Electrocardiographic evaluation of defibrillation shocks delivered to out-of-hospital sudden cardiac arrest patients

Pre-Arrival Care of the Out-of-Hospital Cardiac Arrest Victim

Lay rescuers play a pivotal role in the recognition and initial management of out-of-hospital cardiac arrest. The provision of timely pre-arrival care by lay responders, including cardiopulmonary resuscitation and the use of automated external defibrillator before emergency medical service arrival, is important link in the chain of survival and has been shown to improve outcomes from cardiac arrest. Although physicians are not directly involved in bystander response to cardiac arrest, they play a key role in emphasizing the importance of bystander interventions.

Prediction of Shock-Refractory Ventricular Fibrillation During Resuscitation of Out-of-Hospital Cardiac Arrest

BACKGROUND

Out-of-hospital cardiac arrest due to shock-refractory ventricular fibrillation (VF) is associated with relatively poor survival. The ability to predict refractory VF (requiring ≥3 shocks) in advance of repeated shock failure could enable preemptive targeted interventions aimed at improving outcome, such as earlier administration of antiarrhythmics, reconsideration of epinephrine use or dosage, changes in shock delivery strategy, or expedited invasive treatments.

METHODS

We conducted a cohort study of VF out-of-hospital cardiac arrest to develop an ECG-based algorithm to predict patients with refractory VF. Patients with available defibrillator recordings were randomized 80%/20% into training/test groups. A random forest classifier applied to 3-s ECG segments immediately before and 1 minute after the initial shock during cardiopulmonary resuscitation was used to predict the need for ≥3 shocks based on singular value decompositions of ECG wavelet transforms. Performance was quantified by area under the receiver operating characteristic curve.

RESULTS

Of 1376 patients with VF out-of-hospital cardiac arrest, 311 (23%) were female, 864 (63%) experienced refractory VF, and 591 (43%) achieved functional neurological survival. Total shock count was associated with decreasing likelihood of functional neurological survival, with a relative risk of 0.95 (95% CI, 0.93-0.97) for each successive shock (P<0.001). In the 275 test patients, the area under the receiver operating characteristic curve for predicting refractory VF was 0.85 (95% CI, 0.79-0.89), with specificity of 91%, sensitivity of 63%, and a positive likelihood ratio of 6.7.

CONCLUSIONS

A machine learning algorithm using ECGs surrounding the initial shock predicts patients likely to experience refractory VF, and could enable rescuers to preemptively target interventions to potentially improve resuscitation outcome.

Effect of Amiodarone and Hypothermia on Arrhythmia Substrates During Resuscitation

Background

Amiodarone is administered during resuscitation, but its antiarrhythmic effects during targeted temperature management are unknown. The purpose of this study was to determine the effect of both therapeutic hypothermia and amiodarone on arrhythmia substrates during resuscitation from cardiac arrest.

Methods and Results

We utilized 2 complementary models: (1) In vitro no‐flow global ischemia canine left ventricular transmural wedge preparation. Wedges at different temperatures (36°C or 32°C) were given 5 µmol/L amiodarone (36‐Amio or 32‐Amio, each n=8) and subsequently underwent ischemia and reperfusion. Results were compared with previous controls. Optical mapping was used to measure action potential duration, dispersion of repolarization (DOR), and conduction velocity (CV). (2) In vivo pig model of resuscitation. Pigs (control or targeted temperature management, 32–34°C) underwent ischemic cardiac arrest and were administered amiodarone (or not) after 8 minutes of ventricular fibrillation. In vitro: therapeutic hypothermia but not amiodarone prolonged action potential duration. During ischemia, DOR increased in the 32‐Amio group versus 32‐Alone (84±7 ms versus 40±7 ms, P<0.05) while CV slowed in the 32‐Amio group. Amiodarone did not affect CV, DOR, or action potential duration during ischemia at 36°C. Conduction block was only observed at 36°C (5/8 36‐Amio versus 6/7 36‐Alone, 0/8 32‐Amio, versus 0/7 32‐Alone). In vivo: QTc decreased upon reperfusion from ischemia that was ameliorated by targeted temperature management. Amiodarone did not worsen DOR or CV. Amiodarone suppressed rearrest caused by ventricular fibrillation (7/8 without amiodarone, 2/7 with amiodarone, P=0.041), but not pulseless electrical activity (2/8 without amiodarone, 5/7 with amiodarone, P=0.13).

Conclusions

Although amiodarone abolishes a beneficial effect of therapeutic hypothermia on ischemia‐induced DOR and CV, it did not worsen susceptibility to ventricular tachycardia/ventricular fibrillation during resuscitation.

Analyze Whilst Compressing algorithm for detection of ventricular fibrillation during CPR: A comparative performance evaluation for automated external defibrillators

OBJECTIVE

The aim of this study was to present new combination of algorithms for rhythm analysis during cardiopulmonary resuscitation (CPR) in automated external defibrillators (AED), called Analyze Whilst Compressing (AWC), designed for decreasing pre-shock pause and early stopping of chest compressions (CC) for treating refibrillation.

METHODS

Two stages for AED rhythm analysis were presented, namely, "Standard Analysis Stage" (conventional shock-advisory analysis run over 5 s after CC interruption every two minutes) and "AWC Stage" (two-step sequential analysis process during CPR). AWC steps were run in presence of CC (Step1), and if shockable rhythm was detected then a reconfirmation step was run in absence of CC (Step2, analysis duration 5 s).

RESULTS

In total 16,057 ECG strips from 2916 out-of-hospital cardiac arrest (OHCA) patients treated with AEDs (DEFIGARD TOUCH7, Schiller Médical, France) were subjected patient-wise to AWC training (8559 strips, 1604 patients) and validation (7498 strips, 1312 patients). Considering validation results, "Standard Analysis Stage" presented ventricular fibrillation (VF) sensitivity Se = 98.3% and non-shockable rhythm specificity Sp>99%; "AWC Stage" decision after Step2 reconfirmation achieved Se = 92.1%, Sp>99%.

CONCLUSION

AWC presented similar performances to other AED algorithms during CPR, fulfilling performance goals recommended by standards. AWC provided advances in the challenge for improving CPR quality by: (i) not interrupting chest compressions for prevalent part of non-shockable rhythms (66-83%); (ii) minimizing pre-shock pause for 92.1% of VF patients. AWC required hands-off reconfirmation in 34.4% of cases. Reconfirmation was also common limitation of other reported algorithms (25.7-100%) although following different protocols for triggering chest compression resumption and shock delivery.

Real-world insight into public access defibrillator use over five years

BACKGROUND

Public access defibrillators (PADs) represent unique life-saving medical devices as they may be used by untrained lay rescuers. Collecting representative clinical data on these devices can be challenging. Here, we present results from a retrospective observational cohort study, describing real-world PAD utilisation over a 5-year period.

METHODS

Data were collected between October 2012 and October 2017. Responders voluntarily submitted electronic data downloaded from HeartSine PADs, and patient demographics and other details using a case report form in exchange for a replacement battery and electrode pack.

RESULTS

Data were collected for 977 patients (692 males, 70.8%; 255 females, 26.1%; 30 unknown, 3.1%). The mean age (SD) was 59 (18) years (range <1 year to 101 years). PAD usage occurred most commonly in homes (n=328, 33.6%), followed by public places (n=307, 31.4%) and medical facilities (n=128, 13.1%). Location was unknown in 40 (4.09%) events. Shocks were delivered to 354 patients. First shock success was 312 of 350 patients where it could be determined (89.1%, 95% CI 85.4% to 92.2%). Patients with reported response times ≤5 min were more likely to survive to hospital admission (89/296 (30.1%) vs 40/250 (16.0%), p<0.001). Response time was unknown for 431 events.

CONCLUSION

This is the first study to report global PAD usage in voluntarily submitted, unselected real-world cases and demonstrates the real-world effectiveness of PADs, as confirmed by first shock success.

A Six-Year Prospective Study of Out-of-Hospital Cardiac Arrest Managed by a Voluntary Ambulance Organisation

Objective

To obtain a database on the epidemiology of prehospital cardiac arrest and its management by a voluntary ambulance service, with the view for developing future strategies and service improvement.

Design

A 6-year prospective study from December 1998 to November 2004, using the Utstein-style template.

Setting

A voluntary ambulance service in Hong Kong.

Subjects and methods

Ambulance members had to complete and submit a specially designed data form after managing a cardiac arrest case, together with the ambulance run record and the automated external defibrillator (AED) computer printout, if appropriate.

Main outcome measures

Survival to hospital discharge and return of spontaneous circulation after resuscitation.

Results

A total of 72 cardiac arrests occurred during the period, with patients' age ranging from 29 to 106 years (mean 73.4). Most cardiac arrests occurred at home (46 or 63.9%). There were 58 witnessed cardiac arrests (80.5%), but bystander cardiopulmonary resuscitation (CPR) was started in only nine cases (15.5%) before the arrival of the ambulance crew. Six patients had evidence of rigor mortis or dependent lividity on ambulance arrival. For the 61 patients with electrocardiogram strips, the initial presenting rhythm on the AED was asystole in 45 (73.8%), pulseless electrical activity in 5 (8.2%), and ventricular fibrillation (VF) in 11 (18.0%). The median call-to-arrival time for VF cases (4.0 minutes) was significantly shorter than that of non-VF rhythms (8.5 minutes) [Mann-Whitney U test p=0.008]. Five patients had return of spontaneous circulation after resuscitation, but only one survived to hospital discharge.

Conclusions

Bystander CPR and ambulance response time are two areas requiring urgent improvement in our locality. As the majority of cardiac arrests occurred at home, the cost-effectiveness of public access defibrillation for Hong Kong is unclear. However, strategic placement of AED at high incidence' locations should be seriously considered.

Does the choice of definition for defibrillation and CPR success impact the predictability of ventricular fibrillation waveform analysis?

BACKGROUND

Quantitative analysis of ventricular fibrillation (VF), such as amplitude spectral area (AMSA), predicts shock outcomes. However, there is no uniform definition of shock/cardiopulmonary resuscitation (CPR) success in out-of-hospital cardiac arrest (OHCA). The objective of this study is to investigate post-shock rhythm variations and the impact of shock/CPR success definition on the predictability of AMSA.

METHODS

A total of 554 shocks from 257 OHCA patients with VF as initial rhythm were analyzed. Post-shock rhythms were analyzed every 5s up to 120s and annotated as VF, asystole (AS) and organized rhythm (OR) at serial time intervals. Three shock/CPR success definitions were used to evaluate the predictability of AMSA: (1) termination of VF (ToVF); (2) return of organized electrical activity (ROEA); (3) return of potentially perfusing rhythm (RPPR).

RESULTS

Rhythm changes occurred after 54.5% (N=302) of shocks and 85.8% (N=259) of them occurred within 60s after shock delivery. The observed post-shock rhythm changes were (1) from AS to VF (24.9%), (2) from OR to VF (16.1%), and (3) from AS to OR (12.1%). The area under the receiver operating characteristic curve (AUC) for AMSA as a predictor of shock/CPR success reached its maximum 60s post-shock. The AUC was 0.646 for ToVF, 0.782 for ROEA, and 0.835 for RPPR (p<0.001) respectively.

CONCLUSIONS

Post-shock rhythm is unstable in the first minute after the shock. The predictability of AMSA varies depending on the definition of shock/CPR success and performs best with the return of potentially perfusing rhythm endpoint for OHCA.

Effects of Rotigaptide, a Gap Junction Modifier, on Defibrillation Energy and Resuscitation From Cardiac Arrest in Rabbits

The gap junction modifier Rotigaptide (ZP123), which promotes cellular coupling, was hypothesized to decrease defibrillation thresholds during prolonged ventricular fibrillation (VF). Thirty-two New Zealand white rabbits were randomized to receive saline (control, n = 16) or Rotigaptide (n = 16). Following 4 min of untreated VF, biphasic defibrillation shocks were applied through chest wall patches, starting either at 300 volts (V) (n = 16) or 500 V (n = 16), with 200 V increasing steps to 900 V in case of shock failure. Rotigaptide significantly decreased defibrillation voltage requirements (average cumulative voltage of all shocks: 1206 ± 709 V in control group vs. 844 ± 546 V in treated group, P = .002). Rotigaptide had no effect on heart rate, QRS duration, QT interval, ventricular effective refractory period, monophasic action potential duration or on connexin 43 density using immunofluorescence. Rotigaptide improves the ability to defibrillate after untreated VF.

Risk factor analyses for the return of spontaneous circulation in the asphyxiation cardiac arrest porcine model

Background:

Animal models of asphyxiation cardiac arrest (ACA) are frequently used in basic research to mirror the clinical course of cardiac arrest (CA). The rates of the return of spontaneous circulation (ROSC) in ACA animal models are lower than those from studies that have utilized ventricular fibrillation (VF) animal models. The purpose of this study was to characterize the factors associated with the ROSC in the ACA porcine model.

Methods:

Forty-eight healthy miniature pigs underwent endotracheal tube clamping to induce CA. Once induced, CA was maintained untreated for a period of 8 min. Two minutes following the initiation of cardiopulmonary resuscitation (CPR), defibrillation was attempted until ROSC was achieved or the animal died. To assess the factors associated with ROSC in this CA model, logistic regression analyses were performed to analyze gender, the time of preparation, the amplitude spectrum area (AMSA) from the beginning of CPR and the pH at the beginning of CPR. A receiver-operating characteristic (ROC) curve was used to evaluate the predictive value of AMSA for ROSC.

Results:

ROSC was only 52.1% successful in this ACA porcine model. The multivariate logistic regression analyses revealed that ROSC significantly depended on the time of preparation, AMSA at the beginning of CPR and pH at the beginning of CPR. The area under the ROC curve in for AMSA at the beginning of CPR was 0.878 successful in predicting ROSC (95% confidence intervals: 0.773∼0.983), and the optimum cut-off value was 15.62 (specificity 95.7% and sensitivity 80.0%).

Conclusions:

The time of preparation, AMSA and the pH at the beginning of CPR were associated with ROSC in this ACA porcine model. AMSA also predicted the likelihood of ROSC in this ACA animal model.

Advanced life support therapy on out-of-hospital cardiac arrest patients: an engineering perspective

In the USA alone, several hundred thousand people die of sudden cardiac arrests each year. Basic life support, defined as chest compressions and ventilations, and early defibrillation are the only factors proven to increase the survival of patients with out-of-hospital cardiac arrest and are key elements in the chain of survival defined by the American Heart Association. The current cardiopulmonary resuscitation guidelines treat all patients the same but studies show a need for more individualization of treatment. This review focusses on ideas on how to strengthen the weak parts of the chain of survival including the ability to measure the effects of therapy, improve time efficiency and optimize the sequence and quality of the various components of cardiopulmonary resuscitation.

Biphasic versus monophasic defibrillation in out-of-hospital cardiac arrest: a systematic review and meta-analysis

OBJECTIVE

Biphasic defibrillation is more effective than monophasic one in controlled in-hospital conditions. The present review evaluated the performance of both waveforms in the defibrillation of patients of out-of-hospital cardiac arrest (OHCA) with initial ventricular fibrillation (Vf) rhythm under the context of current recommendations for cardiopulmonary resuscitation.

METHODS

From inception to June 2012, Medline, Embase, and the Cochrane Central Register of Controlled Trials were searched systemically for randomized controlled trials (RCTs) and observational cohort studies that compared the effects of biphasic and monophasic shocks on Vf termination, return of spontaneous circulation (ROSC), and survival to hospital discharge in OHCA patients with initial Vf rhythm. No restrictions were applied regarding language, population, or publication year.

RESULTS

Four RCTs including 572 patients were identified from 131 potentially relevant references for meta-analysis. The synthesis of these RCTs yielded fixed-effect pooled risk ratios (RRs) for biphasic and monophasic waveforms on Vf termination survival to hospital discharge (RR, 1.14; 95% CI, [0.84-1.54]).

CONCLUSION

Biphasic waveforms did not seem superior to monophasic ones with respect to Vf termination, ROSC, or survival to hospital discharge in OHCA patients with initial Vf rhythm under the context of current guidelines. However, most trials were conducted in accordance with previous guidelines for cardiopulmonary resuscitation. Therefore, further trials are needed to clarify this issue.

Comparison of shock-first strategy and cardiopulmonary resuscitation-first strategy in a porcine model of prolonged cardiac arrest

OBJECTIVE

The choice of a shock-first or a cardiopulmonary resuscitation (CPR)-first strategy in the treatment of prolonged cardiac arrest (CA) is still controversial. The purpose of this study was to compare the effects of these strategies on oxygen metabolism and resuscitation outcomes in a porcine model of 8min CA.

METHODS

Ventricular fibrillation (VF) was electrically induced. After 8min of untreated VF, 24 male inbred Wu-Zhi-Shan miniature pigs were randomized to receive either defibrillation first (ID group) or chest compression first (IC group). In the ID group, a shock was delivered immediately. If the defibrillation attempt failed to attain restoration of spontaneous circulation (ROSC), manual chest compressions were rapidly initiated at a rate of 100compressionsmin(-1), and the compression-to-ventilation ratio was 30:2. If VF persisted after five cycles of CPR, a second defibrillation attempt was made. In the IC group, chest compressions were delivered first, followed by a shock.

RESULTS

Hemodynamic variables, the VF waveform and blood gas analysis outcomes were recorded. Oxygen metabolism parameters and the amplitude spectrum area (AMSA) of the VF waveform were computed. There were no significant differences in the rate of ROSC and 24h survival between two groups. The ID group had lower lactic acid levels, higher cardiac output, better oxygen consumption and better oxygen extraction ratio at 4 and 6h after ROSC than the IC group.

CONCLUSIONS

In a porcine model of prolonged CA, the choice of a shock-first or CPR-first strategy did not affect the rate of ROSC and 24h survival, but the shock-first strategy might result in better hemodynamic status and better oxygen metabolism than the CPR-first strategy at the first 6h after ROSC.

Primary outcomes for resuscitation science studies: a consensus statement from the American Heart Association

BACKGROUND AND PURPOSE

The guidelines presented in this consensus statement are intended to serve researchers, clinicians, reviewers, and regulators in the selection of the most appropriate primary outcome for a clinical trial of cardiac arrest therapies. The American Heart Association guidelines for the treatment of cardiac arrest depend on high-quality clinical trials, which depend on the selection of a meaningful primary outcome. Because this selection process has been the subject of much controversy, a consensus conference was convened with national and international experts, the National Institutes of Health, and the US Food and Drug Administration.

METHODS

The Research Working Group of the American Heart Association Emergency Cardiovascular Care Committee nominated subject leaders, conference attendees, and writing group members on the basis of their expertise in clinical trials and a diverse perspective of cardiovascular and neurological outcomes (see the online-only Data Supplement). Approval was obtained from the Emergency Cardiovascular Care Committee and the American Heart Association Manuscript Oversight Committee. Preconference position papers were circulated for review; the conference was held; and postconference consensus documents were circulated for review and comments were invited from experts, conference attendees, and writing group members. Discussions focused on (1) when after cardiac arrest the measurement time point should occur; (2) what cardiovascular, neurological, and other physiology should be assessed; and (3) the costs associated with various end points. The final document underwent extensive revision and peer review by the Emergency Cardiovascular Care Committee, the American Heart Association Science Advisory and Coordinating Committee, and oversight committees.

RESULTS

There was consensus that no single primary outcome is appropriate for all studies of cardiac arrest. The best outcome measure is the pairing of a time point and physiological condition that will best answer the question under study. Conference participants were asked to assign an outcome to each of 4 hypothetical cases; however, there was not complete agreement on an ideal outcome measure even after extensive discussion and debate. There was general consensus that it is appropriate for earlier studies to enroll fewer patients and to use earlier time points such as return of spontaneous circulation, simple "alive versus dead," hospital mortality, or a hemodynamic parameter. For larger studies, a longer time point after arrest should be considered because neurological assessments fluctuate for at least 90 days after arrest. For large trials designed to have a major impact on public health policy, longer-term end points such as 90 days coupled with neurocognitive and quality-of-life assessments should be considered, as should the additional costs of this approach. For studies that will require regulatory oversight, early discussions with regulatory agencies are strongly advised. For neurological assessment of post-cardiac arrest patients, researchers may wish to use the Cerebral Performance Categories or modified Rankin Scale for global outcomes.

CONCLUSIONS

Although there is no single recommended outcome measure for trials of cardiac arrest care, the simple Cerebral Performance Categories or modified Rankin Scale after 90 days provides a reasonable outcome parameter for many trials. The lack of an easy-to-administer neurological functional outcome measure that is well validated in post-cardiac arrest patients is a major limitation to the field and should be a high priority for future development.

Safety and efficacy of defibrillator charging during ongoing chest compressions: a multi-center study

BACKGROUND

Pauses in chest compressions during cardiopulmonary resuscitation have been shown to correlate with poor outcomes. In an attempt to minimize these pauses, the American Heart Association recommends charging the defibrillator during chest compressions. While simulation work suggests decreased pause times using this technique, little is known about its use in clinical practice.

METHODS

We conducted a multi-center, retrospective study of defibrillator charging at three US academic teaching hospitals between April 2006 and April 2009. Data were abstracted from CPR-sensing defibrillator transcripts. Pre-shock pauses and total hands-off time preceding the defibrillation attempts were compared among techniques.

RESULTS

A total of 680 charge-cycles from 244 cardiac arrests were analyzed. The defibrillator was charged during ongoing chest compressions in 448 (65.9%) instances with wide variability across the three sites. Charging during compressions correlated with a decrease in median pre-shock pause [2.6s (IQR 1.9-3.8) vs 13.3s (IQR 8.6-19.5); p < 0.001] and total hands-off time in the 30s preceding defibrillation [10.3s (IQR 6.4-13.8) vs 14.8s (IQR 11.0-19.6); p < 0.001]. The improvement in hands-off time was most pronounced when rescuers charged the defibrillator in anticipation of the pause, prior to any rhythm analysis. There was no difference in inappropriate shocks when charging during chest compressions (20.0% vs 20.1%; p = 0.97) and there was only one instance noted of inadvertent shock administration during compressions, which went unnoticed by the compressor.

CONCLUSIONS

Charging during compressions is underutilized in clinical practice. The technique is associated with decreased hands-off time preceding defibrillation, with minimal risk to patients or rescuers.

Cardiac function and the proinflammatory cytokine response after recovery from cardiac arrest in swine

Increased levels of cytokines have been reported after resuscitation from cardiac arrest. We hypothesized that proinflammatory cytokines, released in response to ischemia/reperfusion, increase following resuscitation and play a role in post-cardiac arrest myocardial dysfunction. Ventricular fibrillation (VF) was induced by coronary occlusion in 20 swine. After 7 min of VF, resuscitation was performed as per guidelines. Plasma levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 were measured 15 min after the start of resuscitation in all animals and at intervals of 6 h in resuscitated animals. Intravascular pressures and cardiac output (CO) were also recorded. TNF-alpha abruptly increased after resuscitation, peaking at 15 min following return of spontaneous circulation, and declined to baseline levels after 3 h. IL-1beta increased more slowly, reaching a maximum 2 h after reperfusion. IL-6 concentrations were not significantly different from control values at any time point. Males demonstrated greater elevations of TNF-alpha and IL-1beta than females. Stroke work was significantly depressed at all time points with a nadir at 15-30 min after reperfusion, corresponding to the peak TNF-alpha values. The anti-TNF-alpha antibody infliximab attenuated the decrease in myocardial function observed 30 min after reperfusion. TNF-alpha increases during recovery from cardiac arrest are associated with depression of left ventricle (LV) function. The effect of TNF-alpha can be attenuated by anti-TNF-alpha antibodies.

Transthoracic defibrillation potential gradients in a closed chest porcine model of prolonged spontaneous and electrically induced ventricular fibrillation

OBJECTIVE

The purpose of this study was to measure the local electrical field or potential gradient, measured with a catheter-based system, required to terminate long duration electrically or ischaemically induced ventricular fibrillation (VF). We hypothesized that prolonged ischaemic VF would be more difficult to terminate when compared to electrically induced VF of similar duration.

METHODS

Thirty anesthetized and instrumented swine were randomized to electrically induced VF or spontaneous, ischaemically induced VF, produced by balloon occlusion of the left anterior descending coronary artery. After 7 min of VF, chest compressions were initiated and rescue shocks were attempted 1 min later. The potential gradient for each shock was measured and the mean values required for defibrillation compared for the VF groups.

RESULTS

The number of shocks and the shock strength required for termination of VF were not significantly different for the groups. The potential gradient of the first successful defibrillating shock was significantly greater in the spontaneous, occlusion-induced VF group (12.80+/-2.82 V/cm vs 9.60+/-2.48 V/cm, p=0.002). The number of refibrillations was greater in the ischaemic group than in the non-ischaemic electrical group (6+/-4 vs 1+/-1, p<0.001). The number of animals requiring a shock at 360J was 2.5 times greater for the ischaemic group.

CONCLUSIONS

Defibrillation of prolonged VF produced by acute myocardial ischaemia requires a significantly greater potential gradient to terminate than prolonged VF induced by electrical stimulation of the right ventricular endocardium. The VF duration used in this study approximates that occurring in victims of out-of-hospital cardiac arrest. Our findings may be of clinical importance in the management of such patients.

Comparison of low-energy versus high-energy biphasic defibrillation shocks following prolonged ventricular fibrillation

INTRODUCTION

Since the initial development of the defibrillator, there has been concern that, while delivery of a large electric shock would stop fibrillation, it would also cause damage to the heart. This concern has been raised again with the development of the biphasic defibrillator.

OBJECTIVE

To compare defibrillation efficacy, postshock cardiac function, and troponin I levels following 150-J and 360-J shocks.

METHODS

Nineteen swine were anesthetized with isoflurane and instrumented with pressure catheters in the left ventricle, aorta, and right atrium. The animals were fibrillated for 6 minutes, followed by defibrillation with either low-energy (n = 8) or high-energy (n = 11) shocks. After defibrillation, chest compressions were initiated and continued until return of spontaneous circulation (ROSC). Epinephrine, 0.01 mg/kg every 3 minutes, was given for arterial blood pressure < 50 mmHg. Hemodynamic parameters were recorded for four hours. Transthoracic echocardiography was performed and troponin I levels were measured at baseline and four hours following ventricular fibrillation (VF).

RESULTS

Survival rates at four hours were not different between the two groups (low-energy, 5 of 8; high-energy, 7 of 11). Results for arterial blood pressure, positive dP/dt (first derivative of pressure measured over time, a measure of left ventricular contractility), and negative dP/dt at the time of lowest arterial blood pressure (ABP) following ROSC were not different between the two groups (p = not significant [NS]), but were lower than at baseline. All hemodynamic measures returned to baseline by four hours. Ejection fractions, stroke volumes, and cardiac outputs were not different between the two groups at four hours. Troponin I levels at four hours were not different between the two groups (12 +/- 11 ng/mL versus 21 +/- 26 ng/mL, p = NS) but were higher at four hours than at baseline (19 +/- 19 ng/mL versus 0.8 +/- 0.5 ng/mL, p < 0.05, groups combined).

CONCLUSION

Biphasic 360-J shocks do not cause more cardiac damage than biphasic 150-J shocks in this animal model of prolonged VF and resuscitation.

Plasma endothelin-1 level at the onset of ischemic ventricular fibrillation predicts resuscitation outcome

BACKGROUND

Endogenous vasopressors, including endothelin-1 (ET-1), have been shown to be elevated in patients following resuscitation from out-of-hospital cardiac arrest and are likely a physiologic response to global ischaemia. The importance of ET-1 in the setting of arrest and resuscitation has not been established. Prior work has demonstrated that ET-1 increases significantly after coronary occlusion. The purpose of this study was to assess changes in ET-1 following induction of ischaemia and VF.

METHODS

VF was induced in 30 anesthetized and instrumented swine by balloon occlusion of the LAD. Blood was collected from the right atrium at baseline and at 5 min intervals following LAD occlusion until VF occurred. After 7 min of VF, resuscitation was attempted in accordance with guidelines. ET-1 and matrix metalloproteinase-9 (MMP-9), a measure of infarct size, were measured using ELISA.

RESULTS

ET-1 and MMP-9 levels increased significantly from baseline within 20 min of occlusion of the LAD. Animals that could not be resuscitated had a higher ET-1 (p=0.031) at VF onset but similar ischaemia time (time to VF) and MMP-9, reflecting infarct size. An ET-1 level >4 pg/ml had a likelihood ratio of 4 for predicting resuscitation failure.

CONCLUSIONS

Elevated levels of ET-1 during acute ischaemia predict resuscitation failure independent of the time to VF. This finding may be due to the known effect of ET-1 on coronary vascular resistance or ventricular compliance, resulting in early ischemic contracture.

Effect of timing and duration of a single chest compression pause on short-term survival following prolonged ventricular fibrillation

BACKGROUND

Pauses during chest compressions are thought to have a detrimental effect on resuscitation outcome. The Guidelines 2005 have recently eliminated the post-defibrillation pause. Previous animal studies have shown that multiple pauses of increasing duration decrease resuscitation success. We investigated the effect of varying the characteristics of a single pause near defibrillation on resuscitation outcome.

METHODS

Part A: 48 swine were anesthetized, fibrillated for 7min and randomized. Chest compressions were initiated for 90s followed by defibrillation and then resumption of chest compressions. Four groups were studied-G2000: 40s pause beginning 20s before, and ending 20s after defibrillation, A1: a 20s pause just before defibrillation, A2: a 20s pause ending 30s prior to defibrillation, and group A3: a 10s pause ending 30s prior to defibrillation. Part B: 12 swine (Group B) were studied with a protocol identical to Part A but with no pause in chest compressions. Primary endpoint was survival to 4h.

RESULTS

The survival rate was significantly higher for groups A1, A2, A3, and B (5/12, 7/12, 5/12, and 5/12 survived) than for the G2000 group (0/12, p<0.05). Survival did not differ significantly among groups A1, A2, A3, and B.

CONCLUSIONS

These results suggest that the Guidelines 2005 recommendation to omit the post-shock pulse check and immediately resume chest compressions may be an important resuscitation protocol change. However, these results also suggest that clinical maneuvers further altering a single pre-shock chest compression pause provide no additional benefit.

The proinflammatory cytokine response following resuscitation in the swine model depends on the method of ventricular fibrillation induction

OBJECTIVES

A systemic inflammatory response has been reported following resuscitation from cardiac arrest. The purpose of this study was to compare the magnitude of the tumor necrosis factor-alpha (TNF-alpha) response in two different swine models of ventricular fibrillation (VF) arrest.

METHODS

This was a randomized comparative trial conducted with domestic swine (N = 28, mean weight 40 kg, range 34-49 kg) of both genders. Anesthetized and instrumented swine were randomized to electrically induced VF (n = 14) or spontaneous VF induced by occlusion of a coronary artery (n = 14). After 8 minutes of VF, countershocks were given and standard advanced cardiac life support was initiated. Resuscitated animals were observed for 3 hours, and hemodynamics, base excess, and TNF-alpha concentrations were measured at intervals.

RESULTS

TNF-alpha concentrations were significantly greater in the ischemic VF group throughout the postresuscitation period. Multivariate modeling demonstrated that the TNF-alpha level was dependent on the method of VF induction and correlated with ischemia time (untreated VF period plus time to restoration of circulation) and the degree of postresuscitation hypoperfusion as reflected in base excess measurements.

CONCLUSIONS

This study demonstrates that TNF-alpha concentrations increase after resuscitation from cardiac arrest and that the TNF-alpha response is more profound in animals subjected to ischemic, spontaneous VF. The observed differences may be due to a longer resuscitation time and persistent postresuscitation hypoperfusion in the ischemic VF group. These differences need to be considered in studies evaluating mechanisms of postresuscitation organ dysfunction and defining mortality markers.

Home use of automated external defibrillators for sudden cardiac arrest

BACKGROUND

The most common location of out-of-hospital sudden cardiac arrest is the home, a situation in which emergency medical services are challenged to provide timely care. Consequently, home use of an automated external defibrillator (AED) might offer an opportunity to improve survival for patients at risk.

METHODS

We randomly assigned 7001 patients with previous anterior-wall myocardial infarction who were not candidates for an implantable cardioverter-defibrillator to receive one of two responses to sudden cardiac arrest occurring at home: either the control response (calling emergency medical services and performing cardiopulmonary resuscitation [CPR]) or the use of an AED, followed by calling emergency medical services and performing CPR. The primary outcome was death from any cause.

RESULTS

The median age of the patients was 62 years; 17% were women. The median follow-up was 37.3 months. Overall, 450 patients died: 228 of 3506 patients (6.5%) in the control group and 222 of 3495 patients (6.4%) in the AED group (hazard ratio, 0.97; 95% confidence interval, 0.81 to 1.17; P=0.77). Mortality did not differ significantly in major prespecified subgroups. Only 160 deaths (35.6%) were considered to be from sudden cardiac arrest from tachyarrhythmia. Of these deaths, 117 occurred at home; 58 at-home events were witnessed. AEDs were used in 32 patients. Of these patients, 14 received an appropriate shock, and 4 survived to hospital discharge. There were no documented inappropriate shocks.

CONCLUSIONS

For survivors of anterior-wall myocardial infarction who were not candidates for implantation of a cardioverter-defibrillator, access to a home AED did not significantly improve overall survival, as compared with reliance on conventional resuscitation methods. (ClinicalTrials.gov number, NCT00047411 [ClinicalTrials.gov].).

Is the tumour necrosis factor-alpha response following resuscitation gender dependent in the swine model?

INTRODUCTION

Reperfusion results in a proinflammatory cytokine response, as has been observed following resuscitation from cardiac arrest. Variations in the inflammatory response have been shown to be gender dependent and mediated by steroid hormones. The purpose of this study was to determine whether the tumour necrosis factor-alpha response following resuscitation was gender dependent.

METHODS

Anaesthetized swine (15 males and 15 females, weighs 32-47 kg) underwent 7 min of electrically induced cardiac arrest, followed by conventional resuscitation and then measurement of tumour necrosis factor-alpha by enzyme-linked immunosorbent assay at intervals for up to 3h. Testosterone and 17-estradiol were measured in 8 males and 8 females.

RESULTS

In all animals 17-estradiol was undetectable. Testosterone exceeded the lower limit of detection in 3 females and 1 male. Levels of tumour necrosis factor-alpha were higher in males than females, from 30 min after resuscitation to 3h. In females, tumour necrosis factor-alpha levels were significantly higher than control values only at 15 min following restoration of circulation; the levels in males demonstrated marked inter-animal variation.

CONCLUSIONS

In this swine model, males demonstrated an augmented post-resuscitation tumour necrosis factor-alpha response when compared with females. This difference was not related to steroid hormone levels.

Rationale and design of the Home Automatic External Defibrillator Trial (HAT)

Most cardiac arrests occur in the home, where emergency medical services (EMS) systems are challenged to provide timely care. Because a large proportion of sudden cardiac arrests (SCAs) are due to ventricular tachycardia or ventricular fibrillation, home use of an automated external defibrillator (AED) might offer an opportunity to decrease mortality in those at risk. Predicting who will have a cardiac arrest in the general population is difficult. Individuals at high risk are usually easily identified and may become candidates for implantable cardioverter defibrillators. It is within the population at lower risk where home AEDs may be most useful. The purpose of the Home Automatic External Defibrillator Trial (HAT) is to test whether providing home access to an AED can improve survival in patients at modest risk of SCA, such as those surviving an anterior myocardial infarction but in whom implantable cardioverter defibrillator therapy is not deemed necessary. Between January 23, 2003, and October 20, 2005, 7001 patients were enrolled, with completion of follow-up scheduled for September 30, 2007. Randomization was conducted in a 1:1 fashion between control therapy, comprising the standard lay response to SCA (calling the EMS and performing cardiopulmonary resuscitation), and the use of an AED first, followed by calling the EMS and performing cardiopulmonary resuscitation. The primary end point is all-cause mortality. Secondary outcomes include survival from SCA (witnessed and unwitnessed, in home and out of home), incremental cost-effectiveness, and quality of life measures for both the patient and the spouse/companion. The results of the trial should be available in mid 2008.

Is all ventricular fibrillation the same? A comparison of ischemically induced with electrically induced ventricular fibrillation in a porcine cardiac arrest and resuscitation model

OBJECTIVES

The standard porcine cardiac arrest model uses electrical induction of ventricular fibrillation. Reported restoration of spontaneous circulation and survival rates in this model are as high as 90% for ventricular fibrillation durations of 7-10 mins, values substantially greater than rates in the clinical population (i.e., 20% to 30%). A high first shock success rate, infrequent refibrillation, and short times for restoration of spontaneous circulation are typical of the model. The purpose of this study was to determine whether ischemic induction of ventricular fibrillation in swine followed by standard advanced cardiac life support would result in short-term outcomes approximating those observed in human victims of out-of-hospital ventricular fibrillation.

DESIGN

Randomized comparative trial.

SETTING

Translational research laboratory.

SUBJECTS

Domestic swine (n = 40, mean weight 40 +/- 4 kg, range 34-47 kg) of both genders.

INTERVENTIONS

Swine were instrumented and randomized to either electrical ventricular fibrillation induction or ischemic ventricular fibrillation, produced by balloon occlusion of the mid-left anterior descending coronary artery (n = 20 per group). Transthoracic impedance was measured and 30 Omega added in series for all animals. The balloon remained inflated during resuscitation efforts in ischemic ventricular fibrillation animals. After 7 mins of ventricular fibrillation, cardiopulmonary resuscitation was initiated and defibrillation was attempted 1 min later. Epinephrine and antiarrhythmics were administered as per guidelines. Resuscitation was terminated if restoration of spontaneous circulation had not occurred after 15 mins of advanced cardiac life support.

MEASUREMENTS AND MAIN RESULTS

Although the number of countershocks required to initially terminate ventricular fibrillation was not different (electrical ventricular fibrillation 1.9 +/- 1.6, ischemic ventricular fibrillation 2.4 +/- 2.0), the refibrillation rate was higher in the ischemic ventricular fibrillation group (4.9 +/- 4 vs. 0.8 +/- 1 episodes/animal, p < .001), resulting in a greater number of shocks before restoration of spontaneous circulation (total shocks for ischemic ventricular fibrillation 9.4 +/- 5.6 vs. electrical ventricular fibrillation 2.7 +/- 2.2, p < .001). Time to restoration of spontaneous circulation was longer in the ischemic ventricular fibrillation group (430 +/- 234 secs vs. 149 +/- 120 secs, p < .001). Restoration of spontaneous circulation rates were not different (electrical ventricular fibrillation 90% vs. ischemic ventricular fibrillation 65%). However, survival to 6 hrs was greater in the electrical ventricular fibrillation group (18 of 20, 90%) than in the ischemic ventricular fibrillation group (8 of 20, 40%, p = .002).

CONCLUSIONS

Resuscitation from ischemic ventricular fibrillation is more difficult than electrical ventricular fibrillation and is characterized by greater time to restoration of spontaneous circulation, frequent refibrillation, greater number of countershocks, higher epinephrine dose during resuscitation efforts, profound cardiac dysfunction, and a short-term survival rate approaching clinical experience. Ischemically induced ventricular fibrillation is a more clinically relevant model for the evaluation of resuscitation interventions.

A percutaneous catheter-based system for the measurement of potential gradients applicable to the study of transthoracic defibrillation

BACKGROUND

The local electric (E) field or potential gradient produced by a shock reliably predicts VF termination. In this study we evaluated a multiple electrode, catheter-based device for closed-chest 3D measurements of E field from transthoracic defibrillation shocks.

METHODS

Catheters with multiple electrodes on the tip were placed in intracardiac locations in anesthetized swine. An empirically derived calibration matrix and custom microprocessor was used to transform simultaneously measured voltages into orthogonal E field vector components. E fields produced in six intracardiac locations by 30 and 300 J shocks were compared in eight animals. Correlations were determined for measured current and E field at various shock strengths at two different transthoracic impedances in five additional animals. VF was induced in 12 animals and E field measured during defibrillation attempts.

RESULTS

The E field measurements resulting for 30 J transthoracic shocks were not significantly different among different intracardiac sites. At 300 J, however, significant differences were observed between sites with the greatest intensities recorded in the coronary sinus and right ventricle. Within animals, the variability of the measurement at each site was small, ranging from 2.8 +/- 1.6% to 5.7 +/- 4.5%. Significant correlations (P < 0.001) between measured E field and peak current were observed at native impedance (34 +/- 4 Omega, r = 0.81) and at adjusted impedance (76 +/- 4 Omega, r = 0.78) with transthoracic shocks of 200, 300, and 360 J. In VF studies, the probability of defibrillation was closely fit by a sigmoidal dose response curve in the coronary sinus E field with an approximate threshold of 4.7 V/cm with 50% defibrillation success at 9.3 V/cm.

CONCLUSIONS

The measured intracardiac E field variability within animals and at a specific site was small, exhibiting a median value of 5.1%, contrasted to median variabilities across animals of 5-11% suggesting the capacity of this measurement system to provide subject specific information on the distribution of E fields. The measured E field magnitudes across animals in the coronary sinus were linearly correlated with applied shock current with a very strong linear relation to effective shock voltage observed in vitro in a saline tank. When evaluated as a predictor of shock success, the observed values were consistent with previously reported critical fields. This technique may be of value in evaluating waveforms for transthoracic defibrillation as well as electrode size, placement, and composition.

Transthoracic Incremental Monophasic Versus Biphasic Defibrillation by Emergency Responders (TIMBER)

Background— Although biphasic, as compared with monophasic, waveform defibrillation for cardiac arrest is increasing in use and popularity, whether it is truly a more lifesaving waveform is unproven.

Methods and Results— Consecutive adults with nontraumatic out-of-hospital ventricular fibrillation cardiac arrest were randomly allocated to defibrillation according to the waveform from automated external defibrillators administered by prehospital medical providers. The primary event of interest was admission alive to the hospital. Secondary events included return of rhythm and circulation, survival, and neurological outcome. Providers were blinded to automated defibrillator waveform. Of 168 randomized patients, 80 (48%) and 68 (40%) consistently received only monophasic or biphasic waveform shocks, respectively, throughout resuscitation. The prevalence of ventricular fibrillation, asystole, or organized rhythms at 5, 10, or 20 seconds after each shock did not differ significantly between treatment groups. The proportion of patients admitted alive to the hospital was relatively high: 73% in monophasic and 76% in biphasic treatment groups ( P =0.58). Several favorable trends were consistently associated with receipt of biphasic waveform shock, none of which reached statistical significance. Notably, 27 of 80 monophasic shock recipients (34%), compared with 28 of 68 biphasic shock recipients (41%), survived ( P =0.35). Neurological outcome was similar in both treatment groups ( P =0.4). Earlier administration of shock did not significantly alter the performance of one waveform relative to the other, nor did shock waveform predict any clinical outcome after multivariate adjustment.

Conclusions— No statistically significant differences in outcome could be ascribed to use of one waveform over another when out-of-hospital ventricular fibrillation was treated.

Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest

BACKGROUND

Cardiopulmonary resuscitation (CPR) and electrical defibrillation are the primary treatment options for ventricular fibrillation (VF). While recent studies have shown that providing CPR prior to defibrillation may improve outcomes, the effects of CPR quality remain unclear. Specifically, the clinical effects of compression depth and pauses in chest compression prior to defibrillation (pre-shock pauses) are unknown.

METHODS

A prospective, multi-center, observational study of adult in-hospital and out-of-hospital cardiac resuscitations was conducted between March 2002 and December 2005. An investigational monitor/defibrillator equipped to measure compression characteristics during CPR was used.

RESULTS

Data were analyzed from 60 consecutive resuscitations in which a first shock was administered for VF. The primary outcome was first shock success defined as removal of VF for at least 5s following defibrillation. A logistic regression analysis demonstrated that successful defibrillation was associated with shorter pre-shock pauses (adjusted odds ratio 1.86 for every 5s decrease; 95% confidence interval 1.10-3.15) and higher mean compression depth during the 30s of CPR preceding the pre-shock pause (adjusted odds ratio 1.99 for every 5mm increase; 95% confidence interval 1.08-3.66).

CONCLUSIONS

The quality of CPR prior to defibrillation directly affects clinical outcomes. Specifically, longer pre-shock pauses and shallow chest compressions are associated with defibrillation failure. Strategies to correct these deficiencies should be developed and consideration should be made to replacing current-generation automated external defibrillators that require long pre-shock pauses for rhythm analysis.

Potential benefit of transesophageal defibrillation: an experimental evaluation

INTRODUCTION

Because of the proximity of the esophagus to the heart, transesophageal defibrillation might increase defibrillation success. We assessed the defibrillation threshold (DFT) of transesophageal defibrillation compared with standard transthoracic defibrillation.

METHODS

Defibrillation success and DFTs were determined in 22 female pigs with high (68+/-4 kg, n=12) or low body weight (39+/-1 kg, n=10). After induction of ventricular fibrillation, biphasic shocks were delivered between two cutaneous patch electrodes (sternal and apical position) or between an esophageal and two cutaneous patch electrodes in a sternal and apical position. The esophageal electrode was integrated into a latex sheath covering a standard transesophageal echocardiography probe.

RESULTS

In 5 of 12 pigs with high body weight, external defibrillation failed despite 3 consecutive 200-J shocks, whereas subsequent transesophageal defibrillation was successful with the first shock. In the remaining 7 pigs, a more than 50% reduction in DFT was obtained with transesophageal defibrillation compared with standard biphasic external defibrillation (67+/-27 vs 164+/-23 J, P<.001). Pigs with lower body weight were successfully defibrillated by both transthoracic and transesophageal shocks. The DFT in pigs with low body weight was significantly lower using transesophageal defibrillation compared with transthoracic shocks (65+/-15 vs 99+/-38 J, P<.05).

CONCLUSIONS

In this animal model, nonresponders to standard external defibrillation could successfully be defibrillated via an esophageal-cutaneous electrode configuration. Overall, an almost 50% DFT reduction was achieved by transesophageal defibrillation. Transesophageal defibrillation may provide an additional tool for terminating VF, which is refractory to external defibrillation, eg, in patients with very high body weight.

Epinephrine and vasopressin during cardiopulmonary resuscitation

Epinephrine (adrenaline) and vasopressin have been by far the most commonly studied vasopressors in experimental cardiac arrest. Despite animal experimental studies suggesting improved outcomes in experimental cardiac arrest, clinical trials of pressor agents have failed to show clear cut benefit from either vasopressin or epinephrine, although few, if any, trials compared pressor agents to a placebo. The action of vasopressors in the heart, particularly beta1-adrenergic stimulation, is associated with adverse cardiac effects including post-resuscitation myocardial dysfunction, worsening ventricular arrhythmias, and increasing myocardial oxygen consumption. Alpha2-adrenergic agonists, in experimental studies, show great promise in improving outcomes in experimental cardiac arrest, but have not been studied in humans. The combination of epinephrine and vasopressin may be effective, but has been incompletely studied. Clinical trials of vasopressor agents, which minimize direct myocardial effects are needed.

Automated External Defibrillators: To What Extent Does the Algorithm Delay CPR?

STUDY OBJECTIVE

Maximizing cardiopulmonary resuscitation (CPR) during resuscitation may improve survival. Resuscitation protocols stack up to 3 shocks to achieve defibrillation, followed by an immediate postdefibrillation pulse check. The purpose of this study is to evaluate outcomes of rhythm reanalyses immediately after shock, stacked shocks, and initial postshock pulse checks in relation to achieving a pulse and initiating CPR.

METHODS

We conducted an observational study of patients with ventricular fibrillation treated by first-tier emergency medical services (EMS). We collected data from EMS, dispatch, and hospital records. Additionally, we analyzed automatic external defibrillator recordings to determine the proportion of cardiac arrest victims who were defibrillated and achieved a pulse according to shock number (single versus stacked shock), proportion of victims with a pulse during the initial postdefibrillation pulse check, and interval from initial shock to CPR.

RESULTS

The study included 481 cardiac arrest subjects. Automatic external defibrillators terminated ventricular fibrillation with the initial shock in 83.6% (n=402) of cases. A second shock terminated ventricular fibrillation in an additional 7.5% (n=36) of cases, and a third shock terminated ventricular fibrillation in 4.8% (n=23) of cases. The initial sequence of 3 shocks failed to terminate ventricular fibrillation in 4.1% (n=20) of cases. In total, automatic external defibrillators performed 560 rhythm reanalyses during the initial shock sequence and delivered 122 "stacked" shocks. Termination of ventricular fibrillation was not synonymous with return of a pulse. The initial shock produced a pulse that was eventually detected in 21.8% (105/481) of cases. Stacked shocks produced a pulse in 10.7% (13/122) of cases. For the 24.5 % (n=118) of cases in which a pulse returned, the pulse was detected during the initial postshock pulse check only 12 times, or 2.5% of all cases. The median interval from initial shock until CPR was 29 (23,41) seconds.

CONCLUSION

Rhythm reanalyses, stacked shocks, and postshock pulse checks had low yield for achieving or detecting return of a pulse. CPR was not initiated until 29 seconds after the initial shock.

Ventricular fibrillation is not provoked by chest compression during post-shock organized rhythms in out-of-hospital cardiac arrest

INTRODUCTION

It has been proposed that chest compression (CC) can provoke recurrent ventricular fibrillation (VF) after defibrillation has restored an organized rhythm (OR). If so this would have major implications for proposed changes in resumption of CC after defibrillation, regardless of rhythm. The aim of this study was to examine our defibrillation data for evidence of post-shock CC-induced VF.

METHODS

In a defibrillation program using police/fire personnel entire electrocardiograms (ECGs) from defibrillator data cards were examined for initial and post-shock rhythms and CC artifact. Successful shock rhythms were defined as either asystole or OR in the first five seconds post-shock, the latter as at least two QRS complexes during this time period. Artifact from CC was assessed for association with recurrent VF during either asystole or OR.

RESULTS

Among 67 patients (pts) defibrillated by police/fire personnel VF recurred at least once in 35 (52%). Entire ECGs were available in 32 of these 35 pts. Chest compression-associated recurrent VF developed in 16 of 32 patients (50%). A total of 78 VF recurrences were observed during the period prior to administration of epinephrine (adrenaline) or other drugs. During post-shock asystole VF recurred 32 times (41% of all recurrent VF episodes); in 19 (59%) VF recurred during CC and in 13 (41%) it was spontaneous. During OR VF recurred 46 times (59% of all recurrent VF episodes); in 36 (78%) VF recurred spontaneously and in only 10 (22%) during CC. Heart rate preceding spontaneous recurrence of VF during OR was 84+/-35 beats/min, and heart rate preceding CC-associated VF recurrence during OR was 46+/-20 beats/min (p > 0.001). There was no statistically significant difference in the width of the QRS complex preceding VF recurrence in the CC-associated and spontaneous VF recurrence groups (p = 0.925).

CONCLUSIONS

VF recurred following successful shocks in 52% of pts. With asystole VF recurred frequently during CC. However, during post-shock OR VF recurred unrelated to CC in most instances. Thus, resumption of CC immediately after shocks that restore an OR is unlikely to provoke recurrent VF, and resumption of CC need not be delayed.

Evolution of a community-wide early defibrillation programme

BACKGROUND

In November 1990, a 2-year trial period was initiated in which police officers in the city of Rochester, Minnesota, were trained in the operation of automated external defibrillators (AEDs). Following the trial, the program was expanded as the city grew in population and area. In 1998 firefighters also were equipped with AEDs, bringing to a total 18 AEDs with police and fire personnel, in addition to paramedic capability.

METHODS

From November 1990 to December 2003, all adult patients with atraumatic cardiac arrest with ventricular fibrillation (VF) as the presenting rhythm were included for analysis. Call-to-shock time intervals, restoration of spontaneous circulation after defibrillation shocks only (without need for vasoactive or inotropic drug administration), and neurologically intact survival (overall performance category (OPC) 1 or 2) were study end-points.

RESULTS

One hundred and ninety-three patients presented in VF. Of these, 80 (41%) were discharged neurologically intact. Of the 159 VF patients whose arrest was bystander-witnessed 73 (46%) were discharged. Survival from non-VF arrest was very low (5%). Assessment of VF survivors demonstrated a quality of life, adjusted for age, gender, and disease, similar to that of the general population.

CONCLUSIONS

These data demonstrate that a relatively high survival can be obtained in a city of this size and area employing a non-tiered community-wide approach within the emergency medical services (EMS) system.

Outcomes after ventricular fibrillation out-of-hospital cardiac arrest: expanding the chain of survival

Coronary heart disease is the most common cause of death in the United States, with ventricular fibrillation (VF) the most common initial rhythm when cardiac disease causes arrest. Survival after VF out-of-hospital cardiac arrest (OHCA) depends on a sequence of events called the chain of survival, which Includes rapid access to emergency medical services, cardiopulmonary resuscitation, defibrillation, and advanced care. Because of widespread implementation of defibrillation programs, more patients survive VF OHCAs, making subsequent care of these patients important. Early hospitalization must focus on potential neurologic injury and therapy targeted at the underlying cardiac disease and antiarrhythmic therapy for long-term secondary prevention of sudden death. Attention to certain cohorts who are at high risk despite their underlying disease, such as women and elderly patients, is necessary. These cohorts may have the greatest response to short-term and long-term therapies for cardiac rehabilitation. With these approaches, long-term survival and quality of life after VF OHCA are favorable. Broadening the focus of the chain of survival to include in-hospital and long-term care will further improve favorable outcomes achieved in an early defibrillation program.

Transthoracic impedance does not affect defibrillation, resuscitation or survival in patients with out-of-hospital cardiac arrest treated with a non-escalating biphasic waveform defibrillator

OBJECTIVE

This is a study of the influence of transthoracic impedance (TTI) on defibrillation, resuscitation and survival in patients with out-of-hospital cardiac arrest (OHCA), treated with a non-escalating impedance-compensating 150 J biphasic waveform defibrillator.

METHODS

Cardiac arrest data from two EMS systems were analyzed retrospectively. All witnessed arrests from patients who presented with a shockable rhythm and were treated initially by BLS personnel were included (n = 102). For each defibrillation and resuscitation outcome variable, we tested differences in mean TTI for successful versus unsuccessful outcome. The effect of call-to-shock time on overall outcome was also examined.

RESULTS

Initial shocks defibrillated 90% [83-95%] (95% confidence interval) of patients. Cumulative success with two shocks was 98% [93-100%] and with three shocks was 99% [95-100%]. TTI averaged 90 +/- 23 Omega. First-shock success, cumulative success through two shocks and cumulative success through the first-shock series were unrelated to TTI, as were BLS ROSC, pre-hospital ROSC, hospital admission and discharge. In contrast and consistent with previous findings, call-to-shock time was highly predictive of survival.

CONCLUSIONS

High impedance patients were defibrillated by the biphasic waveform used in this study at high rates with a fixed energy of 150 J and without energy escalation. Rapid defibrillation rather than differences in patient impedance accounts for resuscitation success.