Detrended fluctuation analysis predicts successful defibrillation for out-of-hospital ventricular fibrillation cardiac arrest

Aims

Repeated failed shocks for ventricular fibrillation (VF) in out-of-hospital cardiac arrest (OOHCA) can worsen the outcome. It is very important to rapidly distinguish between early and late VF. We hypothesised that VF waveform analysis based on detrended fluctuation analysis (DFA) can help predict successful defibrillation.

Methods

Electrocardiogram (ECG) recordings of VF signals from automated external defibrillators (AEDs) were obtained for subjects with OOHCA in Taipei city. To examine the time effect on DFA, we also analysed VF signals in subjects who experienced sudden cardiac death during Holter study from PhysioNet, a publicly accessible database. Waveform parameters including root-mean-squared (RMS) amplitude, mean amplitude, amplitude spectrum analysis (AMSA), frequency analysis as well as fractal measurements including scaling exponent (SE) and DFA were calculated. A defibrillation was regarded as successful when VF was converted to an organised rhythm within 5 s after each defibrillation.

Results

A total of 155 OOHCA subjects (37 successful and 118 unsuccessful defibrillations) with VF were included for analysis. Among the VF waveform parameters, only AMSA (7.61 ± 3.30 vs. 6.30 ± 3.13, P = 0.028) and DFAα2 (0.38 ± 0.24 vs. 0.49 ± 0.24, P = 0.013) showed significant difference between subjects with successful and unsuccessful defibrillation. The area under the curves (AUCs) for AMSA and DFAα2 was 0.63 (95% confidence interval (CI) = 0.52-0.73) and 0.65 (95% CI = 0.54-0.75), respectively. Among the waveform parameters, only DFAα2, SE and dominant frequency showed significant time effect.

Conclusions

The VF waveform analysis based on DFA could help predict first-shock defibrillation success in patients with OOHCA. The clinical utility of the approach deserves further investigation.     

Signal integral for optimizing the timing of defibrillation

Objective

The possibility of successful defibrillation decreases with an increased duration of ventricular fibrillation (VF). Futile electrical shocks are inversely correlated with myocardial contractile function and long-term survival. Previous studies have demonstrated that various ECG waveform analyses predict the success of defibrillation. This study investigated whether the absolute amplitude of pre-shock VF waveform is likely to predict the success of defibrillation.

Methods

ECG recordings of 350 out-of-hospital cardiac arrest (OOHCA) patients were obtained from the automated external defibrillator (AED) and analyzed by the method of signal integral. Successful defibrillation was defined as organized rhythm with heart rate ≥40 beat/min commencing within one min of post-shock period and persisting for a minimum of 30 s.

Results

Signal integral was significantly greater in successful defibrillation than unsuccessful defibrillation (81.76 ± 32.3 mV vs. 34.9 ± 15.33 mV, p < 0.001). The intersection of the sensitivity and specificity curve provided a threshold value of 51 mV. The corresponding values of sensitivity, specificity, positive predictive and negative predictive values for successful defibrillation were 90%, 86%, 80% and 93%, respectively. The receiver operator curve further revealed that signal integral predicted the likelihood of successful defibrillation (area under the curve = 0.949).

Conclusions

Signal integral predicted successful electrical shocks on patients with ventricular fibrillation and have potential to optimize the timing of defibrillation and reduce the number of electrical shocks.     

Beyond the pre-shock pause: the effect of prehospital defibrillation mode on CPR interruptions and return of spontaneous circulation

Aims

The pattern of interruptions to chest compressions in pre-hospital cardiac arrests in Wellington, New Zealand, was examined prospectively to determine whether the mode of defibrillation chosen by paramedics influenced interruptions, shock success and the return of spontaneous circulation (ROSC).

Methods

A prospective observational cohort study of 44 adult cardiac arrests in which 203 shocks were administered by Wellington Free Ambulance (WFA) paramedics was undertaken to compare Code-stat^® electronic records from Medtronic^® Lifepak 12 and Lifepak 15 defibrillators used in semi-automated (AED) or manual mode. Interruptions during the 30 s prior to shock delivery as well as pre-shock and post-shock pauses were calculated. Shock success and ROSC were the outcome measures.

Results

Pre-shock pauses were shorter in manual mode (median 3 s, IQR 2–5) versus AED mode (median 4 s, IQR 3–6; p = 0.003). Interruptions of CPR in the 30 s prior to shock delivery were also shorter in manual mode (median 7 s, IQR 4–11) versus AED mode (median 14 s, IQR 12–16; p = <0.001). Shock success rates and post-shock pauses were not statistically different between modes. ROSC was significantly higher in manual mode (18.49%) versus AED mode (8.33%, p = 0.042).

Conclusion

When paramedics used the defibrillator in manual mode as compared to AED mode, interruptions to CPR during the 30 s prior to shock delivery were significantly reduced and pre-shock pauses were also shorter. This was associated with increased ROSC. Manual defibrillation should be the preferred option for appropriately trained paramedics. Training in this locality has been changed accordingly.     

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 8 min CA.

Methods

Ventricular fibrillation (VF) was electrically induced. After 8 min 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 100 compressions min⁻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 24 h 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 6 h 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 24 h survival, but the shock-first strategy might result in better hemodynamic status and better oxygen metabolism than the CPR-first strategy at the first 6 h after ROSC.     

Increase in pre-shock pause caused by drug administration before defibrillation: An observational, full-scale simulation study

Background

The importance of circulation during cardiopulmonary resuscitation has led to efforts to decrease time without chest compressions (“no-flow time”). The no-flow time from the interruption of chest compressions until defibrillation is referred to as the “pre-shock pause”. A shorter pre-shock pause increases the chance of successful defibrillation. It is unclear whether drug administration affects the length of the pre-shock pause. Our study compares pre-shock pause with and without drug administration in a full-scale simulation.

Methods

This was an observational study in an ambulance including 72 junior physicians and a cardiac arrest scenario. Data were extracted by reviewing video recordings of the resuscitation. Sequences including defibrillation and/or drug administration were identified and assigned to one out of four categories: Defibrillation only (DC-only) and drug administration just prior to defibrillation (Drug + DC) for which the pre-shock pause was calculated, and drug administration alone (Drug-only) for which pre-drug time was calculated.

Results

DC-only sequences were identified in 68/72 simulations, Drug + DC in 24/72, and Drug-only in 33/72. Median pre-shock pauses were 18 s (DC-only) and 32 (Drug + DC), and median pre-drug pause 6. The variation between pauses was statistically significant (p ? 0.001). DC-only and Drug + DC sequences was found in 22/72 simulations. A statistically significant difference of 8 s was found between the median pre-shock pauses: 17 s (DC-only) and 25 (Drug + DC) (p ? 0.001). For un-paired observations, the pre-shock pause increased with 78% and for paired observations 47%.

Conclusions

Drug administration prior to defibrillation was associated with significant increases in pre-shock pauses in this full-scale simulation study.     

Ischaemia-modified albumin predicts the outcome of cardiopulmonary resuscitation: An experimental study

Introduction

Ischaemia-modified albumin (IMA) has recently been shown to be an early and sensitive marker of ischaemia. It is generally accepted that cardiac arrest causes the most severe form of global ischaemia. The aim of the present study was to identify whether IMA is an independent predictor of return of spontaneous circulation (ROSC) in a swine model of cardiac arrest.

Methods

Ventricular fibrillation (VF) was induced in 30 piglets, which were left untreated for 8 min before attempting resuscitation with precordial compression, mechanical ventilation and electrical defibrillation. Electrical defibrillation was attempted after 10 min of VF. Blood samples for IMA determination were drawn at baseline, after 8 min of VF and before delivery of each shock. A binary logistic regression model was implemented for the prediction of animals achieving ROSC from data available before the first defibrillation attempt. Backward stepwise selection was used to extract the final model. Inclusion and exclusion significance levels were 0.1 and 0.05, respectively. Receiver operating characteristic curves were used to determine the diagnostic accuracy, sensitivity and specificity of the parameters and to obtain the appropriate cut-off points.

Results

IMA exhibited 100% sensitivity and 93.8% specificity in defining the subgroup of animals that will achieve ROSC. This high-accuracy prediction had a very early onset (from eighth VF minute) and remained at the same level until the end of the experiment. When combining IMA and coronary perfusion pressure (CPP) measurements from the first CPR cycle in the form of the simple ratio IMA/CPP, a cut-off point of 7 could provide 100% sensitivity and specificity in distinguishing the animals that will achieve ROSC in the upcoming defibrillation attempts.

Conclusions

Until today, CPP has been found to be the only key determinant of successful resuscitation. Our study suggests that IMA can be a predictive index of ROSC even before the initiation of CPR.     

Correlation between coronary perfusion pressure and quantitative ECG waveform measures during resuscitation of prolonged ventricular fibrillation

Introduction

The ventricular fibrillation (VF) waveform is dynamic and predicts defibrillation success. Quantitative waveform measures (QWMs) quantify these changes. Coronary perfusion pressure (CPP), a surrogate for myocardial perfusion, also predicts defibrillation success. The relationship between QWM and CPP has been preliminarily explored. We sought to further delineate this relationship in our porcine model and to determine if it is different between animals with/without ROSC (return of spontaneous circulation).

Hypothesis

A relationship exists between QWM and CPP that is different between animals with/without ROSC.

Methods

Utilizing a prior experiment in our porcine model of prolonged out-of-hospital VF cardiac arrest, we calculated mean CPP, cumulative dose CPP, and percent recovery of three QWM during resuscitation before the first defibrillation: amplitude spectrum area (AMSA), median slope (MS), and logarithm of the absolute correlations (LAC). A random effects linear regression model with an interaction term CPP*ROSC investigated the association between CPP and percent recovery QWM and how this relationship changes with/without ROSC.

Results

For 12 animals, CPP and QWM measures (except LAC) improved during resuscitation. A linear relationship existed between CPP and percent recovery AMSA (coefficient 0.27; 95%CI 0.23, 0.31; p < 0.001) and percent recovery MS (coefficient 0.80; 95%CI 0.70, 0.90; p < 0.001). A linear relationship existed between cumulative dose CPP and percent recovery AMSA (coefficient 2.29; 95%CI 2.0, 2.56; p < 0.001) and percent recovery MS (coefficient 6.68; 95%CI 6.09, 7.26; p < 0.001). Animals with ROSC had a significantly “steeper” dose–response relationship.

Conclusions

There is a linear relationship between QWM and CPP during chest compressions in our porcine cardiac arrest model that is different between animals with/without ROSC.     

The location and incidence of out-of-hospital cardiac arrest in Georgia: : Implications for placement of automated external defibrillators

Objective

Prior studies of automated external defrillator placement strategies for public access defibrillation (PAD) have addressed only the venue of out-of-hospital cardiac arrest (OOHCA) in large urban areas. This study evaluates the relationship between population density and the incidence and location of OOHCA.

Methods

This study was a retrospective analysis of 624,199 Georgia state emergency medical services patient care reports (PCRs) in 2000. The PCR categorized these cardiac arrests by county into 12 location options. Counties were divided into population densities of <100, 100-400, 400-1,000, and >1,000 persons per square mile. The incidence of cardiac arrest for each location type was calculated for each population density group.

Results

The <100 density group had only 21.77% of the state's population but 30.96% of the state's cardiac arrests, whereas the >1,000 density group had 35.46% of the population but only 23.55% of the cardiac arrests (p<0.0001). The relative risk (95% confidence interval) for OOHCA in the <100 density group compared with the >1,000 density group was 2.14 (2.00, 2.29). The percentage of OOHCAs that occurred in the home for each population density group was: <100 persons per square mile, (67.67%); 100-400 persons per square mile, (68.83%); 400-1,000 persons per square mile, (65.75%); and >1,000 persons per square mile (62.09%) (p = 0.0001).

Conclusions

There are variations in incidence and location of OOHCA based on population density in Georgia. As population density increases, the incidence percentage of OOHCAs decreases. However, as population density increases, there is an increase in the percentage of cardiac arrests occurring outside the home, where more OOHCAs could potentially benefit from PAD.     

Treatment of monitored out-of-hospital ventricular fibrillation and pulseless ventricular tachycardia utilising the precordial thump

Background

Few studies have described the value of the precordial thump (PT) as first-line treatment of monitored out-of-hospital cardiac arrest (OHCA) from ventricular fibrillation and pulseless ventricular tachycardia (VF/VT).

Methods

Patient data was extracted from the Victorian Ambulance Cardiac Arrest Registry (VACAR) for all OHCA witnessed by paramedics between 2003 and 2011. Adult patients who suffered a monitored VF/VT of presumed cardiac aetiology were included. Cases were excluded if the arrest occurred after arrival at hospital, or a ‘do not resuscitate’ directive was documented. Patients were assigned into two groups according to the use of the PT or defibrillation as first-line treatment. The study outcomes were: impact of first shock/thump on return of spontaneous circulation (ROSC), overall ROSC, and survival to hospital discharge.

Results

A total of 434 cases met the eligibility criteria, of which first-line treatment involved a PT in 103 (23.7%) and immediate defibrillation in 325 (74.8%) cases. Patient characteristics did not differ significantly between groups. Seventeen patients (16.5%) observed a PT-induced rhythm change, including five cases of ROSC and 10 rhythm deteriorations. Immediate defibrillation resulted in significantly higher levels of immediate ROSC (57.8% vs. 4.9%, p < 0.0001), without excess rhythm deteriorations (12.3% vs. 9.7%, p = 0.48). Of the five successful PT attempts, three required defibrillation following re-arrest. Overall ROSC and survival to hospital discharge did not differ significantly between groups.

Conclusion

The PT used as first-line treatment of monitored VF/VT rarely results in ROSC, and is more often associated with rhythm deterioration.     

The effects of phase duration on defibrillation success of dual time constant biphasic waveforms

Aim of Study

The effects of first and second phase duration of biphasic waveforms on defibrillation success were evaluated in a guinea pig model of ventricular fibrillation (VF). We hypothesized that waveform duration, and especially the first phase duration, played a main role on defibrillation efficacy in comparison to energy, current and voltage, when a dual time constant biphasic shock was employed.

Methods

VF was induced and untreated for 5 s in 30 male guinea pigs, prior to attempting a single defibrillatory shock with one of 5 defibrillation waveforms which had different durations of the first and second phase. A five step up-down protocol was utilized for determining the defibrillation efficacy. After a 3-min interval, the procedure was repeated. A total of 25 cardiac arrest events and defibrillations were investigated for each animal.

Results

The defibrillation waveforms with an intermediate first phase of 5 ms, yielded the highest defibrillation success (p < 0.05). These waveforms also presented significantly lower energy, current and voltage in comparison to waveforms with shorter or longer first phase durations (p < 0.001). However, no differences on defibrillation success were observed among waveforms with different second phase durations varying from 1.5 ms to 3.5 ms.

Conclusions

For dual time constant biphasic waveforms, the first phase duration played a main role on defibrillation success. The intermediate first phase duration of 5 ms, yielded the best defibrillation efficacy compared with shorter or longer first phase durations. While the second phase duration did not affect defibrillation outcomes.     

Continuous chest compression resuscitation in arrested swine with upper airway inspiratory obstruction

Background

This study was designed to compare 24-h survival rates and neurological function of swine in cardiac arrest treated with one of three forms of simulated basic life support CPR.

Methods

Thirty swine were randomized equally among three experimental groups to receive either 30:2 CPR with an unobstructed endotracheal tube (ET) or continuous chest compression (CCC) CPR with an unobstructed ET or CCC CPR with a collapsable rubber sleeve on the ET allowing air outflow but completely restricting air inflow. The swine were anesthetized but not paralyzed. Two min of untreated VF was followed by 9 min of simulated single rescuer bystander CPR. In the 30:2 CPR group, each set of 30 chest compressions was followed by a 15-s pause to simulate the realistic duration of interrupted chest compressions required for a single rescuer to deliver 2 mouth-to-mouth ventilations. The other two groups were provided continuous chest compressions (CCC) without assisted ventilations. At 11 min post-arrest a biphasic defibrillation shock (150 J) was administered followed by a period of advanced cardiac life support.

Results

In the 30:2 group, 8 of 10 animals had good neurological function at 24-h post-resuscitation. In the CCC open airway group, 10 of 10, and in the CCC inspiratory obstructed group, 9 of 10. The number of shocks (P < 0.05) and epinephrine doses (P < 0.05) required for ROSC was greater in the 30:2 CPR group than in the other two groups.

Conclusions

There were no differences in 24-h survival with good neurological function among these three different CPR protocols.     

Survival Increases with CPR by Emergency Medical Services before defibrillation of out-of-hospital ventricular fibrillation or ventricular tachycardia: Observations from the Resuscitation Outcomes Consortium

Background

Immediate defibrillation is the traditional approach to resuscitation of cardiac arrest due to ventricular fibrillation or tachycardia (VF/VT). Delaying defibrillation to provide chest compressions may improve survival. We examined the effect of the duration of Emergency Medical Services (EMS) cardiopulmonary resuscitation (CPR) prior to first defibrillation on survival in patients with out-of-hospital VF/VT.

Materials and methods

From a prospective multi-center observational registry of EMS-treated out-of-hospital cardiac arrest, we identified 1638 EMS-treated cardiac arrests with first recorded rhythm VF/VT or “shockable” and complete data for analysis. Survival to hospital discharge was determined as a function of EMS CPR duration prior to first shock.

Results

Compared to the reference group of first EMS CPR duration ≤45 s, the odds of survival was greater among patients who received between 46 and 195 s of EMS CPR before first shock (46-75 s odds ratio [OR] 1.15, 95% confidence interval [CI] 0.71-1.87; 76-105 s, OR 1.37, 95% CI 0.80-2.35; 106-135 s, OR 1.53, 95% CI 0.96-2.45; 136-165 s, OR 1.24, 95% CI 0.71-2.15; 166-195 s, OR 1.47, 95% CI 0.85-2.52). The benefit of EMS CPR before defibrillation was reduced when the duration of CPR exceeded 195 s (196-225 s, OR 0.95, 95% CI 0.47-1.81; 226-255 s, OR 0.91, 95% CI 0.46-1.79; 256-285 s, OR 0.46, 95% CI 0.17-1.29; 286-315 s, OR 1.29, 95% CI 0.59-2.85). An optimal EMS CPR duration was not identified and no duration achieved statistical significance.

Conclusion

In this observational analysis of VF/VT arrest, between 46 and 195 s of EMS CPR prior to defibrillation was weakly associated with improved survival compared to ≤45 s. Randomized trials are needed to confirm the optimal duration of EMS CPR prior to defibrillation and to assess the impact of first CPR duration on all initial rhythms.     

Performance of a rectilinear biphasic waveform in defibrillation of presenting and recurrent ventricular fibrillation: a prospective multicenter study

Objectives

We tested the hypothesis that shock success differs with initial and recurrent episodes of ventricular fibrillation (VF).

Methods

From September 2008 to March 2010 out-of-hospital cardiac arrest patients with VF as the initial rhythm at 9 study sites were defibrillated by paramedics using a rectilinear biphasic waveform. Shock success was defined as termination of VF within 5 s post-shock. We used generalized estimating equation (GEE) analysis to assess the association between shock type (initial versus refibrillation) and shock success.

Results

Ninety-four patients presented in VF. Mean age was 65.4 years, 78.7% were male, and 80.9% were bystander-witnessed. VF recurred in 75 (79.8%). There were 338 shocks delivered for initial (n = 90) or recurrent (n = 248) VF available for analysis. Initial shocks terminated VF in 79/90 (87.8%) and subsequent shocks in 209/248 (84.3%). GEE odds ratio (OR) for shock type was 1.37 (95% CI 0.68-2.74). After adjusting for potential confounders, the OR for shock type remained insignificant (1.33, 95% CI 0.60-2.53). We observed no significant difference in ROSC (54.7% versus 52.6%, absolute difference 2.1%, p = 0.87) or neurologically intact survival to hospital discharge (21.9% versus 33.3%, absolute difference 11.4%, p = 0.31) between those with and without VF recurrence.

Conclusions

Presenting VF was terminated with one shock in 87.8% of cases. We observed no significant difference in the frequency of shock success between initial versus recurrent VF. VF recurred in the majority of patients and did not adversely affect shock success, ROSC, or survival.     

Nifekalant versus lidocaine for in-hospital shock-resistant ventricular fibrillation or tachycardia

Objective

To compare the efficacy and safety of nifekalant, a pure class III anti-arrhythmic drug, and lidocaine in patients with shock-resistant in-hospital ventricular fibrillation (VF) or ventricular tachycardia (VT).

Patients and methods

Between August 2005 and March 2008, we conducted a prospective, two-arm, cluster observational study, in which participating hospitals were pre-registered either to the nifekalant arm or the lidocaine arm. Patients were enrolled if they had in-hospital VF or VT resistant to at least two defibrillation shocks. Congenital or drug-induced long QT syndrome was excluded. The primary end-point was termination of VF or VT with/without additional shock. The secondary end-points were return of spontaneous circulation (ROSC), 1-month survival and survival to hospital discharge. We also assessed the frequency of adverse events, including asystole, pulseless electrical activity and torsade de pointes.

Results

In total, 55 patients were enrolled. After nifekalant, 22 of 27 patients showed termination of VF or VT, as compared with 15 of 28 patients treated with lidocaine with/without additional shock (odds ratio (OR): 3.8; 95% confidence interval (CI): 1.1-13.0; P = 0.03). Twenty-three of 27 patients given nifekalant showed ROSC, as compared with 15 of 28 patients given lidocaine (OR: 5.0; 95% CI: 1.4-18.2; P = 0.01). There was no difference in 1-month survival or survival to hospital discharge between the nifekalant and lidocaine arms. There was a higher incidence of asystole with lidocaine (7 of 28 patients) than with nifekalant (0 of 27 patients) (P = 0.005). Torsade de pointes was not observed.

Conclusion

Nifekalant was more effective than lidocaine for termination of arrhythmia and for ROSC in patients with shock-resistant in-hospital VF or VT (umin-CTR No. UMIN 000001781).     

Prognostic indicators and outcome prediction model for patients with return of spontaneous circulation from cardiopulmonary arrest: the Utstein Osaka Project

Objective

To determine the most important indicators of prognosis in patients with return of spontaneous circulation (ROSC) following out-of-hospital cardiopulmonary arrest (OHCA) and to develop a best outcome prediction model.

Design and patients

All patients were prospectively recorded based on the Utstein Style in Osaka over a period of 3 years (2005-2007). Criteria for inclusion were a witnessed cardiac arrest, age greater than 17 years, presumed cardiac origin of the arrest, and successful ROSC. Multivariate logistic regression (MLR) analysis was used to develop the best prediction model. The dependent variables were favourable outcome (cerebral-performance category [CPC]: 1-2) and poor outcome (CPC: 3-5) at 1 month after the event. Eight explanatory pre-hospital variables were used concerning patient characteristics and resuscitation. External validation was performed on an independent set of Utstein data in 2007.

Results

Subjects comprised 285 patients in VF and 577 patients with pulseless electrical activity (PEA)/asystole. The percentage of favourable outcomes was 31.9% (91/285) in VF and 5.7% (33/577) in PEA/asystole. The most important prognostic indicators of favourable outcome found by MLR were age (p = 0.10), time from collapse to ROSC (TROSC) (p < 0.01), and presence of pre-hospital ROSC (PROSC) (p = 0.15) for VF and age (p = 0.03), TROSC (p < 0.01), PROSC (p < 0.01), and conversion to VF (p = 0.01) for PEA/asystole. For external validation data, areas under the receiver-operating characteristic curve were 0.867 for VF and 0.873 for PEA/asystole.

Conclusions

A model based on four selected indicators showed a high predictive value for favourable outcome in OHCA patients with ROSC.     

Chest compression quality variables influencing the temporal development of ROSC-predictors calculated from the ECG during VF

Background

Predictive measures that reflect the probability of return of spontaneous circulation (ROSC) if the patient is defibrillated can be calculated from the electrocardiogram during ventricular fibrillation (VF) and ventricular tachycardia (VT). It has not been studied how the quality of chest compressions affect the development of such ROSC predictors.

Materials and methods

We have formulated a model for the effect of chest compressions on the ROSC predictor median-slope (MS). For untreated VF/VT MS is assumed to decay with time and increases in MS are attributed to the effect of chest compressions. The model correlates observed trends in MS with compression quality variables derived from measurements of compression depth and force recorded during out-of-hospital cardiac arrest. Among the quality variables tested were compression rate, depth, duty cycle, leaning depth, force, work and a novel quality indicator termed residual heart force. The model was first developed on an exploration dataset and thereafter validated against independent data.

Results

When testing the indicators one by one, residual heart force (p < 0.0001), force (p < 0.0001) and work (p = 0.0210) were significantly correlated to MS development. In multivariate analysis, residual heart force (p < 0.0001) was the most significant indicator. Adjusting for residual heart force, there was a tendency that increased depth was associated with smaller effect of compressions (p = 0.0330).

Conclusion

Using MS as an indicator of the state of the myocardium, force-based compression quality variables are better indicators of efficient CPR than compression depth. A novel indicator termed residual heart force gives the best correlation with observed trends in MS.     

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 360 J 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.