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

Evaluation of functional and electrical features of automatic external defibrillators in extreme altitude and temperature environments

Aims

Human exposure to high-altitude and/or low-temperature areas is increasing and cardiac arrest in these circumstances represents an increasing proportion of all treated cardiac arrests. However, little is known about the performance of automated external defibrillators (AED) in these circumstances. The objective of this study is to assess the functional and electrical features of 6 commercially available AEDs in extreme environments.

Methods

Accuracy of shockable rhythm detection, the time required for self-test, rhythm analysis, and capacitor charging, together with total energy, peak voltage, peak current, and phasic duration of defibrillation waveform measured after placing the AEDs in simulated high-altitude, simulated low-temperature, and natural composite high-altitude and low-temperature environment for 30 min, were compared to those measured in the standard environment.

Results

All of the shockable rhythms were correctly detected and all of the defibrillation shocks were successfully delivered by the AEDs. However, the time required for self-test, rhythm detection, and capacitor charging was shortened by 1.2% (3 AEDs, maximum 12.4%) in the simulated high-altitude environment, was prolonged by 3.6% (4 AEDs, maximum 40.8%) in the simulated low-temperature environment, and was prolonged by 4.1% (5 AEDs, maximum 52.1%) in the natural environment. Additionally, the total delivered energy was decreased by 2.5% (2 AEDs, maximum 6.8%) in the natural environment.

Conclusion

All of the investigated AEDs functioned properly in simulated and natural environments, but a large variation in the functional and electrical feature change was observed. When performing cardiopulmonary resuscitation in extreme environments, the impact of environmental factors may need consideration.

A combined impedance compensation strategy applied to external automatic defibrillators

Transthoracic impedance is one of the key factors affecting the success of defibrillation. Impedance compensation technique is used to adjust defibrillation parameters according to the transthoracic impedance of the defibrillator. In this paper, a combined impedance compensation strategy is proposed to address the shortcomings of existing compensation strategies. In order to evaluate the performance of the combined compensation strategy, this paper uses the prototype as the experimental machine, and uses two AED with representative impedance compensation strategies as the control machine, and the simulated defibrillation method is used for comparative testing. The results show that the combined impedance compensation has a more steadier distribution over the defibrillation energy and current: compared with the energy-based impedance compensation strategy, this strategy can significantly reduce the peak current (25 Ω: 27.8 vs. 54.7 A; 50 Ω: 20.7 vs. 32.3 A) and average current (25 Ω: 24.8 vs. 37.5 A) of defibrillation at low impedance, and compared with the current impedance compensation strategy, it can significantly reduce the defibrillation energy (150 Ω: 8.6 vs. 1.7 %, 175 Ω: 15.6 vs. 4.9 %, 200 Ω: 21.9 vs. 8.5 %) at high impedance. Impedance compensation is more precise and the current passing during defibrillation is steadier.

Pediatric defibrillation shocks alone do not cause heart damage in a porcine model

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AEDs utilize specific low energy pediatric modes to reduce myocardial damage.

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This study applied various shocks in sinus rhythm without cardiac instrumentation.

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Isolated clinically relevant shock sequences do not result in myocardial damage.

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Typical variations in pediatric shocks did not affect safety and efficacy.

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These results may inform future pediatric resuscitation guidelines.

Aim

Automated external defibrillators (AEDs) use various shock protocols with different characteristics when deployed in pediatric mode. The aim of this study is to assess and compare the safety and efficacy of different AED pediatric protocols using novel experimental approaches.

Methods

Two defibrillation protocols (A and B) were assessed across two studies: Protocol A: escalating (50–75–90 J) defibrillation waveform with higher voltage, shorter duration and equal phase durations. Protocol B; non-escalating (50–50–50 J) defibrillation waveform with lower voltage, longer duration and unequal phase durations.

Experiment 1: Isolated shock damage was assessed following shocks to 12 anesthetized pigs. Animals were randomized into two groups, receiving three shocks from Protocol A (50–75–90 J) or B (50–50–50 J). Cardiac function, cardiac troponin I (cTnI), creatine phosphokinase (CPK) and histopathology were analyzed. Experiment 2: Defibrillation safety and efficacy were assessed through shock success, ROSC, ST-segment deviation and contractility following 16 randomized shocks from protocol A or B delivered to 10 anesthetized pigs in VF.

Results

Experiment 1: No clinically meaningful difference in cTnI, CPK, ST-segment deviation, ejection fraction or histopathological damage was observed following defibrillation with either protocol. No difference was observed between protocols at any timepoint. Experiment 2: all defibrillation types demonstrated shock success and ROSC ≥ 97.5%. Post-ROSC contractility was similar between protocols.

Conclusions

There is no evidence that administration of clinically relevant shock sequences, without experimental confounders, result in significant myocardial damage in this model of pediatric resuscitation. Typical variations in AED pediatric mode settings do not affect defibrillation safety and efficacy.

A framework of current based defibrillation improves defibrillation efficacy of biphasic truncated exponential waveform in rabbits

Defibrillation is accomplished by the passage of sufficient current through the heart to terminate ventricular fibrillation (VF). Although current-based defibrillation has been shown to be superior to energy-based defibrillation with monophasic waveforms, defibrillators with biphasic waveforms still use energy as a therapeutic dosage. In the present study, we propose a novel framework of current-based, biphasic defibrillation grounded in transthoracic impedance (TTI) measurements: adjusting the charging voltage to deliver the desired current based on the energy setting and measured pre-shock TTI; and adjusting the pulse duration to deliver the desired energy based on the output current and intra-shock TTI. The defibrillation efficacy of current-based defibrillation was compared with that of energy-based defibrillation in a simulated high impedance rabbit model of VF. Cardiac arrest was induced by pacing the right ventricle for 60 s in 24 New Zealand rabbits (10 males). A defibrillatory shock was applied with one of the two defibrillators after 90 s of VF. The defibrillation thresholds (DFTs) at different pathway impedances were determined utilizing a 5-step up-and-down protocol. The procedure was repeated after an interval of 5 min. A total of 30 fibrillation events and defibrillation attempts were investigated for each animal. The pulse duration was significantly shorter, and the waveform tilt was much lower for the current-based defibrillator. Compared with energy-based defibrillation, the energy, peak voltage, and peak current DFT were markedly lower when the pathway impedance was > 120 Ω, but there were no differences in DFT values when the pathway impedance was between 80 and 120 Ω for current-based defibrillation. Additionally, peak voltage and the peak current DFT were significantly lower for current-based defibrillation when the pathway impedance was < 80 Ω. In sum, a framework of adjusting the charging voltage and shock duration to deliver constant energy for low impedance and constant current for high impedance via pre-shock and intra-shock impedance measurements, greatly improved the defibrillation efficacy of high impedance by lowering the energy DFT.

Cardioprotective effect of nicorandil against myocardial injury following cardiac arrest in swine

INTRODUCTION

Nicorandil, a vasodilatory drug used to treat angina, was reported to protect against myocardial ischemia-reperfusion injury in various animal models. However, its cardioprotective action following cardiac arrest is unknown. We examined the cardioprotective effects of nicorandil in a porcine model of cardiac arrest and resuscitation.

METHODS

Ventricular fibrillation was induced electrically for 4min in anesthetized domestic swine, followed by cardiopulmonary resuscitation. Sixteen successfully resuscitated animals were randomized to saline control (n=8) or nicorandil (n=8) groups. Nicorandil (150μg/kg) was administered by central intravenous injection at onset of restoration of spontaneous circulation (ROSC), followed by 3μg/kg/min infusion until reperfusion end. Sham-operated animals received surgery only (n=4). Hemodynamic parameters were monitored continuously. Blood samples were taken at baseline, 5, 30, 180, and 360min after ROSC. Left ventricular ejection fraction was assessed by echocardiography at baseline and 6h after ROSC. The animals were euthanized 6h after ROSC, and the cardiac tissue was removed for analysis.

RESULTS

6 h after ROSC, nicorandil had significantly improved all hemodynamic variables (all P<0.05) except the maximum rate of left ventricular pressure decline and heart rate (P>0.05) compared with the control group. Control animals showed elevated cardiac troponin I and lactate levels compared with sham animals, which were significantly decreased following nicorandil treatment (P<0.05). In the saline control group, the adenosine triphosphate (ATP) content was largely reduced but subsequently rescued by nicorandil (P<0.05). Histopathologic injury was reduced with nicorandil treatment. Nicorandil reduced cardiomyocyte apoptosis as evidenced by reduced terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive cells, decreased Bax and caspase-3 expression, and increased Bcl-2 expression in the myocardium (all P<0.05).

CONCLUSION

Nicorandil exhibited cardioprotective effects on myocardial injury following cardiac arrest via improvement in post-resuscitation myocardial dysfunction and energy metabolism, reduction in myocardial histopathologic injury, and antiapoptotic effects.

The effects of second and third phase duration on defibrillation efficacy of triphasic rectangle waveforms

BACKGROUND

Biphasic waveforms are superior to monophasic waveforms for the termination of ventricular fibrillation (VF). However, whether triphasic waveforms are more effective than biphasic ones is still controversial. In the present study, we investigated the effects of second and third phase duration of triphasic rectangle waveform on defibrillation efficacy in a rabbit model of VF.

METHODS

VF was electrically induced and untreated for 30s in 20 New Zealand rabbits. A defibrillatory shock was applied with one of the 7 waveforms: 6 triphasic rectangle waveforms and a biphasic rectangle waveform. The triphasic waveforms had identical first duration but with different second and third phase durations. A 5 step up-and-down protocol was utilized for determining the defibrillation threshold (DFT). After a 5min interval, the procedure was repeated. A total of 35 cardiac arrest events and defibrillations were investigated for each animal.

RESULTS

Two triphasic waveforms with identical first and second phase duration but shorter third phase duration had significantly lower DFT energy than biphasic waveform (0.57±0.18J vs. 0.80±0.28J, p=0.001; 0.60±0.18J vs. 0.80±0.28J, p=0.003). However, no statistical difference in DFT energy was observed between the two triaphsic waveforms that had identical phase duration but different voltages (0.57±0.18J vs. 0.60±0.18J, p=0.638).

CONCLUSIONS

Phase durations played a main role on defibrillation success for triphasic rectangle waveforms. The optimal triphasic rectangle waveforms that composed of identical second and first phase durations but with shorter third pulse were superior to biphasic rectangle waveform for ventricular defibrillation.

A Grouped Up-and-Down Method Used for Efficacy Comparison Between Two Different Defibrillation Waveforms

Electrical defibrillation, which consists of delivering a therapeutic dose of the electrical current to the fibrillating heart with the aid of a defibrillator, is still the only effective way to treat life-threatening ventricular fibrillation (VF). However, the efficacy of electrical therapy for terminating VF is highly dependent on the waveform applied. When new defibrillation waveforms or techniques are developed, their efficacy needs to be accurately evaluated and compared to those in use. A common method for the comparison of defibrillation efficacy is to estimate and compare the individual defibrillation threshold (DFT) by constructing dose response curves or using an up-and-down method. Since DFT is calculated by repetitive and sequential shocks, there will be variability for each measurement and for each individual. This creates a considerable uncertainty for paired comparison. In this paper, a novel grouped up-and-down method is developed for the comparison of defibrillation efficacy between two different defibrillation waveforms or techniques. The efficacy of two commonly used biphasic defibrillation waveforms was compared in a porcine model of cardiac arrest using the developed method. Experimental results demonstrate that the proposed method is more sensitive for efficacy comparison and requires less defibrillation attempts compared with traditional DFT methods.

Average current is better than peak current as therapeutic dosage for biphasic waveforms in a ventricular fibrillation pig model of cardiac arrest

OBJECTIVE

Defibrillation current has been shown to be a clinically more relevant dosing unit than energy. However, the effects of average and peak current in determining shock outcome are still undetermined. The aim of this study was to investigate the relationship between average current, peak current and defibrillation success when different biphasic waveforms were employed.

METHODS

Ventricular fibrillation (VF) was electrically induced in 22 domestic male pigs. Animals were then randomized to receive defibrillation using one of two different biphasic waveforms. A grouped up-and-down defibrillation threshold-testing protocol was used to maintain the average success rate of 50% in the neighborhood. In 14 animals (Study A), defibrillations were accomplished with either biphasic truncated exponential (BTE) or rectilinear biphasic waveforms. In eight animals (Study B), shocks were delivered using two BTE waveforms that had identical peak current but different waveform durations.

RESULTS

Both average and peak currents were associated with defibrillation success when BTE and rectilinear waveforms were investigated. However, when pathway impedance was less than 90Ω for the BTE waveform, bivariate correlation coefficient was 0.36 (p=0.001) for the average current, but only 0.21 (p=0.06) for the peak current in Study A. In Study B, a high defibrillation success (67.9% vs. 38.8%, p<0.001) was observed when the waveform delivered more average current (14.9±2.1A vs. 13.5±1.7A, p<0.001) while keeping the peak current unchanged.

CONCLUSION

In this porcine model of VF, average current was better than peak current to be an adequate parameter to describe the therapeutic dosage when biphasic defibrillation waveforms were used. The institutional protocol number: P0805.

Electrical features of eighteen automated external defibrillators: a systematic evaluation

AIM

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

METHOD

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

RESULTS

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

CONCLUSIONS

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

Current is better than energy as predictor of success for biphasic defibrillatory shocks in a porcine model of ventricular fibrillation

OBJECTIVE

The evidence that monophasic defibrillation success is mainly determined by current is secure. However, modern defibrillators use biphasic waveforms. The aim of this study was to compare energy, peak voltage and peak current in predicting biphasic shock success in a porcine model of ventricular fibrillation (VF) where the impedance varies within a wide of ranges.

METHODS

In 14 domestic male pigs weighing between 27 and 38 kg, VF was electrically induced and untreated for 15 s. Animals were randomized to receive defibrillation attempts from one of two defibrillators with different impedance compensation methods. A grouped up-and-down defibrillation threshold testing protocol was used to maintain the average success rate in the neighborhood of 50%. After a recovery interval of 5 min, the testing sequence was repeated for a total of 60 test shocks for each animal.

RESULTS

A high defibrillation success was observed when high peak current was delivered. The area under ROC curve for predicting shock success was 0.681 for peak current, 0.585 for peak voltage and 0.562 for energy. The odds ratio revealed that peak current was a better predictor (OR=1.321, p<0.001) for defibrillation outcome compared with energy (OR=0.979, p<0.001) and peak voltage (OR=1.000, p=0.69) when multivariable logistic regression was conducted.

CONCLUSION

In this porcine model of VF within a wide range of transthoracic impedance, peak current was a better indicator for shock success than the currently used energy for biphasic defibrillatory shocks. This finding may encourage design of new current-based biphasic defibrillators.