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At least 865 records · Page 48Linked to original sources
PubMed1997

Can a class III antiarrhythmic drug improve electrical defibrillation efficacy during ventricular fibrillation?

OBJECTIVES: We tested whether a new class III drug (MS-551) administered during ventricular fibrillation (VF) could decrease the defibrillation threshold (DFT) in anesthetized canine hearts. BACKGROUND: Pretreatment with class III antiarrhythmic agents is known to enhance electrical defibrillation efficacy. METHODS: In a preliminary study (n = 10), we ascertained the validity of DFT determination by a sequence of incremental defibrillation shocks in a single fibrillation/defibrillation episode. We then compared the DFTs after 130 s of VF with and without administration of MS-551 (2 mg/kg body weight) at 10 s after the onset of VF in 12 open chest dogs and 8 closed chest dogs. RESULTS: MS-551 decreased the DFT in both experimental models (open chest [mean +/- SD]: from 416 +/- 106 to 318 +/- 92 V, p < 0.05; closed chest: from 714 +/- 75 to 615 +/- 112 V, p < 0.05). The change (delta) in DFT in each heart was inversely correlated with the drug-induced prolongation of VF cycle length before the defibrillation attempt (delta DFT vs. delta VF cycle length 10 s before the first discharge: r = -0.58 and -0.81, p < 0.05). CONCLUSIONS: MS-551 given after the induction of VF improved defibrillation efficacy. Class III antiarrhythmic agents deserve consideration when VF is resistant to electrical defibrillation during cardiopulmonary resuscitation.

Action Potentials↗
PubMed1997

Effects of myocardial ischemia on ventricular fibrillation inducibility and defibrillation efficacy.

OBJECTIVES: This study investigated the effects of acute global ischemia on the vulnerable window, the upper limit of vulnerability and the defibrillation threshold. BACKGROUND: Myocardial ischemia, an important factor for arrhythmogenesis and sudden death, may affect the inducibility of ventricular fibrillation by T wave shocks as well as the defibrillation threshold. However, studies of the effect of ischemia on the defibrillation threshold remain inconclusive, and the effect of ischemia on recently established variables of ventricular fibrillation vulnerability is still unknown. METHODS: Ten isolated, perfused rabbit hearts were immersed in a tissue bath between two shock plate electrodes. Truncated 5-ms biphasic shocks were used to determine the vulnerable window, the upper limit of vulnerability and the defibrillation threshold. Measurements were performed during baseline and at 10 to 15 min of acute ischemia induced by an 80% reduction of coronary flow. The effects of ischemia were monitored by measuring the dispersion of ventricular activation and repolarization using multiple monophasic action potential recordings. RESULTS: Acute ischemia caused an increase in dispersion of activation (baseline vs. ischemia [mean +/- SD]: 22 +/- 6 vs. 34 +/- 10 ms, p < 0.001) and dispersion of repolarization (37 +/- 16 vs. 69 +/- 29 ms, p < 0.01). The width of the vulnerable window increased from 25 +/- 22 ms during baseline to 75 +/- 26 ms during ischemia (p = 0.001). The upper limit of vulnerability (baseline vs. ischemia: 294 +/- 44 vs. 274 +/- 53 V, p = 0.21) and the defibrillation threshold (271 +/- 33 vs. 268 +/- 42 V, p = 0.74) remained unchanged during ischemia. CONCLUSIONS: Acute global ischemia caused a threefold increase in the width of the vulnerable window. This increase was associated with increased heterogeneity of ventricular activation and repolarization. Despite these marked changes, the upper limit of vulnerability and the defibrillation threshold were not affected by acute myocardial ischemia. Thus, the previously reported similarity between both measures was maintained under these adverse conditions.

Action Potentials↗
PubMed2001

Correlation between defibrillation shock outcome and coherence in electrocardiograms.

Cycle periods in ECG during VF are correlated with periods of reentrant activation. The ECGs recorded from different locations on the thorax were contributed to from electrical activations within the heart in approximately inverse proportion of their distance from the recording sites. Similarity in cycle periods between ECGs recorded from two locations, therefore, can be used as an index of spatiotemporal similarity in the rate of activation. In the present study coherence was used, which is a mathematical function that measures the degree of similarity that two signals exhibit at specific cycle periods, to test if spatiotemporal similarity in cycle periods between pairs of orthogonal ECGs was correlated with defibrillation shock outcome. The authors estimated time-varying coherence from orthogonal ECGs during 10 seconds of electrically induced VF, which was terminated with a defibrillation shock with a 50% probability of successful outcome. Defibrillation shocks were delivered between a coil electrode placed at the right ventricular apex and a subdermal patch electrode. Time-varying coherencies between pairs of ECGs were estimated using an adaptive least mean square algorithm. Time-coherence surfaces were integrated within a frequency region centered at the dominant frequency. Data were collected from ten dogs during 206 (48%) successful and 221 (52%) unsuccessful trials. The results showed that coherencies between the sagittal-transverse pair were 10%-15% higher (P < 0.05) for successful than unsuccessful trials. The correlation between coherence and defibrillation outcome suggests that more defibrillation shocks occurred when the degree of spatial similarity in the rate of activations was higher terminated VF, than those that occurred at other times. These results are consistent with a hypothesis, recently proposed by others, that more uniform activation within regions of the heart that receive low potential gradients during shock may increase the probability of successful defibrillation.

Animals↗
PubMed2003

Dose-response relationship for successful internal atrial defibrillation.

The dose-response relationship for successful defibrillation has been determined in man for the ventricle but not for the atrium. The purpose of this study was to determine the dose-response relationship for internal atrial defibrillation in humans. Seventy-seven consecutive patients underwent internal atrial defibrillation for acute (n = 14) or chronic AF (n = 63). Shocks were delivered in 40-V increments between electrodes positioned in the coronary sinus and the right atrium until successful conversion or a maximum of 400 V was reached. The shock strength versus success of shock data were subjected to a Kaplan-Meier survival analysis combined with a nonparametric probability analysis to arrive at the dose-response relationship. Using this relationship, comparisons were made between acute and chronic AF and clinical relevant conversion percentages (20, 50, 80 and 95%) were estimated and were compared with the conventional mean threshold. There were significant dose-response relationships in both patients groups (P < 0.05). The Kaplan-Meier analysis comparing patients with chronic and acute AF showed significant differences in their dose-response relationships (P < 0.001). The estimated shock intensity for 95% conversion in patients with acute and chronic AF was 279 V (2.9 J) and 433 V (6.6 J), respectively (P < 0.001). The conventional mean defibrillation threshold in patients with acute (192 +/- 15 V. 1.4 +/- 0.2 J) and chronic AF (343 +/- 8 V, 4.4 +/- 0.2 J) predicted the 60% and 45% chance of successful conversion, respectively. In conclusion, this study demonstrates that single shock conversion data can be used to determine a dose-response relationship, which can be used to estimate the shock intensity required for specific successful atrial defibrillation efficacy and to compare different clinical factors that affect defibrillation efficacy.

Aged↗
PubMed2001

Electroporation in a model of cardiac defibrillation.

INTRODUCTION: It is known that high-strength shock disrupts the lipid matrix of the myocardial cell membrane and forms reversible aqueous pores across the membrane. This process is known as "electroporation." However, it remains unclear whether electroporation contributes to the mechanism of ventricular defibrillation. The aim of this computer simulation study was to examine the possible role of electroporation in the success of defibrillation shock. METHODS AND RESULTS: Using a modified Luo-Rudy-1 model, we simulated two-dimensional myocardial tissue with a homogeneous bidomain nature and unequal anisotropy ratios. Spiral waves were induced by the S1-S2 method. Next, monophasic defibrillation shocks were delivered externally via two line electrodes. For nonelectroporating tissue, termination of ongoing fibrillation succeeded; however, new spiral waves were initiated, even with high-strength shock (24 V/cm). For electroporating tissue, high-strength shock (24 V/cm) was sufficient to extinguish ongoing fibrillation and did not initiate any new spiral waves. Weak shock (16 to 20 V/cm) also extinguished ongoing fibrillation; however, in contrast to the high-strength shock, new spiral waves were initiated. Success in defibrillation depended on the occurrence of electroporation-mediated anodal-break excitation from the physical anode and the virtual anode. Some excitation wavefronts following electrical shock used a deexcited area with recovered excitability as a pass-through point; therefore, electroporation-mediated anodal-break excitation is necessary to block out the pass-through point, resulting in successful defibrillation. CONCLUSION: The electroporation-mediated anodal-break excitation mechanism may play an important role in electrical defibrillation.

Action Potentials↗
PubMed2002

Large sample test of defibrillation waveform sensitivity.

INTRODUCTION: An unknown mechanism causes defibrillation efficacy to be sensitive to the temporal pattern (waveform) of the delivered energy. Using a guinea pig model, we tested hypotheses in 140 defibrillation waveforms. METHODS AND RESULTS: Two hundred seven male guinea pigs (950 +/- 100 g) were instrumented to continuously monitor the ECG and an optical plethysmographic signal from a forepaw. Two amplifiers served as a voltage-based defibrillator with a maximum output of 400 V at 2 A. Defibrillation electrodes (12-mm diameter) were placed 40 mm apart on the thorax. Thirty ventricular fibrillation episodes were induced where the first 10 episodes were used to estimate ED50 for a biphasic pulse (7/2 msec) and the remaining episodes were defibrillated with 18 test waveforms and two control waveforms all at the ED50 energy. Seven groups of 20 waveforms were tested. We directly tested hypotheses based on charge banking/burping, frequency concentration, and stimulus strength/duration. Of the hypotheses tested, nine are able to predict at least a 10% change in efficacy (P < 0.05): parabolic fit to duration; maximum, minimum, and remaining delivered charge; power at peak frequency; stimulus charge; and maximum, minimum, and maximum of the absolute value of stimulus strength. However, of these, only three are independent predictors of waveform efficacy (P < 0.05, near-minimum residual variance): power at peak frequency; parabolic fit to the stimulus duration; and minimum stimulus strength. CONCLUSION: Stimulus strength and duration are the main determinants of the efficacy of a defibrillation waveform.

Animals↗
PubMed2000

[Does public access to defibrillators have a chance in Germany?--On the US model, legal considerations and justification].

PURPOSE: The introduction of public access to defibrillation via automated external defibrillators makes it possible to reduce the incidence of sudden cardiac arrest cases. Since they may expect civil and criminal liability after negligence causing damage, many German potential First Responders might hesitate to use an AED. METHODS: After we demonstrate the medical reasons and compare the legal situation of Public Access Defibrillation between the USA and Germany we analyse a possible hesitation of German First Responders. RESULTS: More than 30 states of the USA provide immunity from civil liability after a public access defibrillation followed by damage due to negligence. However, only an AED-trained US-First Responder is granted immunity from civil liability. In Germany there is no immunity from civil and criminal liability in case of public access defibrillation with damage caused by negligence. CONCLUSION: German law will not decrease any possible hesitation by First Responders. For a successful system of public access defibrillation, revision of the legal situation is mandatory.

Cardiopulmonary Resuscitation↗
PubMed1987

[Distribution of electric potentials in intra- and extracardiac defibrillation].

The implantable defibrillator is a device to treat refractory ventricular tachyarrhythmias. This study was done to evaluate the determinants of defibrillator performance which are not known completely. Different defibrillation electrodes were attached to beating and non-beating isolated pig-hearts (n = 15) and the electric field resulting from defibrillation measured over a distance of 3 mm. From 5 to 20 J a non-linear relation was found between delivered shock energies and the amplitudes of the recorded voltage waveforms. Using two patch electrodes maximal amplitudes were monitored apical in the right (4.6 +/- 0.5 V) and left ventricle (2.1 +/- 0.3 V). The atria only showed 10-25% of the maximal amplitudes. The combination of a patch and a catheter electrode showed similar efficiency. Two catheter electrodes reduced the apical (1.2 +/- 0.1 V) and increased the atrial amplitude (0.75 +/- 0.06 V). The recorded amplitudes in myocardium were half as much compared with blood-/sodium chloride indicating the twofold higher resistance of myocardial tissue. These experiments quantify the dependence of the efficiency of automatic implantable defibrillator systems on the sort and localization of the defibrillation electrodes.

Animals↗
PubMed1988

Use of the automatic external defibrillator in the management of out-of-hospital cardiac arrest.

The automatic external defibrillator is a simple device that can be used by nonprofessional rescuers to treat cardiac arrest. In 1287 consecutive patients with out-of-hospital cardiac arrest, we assessed the results of initial treatment with this device by firefighters who arrived first at the scene, as compared with the results of standard defibrillation administered by paramedics who arrived slightly after the firefighters. Of 276 patients who were initially treated by firefighters using the automatic defibrillator, 84 (30 percent) survived to hospital discharge (expected rate according to a logistic model, 17 percent; P less than 0.001), as compared with 44 (19 percent) of 228 patients when fire-fighters delivered only basic cardiopulmonary resuscitation and the first defibrillation was performed after the arrival of the paramedic team. Few patients with conditions other than ventricular fibrillation survived. In a multivariate analysis of characteristics that influenced survival after ventricular fibrillation, a better survival rate was related to a witnessed collapse (odds ratio, 3.9; 95 percent confidence interval, 2.0 to 7.6), younger age (odds ratio, 1.2; 95 percent confidence interval, 1.0 to 1.4), the presence of "coarse" (higher-amplitude) fibrillation (odds ratio, 4.2; 95 percent confidence interval, 1.6 to 11.0), a shorter response time for paramedics (odds ratio, 1.4; 95 percent confidence interval, 1.0 to 2.1), and initial treatment by firefighters using an automatic external defibrillator (odds ratio, 1.8; 95 percent confidence interval, 1.1 to 2.9). These findings support the widespread use of the automatic external defibrillator as an important part of the treatment of out-of-hospital cardiac arrest, although the overall impact of the use of this device on community survival rates is still uncertain.

Aged↗
PubMed2002

The prediction of defibrillation outcome using a new combination of mean frequency and amplitude in porcine models of cardiac arrest.

UNLABELLED: We estimated the predictive power with respect to defibrillation outcome of ventricular fibrillation (VF) mean frequency (FREQ), mean peak-to-trough amplitude (AMPL), and their combination. We examined VF electrocardiogram signals of 64 pigs from 4 different cardiac arrest models with different durations of untreated VF, different durations of cardiopulmonary resuscitation, and use of different drugs (epinephrine, vasopressin, N-nitro-L-arginine methyl ester, or saline placebo). The frequency domain was restricted to the range from 4.33 to 30 Hz. In the 10-s epoch between 20 and 10 s before the first defibrillation shock, FREQ and AMPL were estimated. We introduced the survival index (SI; 0.68 Hz(-1). FREQ + 12.69 mV(-1). AMPL) by use of multiple logistic regression. Kruskal-Wallis nonparametric one-way analysis was used to analyze the different porcine models for significant difference. The variables FREQ, AMPL, and SI were compared with defibrillation outcome by means of univariate logistic regression and receiver operating characteristic curves. SI increased predictive power compared with AMPL or FREQ alone, resulting in 89% sensitivity and 86% specificity. The probabilities of predicting defibrillation outcome for FREQ, AMPL, and SI were 0.85, 0.89 and 0.90, respectively. FREQ, AMPL, and SI values were not sensitive in regard to the four different cardiac arrest models but were significantly different for vasopressin and epinephrine animals. IMPLICATIONS: We present a retrospective data analysis to evaluate the predictive power of different ventricular fibrillation electrocardiogram variables in pigs with respect to defibrillation outcome. We showed that our combination of variables leads to an improved forecast, which may help to reduce harmful unsuccessful defibrillation attempts.

Algorithms↗
PubMed1980

Influence of ventilation phase on transthoracic impedance and defibrillation effectiveness.

The influence of the phase of ventilation on the transthoracic impedance and defibrillation success was studied in 6 mongrel dogs. Ventricular fibrillation was induced by a transvenous bipolar catheter electrode. Defibrillation was attempted after 1 min of ventricular fibrillation. The initial stored energy levels were 20 watt-sec for the 1st two shocks, one delivered in inspiration and one in expiration. If the shock at the initial energy level was not successful, the energy level was increased by 10 watt-sec before the next energy level shock. Initial discharge was given at inspiration in half of the animals and at expiration in the other half. The transthoracic impedance to defibrillator discharge was measured with each shock. The study revealed a significantly higher transthoracic impedance with inspiration (76.3 +/- 13 ohms versus 68.4 +/- 12 ohms expiration, p less than 0.01), and a significant decrease in defibrillation success rate when shocks were delivered in inspiration (10%) compared to expiration (50%). The phase of ventilation is an important determinant of transthoracic impedance to defibrillator discharge and has a significant influence on defibrillation effectiveness.

Animals↗
PubMed1980

The effect of newer antiarrhythmic drugs on defibrillation threshold.

This study was conducted to determine the effects of clofilium phosphate and bretylium tosylate on ventricular defibrillation threshold. Dogs were anesthetized with pentobarbital and subjected to repeated fibrillation-defibrillation episodes. Defibrillation thresholds were determined at 15-min intervals, using underdamped 5--6 msec sinusoidal current shocks, from 30 min before drug injection to 120 min after injection. Eight dogs were given clofilium phosphate (0.34 mg/kg, iv). Another 10 dogs were given bretylium tosylate (10.0 mg/kg, iv). Both drugs lowered defibrillation threshold from 15--90 min after injection. The maximum clofilium effect was a 31% decrease in threshold current and a 54% decrease in threshold energy. The greatest decrease in defibrillation threshold produced by bretylium was 16% for current and 31% for energy. These drug induced changes in defibrillation threshold are of potential clinical benefit if they occur in human subjects at doses which are effective for control of ventricular arrhythmias.

Animals↗
PubMed1996

Early defibrillation: lessons learned.

Recovery from nontraumatic cardiac arrest depends on the presence of all the elements in the chain of survival. Early defibrillation is critical because ventricular fibrillation is the most common initial dysrhythmia of sudden cardiac arrest, defibrillation is the only treatment, and survival from ventricular fibrillation is determined by time. Out-of-hospital studies have demonstrated that defibrillation provided by first responders improves survival. Technologic advances have simplified defibrillation delivery through the development of automated external defibrillators (AEDs). Early defibrillation programs with AEDs are quickly becoming a standard of care for emergency medical services systems throughout the United States. Improvement in in-hospital survival rates from cardiac arrest is not as evident as in the emergency medical services community. Medical centers need to assess response times to cardiac arrest and implement AED programs. All nurses should learn to use an AED as part of basic life support training.

Aged↗
PubMed2004

Attenuated adult biphasic shocks for prolonged pediatric ventricular fibrillation: support for pediatric automated defibrillators.

OBJECTIVE: To evaluate published data regarding the treatment of prolonged pediatric defibrillation, with special emphasis on the use of attenuated adult biphasic shocks for pediatric defibrillation. DESIGN: Review relevant human and animal literature. RESULTS: Rhythm analysis algorithms from two manufacturers of automated external defibrillators can accurately distinguish shockable from nonshockable rhythms in children. Theoretical considerations and transthoracic impedance data from animals and children suggest that pediatric defibrillation doses should not necessarily vary in a simple weight-based manner. Two piglet studies have established that an attenuated adult biphasic dosage can be successfully used for 3.5- to 24-kg animals in ventricular fibrillation. One study established that the attenuated adult biphasic dosage was at least as safe and effective as the standard monophasic weight-based dosing. CONCLUSION: This review supports the American Heart Association's new guidelines for pediatric automated external defibrillator usage: "Automated external defibrillators may be used for children 1 to 8 yrs of age who have no signs of circulation. Ideally the device should deliver a pediatric dose. The arrhythmia detection system used in the device should demonstrate high specificity for pediatric shockable rhythms, i.e., it will not recommend delivery of a shock for nonshockable rhythms."

Adult↗
PubMed2004

Amplitude spectrum area: measuring the probability of successful defibrillation as applied to human data.

OBJECTIVE: The objective of our study was to examine the effectiveness of an electrocardiographic predictor, amplitude spectral area (AMSA), for the optimal timing of defibrillation shocks in human victims of cardiac arrest. Based on the spectral characteristics of ventricular fibrillation potentials, we examined the probability of successful conversion to an organized viable rhythm, including the return of spontaneous circulation. The incentive was to predict the likelihood of successful defibrillation and thereby improve outcomes by minimizing interruptions in chest compression and minimizing electrically induced myocardial injury due to repetitive high-current shocks. DESIGN: Observational study on human electrocardiographic recordings during cardiopulmonary resuscitation. SETTING: Medical research laboratory of a university-affiliated research and educational institute. PATIENTS: Victims of out-of-hospital cardiac arrest. INTERVENTIONS: Iteration of electrocardiographic records, representing lead 2 equivalent recordings on 108 defibrillation attempts with an automated external defibrillator, of 46 victims of cardiac arrest due to ventricular fibrillation. MEASUREMENTS AND MAIN RESULTS: Three seconds of ventricular fibrillation, recorded immediately preceding delivery of a shock, were analyzed utilizing the AMSA algorithm. AMSA represents a numerical value based on the sum of the magnitude of the weighted frequency spectrum between 3 and 48 Hz. The greater the AMSA value, the greater was the probability of reversal of ventricular fibrillation. At an AMSA value of >13.0 mV-Hz, successful defibrillation yielded a sensitivity of .91 and a specificity of .94. CONCLUSION: AMSA predicts the success of electrical defibrillation with high specificity. AMSA therefore serves to minimize interruptions of precordial compression and the myocardial damage caused by delivery of repetitive and ineffective electrical shocks.

Databases, Factual↗
PubMed1993

Estimating the 95% effective defibrillation dose.

Minimum squared error (MinSE) testing protocols and a MinSE estimator are presented which accurately estimate the voltage that defibrillates 95% of the time (the ED95). The MinSE experimental procedures, presented in the form of lookup tables, detail the response to successful and unsuccessful trials. The lookup tables also show the ED95 estimates calculated from the observed results using the MinSE estimator. Two assumptions are required to develop the look-up tables: 1) the dose-response curve, chosen using a statistical analysis of a retrospective sample, and 2) the distribution of the ED95's in the population. The MinSE estimator and experimental procedure are examined in a prospective study of five dogs (19-25 kg, heart weights 139.3-236.9 gm) using nonthoracotomy implantable defibrillator electrodes and a biphasic defibrillation waveform (3.5 ms first phase, 2.0 ms second phase). Employing an ED95 population distribution assumption applicable to most implantable defibrillator electrodes and waveforms, e.g., the ED95 is between 0.0 and 800.0 V, the measured rms error was 15% of the mean measured ED95 for the MinSE, four test shock, ED95 estimates. If the protocols are designed with an ED95 population distribution assumption for animals of the same species and size, and defibrillation is constrained to one electrode configuration and waveform, the estimates improve by 3.8%. Using techniques from the Bayesian statistics literature, the MinSE approach can be extended to a variety of defibrillation parameter estimation problems.

Algorithms↗
PubMed2006

Experimental evidence of improved transthoracic defibrillation with electroporation-enhancing pulses.

There is considerable work on defibrillation wave form optimization. This paper determines the impedance changes during defibrillation, then uses that information to derive the optimum defibrillation wave form. METHODS PART I: Twelve guinea pigs and six swine were used to measure the current wave form for square voltage pulses of a strength which would defibrillate about 50% of the time. In guinea pigs, electrodes were placed thoracically, abdominally and subcutaneously using two electrode materials (zinc and steel) and two electrode pastes (Core-gel and metallic paste). RESULTS PART I: The measured current wave form indicated an exponentially increasing conductance over the first 3 ms, consistent with enhanced electroporation or another mechanism of time-dependent conductance. We fit this current with a parallel conductance composed of a time-independent component (g0 = 1.22 +/- 0.28 mS) and a time-dependent component described by g delta (1-e(-t/tau)), where g delta = 0.95 +/- 0.20 mS and tau = 0.82 +/- 0.17 ms in guinea pigs using zinc and Cor-gel. Different electrode placements and materials had no significant effect on this fit. From our fit, we determined the stimulating wave form that would theoretically charge the myocardial membrane to a given threshold using the least energy from the defibrillator. The solution was a very short, high voltage pulse followed immediately by a truncated ascending exponential tail. METHODS PART II: The optimized wave forms and similar nonoptimized wave forms were tested for efficacy in 25 additional guinea pigs and six additional swine using methods similar to Part I. RESULTS PART II: Optimized wave forms were significantly more efficacious than similar nonoptimized wave forms. In swine, a wave form with the short pulse was 41% effective while the same wave form without the short pulse was 8.3% effective (p < 0.03) despite there being only a small difference in energy (111 J versus 116 CONCLUSIONS: We conclude that a short pulse preceding a defibrillation pulse significantly improves efficacy, perhaps by enhancing electroporation.

Animals↗
PubMed1985

Implantable defibrillator electrode systems: a brief review.

Since the first report of a defibrillation attempt with an intracardiac catheter electrode nearly 30 years ago, investigators have developed implantable electrode systems consisting of metal disks, endocardial catheters, and epicardial patches. These early efforts demonstrated the feasibility of low-energy reversion of ventricular tachyarrhythmias, and also provided some insight into the mechanisms of fibrillation and defibrillation. This review describes the evolution of implantable defibrillator electrode systems. Early investigators attempted defibrillation with submuscularly implanted metal disks or a disk electrode paired with an endocardial catheter electrode. Electrode design emphasis turned to transvenous catheter systems with electrodes placed in the right ventricle and right atrium. A more successful configuration placed the proximal electrode in the superior vena cava. In an effort to ensure proper placement of the distal electrode in humans, the catheter was replaced with an epicardial patch. More recently, a combination of electrodes and multiple pulses has substantially reduced the energy required to defibrillate. Effective electrode systems that can convert lethal arrhythmias with a minimum of energy will aid in making implantable cardioverters and defibrillators the therapy of choice in patients at high risk of sudden coronary death.

Arrhythmias, Cardiac↗