The effects of a newly developed miniaturized mechanical chest compressor on outcomes of cardiopulmonary resuscitation in a porcine model*.

OBJECTIVE: When the duration of cardiac arrest is prolonged, reperfusion of the vital organs by effective chest compression is the most important intervention for successful resuscitation. We investigated the effects of a newly developed miniaturized chest compressor on the outcomes of cardiopulmonary resuscitation. DESIGN: Prospective, randomized, controlled experimental study. SETTING: University-affiliated animal research laboratory. SUBJECTS: Thirty male domestic pigs. INTERVENTIONS: Ventricular fibrillation was induced in 30 male domestic pigs weighing 35 ± 2 kg. Cardiopulmonary resuscitation was initiated after 7 mins of untreated ventricular fibrillation. The animals were randomized to receive mechanical chest compression with a miniaturized chest compressor, a LUCAS device or a Thumper device. After 5 mins of cardiopulmonary resuscitation, a 150-J defibrillation was delivered. If resuscitation was not successful, cardiopulmonary resuscitation was continued for 2 mins before the next defibrillation. The protocol was continued until successful resuscitation or for a total of 15 mins of cardiopulmonary resuscitation. The animals were observed for 72 hrs after resuscitation. MEASUREMENTS AND MAIN RESULTS: The miniaturized chest compressor generated significantly greater coronary perfusion pressure, end-tidal PCO2, carotid blood flow, and intrathoracic negative pressure, with significantly lower compression depth and fewer rib fractures when compared with both the LUCAS and Thumper devices. Both the miniaturized chest compressor and LUCAS devices required lower numbers of defibrillation for successful resuscitation when compared with the Thumper device. This was associated with lower prevalence of recurrent ventricular fibrillation and better postresuscitation myocardial and neurological function when compared with the Thumper device. CONCLUSIONS: The miniaturized chest compressor improves hemodynamic efficacy and the success of cardiopulmonary resuscitation with significantly less injury, which is as effective as the LUCAS device. It may provide a new option for cardiopulmonary resuscitation.

Preserved heart rate variability during therapeutic hypothermia correlated to 96 hrs neurological outcomes and survival in a pig model of cardiac arrest.

OBJECTIVE: Therapeutic hypothermia initiated with cardiopulmonary resuscitation improves neurologic outcomes and survival after prolonged cardiac arrest. However, the potential mechanism by which hypothermia improves neurologic outcomes remains unclear. In the current study, we investigated the effect of rapid head cooling on 96-hr neurologic outcomes and survival by heart rate variability analysis in a pig model of prolonged cardiac arrest. DESIGN: Prospective randomized controlled animal study. SETTING: University-affiliated research laboratory. SUBJECTS: Yorkshire-X domestic pigs (Sus scrofa). INTERVENTIONS: A protocol of 10 mins of untreated ventricular fibrillation followed by 5 mins of cardiopulmonary resuscitation in a pig model of cardiac arrest was used in this study. Sixteen male domestic pigs weighing between 39 and 45 kg were randomized into two groups, hypothermia (n = 8) and control (n = 8). For the hypothermia group, intranasal-induced head cooling was initiated with cardiopulmonary resuscitation and persisted for 4 hrs after resuscitation. For the control group, cardiopulmonary resuscitation was started with normothermia. MEASUREMENTS AND MAIN RESULTS: Time and frequency domain heart rate variability was calculated in 5-min sections of electrocardiographic recordings at baseline and 4 hrs after resuscitation. Neurologic outcomes were evaluated every 24 hrs during the 96-hr postresuscitation observation period. No differences in the baseline measurement and resuscitation outcome were observed between the groups. However, the 96-hr cerebral performance categories of the hypothermic group were significantly lower than control (1.0 ± 0.0 vs. 4.0 ± 1.9, p = .003). Four hrs after resuscitation, mean RR interval, heart rate variability triangular index, and normalized very-low-frequency power were restored to baseline in the hypothermia group. Square root of the mean squared differences of successive RR intervals and SD of instantaneous RR intervals were significantly improved in the cooled animals compared with controls. A significant correlation between 4-hr heart rate variability and 96-hr cerebral performance category was observed in this study. CONCLUSION: Selective head cooling maintains a certain level of autonomic nervous system function in this pig model of cardiac arrest. The preserved heart rate variability during postresuscitation hypothermia was associated with favorable 96-hr neurologic recovery and survival.

Defibrillation delivered during the upstroke phase of manual chest compression improves shock success.

OBJECTIVE: The current standard of manual chest compression during cardiopulmonary resuscitation requires pauses for rhythm analysis and shock delivery. However, interruptions of chest compression greatly decrease the likelihood of successful defibrillations, and significantly better outcomes are reported if this interruption is avoided. We therefore undertook a prospective randomized controlled animal study in an electrically induced ventricular fibrillation pig model to assess the effects of timing of defibrillation on the manual chest compression cycle on the defibrillation threshold. DESIGN: Prospective, randomized, controlled animal study. SETTING: University-affiliated research laboratory. SUBJECTS: Yorkshire-X domestic pigs (Sus scrofa). INTERVENTIONS: In eight domestic male pigs weighing between 24 and 31 kg, ventricular fibrillation was electrically induced and untreated for 10 secs. Manual chest compression was then performed and continued for 25 secs with the protection of an isolation blanket. The depth and frequency of chest compressions were guided by a cardiopulmonary resuscitation prompter. Animals were randomized to receive a biphasic electrical shock in five different compression phases with a predetermined energy setting. A control phase was chosen at a constant 2 secs after discontinued chest compression. A grouped up-down defibrillation threshold testing protocol was used to compare the success rate at different coupling phases. After a recovery interval of 4 mins, the sequence was repeated for a total of 60 test shocks for each animal. MEASUREMENTS AND MAIN RESULTS: No difference in coronary perfusion pressure before delivering of the shock was observed among the six study phases. The defibrillation success rate, however, was significantly higher when shocks were delivered in the upstroke phase of manual chest compression. CONCLUSION: Defibrillation efficacy is maximal when electrical shock is delivered during the upstroke phase of manual chest compression.

Electrocardiographic analysis during uninterrupted cardiopulmonary resuscitation.

OBJECTIVE: Prior studies have shown that interruptions of chest compressions could result in high failure rates of resuscitation. Chest compression artifacts force the interruption of compressions before electrocardiographic rhythm analysis. It was the goal of this study to evaluate the accuracy of an automated electrocardiographic rhythm analysis algorithm designed to attenuate compression-induced artifact and minimize uninterrupted chest compressions. DESIGN: Retrospective diagnostic analysis. SETTING: Out-of-hospital cardiopulmonary resuscitation. SUBJECTS: Eight hundred thirty-two patients. INTERVENTIONS: Patients were treated with defibrillation and cardiopulmonary resuscitation. Continuous data were recorded using automated external defibrillators with concurrent measurement of electrocardiographic and sternal motion during chest compressions. MEASUREMENTS AND RESULTS: Human electrocardiographics recorded by automated external defibrillators were annotated and randomly selected to build distinct training and testing databases. The artifact reduction and tolerant filter was applied to the electrocardiographic signal. The algorithm was optimized with the training database (sensitivity, 93.9%; specificity, 91.2%) and tested with the testing database (sensitivity, 92.1%; specificity, 90.5%). Average attenuation of compression-induced artifact was more than 35 dB. CONCLUSIONS: Shockable ventricular arrhythmias can be differentiated from electrocardiographic rhythms not requiring defibrillation in the presence of chest compression-induced artifact with sensitivity and specificity above 90%. With the artifact reduction and tolerant filter, it is possible to effectively eliminate pre- and postshock compression pauses.

Electrocardiogram waveforms for monitoring effectiveness of chest compression during cardiopulmonary resuscitation.

BACKGROUND: Newer guidelines address the importance of effective chest compressions, citing evidence that this primary intervention is usually suboptimally performed during cardiopulmonary resuscitation. We therefore sought a readily available option for monitoring the effectiveness of chest compressions, specifically using the electrocardiogram. METHODS AND RESULTS: Ventricular fibrillation was induced by coronary artery occlusion and untreated for 5 mins. Male domestic pigs weighing 40 +/- 2 kg were randomized to optimal or suboptimal chest compressions after onset of ventricular fibrillation. Optimal depth of mechanical compression in six animals was defined as a decrease of 25% in anterior posterior diameter of the chest during compression. Suboptimal compression, also in six animals, was defined as a decrease of 17.5% in anterior posterior diameter. For each group, the chest compressions were maintained at a rate of 100 per min. After 3 mins of chest compression, defibrillation was attempted with a 150-J biphasic shock. All animals had return of spontaneous circulation after optimal compressions. This contrasted with suboptimal compressions, after which none of the animals had return of spontaneous circulation. Amplitude spectrum area values, representing the electrocardiographic amplitude frequency spectral area computed from conventional precordial leads, like coronary perfusion pressure and end tidal PCO2, were predictive of outcomes. CONCLUSION: The effectiveness of chest compressions was reflected in the amplitude spectrum area values. Accordingly, the amplitude spectrum area predictor may be incorporated in current automated external defibrillators to monitor and prompt the effectiveness of chest compression during cardiopulmonary resuscitation.

Identifying potentially shockable rhythms without interrupting cardiopulmonary resuscitation.

OBJECTIVE: Current versions of automated external defibrillators (AEDs) mandate interruptions of chest compression for rhythm analyses because of artifacts produced by chest compressions. Interruption of chest compressions reduces likelihood of successful resuscitation by as much as 50%. We sought a method to identify a shockable rhythm without interrupting chest compressions during cardiopulmonary resuscitation (CPR). DESIGN: Experimental study. SETTING: Weil Institute of Critical Care Medicine, Rancho Mirage, CA. SUBJECTS: None. INTERVENTIONS: Electrocardiographs (ECGs) were recorded in conjunction with AEDs during CPR in human victims. A shockable rhythm was defined as disorganized rhythm with an amplitude > 0.1 mV or, if organized, at a rate of > or = 180 beats/min. Wavelet-based transformation and shape-based morphology detection were used for rhythm classification. Morphologic consistencies of waveform representing QRS components were analyzed to differentiate between disorganized and organized rhythms. For disorganized rhythms, the amplitude spectrum area was computed in the frequency domain to distinguish between shockable ventricular fibrillation and nonshockable asystole. For organized rhythms, in victims in whom the absence of a heartbeat was independently confirmed, the heart rate was estimated for further classification. MEASUREMENTS AND MAIN RESULTS: To derive the algorithm, we used 29 recordings on 29 patients from the Creighton University ventricular tachyarrhythmia database. For validation, the algorithm was tested on an independent population of 229 victims, including recordings of both ECG and depth of chest compressions obtained during suspected out-of-hospital sudden death. The recordings included 111 instances in which the ECG was corrupted during chest compressions. A shockable rhythm was identified with a sensitivity of 93% and a specificity of 89%, yielding a positive predictive value of 91%. A nonshockable rhythm was identified with a sensitivity of 89%, a specificity of 93%, and a positive predictive value of 91% during uninterrupted chest compression. CONCLUSIONS: The algorithm fulfilled the potential lifesaving advantages of allowing for uninterrupted chest compression, avoiding pauses for automated rhythm analyses before prompting delivery of an electrical shock.

The amplitude spectrum area correctly predicts improved resuscitation and facilitated defibrillation with head cooling.

OBJECTIVES: When systemic hypothermia was maintained before inducing cardiac arrest, the likelihood of successful defibrillation and meaningful survival was increased. When hypothermia is induced during cardiopulmonary resuscitation, mortality is also improved. With the introduction of the amplitude spectrum area as a predictor of the success of electrical defibrillation, we investigated the effect of preferential head cooling initiated coincident with cardiopulmonary resuscitation on amplitude spectrum area as a predictor. We hypothesized that rapid head cooling initiated coincident with cardiopulmonary resuscitation improves amplitude spectrum area, and therefore is predictive of successful defibrillation. DESIGN: Prospective randomized controlled study. SETTING: University-affiliated research institute. SUBJECTS: Domestic pigs. INTERVENTIONS: Sixteen pigs, weighing 40.6 +/- 1.4 kg, were randomized to the hypothermia (n = 8), or control (n = 8) group. Ventricular fibrillation was induced and untreated for 10 mins. Cardiopulmonary resuscitation was then initiated for 5 mins followed by attempted defibrillation with a biphasic 150-J electric shock. Coincident with starting cardiopulmonary resuscitation, hypothermia was induced with evaporative intranasal cooling using a perfluorochemical. If spontaneous circulation was not restored after defibrillation, cardiopulmonary resuscitation was resumed for 1 min before the next defibrillation attempt until the animal was either successfully resuscitated or for a total of 15 mins. The target core temperature was 34 degrees C. Control animals were identically treated except for hypothermia. MEASUREMENTS AND MAIN RESULTS: Five seconds of ventricular fibrillation waveform were recorded immediately preceding delivery of a shock. The ventricular fibrillation waveforms were analyzed using the amplitude spectrum area algorithm. A smaller epinephrine dose (60 +/- 32.1 vs. 30 +/- 0 mg/mL, p = .01) and shorter cardiopulmonary resuscitation duration (365 +/- 42 sec vs. 600 +/- 243 sec, p = .01) were required to achieve return of spontaneous circulation in the hypothermia group, compared with control. Five minutes after starting cardiopulmonary resuscitation, head temperature was reduced from 38 degrees C to 34 degrees C in the hypothermia group (p = .028). Hypothermia improved the success of electrical shocks before return of spontaneous circulation (88 +/- 18% vs. 66 +/- 19%, p = .034). Both the amplitude spectrum area values of initial shock (26.1 +/- 5.3 vs. 21.4 +/- 2.16 mV-Hz, p = .049) and total shocks (26.1 +/- 5.3 vs. 21.4 +/- 2.16 mV-Hz, p = .006) were significantly higher in the hypothermia group than control. CONCLUSIONS: Amplitude spectrum area served as a useful predictor for improved resuscitation and facilitated defibrillation in the setting of rapid head cooling initiated coincident with cardiopulmonary resuscitation.

Miniaturized mechanical chest compressor: a new option for cardiopulmonary resuscitation.

AIM OF STUDY: After cardiac arrest, uninterrupted chest compressions with restoration of myocardial blood flow facilitates restoration of spontaneous circulation. We recognized that this may best be accomplished with a mechanical device and especially so during transport. We therefore sought to develop a lightweight, portable chest compressor which may be carried on the belt or attached to the oxygen tank typically carried on the back of the first response rescuer. A miniaturized pneumatic chest compressor (MCC) weighing less than 2 kg was developed and compared with a currently marketed "Michigan Thumper", which weighed 19 kg. We hypothesized that the 2 kg, low profile, portable device will be as effective as the standard pneumatic Thumper for restoring circulation during CPR. MATERIAL AND METHODS: Ventricular fibrillation was electrically induced in 10 domestic male pigs weighing 39+/-2 kg, and untreated for 5 min. Animals were then randomized to receive chest compressions with either the MCC or the Thumper. After 5 min of mechanical chest compression, defibrillation was attempted with a 150 J biphasic shock. Coronary perfusion pressure (CPP) and end tidal PCO(2) (EtPCO(2)) were measured by conventional techniques together with right carotid artery blood flow (CBF). RESULTS: Four of five animals compressed with the Thumper and each animal compressed with the MCC were successfully resuscitated. No significant differences in CPP, EtPCO(2), CBF and post-resuscitation myocardial function were observed between groups. Resuscitated animals survived for more than 72 h without neurological impairment. CONCLUSION: The low profile, 2 kg miniaturized chest compressor is as effective as the conventional Thumper in an experimental model of CPR.

Adverse outcomes of interrupted precordial compression during automated defibrillation.

BACKGROUND: Current versions of automated external defibrillators (AEDs) require frequent stopping of chest compression for rhythm analyses and capacity charging. The present study was undertaken to evaluate the effects of these interruptions during the operation of AEDs. METHODS AND RESULTS: Ventricular fibrillation was electrically induced in 20 male domestic swine weighing between 37.5 and 43 kg that were untreated for 7 minutes before CPR was started. Defibrillation was attempted with up to 3 sequential 150-J biphasic shocks, but each was preceded by 3-, 10-, 15-, or 20-second interruptions of chest compression. The interruptions corresponded to those that were mandated by commercially marketed AEDs for rhythm analyses and capacitor charge. The sequence of up to 3 electrical shocks and delays were repeated at 1-minute intervals until the animals were successfully resuscitated or for a total of 15 minutes. Spontaneous circulation was restored in each of 5 animals in which precordial compression was delayed for 3 seconds before the delivery of the first and subsequent shocks but in none of the animals in which the delay was >15 seconds before the delivery of the first and subsequent shocks. Longer intervals of CPR interventions were required, and there was correspondingly greater failure of resuscitation in close relationship to increasing delays. The durations of interruptions were inversely related to the durations of subthreshold levels of coronary perfusion pressure. Postresuscitation arterial pressure and left ventricular ejection fraction were more severely impaired with increasing delays. CONCLUSIONS: Interruptions of precordial compression for rhythm analyses that exceed 15 seconds before each shock compromise the outcome of CPR and increase the severity of postresuscitation myocardial dysfunction.

Evolution of the stone heart after prolonged cardiac arrest.

OBJECTIVES: We hypothesized that progressive impairment in diastolic function during cardiopulmonary resuscitation (CPR) precedes evolution of the "stone heart" after failure of CPR. We therefore measured sequential changes in left ventricular (LV) volumes and free-wall thickness of the heart during CPR in an experimental model. DESIGN: Prospective, observational animal study. SETTING: Medical research laboratory in an university-affiliated research and educational institute. SUBJECTS: Domestic pigs. METHODS: Ventricular fibrillation (VF) was induced in 40 anesthetized male domestic pigs weighing between 38 kg and 43 kg. After 4 min, 7 min, or 10 min of untreated VF, electrical defibrillation was attempted. Failing to reverse VF in each instance, precordial compression at a rate of 80/min was begun coincident with mechanical ventilation. Coronary perfusion pressures (CPPs) were computed from the differences in time-coincident diastolic aortic and right atrial pressures. Left ventricular (LV) systolic and diastolic ventricular volumes and thickness of the LV free wall were estimated with transesophageal echocardiography. The stroke volumes (SVs) were computed from the differences in decompression diastolic and compression systolic volumes. Free-wall thickness was measured on the hearts at autopsy. RESULTS: Significantly greater CPPs were generated with the 4 min of untreated cardiac arrest. Progressive reductions in LV diastolic and SV and increases in LV free-wall thickness were documented with increasing duration of untreated VF. A stone heart was confirmed at autopsy in each animal that failed resuscitative efforts. Correlations with indicator dilution method and physical measurements at autopsy corresponded closely with the echocardiographic measurements. CONCLUSION: Progressive impairment in diastolic function terminates in a stone heart after prolonged intervals of cardiac arrest.

Predicting the success of defibrillation by electrocardiographic analysis.

BACKGROUND: We investigated an electrocardiographic signal analysis technique for predicting whether an electrical shock would reverse ventricular fibrillation (VF) in an effort to minimize the damaging effects of repetitive shocks during CPR. METHODS AND RESULTS: An established model of CPR was utilized. VF was electrically induced in anesthetized 40 kg domestic pigs. Defibrillation was attempted after either 4 or 7 min of untreated VF. Failing to reverse VF, a 1 min interval of precordial compression and mechanical ventilation preceded each subsequent defibrillation attempt. The amplitude frequency spectrum of digitally filtered VF wavelets was computed with Fourier analysis during uninterrupted precordial compression from conventional right infraclavicular and left apical electrodes. Of a total of 34 electrical defibrillation attempts, 24 animals were restored to spontaneous circulation (ROSC). An amplitude spectrum analysis (AMSA) value of 21 mV Hz had a negative predictive value of 0.96 and a positive predictive value of 0.78. CONCLUSIONS: AMSA predicted when an electrical shock failed to restore spontaneous circulation during CPR with a high negative predictive value. This method potentially fulfills the need for minimizing ineffective defibrillation attempts and their attendant adverse effects on the myocardium.

Myocardial dysfunction after electrical defibrillation.

We hypothesized that electrical shocks that defibrillate hearts successfully also produce myocardial injury, but only in settings in which the myocardium is underperfused. Myocardial function was measured in isolated, conventionally perfused or underperfused rat hearts during sinus rhythm and conventionally perfused or underperfused hearts during ventricular fibrillation (VF) after delivery of a sham, a 0.4 J, or a 0.7 J shock. In underperfused hearts, the dP/dt, negative dP/dt, left ventricular diastolic pressure and left ventricular pressure-volume relationships demonstrated significant impairment in myocardial function. Impairment increased with the higher energy shocks. This contrasted with normally perfused hearts, whether in sinus rhythm or during VF, in which shocks resulted in no significant impairment. Electrical shocks therefore produce myocardial injury but only when myocardial perfusion is reduced.

Miniaturized mechanical chest compressor improves calculated cerebral perfusion pressure without compromising intracranial pressure during cardiopulmonary resuscitation in a porcine model of cardiac arrest.

OBJECTIVE: One of the major goals of cardiopulmonary resuscitation (CPR) is to provide adequate oxygen delivery to the brain for minimizing cerebral injury resulted from cardiac arrest. The optimal chest compression during CPR should effectively improve brain perfusion without compromising intracranial pressure (ICP). Our previous study has demonstrated that the miniaturized mechanical chest compressor improved hemodynamic efficacy and the success of CPR. In the present study, we investigated the effects of the miniaturized chest compressor (MCC) on calculated cerebral perfusion pressure (CerPP) and ICP. METHODS: Ventricular fibrillation was electrically induced and untreated for 7min in 13 male domestic pigs weighing 39±3kg. The animals were randomized to receive mechanical chest compression with the MCC (n=7), or the Thumper device (n=6). CPR was performed for 5min before defibrillation attempt by a single 150J shock. At 2.5min of CPR, the epinephrine at a dose of 20µg/kg was administered. Additional epinephrine was administered at an interval of 3min thereafter. If resuscitation was not successful, CPR was resumed for an additional 2min prior to the next defibrillation until successful resuscitation or for a total of 15min. Post-resuscitated animals were observed for 2h. RESULTS: Significantly greater intrathoracic positive and negative pressures during compression and decompression phases of CPR were observed with the MCC when compared with the Thumper device. The MCC produced significantly greater coronary perfusion pressure and end-tidal carbon dioxide. There were no statistically significant differences in systolic and mean ICP between the two groups; however, both of the measurements were slightly greater in the MCC treated animals. Interestingly, the diastolic ICP was significantly lower in the MCC group, which was closely related to the significantly lower negative intrathoracic pressure in the animals that received the MCC. Most important, systolic, diastolic and mean calculated CerPP were all significantly greater in the animals receiving the MCC. CONCLUSIONS: In the present study, mechanical chest compression with the MCC significantly improved calculated CerPP but did not compromise ICP during CPR. It may provide a safe and effective chest compression during CPR. Protocol number: P1205.

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 ≥40beat/min commencing within one min of post-shock period and persisting for a minimum of 30s. RESULTS: Signal integral was significantly greater in successful defibrillation than unsuccessful defibrillation (81.76±32.3mV vs. 34.9±15.33mV, p<0.001). The intersection of the sensitivity and specificity curve provided a threshold value of 51mV. 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.

An algorithm used for ventricular fibrillation detection without interrupting chest compression.

Ventricular fibrillation (VF) is the primary arrhythmic event in the majority of patients suffering from sudden cardiac arrest. Attention has been focused on this particular rhythm since it is recognized that prompt therapy, especially electrical defibrillation, may lead to a successful outcome. However, current versions of automated external defibrillators (AEDs) mandate repetitive interruptions of chest compression for rhythm analyses since artifacts produced by chest compression during cardiopulmonary resuscitation (CPR) preclude reliable electrocardiographic (ECG) rhythm analysis. Yet, repetitive interruptions in chest compression are detrimental to the success of defibrillation. The capability for rhythm analysis without requiring "hands-off" intervals will allow for more effective resuscitation. In this paper, a novel continuous-wavelet-transformation-based morphology consistency evaluation algorithm was developed for the detection of disorganized VF from organized sinus rhythm (SR) without interrupting the ongoing chest compression. The performance of this method was evaluated on both uncorrupted and corrupted ECG signals recorded from AEDs obtained from out-of-hospital victims of cardiac arrest. A total of 232 patients and 31,092 episodes of either VF or SR were accessed, in which 8195 episodes were corrupted by artifacts produced by chest compressions. We also compared the performance of this method with three other established algorithms, including VF filter, spectrum analysis, and complexity measurement. Even though there was a modest decrease in specificity and accuracy when chest compression artifact was present, the performance of this method was still superior to other reported methods for VF detection during uninterrupted CPR.

The optimal phasic relationship between synchronized shock and mechanical chest compressions.

OBJECTIVE: Pauses for shock delivery in chest compressions are detrimental to the success of resuscitation and may be eliminated with the use of mechanical chest compressors. However, the optimal phasic relationship between mechanical chest compression and defibrillation is still unknown. We therefore undertook a study to assess the effects of timing of defibrillation in the mechanical chest compression cycle on the defibrillation threshold (DFT) using a porcine model of cardiac arrest. METHODS: Ventricular fibrillation was electrically induced and untreated for 10s in 8 domestic pigs weighing between 26 and 30 kg. Mechanical chest compression was then continuously performed for 25s, followed by a biphasic electrical shock which was delivered to the animal at 6 randomized coupling phases, including a control phase, with a pre-determined energy setting. The control phase was chosen at a constant 2s following discontinued chest compression. A novel grouped up-and-down DFT testing protocol was used to compare the success rate at different coupling phases. After a recovery interval of 4 min, the testing sequence was repeated, resulting in a total of 60 test shocks delivered to each animal. RESULTS: No difference between the delivered shock energy, voltage and current were observed among the 6 study phases. The defibrillation success rate, however, was significantly higher when shocks were delivered in the upstroke phase of mechanical chest compression. CONCLUSION: Defibrillation efficacy is maximal when electrical shock is delivered in the upstroke phase of mechanical chest compression.

The resuscitation blanket: a useful tool for "hands-on" defibrillation.

AIM OF STUDY: We investigated the safety, feasibility and efficacy of a resuscitation blanket designed with the intent to protecting the rescuer from the risk of receiving electrical current during defibrillation which, would allow for uninterrupted chest compressions. METHODS: Fifteen pigs weighing between 22 and 40 kg were investigated with an established model of cardiac arrest and CPR. CPR was performed with the interposition of the blanket between the rescuer's hands and the chest of the animal. Defibrillation voltage and current over the blanket were measured. Hemodynamics, including coronary perfusion pressure (CPP), end-tidal CO(2) (EtCO(2)) and 50% successful defibrillation threshold (DFT50) were measured and compared during CPR with and without the blanket. RESULTS: Leakage through the blanket was nominal. Voltages of 42.0, 56.6 and 105 V and mean leakage currents of 1.1, 1.4 and 3.3 microA were measured above the blanket for 150, 200 and 360 J defibrillation shocks. CPP and EtCO(2) in the animals during chest compression with the resuscitation blanket were not significantly different compared to those measured without the blanket. However, when the blanket was not utilized, CPP decreased (P<0.05) during the 15-s hands-off interruption prior to defibrillation. Defibrillation threshold was significantly lower when the blanket was used. CONCLUSION: The resuscitation blanket is a safe and useful tool which protects the rescuer from hands-on defibrillation shocks, allowing for uninterrupted chest compressions, and therefore improving defibrillation success.

Comparison of efficacy of pulsed biphasic waveform and rectilinear biphasic waveform in a short ventricular fibrillation pig model.

AIM OF STUDY: The waveform designs and their relative defibrillation efficacy of external biphasic waveforms may differ remarkably among manufacturers. In this study, we compared pulsed biphasic waveform (PBW) with rectilinear biphasic waveform (RBW) and their effects on terminating ventricular fibrillation (VF). METHODS: VF was electrically induced and untreated for 10s in 6 domestic pigs weighing between 56 and 70 kg. The animals were then randomized to attempt defibrillation with either a PBW or RBW shock at energy levels of 50-200 J. If the delivered shock failed to terminate VF, a 150 J rescue shock was delivered with the same waveform. After a recovery interval of 4 min, the sequences were repeated for a total of 60 test shocks. The 50% and 80% defibrillation thresholds (DFT) were then calculated for the compared waveforms. RESULTS: No differences were observed in energy DFT50 and DFT80. Although the peak current and average current of the PBW were higher than RBW, there was no change observed in ST segment following shocks with both waveforms. CONCLUSION: In the setting of this experiment, there was no difference in terms of defibrillation efficacy and myocardial injury related to the electrical shocks of the two waveforms.

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

AIM OF STUDY: Impedance compensation methods differ markedly among manufacturers and can play an important role in defibrillation success. In this study we compared the efficacy of two different commercial defibrillators based on defibrillation success in a high impedance porcine model of cardiac arrest. The first defibrillator (A) compensates high impedance by controlling current with fixed shock duration, while the second defibrillator (B) by prolonging the shock duration. METHODS: In 10 domestic male pigs weighing between 17 and 28 kg, ventricular fibrillation was electrically induced and untreated for 15s. Animals were randomized to receive defibrillations with either defibrillator A or defibrillator B, at maximum energy settings of which were 200 J for the defibrillator A and 360 J for the defibrillator B. A grouped up-down defibrillation threshold testing protocol was used to compare the success rate between the two defibrillators. A variable resistance, ranging from 80 to 200 ohm was placed in series with the defibrillation pads. After a recovery interval of 5 min, the sequence was repeated for a total of 60 test shocks for each animal. RESULTS: The measured total pathway impedance was in a range of 108-278 ohm. The combined success rate was 49.5% for the two defibrillators in a total of 600 testing shocks. The success rate was significantly higher when the defibrillator A was employed in comparison with defibrillator B (63% vs. 36%, p=0.0001). CONCLUSION: For transthoracic impedances greater than average, the current-based compensation technique was more effective than the duration-based compensation technique.