Cardiopulmonary resuscitation-some physiological considerations

The Right Ventricle Is Dilated During Resuscitation From Cardiac Arrest Caused by Hypovolemia: A Porcine Ultrasound Study

OBJECTIVES

Dilation of the right ventricle during cardiac arrest and resuscitation may be inherent to cardiac arrest rather than being associated with certain causes of arrest such as pulmonary embolism. This study aimed to compare right ventricle diameter during resuscitation from cardiac arrest caused by hypovolemia, hyperkalemia, or primary arrhythmia (i.e., ventricular fibrillation).

DESIGN

Thirty pigs were anesthetized and then randomized to cardiac arrest induced by three diffrent methods. Seven minutes of untreated arrest was followed by resuscitation. Cardiac ultrasonographic images were obtained during induction of cardiac arrest, untreated cardiac arrest, and resuscitation. The right ventricle diameter was measured. Primary endpoint was the right ventricular diameter at the third rhythm analysis.

SETTING

University hospital animal laboratory.

SUBJECTS

Female crossbred Landrace/Yorkshire/Duroc pigs (27-32 kg).

INTERVENTIONS

Pigs were randomly assigned to cardiac arrest caused by either hypovolemia, hyperkalemia, or primary arrhythmia.

MEASUREMENTS AND MAIN RESULTS

At the third rhythm analysis during resuscitation, the right ventricle diameter was 32 mm (95% CI, 29-35) in the hypovolemia group, 29 mm (95% CI, 26-32) in the hyperkalemia group, and 25 mm (95% CI, 22-28) in the primary arrhythmia group. This was larger than baseline for all groups (p = 0.03). When comparing groups at the third rhythm analysis, the right ventricle was larger for hypovolemia than for primary arrhythmia (p < 0.001).

CONCLUSIONS

The right ventricle was dilated during resuscitation from cardiac arrest caused by hypovolemia, hyperkalemia, and primary arrhythmia. These findings indicate that right ventricle dilation may be inherent to cardiac arrest, rather than being associated with certain causes of arrest. This contradicts a widespread clinical assumption that in hypovolemic cardiac arrest, the ventricles are collapsed rather than dilated.

The combined use of mechanical CPR and a carry sheet to maintain quality resuscitation in out-of-hospital cardiac arrest patients during extrication and transport

BACKGROUND

Quality of manual cardiopulmonary resuscitation (CPR) during extrication and transport of out-of-hospital cardiac arrest victims is known to be poor. Performing manual CPR during ambulance transport poses significant risk to the attending emergency medical services crew. We sought to use pre-hospital video recording to objectively analyse the impact of introducing mechanical CPR with an extrication sheet (Autopulse, Zoll) to an advanced, second-tier cardiac arrest response team.

METHODS

The study was conducted prospectively using defibrillator downloads and analysis of pre-hospital video recording to measure the quality of CPR during extrication from scene and ambulance transport of the OHCA patient. Adult patients with non-traumatic OHCA were included. The interruption to manual CPR to during extrication and to deploy the mechanical CPR device was analysed.

RESULTS

In the manual CPR group, 53 OHCA cases were analysed for quality of CPR during extrication. The median time that chest compression was interrupted to allow the patient to be carried from scene to the ambulance was 270 s (IQR 201-387 s). 119 mechanical CPR cases were analysed. The median time interruption from last manual compression to first Autopulse compression was 39 s (IQR 29-47 s). The range from last manual compression to first Autopulse compression was 14-118 s.

CONCLUSION

Mechanical CPR used in combination with an extrication sheet can be effectively used to improve the quality of resuscitation during extrication and ambulance transport of the refractory OHCA patient. The time interval to deploy the mechanical CPR device can be shortened with regular simulation training.

The role of Levosimendan in cardiopulmonary resuscitation

Although initial resuscitation from cardiac arrest (CA) has increased over the past years, long term survival rates remain dismal. Epinephrine is the vasopressor of choice in the treatment of CA. However, its efficacy has been questioned, as it has no apparent benefits for long-term survival or favorable neurologic outcome. Levosimendan is an inodilator with cardioprotective and neuroprotective effects. Several studies suggest that it is associated with increased rates of return of spontaneous circulation as well as improved post-resuscitation myocardial function and neurological outcome. The purpose of this article is to review the properties of Levosimendan during cardiopulmonary resuscitation (CPR) and also to summarize existing evidence regarding the use of Levosimendan in the treatment of CA.

Conceptual models of coronary perfusion pressure and their relationship to defibrillation success in a porcine model of prolonged out-of-hospital cardiac arrest

INTRODUCTION

The amount of myocardial perfusion required for successful defibrillation after cardiac arrest is unknown. Coronary perfusion pressure (CPP) is a surrogate for myocardial perfusion. One limited clinical study identifies a threshold of 15 mmHg required for return of spontaneous circulation (ROSC). Our exploration of threshold and dose models of CPP during the initial bout of CPR indicates higher levels than previously demonstrated are required. CPP required for shock success throughout on-going resuscitation is unknown and other conceptual models of CPP have not been explored.

HYPOTHESIS

An array of conceptual models of CPP is associated with and predicts defibrillation success throughout resuscitation.

METHODS

Data from 6 porcine cardiac arrest studies were pooled. Mean and area under the curve (AUC) CPP were derived for 30-s epochs. Five conceptual models of CPP were analyzed: threshold, delta, cumulative delta, dose, and cumulative dose. Comparative statistics were performed with one-way ANOVA and two-tailed t-test. Regression models assessed CPP trends and prediction of ROSC.

RESULTS

For 316 defibrillation attempts in 124 animals, those resulting in ROSC (n=75) had significantly higher threshold, delta, cumulative delta, dose, and cumulative dose CPP than those without. All conceptual models except delta CPP had significantly different values across successive defibrillation attempts and all five models were significant predictors of ROSC, along with experimental design.

CONCLUSIONS

Threshold, delta, cumulative delta, dose, and cumulative dose CPP predict individual defibrillation success throughout resuscitation.

Resuscitation feedback and targeted education improves quality of pre-hospital resuscitation in Scotland

BACKGROUND

Out-of-hospital cardiac arrest (OHCA) is a leading cause of mortality and serious neurological morbidity in Europe. Recent studies have demonstrated the adverse physiological consequences of poor resuscitation technique and have shown that quality of cardiopulmonary resuscitation (CPR) is a critical determinant of outcome from OHCA. Telemetry of the defibrillator transthoracic impedance (TTI) trace can objectively measure quality of pre-hospital resuscitation. This study aims to analyse the impact of targeted resuscitation feedback and training on quality of pre-hospital resuscitation.

METHODS

Prospective, single centre, cohort study over 13 months (1st December 2009-31st December 2010). Baseline pre-hospital resuscitation data was gathered over a 3-month period. Modems (n=40) were fitted to defibrillators on ambulance vehicles. Following a resuscitation attempt, the event was sent via telemetry and the TTI trace analysed. Outcome measures were time spent performing chest compressions, compression rate, the interval required to deliver a defibrillator shock and use of automatic or manual cardiac rhythm analysis. Targeted resuscitation classes were introduced and all ambulance crews received feedback following a resuscitation attempt. Pre-hospital resuscitation quality pre and post intervention were compared.

RESULTS

111 resuscitation traces were analysed. Mean hands-on-chest time improved significantly following feedback and targeted resuscitation training (73.0% vs 79.3%, p=0.007). There was no significant change in compression rate during the study period. There was a significant reduction in median time-to-shock interval from 20.25s (IQR 15.50-25.50s) to 13.45 s (IQR 2.25-22.00 s) (p=0.006). Automatic rhythm recognition fell from 50% to 28.6% (p=0.03) following intervention.

CONCLUSION

Telemetry and analysis of the TTI trace following OHCA allows objective evaluation of the quality of pre-hospital resuscitation. Targeted resuscitation training and ambulance feedback improves the quality of pre-hospital resuscitation. Further studies are required to establish possible survival benefit from this technique.

Coronary perfusion pressure and return of spontaneous circulation after prolonged cardiac arrest

INTRODUCTION

The amount of myocardial perfusion required for successful defibrillation after prolonged cardiac arrest is not known. Coronary perfusion pressure (CPP) is a surrogate for myocardial perfusion. One limited clinical study reported that a threshold of 15 mmHg was necessary for return of spontaneous circulation (ROSC), and that CPP was predictive of ROSC. A distinction between threshold and dose of CPP has not been reported.

OBJECTIVE

To test the hypothesis that swine achieving ROSC will have higher preshock mean CPP and higher preshock area under the CPP curve (AUC) than swine not attaining ROSC.

METHODS

Data from four similar swine cardiac arrest studies were retrospectively pooled. Animals had undergone 8-11 minutes of untreated ventricular fibrillation, 2 minutes of mechanical cardiopulmonary resuscitation (CPR), administration of drugs, and 3 more minutes of CPR prior to the first shock. Mean CPP +/- standard error of the mean (SEM) was derived from the last 20 compressions of each 30-second epoch of CPR and compared between ROSC/no-ROSC groups by repeated-measures analysis of variance (RM-ANOVA). AUC for all compressions delivered over the 5 minutes was calculated by direct summation and compared by Kruskal-Wallis test. Prediction of ROSC was assessed by logistic regression.

RESULTS

Throughout the first 5 minutes of CPR (n = 80), mean CPP +/- SEM was consistently higher in animals with ROSC (n = 63) (maximum CPP 41.2 +/- 0.6 mmHg) than animals with no ROSC (maximum CPP 20.1 +/- 0.3 mmHg) (p = 0.0001). Animals with ROSC received more total reperfusion (43.9 +/- 17.6 mmHg x 10(2)) than animals without ROSC (21.4 +/- 13.7 mmHg x 10(2)) (p < 0.001). Two regression models identified CPP (odds ratio [OR] 1.11; 95% confidence interval [CI] 1.05, 1.18) and AUC (OR 1.10; 95% CI 1.05, 1.16) as predictors of ROSC. Experimental study also predicted ROSC in each model (OR 1.70; 95% CI 1.15, 2.50; and OR 1.59; 95% CI 1.12, 2.25, respectively).

CONCLUSION

Higher CPP threshold and dose are associated with and predictive of ROSC.

Nitroglycerin and epinephrine improve coronary perfusion pressure in a porcine model of ventricular fibrillation arrest: a pilot study

BACKGROUND

Cardiac arrest remains one of the leading causes of death worldwide. European Resuscitation Council Guidelines for Resuscitation 2005 recommend epinephrine for its treatment.

OBJECTIVES

To estimate whether the administration of a vasodilatator such as nitroglycerin in combination with epinephrine during cardiopulmonary resuscitation would improve resuscitation outcome in an established model of ventricular fibrillation.

DESIGN

Prospective, randomized, blinded, controlled study.

SETTING

Animal research laboratory. Ventricular fibrillation was induced in 20 Landrace/Large-White pigs. It remained untreated for 8 min before attempting resuscitation precordial compressions, mechanical ventilation, and electrical defibrillation. Animals were randomized into two groups, 10 animals each. Group A received saline as placebo (10 mL dilution, bolus) and epinephrine (0.02 mg/kg). Group B received nitroglycerin (50 microg/kg) and epinephrine (0.02 mg/kg) during cardiopulmonary resuscitation. Electrical defibrillation was attempted after 10 min of ventricular fibrillation.

RESULTS

Four animals in group A restored spontaneous circulation in comparison to eight in Group B. Coronary perfusion pressure (p < 0.0001) was significantly increased in Group B during cardiopulmonary resuscitation.

CONCLUSION

A vasodilatator, when administered in combination with a vasopressor such as epinephrine during cardiopulmonary resuscitation, increases coronary perfusion pressure.

Vasopressin and epinephrine in the treatment of cardiac arrest: an experimental study

BACKGROUND

Epinephrine remains the drug of choice for cardiopulmonary resuscitation. The aim of the present study is to assess whether the combination of vasopressin and epinephrine, given their different mechanisms of action, provides better results than epinephrine alone in cardiopulmonary resuscitation.

METHODS

Ventricular fibrillation was induced in 22 Landrace/Large-White piglets, which were left untreated for 8 minutes before attempted resuscitation with precordial compression, mechanical ventilation and electrical defibrillation. Animals were randomized into 2 groups during cardiopulmonary resuscitation: 11 animals who received saline as placebo (20 ml dilution, bolus) + epinephrine (0.02 mg/kg) (Epi group); and 11 animals who received vasopressin (0.4 IU/kg/20 ml dilution, bolus) + epinephrine (0.02 mg/kg) (Vaso-Epi group). Electrical defibrillation was attempted after 10 minutes of ventricular fibrillation.

RESULTS

Ten of 11 animals in the Vaso-Epi group restored spontaneous circulation in comparison to only 4 of 11 in the Epi group (p = 0.02). Aortic diastolic pressure, as well as, coronary perfusion pressure were significantly increased (p < 0.05) during cardiopulmonary resuscitation in the Vaso-Epi group.

CONCLUSION

The administration of vasopressin in combination with epinephrine during cardiopulmonary resuscitation results in a drastic improvement in the hemodynamic parameters necessary for the return of spontaneous circulation.

Levosimendan improves the initial outcome of cardiopulmonary resuscitation in a swine model of cardiac arrest

BACKGROUND

Cardiac arrest remains the leading cause of death in Western societies. Advanced Life Support guidelines propose epinephrine (adrenaline) for its treatment. The aim of this study was to assess whether a calcium sensitizer agent, such as levosimendan, administered in combination with epinephrine during cardiopulmonary resuscitation, would improve the initial resuscitation success.

METHODS

Ventricular fibrillation was induced in 20 Landrace/Large-White piglets, and left untreated for 8 min. Resuscitation was then attempted with precordial compressions, mechanical ventilation and electrical defibrillation. The animals were randomized into two groups (10 animals each): animals in Group A received saline as placebo (10 ml dilution, bolus) + epinephrine (0.02 mg/kg), and animals in Group B received levosimendan (0.012 mg/kg/10 ml dilution, bolus) + epinephrine (0.02 mg/kg) during cardiopulmonary resuscitation. Electrical defibrillation was attempted after 10 min of ventricular fibrillation.

RESULTS

Four animals in Group A showed restoration of spontaneous circulation and 10 in Group B (P = 0.011). The coronary perfusion pressure, saturation of peripheral oxygenation and brain regional oxygen saturation were significantly higher during cardiopulmonary resuscitation in Group B.

CONCLUSIONS

A calcium sensitizer agent, when administered during cardiopulmonary resuscitation, significantly improves initial resuscitation success and increases coronary perfusion pressure during cardiopulmonary resuscitation.

An observational study of bispectral index monitoring for out of hospital cardiac arrest

Cerebral resuscitation is the most important goal of advanced life support. Currently, there are no objective monitoring methods available to gauge the effectiveness of advanced life support on cerebral resuscitation. We assessed the utility of bispectral index (BIS) monitoring during cardiopulmonary resuscitation as a marker of cerebral resuscitation. Twenty one patients with out of hospital cardiac arrest had a BIS monitor applied during the resuscitation, in addition to standard advanced life support. The BIS monitor was also applied to a cadaver to assess the role of artefact. Illustrative data are presented, outlining the process of evaluation undertaken. A major component of the BIS tracing during external chest compressions appears to be due to movement artefact. Our pilot data indicate that with current technology, BIS monitoring is not a clinically reliable marker of the efficacy of external chest compressions.

Treatment of out-of-hospital cardiac arrest with LUCAS, a new device for automatic mechanical compression and active decompression resuscitation

Lund University Cardiopulmonary Assist System (LUCAS) is a new gas-driven CPR device providing automatic chest compression and active decompression. This is a report of the first 100 consecutive cases treated with LUCAS due to out-of-hospital cardiac arrest (58% asystole, 42% ventricular fibrillation (VF)). Safety aspects were also investigated and it was found that LUCAS can be used safely regarding noise levels and oxygen concentrations within the ambulance. A crash test (10G) showed no displacement of the device from the manikin. Of the 71 patients with witnessed cardiac arrest, 39% received bystander CPR. In those 28 patients where LUCAS-CPR was initiated more than 15 min after the ambulance alarm and in the 29 unwitnessed cases, none survived for 30 days. Of the 43 witnessed cases treated with LUCAS within 15 min, 24 had VF and 15 (63%) of these cases achieved a stable return of spontaneous circulation (ROSC) and 6 (25%) of them survived with a good neurological recovery after 30 days; 5 (26%) of the 19 patients with asystole achieved ROSC and 1 (5%) survived for over 30 days. One patient where ROSC could not be achieved was transported with on-going LUCAS-CPR to the catheter laboratory and after PCI for an occluded LAD a stable ROSC occurred, but the patient never regained consciousness and died 15 days later. To conclude, establishment of an adequate cerebral circulation as quickly as possible after cardiac arrest is mandatory for a good outcome. In this report patients with a witnessed cardiac arrest receiving LUCAS-CPR within 15 min from the ambulance call had a 30-day survival of 25% in VF and 5% in asystole, but if the interval was more than 15 min, there were no 30-day survivors.

Reducing no flow times during automated external defibrillation

There has recently been an increased attention focused on the importance of reducing time without blood flow from chest compressions (no flow time, NFT) during cardiopulmonary resuscitation (CPR). In this study we have analyzed and quantified the NFTs during external automatic defibrillation in 105 cardiac arrest patients. We found that for around half of the time (about 10 min), these patients were not perfused. We have proposed methods to reduce NFT in connection with analyses and shocks. The key factors were rhythm analysis during ongoing CPR, capacitor charging during analysis, 1 min of CPR immediately after a shock (with rhythm analysis during CPR at the end of the 1 min), and distinguishing between asystole and organized rhythm in analyses to skip pulse check if asystole. The potential reduction in NFT using these methods was calculated theoretically and we found a reduction in the total NFT of about 4.5 and 1 min, respectively, in the subgroups of patients having at least one shock and patients having received no shocks. In the present study, the median NFT ratio could theoretically be reduced from 51% to 34% or 49% to 39% depending on if the patient would have a shockable rhythm or not. By introducing the proposed methods into an AED, the NFT would be significantly reduced, hopefully increasing the survival.

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

STUDY OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Delaying shock for cardiopulmonary resuscitation: does it save lives?

PURPOSE OF REVIEW

Out-of-hospital cardiac arrest claims more than 450,000 lives annually in North America. Many communities have dedicated significant resources to provide rapid defibrillator response for patients in ventricular fibrillation. In spite of these efforts, mortality from out-of-hospital cardiac arrest has not improved significantly. Emerging evidence suggests some patients in ventricular fibrillation arrest may be harmed by immediate defibrillation.

RECENT FINDINGS

Recent laboratory studies have shown benefit in performing a period of chest compressions (cardiopulmonary resuscitation) prior to defibrillation in models with more than 4 minutes of induced ventricular fibrillation. During the initial 4 minutes the heart is more amenable to electrical defibrillation. Between 4-10 minutes, chest compressions create some coronary perfusion and fill the left ventricle to prepare the heart for electric shock. These findings, in conjunction with most emergency medical service response times reported to be 5-8 minutes, have prompted human investigation into a strategy of chest compression first. A recent randomized controlled trial reported a fivefold increase in survival for patients with more than 5 minutes of VF who received 3 minutes of chest compressions prior to defibrillation compared with those who had not.

SUMMARY

Current guidelines call for rapid defibrillation as the most important 'link' in the 'chain of survival'. For most ventricular fibrillation patients who have professional rescuers arrive after 5-8 minutes of ventricular fibrillation, however, immediate defibrillation is likely to be ineffective. Counterintuitively, these patients may benefit from a period of chest compressions prior to being shocked.

The Department of Health National Defibrillator Programme: analysis of downloads from 250 deployments of public access defibrillators

From April 2000 to November 2002, the Department of Health (England) placed 681 automated external defibrillators (AEDs) in 110 public places for use by volunteer lay first responders. An audit has been undertaken of the first 250 deployments, of which 182 were for confirmed cardiac arrest. Of these, 177 were witnessed whilst 5 occurred in situations that were remote or initially inaccessible to the responders. The response interval between collapse and the initiation of CPR or AED placement was estimated to be 3-5 min in most cases. Ventricular fibrillation or rapid ventricular tachycardia (one case) was the first recorded rhythm in 146 cases (82%). In all, 44 of the 177 witnessed cases are known to have survived to hospital discharge (25%). Complete downloads are available for 173 witnessed cases and of these 140 were shocked: first-shock success, defined as termination of the fibrillatory waveform for 5 s or more, was achieved in 132 of them. When data quality permitted, the downloads were analysed with special reference to the numbers of compressions given and also to interruptions in compression sequences for ventilations, for rhythm analysis by the AED, for clinical checks, and for unexplained operator delays. The average rate of compressions during sequences was 120 min(-1), but because of interruptions, the actual number administered over a full minute from the first CPR prompt was a median of only 38. The speed of response by the lay first responders in relation to AED use was similar to that reported for healthcare professionals.

Magnetic resonance imaging during untreated ventricular fibrillation reveals prompt right ventricular overdistention without left ventricular volume loss

BACKGROUND

Most out-of-hospital ventricular fibrillation (VF) is prolonged (>5 minutes), and defibrillation from prolonged VF typically results in asystole or pulseless electrical activity. Recent visual epicardial observations in an open-chest, open-pericardium model of swine VF indicate that blood flows from the high-pressure arterial system to the lower-pressure venous system during untreated VF, thereby overdistending the right ventricle and apparently decreasing left ventricular size. Therefore, inadequate left ventricular stroke volume after defibrillation from prolonged VF has been postulated as a major contributor to the development of pulseless rhythms.

METHODS AND RESULTS

Ventricular dimensions were determined by MRI for 30 minutes of untreated VF in a closed-chest, closed-pericardium model in 6 swine. Within 1 minute of untreated VF, mean right ventricular volume increased by 29% but did not increase thereafter. During the first 5 minutes of untreated VF, mean left ventricular volume increased by 34%. Between 20 and 30 minutes of VF, stone heart occurred as manifested by dramatic thickening of the myocardium and concomitant substantial decreases in left ventricular volume.

CONCLUSIONS

In this closed-chest swine model of VF, substantial right ventricular volume changes occurred early and did not result in smaller left ventricular volumes. The changes in ventricular volumes before the late development of stone heart do not explain why defibrillation from brief duration VF (<5 minutes) typically results in a pulsatile rhythm with return of spontaneous circulation, whereas defibrillation from prolonged VF (5 to 15 minutes) does not.

[Transthoracic defibrillation. Physiologic and pathophysiologic principles and their role in the outcome of resuscitation]

As one major link in the chain of survival, early transthoracic (external) cardiac defibrillation is aimed at the termination of ventricular flutter and ventricular fibrillation. Most important to the success of defibrillation is the passage of a defined amount of current through a critical mass of heart muscle. Different transthoracic resistances reduce the effective density of the current within the heart. As for other therapeutic intervention procedures, recommendations for the optimal strength of current to be applied to the fibrillating heart need to be evaluated and defined for therapeutical defibrillation too. Unnecessarily high current density causes damage to the heart and should be prevented. By using biphasic waveforms in contrast to monophasic impulses, the amount of current can be reduced but the same or even higher efficacy is attained. Therefore possible myocardial damage might be clearly reduced. Even with individually altered thoracic impedance effective conversion of cardiac rhythm can be achieved by device-controlled compensation and biphasic waveforms. According to their different mechanisms or origin (electrically induced or spontaneously caused by organic heart disease) the probability of successful conversion of the cardiac rhythm by one single electrical impulse varies. The optimum point in time for defibrillation during resuscitation needs to be redefined. In order to improve comparability, further studies should use standardized definitions for successful defibrillation relating to the resulting cardiac rhythm.