The statistics of a practical seizure warning system.

Statistical methods for evaluating seizure prediction algorithms are controversial and a primary barrier to realizing clinical applications. Experts agree that these algorithms must, at a minimum, perform better than chance, but the proper method for comparing to chance is in debate. We derive a statistical framework for this comparison, the expected performance of a chance predictor according to a predefined scoring rule, which is in turn used as the control in a hypothesis test. We verify the expected performance of chance prediction using Monte Carlo simulations that generate random, simulated seizure warnings of variable duration. We propose a new test metric, the difference between algorithm and chance sensitivities given a constraint on proportion of time spent in warning, and use a simple spectral power-based measure to demonstrate the utility of the metric in four patients undergoing intracranial EEG monitoring during evaluation for epilepsy surgery. The methods are broadly applicable to other scoring rules. We present them as an advance in the statistical evaluation of a practical seizure advisory system.

Outcome prediction for guidance of initial resuscitation protocol: Shock first or CPR first.

BACKGROUND: Ventricular fibrillation (VF) is treated optimally with a defibrillation shock shortly after patient collapse, but may benefit from initial cardiopulmonary resuscitation (CPR) if the shock is delayed. An objective measure of potential responsiveness to defibrillation could help decide optimal initial therapy. METHODS AND RESULTS: a new electrocardiogram (ECG) analysis algorithm was compared with response interval (call-to-shock) for prediction of patient outcome in a population of 87 VF patients in the Rochester, Minnesota area. In a retrospective analysis, both call-to-shock interval (p = 0.009) and ECG analysis (p < 0.001) predicted neurologically intact survival, with ECG analysis the stronger predictor (p = 0.034). When applied to advising initial patient treatment, ECG analysis compared favorably with the call-to-shock interval. Using a 7 min call-to-shock time criterion, 69% of patients would receive shocks first treatment using ECG analysis versus 67% using the call-to-shock interval (p = NS), 94% of survivors would retain successful shocks first treatment versus 85% (p = NS), and 48% of non-survivors receive alternate CPR-first treatment versus 45% (p = NS). Similarly, no significant differences were observed between ECG analysis and call-to-shock interval using an 8 min criterion. CONCLUSIONS: Both call-to-shock interval and a real-time ECG analysis are predictive of patient outcome. The ECG analysis is more predictive of neurologically intact survival. Moreover, the ECG analysis is dependent only upon the patient's condition at the time of treatment, with no need for knowledge of the response interval, which may be difficult to estimate at the time of treatment.

Transthoracic impedance does not affect defibrillation, resuscitation or survival in patients with out-of-hospital cardiac arrest treated with a non-escalating biphasic waveform defibrillator.

OBJECTIVE: This is a study of the influence of transthoracic impedance (TTI) on defibrillation, resuscitation and survival in patients with out-of-hospital cardiac arrest (OHCA), treated with a non-escalating impedance-compensating 150 J biphasic waveform defibrillator. METHODS: Cardiac arrest data from two EMS systems were analyzed retrospectively. All witnessed arrests from patients who presented with a shockable rhythm and were treated initially by BLS personnel were included (n = 102). For each defibrillation and resuscitation outcome variable, we tested differences in mean TTI for successful versus unsuccessful outcome. The effect of call-to-shock time on overall outcome was also examined. RESULTS: Initial shocks defibrillated 90% [83-95%] (95% confidence interval) of patients. Cumulative success with two shocks was 98% [93-100%] and with three shocks was 99% [95-100%]. TTI averaged 90 +/- 23 Omega. First-shock success, cumulative success through two shocks and cumulative success through the first-shock series were unrelated to TTI, as were BLS ROSC, pre-hospital ROSC, hospital admission and discharge. In contrast and consistent with previous findings, call-to-shock time was highly predictive of survival. CONCLUSIONS: High impedance patients were defibrillated by the biphasic waveform used in this study at high rates with a fixed energy of 150 J and without energy escalation. Rapid defibrillation rather than differences in patient impedance accounts for resuscitation success.

Immediate termination of fibrillation at 50% probability of overall success correlates with defibrillation dose-response curve width.

INTRODUCTION: Issues in transthoracic defibrillation, including waveform shape, fixed versus escalating dose protocol, and low- versus high-energy shocks, can be addressed by examining the defibrillation dose-response curve. We tested the hypothesis that, for commonly used defibrillation waveforms, the steepness of the overall defibrillation dose-response curve, measured as normalized curve width, correlates with the probability of a successful defibrillation being immediate at the shock intensity producing 50% success. METHODS AND RESULTS: We used 16 isolated rabbit hearts to determine probability of overall success as a function of shock intensity and probability that a successful defibrillation is immediate rather than progressive (followed by several extrasystoles) at the shock intensity producing 50% overall defibrillation success. Two waveform pairs were tested--a monophasic damped sine versus a biphasic truncated exponential waveform commonly used for transthoracic defibrillation, and a monophasic/biphasic truncated exponential waveform pair similar to those used in internal cardioverter defibrillators. There was a close correlation between probability of a successful defibrillation being immediate at 150 and normalized curve width for the defibrillation dose-response curve. CONCLUSION: Our findings suggest that a high probability of successful defibrillation being immediate at low shock intensities is correlated with a narrow normalized curve width for the defibrillation dose-response curve.

Automated external defibrillator use by untrained bystanders: can the public-use model work?

OBJECTIVE: For automated external defibrillators (AEDs) to be practical for broad public use, responders must be able to use them safely and effectively. This study's objective was to determine whether untrained laypersons could accurately follow the visual and voice prompt instructions of an AED. METHODS: Each of four different AED models (AED1, AED2, AED3, and AED4) was randomly assigned to a different group of 16 untrained volunteers in a simulated cardiac arrest. Four usability indicators were observed: 1) number of volunteers able to apply the pads to the manikin skin, 2) appropriate pad positioning, 3) time from room entry to shock delivery, and 4) safety in terms of touching the patient during shock delivery. RESULTS: Some of the 64 volunteers who participated in the study failed to open the pad packaging or remove the lining, or placed the pads on top of clothing. Fifty-percent of AED2 pads and 44% of AED3 pads were not placed directly on the manikin skin compared with 100% of AED1 and AED4 pads. Adjacent pad displacements that potentially could affect defibrillation efficacy were observed in 6% of AED1, 11% of AED2, 0% of AED3, and 56% of AED4 usages. Time to deliver a shock was within 3.5 minutes for all AEDs, although the median times for AED1 and AED4 were the shortest at 1.6 and 1.7 minutes, respectively. No significant volunteer contact with the manikin occurred during shock delivery. CONCLUSIONS: This study demonstrated that the AED user interface significantly influences the ability of untrained caregivers to appropriately place pads and quickly deliver a shock. Avoiding grossly inappropriate pad placement and failure to place AED pads directly on skin may be correctable with improvements in the AED instruction user interface.

AED use in businesses, public facilities and homes by minimally trained first responders.

BACKGROUND: Automated external defibrillators (AEDs) have become increasingly available outside of the Emergency Medical Systems (EMS) community to treat sudden cardiac arrest (SCA). We sought to study the use of AEDs in the home, businesses and other public settings by minimally trained first responders. The frequency of AED use, type of training offered to first responders, and outcomes of AED use were investigated. In addition, minimally trained responders were asked if they had encountered any safety problems associated with the AED. METHODS: We conducted a telephone survey of businesses and public facilities (2683) and homes (145) owning at least one AED for at least 12 months. Use was defined as an AED taken to a medical emergency thought to be a SCA, regardless of whether the AED was applied to the patient or identified a shockable rhythm. RESULTS: Of owners that participated in the survey, 13% (209/1581) of businesses and 5% (4/73) of homes had responded with the AED to a suspected cardiac arrest. Ninety-five percent of the businesses/public facilities offered training that specifically covered AED use. The rate of use for the AEDs was highest in residential buildings, public places, malls and recreational facilities with an overall usage rate of 11.6% per year. In-depth interviews were conducted with lay responders who had used the AED in a suspected cardiac arrest. In the four cases where the AED was used solely by a lay responder, all four patients survived to hospital admission and two were known to be discharged from the hospital. There were no reports of injury or harm. CONCLUSIONS: This survey demonstrates that AEDs purchased by businesses and homes were frequently taken to suspected cardiac arrests. Lay responders were able to successfully use the AEDs in emergency situations. Further, there were no reports of harm or injury to the operators, bystanders or patients from lay responder use of the AEDs.