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PubMed1988

Comparison of defibrillation efficacy in humans using a new catheter and superior vena cava spring-left ventricular patch electrodes.

The automatic implantable cardioverter-defibrillator currently utilizes an electrode system that requires a major operation for implantation. Effective defibrillation using an implantable cardioverter-defibrillator catheter positioned transvenously would eliminate the morbidity associated with such surgery. Fifteen patients undergoing defibrillator implantation were studied to compare the efficacy of the catheter with that of the superior vena cava spring (6.7 cm2, anode)-left ventricular patch (13.5 cm2, cathode) electrode system using truncated exponential waveforms with 60% tilt. The catheter is 11F in diameter and tripolar. A distal platinum-iridium tip used for pacing was separated by 4 mm from a middle 4.3 cm2 platinum electrode; these were positioned at the right ventricular apex. The proximal 8.5 cm2 platinum electrode was situated at the superior vena cava-right atrial junction. Defibrillation was performed using the middle (cathode) and proximal (anode) electrodes. Ventricular fibrillation was induced by alternating current six times, and defibrillation shocks of 1, 5, 10, 15, 20 or 25 J were given in random order, first using the catheter and then the spring-patch system. Rescue shocks of higher energy were given if there was failure. Although very low energy levels appeared to be slightly more efficacious when using the spring-patch system, there was no statistically significant difference between the electrode systems for any of the energies tested. Permanent implantation of the catheter would have been suitable in 45% of the patients, as compared with 54% of patients with the spring-patch system (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

A new rhythm library for testing automatic external defibrillators: performance of three devices.

A library of arrhythmias obtained from patients with cardiac arrest was developed. Such a data base will permit both in vitro testing of the rhythm analysis system of automatic external defibrillators before clinical field trials are conducted and comparison of devices. Defibrillators equipped with voice/electrocardiographic tape recorders and used in the prehospital defibrillation programs in Iowa and King County, Washington provided the rhythm source. From these recordings, segments of ventricular fibrillation with minimal artifact and a duration of greater than or equal to 6 s were selected. Segments of ventricular fibrillation (n = 102) were categorized by average peak amplitude as fine (1 to less than 3 mm), medium (3 to less than 7 mm), coarse (7 to less than 12 mm) and extra coarse (greater than or equal to 12 mm), and transcribed onto high fidelity videocassette tapes. Nonventricular fibrillation cardiac arrest rhythms (n = 144), which included wide complex idioventricular rhythms, ventricular and supraventricular tachycardias, asystole and artifact, were also transcribed. Automatic external defibrillators developed by three manufacturers reached a treat (shock) decision on 88 to 93% of the ventricular fibrillation rhythms and on 5 to 10% of the nonventricular fibrillation rhythms. The latter decisions were defined as false positive, though for many rapid nonventricular fibrillation rhythms, countershock may be the appropriate treatment response. There were no statistically significant differences among the three devices in the shock/no shock decisions. A variety of ventricular fibrillation arrhythmias and terminology to express the preclinical performance of automatic external defibrillators are defined. Three commercially available automatic external defibrillators appear to successfully identify ventricular fibrillation and nonventricular fibrillation rhythms.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1993

Importance of electrode design, lead configuration and impedance for successful low energy transcatheter atrial defibrillation in dogs.

OBJECTIVES: We assessed the feasibility of low energy endocardial defibrillation in a canine model of atrial fibrillation, comparing catheters with large surface area electrodes and standard electrode catheters, and evaluated the effects of lead configuration and circuit impedance on defibrillation energy requirements. BACKGROUND: Although recent animal studies have demonstrated the feasibility of low energy endocardial atrial defibrillation, their results have been conflicting with regard to important methodologic aspects. METHODS: In 14 anesthetized greyhounds, atrial fibrillation was induced by rapid atrial pacing and maintained by vagal stimulation. Two large surface area braided electrode catheters and two standard electrode catheters were introduced percutaneously, one of each, in the right atrial appendage and right ventricular apex. A cutaneous patch electrode was placed on the left thorax. Biphasic shocks synchronized to the ventricular electrogram were used to terminate atrial fibrillation. Seven configurations were evaluated. Three used standard electrodes: proximal atrial cathode to distal atrial, ventricular or cutaneous anode. Four used braided electrodes: three with atrial cathode to ventricular, cutaneous or combined anode; one with ventricular cathode to atrial anode. RESULTS: Defibrillation with standard electrode catheters was associated with high impedance (576 +/- 112 omega) and low success rates for all configurations (28% success at < or = 40 J, no successes at 10 J). Low energy defibrillation was readily achieved with the braided electrodes with significantly lower impedance (75 +/- 13 omega, p < 0.0001). Ventricular fibrillation did not occur. The success rate of cardioversion increased in a dose-response manner, allowing fitting of a sigmoid curve and calculation of energy associated with 50% (ED50) and 90% (ED90) success. The most successful configuration was ventricular cathode/atrial anode (ED50 1.5 +/- 0.4 J), and the least successful was atrial anode/cutaneous patch (ED50 6.5 +/- 3.2 J, p = 0.0001). CONCLUSIONS: Low energy atrial defibrillation is feasible using large surface area electrodes but not with standard electrode catheters owing to high impedance. An intracardiac anode provides lower impedance and higher success rates than are provided by a cutaneous anode.

Analysis of Variance↗
PubMed1989

Low energy level internal defibrillation during cardiopulmonary bypass.

Low energy level internal direct current shocks were used to defibrillate the hearts of 168 patients during procedures performed on cardiopulmonary bypass. In all cases, the core temperature was greater than 32 degrees C and care was taken to correct hypokalaemia and acid-base balance prior to defibrillation. In 78 patients (46%), defibrillation required 2 joules or less, and in 139 (82.7%) cases, defibrillation was effected with 4 joules or less. Only 4 patients required more than 10 joules to defibrillate the heart. This study shows that it is possible to defibrillate hearts during cardiopulmonary bypass with energy levels well below the 20-30 joule shocks commonly used.

Adolescent↗
PubMed1996

Current-based transthoracic defibrillation.

This study examines in a prospective, multicenter trial the feasibility and advantage of current-based, transthoracic defibrillation. Current-based, damped, sinusoidal waveform shocks of 18, 25, 30, 35, or 40 amperes (A) were administered beginning with 25 A for polymorphic ventricular tachycardia (VT) and ventricular fibrillation (VF) or 18 A for monomorphic VT; success rates were compared with those of energy-based shocks beginning at 200 J for VF/polymorphic VT and 100 J for VT. The current-based shocks were delivered from custom-modified defibrillators that determined impedance in advance of any shock using a "test-pulse" technique; the capacitor then charged to the exact energy necessary to deliver the operator-selected current against the impedance determined by the defibrillator. Three hundred sixty-two patients received > 1 shock for VF, polymorphic VT, or monomorphic VT: 569 current- based shocks and 420 energy-based shocks. Current-based shocks of 35/40 A achieved success rates of up to 74% for VF/polymorphic VT; 30 A shocks terminated 88% of monomorphic VT episodes. Energy-based shocks of 300 J terminated 72% of VF/polymorphic VT; 200-J shocks terminated 89% of monomorphic VT. We could not demonstrate a significant increase in the success rate of current-based shocks over energy-based shocks for patients with high transthoracic impedance; this may be due to inadequate sample size. Thus, current-based defibrillation is clinically feasible and effective. A larger study will be needed to test whether current-based defibrillation is superior to energy-based defibrillation.

Electric Countershock↗
PubMed1980

Dependence of defibrillation threshold upon extracellular/intracellular K+ concentrations.

The effect of increasing extracellular potassium concentration (Ko) upon electrical ventricular defibrillation threshold was investigated in pentobarbital anesthetized dogs treated with intravenous potassium chloride. Defibrillation threshold fell duirng potassium intoxication. The percent decrease in defibrillation threshold was linearly related to the logarithm of Ko and to the potassium equilibrium potential (Ek), calculated from measured extracellular and intracellular potassium concentrations of ventricular muscle. In dogs supported by left ventricular bypass in order to maintain the circulation during potassium intoxication, the values of Ko and Ek required for spontaneous, K+ induced defibrillation (electrical defibrillation threshold = zero) were 16.6 mEq/L and -46 mV compared to the normal values of 3.9 mEq/L and -84 mV. Changes in defibrillation threshold related to changes in Ek may be significant events in digitalis intoxication and in myocardial anoxia during prolonged fibrillation.

Animals↗
PubMed1995

Mechanisms of defibrillation. Critical points and the upper limit of vulnerability.

The upper limit of vulnerability hypothesis for defibrillation states that a successful defibrillation shock must both stop the fibrillation wave fronts on the heart at the time that the shock is delivered and not start new wave fronts that will lead to reentrant circuits being formed, causing the heart to refibrillate. Mapping studies have demonstrated that defibrillation shocks can halt all wave fronts on the heart but fibrillation will begin again with an initial activation pattern that is different from the activation pattern on the heart just before the shock is delivered. In a fashion similar to the reinitiation of fibrillation following a failed defibrillation shock, properly sized and timed shocks can be delivered to the heart during paced rhythm to induce functional reentry that will initiate fibrillation. If the shocks are made incrementally larger, a shock level will be reached that is high enough not to start fibrillation in regular rhythm regardless of when it is delivered during the cardiac cycle. This shock level is called the upper limit of vulnerability. In this study, the formation of reentrant circuits with defibrillation-sized shocks and how this formation of reentrant circuits may be related to mechanism of defibrillation, via the upper limit of vulnerability hypothesis are discussed.

Action Potentials↗
PubMed1996

Defibrillation success is associated with myocardial organization. Spatial coherence as a new method of quantifying the electrical organization of the heart.

The relationship between the degree of electrical organization of ventricular fibrillation (VF) and defibrillation success was investigated in this study using a new technique to quantify organization--spatial coherence. This technique employs the use of the magnitude-squared coherence spectrum to analyze multichannel electrograms obtained during a cardiac mapping study. Magnitude-squared coherence values for all possible pairs of electrograms recorded from an epicardial plaque consisting of 112 electrodes were computed. Average coherence was plotted versus electrode separation distance, and the data were fit with an exponentially decaying curve. Two parameters indicative of myocardial organization were extracted from the curve. The coherence length (d) was defined as the distance (mm) at which the average coherence dropped to a given level, and the coherence strength was defined as the average coherence value at a given distance. Higher values for these parameters were hypothesized to indicate higher levels of organization. The spatial coherence technique was tested previously in a canine study of ventricular fibrillation (VF) and normal sinus rhythm, and the results suggested that spatial coherence parameters may be used to compare cardiac rhythms in terms of their organization. To test the hypothesis that organization is related to defibrillation success, 164 mapping sessions recorded during repeated VF induction and defibrillation trials using a monophasic waveform were performed in a close-chested canine study (n = 9) using a fixed energy and VF duration (10 seconds). Three coherence lengths and five coherence strengths were calculated for each VF episode. Results using a two-way analysis of variance with blocking between dogs showed that all of the coherence length and three of the coherence strength parameters were higher for those VF episodes that were successfully defibrillated than for those that were not (P < .05). Energy delivered and transmyocardial impedance were not significantly different between the groups. The authors conclude (1) the organization of a VF episode, as reflected in the spatial coherence parameters, is related to defibrillation success and may be partially responsible for the probabilistic nature of defibrillation and (2) the spatial coherence technique provides a means of quantifying myocardial electrical organization and is an important experimental tool that may be used to obtain a better understanding of VF and its termination.

Animals↗
PubMed1998

Effects of magnesium sulfate on electrical ventricular defibrillation of dogs.

Magnesium ion infusion has been reported for treatment of hypomagnesemia often associated with myocardial infarction and with surgeries involving cardiopulmonary bypass (CPB). Magnesium infusion before CPB has been reported to adversely affect the ability to defibrillate after CPB. However, there are also reports of magnesium ion infusion facilitating defibrillation of refractory ventricular fibrillation. This study evaluated the isolated effect of magnesium ion infusion on the shock intensity requirements for electrical defibrillation. The electric current required to defibrillate with 50% success (the ED50) was estimated in five mongrel dogs at baseline and again after each of four magnesium sulfate (80 mg/kg) infusions. The total serum magnesium level increased from 2.32 +/- 0.08 mg/dL (mean +/- SD) to 7.92 +/- 0.80 mg/dL. The mean estimated ED50 decreased from 12.8 +/- 2.9 A at baseline, to 11.1 +/- 0.8 A after the fourth infusion (P < .05), decreasing the delivered energy by 25%. Magnesium sulfate infusion was associated with a significant decrease in the electrical requirements for defibrillation. Key words: magnesium, electrical ventricular defibrillation.

Animals↗
PubMed1984

Limitation on effectiveness of rapid defibrillation by emergency medical technicians in a rural setting.

First-responding emergency medical technicians (EMTs) trained to defibrillate have been shown to increase survival from prehospital ventricular fibrillation (VF) almost fourfold in Washington's King County. Using Nebraska ambulance rescue run data from 1982 and published information relating ambulance response time to the likelihood that a patient would be in VF, we constructed a model to analyze the difference in expected results for EMT defibrillation among communities of varying population. The model predicts that EMTs in urban Nebraska (mean population 242,000) will use the defibrillator once every six weeks. EMTs in intermediate cities (mean population 22,300) will defibrillate once a year. In rural Nebraska (mean population 1,500), the defibrillator will be used once every 5.6 years. Despite these figures, the model predicts relatively low cost per life saved (ranging from $566 in urban areas to $4,785 in rural Nebraska). The major problem with EMT defibrillation in rural areas is maintenance of skills and continuing education.

Education, Continuing↗
PubMed1988

An innovative approach to medical control: semiautomatic defibrillators with solid-state memory modules for recording cardiac arrest events.

We evaluated the use of microprocessor-based memory modules incorporated into automatic external defibrillators. These solid-state modules store information about each clinical use, including selected segments of the ECG rhythm and notations on defibrillator operation. A playback unit provides annotated printouts of the recorded information. The purpose of our evaluation was to determine whether this memory module could adequately support medical control "run-reviews" when compared with dualfunction (voice and ECG) tape recordings. A total of 41 resuscitation attempts by emergency medical technicians trained to defibrillate (EMT-Ds) were evaluated in five preselected performance areas: defibrillation skills, command and communication at the scene, patient assessment and support, safety, and speed. When performance was reviewed using the tape recordings, the average EMT-D performance score was 16.2 (maximum, 20); when reviewed using the printouts from the medical control modules, the average score, 7.2, was significantly lower (P less than .01). The lower scores with the medical control module occurred because not all five areas of skill could be evaluated adequately by the memory module approach. Assessment of the areas of communication/command at the scene, patient assessment/support, and safety required verbal tape recordings. The medical control module appeared superior to the tape recordings at providing a quick, convenient, and accurate evaluation of rhythm assessment, shock decisions, time intervals, and defibrillator performance. They make several features of medical control review easier and more convenient, and may encourage implementation of early defibrillation programs. We conclude, however, that medical control modules cannot replace on-scene tape recordings for adequate medical control of EMT-D programs.

Automation↗
PubMed1988

New perspectives on rural EMT defibrillation.

In recent years, several studies have produced contradictory data regarding the impact of emergency medical technicians trained in defibrillation on hospital admission and dismissal survival rates in rural areas. Fourteen communities (service area populations, 4,000 to 36,000) in rural south-eastern Minnesota participated in a two-year crossover study to further define the factors necessary for success. Automatic external defibrillators were used to defibrillate and record patient rhythms in the treatment group and to only record in the control group. Although six of 36 patients (17%) in ventricular fibrillation who experienced a witnessed arrest survived in communities using automatic external defibrillators, compared with one of 27 (4%) in the control group, five of the six survivors were from a single large community with a 911 system, full-time emergency medical technicians, police first-responders, and a well-equipped emergency facility. Our data suggest that certain prerequisites, especially CPR prior to ambulance arrival and collapse to defibrillation times of less than ten minutes, are clearly essential to produce significant benefits from emergency medical technicians trained in defibrillation in rural communities.

Aged↗
PubMed1998

Use of automated external defibrillators by police officers for treatment of out-of-hospital cardiac arrest.

OBJECTIVE: To determine the feasibility of police officers providing defibrillation with automated external defibrillators (AEDs) and to assess the effectiveness of this strategy in reducing time to defibrillation of victims of out-of-hospital sudden cardiac arrest. METHODS: This was a prospective, interventional cohort study with historical controls conducted in 7 suburban communities in which police usually arrived at the scene of medical emergencies before EMS personnel. All adult patients who suffered cardiac arrest before EMS arrival and on whom EMS personnel attempted resuscitation were enrolled. Police officers who were trained to use and equipped with AEDs during the intervention phase were dispatched simultaneously with EMS to medical emergencies. Police were instructed to use the AED immediately on determination of pulselessness. Outcome measures were the difference between control and intervention phases in interval from the time the call was received at dispatch to the time of first defibrillation and in rate of survival to hospital discharge for patients initially in ventricular fibrillation. RESULTS: EMS personnel attempted 183 resuscitations in the control phase and 283 during the intervention; of these, 80 (44%) and 127 (45%), respectively, involved patients with initial ventricular fibrillation rhythms. Mean time to defibrillation decreased from 11.8+/-4.7 minutes in the control phase to 8.7+/-3.7 minutes in the intervention phase (P<.0001). Survival to hospital discharge of patients in ventricular fibrillation did not differ between phases (6% control versus 14% intervention, P=.1). When police arrived before EMS personnel, shock administered by police compared with shock administered by EMS was associated with improved survival (26% [12/46] versus 3% [1/29], P=.01). Logistic regression analysis revealed AED use was an independent predictor of survival to hospital discharge. CONCLUSION: In 7 suburban communities, police use of AEDs decreased time to defibrillation and was an independent predictor of survival to hospital discharge.

Adult↗
PubMed2001

Does paddle force applied during defibrillation meet advanced life support guidelines of the European Resuscitation Council?

OBJECTIVES: to determine whether paddle force applied during defibrillation meets the 12 kg (approximately 120 N) force recommended by the advanced life support (ALS) guidelines of the European Resuscitation Council (ERC). MATERIALS AND METHODS: an adult mannequin was "defibrillated" using standard defibrillation paddles instrumented to measure paddle force. Paddle force was recorded at the time the discharge buttons on the paddle handles were depressed. RESULTS: 54 doctors and nurses performed simulated defibrillation on a mannequin. Median sternal paddle force was 60.6 N (range 26.1-132.8 N) and median apical paddle force was 59.5 N (range 18.6-118.5 N). Only 3/54 operators (5.6%) applied sternal paddle force equal to or in excess of ERC recommendations. No operator applied apical paddle force equal to or in excess of ERC recommendations. CONCLUSIONS: force applied to defibrillation paddles does not meet guidelines of the European Resuscitation Council. Greater emphasis during advanced life support training should be placed on the importance of firm paddle force during defibrillation.

Adult↗
PubMed2001

Analysing ventricular fibrillation ECG-signals and predicting defibrillation success during cardiopulmonary resuscitation employing N(alpha)-histograms.

Mean fibrillation frequency may predict defibrillation success during cardiopulmonary resuscitation (CPR). N(alpha)-histogram analysis should be investigated as an alternative. After 4 min of cardiac arrest, and 3 versus 8 min of CPR, 25 pigs received either vasopressin or epinephrine (0.4, 0.4, and 0.8 U/kg vasopressin versus 45, 45, and 200 microg/kg epinephrine) every 5 min with defibrillation at 22 min. Before defibrillation, the N(alpha)-parameter histogramstart/histogramwidth and the mean fibrillation frequency in resuscitated versus non-resuscitated pigs were 2.9+/-0.4 versus 1.7+/-0.5 (P=0.0000005); and 9.5+/-1.7 versus 6.9+/-0.7 (P=0.0003). During the last minute prior to defibrillation, histogramstart/histogramwidth of > or =2.3 versus mean fibrillation frequency > or =8 Hz predicted successful defibrillation with subsequent return of a spontaneous circulation for more than 60 min with sensitivity, specificity, positive predictive value and negative predictive value of 94 versus 82%, 96 versus 89%, 98 versus 93% and 90 versus 74%, respectively. We conclude, that N(alpha)-analysis was superior to mean fibrillation frequency analysis during CPR in predicting defibrillation success, and distinction between vasopressin versus epinephrine effects.

Algorithms↗
PubMed2001

Are European Resuscitation Council recommendations for paddle force achievable during defibrillation?

Transthoracic impedance (TTI) is an important determinant of success in defibrillation. Low TTI increases transmyocardial current and therefore increases the chance of depolarising a critical mass of myocardium. A major component of TTI occurs at the paddle-skin interface and is minimised by pressure applied to the defibrillation paddles. The International Liaison Committee on Resuscitation (ILCOR) 2000 guidelines recommend that 'firm force' should be applied to both paddles, whereas previous European Resuscitation Council (ERC) 1992 guidelines were more precise, recommending that 12 kg of force should to be applied. We assessed whether defibrillator operators are capable of achieving 12 kg paddle force. Fifty advanced life support-trained doctors and nurses attempted to achieve 12 kg paddle force while simulating defibrillation on a resuscitation doll. The median value of the maximum pressures obtainable was 10.1 (max 16.0; min 5.0) kg force. Only 14% could achieve > or =12 kg force on both paddles for defibrillation. Men achieved more force than women (10.7 vs. 8.1 kg force; P<0.01), and there was a correlation between maximum force achieved and operator height (r2=0.27) and dominant hand-grip strength (r2=0.34). The ERC recommendation of 12 kg paddle force is not achievable by the majority of defibrillator operators.

Cardiography, Impedance↗
PubMed1998

Effects of positive end-expiratory pressure on transthoracic impedance--implications for defibrillation.

The success of defibrillation is determined by trans-myocardial current. This current is inversely proportional to transthoracic impedance (TTI). We proposed that increasing lung volume using positive end-expiratory pressure (PEEP) would increase TTI. 12 healthy subjects aged 21-37 years (6 male) were recruited. TTI between self-adhesive defibrillation pads placed in the standard antero-apical position was measured at 30 kHz at end-expiration using Bodystat MultiScan 5000 equipment. PEEP at 2.5, 5.0, 10.0, 20.0 and 40.0 cm H2O was generated using a standard continuous positive airways pressure (CPAP) circuit. Data were analysed using linear regression and paired t-tests comparing baseline TTI with that at a given PEEP. Mean (+/- S.D.) baseline TTI was 65.7 +/- 6.9 omega. TTI increased linearly with increasing PEEP (r2 = 0.99; P < 0.001). Mean percentage increases in TTI were 0.6% at 2.5 cm H2O PEEP (P = 0.05), 1.5%, at 5.0 cm H2O PEEP (P < 0.001), 3.1% at 10.0 cm H2O PEEP (P < 0.001), 5.6% at 20.0 cm H2O PEEP (P < 0.001) and 10.4% at 40.0 cm H2O PEEP (P < 0.001). PEEP increases TTI, proportionately reducing transthoracic current during defibrillation. Clinically, high levels of PEEP (20-40 cm H2O) may occur during ventilation of patients at cardiac arrest and in acute asthmatics. To maximise peak defibrillation current, PEEP should either be minimised prior to defibrillation or consideration should be given to earlier use of high energy levels for defibrillation.

Adult↗
PubMed2002

Public access defibrillation.

Very early defibrillation, within the first few minutes of VF cardiac arrest, results in significantly improved survival rates [1,10-12,34]. Most EMS systems cannot consistently provide defibrillation within the first few minutes following cardiac arrest. Defibrillation within the first few minutes following collapse is potentially achievable through the use of AEDs and PAD [9-14,62]. The delivery of defibrillation with AEDs has been made more efficient through the use of impedance-compensated defibrillation, larger pad sizes, and biphasic waveforms [34]. The technology is simple and easy to use. Preliminary cost-effectiveness analysis indicates that PAD and first-responder defibrillation are economically as attractive as other interventions in cardiac arrest [44]. Effective PAD requires significant investment in time, energy, informed planning, and rigorous quality improvement; however, the benefits are enormous. Reported VF survival rates can approach 50% or higher [11,12,62]. PAD provides the potential opportunity to transform cardiac arrest into a survivable event for most victims by making the community the ultimate coronary care unit.

Automation↗