant to automated external defibrillator use. Collectively, these data support the notion that human factors associated with ease of use may play a critical factor in survival rates achieved by specific devices.

Adult↗
PubMed2004

The use of automated external defibrillators by non-medical first responders in Finland.

OBJECTIVE: To assess the spread of automated external defibrillators and their use by non-medical first responders in Finland. METHODS: A structured survey was mailed to all voluntary and ordinary fire brigades in Finland. The questions were related to the purchase, experience of use and anticipated benefits from the devices. RESULTS: Approximately 90% of all users (133 providers) in the target group of non-medical first responders answered. The number of automated external defibrillators in use by these operators has increased progressively since 1992. Most respondents possessed only one automated external defibrillator, and a median of 12 users were trained to use each device. A total of 85% of the respondents retrained at least once a year, and 94% checked the device on a daily basis. Half of the users had written authorization to use the automated external defibrillator, and two thirds had written instructions on how to operate it. Each automated external defibrillator was used on average five to 10 times annually. Although none of the respondents could provide data on how many cardiac arrests they had attended or the success of resuscitation during the preceding year, 94% reported that they considered the automated external defibrillator useful, and 80% thought that the cost-benefit of the device was either very good or good. CONCLUSION: Although there are many automated external defibrillators in use by non-medical first responders in Finland, the results of this study show that there are large variations between individual fire brigades regarding the use of these devices as part of the first response system. This is considered to be caused by the lack of national standards and regulations, which should define a full integration of first-responder programmes into the emergency medical service system.

Education, Nonprofessional↗
PubMed2000

Theoretical predictions of the optimal monophasic and biphasic defibrillation waveshapes.

The truncated decaying exponential waveshape has become the de facto standard for implantable cardiac defibrillators. However, the optimal defibrillation waveshape with respect to delivered energy remains unknown. To this end, this study has derived the theoretically optimal waveshapes for monophasic and biphasic defibrillation shocks as predicted from a lumped-component model of cardiac tissue in conjunction with the "charge-banking" and "charge-burping" hypotheses of defibrillation. These derivations predict that a truncated ascending exponential waveshape--with a shock time constant, tau s, always equal to the underlying tissue time constant, tau m--minimizes the delivered energy required for defibrillation. These predictions are qualitatively consistent with available experimental data. Thus, to the extent that "charge-banking" and "charge-burping" are assumed to be valid and accurate models of defibrillation, these derivations identify the theoretical "gold standards" of defibrillation waveshapes requiring minimum delivered energy.

Electric Countershock↗
PubMed1989

One year's experience of early defibrillation in Stockholm.

The effects of resuscitation on patients who died suddenly out of hospital were evaluated after the introduction of early defibrillation performed by ambulance personnel using semi-automatic defibrillators. Resuscitation attempts were initiated in 548 patients during the 1-year study period. Mean ambulance delay was 7.5 min, 22% of the cardiac arrest patients had received bystander cardiopulmonary resuscitation (CPR). Sensitivity and specificity for the semi-automatic defibrillator in the interpretation of ventricular fibrillation was found to be 97 and 100% respectively. Only 28 (14%) of the 206 defibrillated patients regained circulation and were admitted for further hospital care. Only three survived to be discharged. Among the 342 patients in whom defibrillation was not indicated, 16 (5%) regained circulation and were admitted for further hospital care and one (0.3%) survived to be discharged. Semi-automatic defibrillators seem reliable, safe and inexpensive; however, the isolated addition of defibrillation to basal ambulance service seems to be inadequate in Stockholm. We need to evaluate what further resources are of importance to guarantee a successful outcome.

Ambulances↗
PubMed1987

Internal ventricular defibrillation with sequential pulse countershock in pigs: comparison with single pulses and effects of pulse separation.

We compared single to sequential pulse shocks with different pulse separations on internal cardiac defibrillation by using a catheter and plaque electrodes in open-chest halothane-anesthetized pigs. Ten seconds after fibrillation onset, defibrillation was attempted using trapezoidal pulses of 65% tilt, approximately 5 ms duration and fixed outputs from 1.0 to 50 joules (J). With single pulses, minimum defibrillation energy for the catheter alone was 2.4 +/- 0.3 J/kg (mean +/- standard error) and 2.1 +/- 0.2 J/kg for the catheter tip to plaque configuration. With sequential pulse shocks, the first pulse delivered via the catheter and the second pulse from the catheter tip to the plaque electrode, the energy necessary for defibrillation was dependent on the separation time between the two pulses (2.0 +/- 0.2, 1.5 +/- 0.2, 0.9 +/- 0.1, 1.3 +/- 0.3, 0.6 +/- 0.2, and 1.2 +/- 0.2 J/kg at 100, 10, 1, 0.5, 0.2, and 0.1 ms, respectively). Further, at the 0.2 ms separation, 100% of the animals could be defibrillated with less than 2.0 J/kg (35 J total). We conclude that sequential pulse defibrillation provides a significant improvement over single pulse defibrillation. The optimum separation between the sequential pulses in this study was 0.2 ms.

Animals↗