Derivation of a termination-of-resuscitation guideline for emergency medical technicians using automated external defibrillators

OBJECTIVES

To determine the association between characteristics of cardiac arrest and survival to hospital discharge following failed resuscitation by defibrillation-trained emergency medical technicians (EMT-Ds), and to propose an out-of-hospital termination-of-resuscitation (TOR) guideline for EMT-Ds.

METHODS

A 22-month retrospective review of 700 out-of-hospital primary cardiac arrest patients in a large emergency medical services (EMS) system who received exclusively EMT-D care.

RESULTS

Seven hundred primary cardiac arrest patients were identified. Follow-up was obtained in 662 cases (94.6%). Of these, 36 (5.4%) achieved a return of spontaneous circulation (ROSC) prior to transport. Among the 626 patients who failed to achieve ROSC at any time, two (0.3%) survived to discharge. Multivariate analysis showed that ROSC at any time had the strongest association with survival [odds ratio (OR) 45.5; 95% confidence interval (95% CI) = 8.5 to 243.7]. A shock prior to transport (OR 6.9; 95% CI = 1.2 to 40.3) and cardiac arrest witnessed by EMS personnel (OR 4.4; 95% CI = 1.0 to 18.5) were also independently associated with survival. These variables were incorporated into a TOR guideline. The guideline was 100% sensitive (95% CI = 99.1 to 100) in identifying survivors and had 100% negative predictive value (95% CI = 75.3 to 100) for identifying nonsurvivors of out-of-hospital cardiac arrest in the study population.

CONCLUSIONS

In this EMS system, cardiac arrest patients may be considered for out-of-hospital TOR following EMT-D resuscitation attempts when there has been no ROSC, no shock has been given, and the arrest was not witnessed by EMS personnel. These guidelines require prospective validation.

Clinical evaluation of a policy of early repeated internal cardioversion for recurrence of atrial fibrillation

INTRODUCTION

The clinical value of cardioversion (CV) of persistent atrial fibrillation (AF) is limited by the high rate of early AF recurrence, which may be related to the persistence of atrial electrical remodeling. We examined the hypothesis that the likelihood of maintaining sinus rhythm after CV of persistent AF is significantly enhanced by a policy of early repeated CV.

METHODS AND RESULTS

Fifty-nine patients with persistent AF underwent internal CV (CV 1). Those patients cardioverted were monitored with daily transtelephonic ECG. In the event of AF recurrence, these patients were admitted rapidly for repeat CV (CV 2) and, if further recurrence occurred, a third CV (CV 3) was performed. Daily ECG monitoring was continued until 1 month of sinus rhythm was maintained or a total of three CVs were performed. Of the 59 patients undergoing CV 1, 43 were discharged in sinus rhythm and 29 subsequently had AF recurrence during monitoring. Twenty-three of these underwent CV 2 and 11 of these underwent CV 3. Of those having repeated CVs, only 4 patients maintained sinus rhythm for 1 month (3 after CV 2 and 1 after CV 3). The remaining patients had repeated AF recurrence during the monitoring period. Mean time from AF recurrence to CV 2 was 20+/-13 hours and from AF recurrence to CV 3 was 13+/-7.2 hours. Atrial effective refractory periods increased from 189+/-16 msec at CV 1 to 215+/-18 msec at CV 3 (P < 0.05), indicating reversal of atrial electrical remodeling during this period.

CONCLUSION

A policy of early repeated CVs for AF recurrence has very limited clinical value despite evidence of reversal of atrial electrical remodeling. The time between AF recurrence and repeat CV may need to be reduced further if such a policy is to succeed.

The Low Energy Safety Study (LESS): rationale, design, patient characteristics, and device utilization

BACKGROUND

A 10-J energy safety margin has traditionally been used in programming implantable cardioverter defibrillators (ICDs). The Low Energy Safety Study (LESS) tests the hypothesis that programming shocks to lower energy margins is safe and effective.

METHODS

Patients with standard ICD indications undergo defibrillation threshold testing (DFT) at the time of ICD implant, with reconfirmation of lowest successful energy twice (DFT++). Patients are randomized to 2 groups: the first has the initial 2 shocks for ventricular fibrillation conversion programmed at 2 energy steps above DFT++ (typically 4-6 J, maximum 10 J) with subsequent shocks at maximum energy, and the second has all shocks programmed at maximum energy. Patients are followed up every 3 months for 2 years to assess shock conversion efficacy of spontaneous arrhythmias. In a subgroup of patients, there is a second randomization to energy levels of 0, 1, 2, 3, or 4 steps above implant DFT++ for conversion testing of 3 induced ventricular fibrillation episodes at prehospital discharge, 3 months, and 12 months after implant.

RESULTS

Enrollment is complete (702 patients), but follow-up results are pending. There were no significant variations in implant indications and baseline antiarrhythmic drug use over the 3-year enrollment period, although an increase in the percentage of dual-chamber ICDs implanted occurred, with the majority (65%) of implanted ICDs being dual-chamber devices by the end of the enrollment period.

CONCLUSION

The results of LESS should facilitate the development of algorithms for programming ICD energy safety margins.

Initial energy setting, outcome and efficiency in direct current cardioversion of atrial fibrillation and flutter

OBJECTIVES

The purpose of this study was to design a more efficient protocol for the electrical cardioversion of atrial arrhythmias.

BACKGROUND

Guidelines for electrical cardioversion of atrial arrhythmias recommend starting with low energy shocks, which are often ineffective.

METHODS

We recorded the sequence of shocks in 1,838 attempts at cardioversion for atrial fibrillation (AF) and 678 attempts at cardioversion for atrial flutter. These data were used to calculate the probability of success for each shock of a standard series and the probability of success with a single shock at each intensity. In 150 cases, a rhythm strip with the time of each shock allowed us to calculate the time expended on unsuccessful shocks.

RESULTS

We analyzed the effects of 5,152 shocks delivered to patients for AF and 1,238 shocks delivered to patients for atrial flutter. The probability of success on the first shock in AF of > 30 days duration was 5.5% at < 200 J, 35% at 200 J and 56% at 360 J. In atrial flutter, an initial 100 J shock worked in 68%. In AF of >30 days duration, shocks of < 200 J had a 6.1% probability of success; this fell to 2.2% with a duration >180 days. In those with AF for >180 days, the initial use of a 360 J shock was associated with the eventual use of less electrical energy than with an initial shock of < or =100 J (581 +/- 316 J vs. 758 +/- 433 J, p < 0.01, Mann-Whitney U test).

CONCLUSIONS

An initial energy setting of > or =360 J can achieve cardioversion of AF more efficiently in patients than traditional protocols, particularly with AF of longer duration.

Influence of mobile phones on accuracy of ECG interpretation algorithm in automated external defibrillator

BACKGROUND

Automated External Defibrillators (AED) are a recommended tool for out-of-hospital emergency medical services. Mobile phones (GSM) are a potential source of electromagnetic interference which may cause failure of ECG interpretation and subsequent inappropriate action of AED's.

METHODS

We evaluated the influence of 900 MHz GSM phones on the accuracy of automatic ECG interpretation with a GSM Mobile Station Tester with adjustable power and mode of transmission (Hewlett-Packard HP5515A), GSM phones (Alcatel, Ericsson, Nokia, Panasonic), ECG simulator (Metron) and four AEDs (Fore Runner-Hewlett-Packard, Heartstart 3000-Laerdal, Cardio-Aid 100-Artema, Heartstream XLT-Agilent). The protocol included 18 different ECG patterns, different ECG voltages, and different power and mode of transmission.

RESULTS

The first stage of the protocol included minimal power of signal transmitted from GSM Mobile Station Tester and maximum power of GSM phone's signal--hence maximal potential interference to AED. The protocol was based on close direct contact between the GSM phone and the AED device. Regardless of the ECG pattern, with both 0.5 and 1.0 mV ECG voltage, and the GSM phone placed on various parts of AED device or at the patient cable, no failure of AED algorithm occurred. No detectable noise was seen at AED's ECG display.

CONCLUSION

AEDs seems to be well protected against clinically significant failure caused by noise from 900 MHz GSM phones.

Effects of bystander first aid, defibrillation and advanced life support on neurologic outcome and hospital costs in patients after ventricular fibrillation cardiac arrest

OBJECTIVE

To evaluate the effects of basic life support, time to first defibrillation and emergency medical service arrival time on neurologic outcome and expenses for hospital care in patients after cardiac arrest.

SETTING

Large urban emergency medical services system and emergency department in a 2000-bed university hospital.

DESIGN

Outcome and cost benefit analysis of patients admitted to the hospital after witnessed, out-of-hospital, ventricular fibrillation cardiac arrest from October 1, 1991, until December 31, 1997.

PATIENTS

Out of 1054 patients with out-of-hospital cardiac arrest, 276 were eligible.

MEASUREMENTS AND RESULTS

The effects of basic and advanced life support measures on neurologic outcome and hospital expenses were evaluated. In contrast to intubation (odds ratio 1.08; 95% CI: 0.51-2.31; p=0.84), basic life support (odds ratio 0.44; 95% CI: 0.24-0.77; p=0.004) and time to first defibrillation (odds ratio 1.08; 95% CI: 1.03-1.13; p=0.001) were significantly correlated with good neurologic outcome. Among the patients who did not receive basic life support, the average cost per patient with good neurologic outcome significantly increased with the delay of the first defibrillation (p<0.001).

CONCLUSIONS

In contrast to intubation, bystander basic life support and time to first defibrillation were significantly associated with good neurologic outcome and resulted in fewer expenses spent on in-hospital efforts.

[Electrical conversion of atrial fibrillation. Superior effects of biphasic transthoracic method when compared with the conventional monophasic method]

Can biphasic electrical conversion of atrial fibrillation replace the standard monophasic method? This report reviews factors facilitating the electrical conversion of atrial fibrillation and describes a clinical trial, showing superior effects of biphasic versus monophasic electrical conversion of atrial fibrillation. We conclude that the most important factors for successful electrical conversion of atrial fibrillations are 1) a biphasic impulse, 2) low transthoracic impedance and 3) a short history of atrial fibrillation.

Cardiac arrest management

Approximately 1,000 people in the United States suffer cardiac arrest each day, most often as a complication of acute myocardial infarction (AMI) with accompanying ventricular fibrillation or unstable ventricular tachycardia. Increasing the number of patients who survive cardiac arrest and minimizing the clinical sequelae associated with cardiac arrest in those who do survive are the objectives of emergency medical personnel. In 1990, the American Heart Association (AHA) suggested the chain of survival concept, with four links--early access, cardiopulmonary resuscitation (CPR), defibrillation, and advanced care--as the way to approach cardiac arrest. The recently published International Resuscitation Guidelines 2000 of the AHA have addressed advances in our understanding of the chain of survival. While the chain of survival concept has withstood a decade of scrutiny, there are only a few scientifically rigorous research studies that support changes in prehospital patient care. Additional research efforts carried out in the prehospital setting are needed to support the concepts included in the chain of survival for cardiac arrest patients. Participants at the second Turtle Creek Conference, a meeting of experts in the field of emergency medicine held in Dallas, Texas, on March 29-31, 2000, discussed these and other issues associated with prehospital emergency care in the cardiac arrest patient. This paper addresses a number of the issues associated with each of the links of the chain of survival, the evidence that exists, and what should be done to achieve the clinical evidence needed for true clinical significance. Also included in this paper are the consensus statements developed from small discussion groups held after the main presentation. These comments provide another perspective to the problems and to possible approaches to deal with them.

Waveform analysis of biphasic external defibrillators

BACKGROUND AND OBJECTIVE

All internal defibrillators and some external defibrillators use biphasic waveforms. The study analysed the discharged waveform pulses of two manual and two semi-automated biphasic external defibrillators.

METHODS AND RESULTS

The defibrillators were discharged into resistive loads of 25, 50 and 100 Omega simulating the patient's transthoracic impedance. The tested biphasic defibrillators differed in initial current as well as initial voltage, varying from 10.9 to 73.3 A and from 482.8 to 2140.0 V, respectively. The energies of the manual defibrillators set at 100, 150 and 200 J deviated by up to +19.1 or -28.9% from the selected energy. Impedance-normalised delivered energy varied from 1.0 to 12.5 J/Omega. Delivered energy, shock duration and charge flow were examined with respect to the total pulse, its splitting into positive and negative phases and their impedance dependence. For three defibrillators pulse duration increased with the resistive load, whereas one defibrillator always required 9.9 ms. All tested defibrillators showed a higher charge flow in the positive phase. Defibrillator capacitance varied between approximately 200 and 100 mu F and internal resistance varied from 2.0 to 7.6 Omega. Defibrillator waveform tilt ranged from -13.1 to 61.4%.

CONCLUSIONS

The tested defibrillators showed remarkable differences in their waveform design and their varying dependence on transthoracic impedance.

Shortening the second phase duration of biphasic shocks: effects of class III antiarrhythmic drugs on defibrillation efficacy in humans

INTRODUCTION

The specific waveform providing optimal defibrillation threshold (DFT) is unknown. We compared the defibrillation efficacy of biphasic pulses with second phases (P2) of 2 and 5 msec in a randomized prospective clinical study.

METHODS AND RESULTS

Intraoperative DFTs of 62 patients (age 54 +/- 13 years; ejection fraction 43% +/- 17%; amiodarone 47%, d,l-sotalol 13%) were determined in random order using a binary search protocol. Anodal shocks of 60% tilt first phases (P1) and P2 of 2 msec/5 msec were delivered from two 100-microF capacitors between the right ventricular electrode and the test housing of a Phylax 06/XM device. Mean DFT was significantly lower using the shorter P2 (9.5 +/- 4.5 J vs 11.3 +/- 5.2 J; P < 0.0001). According to subgroup analysis, the effect of changing P2 duration was only influenced by antiarrhythmic treatment. DFT decreased markedly using the shorter P2 in patients treated with amiodarone (10.7 +/- 4.9 J vs 13.4 +/- 5.6 J; P < 0.00001) or d,l-sotalol (6.1 +/- 3.3 J vs 9.1 +/- 4.6 J; P < 0.05). The difference in patients not treated with Class III drugs was found to be insignificant. Chronic amiodarone treatment increased DFT only when the longer P2 was used.

CONCLUSION

Biphasic shocks with shorter P2 should be used in patients undergoing Class III antiarrhythmic treatment.

Emergency medical equipment. Final rule

This action responds to the Aviation Medical Assistance Act of 1998 by requiring that air carrier operators carry automated external defibrillators on large, passenger-carrying aircraft and augment currently required emergency medical kits. It affects those air carrier operations for which at least one flight attendant is required and includes provisions designed to provide the option of treatment of serious medical events during flight time.