Determinants of successful transthoracic defibrillation and outcome in ventricular fibrillation

Predictors of Transthoracic Impedance in Patients Who Underwent Elective Electrical Cardioversion

Successful synchronized direct current cardioversion (DCCV) requires adequate current delivery to the heart. However, adequate current for successful DCCV has not yet been established. Transmyocardial current depends on 2 factors: input energy and transthoracic impedance (TTI). Although factors affecting TTI have been studied in animal models, factors affecting TTI in humans have not been well established. Herein, we explored the potential factors that affect TTI in humans. A retrospective review of patients who underwent DCCV at a large quaternary medical center between October 2019 and August 2021 was conducted. Pertinent clinical information, including demographics, echocardiography findings, laboratory findings, and body characteristics, was collected. Cardioversion details, including joules delivered and TTI, were recorded by the defibrillator for each patient's first shock. Predictors of thoracic impedance were assessed using regression analysis. A total of 220 patients (29% women) were included in the analysis; 143 of the patients (65%) underwent DCCV for atrial fibrillation and 77 (35%) underwent DCCV for atrial flutter. The mean impedance in our population was 73 ± 18 Ω. In a regression model with high impedance defined as the upper quartile of our cohort, body mass index (BMI), female sex, obstructive sleep apnea, and chronic kidney disease (all p values <0.05) were significantly associated with high impedance. According to a receiver operating characteristic analysis, BMI has a high predictive value for high impedance, with an area under the curve of 0.76. In conclusion, our study reveals that elevated BMI, female sex, sleep apnea, and chronic kidney disease were predictors of higher TTI. These factors may help determine the appropriate initial shock energy in patients who underwent DCCV for atrial fibrillation and flutter.

A Systematic Review of the Transthoracic Impedance during Cardiac Defibrillation

For cardiac defibrillator testing and design purposes, the range and limits of the human TTI is of high interest. Potential influencing factors regarding the electronic configurations, the electrode/tissue interface and patient characteristics were identified and analyzed. A literature survey based on 71 selected articles was used to review and assess human TTI and the influencing factors found. The human TTI extended from 12 to 212 Ω in the literature selected. Excluding outliers and pediatric measurements, the mean TTI recordings ranged from 51 to 112 Ω with an average TTI of 76.7 Ω under normal distribution. The wide range of human impedance can be attributed to 12 different influencing factors, including shock waveforms and protocols, coupling devices, electrode size and pressure, electrode position, patient age, gender, body dimensions, respiration and lung volume, blood hemoglobin saturation and different pathologies. The coupling device, electrode size and electrode pressure have the greatest influence on TTI.

Early prognostic value of an Algorithm based on spectral Variables of Ventricular fibrillAtion from the EKG of patients with suddEn cardiac death: A multicentre observational study (AWAKE)

OBJECTIVE

Ventricular fibrillation (VF)-related sudden cardiac death (SCD) is a leading cause of mortality and morbidity. Current biological and imaging parameters show significant limitations on predicting cerebral performance at hospital admission. The AWAKE study (NCT03248557) is a multicentre observational study to validate a model based on spectral ECG analysis to early predict cerebral performance and survival in resuscitated comatose survivors.

METHODS

Data from VF ECG tracings of patients resuscitated from SCD will be collected using an electronic Case Report Form. Patients can be either comatose (Glasgow Coma Scale - GCS - ≤8) survivors undergoing temperature control after return of spontaneous circulation (RoSC), or those who regain consciousness (GCS=15) after RoSC; all admitted to Intensive Cardiac Care Units in 4 major university hospitals. VF tracings prior to the first direct current shock will be digitized and analyzed to derive spectral data and feed a predictive model to estimate favorable neurological performance (FNP). The results of the model will be compared to the actual prognosis.

RESULTS

The primary clinical outcome is FNP during hospitalization. Patients will be categorized into 4 subsets of neurological prognosis according to the risk score obtained from the predictive model. The secondary clinical outcomes are survival to hospital discharge, and FNP and survival after 6 months of follow-up. The model-derived categorisation will be also compared with clinical variables to assess model sensitivity, specificity, and accuracy.

CONCLUSIONS

A model based on spectral analysis of VF tracings is a promising tool to obtain early prognostic data after SCD.

A Case of Persistent and Recurrent Ventricular Fibrillation with Successful Resuscitation and Good Neurological Outcome

A 49-year-old man suffering from chest pain collapsed on arrival at an emergency department. Ventricular fibrillation was confirmed and he survived neurologically normal after 22 defibrillation shocks. This case attests that persistent and recurrent ventricular fibrillation is still compatible with good neurological outcome. Energetic and persistent efforts should be continued in such cases. Amiodarone should be considered early in the course of refractory ventricular fibrillation.

Minor Variations in Electrode Pad Placement Impact Defibrillation Success

Defibrillation is essential for resuscitating patients with ventricular fibrillation (VF), but shocks often fail to defibrillate. We hypothesized that small variations in pad placement affect shock success, and that defibrillation waveform and shock dose could compensate for suboptimal pad placement. In 10 swine experiments, electrode pads were attached at 3 adjacent anterolateral positions, less than 3 centimeters apart. At each position, 24 episodes of VF were induced and shocked, 8 episodes for each of 3 defibrillation therapies. This resulted in 9 tested combinations of pad position and defibrillation therapy, with 80 episodes of VF for each combination. An episode consisted of 15 seconds of untreated VF, followed by a first shock and, if necessary, a repeat shock. Episodes were separated by four minutes of recovery. Both electrode pad position and therapy order were randomized by experiment. Primary outcome was defined as successful VF termination after the first shock; secondary outcome was the cumulative success of the first and second shocks. First shock efficacy varied widely across the 9 tested combinations of pad position and defibrillation therapy, ranging from 11.3% to 86.3%. When grouped by therapy, first shock efficacy varied significantly between the 3 pad positions: 38.3%, 48.3%, 36.7% (p = 0.02, ANOVA), and, when grouped by pad position, it varied significantly between therapies: 15.0%, 32.5%, 75.8% (p < 0.001, ANOVA). Cumulative 2-shock success varied significantly with therapy (p < 0.001, ANOVA) but not with pad position (p = 0.30, ANOVA). The lowest first shock success was at one position in 6 of 10 animals, at another position in 4 of 10 animals, and never at the third position. Small variations in pad placement can significantly affect defibrillation shock efficacy. However, anatomical variation between individuals and the challenging conditions of real-world resuscitations make optimal pad placement impractical. Suboptimal pad placement can be overcome with defibrillation waveform and shock dose.

Electrical features of eighteen automated external defibrillators: a systematic evaluation

AIM

Assessment and comparison of the electrical parameters (energy, current, first and second phase waveform duration) among eighteen AEDs.

METHOD

Engineering bench tests for a descriptive systematic evaluation in commercially available AEDs. AEDs were tested through an ECG simulator, an impedance simulator, an oscilloscope and a measuring device detecting energy delivered, peak and average current, and duration of first and second phase of the biphasic waveforms. All tests were performed at the engineering facility of the Lombardia Regional Emergency Service (AREU).

RESULTS

Large variations in the energy delivered at the first shock were observed. The trend of current highlighted a progressive decline concurrent with the increases of impedance. First and second phase duration varied substantially among the AEDs using the exponential biphasic waveform, unlike rectilinear waveform AEDs in which phase duration remained relatively constant.

CONCLUSIONS

There is a large variability in the electrical features of the AEDs tested. Energy is likely not to be the best indicator for strength dose selection. Current and shock duration should be both considered when approaching the technical features of AEDs. These findings may prompt further investigations to define the optimal current and duration of the shock waves to increase the success rate in the clinical setting.

Analysis of transthoracic impedance during real cardiac arrest defibrillation attempts in older children and adolescents: are stacked-shocks appropriate?

BACKGROUND

In 2005, the AHA changed the treatment recommendation for shockable rhythms from 3 transthoracic stacked-shocks to a single shock followed by immediate chest compressions. The stacked-shock recommendation was based on low first-shock efficacy of monophasic waveforms and the theoretical decrease in transthoracic impedance (TTI) following each shock. The objective of this study was to characterize TTI following biphasic defibrillation attempts in children ≥ 8 yrs during cardiac arrest to assess whether a stacked-shock approach may be appropriate to improve defibrillation success.

METHODS

TTI (Ohms (Ω)) was collected via standard anterior-apical defibrillator electrode pads during consecutive in-hospital cardiac arrest biphasic defibrillation attempts in children ≥ 8 yrs. Analytic data points for TTI were: 0.1s pre-shock (baseline); post-shock at 0.1, 0.5, 1.0, 1.5, and 2.0 s. TTI variables analyzed with descriptive summaries/paired t-test. p values < 0.05 considered statistically significant after correction for multiple comparisons.

RESULTS

Analysis yielded 13 evaluable shock events during 5 cardiac arrests (mean age 14.3 ± 5 yrs, weight 47.4 ± 7.3 kg) between September 2006 and May 2009. Compared to 0.1s pre-shock baseline values (56.8 ± 23.4 Ω), TTI was significantly lower immediately 0.1s post-shock (55.2 ± 22.2 Ω, p = 0.003). Post-shock mean difference from baseline was 1.6 Ω at 0.1s (p = 0.015), 1.4 Ω at 0.5s (p = 0.019) 1.4 Ω at 1.0 s (p = 0.023), 1.1 Ω at 1.5 s (p = 0.028), and 0.95 Ω at 2.0 s (p = 0.096). Time to recharge our clinical defibrillators to standard biphasic shock dose was 2.80 ± 0.05 s.

CONCLUSIONS

During cardiac arrests in children ≥ 8 yrs, TTI decreased after biphasic shocks, but the limited magnitude and duration of TTI changes suggest that stacked-shocks would not improve defibrillation success.

A comparison of defibrillation efficacy between different impedance compensation techniques in high impedance porcine model

AIM OF STUDY

Impedance compensation methods differ markedly among manufacturers and can play an important role in defibrillation success. In this study we compared the efficacy of two different commercial defibrillators based on defibrillation success in a high impedance porcine model of cardiac arrest. The first defibrillator (A) compensates high impedance by controlling current with fixed shock duration, while the second defibrillator (B) by prolonging the shock duration.

METHODS

In 10 domestic male pigs weighing between 17 and 28 kg, ventricular fibrillation was electrically induced and untreated for 15s. Animals were randomized to receive defibrillations with either defibrillator A or defibrillator B, at maximum energy settings of which were 200 J for the defibrillator A and 360 J for the defibrillator B. A grouped up-down defibrillation threshold testing protocol was used to compare the success rate between the two defibrillators. A variable resistance, ranging from 80 to 200 ohm was placed in series with the defibrillation pads. After a recovery interval of 5 min, the sequence was repeated for a total of 60 test shocks for each animal.

RESULTS

The measured total pathway impedance was in a range of 108-278 ohm. The combined success rate was 49.5% for the two defibrillators in a total of 600 testing shocks. The success rate was significantly higher when the defibrillator A was employed in comparison with defibrillator B (63% vs. 36%, p=0.0001).

CONCLUSION

For transthoracic impedances greater than average, the current-based compensation technique was more effective than the duration-based compensation technique.

Bench study of the accuracy of a commercial AED arrhythmia analysis algorithm in the presence of electromagnetic interferences

This paper presents a bench study on a commercial automated external defibrillator (AED). The objective was to evaluate the performance of the defibrillation advisory system and its robustness against electromagnetic interferences (EMI) with central frequencies of 16.7, 50 and 60 Hz. The shock advisory system uses two 50 and 60 Hz band-pass filters, an adaptive filter to identify and suppress 16.7 Hz interference, and a software technique for arrhythmia analysis based on morphology and frequency ECG parameters. The testing process includes noise-free ECG strips from the internationally recognized MIT-VFDB ECG database that were superimposed with simulated EMI artifacts and supplied to the shock advisory system embedded in a real AED. Measurements under special consideration of the allowed variation of EMI frequency (15.7-17.4, 47-52, 58-62 Hz) and amplitude (1 and 8 mV) were performed to optimize external validity. The accuracy was reported using the American Heart Association (AHA) recommendations for arrhythmia analysis performance. In the case of artifact-free signals, the AHA performance goals were exceeded for both sensitivity and specificity: 99% for ventricular fibrillation (VF), 98% for rapid ventricular tachycardia (VT), 90% for slow VT, 100% for normal sinus rhythm, 100% for asystole and 99% for other non-shockable rhythms. In the presence of EMI, the specificity for some non-shockable rhythms (NSR, N) may be affected in some specific cases of a low signal-to-noise ratio and extreme frequencies, leading to a drop in the specificity with no more than 7% point. The specificity for asystole and the sensitivity for VF and rapid VT in the presence of any kind of 16.7, 50 or 60 Hz EMI simulated artifact were shown to reach the equivalence of sensitivity required for non-noisy signals. In conclusion, we proved that the shock advisory system working in a real AED operates accurately according to the AHA recommendations without artifacts and in the presence of EMI. The results may be affected for specificity in the case of a low signal-to-noise ratio or in some extreme frequency setting.

Future shock: automatic external defibrillators

PURPOSE OF REVIEW

This review provides a practical overview of the performance capabilities of automatic external defibrillators (AEDs), and of advances in technology and dissemination programmes for these devices.

RECENT FINDINGS

Arrhythmia analysis by AEDs is extremely reliable in most settings (sensitivity 81-100%, specificity 99.9-97.6%). Accurate detection of arrhythmias has also been demonstrated in children, leading the US Food and Drug Administration to approve the use of several AEDs in children aged 8 years or younger. Factors that potentially may reduce the quality of arrhythmia detection are the presence of wide complex supraventricular tachycardia and location of an arrythmic event near to high-power lines. AED use by professional basic life support providers resulted in increased survival in the prehospital setting. However, provision of AEDs to nonmedical rescue services did not result in universal improvement in patient outcome. Public access defibrillation programmes have led to higher rates of survival from cardiac arrest. The role of AEDs in hospitals has yet to be elucidated, although in-hospital mortality from ventricular arrhythmias has been shown to decrease following AED deployment.

SUMMARY

Given the correct setting, AEDs can ensure that defibrillation is not limited by lack of medical knowledge or difficulties in decision making. However, event-related variables and operator-related factors, that are yet to be determined, can significantly affect the efficacy of automatic external defibrillation.

Waveform analysis of ventricular fibrillation to predict defibrillation

PURPOSE OF REVIEW

Ventricular fibrillation occurs during many cases of cardiac arrest and is treated with rescue shocks. Coarse ventricular fibrillation occurs earlier after the onset of cardiac arrest and is more likely to be converted to an organized rhythm with pulses by rescue shocks. Less organized or fine ventricular fibrillation occurs later, has less power concentrated within narrow frequency bands and lower amplitude, and is less likely to be converted to an organized rhythm by rescue shocks. Quantitative analysis of the ventricular fibrillation waveform may distinguish coarse ventricular fibrillation from fine ventricular fibrillation, allowing more appropriate delivery of rescue shocks.

RECENT FINDINGS

A variety of studies in animals and humans indicate that there is underlying structure within the ventricular fibrillation waveform. Highly organized or coarse ventricular fibrillation is characterized by large power contributions from a few component frequencies and higher amplitude. Amplitude, decomposition into power spectra, or probability-based, nonlinear measures all can quantify the organization of human ventricular fibrillation waveforms. Clinical data have accumulated that these quantitative measures, or combinations of these measures, can predict the likelihood of rescue shock success, restoration of circulation, and survival to hospital discharge.

SUMMARY

Many quantitative ventricular fibrillation measures could be implemented in current generations of monitors/defibrillators to assist the timing of rescue shocks during clinical care. Emerging data suggest that a period of chest compressions or reperfusion can increase the likelihood of successful defibrillation. Therefore, waveform-based prediction of defibrillation success could reduce the delivery of failed rescue shocks.

The Department of Health National Defibrillator Programme: analysis of downloads from 250 deployments of public access defibrillators

From April 2000 to November 2002, the Department of Health (England) placed 681 automated external defibrillators (AEDs) in 110 public places for use by volunteer lay first responders. An audit has been undertaken of the first 250 deployments, of which 182 were for confirmed cardiac arrest. Of these, 177 were witnessed whilst 5 occurred in situations that were remote or initially inaccessible to the responders. The response interval between collapse and the initiation of CPR or AED placement was estimated to be 3-5 min in most cases. Ventricular fibrillation or rapid ventricular tachycardia (one case) was the first recorded rhythm in 146 cases (82%). In all, 44 of the 177 witnessed cases are known to have survived to hospital discharge (25%). Complete downloads are available for 173 witnessed cases and of these 140 were shocked: first-shock success, defined as termination of the fibrillatory waveform for 5 s or more, was achieved in 132 of them. When data quality permitted, the downloads were analysed with special reference to the numbers of compressions given and also to interruptions in compression sequences for ventilations, for rhythm analysis by the AED, for clinical checks, and for unexplained operator delays. The average rate of compressions during sequences was 120 min(-1), but because of interruptions, the actual number administered over a full minute from the first CPR prompt was a median of only 38. The speed of response by the lay first responders in relation to AED use was similar to that reported for healthcare professionals.

A trial of self-adhesive patch electrodes and hand-held paddle electrodes for external cardioversion of atrial fibrillation (MOBIPAPA)

AIMS

External electrical cardioversion is the method of choice to terminate persistent atrial fibrillation. Whether the type of shock electrode affects cardioversion success is not known. We tested whether hand-held steel electrodes improve cardioversion outcome with monophasic or biphasic shocks when compared with adhesive patch electrodes.

METHODS AND RESULTS

Two hundred and one consecutive patients with persistent atrial fibrillation (147 male, mean age 63+/-1 years, duration of atrial fibrillation 6.3+/-1 months) were randomly assigned to cardioversion using either a sinusoidal monophasic or a truncated exponential biphasic shock wave form. The first half of patients were cardioverted using adhesive patch electrodes, the second half using hand-held steel paddle electrodes, and all patients using an anterior-posterior electrode position. Paddle electrodes successfully cardioverted 100/104 patients (96%) and patch electrodes 85/97 patients (88%, P=0.04). This effect was comparable to that of biphasic shocks: biphasic shocks cardioverted 102/104 patients (98%) and monophasic shocks 83/97 patients (86%, P=0.001). A beneficial effect of paddle electrodes was observed for both shock wave forms. After cross-over from an ineffective monophasic to a biphasic shock, cardioversion was successful in 198/201 (98.5%) patients. Unsuccessful cardioversion after cross-over (3/201 patients) only occurred with patch electrodes (P=0.07).

CONCLUSION

Hand-held paddle electrodes increase success of external cardioversion of atrial fibrillation in this trial. This increase is of similar magnitude as the increase in cardioversion success achieved with biphasic shocks. A combination of biphasic shocks, paddle electrodes, and an anterior-posterior electrode position renders outcome of external cardioversion almost always successful (104/104 patients in this trial).

Ventricular Fibrillation Median Frequency May Not Be Useful for Monitoring During Cardiac Arrest Treated with Endothelin-1 or Epinephrine

In this study, we evaluated whether median fibrillation frequency (MF) and mean fibrillation amplitude (AMP) reflect coronary perfusion pressure (CoPP) and predict successful defibrillation. MF, AMP, and CoPP were measured during prolonged ventricular fibrillation (VF) cardiac arrest and resuscitation in pigs. After 5 min of VF, cardiopulmonary resuscitation was started. At 10 min, the pigs received randomly a single dose of endothelin-1 50 mug (n = 7), 100 mug (n = 7), or 200 mug (n = 5), or repeated doses of epinephrine 0.04 mg/kg (n = 6), or saline (n = 6) every 3 min. At 25 min, the pigs were defibrillated to achieve restoration of spontaneous circulation (ROSC). In a nonparametric spectral analysis of the individual MF versus CoPP and AMP versus CoPP curves, we found no link between the different curves in different animals or therapies. No difference was found in MF in pigs with ROSC (n = 8) compared with animals not achieving ROSC (n = 23) immediately before defibrillation (P = 0.85). Our data suggest that, in prolonged VF cardiac arrest, MF and AMP might not be useful tools to reflect myocardial perfusion.

Preliminary in-hospital experience with a fully automatic external cardioverter-defibrillator

BACKGROUND

Ventricular fibrillation (VF) and ventricular tachycardia (VT) are frequently present as initial rhythms during in-hospital cardiac arrest. Although ample evidence exists to support the need for rapid defibrillation, the response to in-hospital cardiac arrest remains without major advances in recent years. The delay between the arrhythmic event and intervention is still a challenge for clinical practice.

OBJECTIVE

To analyze the performance and safety of in-hospital use of a programmable, fully automatic external cardioverter-defibrillator (AECD).

METHODS

We conducted a prospective study at the Emergency Department of a university hospital. A total of 55 patients considered to be at risk of sustained VT/VF were included. Patients underwent monitoring of their cardiac rhythm by the AECD. Upon detection of a ventricular tachyarrhythmia, the AECD was programmed to automatically deliver shock therapy.

RESULTS

We recorded 19 episodes of VT/VF in 3 patients. The median time between the beginning of the arrhythmia and the first defibrillation was 33.4 s (21-65 s). One episode of spontaneous reversion of VT was documented 20 s after its origin and shock therapy was aborted. The defibrillation success was 94.4% (17/18) for the first shock and 100% (1/1) for the second shock. No case of inappropriate shock discharge was registered during the study period.

CONCLUSION

The AECD has the feasibility to combine long-term monitoring with automatic defibrillation safely and effectively. It presents the possibility of providing rapid identification of, and response to, in-hospital ventricular tachyarrhythmias.

Is optimal paddle force applied during paediatric external defibrillation?

INTRODUCTION

Optimal paddle force minimises transthoracic impedance; a factor associated with increased defibrillation success. Optimal force for the defibrillation of children < or =10 kg using paediatric paddles has previously been shown to be 2.9 kgf, and for children >10 kg using adult paddles is 5.1 kgf. We compared defibrillation paddle force applied during simulated paediatric defibrillation with these optimal values.

METHODS

72 medical and nursing staff who would be expected to perform paediatric defibrillation were recruited from a University teaching hospital. Participants, blinded to the nature of the study, were asked to simulate defibrillation of an infant manikin (9 months of age) and a child manikin (6 years of age) using paediatric or adult paddles, respectively, according to guidelines. Paddle force (kgf) was measured at the time of simulated shock and compared with known optimal values.

RESULTS

Median paddle force applied to the infant manikin was 2.8 kgf (max 9.6, min 0.6), with only 47% operators attaining optimal force. Median paddle force applied to the child manikin was 3.8 kgf (max 10.2, min 1.0), with only 24% of operators attaining optimal force.

CONCLUSION

Defibrillation paddle force applied during paediatric defibrillation often falls below optimal values.

What is the optimal paddle force during paediatric external defibrillation?

INTRODUCTION

Transthoracic impedance (TTI) is a major determinant of transmyocardial current flow, and therefore, the success of defibrillation. European Resuscitation Council (ERC) paediatric guidelines recommend that 'firm' paddle force should be applied to the paddles during defibrillation. No study has yet established the optimal paddle force required to minimise TTI in children of different ages.

METHODS

Eighty patients aged 10 weeks to 17 yrs undergoing general anaesthesia for routine surgery were studied. Using defibrillation paddles placed in an anterior-apical position, TTI (Omega) was measured for increasing values of force from 0.5 kgf (baseline) to 6.5 kgf. The optimal force, the force to achieve 95% of the overall reduction in TTI, was then determined. According to current guidelines, paediatric paddles (surface area 16 cm2) were used for infants (< or =10 kg) and adult paddles (82 cm2) for older children. Optimal force was then calculated for infants < or =10 kg, children >10 kg and < or =8 yrs and children 9-17 yrs age.

RESULTS

Increasing paddle force from 0.5 kgf progressively decreased TTI. Optimal force using paediatric paddles was 2.9 kgf in infants. Optimal force using adult paddles was 5.1 kgf in children >10 kg but < or = 8 yrs and 5.3 kgf in children aged 9-17 yrs.

CONCLUSIONS

Force is an important determinant of TTI and therefore, outcome of defibrillation. It is recommended that a minimum of 3 kgf be applied to paddles when defibrillating infants with paediatric paddles, and a minimum of 5 kgf be applied to all older children when adult paddles are used.

Comparison of six clinically used external defibrillators in swine

BACKGROUND

External defibrillation has long been practiced with two types of monophasic waveforms, and now four biphasic waveforms are also widely available. Although waveforms and clinical dosing protocols differ among defibrillators, no studies have adequately compared performance of the monophasic or the biphasic waveforms. This is the first study to compare defibrillation efficacy among biphasic external defibrillators, and does so as part of a study comparing all commonly available waveforms using their respective manufacturer-provided and clinically used doses.

METHODS AND RESULTS

Efficacy of six waveforms was tested in 852 short-duration ventricular fibrillation episodes in 14 swine. Protocol 1: 200-J monophasic damped sine (MDS) and monophasic truncated exponential (MTE) shocks were compared to 150-J biphasic shocks in six swine at the low-impedance of these animals. Protocol 2: Four commercially available biphasic defibrillators were compared using their respective manufacturer-recommended dose protocols in eight swine at low and simulated high-impedance. At low-impedance, all biphasic shocks achieved near-perfect success, while efficacy was significantly lower for MDS (67%) and MTE (30%) shocks. In protocol 2, first-shock success rates of the four biphasic defibrillators were uniformly high (97, 100, 100, and 94%) for low-impedance shocks, and decreased for high-impedance shocks (62, 92, 82, and 64%). There were statistically significant differences in efficacy among devices.

CONCLUSIONS

Commonly used MDS and MTE waveforms provide markedly dissimilar efficacies. Despite impedance-compensation schemes in biphasic defibrillators, impedance has an impact on their efficacy. At high-impedance, modest efficacy differences exist among clinically available biphasic defibrillators, reflecting differences in both waveforms and manufacturer-provided doses.

Analysing the ventricular fibrillation waveform

The surface electrocardiogram associated with ventricular fibrillation has been of interest to researchers for some time. Over the last few decades, techniques have been developed to analyse this signal in an attempt to obtain more information about the state of the myocardium and the chances of successful defibrillation. This review looks at the implications of analysing the VF waveform and discusses the various techniques that have been used, including fast Fourier transform analysis, wavelet transform analysis and mathematical techniques such as chaos theory.

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.

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 to analyze ventricular fibrillation signals

Prediction of the success of defibrillation to avoid myocardial injury and performance feedback during CPR requires algorithms to analyze ventricular fibrillation signals. This report reviews investigations on different parameters of ventricular fibrillation electrocardiographic signals, including amplitude, frequency, bispectral analysis, amplitude spectrum area, wavelets, nonlinear dynamics, N(alpha) histograms, and combinations of several of these parameters. To date, no satisfactory methods have been found that cope with CPR artifacts and show adequate predictive power of successful defibrillation. The usual limitations of the studies are the small number of subjects, which precludes separation into training and test data. Because many investigations are animal studies of untreated short ventricular fibrillation, the results may be different for prolonged ventricular fibrillation in humans. The universality of threshold values has to be examined, and promising new parameters have to be monitored over longer time periods and analyzed for the effects of chest compressions, ventilation, and concomitant vasopressor therapy.

THERAPEUTIC PROCEDURES IN THE EMERGENCY DEPARTMENT PATIENT WITH ACUTE MYOCARDIAL INFARCTION

Life-threatening cardiac arrhythmias and other peri-infarct complications are often unexpected and commonly present with little warning. The therapeutic procedures reviewed often require immediate implementation and should be second nature to any physician involved in the management of patients with an AMI.

"Probability of successful defibrillation" as a monitor during CPR in out-of-hospital cardiac arrested patients

The frequency spectrum of the ECG in ventricular fibrillation (VF) correlates with myocardial perfusion and might predict defibrillation success defined as return of spontaneous circulation (ROSC). The predictive power increases when more spectral variables are combined, but the complex information can be difficult to handle during the intensity of CPR. We therefore developed a method for expressing this multidimensional information in a single reproducible variable reflecting the probability of defibrillation success. This is based on the highest performing predictor for ROSC after 883 shocks given to 156 patients with VF. This was a combination of two decorrelated spectral features based on a principal component analysis of an original feature set with information on centroid frequency, peak power frequency, spectral flatness and energy. The function "Probability of defibrillation success" (P(ROSC)(v)) was developed by a 2-dimensional histogram technique. P(ROSC)(v) discriminated between shocks followed by ROSC and No-ROSC (P<0.0001). The present methodology indicates a possible way to develop a CPR monitor.

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.

The effects of repeated doses of vasopressin or epinephrine on ventricular fibrillation in a porcine model of prolonged cardiopulmonary resuscitation

This study evaluated ventricular fibrillation mean frequency and amplitude to predict defibrillation success in a porcine cardiopulmonary resuscitation (CPR) model using repeated administration of vasopressin or epinephrine. After 4 min of cardiac arrest and 3 min of CPR, 10 pigs were randomly assigned to receive either vasopressin (early vasopressin: 0.4, 0.4, and 0.8 units/kg, respectively, n = 5) or epinephrine (early epinephrine: 45, 45, and 200 microg/kg, respectively, n = 5). Another 11 animals were randomly allocated after 4 min of cardiac arrest and 8 min of CPR to receive every 5 min either vasopressin (late vasopressin: 0.4 and 0. 8 units/kg, respectively, n = 5) or epinephrine (late epinephrine: 45 and 200 microg/kg, n = 6). Ventricular fibrillation mean frequency and amplitude on defibrillation were significantly higher in the vasopressin groups than in the epinephrine groups, respectively. In vasopressin versus epinephrine animals, mean frequency immediately before defibrillation was 9.6 +/- 1.5 Hz vs 7. 0 +/- 0.7 Hz (P < 0.001), mean amplitude was 0.65 +/- 0.26 mV vs 0. 21 +/- 0.14 mV (P < 0.001, and coronary perfusion pressure was 27 +/- 9 mm Hg vs 8 +/- 4 mm Hg (P < 0.00001), respectively. In contrast to no epinephrine animals, all vasopressin animals were successfully defibrillated and survived 1 h (P < 0.05). Mean fibrillation frequency and amplitude predicted successful defibrillation and may serve as noninvasive markers to monitor continuing CPR efforts. Furthermore, vasopressin was superior to epinephrine in maintaining these variables above a threshold necessary for successful defibrillation.

Initial clinical experience with a fully automatic in-hospital external cardioverter defibrillator

Sudden cardiac death due to ventricular tachyarrhythmia remains a significant problem in the in-hospital setting. Although the probability of survival is closely correlated with the rapidity of a response by qualified personnel, response times can be prolonged, even in specialized care units. In an effort to decrease response time, a fully automatic external cardioverter defibrillator was recently devised. This device was evaluated in the in-hospital setting to assess safety and efficacy. A total of 79 patients were studied in a multicenter trial. Patients were monitored with fully functional devices in the electrophysiology laboratory (51 patients) and in the cardiac care unit (28 patients). Performance of the device was assessed by comparing automatic responses to any sustained change in cardiac rhythm, either spontaneous or induced, to a retrospective review of stored ECG data and programmed parameters. During a total duration of 964 hours of monitoring, there were 99 episodes of sustained tachycardia. Therapy was appropriately delivered or advised in all episodes. Therapy was advised in one episode of supraventricular tachycardia. There were no episodes of inappropriate therapy delivery. There were no complications or adverse events. The device performed with a sensitivity of 100% and specificity of 98.8% with an average response time of 22 seconds. In conclusion, this automatic external defibrillator was safe, effective, and functioned as designed. Significant improvement in response time to life-threatening ventricular tachyarrhythmia in the in-hospital setting would be expected if this technology was widely adopted.

Electrocardiographic prediction of the success of cardiac resuscitation

OBJECTIVES

To identify a method for predicting the success or failure of a defibrillatory shock such as to avoid potentially detrimental interruptions of cardiopulmonary resuscitation (CPR). Such a method would also guide more optimal programming of automated external defibrillators.

DESIGN

Prospective, observational animal study.

SETTING

Medical research laboratory in a university-affiliated research and educational foundation.

SUBJECTS

Domestic pigs.

INTERVENTIONS

Ventricular fibrillation (VF) was electrically induced in 66 domestic pigs. After an interval of between 3 and 5 mins of untreated VF, precordial compression was begun. Electrocardiographic lead 2 was monitored and artifacts produced during precordial compression were removed by digital filtering.

MEASUREMENTS AND MAIN RESULTS

In the derivation study, electrical defibrillation restored spontaneous circulation in 30 of the 66 animals. Successfully resuscitated animals had significantly greater coronary perfusion pressure, maximum VF amplitude, mean VF amplitude, and dominant VF frequency. No animals were resuscitated if the coronary perfusion pressure was <8 mm Hg, maximum amplitude was <0.48 mV, mean amplitude was <0.25 mV, or dominant frequency <9.9 Hz independently of the duration of untreated VF. When mean amplitude and dominant frequency were combined, the predictability was further improved. In an additional validation study of 14 animals, consecutive defibrillations were uniformly unsuccessful if the combination of mean amplitude and dominant frequency did not exceed the threshold values obtained in derivation study.

CONCLUSION

Mean VF amplitude alone or in combination with dominant frequency of VF was expressed as a numerical score. It served as an objective noninvasive measurement on a par with that of coronary perfusion pressure for predicting the success of defibrillation. As such, it minimizes the detriment of repetitively interrupting mechanical interventions during CPR for electrical defibrillation when an electrical shock predictably fails to restore an effective rhythm.

Effects of transthoracic impedance and peak current flow on defibrillation success in a prehospital setting

STUDY OBJECTIVE

To assess whether transthoracic impedance and peak current are determinants of defibrillation success in patients with out-of-hospital ventricular fibrillation (VF).

METHODS

A retrospective cohort study was carried out in a suburban Canadian EMS system. Participants were patients who experienced out-of-hospital cardiac arrest in the regional municipality of Ottawa-Carleton, had VF rhythm at presentation, and received countershocks from the Laerdal Heartstart 2000 automated external defibrillator.

RESULTS

A total of 310 patients met the inclusion criteria. Collectively they received 717 countershocks. The first shocks were successful in converting VF rhythm 25.5% of the time. The most important determinant of shock success was the interval from when the call was received until delivery of the first shock (P<.01). Length of time at scene, current, impedance, and patient age were not significant determinants of success of first shock. The time interval until first shock was also a determinant of survival (P<.01). EMS response time, whether the arrest was witnessed, initial impedance, and current were not determinants of survival.

CONCLUSION

OHCA shock success and survival are associated with EMS system factors such as the interval from when the call was received until delivery of the first shock. The importance of impedance and peak current remain theoretic for out-of-hospital defibrillation success and did not influence defibrillation success in this study.

Clinical efficacy of the wearable cardioverter-defibrillator in acutely terminating episodes of ventricular fibrillation

The findings of our initial study demonstrate for the first time the ability to terminate induced VT/VF reliably (100% of all episodes) by a single, monophasic 230-J shock delivered by the Wearable Cardioverter-Defibrillator (WCD). Although limited by sample size, our data suggest the WCD could be used as a feasible bridge to definitive implantation of an implantable cardioverter-defibrillator in patients in whom risk stratification for sudden death is not completed.

A rule for early outcome classification of out-of-hospital cardiac arrest patients presenting with ventricular fibrillation

The aim of the study was to develop a scoring system for outcome classification at the start of prehospital first tier resuscitation for patients with cardiac arrest from ventricular fibrillation (VF). We studied a consecutive sample of 100 out-of-hospital cardiac arrest patients, presenting with VF of presumed cardiac etiology on arrival of the first tier (in a two-tiered urban Emergency Medical Services system). The number of patients discharged was 29 ('survivors') and 71 died ('non-survivors'). The electrocardiography (ECG) tracings recorded during resuscitation using a semi-automatic defibrillator were retrospectively analysed. For each patient, VF amplitude in mV (VF_a) and the number of base-line crossings per second (VF_blc) were calculated. Fisher's linear discriminant analysis was applied to discriminate between survivors and non-survivors using the variables VF_a, VF_blc and age. Patients were classed as potential survivors or non-survivors using a survival index = 0.6*(VF_a) + 0.4*(VF_blc)-4.0. If for a given patient the survival index is < 0, he is classified in the non-survivor group, if the survival index is > 0, he is classified in the survivor group. Using this index 79% of the survivors and 70% of the non-survivors could be classified correctly. Adding age to the formula increased the correct classification of survivors to 86 and 73% for the non-survivors. The survival index provides a research tool for the discrimination between potential survivors and non-survivors, which opens the possibility for the development of alternative treatment protocols in cardiac arrest.

Current concepts in electrical defibrillation

The electrical defibrillator has been proven to be a life-saving device in the treatment of cardiac arrest due to ventricular tachycardia or ventricular fibrillation. An understanding of the physiology and technology behind this device is useful for providers of emergency care. In this article, we review the current concepts in electrical defibrillation and briefly discuss the developmental history. The physiology and the technical considerations will make up the bulk of the discussion. The latest developments in electrical defibrillation also will be reviewed.

The effects of normothermic and hypothermic cardiopulmonary bypass on defibrillation energy requirements and transmyocardial impedance. Implications for implantable cardioverter-defibrillator implantation

The influence of normothermic and hypothermic cardiopulmonary bypass on defibrillation energy requirements and transcardiac impedance is not well characterized. However, this relationship is of clinical importance during automatic defibrillator implantation done with concomitant cardiac surgery, and there is anecdotal information that criteria for successful implantation are harder to achieve after such operations. We studied the effect of controlled hypothermia on defibrillation energy requirements and transcardiac impedance in a canine model of cardiopulmonary bypass in which 26 animals underwent right atrial and femoral arterial cannulation, as well as continuous hemodynamic and intramyocardial temperature monitoring. The defibrillation energy requirements were evaluated at 60-minute intervals with an epicardial patch system, and transcardiac impedance was measured before and after the multiple inductions and terminations of ventricular fibrillation. In group 1 (n = 10) defibrillation energy requirements were evaluated immediately after initiation of cardiopulmonary bypass at 37 degrees C (T0), after gradual cooling to 28 degrees C (T1), and after rewarming to 37 degrees C (T2). Group 2 (n = 16) comprised time controls that were identically instrumented and studied, but maintained at 37 degrees C throughout. Percent successful defibrillation was plotted against delivered energy, and the raw data fit by logistic regression. The energy at which 50% of shocks were successful (E50) was 3.23 +/- 0.89 joules at T0, 5.12 +/- 1.85 joules at T1, and 4.42 +/- 1.22 joules at T2 in group 1; this was not significantly different from the corresponding group 2 E50 values, which were 3.11 +/- 1.39 joules, 4.95 +/- 2.47 joules, and 5.59 +/- 3.18 joules, respectively. Both groups demonstrated a significant increase in E50 during the first hour of cardiopulmonary bypass (mean increase from T0 to T1 was 1.89 joules in group 1 and 1.84 joules in group 2, p < 0.05). Transmyocardial impedance fell progressively during the group 2 experiments from 73.6 +/- 12.9 omega at the beginning of the T0 shock series to 61.4 +/- 8.9 omega at the end of the T2 shock series. A similar reduction in transmyocardial impedance was observed during the course of all the group 1 experiments; however, at the beginning of the T1 shock series impedance was significantly elevated to 77.4 +/- 12.3 omega (p < 0.05 compared with group 2 and with end T0 in group 1). There was no relationship between defibrillation energy requirements and transcardiac impedance; there was also no correlation between either of these parameters and intramyocardial extracellular pH or left ventricular end-diastolic pressure.(ABSTRACT TRUNCATED AT 400 WORDS)

Monitoring normal and aberrant electrocardiographic activity from an endotracheal tube: comparison of the surface, esophageal, and tracheal electrocardiograms

INTRODUCTION

We designed an endotracheal (ET) tube with orthogonally spaced ECG cuff electrodes. This ET tube was evaluated in dogs and sheep to determine (1) whether ECGs recorded from our tube were sufficient to make accurate clinical decisions concerning heart rate and rhythm; and (2) whether metallic cuff electrodes in direct contact with the trachea could induce mucosal burn injury during episodes of defibrillation.

METHODS

Using experimental animals, we obtained ECGs from their tracheae and compared our findings with ECGs obtained from surface and esophageal electrodes. The electrical activity of the heart was modified by increasing the depth of anesthesia, occluding the left coronary artery, and administering beta-adrenergic drugs. Before the dogs were euthanized, they were subjected to episodes of transthoracic and intrathoracic defibrillation at energy levels of 200 to 400 J. A postmortem pathological examination of the trachea was performed to determine the incidence of mucosal burn injury.

RESULTS

Tracheal electrocardiography provided valid information on heart-rate monitoring and certain morphology profiles. The R-R, PR, QRS, and QT intervals measured from the trachea had a correlation of 1.0, 0.96, 0.83, and 0.98, respectively, when compared with the same intervals obtained from surface electrodes. Two tracheae subjected to intrathoracic defibrillation at > 300 J revealed evidence of minor burn injury. Some localized epithelium loss was displayed in all tracheae; we attributed this to tracheal intubation.

CONCLUSION

Tracheal electrocardiography may be useful in trauma patients who require intubation where injury precludes placement of chest ECG electrodes.

Prehospital cardiac arrest treated by urban first-responders: profile of patient response and prediction of outcome by ventricular fibrillation waveform

STUDY OBJECTIVES

To determine the speed and characteristics of patient response to urban first-responder defibrillation and to determine whether amplitude of ventricular fibrillation (VF) can predict outcome in these patients.

TYPE OF PARTICIPANTS

All adult patients in prehospital VF treated by fire department first-responders (265).

DESIGN AND INTERVENTIONS

A prospective observational study occurring between February 1, 1989, and January 1, 1991. Patients were defibrillated according to advanced cardiac life support and first-responder protocols. ECG and time data were recorded digitally.

MAIN RESULTS

Sixty-five percent of patients converted from VF to a more stable rhythm at least once during first-responder monitoring. Fifty-four percent of converted patients refibrillated at least once, and 42% of all stable conversions occurred after at least one episode of refibrillation. Seventy percent of all refibrillations occurred less than six minutes after the defibrillator was turned on, and 23% occurred after more than ten minutes. The proportion of stable conversions decreased from 30% on first conversion to 2% on fourth conversion. With each successive conversion the interval to refibrillation grew shorter, and development of a pulse or blood pressure became less likely. Presence of blood pressure or pulse after conversion had a sensitivity for hospital discharge of 54% and a specificity of 98%. Maximum VF amplitude before countershock was highly predictive of postshock rhythm, stable conversion in the field, time interval before refibrillation, inpatient admission, and hospital discharge. VF amplitude was unrelated to response interval or interval to defibrillation but was positively related to bystander CPR. Logistic regression identified VF amplitude as the most important predictor of hospital discharge; traditional variables such as response interval and bystander CPR were not predictive once amplitude had been accounted for. Changes in VF amplitude during the course of resuscitation efforts were frequent and also predictive of outcome.

CONCLUSION

Patients in VF who were treated by early countershock refibrillated much more frequently than previously reported. Refibrillations occur both early and late. Initial VF maximum amplitude is strongly predictive of outcome. Future reports of VF cardiac arrest should control for this previously neglected variable. Increased amplitude of VF during repeated refibrillation episodes is associated with increased hospital discharge, so future studies of advanced cardiac life support interventions should explore changes in VF amplitude as an outcome variable.

Rhythm changes during resuscitation from ventricular fibrillation

Defibrillation of patients with primary ventricular fibrillation (VF) results in a variety of rhythm changes. We analysed these changes in rhythm in 200 patients, using the American Heart Association's recommendation of two defibrillations prior to drug therapy. Sixty-three (31.5%) patients were immediate survivors with 38 (19%) being discharged from hospital alive. There was no difference between the age of immediate survivors (66.5 years, S.D. = 11.2) and non-survivors (68.3 years, S.D. = 13.7, P = 0.37). Immediate survivors were significantly more likely to be discharged alive from hospital if they were younger (70.0 years, S.D. 8.5 vs. 62.1 years, S.D. 15.8, P = 0.014). Increasing delays to the initiation of basic life support (CPR) and to defibrillation were associated with significantly less likelihood of cardioversion to sinus rhythm (P < 0.005 and P < 0.002, respectively). Those patients who stayed in VF were not more likely to be defibrillated into asystole or electro-mechanical dissociation. Seventeen percent (34) of patients were defibrillated to sinus rhythm after the first defibrillation and 14% (19) after the second, with similar hospital discharge rates (62% and 58%, respectively). Sixty percent (32) of patients in sinus rhythm, after two defibrillations, were discharged alive, compared to only 4% (6) of those patients not in sinus rhythm after two defibrillations. Our data provide new information on rhythm changes during resuscitation and supports the need for the earliest possible initiation of basic life support and defibrillation to improve survival from cardiac arrest due to ventricular fibrillation.