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.     

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.     

Clinical experience with a low-energy pulsed biphasic waveform in out-of-hospital cardiac arrest

The efficiency of a pulsed biphasic waveform (PBW) was compared with that of biphasic truncated exponential (BTE) waveforms. First defibrillation shock outcome was studied in a population of 104 out-of-hospital cardiac arrest patients in ventricular fibrillation as the presenting rhythm. The call to first shock time was 8.2+/-5.4 min. At 5s post-shock, defibrillation efficiency was 90%. The arrest was witnessed in only 50% of the patients and only 5% received bystander CPR. Despite these limitations 38% of the patients achieved restoration of a spontaneous circulation at departure from scene and 9.8% were discharged from the hospital. These observations demonstrate a rate of first shock success in termination of ventricular fibrillation comparable to that reported with biphasic truncated exponential waveforms in out-of-hospital cardiac arrest.     

胺碘酮原液和稀释液对心室颤动转复作用及血流动力学的影响

目的 通过猪心室颤动(VF)模型,观察胺碘酮原液、稀释液以及单纯标准CPR对心肺复苏效果的影响.方法 21头北京长白猪,应用程控刺激仪诱导VF,VF 3 min后,将动物随机(随机数字法)分为3组.①单纯CPR组:只进行单纯标准CPR;②胺碘酮原液组:予胺碘酮原液5 mg/kg快速(＜3 s)静推,生理盐水20 mL冲管,观察30 s后开始CPR;③胺碘酮稀释液组:予胺碘酮5 mg/mg溶于20 mL生理盐水用30 s缓慢静推,20 mL生理盐水冲管,观察30 s后开始CPR.VF 5 min若猪未恢复自主循环(ROSC),给予电击除颤,并再次给予CPR,依此类推如15 min后猪仍未ROSC则宣布猪死亡.结果 CPR组及胺碘酮原液组复苏成功率高于胺碘酮稀释液组[85.7%vs.71.4%vs.42.9%],但差异均无统计学意义(P＞0.05).标准CPR组除颤能量(450±150)J高于胺碘酮原液组(200±77)J(P=0.009)及稀释液组(330±125)J,P=0.170.标准CPR组除颤次数(3±1)多于胺碘酮原液组(1.3±0.5),P＜0.05.ROSC 10 min时胺碘酮原液组的平均动脉压(MAP)和冠脉灌注压(CPP)明显低于稀释液组和CPR组(P＜0.05),而ROSC 0.5 h以后胺碘酮原液组和稀释液组之间MAP和CPP差异无统计学意义(P＞0.05).结论 心肺复苏时应用胺碘酮原液可以减少除颤次数和能量;较标准CPR和快速推注胺碘酮原液,胺碘酮稀释液缓慢推注有增加死亡率的可能.     

长时程室颤先行心肺复苏对复苏效果的影响及机制研究

目的 比较7 min室颤先行心肺复苏2 min后除颤与直接除颤的复苏效果,并探讨其机制.方法 建立猪闭胸电诱发室颤模型,CPR First组优先心肺复苏2 min后连续三次除颤,Shock First组直接予连续三次除颤,观察冠脉灌注压、室颤波频率和振幅变化,计算除颤成功率和自主循环恢复率.结果 CPR First组先行心肺复苏2 min后可提高初次除颤前的冠脉灌注压、室颤波的频率和振幅, CPR First组比Shock First组有高的除颤成功率和自主循环恢复率(P＜0.05).结论 7 min室颤除颤前先行胸外按压和人工呼吸可明显提高复苏成功率,其机制与增加冠脉灌注,改善心脏能量储备,提高室颤波的频率和振幅有关.     

Energy doses for treatment of out-of-hospital pediatric ventricular fibrillation

AIM: To investigate the energy dose used to treat out-of-hospital pediatric ventricular fibrillation and the survival rates of these patients. METHODS: We reviewed three emergency medical systems (EMS) for their reports of patients under 1 month to 18 years who received shocks for ventricular fibrillation to determine the energy of each shock as well as other patient and care characteristics. Each patient's weight was estimated at the age-appropriate 50th and 95th percentiles. Patients were then grouped as receiving recommended energy doses (2 to < or = 4 J/kg), moderately high energy doses (> 4-6 J/kg), and high energy doses (> 6 J/kg). RESULTS: Of 57 patients identified, 54% were male, with a mean age of 11 years, range 2 months to 17 years. Ventricular fibrillation was the initial rhythm in 80% (43/54) of patients. The mean number of shocks delivered was 3, with < or = 2 shocks delivered to 28 (49%) and > or = 5 shocks delivered to 10 (18%) patients. When evaluating all 185 shocks using the 50th percentile estimated weight, 45 (24%) shocks were at recommended doses, 56 (30%) were at moderately high energy doses, and 84 (45%) were high energy doses. Elevated energy dose was associated with an increasing number of shocks and lack of bystander CPR (p < .05). Nineteen (33%) patients survived to hospital discharge having received total doses up to 73 J/kg. Energy dose was not related to survival. CONCLUSION: In this observational, multicenter out of hospital experience, children received a wide range of defibrillation doses, often exceeding recommended doses and equivalent to adult energy levels. Survival occurred at low and very high energy doses.     

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 90 Ω 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 ± 2.1 A vs. 13.5 ± 1.7 A, 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.     

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.     

不同能量双相方波体外除颤的实验研究

目的 比较低能量和高能量双相方波（BSW）体外除颤的效能和电击引起的心肌损伤程度,以探讨RBW体外除颤的更理想的能量水平。方法 建立成年猪闭胸电诱发室颤模型,将18只猪随机分为三组,每组6只,用BSW50-50-50J、30-50—75J和120-150—200J三种能量方案分别体外除颤治疗持续3min无干预室颤。结果 30J不能体外除颤成功,50J和120J的首次成功比例为5／6,三组总的除颤成功率都为100％,所有动物除颤后立即恢复自主循环,存活超过24h,低能量较高能量除颤后的心电图损伤性ST-T改变较少,复苏后心功能下降,但血流动力学参数组间比较差异无统计学意义。结论 在本研究中,30J不能体外除颤成功,BSW的低能量50J和120J有相似的体外除颤效能,BSW比较理想的首次体外除颤能量为50J。     

Spontaneous gasping decreases intracranial pressure and improves cerebral perfusion in a pig model of ventricular fibrillation

INTRODUCTION: Spontaneous gasping is associated with increased survival in animal models of cardiac arrest and in observational studies of humans. The potential beneficial effect of gasping on cerebral perfusion may underlie the observed survival benefit, but mechanisms remain unknown. HYPOTHESIS: We hypothesized that spontaneous gasping in a pig model of ventricular fibrillation (VF) decreases intracranial pressure (ICP) and increases cerebral perfusion pressure (CePP) during VF in a pig model. METHODS: The 13 female farm pigs, weighing between 16 and 33 kg, were anesthetized with propofol and intubated, and then had VF induced for 8 min without intervention. Intrathoracic pressure (ITP), aortic pressure (AoP), and ICP were measured continuously. CePP and ITP were recorded simultaneously during three maximal gasps and correlated with gasping by Spearman rank correlation. RESULTS: Gasping during VF occurred in 13/13 pigs and followed a crescendo-decrescendo pattern. Each gasp was associated with a biphasic AoP (initial fall, then rise) and ICP (initial rise, then fall) morphology. Time to first gasp (r(2)=0.06), time to maximal gasp (r(2)=0.02), duration of gasping (r(2)=0.11) and frequency of gasping (r(2)=0.32) did not correlate significantly with CePP during gasping while depth of gasping exhibited a weak but significant correlation with CePP (r(2)=0.35, p=0.05). Maximal gasping occurred at 202+/-34 s from onset of VF and resulted in an average decrease in ICP from 27.4+/-5.8 to 20+/-6.7 mmHg, p<0.01 along with an increase in CePP from -0.05+/-10.9 to 11.5+/-12.6 mmHg, p<0.05. CONCLUSIONS: Spontaneous gasping during cardiac arrest decreased intra-cranial pressure and increased cerebral perfusion pressure significantly. These results may help explain why gasping is associated with improved cardiac arrest survival rates. Based upon this new understanding of the physiology of gasping, we speculate that investigation of devices that can enhance the physiological effects of gasping on intracranial pressure and cerebral perfusion should be prioritized.     

Predictors of resuscitation outcome in a swine model of VF cardiac arrest: A comparison of VF duration,presence of acute myocardial infarction and VF waveform

Introduction

Factors that affect resuscitation to a perfusing rhythm (ROSC) following ventricular fibrillation (VF) include untreated VF duration, acute myocardial infarction (AMI), and possibly factors reflected in the VF waveform. We hypothesized that resuscitation of VF to ROSC within 3 min is predicted by the VF waveform, independent of untreated VF duration or presence of acute MI.

Methods

AMI was induced by the occlusion of the left anterior descending coronary artery. VF was induced in normal (N = 30) and AMI swine (N = 30). Animals were resuscitated after untreated VF of brief (2 min) or prolonged (8 min) duration. VF waveform was analyzed before the first shock to compute the amplitude-spectral area (AMSA) and slope.

Results

Unadjusted predictors of ROSC within 3 min included untreated VF duration (8 min vs 2 min; OR 0.11, 95%CI 0.02–0.54), AMI (AMI vs normal; OR 0.11, 95%CI 0.02–0.54), AMSA (highest to lowest tertile; OR 15.5, 95%CI 1.7–140), and slope (highest to lowest tertile; OR 12.7, 95%CI 1.4–114). On multivariate regression, untreated VF duration (P = 0.011) and AMI (P = 0.003) predicted ROSC within 3 min. Among secondary outcome variables, favorable neurological status at 24 h was only predicted by VF duration (OR 0.22, 95% CI 0.05–0.92).

Conclusions

In this swine model of VF, untreated VF duration and AMI were independent predictors of ROSC following VF cardiac arrest. AMSA and slope predicted ROSC when VF duration or the presence of AMI were unknown. Importantly, the initial treatment of choice for short duration VF is defibrillation regardless of VF waveform.     

External exponential biphasic versus monophasic shock waveform: efficacy in ventricular fibrillation of longer duration

Ventricular fibrillation (VF) duration may be a factor in determining the defibrillation energy for successful defibrillation. Exponential biphasic waveforms have been shown to defibrillate with less energy than do monophasic waveforms when used for external defibrillation. However, it is unknown whether this advantage persists with longer VF duration. We tested the hypothesis that exponential biphasic waveforms have lower defibrillation energy as compared to exponential monophasic waveforms even with longer VF duration up to 1 minute. In a swine model of external defibrillation (n = 12, 35 +/- 6 kg), we determined the stored energy at 50% defibrillation success (E50) after both 10 seconds and 1 minute of VF duration. A single exponential monophasic (M) and two exponential biphasic (B1 and B2) waveforms were tested with the following characteristics: M (60 microF, 70% tilt), B1 (60/60 microF, 70% tilt/3 ms pulse width), and B2 (60/20 microF, 70% tilt/3 ms pulse width) where the ratio of the phase 2 leading edge voltage to that of phase 1 was 0.5 for B1 and 1.0 for B2. E50 was measured by a Bayesian technique with a total often defibrillation shocks in each waveform and VF duration randomly. The E50 (J) for M, B1, and B2 were 131 +/- 41, 57 +/- 18,* and 60 +/- 26* with 10 seconds of VF duration, respectively, and 114 +/- 62, 77 +/- 45,* and 72 +/- 53* with 1 minute of VF duration, respectively (*P < 0.05 vs M). There was no significant difference in the E50 between 10 seconds and 1 minute of VF durations for each waveform. We conclude that (1) the E50 does not significantly increase with lengthening VF durations up to 1 minute regardless of the shock waveform, and (2) external exponential biphasic shocks are more effective than monophasic waveforms even with longer VF durations.     

Comparison of defibrillation efficacy between two pads placements in a pediatric porcine model of cardiac arrest

Objective

The placement of defibrillation pads at ideal anatomical sites is one of the major determinants of transthoracic defibrillation success. However, the optimal pads position for ventricular defibrillation is still undetermined. In the present study, we compared the effects of two different pads positions on defibrillation success rate in a pediatric porcine model of cardiac arrest.

Methods

Eight domestic male pigs weighing 12–15 kg were randomized to receive shocks using either the anterior–posterior (AP) or the anterior–lateral (AL) position with pediatric pads. Ventricular fibrillation (VF) was electrically induced and untreated for 30 s. A sequence of randomized biphasic electrical shocks ranging from 10 to 100 J was attempted. If the defibrillation failed to terminate VF, a 100 J rescuer shock was then delivered. After a recovery interval of 5 min, the sequence was repeated for a total of approximately 30 test shocks were attempted for each animal. The dose response curves were constructed and the defibrillation thresholds were compared between groups.

Results

The aggregated success rate was 65.6% for AP placement and 43.0% for AL one (p = 0.0005) when shock energy was between 10 and 70 J. A significantly lower 50% defibrillation threshold was obtained for AP pads placement compared with traditional AL pads position (2.1 ± 0.4 J/kg vs. 3.6 ± 0.9 J/kg, p = 0.041).

Conclusion

In this pediatric porcine model of cardiac arrest, the anterior–posterior placement of pediatric pads yielded a higher success rate by lowering defibrillation threshold compared to the anterior–lateral position.     

Coagulopathy during cardiac arrest and resuscitation in a swine model of electrically induced ventricular fibrillation

Aims

Coagulopathy is often present after resuscitation from cardiac arrest but plays an undefined role in the post cardiac arrest syndrome. The aim of this study was to characterize coagulation changes during cardiac arrest and post-resuscitation care in order to direct further focused study.

Methods

Ventricular fibrillation (VF) was induced electrically in immature male swine, followed by normothermic American Heart Association Advanced Cardiac Life Support and a uniform post-resuscitation goal-directed resuscitation protocol. PT, aPTT, fibrinogen, Thrombelastography (TEG), platelet contractile force (PCF), clot elastic modulus (CEM), and collagen-induced platelet aggregation were compared at baseline, at 8 min of VF, during the 3rd round of chest compressions (CPR), and at 15, 90, 180, and 360 min after return of circulation using repeated measures ANOVA.

Results

8/18 (44%) animals were resuscitated after 10.9 ± 0.9 min of VF and 7.6 ± 3.4 min of CPR. TEG revealed a significant impairment in clot strength (MA) and clot formation kinetics (K, alpha angle) arising during CPR, followed by a brief prolongation of clot onset times (R) after return of circulation. Both PCF and CEM fell significantly during CPR (PCF by 50%, CEM by 47% of baseline) and platelet aggregation was significantly decreased during CPR. Coagulation changes were partially recovered by 3 h of post-resuscitation care.

Conclusion

Whole blood coagulation was rapidly impaired during CPR after electrically induced VF in this swine model by impaired platelet aggregation/contractile function and clotting kinetics. Further platelet-specific study is indicated.     

A phased approach to cardiac arrest resuscitation involving ventricular fibrillation and pulseless ventricular tachycardia

With the release of the 2010 American Heart Association (AHA) Guidelines for cardiopulmonary resuscitation and emergency cardiac care, evidence regarding management of out-of-hospital cardiac arrest suggests a more fundamental approach. To aid in understanding and learning, this article proposes a method that optimizes the timing and delivery of evidence-proven therapies with a 3-phase approach for out-of-hospital resuscitation from ventricular fibrillation and pulseless ventricular tachycardia. Although this model is not a new concept, it is largely based on the 2010 AHA Guidelines, enhancing the philosophy of the "CAB" concept (Chest compressions/Airway management/Breathing rescue).     

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

Aim of studyImpedance 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.MethodsIn 10 domestic male pigs weighing between 17 and 28 kg, ventricular fibrillation was electrically induced and untreated for 15 s. 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.ResultsThe 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).ConclusionFor transthoracic impedances greater than average, the current-based compensation technique was more effective than the duration-based compensation technique.     

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.     

Comparison of the efficacy of nifekalant and amiodarone in a porcine model of cardiac arrest

Objective

To compare the efficacy of nifekalant and amiodarone in the treatment of cardiac arrest in a porcine model.

Methods

After 4 min of untreated ventricular fibrillation, animals were randomly treated with nifekalant (2 mg kg⁻¹), amiodarone (5 mg kg⁻¹) or saline placebo (n = 12 pigs per group). Precordial compression and ventilation were initiated after drug administration and defibrillation was attempted 2 min later. Hemodynamics were continuously measured for 6 h after successful resuscitation.

Results

Compared with saline, nifekalant and amiodarone equally decreased the number of electric shocks, defibrillation energy, epinephrine dose, and duration of cardiopulmonary resuscitation required for successful resuscitation (P < 0.01). The incidence of restoration of spontaneous circulation (ROSC) and the 24-h survival rate were higher in both antiarrhythmic drug groups (P < 0.05) vs. the saline group. Furthermore, post-resuscitation myocardial dysfunction at 4-6 h after successful resuscitation was improved in animals given antiarrhythmic drugs as compared with the saline group (P < 0.05). There were no differences between nifekalant and amiodarone for any of these parameters.

Conclusion

The effect of nifekalant was similar to that of amiodarone for improving defibrillation efficacy and for the treatment of cardiac arrest. Administration of either nifekalant or amiodarone before defibrillation increased the ROSC and 24-h survival rates and improved post-resuscitation cardiac function in this porcine model.     

Effect of cardiopulmonary resuscitation on restoration of myocardial ATP in prolonged ventricular fibrillation

Background

There has been controversy over whether a short period of cardiopulmonary resuscitation (CPR) prior to defibrillation improves survival in patients who experienced a sudden cardiac arrest. However, there have been no reports about whether CPR restores the myocardial energy source during prolonged ventricular fibrillation (VF). The aim of this study is to investigate the effect of CPR in restoring myocardial high energy phosphates during prolonged VF.

Methods and results

Seventy-two adult male Sprague-Dawley rats were used in this study. Baseline adenosine triphosphate (ATP) and adenosine diphosphate (ADP) prior to induction of VF were measured in nine rats, the No-VF group. Sixty-three rats were subjected to 4 min of untreated VF. Animals were then randomized into two groups: No-CPR (n = 37) and CPR (n = 26). In the No-CPR group, ATPs and ADPs were measured at 4 min (No-CPR4), 6 min (No-CPR6), 8 min (No-CPR8) or 10 min (No-CPR10) after the induction of VF. The CPR group received 2 min (CPR2), 4 min (CPR4) or 6 min (CPR6) of mechanical chest compressions before ATP was measured.Myocardial ATP (nmol/mg protein) was decreased as VF duration was prolonged (No-VF: 5.49 ± 1.71, No-CPR4: 4.27 ± 1.58, No-CPR6: 4.13 ± 1.31, No-CPR8: 3.77 ± 1.42, No-CPR10: 3.52 ± 0.90, p < 0.05 between each of No-CPRs vs. No-VF). Two minutes of CPR restored myocardial ATP to the level of No-VF group (5.27 ± 1.67 nmol/mg protein in CPR2, p > 0.05 vs. No-VF group). However, myocardial ATP (nmol/mg protein) decreased if the duration of CPR was longer than 2 min (CPR4: 3.77 ± 1.05, CPR6: 3.49 ± 1.08, p < 0.05 between CPR4 and CPR6 vs. No-VF).

Conclusions

CPR for 2 min helps to maintain myocardial ATP after prolonged VF.