Survival to leave hospital from ventricular fibrillation

Fixed-energy biphasic waveform defibrillation in a pediatric model of cardiac arrest and resuscitation

OBJECTIVE

For adults, 150-J fixed-energy, impedance-compensating biphasic truncated exponential (ICBTE) shocks are now effectively used in automated defibrillators. However, the high energy levels delivered by adult automated defibrillators preclude their use for pediatric patients. Accordingly, we investigated a method by which adult automated defibrillators may be adapted to deliver a 50-J ICBTE shock for pediatric defibrillation.

DESIGN

Prospective, randomized study.

SETTING

A university-affiliated research institution.

SUBJECT

Domestic piglets.

INTERVENTIONS

We initially investigated four groups of anesthetized mechanically ventilated piglets weighing 3.8, 7.5, 15, and 25 kg. Ventricular fibrillation was induced with an AC current delivered to the right ventricular endocardium. After 7 mins of untreated ventricular fibrillation, a conventional manual defibrillator was used to deliver up to three 50-J ICBTE shocks. If ventricular fibrillation was not reversed, a 1-min interval of precordial compression preceded a second sequence of up to three shocks. The protocol was repeated until spontaneous circulation was restored, or for a total of 15 mins. In a second set of experiments, we evaluated a 150-J biphasic adult automated defibrillator that was operated in conjunction with energy-reducing electrodes such as to deliver 50-J shocks. The same resuscitation protocol was then exercised on piglets weighing 3.7, 13.5, and 24.2 kg.

MEASUREMENTS AND MAIN RESULTS

All animals were successfully resuscitated. Postresuscitation hemodynamic and myocardial function quickly returned to baseline values in both experimental groups, and all animals survived.

CONCLUSION

An adaptation of a 150-J biphasic adult automated defibrillator in which energy-reducing electrodes delivered 50-J shocks successfully resuscitated animals ranging from 3.7 to 25 kg without compromise of postresuscitation myocardial function or survival.

A comparison of biphasic and monophasic waveform defibrillation after prolonged ventricular fibrillation

STUDY OBJECTIVE

To compare the effects of biphasic defibrillation waveforms and conventional monophasic defibrillation waveforms on the success of initial defibrillation, postresuscitation myocardial function, and duration of survival after prolonged duration of untreated ventricular fibrillation (VF), including the effects of epinephrine.

DESIGN

Prospective, randomized, animal study.

SETTING

Animal laboratory and university-affiliated research and educational institute.

PARTICIPANTS

Domestic pigs.

INTERVENTIONS

VF was induced in 20 anesthetized domestic pigs receiving mechanical ventilation. After 10 min of untreated VF, the animals were randomized. Defibrillation was attempted with up to three 150-J biphasic waveform shocks or a conventional sequence of 200-J, 300-J, and 360-J monophasic waveform shocks. When reversal of VF was unsuccessful, precordial compression was performed for 1 min, with or without administration of epinephrine. The protocol was repeated until spontaneous circulation was restored or for a maximum of 15 min.

MEASUREMENTS AND RESULTS

No significant differences in the success of initial resuscitation or in the duration of survival were observed. However, significantly less impairment of myocardial function followed biphasic shocks. Administration of epinephrine reduced the total electrical energy required for successful resuscitation with both biphasic and monophasic waveform shocks.

CONCLUSIONS

Lower-energy biphasic waveform shocks were as effective as conventional higher-energy monophasic waveform shocks for restoration of spontaneous circulation after 10 min of untreated VF. Significantly better postresuscitation myocardial function was observed after biphasic waveform defibrillation. Administration of epinephrine after prolonged cardiac arrest decreased the total energy required for successful resuscitation.

The effects of biphasic and conventional monophasic defibrillation on postresuscitation myocardial function

OBJECTIVES

The purpose of this study was to compare the effects of biphasic defibrillation waveforms and conventional monophasic defibrillation waveforms on the success of initial defibrillation, postresuscitation myocardial function and duration of survival after prolonged ventricular fibrillation (VF).

BACKGROUND

We have recently demonstrated that the severity of postresuscitation myocardial dysfunction was closely related to the magnitude of the electrical energy of the delivered defibrillation shock. In the present study, the effects of fixed 150-J low-energy biphasic waveform shocks were compared with conventional monophasic waveform shocks after prolonged VF.

METHODS

Twenty anesthetized, mechanically ventilated domestic pigs were investigated. VF was induced with an AC current delivered to the right ventricular endocardium. After either 4 or 7 min of untreated ventricular fibrillation (VF), the animals were randomized for attempted defibrillation with up to three 150-J biphasic waveform shocks or conventional sequence of 200-, 300- or 360-J monophasic waveform shocks. If VF was not reversed, a 1-min interval of precordial compression preceded a second sequence of up to three shocks. The protocol was repeated until spontaneous circulation was restored or for a total of 15 min.

RESULTS

Monophasic waveform defibrillation after 4 or 7 min of untreated VF resuscitated eight of 10 pigs. All 10 pigs treated with biphasic waveform defibrillation were successfully resuscitated. Transesophageal echo-Doppler, arterial pressure and heart rate measurements demonstrated significantly less impairment of cardiovascular function after biphasic defibrillation.

CONCLUSIONS

Lower-energy biphasic waveform shocks were as effective as conventional higher energy monophasic waveform shocks for restoration of spontaneous circulation after 4 and 7 min of untreated VF. Significantly better postresuscitation myocardial function was observed after biphasic waveform defibrillation.

High-energy defibrillation increases the severity of postresuscitation myocardial dysfunction

BACKGROUND

The fatal outcome of victims after initially successful resuscitation from cardiac arrest has been attributed both to global myocardial ischemia during the interval of cardiac arrest and to the adverse effects of reperfusion. The present study was prompted by earlier experimental observation that the magnitude of myocardial dysfunction was in part related to the energy delivered during electrical defibrillation.

METHODS AND RESULTS

Ventricular fibrillation (VF) was induced in 15 Sprague-Dawley rats. Precordial compression was begun together with mechanical ventilation after 4 minutes of untreated VF and continued for 6 minutes. Spontaneous circulation was restored in each animal after external defibrillation with a single stored 2-, 10-, or 20-J countershock. Cardiac index and the rate of left ventricular pressure rise at left ventricular pressure of 40 mm Hg (dP/dt40) and fall (negative dP/dt) during the 240-minute interval after successful resuscitation were decreased, and left ventricular diastolic pressure was increased. These decreases in myocardial function were closely related to the energy of electrical defibrillation. After a 20-J shock, animals survived for only 5+/-3 hours; after a 10-J shock, animals survived for 15+/-4 hours; and after a 2-J shock, all animals survived for >24 hours.

CONCLUSIONS

The severity of postresuscitation myocardial dysfunction is related, at least in part, to the magnitude of the electrical energy of the delivered shock.

Myocardial injury after electrical therapy for cardiac arrhythmias assessed by troponin-T release

Episodes of ventricular fibrillation with subsequent intracardiac, and to a lesser extent, external defibrillation give rise to a statistically significant increase in S-troponin T, S-CK-MB(mass) and S-myoglobin indicative of a minor myocardial injury or dysfunction. In contrast, no such signs were observed after external direct-current conversion of atrial fibrillation using high energies, or after pace-terminated ventricular tachycardia.

Altered cardiac oxygen extraction, lactate production and coronary blood flow after large dose transthoracic DC countershocks

Although problems such as hypotension and pulmonary edema complicate the use of transthoracic DC countershocks, the mechanisms are not clear. In anesthetized dogs at 1 minute after only two defibrillator shocks there was a brief rise in coronary sinus lactate, exceeding arterial concentrations. Larger rises in lactate were seen after five shocks, indicating myocardial production of lactate. By contrast in eight animals given dummy shocks the heart always extracted lactate. At 2 minutes after five shocks mean myocardial oxygen extraction (6.5 +/- 0.6 mL/100 mL/100 mL blood; n = 4; P < 0.001), and remained so until 3 minutes after shocks, without significant increase in the lipid peroxidation product malondialdehyde in coronary sinus or arterial blood. Great cardiac venous blood flow, measured by thermodilution, rose after five shocks, and the heart rate pressure product also increased at 1-2 minutes. This transient failure of oxygen extraction, in the presence of arterial normoxia, hyperemia, and increased cardiac work, is best accounted for by a central effect of countershocks on myocardial cellular respiration.

Mortality within hospital after resuscitation from ventricular fibrillation outside hospital

OBJECTIVE

To determine factors related to mortality within hospital after successful resuscitation from ventricular fibrillation outside hospital by a mobile coronary care unit manned by a physician.

DESIGN

Retrospective review of records of patients resuscitated and admitted to hospital between 1 January 1966 and 31 December 1987.

SETTING

Mobile coronary care unit, coronary care unit, and cardiology department.

PATIENTS

281 patients (227 male), aged 14-82 (mean 58) successfully resuscitated from ventricular fibrillation outside hospital of whom 182 (65%) developed ventricular fibrillation before the arrival of the mobile coronary care unit. The aetiology of ventricular fibrillation was acute myocardial infarction in 194 patients (69%), ischaemic heart disease without infarction in 71 (25%), and other or unknown in 16 (6%).

MAIN OUTCOME MEASURES

Death within hospital.

RESULTS

There were 91 deaths in hospital (32%). Factors on univariate analysis significantly associated with increased mortality were patient age > or = 60 years, previous myocardial infarction or cerebrovascular disease, prior digoxin or diuretic treatment, collapse without prior chest pain or with pain lasting 30 minutes or less, defibrillation delayed by > or = 5 min, > or = four shocks required to correct ventricular fibrillation, left ventricular failure or pulmonary oedema and cardiogenic shock after successful defibrillation, and coma on admission to hospital. On multivariate analysis the most important factors (in rank order) were cardiogenic shock after defibrillation, coma on admission to hospital, age > or = 60 years and the requirement for four or more shocks to correct ventricular fibrillation.

CONCLUSIONS

The in-hospital mortality of patients resuscitated from ventricular fibrillation outside hospital was related to patient characteristics before the cardiac arrest and to the immediate haemodynamic and neurological status after correction of ventricular fibrillation as well as to factors at the resuscitation itself. The in-hospital mortality of this study compares favourably with the results obtained by units staffed by paramedical workers and emergency medical technicians, although 35% (99/281) of the patients had ventricular fibrillation after the arrival of the mobile unit and defibrillation was thus rapid.

Failure of countershock-type pulses in vitro to adversely alter mitochondrial oxidative phosphorylation

STUDY OBJECTIVE

The aim of the study was to investigate a potential mechanism of myocardial injury after DC countershock. The effect of countershock-type electrical discharges on rabbit heart mitochondrial oxygen consumption was measured in vitro using a novel respiration cell.

MEASUREMENTS AND MAIN RESULTS

Mitochondria were isolated from the hearts of adult Dutch and New Zealand White rabbits. Single rectangular shocks (voltage gradients 20 to 80 V/cm; 5 ms duration) caused no significant changes in state 3 oxygen consumption in standard incubation medium. Single and multiple defibrillator shocks (critically damped sine waveform; 5 ms duration) with peak voltage gradients of 242 to 659 V/cm similarly had no significant effect on state 3 oxygen consumption.

CONCLUSION

At voltage gradients similar to and greater than those causing myocardial cell injury and necrosis, electrical discharges do not directly depress mitochondrial function. Therefore, the reduction in mitochondrial oxygen consumption observed following transthoracic shocks in vivo may invoke other mechanisms (eg, intracellular calcium influx, high circulating noradrenaline, or free radical formation in the intact heart).

Prediction of hospital discharge in immediate survivors of ventricular fibrillation or asystole

Survival from ventricular fibrillation and asystole is influenced by variables measured during resuscitation that affect both immediate survival and discharge from hospital. These variables have been used to develop a formula to calculate an individuals chances of immediate survival and hospital discharge. It has allowed this heterogenous group to be subdivided into groups which can be compared both within and between institutions for the purposes of audit and evaluation of resuscitation protocols. This study evaluates the addition of clinical parameters to the prognostic index. One hundred twelve immediate survivors of ventricular fibrillation or asystole were examined immediately after resuscitation and clinical parameters measured and recorded. At the same time parameters previously described were recorded. The increase in the numbers of survivors improved the reliability (area under the receiver operator curve (ROC) improved from 0.79 to 0.83) of the index for predicting hospital discharge. Addition of the clinical variables of conscious state, respiratory state, blood pressure and pulse rate improved the prognostic index further to an ROC area of 0.86. This ensures that the predictive power of the new index is now highly reliable for predicting hospital discharge after successful resuscitation from ventricular fibrillation and asystole.

A cellular transtelephonic defibrillator for management of cardiac arrest outside the hospital

A cellular transtelephonic defibrillator facilitates early defibrillation in remote areas and involves electrocardiographic diagnosis and defibrillation control by a physician remote from but in voice contact with the patient-unit operator. The patient unit contains a microprocessor, microphone, defibrillator, electrocardiogram/defibrillator electrode pads and cellular telephone. Activation of the patient-unit initiates automatic dialing and contact with the remotely sited base station within 35 to 50 seconds. The physician at the base station identifies the rhythm and controls defibrillator charging and discharge. The minimal interaction required between the system and the local operator makes it suitable for use by minimally trained first responders. The cellular transtelephonic defibrillator has been tested in 211 calls responded to by a physician-manned mobile coronary care unit over distances up to 15 miles in an urban area. Satisfactory electrocardiographic transmission and voice communication were established in 172 of 211 calls (81.5%). In 39 (18.5%), connection with the base station either could not be established or maintained mainly because of geographic location or battery failure. One hundred direct current shocks of 50 to 360 J were effectively administered to 22 patients with 48 episodes of ventricular fibrillation or ventricular tachycardia with successful correction of 46 of 48 episodes using 1 to 4 shocks per episode. Widespread distribution of such devices could improve survival in patients with cardiac arrest outside the hospital.

Determinants of successful transthoracic defibrillation and outcome in ventricular fibrillation

OBJECTIVE

To examine factors determining defibrillation success and outcome in patients with ventricular fibrillation.

DESIGN

Observational prospective study of age, sex, transthoracic impedance, site of cardiac arrest, ventricular fibrillation duration and amplitude, primary or secondary ventricular fibrillation, aetiology, number of shocks to correct ventricular fibrillation, and drug treatment.

SETTING

A teaching hospital and a mobile coronary care unit with a physician.

PATIENTS

70 consecutive patients (50 male, 20 female) mean age 66.5 years.

INTERVENTIONS

Before the first countershock was administered transthoracic impedance using a 30 kHz low amplitude AC current passed through 8 cm/12 cm self-adhesive defibrillator electrode pads applied in the anteroapical position was measured. The first two shocks were 200 J delivered energy (low energy) and further shocks of 360 J (high energy) were given if required.

MAIN OUTCOME MEASURES

Countershock success and outcome from ventricular fibrillation.

RESULTS AND CONCLUSIONS

First shock success was significantly greater in inhospital arrests (37/53) than in out-of-hospital arrests (5/17) and in those receiving antiarrhythmic treatment (13/15, 86.7%) v (27/51, 52.9%). Transthoracic impedance was similar in those who were successfully defibrillated with one or two 200 J shocks (98.7 (26) omega) and those who required one or more 360 J shocks (91.4 (23) omega). Success rates with two 200 J shocks were similar in those patients with "high" transthoracic impedance (that is, greater than 115 omega) and those with transthoracic impedance (less than or equal to 115 omega) (8/12 (67%) v 44/58 (76%]. Fine ventricular fibrillation was significantly more common in the patients with a transthoracic impedance of greater than 95 omega (41% (13/32] than in those with a transthoracic impedance less than or equal to 95 omega (13% (5/38]. Death during arrest was significantly more common in patients who needed high energy shocks (14/18 (78%] than in those who needed low energy shocks (16/52 (31%]. Multiple regression analysis identified ventricular fibrillation with an amplitude of greater than or equal to 0.5 mV, age less than or equal to 70 years, and arrests that needed less than or equal to two shocks for defibrillation, in rank order as independent predictors of survival to discharge.

Metabolic changes and mitochondrial dysfunction early following transthoracic countershock in dogs

The mechanisms of myocardial injury and necrosis following transthoracic shocks from a direct current cardiac defibrillator were investigated in adult greyhounds. Myocardial lactate extraction became negative maximally at 1 minute, following two (mean -22% +/- SEM23) or five (-193% +/- 135) shocks and returned to baseline in 6-15 minutes. Myocardial necrosis assessed at 4 hours following the shock period was 0.05 g (+/- 0.03) after two shocks, 6.69 g (+/- 1.76) after five shocks and zero in controls. In further experiments, dogs received five or zero (dummy) shocks and mitochondria were isolated from their hearts following excision within 1 minute of receiving the final shock. Maximal oxygen consumption in right ventricular mitochondria was lower than the unshocked controls with both glutamate (66.9 +/- 9.4 nanoatoms of oxygen/mg per minute, n = 9 vs 86.6 +/- 13.6 nanoatoms/mg per minute, n = 7) and succinate (96.2 +/- 8.7 nanoatoms/mg per minute, n = 9 vs 119.5 +/- 14.4 nanoatoms/mg per minute, n = 7) as substrates. Using electron spin resonance spectroscopy, an increase in a peroxyl-free radical with g = 2.031 was detected in myocardial tissue after two internal shocks (50 joules stored energy, 0.5-minute intervals). We conclude that mitochondrial dysfunction and free-radical generation are likely contributors to cellular injury following multiple countershocks.