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PubMed1998

Encircling overlapping multipulse shock waveforms for transthoracic defibrillation.

OBJECTIVES: This study was performed to determine the efficacy of new encircling overlapping multipulse, multipathway waveforms for transthoracic defibrillation. BACKGROUND: Alternative waveforms for transthoracic defibrillation may improve shock success. METHODS: First, we determined the shock success achieved by three different waveforms at varying energies (18-150 J) in 21 mongrel dogs after short-duration ventricular fibrillation. The waveforms tested included the traditional damped sinusoidal waveform, a single pathway biphasic waveform, and a new encircling overlapping multipulse waveform delivered from six electrode pads oriented circumferentially. Second, in 11 swine we compared the efficacy of encircling overlapping multipulse shocks given from six electrode pads and three capacitors versus encircling overlapping shocks given from a device utilizing three electrodes and one capacitor. RESULTS: In the first experiment, the encircling overlapping waveform performed significantly better than biphasic and damped sinusoidal waveforms at lower energies. The shock success rate of the overlapping waveform (six pads) ranged from 67+/-4% (at 18-49 J energy) to 99+/-3% at > or = 150 J; at comparable energies biphasic waveform shock success ranged from 26+/-5% (p < 0.01 vs. encircling overlapping waveforms) to 99+/-5% (p = NS). Damped sinusoidal waveform shock success ranged from 4+/-1% (p < 0.01 vs. encircling overlapping waveform) to 73+/-9% (p = NS). In the second experiment the three electrode pads, one capacitor encircling waveform achieved shock success rates comparable with the six-pad, three-capacitor waveform; at 18-49 J, success rates were 45+/-15% versus 57+/-12%, respectively (p = NS). At 100 J, success rates for both were 100%. CONCLUSIONS: We conclude that encircling overlapping multipulse multipathway waveforms facilitate transthoracic defibrillation at low energies. These waveforms can be generated from a device that requires only three electrodes and one capacitor.

Animals↗
PubMed1999

Defibrillation-guided radiofrequency ablation of atrial fibrillation secondary to an atrial focus.

OBJECTIVES: Our aim was to evaluate a potential focal source of atrial fibrillation (AF) by unmasking spontaneous early reinitiation of AF after transvenous atrial defibrillation (TADF), and to describe a method of using repeated TADF to map and ablate the focus. BACKGROUND: Atrial fibrillation may develop secondary to a rapidly discharging atrial focus that the atria cannot follow synchronously, with suppression of the focus once AF establishes. Focus mapping and radiofrequency (RF) ablation may be curative but is limited if the patient is in AF or if the focus is quiescent. Early reinitiation of AF has been observed following defibrillation, which might have a focal mechanism. METHODS: We performed TADF in patients with drug-refractory lone AF using electrodes in the right atrium (RA) and the coronary sinus. When reproducible early reinitiation of AF within 2 min after TADF was observed that exhibited a potential focal mechanism, both mapping and RF ablation were performed to suppress AF reinitiation. Clinical and ambulatory ECG monitoring was used to assess AF recurrence. RESULTS: A total of 44 lone AF patients (40 men, 4 women; 32 persistent, 12 paroxysmal AF) with a mean age of 58+/-13 years underwent TADF. Sixteen patients had early reinitiation of AF after TADF, nine (20%; 5 paroxysmal) exhibited a pattern of focal reinitiation. Earliest atrial activation was mapped to the right superior (n = 4) and the left superior (n = 3) pulmonary vein, just inside the orifice, in the seven patients who underwent further study. At the onset of AF reinitiation, the site of earliest activation was 86+/-38 ms ahead of the RA reference electrogram. The atrial activities from this site were fragmented and exhibited progressive cycle-length shortening with decremental conduction to the rest of the atrium until AF reinitiated. Radiofrequency ablation at the earliest activation site resulted in suppression of AF reinitiation despite pace-inducibility. Improved clinical outcome was observed over 8+/-4 months' follow-up. CONCLUSIONS: Transvenous atrial defibrillation can help to unmask, map, and ablate a potential atrial focus in patients with paroxysmal and persistent AF. A consistent atrial focus is the cause of early reinitiation of AF in 20% of patients with lone AF, and these patients may benefit from this technique.

Atrial Fibrillation↗
PubMedDate not supplied

Problems associated with the Z-fold region of defibrillation electrodes.

To examine performance failures of automatic external defibrillator (AED) self-adhesive electrodes, a retrospective analysis of patient reports and electrodes was conducted in a suburban emergency medical service (EMS) system. In all cases, only records from out-of-hospital cardiac arrests (OHCA) were used if the EMS was activated and an AED was used. Electrode failures were assessed as follows: 1) EMS staff returned defibrillation electrodes when they were unable to resolve repeated "Check Electrode" messages, and 2) an audit of selected records was used to determine the frequency of electrode problems during calls. Of 302 OHCA calls during the study period, 22 (7%) resulted in returned electrodes. Defects (cracks or faults) in the internal conductor were present in 37 (86%) of the 43 returned electrodes; 2 (5%) possessed dehydrated conductive gel, and in 4 (9%) electrodes no faults could be identified. Of the 21 complete sets of defective electrodes, 16 (76%) had faults in both electrodes. Chart review revealed at least one "check electrode" message occurring in 21 (60%) of 35 OHCA reports. The electrode checks were present for a total of over 83 min, representing 11% of the call times. Paramedics were required to change electrodes in 9 (26%) of the 35 cases, resolving the malfunction in all instances. Electrode malfunction appears to be a common prehospital problem; the conductor is responsible for the majority of electrode problems and is probably subjected to the most stress during storage and handling. More reliable, durable defibrillation electrodes are required for OHCA treatment. Other strategies for electrode storage and quality control are also discussed.

Electric Countershock↗
PubMed1997

Sensitivity of transvenous defibrillation models to adaptive mesh density and resolution: the potential for interactive solution times.

The voltage gradients induced in ventricular myocardium by an electric shock have been shown to correlate to the probability of the shock producing a successful defibrillation. Finite element modeling is one method for computing these voltage gradients, although the meshing of complex biomedical domains is difficult on a patient-specific basis. We recently described an adaptive algorithm that automates the generation of finite element meshes for complex 3-D domains from bitmapped images. This article examines the sensitivity of the computed distribution of ventricular voltage gradients to the resolution of the images and to the adapted density of the mesh. The results allow us to establish an adaptation stopping criterion and a minimum input image resolution for modeling transvenous defibrillation. The sensitivity to adapted mesh density was analyzed by comparing voltage gradient histograms from successively finer meshes to histograms from a uniform mesh at the maximum possible density. Comparisons were made using the Kolmogorov-Smirnov test with the number of samples required to detect a 5% difference in the histograms at the 0.05 significance level. Adaptation to a global current density error estimate of 5% or less was required in order to achieve acceptance of the null hypothesis that the distributions were the same in all cases. Defibrillation efficacy, however, is predicted from the voltage gradient in the first quartile, and the results suggest that this region of the cumulative histogram converges faster during mesh adaptation than the histogram as a whole. We also compared histograms from models generated from successively finer input images. The histogram of each model was compared with the histogram obtained from the finest possible resolution. In all cases, the null hypothesis of no difference was accepted at resolutions of 2.3 x 2.3 x 3.0 mm. The average time required to build and adapt models to a 5% accuracy at the first quartile at this resolution was 1.8 min. on a common workstation. We believe that this demonstrates a potential for the eventual synthesis of finite element computations into interactive electrode placement tools on a subject-specific basis.

Algorithms↗
PubMed2004

Who left the defibrillator on?

BACKGROUND: Two related scenarios involving defibrillator devices reveal how inadvertent hazardous design can go unnoticed until engineers or patient safety personnel use human factors engineering (HFE) analysis. The first adverse event, in which the device was inadvertently turned off while being used to externally pace the patient's heart, resulted in an increased length of stay. The second scenario describes a similar close call and the useless acts of sanctioning the nurse and firing the engineer technician. COMMENTS AND RECOMMENDATIONS: Feedback to the end user about a device's status is an important design issue. It does not take much expertise to detect when there are problems with "dialogue" from the device to the person (that is, feedback). Many HFE issues have been cited in emergency care areas, and many medical devices--not just defibrillators--do not have readable and understandable feedback to the end user or the kind of automation that would make the wrong action harder to accomplish. All the interactions of multifunction devices with end users in a hectic, noisy, and dynamic environment need to be usability tested and validated. Nurses and engineering personnel can be trained to more easily see HFE design issues--and not dismiss them as individual failings or "someone else's job." Medical device companies are starting to follow the guidelines and regulations that should help prevent adverse events. CONCLUSION: The defibrillator's design problems had successfully masqueraded as "expected" glitches with hospital electrical utilities, personnel shortcomings, and personality problems. Adverse events related to seemingly simple devices can be prevented with HFE analysis.

Data Display↗
PubMedDate not supplied

Locations of cardiac arrest: affirmation for community Public Access Defibrillation (PAD) Program.

BACKGROUND: The purpose of this study was to describe the regional locations of cardiac arrest, and to identify public locations and the annual incidence of arrests within the identified locations, in order to help to determine optimal placement of Automatic External Defibrillators (AEDs) under the regional Public Access Defibrillation (PAD) Program. This is a retrospective study. METHODS: The locations of cardiac arrest were abstracted from Ambulance Call Reports (ACRs) collected by the Essex-Kent Base Hospital Centre from regional ambulance services throughout the City of Windsor, and the Counties of Essex and Kent, Ontario, Canada, from 01 January 1994 through 31 December 2000. Arrest locations were grouped into five categories, and then the number of public venues was determined. Public Sites were grouped into 28 Public Locations. Also included in the Public Sites were both General Industry and Outdoors categories. Categories identified but excluded from Public Sites were Institutions and Private Residences. RESULTS: During the study, 2,295 arrests occurred, 152 cases were excluded, 2,142 arrests were categorized, (average annual incidence of 306 +/- 50.4 cardiac arrests), 329 (15.4%) of which were in Public Sites. Nineteen public venues had an average of > 1 arrest/year, and nine public venues had an average of < or = 1 arrest/year during the study, period. Calculations of the annual incidence of arrests for each public location were completed. CONCLUSIONS: These findings have significant prehospital emergency cardiac care implications for communities that wish to strengthen/improve their responses to out-of-hospital cardiac arrests. Public Access Defibrillation Programs should identify the site-specific incidence of arrest within their communities in order to provide legitimacy for funding and planning of programs. Training and availability of AEDs will reduce the time to first shock, thus strengthening the chain-of-survival and will save more lives.

Ambulances↗
PubMed1997

Pharmacologic enhancement of atrial electrical defibrillation efficacy: role of ibutilide.

The study was designed to identify the influence of ibutilide on activation during atrial fibrillation (AF) and determine its role in enhancing the efficacy of electrical conversion of AF. Vagally-mediated acute AF was induced in 12 anesthetized dogs. In 5 dogs, a cross-shaped epicardial patch containing 16 recording electrodes was placed on the right atrium. In 7 dogs, defibrillation patch electrodes overlying both atria were used to deliver biphasic shocks (50% tilt; 90 microF). Measurements were made at baseline and following ibutilide (0.075 mg/kg bolus followed by 0.075 mg/kg infusion over 10 minutes). Right atrial multisite electrogram recordings revealed significant prolongation in AF cycle length at all sites following ibutilide. In all dogs, AF cycle length increased with ibutilide from 90 +/- 23 to 130 +/- 49 ms (p < 0.005). Whereas, atrial defibrillation threshold decreased from 0.83 +/- 0.5 to 0.53 +/- 0.29 J (p = 0.020). In conclusion, ibutilide prolongs cycle length of canine vagally-mediated acute AF. Furthermore, ibutilide facilitates electrical conversion of AF by lowering energy requirement. Thus, controlled drug infusion in conjunction with electrical defibrillation may be useful for managing AF.

Animals↗
PubMed1999

Optical transmembrane potential recordings during intracardiac defibrillation-strength shocks.

BACKGROUND: The prolongation of the action potential after defibrillation-strength shocks is believed to be a critical component of defibrillation. The response of the transmembrane potential to the shock may affect this prolongation. We studied the effects of an intracardiac shock on the transmembrane potential and action potential duration at multiple sites on the epicardium using a voltage-sensitive dye and optical mapping system. METHODS AND RESULTS: A laser scanner recorded optical action potentials with voltage-sensitive dye at 63 spots on both the left and right ventricles of six isolated, perfused rabbit hearts. Hearts were paced with epicardial point stimulation followed by the delivery of a 2 A and 20 ms rectangular waveform shock during the relative refractory period. The shock was given between right atrial and right ventricular electrodes. Of 621 total spots analyzed, 241 spots hyperpolarized and 76 spots depolarized with a right ventricular anode, whereas 159 spots hyperpolarized and 145 spots depolarized with a right ventricular cathode (P < 0.05). Both hyperpolarized and depolarized spots exhibited prolonged action potential duration, although prolongation was greater with depolarizing responses (16.7 +/- 9 ms vs. 13.3 +/- 13.4 ms, p<0.001). Hyperpolarized and depolarized spots were not randomly distributed, but clustered into regions. The size of the hyperpolarized regions was larger than the depolarized regions with RV anodal stimulation (27 +/- 20 spots/hyperpolarized region vs. 8.5 +/- 9 spots/depolarized region, p < 0.03) but not with RV cathodal stimulation. With reversal of electrode polarity, spots hyperpolarized near the shocking electrodes frequently did not reverse polarization but remained hyperpolarized. CONCLUSIONS: Distinct regions of either polarization occur during intracardiac defibrillation-strength shocks. Although hyperpolarizing membrane responses were observed more often than depolarizing responses, depolarizing membrane polarization resulted in greater action potential prolongation. The absence of sign change in polarization in some regions with shocks of opposite polarities suggests that nonlinear intrinsic membrane properties are operative during strong electrical stimulation.

Action Potentials↗
PubMed1999

Azimilide decreases defibrillation voltage requirements and increases spatial organization during ventricular fibrillation.

INTRODUCTION: Drugs with class III antiarrhythmic properties generally decrease defibrillation threshold (DFT). However, the concentration effect relation for this effect and drug effects on ventricular fibrillation (VF) itself are not well understood. The objectives of this study were to determine the effect of azimilide (NE-10064), a new class III agent, on DFT, and on spatial organization during VF. METHODS: Defibrillation patch electrodes were sutured to the right and left ventricular epicardium in 12 open-chest anesthetized dogs. The delayed up-down algorithm was used to measure DFT and to estimate the shock strength (voltage) with a 50% probability of successful defibrillation (V50). The magnitude squared coherence (MSC), which measures the spatial relation in the frequency domain, was measured during VF between two unipolar epicardial electrodes 3 mm apart. The V50, MSC, electrophysiologic parameters, and plasma concentrations were determined before and after four cumulative i.v. doses of azimilide (2, 7, 17, and 30 mg/kg). RESULTS: Azimilide elicited a dose dependent reduction of V50 and increase in MSC. Compared with baseline, azimilide lowered mean V50 by 2 +/- 9%, 10 +/- 18%, 11 +/- 14% and 19 +/- 5%, and increased MSC by 17 +/- 20%, 32 +/- 31%, 20 +/- 44% and 27 +/- 20% (p < 0.05 for dose effect) at 2, 7, 17 and 30 mg/kg, respectively. Mean increases in monophasic action potential duration at 90% repolarization (3-11%), ventricular effective refractory period (6-13%) at 400 msec paced cycle length, and VF cycle length (5-37%) (p < 0.01 for dose effect) were observed with the 4 increasing doses of azimilide, respectively. CONCLUSION: Azimilide significantly decreases DFT and increases coherence in VF in a dose dependent manner.

Algorithms↗
PubMed2003

Delayed afterdepolarization inhibitor: a potential pharmacologic intervention to improve defibrillation efficacy.

INTRODUCTION: Electrical and optical mapping studies of defibrillation have demonstrated that following shocks of strength near the defibrillation threshold (DFT), the first several postshock cycles always arise focally. No immediate postshock reentry was observed. Delayed afterdepolarizations (DADs) have been suggested as a possible cause of this rapid repetitive postshock activity. The aim of this study was to test the hypothesis that DFT is decreased by application of a DAD inhibitor. METHODS AND RESULTS: Six pigs (30-35 kg) were studied. First, control DFT was determined using a three-reversal up/down protocol. Each shock (RV-SVC, biphasic, 6/4 msec) was delivered after 10 seconds of ventricular fibrillation (VF). Then, flunarizine (a DAD inhibitor) was injected intravenously (2 mg/kg bolus and 4 mg/kg/hour maintenance) and the DFT was again determined. A third DFT was determined 50 minutes after drug infusion was terminated to allow the drug to wash out. DFT after flunarizine application (520 +/- 90 V, 14 +/- 3 J) was significantly lower than control DFT (663 +/- 133 V, 23 +/- 4 J). After the drug washed out, DFT (653 +/- 107 V, 22 +/- 4 J) returned to the control DFT value (P = 0.6). Flunarizine reduced the DFT approximately 22% by leading-edge voltage and approximately 40% by energy. CONCLUSION: Flunarizine, a DAD inhibitor, significantly improved defibrillation efficacy. This finding suggests that DADs could be the source of the rapid repetitive focal activation cycles arising after failed near-DFT shocks before degeneration back into VF. Future studies are needed to investigate the cause of the earliest postshock activation and to determine if the DADs are responsible.

Animals↗
PubMed2004

Analysis of the defibrillation efficacy for 5-ms waveforms.

INTRODUCTION: Empirical studies have shown that biphasic defibrillation waveforms are more efficacious than monophasic waveforms. However, a more systematic approach to waveform development might be more productive. This study tested 147 multiphasic waveforms uniformly sampled from all possible 5-ms waveforms. METHODS AND RESULTS: One hundred ninety-eight guinea pigs (850-1,050 g) received 30 episodes of ventricular fibrillation followed by transthoracic defibrillation. The first 10 shocks were used to determine the ED(50) for a biphasic control. Then, 20 waveforms including 2 controls were tested once at the ED(50). Of the 147 waveforms tested here, 21 waveforms showed equivalent or greater efficacies than the biphasic control, with one being statistically more efficacious (P < 0.05). Two fundamental assumptions were addressed: (1) similarly efficacious waveforms are analytically similar, and (2) a single optimal waveform can be described. The mean percentage of similarly efficacious waveforms with similar shapes was greater than zero in the most efficacious 21 waveforms (P = 0.023), but less efficacious waveforms showed randomly distributed shapes. Cluster analysis revealed that the best waveforms share a major phase containing most of the defibrillation energy. The optimal waveform shape extrapolated from the sample waveforms was a 2.5/1-ms biphasic-type waveform (highest correlation r = 0.701, P < 0.001). CONCLUSION: This work supports the assumption that efficacious waveforms are similarly shaped and the notion that one single optimum exists.

Animals↗
PubMed1989

[Is early defibrillation in the emergency-first aid call system useful?].

In a model study, 115 firemen and ambulance emergency personnel were trained in a 12-hour course to use conventional defibrillators prior to the arrival of an emergency care physician for treating patients with ventricular fibrillation. Subsequently, 178 firemen were trained in a 6-hour course to use semi-automatic defibrillators. A total of 252 resuscitations were evaluated with the help of tape recordings. The survival rate of 124 patients with ventricular fibrillation was statistically significantly higher after defibrillation by ambulance personnel if the emergency physician arrived in less than 14 minutes after the emergency call. A group of 109 patients who underwent only cardiopulmonary resuscitation until the arrival of the emergency physician served as a control.

Aged↗
PubMed1982

Ventricular defibrillation -- a comparative trial using 175-J and 320-J shocks.

We compared the effects of initial electrical shocks using 175 and 320 J (joules) in 249 patients with ventricular fibrillation. Survival was unrelated to the energy level used for defibrillation. Reversion to an organized rhythm occurred in a similar proportion of both treatment groups after one or two shocks. The rhythm identified after the first shock was related to outcome (the survival rate was 42 per cent in patients with supraventricular rhythm, 30 per cent in persistent ventricular fibrillation, 26 per cent in idioventricular rhythm, and 14 per cent in asystole; P less than 0.02). Fibrillation recurred in 68 per cent of patients who had been initially defibrillated to an organized rhythm. Repeated shocks at the higher energy level resulted in a higher incidence of atrioventricular block after defibrillation (24 per cent of patients receiving 320 J and 9 per cent of those receiving shocks of lower energy; P less than 0.005). Patients who survived required fewer shocks than patients who later died in the hospital (2.6 shocks as compared with 3.6; P less than 0.005). We conclude that initial defibrillatory shocks using 175 J are as safe and effective as shocks of nearly twice that energy level.

Electric Countershock↗
PubMed1986

Treatment of malignant ventricular arrhythmias with endocardial resection and implantation of the automatic cardioverter-defibrillator.

Although ventricular resection guided by endocardial mapping has been a successful treatment for drug-refractory ventricular arrhythmias, 20 to 30 percent of patients still have postoperative sustained ventricular tachycardia or sudden death. To improve the outcome of the procedure, we implanted an automatic cardioverter-defibrillator in conjunction with endocardial resection in 28 patients, all of whom had had previous myocardial infarctions and between one and five cardiac arrests. There were three perioperative deaths. During follow-up of 8 to 51 months (mean, 25), 4 of the 25 survivors had recurrences of hypotensive ventricular tachycardia, which in all instances were automatically terminated by the implanted device. One patient, whose automatic cardioverter-defibrillator was not functional, died suddenly. We conclude that patients undergoing mapping-directed endocardial resection can be provided with additional protection against recurrent ventricular tachyarrhythmias or sudden death by implantation of an automatic cardioverter-defibrillator.

Adult↗
PubMed2002

Precountershock cardiopulmonary resuscitation improves ventricular fibrillation median frequency and myocardial readiness for successful defibrillation from prolonged ventricular fibrillation: a randomized, controlled swine study.

STUDY OBJECTIVE: After prolonged ventricular fibrillation (VF), precountershock cardiopulmonary resuscitation (CPR) will improve myocardial "readiness" for defibrillation compared with immediate defibrillation. METHODS: After 10 minutes of untreated VF, 32 swine (27+/-1 kg) were randomly assigned to receive immediate countershocks (DEFIB), CPR for 3 minutes followed by countershocks (CPR), or CPR for 3 minutes plus intravenous epinephrine followed by countershocks (CPR+EPI). VF waveform was evaluated by fast Fourier transformation. RESULTS: VF amplitude and median frequency by fast Fourier transformation decreased during the untreated VF interval in all groups, and the median frequency subsequently increased during each minute of precountershock CPR. Although the VF median frequency in the 3 groups did not differ after 10 minutes of untreated VF (8.9+/-0.8 Hz versus 8.4+/-0.5 Hz versus 7.3+/-0.5 Hz, respectively), immediately before the first shock the VF median frequency was much lower in the DEFIB group than in either the CPR or CPR+EPI groups (8.9+/-0.8 Hz versus 13.1+/-0.8 Hz versus 13.8+/-0.9 Hz, respectively; P <.01). None of the 10 animals in the DEFIB group attained return of spontaneous circulation after the first set of shocks versus 5 of 10 animals in the CPR group and 6 of 12 animals in the CPR+EPI group (DEFIB versus each CPR group; P <.05). Cardiac output 1 hour after resuscitation was substantially worse in the DEFIB group than in the CPR or CPR+EPI groups (74+/-7 mL/kg per minute versus 119+/-7 mL/kg per minute versus 104+/-15 mL/kg per minute; P <.05). CONCLUSION: Precountershock CPR can result in substantial physiologic benefits compared with immediate defibrillation in the setting of prolonged VF. Moreover, these benefits can be attained with or without the addition of intravenous epinephrine.

Animals↗
PubMed2002

Effect of shock polarity on the efficacy of transthoracic atrial defibrillation.

BACKGROUND: The energy requirement for internal ventricular defibrillation is reduced by reversal of shock polarity. The influence of shock polarity on the efficacy of transthoracic atrial defibrillation is unknown. METHODS: This prospective, randomized study enrolled 110 consecutive patients who were referred for elective cardioversion of persistent atrial fibrillation (AF). The electrodes were placed in the anteroposterior position. The patients were randomized to receive either standard (anterior pad = cathode) or reversed polarity (anterior pad = anode) shocks with a damped sinusoidal monophasic waveform. A step-up protocol was used to estimate the cardioversion threshold. The initial shock energy was 50 J, with subsequent increments to 100, 200, 300, and 360 J in the event of cardioversion failure. RESULTS: Sixty-four percent of the patient population were men, with a mean age of 66 +/- 13 years and a mean duration of AF of 242 +/- 556 days. The overall success rates of cardioversion were 84% for standard polarity and 78% for reversed polarity (P not significant). Among the patients who were successfully cardioverted, the mean atrial defibrillation threshold was 198 +/- 103 J for standard polarity and 212 +/- 107 J for reversed polarity (P not significant). CONCLUSIONS: Reversal of shock polarity does not improve transthoracic cardioversion efficacy with a standard damped sinusoidal monophasic waveform. Alternate strategies should be considered for patients who fail external cardioversion, such as adjunctive pharmacologic treatment, use of a biphasic shock waveform, or internal cardioversion.

Aged↗
PubMedDate not supplied

Possibilities for predictive measurement of the transthoracic impedance in defibrillation.

Transthoracic electrical defibrillation is administered by high voltages and currents applied through large size electrodes. Therefore, the defibrillator load impedance becomes an essential factorfor the efficacy of the procedure. Attempts at prediction of transthoracic impedance by pre-shock measurement with low-amplitude high-frequency current have yielded apparently promising results. A reassessment was undertaken of the comparison between transthoracic impedance measured over a wide frequency range (bioimpedance spectroscopy) and measured during the shock. An estimation of the possibilities for pre-shock 'prediction ' of the impedance was performed, to allow adequate selection of the defibrillation energy or current with the intention of increasing the possibility for positive results with the first shock. Data were obtained from experimental fibrillation/defibrillation cycles on dogs andfrom cardioversion of atrial fibrillation or flutter in patients. The final results suggest that high-frequency low-amplitude impedance measurements cannot predict the corresponding value during the shock with very high accuracy, as differences up to 15-17% were found using biphasic pulses in patients. However, the method can be used for approximate assessments.

Adult↗
PubMedDate not supplied

Defibrillator-embedded rapid recovery electrocardiogram amplifier.

One of the most important performances of the defibrillator-embedded amplifier-monitor-recorder tract, connected to defibrillator electrodes, is its rapid recovery after the application of the shock pulse. Practically near-immediate restoration of the signal trace is mandatory for studies of post-shock effects on the myocardium. Automatic analysis of the electrocardiogram signal in public-access defibrillation, aiming for about 100% correct recognition of shockable and non-shockable rhythms, now requires fast amplifier settling, as the decision time should not exceed 10-20 s. Two circuits of post-shock amplifier transient suppressors were developed with non-linear feedback, resulting in second-order high-pass filtering, with gradual return to normally accepted first-order response. Simulation and testing in real conditions resulted in recovery periods in the range of 1-2 s for an amplifier tract of 1-30 Hz bandwidth, depending on the pulse waveform and electrode type.

Amplifiers, Electronic↗