Instantaneous amplitude: Association of ventricular fibrillation waveform measures at time of shock with outcome in out-of-hospital cardiac arrest

BACKGROUND

Prompt defibrillation is key to successful resuscitation from ventricular fibrillation out-of-hospital cardiac arrest (VF-OHCA). Preliminary evidence suggests that the timing of shock relative to the amplitude of the VF ECG waveform may affect the likelihood of resuscitation. We investigated whether the VF waveform amplitude at the time of shock (instantaneous amplitude) predicts outcome independent of other validated waveform measures.

METHODS

We conducted a retrospective study of VF-OHCA patients ≥18 old. We evaluated three VF waveform measures for each shock: instantaneous amplitude at the time of shock, and maximum amplitude and amplitude spectrum area (AMSA) over a 3-s window preceding the shock. Linear mixed-effects modeling was used to determine whether instantaneous amplitude was associated with shock-specific return of organized rhythm (ROR) or return of spontaneous circulation (ROSC) independent of maximum amplitude or AMSA.

RESULTS

The 566 eligible patients received 1513 shocks, resulting in ROR of 62.0% (938/1513) and ROSC of 22.3% (337/1513). In unadjusted regression, an interquartile increase in instantaneous amplitude was associated with ROR (Odds ratio [OR] [95% confidence interval] = 1.27 [1.11-1.45]) and ROSC (OR = 1.27 [1.14-1.42]). However, instantaneous amplitude was not associated with ROR (OR = 1.13 [0.97-1.30]) after accounting for maximum amplitude, nor with ROR (OR = 1.00 [0.87-1.15]) or ROSC (OR = 1.05 [0.93-1.18]) after accounting for AMSA. By contrast, AMSA and maximum amplitude remained independently associated with ROR and ROSC.

CONCLUSIONS

We did not observe an independent association between instantaneous amplitude and shock-specific outcomes. Efforts to time shock to the maximal amplitude of the VF waveform are unlikely to affect resuscitation outcome.

Prediction of Shock-Refractory Ventricular Fibrillation During Resuscitation of Out-of-Hospital Cardiac Arrest

BACKGROUND

Out-of-hospital cardiac arrest due to shock-refractory ventricular fibrillation (VF) is associated with relatively poor survival. The ability to predict refractory VF (requiring ≥3 shocks) in advance of repeated shock failure could enable preemptive targeted interventions aimed at improving outcome, such as earlier administration of antiarrhythmics, reconsideration of epinephrine use or dosage, changes in shock delivery strategy, or expedited invasive treatments.

METHODS

We conducted a cohort study of VF out-of-hospital cardiac arrest to develop an ECG-based algorithm to predict patients with refractory VF. Patients with available defibrillator recordings were randomized 80%/20% into training/test groups. A random forest classifier applied to 3-s ECG segments immediately before and 1 minute after the initial shock during cardiopulmonary resuscitation was used to predict the need for ≥3 shocks based on singular value decompositions of ECG wavelet transforms. Performance was quantified by area under the receiver operating characteristic curve.

RESULTS

Of 1376 patients with VF out-of-hospital cardiac arrest, 311 (23%) were female, 864 (63%) experienced refractory VF, and 591 (43%) achieved functional neurological survival. Total shock count was associated with decreasing likelihood of functional neurological survival, with a relative risk of 0.95 (95% CI, 0.93-0.97) for each successive shock (P<0.001). In the 275 test patients, the area under the receiver operating characteristic curve for predicting refractory VF was 0.85 (95% CI, 0.79-0.89), with specificity of 91%, sensitivity of 63%, and a positive likelihood ratio of 6.7.

CONCLUSIONS

A machine learning algorithm using ECGs surrounding the initial shock predicts patients likely to experience refractory VF, and could enable rescuers to preemptively target interventions to potentially improve resuscitation outcome.

Title: Age, sex, and survival following ventricular fibrillation cardiac arrest: a mechanistic evaluation of the ECG waveform: Short title: Age, sex, and survival via VF waveform in OHCA

BACKGROUND

Studies of outcome differences by sex in out-of-hospital cardiac arrest (OHCA) have produced mixed results that may depend on age, a potential surrogate for menopausal status.

OBJECTIVE

We used quantitative measures of ventricular fibrillation (VF) waveforms - indicators of the myocardium's physiology - to assess whether survival differences according to sex and age group may be mediated via a biologic mechanism.

METHODS

We conducted a cohort study of VF-OHCA in a metropolitan EMS system. We used multivariable logistic regression to assess the association of survival to hospital discharge with sex and age group (<55, ≥55 years). We determined the proportion of outcome difference mediated by VF waveform measures: VitalityScore and amplitude spectrum area (AMSA).

RESULTS

Among 1526 VF-OHCA patients, the average age was 62 years, and 29% were female. Overall, younger women were more likely to survive than younger men (survival 67% vs 54%, p=0.02), while survival among older women and older men did not differ (40% vs 44%, p=0.3). Adjusting for Utstein characteristics, women <55 compared to men <55 had greater odds of survival to hospital discharge (OR=1.93, 95% CI 1.23-3.09), an association not observed between the ≥55 groups. Waveform measures were more favorable among women and mediated some of the beneficial association between female sex and survival among those <55 years: 47% for VitalityScore and 25% for AMSA.

CONCLUSIONS

Women <55 years were more likely to survive than men <55 years following VF-OHCA. The biologic mechanism represented by VF waveform mediated some, though not all, of the outcome difference.

Clinical Policy: Critical Issues in the Management of Adult Patients Presenting to the Emergency Department With Mild Traumatic Brain Injury: Approved by ACEP Board of Directors, February 1, 2023 Clinical Policy Endorsed by the Emergency Nurses Association (April 5, 2023)

This 2023 Clinical Policy from the American College of Emergency Physicians is an update of the 2008 “Clinical Policy: Neuroimaging and Decisionmaking in Adult Mild Traumatic Brain Injury in the Acute Setting.” A writing subcommittee conducted a systematic review of the literature to derive evidence-based recommendations to answer the following questions: 1) In the adult emergency department patient presenting with minor head injury, are there clinical decision tools to identify patients who do not require a head computed tomography? 2) In the adult emergency department patient presenting with minor head injury, a normal baseline neurologic examination, and taking an anticoagulant or antiplatelet medication, is discharge safe after a single head computed tomography? and 3) In the adult emergency department patient diagnosed with mild traumatic brain injury or concussion, are there clinical decision tools or factors to identify patients requiring follow-up care for postconcussive syndrome or to identify patients with delayed sequelae after emergency department discharge? Evidence was graded and recommendations were made based on the strength of the available data. Widespread and consistent implementation of evidence-based clinical recommendations is warranted to improve patient care.

Continuous Assessment of Ventricular Fibrillation Prognostic Status during CPR: Implications for Resuscitation

BACKGROUND

Ventricular fibrillation (VF) waveform measures reflect myocardial physiologic status. Continuous assessment of VF prognosis using such measures could guide resuscitation, but has not been possible due to CPR artifact in the ECG. A recently-validated VF measure (termed VitalityScore), which estimates the probability (0-100%) of return-of-rhythm (ROR) after shock, can assess VF during CPR, suggesting potential for continuous application during resuscitation.

OBJECTIVE

We evaluated VF using VitalityScore to characterize VF prognostic status continuously during resuscitation.

METHODS

We characterized VF using VitalityScore during 60 seconds of CPR and 10 seconds of subsequent pre-shock CPR interruption in patients with out-of-hospital VF arrest. VitalityScore utility was quantified using area under the receiver operating characteristic curve (AUC). VitalityScore trends over time were estimated using mixed-effects models, and associations between trends and ROR were evaluated using logistic models. A sensitivity analysis characterized VF during protracted (100-second) periods of CPR.

RESULTS

We evaluated 724 VF episodes among 434 patients. After an initial decline from 0-8 seconds following VF onset, VitalityScore increased slightly during CPR from 8-60 seconds (slope: 0.18 %/min). During the first 10 seconds of subsequent pre-shock CPR interruption, VitalityScore declined (slope: -14 %/min). VitalityScore predicted ROR throughout CPR with AUCs 0.73-0.75. Individual VitalityScore trends during 8-60 seconds of CPR were marginally associated with subsequent ROR (adjusted odds ratio for interquartile slope change (OR)=1.10, p=0.21), and became significant with protracted (≥100 seconds) CPR duration (OR=1.28, p=0.006).

CONCLUSION

VF prognostic status can be continuously evaluated during resuscitation, a development that could translate to patient-specific resuscitation strategies.

Investigating the Airway Opening Index during Cardiopulmonary Resuscitation

INTRODUCTION

Chest compressions during CPR induce oscillations in capnography (E_TCO₂) waveforms. Studies suggest E_TCO₂ oscillation characteristics are associated with intrathoracic airflow dependent on airway patency. Oscillations can be quantified by the Airway Opening Index (AOI). We sought to evaluate multiple methods of computing AOI and their association with return of spontaneous circulation (ROSC).

METHODS

We conducted a retrospective study of 307 out-of-hospital cardiac arrest (OHCA) cases in Seattle, WA during 2019. E_TCO₂ and chest impedance waveforms were annotated for the presence of intubation and CPR. We developed four methods for computing AOI based on peak E_TCO₂ and the oscillations in E_TCO₂ during CCs (ΔE_TCO₂). We examined the feasibility of automating ΔE_TCO₂ and AOI calculation and evaluated differences in AOI across the methods using nonparametric testing (p=0.05).

RESULTS

Median [interquartile range] AOI across all cases using Methods 1-4 was 28.0% [17.9-45.5%], 20.6% [13.0-36.6%], 18.3% [11.4-30.4%], and 22.4% [12.8-38.5%], respectively (p<0.001). Cases with ROSC had a higher median AOI than those without ROSC across all methods, though not statistically significant. Cases with ROSC had a significantly higher median [interquartile range] ΔE_TCO₂ of 7.3 mmHg [4.5-13.6 mmHg] compared to those without ROSC (4.8 mmHg [2.6-9.1 mmHg], p<0.001).

CONCLUSION

We calculated AOI using four proposed methods resulting in significantly different AOI. Additionally, AOI and ΔE_TCO₂ were larger in cases achieving ROSC. Further investigation is required to characterize AOI's ability to predict OHCA outcomes, and whether this information can improve resuscitation care.

A pilot evaluation of respiratory mechanics during prehospital manual ventilation

INTRODUCTION

Respiratory mechanics, such as tidal volume (V_T) and inspiratory pressures, may affect outcome in hospitalized patients with respiratory failure. Little is known about respiratory mechanics in the prehospital setting.

METHODS

In this prospective, pilot investigation of patients receiving prehospital advanced airway placement, paramedics applied a device to measure respiratory mechanics. We evaluated tidal volume (V_T) per predicted body weight (V_TPBW) to determine the proportion of breaths within the lung-protective range of 4-10 mL/kg per PBW overall, according to ventilation bag volume (large versus small) and cardiac arrest status (active CPR, post-ROSC, non-arrest).

RESULTS

Over 16-months, 7371 post-intubation breaths were measured in 54 patients, 32 patients with cardiac arrest and 22 with other conditions. Paramedics ventilated 19 patients with a small bag and 35 patients with a large bag. Overall, mean V_T was 435 mL (95% CI 403, 467); V_TPBW was 7.0 mL/kg (95% CI 6.4, 7.6) with 75% within the lung-protective range. Mean V_TPBW and peak pressure differed according to arrest status (absolute difference -0.36 mL/kg and 32 cmH₂O for active CPR compared to post-ROSC), though not according to bag size.

CONCLUSIONS

We observed that measuring respiratory mechanics in the prehospital setting was feasible. Tidal volumes were generally delivered within a safe range. Respiratory mechanics varied most significantly with active CPR with lower V_TPBW and higher peak pressures, though did not seem to be affected by bag size. Future work might examine the relationship between respiratory mechanics and outcomes, which may identify opportunities to improve clinical outcomes.

A method for continuous rhythm classification and early detection of ventricular fibrillation during CPR

AIM

We developed a method which continuously classifies the ECG rhythm during CPR in order to guide clinical care.

METHODS

We conducted a retrospective study of 432 patients treated following out-of-hospital cardiac arrest. Continuous ECG sequences from two-minute CPR cycles were extracted from defibrillator recordings and further divided into five-second clips. We developed an algorithm using wavelet analysis, hidden semi-Markov modeling, and random forest classification. The algorithm classifies individual clips as asystole, organized rhythm, ventricular fibrillation, or Inconclusive, while integrating information from previous clips. Classifications were compared to manual annotations to estimate accuracy in an independent validation dataset. Continuous sequences were classified as shockable, non-shockable, or Inconclusive; classifications were used to compute shock sensitivity and specificity.

RESULTS

Of 432 patient-cases, 290 were used for development and 142 for validation. In the 12,294 validation ECG clips during CPR, accuracies were 0.88 (95% CI 0.85-0.91) for asystole, 0.98 (95% CI 0.98-0.99) for organized rhythm, and 0.97 (95% CI 0.96-0.97) for ventricular fibrillation, with 43% classified as Inconclusive. Of 457 continuous sequences, shock sensitivity was 0.90 (95% CI 0.86, 0.93), shock specificity was 0.98 (95% CI 0.93, 0.99), and 7% were Inconclusive. Median delay to ventricular fibrillation recognition was 10 (IQR 5, 32) seconds.

CONCLUSION

An automated algorithm continuously classified the primary resuscitation rhythms-asystole, organized rhythms, and ventricular fibrillation-with 88-98% accuracy, enabling accurate shock advisory guidance during most two-minute CPR cycles. Additional investigation is required to understand how algorithm implementation could affect rescuer actions and clinical outcomes.

Machine learning and feature engineering for predicting pulse presence during chest compressions

Current resuscitation protocols require pausing chest compressions during cardiopulmonary resuscitation (CPR) to check for a pulse. However, pausing CPR when a patient is pulseless can worsen patient outcomes. Our objective was to design and evaluate an ECG-based algorithm that predicts pulse presence with or without CPR. We evaluated 383 patients being treated for out-of-hospital cardiac arrest with real-time ECG, impedance and audio recordings. Paired ECG segments having an organized rhythm immediately preceding a pulse check (during CPR) and during the pulse check (without CPR) were extracted. Patients were randomly divided into 60% training and 40% test groups. From training data, we developed an algorithm to predict the clinical pulse presence based on the wavelet transform of the bandpass-filtered ECG. Principal component analysis was used to reduce dimensionality, and we then trained a linear discriminant model using three principal component modes as input features. Overall, 38% (351/912) of checks had a spontaneous pulse. AUCs for predicting pulse presence with and without CPR on test data were 0.84 (95% CI (0.80, 0.88)) and 0.89 (95% CI (0.86, 0.92)), respectively. This ECG-based algorithm demonstrates potential to improve resuscitation by predicting the presence of a spontaneous pulse without pausing CPR with moderate accuracy.

Insights From the Ventricular Fibrillation Waveform Into the Mechanism of Survival Benefit From Bystander Cardiopulmonary Resuscitation

Background

The mechanism by which bystander cardiopulmonary resuscitation (CPR) improves survival following out‐of‐hospital cardiac arrest is unclear. We hypothesized that ventricular fibrillation (VF) waveform measures, as surrogates of myocardial physiology, mediate the relationship between bystander CPR and survival.

Methods and Results

We performed a retrospective cohort study of adult, bystander‐witnessed patients with out‐of‐hospital cardiac arrest with an initial rhythm of VF who were treated by a metropolitan emergency medical services system from 2005 to 2018. Patient, resuscitation, and outcome variables were extracted from emergency medical services and hospital records. A total of 3 VF waveform measures (amplitude spectrum area, peak frequency, and median peak amplitude) were computed from a 3‐second ECG segment before the initial shock. Multivariable logistic regression estimated the association between bystander CPR and survival to hospital discharge adjusted for Utstein elements. Causal mediation analysis quantified the proportion of survival benefit that was mediated by each VF waveform measure. Of 1069 patients, survival to hospital discharge was significantly higher among the 814 patients who received bystander CPR than those who did not (0.52 versus 0.43, respectively; P<0.01). The multivariable‐adjusted odds ratio for bystander CPR and survival was 1.6 (95% CI, 1.2, 2.1), and each VF waveform measure attenuated this association. Depending on the specific waveform measure, the proportion of mediation varied: 53% for amplitude spectrum area, 31% for peak frequency, and 29% for median peak amplitude.

Conclusions

Bystander CPR correlated with more robust initial VF waveform measures, which in turn mediated up to one‐half of the survival benefit associated with bystander CPR. These results provide insight into the biological mechanism of bystander CPR in VF out‐of‐hospital cardiac arrest.

A method to predict ventricular fibrillation shock outcome during chest compressions

BACKGROUND

Out-of-hospital ventricular fibrillation (VF) cardiac arrest is a leading cause of death. Quantitative analysis of the VF electrocardiogram (ECG) can predict patient outcomes and could potentially enable a patient-specific, guided approach to resuscitation. However, VF analysis during resuscitation is confounded by cardiopulmonary resuscitation (CPR) artifact in the ECG, challenging continuous application to guide therapy throughout resuscitation. We therefore sought to design a method to predict VF shock outcomes during CPR.

METHODS

Study data included 4577 5-s VF segments collected during and without CPR prior to defibrillation attempts in N = 1151 arrest patients. Using training data (460 patients), an algorithm was designed to predict the VF shock outcomes of defibrillation success (return of organized ventricular rhythm) and functional survival (Cerebral Performance Category 1-2). The algorithm was designed with variable-frequency notch filters to reduce CPR artifact in the ECG based on real-time chest compression rate. Ten ECG features and three dichotomous patient characteristics were developed to predict outcomes. These variables were combined using support vector machines and logistic regression. Algorithm performance was evaluated by area under the receiver operating characteristic curve (AUC) to predict outcomes in validation data (691 patients).

RESULTS

AUC (95% Confidence Interval) for predicting defibrillation success was 0.74 (0.71-0.77) during CPR and 0.77 (0.74-0.79) without CPR. AUC for predicting functional survival was 0.75 (0.72-0.78) during CPR and 0.76 (0.74-0.79) without CPR.

CONCLUSION

A novel algorithm predicted defibrillation success and functional survival during ongoing CPR following VF arrest, providing a potential proof-of-concept towards real-time guidance of resuscitation therapy.

A Method to Detect Presence of Chest Compressions During Resuscitation Using Transthoracic Impedance

OBJECTIVE

Interruptions in chest compressions during treatment of out-of-hospital cardiac arrest are associated with lower likelihood of successful resuscitation. Real-time automated detection of chest compressions may improve CPR administration during resuscitation, and could facilitate application of next-generation ECG algorithms that employ different parameters depending on compression state. In contrast to accelerometer sensors, transthoracic impedance (TTI) is commonly acquired by defibrillators. We sought to develop and evaluate the performance of a TTI-based algorithm to automatically detect chest compressions.

METHODS

Five-second TTI segments were collected from patients with out-of-hospital cardiac arrest treated by one of four defibrillator models. Segments with and without chest compressions were collected prior to each of the first four defibrillation shocks (when available) from each case. Patients were divided randomly into 40% training and 60% validation groups. From the training segments, we identified spectral and time-domain features of the TTI associated with compressions. We used logistic regression to predict compression state from these features. Performance was measured by sensitivity and specificity in the validation set. The relationship between performance and TTI segment length was also evaluated.

RESULTS

The algorithm was trained using 1859 segments from 460 training patients. Validation sensitivity and specificity were >98% using 2727 segments from 691 validation patients. Validation performance was significantly reduced using segments shorter than 3.2 s.

CONCLUSIONS

A novel method can reliably detect the presence of chest compressions using TTI. These results suggest potential to provide real-time feedback in order to improve CPR performance or facilitate next-generation ECG rhythm algorithms during resuscitation.

Ventricular Fibrillation Waveform Analysis During Chest Compressions to Predict Survival From Cardiac Arrest

BACKGROUND

Quantitative measures of the ventricular fibrillation (VF) ECG waveform can assess myocardial physiology and predict cardiac arrest outcomes, making these measures a candidate to help guide resuscitation. Chest compressions are typically paused for waveform measure calculation because compressions cause ECG artifact. However, such pauses contradict resuscitation guideline recommendations to minimize cardiopulmonary resuscitation interruptions. We evaluated a comprehensive group of VF measures with and without ongoing compressions to determine their performance under both conditions for predicting functionally-intact survival, the study's primary outcome.

METHODS

Five-second VF ECG segments were collected with and without chest compressions before 2755 defibrillation shocks from 1151 out-of-hospital cardiac arrest patients. Twenty-four individual measures and 3 combination measures were implemented. Measures were optimized to predict functionally-intact survival (Cerebral Performance Category score ≤2) using 460 training cases, and their performance evaluated using 691 independent test cases.

RESULTS

Measures predicted functionally-intact survival on test data with an area under the receiver operating characteristic curve ranging from 0.56 to 0.75 (median, 0.73) without chest compressions and from 0.53 to 0.75 (median, 0.69) with compressions ( P<0.001 for difference). Of all measures evaluated, the support vector machine model ranked highest both without chest compressions (area under the receiver operating characteristic curve, 0.75; 95% CI, 0.73-0.78) and with compressions (area under the receiver operating characteristic curve, 0.75; 95% CI, 0.72-0.78; P=0.75 for difference).

CONCLUSIONS

VF waveform measures predict functionally-intact survival when calculated during chest compressions, but prognostic performance is generally reduced compared with compression-free analysis. However, support vector machine models exhibited similar performance with and without compressions while also achieving the highest area under the receiver operating characteristic curve. Such machine learning models may, therefore, offer means to guide resuscitation during uninterrupted cardiopulmonary resuscitation.

Ventricular fibrillation waveform measures combined with prior shock outcome predict defibrillation success during cardiopulmonary resuscitation

AIM

Amplitude Spectrum Area (AMSA) and Median Slope (MS) are ventricular fibrillation (VF) waveform measures that predict defibrillation shock success. Cardiopulmonary resuscitation (CPR) obscures electrocardiograms and must be paused for analysis. Studies suggest waveform measures better predict subsequent shock success when combined with prior shock success. We determined whether this relationship applies during CPR.

METHODS

AMSA and MS were calculated from 5-second pre-shock segments with and without CPR, and compared to logistic models combining each measure with prior return of organized rhythm (ROR).

RESULTS

VF segments from 692 patients were analyzed during CPR before 1372 shocks and without CPR before 1283 shocks. Combining waveform measures with prior ROR increased areas under receiver operating characteristic curves for AMSA/MS with CPR (0.66/0.68 to 0.73/0.74, p<0.001) and without CPR (0.71/0.72 to 0.76/0.76, p<0.001).

CONCLUSIONS

Prior ROR improves prediction of shock success during CPR, and may enable waveform measure calculation without chest compression pauses.

Ventricular fibrillation waveform measures and the etiology of cardiac arrest

BACKGROUND

Early determination of the acute etiology of cardiac arrest could help guide resuscitation or post-resuscitation care. In experimental studies, quantitative measures of the ventricular fibrillation waveform distinguish ischemic from non-ischemic etiology.

METHODS

We investigated whether waveform measures distinguished arrest etiology among adults treated by EMS for out-of-hospital ventricular fibrillation between January 1, 2006-December 31, 2014. Etiology was classified using hospital information into three exclusive groups: acute coronary syndrome (ACS) with ST elevation myocardial infarction (STEMI), ACS without ST elevation (non-STEMI), or non-ischemic arrest. Waveform measures included amplitude spectrum area (AMSA), centroid frequency (CF), mean frequency (MF), and median slope (MS) assessed during CPR-free epochs immediately prior to the initial and second shock. Waveform measures prior to the initial shock and the changes between first and second shock were compared by etiology group. We a priori chose a significance level of 0.01 due to multiple comparisons.

RESULTS

Of the 430 patients, 35% (n=150) were classified as STEMI, 29% (n=123) as non-STEMI, and 37% (n=157) with non-ischemic arrest. We did not observe differences by etiology in any of the waveform measures prior to shock 1 (Kruskal-Wallis Test) (p=0.28 for AMSA, p=0.07 for CF, p=0.63 for MF, and p=0.39 for MS). We also did not observe differences for change in waveform between shock 1 and 2, or when the two acute ischemia groups (STEMI and non-STEMI) were combined and compared to the non-ischemic group.

CONCLUSION

This clinical investigation suggests that waveform measures may not be useful in distinguishing cardiac arrest etiology.

Short ECG segments predict defibrillation outcome using quantitative waveform measures

AIM

Quantitative waveform measures of the ventricular fibrillation (VF) electrocardiogram (ECG) predict defibrillation outcome. Calculation requires an ECG epoch without chest compression artifact. However, pauses in CPR can adversely affect survival. Thus the potential use of waveform measures is limited by the need to pause CPR. We sought to characterize the relationship between the length of the CPR-free epoch and the ability to predict outcome.

METHODS

We conducted a retrospective investigation using the CPR-free ECG prior to first shock among out-of-hospital VF cardiac arrest patients in a large metropolitan region (n=442). Amplitude Spectrum Area (AMSA) and Median Slope (MS) were calculated using ECG epochs ranging from 5s to 0.2s. The relative ability of the measures to predict return of organized rhythm (ROR) and neurologically-intact survival was evaluated at different epoch lengths by calculating the area under the receiver operating characteristic curve (AUC) using the 5-s epoch as the referent group.

RESULTS

Compared to the 5-s epoch, AMSA performance declined significantly only after reducing epoch length to 0.2s for ROR (AUC 0.77-0.74, p=0.03) and with epochs of ≤0.6s for neurologically-intact survival (AUC 0.72-0.70, p=0.04). MS performance declined significantly with epochs of ≤0.8s for ROR (AUC 0.78-0.77, p=0.04) and with epochs ≤1.6s for neurologically-intact survival (AUC 0.72-0.71, p=0.04).

CONCLUSION

Waveform measures predict defibrillation outcome using very brief ECG epochs, a quality that may enable their use in current resuscitation algorithms designed to limit CPR interruption.

Pediatric Intubation by Paramedics in a Large Emergency Medical Services System: Process, Challenges, and Outcomes

STUDY OBJECTIVE

Pediatric intubation is a core paramedic skill in some emergency medical services (EMS) systems. The literature lacks a detailed examination of the challenges and subsequent adjustments made by paramedics when intubating children in the out-of-hospital setting. We undertake a descriptive evaluation of the process of out-of-hospital pediatric intubation, focusing on challenges, adjustments, and outcomes.

METHODS

We performed a retrospective analysis of EMS responses between 2006 and 2012 that involved attempted intubation of children younger than 13 years by paramedics in a large, metropolitan EMS system. We calculated the incidence rate of attempted pediatric intubation with EMS and county census data. To summarize the intubation process, we linked a detailed out-of-hospital airway registry with clinical records from EMS, hospital, or autopsy encounters for each child. The main outcome measures were procedural challenges, procedural success, complications, and patient disposition.

RESULTS

Paramedics attempted intubation in 299 cases during 6.3 years, with an incidence of 1 pediatric intubation per 2,198 EMS responses. Less than half of intubations (44%) were for patients in cardiac arrest. Two thirds of patients were intubated on the first attempt (66%), and overall success was 97%. The most prevalent challenge was body fluids obscuring the laryngeal view (33%). After a failed first intubation attempt, corrective actions taken by paramedics included changing equipment (33%), suctioning (32%), and repositioning the patient (27%). Six patients (2%) experienced peri-intubation cardiac arrest and 1 patient had an iatrogenic tracheal injury. No esophageal intubations were observed. Of patients transported to the hospital, 86% were admitted to intensive care and hospital mortality was 27%.

CONCLUSION

Pediatric intubation by paramedics was performed infrequently in this EMS system. Although overall intubation success was high, a detailed evaluation of the process of intubation revealed specific challenges and adjustments that can be anticipated by paramedics to improve first-pass success, potentially reduce complications, and ultimately improve clinical outcomes.

Does preexisting antiplatelet treatment influence postthrombolysis intracranial hemorrhage in community-treated ischemic stroke patients? An observational study

OBJECTIVES

Intracranial hemorrhage (ICH) after acute stroke thrombolysis is associated with poor outcomes. Previous investigations of the relationship between preexisting antiplatelet use and the safety of intravenous (IV) thrombolysis have been limited by low event rates. The objective of this study was to determine whether preexisting antiplatelet therapy increased the risk of ICH following acute stroke thrombolysis. The primary hypothesis was that antiplatelet use would not be associated with radiographic evidence of ICH after controlling for relevant confounders.

METHODS

Consecutive cases of thrombolysis patients treated in the emergency department (ED) were identified using multiple methods. Retrospective data were collected from four hospitals from 1996 to 2004 and 24 other hospitals from 2007 to 2010 as part of a cluster-randomized trial. The same chart abstraction tool was used during both time periods, and data were subjected to numerous quality control checks. Hemorrhages were classified using a prespecified methodology: ICH was defined as presence of hemorrhage in radiographic interpretations of follow-up imaging (primary outcome). Symptomatic ICH (sICH) was defined as radiographic ICH with associated clinical worsening. A multivariable logistic regression model was constructed to adjust for clinical factors previously identified to be related to postthrombolysis ICH. Sensitivity analyses were conducted where the unadjusted and adjusted results from this study were combined with those of previously published external studies on this topic via meta-analytic techniques.

RESULTS

There were 830 patients included, with 47% having documented preexisting antiplatelet treatment. The mean (± standard deviation [SD]) age was 69 (± 15) years, and the cohort was 53% male. The unadjusted proportion of patients with any ICH was 15.1% without antiplatelet use and 19.3% with antiplatelet use (absolute risk difference = 4.2%, 95% confidence interval [CI] = -1.2% to 9.6%); for sICH this was 6.1% without antiplatelet use and 9% with antiplatelet use (absolute risk difference = 3.1%, 95% CI = -1% to 6.7%). After adjusting for confounders, antiplatelet use was not significantly associated with radiographic ICH (odds ratio [OR] = 1.1, 95% CI = 0.8 to 1.7) or sICH (OR = 1.3, 95% CI = 0.7 to 2.2). In patients 81 years and older, there was a higher risk of radiographic ICH (absolute risk difference = 11.9%, 95% CI = 0.1% to 23.6%). The meta-analyses combined the findings of this investigation with previous similar work and found increased unadjusted risks of radiographic ICH (absolute risk difference = 4.9%, 95% CI = 0.7% to 9%) and sICH (absolute risk difference = 4%, 95% CI = 2.3% to 5.6%). The meta-analytic adjusted OR of sICH for antiplatelet use was 1.6 (95% CI = 1.1 to 2.4).

CONCLUSIONS

The authors did not find that preexisting antiplatelet use was associated with postthrombolysis ICH or sICH in this cohort of community treated patients. Preexisting tobacco use, younger age, and lower severity were associated with lower odds of sICH. The meta-analyses demonstrated small, but statistically significant increases in the absolute risk of radiographic ICH and sICH, along with increased odds of sICH in patients with preexisting antiplatelet use.

Abstract WMP64: Prehospital Triage To Comprehensive Stroke Centers: GCS Identifies Patients At Increased Risk For Death, ICH, Or SAH

INTRODUCTION: Regionalization of stroke care is occurring nationwide, but evidence-based criteria for prehospital triage to comprehensive stroke centers are lacking. We assessed the hypothesis that a prehospital clinical decision rule can identify a group of patients more likely to require comprehensive stroke services--those with an increased risk of in-hospital mortality, ICH, or SAH.

METHODS: This study represents a retrospective cohort of patients seen by an urban EMS system from 2000-2003. Subjects were included if they had either a prehospital diagnosis of “stroke/TIA” or a prehospital diagnosis of “decreased level of consciousness” or “headache” and signs and symptoms suggestive of a cerebrovascular event. The primary outcome was a composite of in-hospital mortality, ICH, or SAH. Multivariate logistic regression was used to derive a clinical prediction rule.

RESULTS: In 1682 subjects, the discharge diagnoses included TIA (n = 282, 17%), ischemic stroke (n = 433, 26%), ICH (n = 102, 6%), and SAH (n = 30, 2%). There were 221 patients (13%) who experienced the primary outcome: 67 (4%) with non-fatal ICH or SAH and 154 (9%) who died. Using GCS score alone, the area under ROC curve was 0.72, and GCS ≤ 10 resulted in a sensitivity of 0.48 (95%CI 0.42, 0.55) and specificity of 0.88 (95%CI 0.87, 0.90). A six-point prehospital stroke triage score (PSTS) was also derived: nausea/vomiting (1 point), systolic BP ≥ 175 (1 point), GCS 7-10 (2 points) and GCS 3-6 (4 points). The area under ROC curve for the PSTS was 0.74. Test characteristics for PSTS and GCS were similar (Table).

CONCLUSION: GCS alone performed similarly to a six-point clinical decision rule for the prehospital identification of patients at increased risk of death, ICH or SAH. GCS has potential utility as a criterion for the prehospital triage to comprehensive stroke centers.

Diagnostic characteristics of S100A8/A9 in a multicenter study of patients with acute right lower quadrant abdominal pain

OBJECTIVES

Over the past decade, clinicians have become increasingly reliant on computed tomography (CT) for the evaluation of patients with suspected acute appendicitis. To limit the radiation risks and costs of CT, investigators have searched for biomarkers to aid in diagnostic decision-making. We evaluated one such biomarker, calprotectin or S100A8/A9, and determined the diagnostic performance characteristics of a developmental biomarker assay in a multicenter investigation of patients presenting with acute right lower quadrant abdominal pain.

METHODS

This was a prospective, double-blinded, single-arm, multicenter investigation performed in 13 emergency departments (EDs) from August 2009 to April 2010 of patients presenting with acute right lower quadrant abdominal pain. Plasma samples were tested using the investigational S100A8/A9 assay. The primary outcome of acute appendicitis was determined by histopathology for patients undergoing appendectomy or 2-week telephone follow-up for patients discharged without surgery. The sensitivity, specificity, negative likelihood ratio (LR-), and positive likelihood ratio (LR+) of the biomarker assay were calculated using the prespecified cutoff value of 14 units. A post hoc stability study was performed to investigate the potential effect of time and courier transport on the measured value of the S100A8/A9 assay test results.

RESULTS

Of 1,052 enrolled patients, 848 met criteria for analysis. The median age was 24.5 years (interquartile range [IQR] = 16-38 years), 57% were female, and 50% were white. There was a 27.5% prevalence of acute appendicitis. The sensitivity and specificity for the investigational S100A8/A9 assay in diagnosing acute appendicitis were estimated to be 96% (95% confidence interval [CI] = 93% to 98%) and 16% (95% CI = 13% to 19%), respectively. The LR- ratio was 0.24 (95% CI = 0.12 to 0.47), and the LR+ was 1.14 (95% CI = 1.10 to 1.19). The post hoc stability study demonstrated that in the samples that were shipped, the estimated time coefficient was 7.6 × 10(-3) ± 2.0 × 10(-3) log units/hour, representing an average increase of 43% in the measured value over 48 hours; in the samples that were not shipped, the estimated time coefficient was 2.5 × 10(-3) ± 0.4 × 10(-3) log units/hour, representing a 13% increase on average in the measured value over 48 hours, which was the maximum delay allowed by the study protocol. Thus, adjusting the cutoff value of 14 units by the magnitude of systematic inflation observed in the stability study at 48 hours would result in a new cutoff value of 20 units and a "corrected" sensitivity and specificity of 91 and 28%, respectively.

CONCLUSIONS

In patients presenting with acute right lower quadrant abdominal pain, we found the investigational enzyme-linked immunosorbent assay (ELISA) test for S100A8/A9 to perform with high sensitivity but very limited specificity. We found that shipping effect and delay in analysis resulted in a subsequent rise in test values, thereby increasing the sensitivity and decreasing the specificity of the test. Further investigation with hospital-based laboratory analyzers is the next critical step for determining the ultimate clinical utility of the ELISA test for S100A8/A9 in ED patients presenting with acute right lower quadrant abdominal pain.

Phrenoesophageal ligament re-visited

The phrenoesophageal ligament, attaching the esophagus to the diaphragm, has been given little emphasis in anatomy teaching. This study was undertaken to examine the macroscopic and microscopic structure of the phrenoesophageal ligament. The results indicate that the ligament is a distinct structure bridging the space between the esophageal wall and the margins of the esophageal hiatus. This ligament appears to arise from both the endothoracic fascia and the transversalis fascia and is composed of abundant collagen and elastic lamellae. Toward the wall of the esophagus, the ligament divides into a prominent upper leaf and an ill-defined lower leaf before inserting into the wall of the esophagus. Histological study reveals that the ligament has a substantial and deep insertion into the wall of the esophagus. It appears that the ligament plays an important role in anchoring the lower esophagus and maintaining gastroesophageal competence.

Development of the ventilatory response to hypoxia in Swiss CD-1 mice

We examined developmental changes in breathing pattern and the ventilatory response to hypoxia (7.4% O(2)) in unanesthetized Swiss CD-1 mice ranging in age from postnatal day 0 to 42 (P(0)-P(42)) using head-out plethysmography. The breathing pattern of P(0) mice was unstable. Apneas were frequent at P(0) (occupying 29 +/- 6% of total time) but rare by P(3) (5 +/- 2% of total time). Tidal volume increased in proportion to body mass ( approximately 10-13 ml/kg), but increases in respiratory frequency (f) (55 +/- 7, 130 +/- 13, and 207 +/- 20 cycles/min for P(0), P(3), and P(42), respectively) were responsible for developmental increases in minute ventilation (690 +/- 90, 1,530 +/- 250, and 2,170 +/- 430 ml. min(-1). kg(-1) for P(0), P(3), and P(42), respectively). Between P(0) and P(3), increases in f were mediated by reductions in apnea and inspiratory and expiratory times; beyond P(3), increases were due to reductions in expiratory time. Mice of all ages showed a biphasic hypoxic ventilatory response, which differed in two respects from the response typical of most mammals. First, the initial hyperpnea, which was greatest in mature animals, decreased developmentally from a maximum, relative to control, of 2.58 +/- 0.29 in P(0) mice to 1. 32 +/- 0.09 in P(42) mice. Second, whereas ventilation typically falls to or below control in most neonatal mammals, ventilation remained elevated relative to control throughout the hypoxic exposure in P(0) (1.73 +/- 0.31), P(3) (1.64 +/- 0.29), and P(9) (1. 34 +/- 0.17) mice but not in P(19) or P(42) mice.

Preoperative staging of rectal cancer

With the widespread introduction of preoperative radiotherapy for rectal cancer and the development of transanal endoscopic microsurgery for selected early lesions, preoperative radiological staging of these tumours has taken on increasing importance. This study is a systematic review to evaluate computed tomography (CT), endorectal sonography (ES) and magnetic resonance imaging (MRI) as preoperative staging modalities in rectal cancer. A Medline-based search identifying studies using CT, ES, or MRI in preoperative staging of rectal cancer between 1980 and 1998 was undertaken. The list of papers was supplemented by extensive cross-checking of citation lists. Studies were included if they met predetermined criteria. Data from the accepted studies were entered into pooled tables comparing radiological and pathological staging results for each modality both in determining bowel wall penetration and involvement of lymph nodes. Accuracy, sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio and negative likelihood ratio were determined for the pooled results. Eighty-three studies from 78 papers including 4,897 patients met the inclusion criteria. In determining the wall penetration of the tumour the values for sensitivity for CT, ES, MRI and MRI with endorectal coil were 78%, 93%, 86% and 89%; for specificity 63%, 78%, 77% and 79%; and for accuracy 73%, 87%, 82% and 84%, respectively. In determining the nodal involvement by tumour the sensitivity values for CT, ES, MRI and MRI with endorectal coil 52%, 71%, 65% and 82%; for specificity 78%, 76%, 80% and 83%; and for accuracy 66%, 74%, 74% and 82%, respectively. MRI with an endorectal coil is the single investigation that most accurately predicts pathological stage in rectal cancer.

Some computer-based decision support tools for the rehabilitation manager

The recent introduction of the Management Information System (MIS) guidelines has sparked much interest among health care institutions across Canada regarding proper approaches to the recording and interpretation of various financial and workload indicators. While the benefits of the MIS guidelines are widely acknowledged, much less attention has been directed to how departmental managers can analyze and make use of the vast amount of information generated. In this paper we attempt to review some of the computer-based decision-support tools that may be useful to the manager of the rehabilitation services department in analyzing the various MIS data that are collected. The data are assumed to be available through a computerized rehabilitation information system which includes workload measures. The quantitative models reviewed in this paper include basic descriptive statistics, deviation, trend and what-if-analysis and graph-plotting. Although the use of such tools can assist the rehabilitation manager in the routine decision-making process, it is very important that we ask the right questions and employ the proper model to make the most rational and best decision. In this respect, ongoing training in general problem-solving skills, decision-making processes, and use of computer-based decision-support tools may be very beneficial.