Interactions between CPR and defibrillation waveforms: effect on resumption of a perfusing rhythm after defibrillation

Sudden Cardiac Death in the Young

Although the occurrence of sudden cardiac death (SCD) in a young person is a rare event, it is traumatic and often widely publicized. In recent years, SCD in this population has been increasingly seen as a public health and safety issue. This review presents current knowledge relevant to the epidemiology of SCD and to strategies for prevention, resuscitation, and identification of those at greatest risk. Areas of active research and controversy include the development of best practices in screening, risk stratification approaches and postmortem evaluation, and identification of modifiable barriers to providing better outcomes after resuscitation of young SCD patients. Institution of a national registry of SCD in the young will provide data that will help to answer these questions.

Cardiopulmonary resuscitation in real life: the most frequent fears of lay rescuers

INTRODUCTION

Surviving cardiac arrest depends on early cardiopulmonary resuscitation (CPR). Only one third of cardiac arrest victims receive prompt CPR in spite of well-attended Basic Life Support (BLS) courses. Our study aimed to investigate that how many lay rescuers, capable of performing CPR, would do so, and to analyse their impeding fears.

MATERIALS AND METHODS

After each BLS course for lay rescuers (American Heart Association (AHA) CPR for family and friends), an anonymous questionnaire was distributed asking participants whether they would perform CPR on an adult or on a child in a real case of cardiac arrest. In the case of a negative response, we questioned them why.

RESULTS

A total of 1000 questionnaires were analysed. The sample group was predominantly made up of males (77.7%), Italians (82.2%), individuals aged between 26 and 35 years (41.2%) and individuals possessing a high-school diploma (61.8%). The percentages that would perform CPR on an unknown adult or child were different (86.2% vs. 73.9% p = 0.005). The prevalent fears were regarding infection, being incapable, legal implications and causing damage and fear in general. The first three differ significantly in adult and paediatric cases. Subdividing the population according to sex, age and education did not demonstrate significant differences regarding willingness to perform adult or paediatric CPR.

CONCLUSIONS

This descriptive study demonstrates that the percentage that would really perform CPR is too low, particularly in the case of a child. Part of the course should be dedicated to discussing these arguments to ensure that all those capable of performing good CPR would immediately do so.

Transmural recording of shock potential gradient fields, early postshock activations, and refibrillation episodes associated with external defibrillation of long-duration ventricular fibrillation in swine

BACKGROUND

Knowledge of the shock potential gradient (nablaV) and postshock activation is limited to internal defibrillation of short-duration ventricular fibrillation (SDVF).

OBJECTIVE

The purpose of this study was to determine these variables after external defibrillation of long-duration VF (LDVF).

METHODS

In six pigs, 115-20 plunge needles with three to six electrodes each were inserted to record throughout both ventricles. After the chest was closed, the biphasic defibrillation threshold (DFT) was determined after 20 seconds of SDVF with external defibrillation pads. After 7 minutes of LDVF, defibrillation shocks that were less than or equal to the SDVF DFT strength were given.

RESULTS

For DFT shocks (1632 +/- 429 V), the maximum minus minimum ventricular voltage (160 +/- 100 V) was 9.8% of the shock voltage. Maximum cardiac nablaV (28.7 +/- 17 V/cm) was 4.7 +/- 2.0 times the minimum nablaV (6.2 +/- 3.5 V/cm). Although LDVF did not increase the DFT in five of the six pigs, it significantly lengthened the time to earliest postshock activation following defibrillation (1.6 +/- 2.2 seconds for SDVF and 4.9 +/- 4.3 seconds for LDVF). After LDVF, 1.3 +/- 0.8 episodes of spontaneous refibrillation occurred per animal, but there was no refibrillation after SDVF.

CONCLUSION

Compared with previous studies of internal defibrillation, during external defibrillation much less of the shock voltage appears across the heart and the shock field is much more even; however, the minimum nablaV is similar. Compared with external defibrillation of SDVF, the biphasic external DFT for LDVF is not increased; however, time to earliest postshock activation triples. Refibrillation is common after LDVF but not after SDVF in these normal hearts, indicating that LDVF by itself can cause refibrillation without requiring preexisting heart disease.

In-hospital resuscitation

A recent world expert conference on resuscitation and emergency cardiac care led to evidence-based international guidelines for cardiopulmonary resuscitation (CPR). Several changes to CPR interventions were recommended, and will have to be implemented into clinical practice. The poor prognosis of patients who suffer in-hospital cardiac arrest may be improved with developments in CPR interventions. In the present review the most important changes recommended by the new CPR guidelines and the latest promising CPR investigations are described, focusing on their impact on in-hospital resuscitation.

Assessment of a three-phase model of out-of-hospital cardiac arrest in patients with ventricular fibrillation

AIM

Cardiac arrest with ventricular fibrillation (VF) has been divided into three phases in which phase-specific therapy may improve outcome. The aim of this study was to assess the relationship between call-to-shock time, bystander CPR (BCPR), and cardiac arrest outcomes.

METHODS

In a retrospective analysis of prospectively-acquired data from witnessed VF out-of-hospital cardiac arrests (OHCA), patients were classified as phases 1, 2, or 3 based on call-to-shock time (<5, 5-8, and >8 min) and further stratified based on performance of BCPR. Groups were compared with regard to survival, neurological outcome, and restoration of spontaneous circulation (ROSC) with defibrillation only (no ALS interventions to achieve sustained ROSC).

RESULTS

Survival, neurologically intact survival, and ROSC with defibrillation were different between phases 1 and 2 (p=0.014 and p=0.005, p<0.01) but not between phases 2 and 3. Patients were further classified as having received BCPR (N=111) or no BCPR (N=107). Neurologically intact survival with and without BCPR, respectively, was 61% versus 72% (phase 1), 44% versus 41% (phase 2), and 42% versus 29% (phase 3). ROSC with defibrillation only with and without BCPR, respectively, was 64% versus 56% (phase 1), 37.0% versus 29% (phase 2), and 33% versus 8% (phase 3). ROSC with defibrillation alone was statistically higher in univariate analysis in phase 3 with BCPR (p=0.033) but not in multivariate analysis (p=0.068).

CONCLUSIONS

BCPR did not significantly improve survival in any phase of OHCA, though there was a trend toward increased neurologically intact survival and increased ROSC with defibrillation alone in phase 3.

How Sudden Is Sudden Cardiac Death?

Background— Out-of-hospital sudden cardiac death (SCD) is a frequent cause of death. Survival rates remain low despite increasing efforts in medical care. Better understanding of the circumstances of SCD could be helpful in developing preventive measures and facilitating proper reactions to such a pending event.

Methods and Results— Information on cases of out-of-hospital SCD was collected in the Berlin, Germany, emergency medical system via a questionnaire. Bystander interviews were performed by the emergency physician on scene immediately after declaration of death or return of circulation. Of 5831 rescue missions, 406 involved patients with presumed cardiac arrest. Sixty-six percent had a known cardiac disease. In 72%, the arrest occurred at home, and in 67%, it occurred in the presence of an eyewitness. Information on symptoms immediately preceding the arrest was available in 80% (n=323) of all 406 patients and in 274 of those with witnessed arrest. Symptoms were identical in the 2 groups. Typical angina was present for a median of 120 minutes in 25% of the 274 patients with witnessed arrest and in 33% with a symptom duration of less than 1 hour.

Conclusions— SCD occurs most often at home in the presence of relatives and after a longer period of typical warning symptoms. Although the much-hailed use of public access defibrillation is supported by several studies, the present results raise the question of whether educational measures and targeted educational programs tailored for patients at risk and their relatives should have a higher priority.

The three-phase model of cardiac arrest as applied to ventricular fibrillation in a large, urban emergency medical services system

BACKGROUND

Cardiac arrest is responsible for significant morbidity and mortality, with consistently poor outcomes despite the rapid availability of prehospital personnel for defibrillation attempts in patients with ventricular fibrillation (VF). Recent evidence suggests a period of cardiopulmonary resuscitation (CPR) prior to defibrillation attempts may improve outcomes in patients with moderate time since collapse (4-10 min).

OBJECTIVES

To determine cardiac arrest outcomes in our community and explore the relationship between time since collapse, performance of bystander CPR, and survival.

METHODS

Non-traumatic cardiac arrest data were collected prospectively over an 18-month period. Patients were excluded for: age <18 years, a "Do Not Attempt Resuscitation" (DNAR) directive, determination of a non-cardiac etiology for arrest, and an initially recorded rhythm other than VF. Patients were stratified by time since collapse (<4, 4-10, > 10 min, and unknown) and compared with regard to survival and neurological outcome. In addition, patients with and without bystander CPR were compared with regard to survival.

RESULTS

: A total of 1141 adult non-traumatic cardiac arrest victims were identified over the 18-month study period. This included 272 patients with VF as the initially recorded rhythm. Of these, 185 had a suspected cardiac etiology for the arrest; survival to hospital discharge was 15% in this group, with 82% of these having a good outcome or only moderate disability. Survival was highest among patients with time since collapse of less than 4 min and decreased with increasing time since collapse. There were no survivors among patients with time since collapse greater than 10 min. Among patients with time since collapse of 4 min or longer, survival was significantly higher with the performance of bystander CPR; there was no survival advantage to bystander CPR among patients with time since collapse less than 4 min.

CONCLUSIONS

The performance of bystander CPR prior to defibrillation by EMS personnel is associated with improved survival among patients with time since collapse longer than 4 min but not less than 4 min. These data are consistent with the three-phase model of cardiac arrest.

Cardiopulmonary resuscitation algorithms, defibrillation and optimized ventilation during resuscitation

PURPOSE OF REVIEW

In 2005, the American Heart Association released its Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. This article reviews the treatment algorithms for Advanced Cardiac Life Support, citing the evidence on which the Guidelines are based. Additional focus is placed on defibrillation and optimized ventilation.

RECENT FINDINGS

Major changes include a reorganization of the algorithms for cardiac arrest. Emphasis on effective cardiopulmonary resuscitation is placed as the key to improved survival. Single defibrillation shocks are recommended (compared with three 'stacked' shocks) with immediate provision of cardiopulmonary resuscitation and minimal interruptions in chest compressions. The recommended chest compression : ventilation rate for single rescuers has been changed to 30:2.

SUMMARY

Despite advances in resuscitation science, basic life support remains the key to improving survival outcomes. Ultimately, as new knowledge is gained, we believe resuscitation therapies will be more individualized, on the basis of pathophysiology and etiology of the initial cardiac arrest.

The effect of global hypoxia on myocardial function after successful cardiopulmonary resuscitation in a laboratory model

Most laboratory studies of cardiac arrest use models of ventricular fibrillation, but in the emergency room, operating room or intensive care unit, cardiac arrest frequently results from asphyxia. We sought to investigate the effect of different durations of asystole secondary to asphyxia on myocardial function after resuscitation. In a laboratory based experimental series, anaesthetized rats received either 4 or 8 min of asphyxial cardiac arrest, and following standardized resuscitation, serial transthoracic echocardiography was performed. Severe depression of left ventricular fractional shortening occurred in both groups with partial recovery only in the 4-min arrest group, while left ventricular end-diastolic diameter was increased in the 4-min group. The pH, HCO3(-) and SBE were reduced in both groups after resuscitation, but the degree of acidosis was greater in the 8-min group. In this model, transthoracic echocardiography demonstrated both systolic and diastolic impairment following asphyxial cardiac arrest, and a clear dose-effect relationship between duration of asphyxia and degree of impairment. A shorter duration of asphyxia was associated with a lesser increase in left ventricular end-diastolic dimension, compared with more protracted asphyxia; the shorter arrest was associated with better recovery of contractile function and acidosis. Increased duration of asphyxia causes increased systolic and diastolic dysfunction. These findings may have significant implications for resuscitative therapeutics. ECHO assessment may permit specific targeting of therapy directed towards systolic or diastolic function during CPR.

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 biphasic waveform defibrillation at very high and very low energies: a comparison with monophasic waveforms in an animal model of ventricular fibrillation

The purpose of this study was to compare truncated exponential biphasic waveform versus truncated exponential monophasic waveform shocks for transthoracic defibrillation over a wide range of energies. Biphasic waveforms are more effective than monophasic shocks for defibrillation at energies of 150-200 Joules (J) but there are few data available comparing efficacy and safety of biphasic versus monophasic defibrillation at energies of <150 J or >200 J. Thirteen adult swine (weighing 18-26 kg, mean 20 kg) were deeply anesthetized and intubated. After 15 s of electrically-induced ventricular fibrillation (VF), each pig received truncated exponential monophasic shocks (10 ms) and truncated exponential biphasic shocks (5/5 ms) in random order. Energy doses ranged from 70 to 360 J. Success was defined as termination of VF at 5 s post-shock. For both biphasic and monophasic waveforms success rate rose as energy was increased. Biphasic waveform shocks (5/5 ms) were superior to 10 ms monophasic waveform shocks at the very low energy levels (at 70 J, biphasic: 80+/-9%, monophasic; 32+/-11% and at 100 J, biphasic; 96+/-3% and monophasic 39+/-11%, both P < 0.01). No significant differences in shock success were seen between biphasic and monophasic waveform shocks at 200 J or higher energy levels. Shock success of > 75% was achieved with 200 J (10 J/kg) for both waveforms. Pulseless electrical activity (PEA) or ventricular asystole occurred in 4 animals receiving monophasic shocks and 1 animal receiving biphasic shocks. Biphasic waveform shocks (5/5 ms) for transthoracic defibrillation were superior to monophasic shocks (10 ms) at low energy levels. Percent success increased with increasing energies. PEA occurred infrequently with either waveform.