Association of the COVID-19 Pandemic on Treatment Times for ST-Elevation Myocardial Infarction: Observations from the Los Angeles County Regional System

Previous studies have documented longer treatment times and worse outcomes for patients with ST-elevation myocardial infarction (STEMI) who underwent primary percutaneous coronary intervention (PCI) during the COVID-19 pandemic. The objective of the present study was to evaluate the impact of the COVID-19 pandemic on treatment times and outcomes for patients with STEMI who underwent primary PCI within a regional system of care. This was a retrospective study using data from the Los Angeles County Emergency Medical Services Agency. Data on the emergency medical service activations were abstracted for patients with STEMI from March 19, 2020 to January 31, 2021, during the COVID-19 pandemic and for the same interval the previous year. All adult patients (≥18 years) with STEMI who underwent emergent coronary angiography were included. The primary end point was the first medical contact (FMC) to device time. The secondary end points included treatment time intervals, vascular complications, need for emergent coronary artery bypass surgery, length of hospital stay, and in-hospital mortality. During the study period, 3,017 patients underwent coronary angiography for STEMI, 1,893 patients pre-COVID-19 and 1,124 patients during COVID-19 (40% lower). A total of 2,334 patients (77%) underwent PCI. During the COVID-19 period, rates of PCI were significantly lower compared with the control period (75.1% vs 78.7%, p = 0.02). FMC to device time was shorter during the COVID-19 period compared with the control period (median 77.0 vs 81.0 minutes, p = 0.004). For patients with STEMI complicated by out-of-hospital cardiac arrest, FMC to device time was similar during the COVID-19 period compared with the control period (median 95.0 [33.0] vs 100.0 [40.0] minutes, p = 0.34). Vascular complications, the need for emergent bypass surgery, length of hospital stay, and in-hospital mortality were similar between the periods. In conclusion, in this large regional system of care, we found a relatively small but significant decrease in treatment times, yet overall, similar clinical outcomes for patients with STEMI who underwent primary PCI and were treated during the COVID-19 period compared with a control period. These findings suggest that mature cardiac systems of care were able to maintain efficient care despite the challenges of the COVID-19 pandemic.

A Novel Algorithm for Improving the Prehospital Diagnostic Accuracy of ST-Segment Elevation Myocardial Infarction

INTRODUCTION

Early detection of ST-segment elevation myocardial infarction (STEMI) on the prehospital electrocardiogram (ECG) improves patient outcomes. Current software algorithms optimize sensitivity but have a high false-positive rate. The authors propose an algorithm to improve the specificity of STEMI diagnosis in the prehospital setting.

METHODS

A dataset of prehospital ECGs with verified outcomes was used to validate an algorithm to identify true and false-positive software interpretations of STEMI. Four criteria implicated in prior research to differentiate STEMI true positives were applied: heart rate <130, QRS <100, verification of ST-segment elevation, and absence of artifact. The test characteristics were calculated and regression analysis was used to examine the association between the number of criteria included and test characteristics.

RESULTS

There were 44,611 cases available. Of these, 1,193 were identified as STEMI by the software interpretation. Applying all four criteria had the highest positive likelihood ratio of 353 (95% CI, 201-595) and specificity of 99.96% (95% CI, 99.93-99.98), but the lowest sensitivity (14%; 95% CI, 11-17) and worst negative likelihood ratio (0.86; 95% CI, 0.84-0.89). There was a strong correlation between increased positive likelihood ratio (r2 = 0.90) and specificity (r2 = 0.85) with increasing number of criteria.

CONCLUSIONS

Prehospital ECGs with a high probability of true STEMI can be accurately identified using these four criteria: heart rate <130, QRS <100, verification of ST-segment elevation, and absence of artifact. Applying these criteria to prehospital ECGs with software interpretations of STEMI could decrease false-positive field activations, while also reducing the need to rely on transmission for physician over-read. This can have significant clinical and quality implications for Emergency Medical Services (EMS) systems.

The Correlation Between COVID-19 Hospitalizations and Emergency Medical Services Responses for Time-Sensitive Emergencies During the COVID-19 Pandemic

OBJECTIVE

COVID-19 has had significant secondary effects on health care systems, including effects on emergency medical services (EMS) responses for time-sensitive emergencies. We evaluated the correlation between COVID-19 hospitalizations and EMS responses for time-sensitive emergencies in a large EMS system.

METHODS

This was a retrospective study using data from the Los Angeles County EMS Agency. We abstracted data on EMS encounters for stroke, ST-elevation myocardial infarction (STEMI), out-of-hospital cardiac arrest (OHCA), and trauma from April 5, 2020 to March 6, 2021 and for the same time period in the preceding year. We also abstracted daily hospital admissions and censuses (total and intensive care unit [ICU]) for COVID-19 patients. We designated November 29, 2020 to February 27, 2021 as the period of surge. We calculated Spearman's correlations between the weekly averages of daily hospital admissions and census and EMS responses overall and for stroke, STEMI, OHCA, and trauma.

RESULTS

During the study period, there were 70,616 patients admitted for confirmed COVID-19, including 12,467 (17.7%) patients admitted to the ICU. EMS responded to 899,794 calls, including 9,944 (1.1%) responses for stroke, 3,325 (0.4%) for STEMI, 11,207 (1.2%) for OHCA, and 114,846 (12.8%) for trauma. There was a significant correlation between total hospital COVID-19 positive patient admissions and EMS responses for all time-sensitive emergencies, including a positive correlation with stroke (0.41), STEMI (0.37), OHCA (0.78), and overall EMS responses (0.37); and a negative correlation with EMS responses for trauma (-0.48). ICU COVID-19 positive patient admissions also correlated with increases in EMS responses for stroke (0.39), STEMI (0.39), and OHCA (0.81); and decreased for trauma (-0.53). Similar though slightly weaker correlations were found when evaluating inpatient census. During the period of surge, the correlation with overall EMS responses increased substantially (0.88) and was very strong with OHCA (0.95).

CONCLUSION

We found significant correlation between COVID-19 hospitalizations and the frequency of EMS responses for time-sensitive emergencies in this regional EMS system. EMS systems should consider the potential effects of this and future pandemics on EMS responses and prepare to meet non-pandemic resource needs during periods of surge, particularly for time-sensitive conditions.

Establishing a multicenter, preclinical consortium in resuscitation: A pilot experimental trial evaluating epinephrine in cardiac arrest

BACKGROUND

Large animal studies are an important step in the translation pathway, but single laboratory experiments do not replicate the variability in patient populations. Our objective was to demonstrate the feasibility of performing a multicenter, preclinical, randomized, double-blinded, placebo-controlled cardiac arrest trial. We evaluated the effect of epinephrine on coronary perfusion pressure (CPP) as previous single laboratory studies have reported mixed results.

METHODS

Forty-five swine from 5 different laboratories (Ann Arbor, MI; Baltimore, MD; Los Angeles, CA; Pittsburgh, PA; Toronto, ON) using a standard treatment protocol. Ventricular fibrillation was induced and left untreated for 6 min before starting continuous cardiopulmonary resuscitation (CPR). After 2 min of CPR, 9 animals from each lab were randomized to 1 of 3 interventions given over 12 minutes: (1) Continuous IV epinephrine infusion (0.00375 mg/kg/min) with placebo IV normal saline (NS) boluses every 4 min, (2) Continuous placebo IV NS infusion with IV epinephrine boluses (0.015 mg/kg) every 4 min or (3) Placebo IV NS for both infusion and boluses. The primary outcome was mean CPP during the 12 mins of drug therapy.

RESULTS

There were no significant differences in mean CPP between the three groups: 14.4 ± 6.8 mmHg (epinephrine Infusion), 16.9 ± 5.9 mmHg (epinephrine bolus), and 14.4 ± 5.5 mmHg (placebo) (p = NS). Sensitivity analysis demonstrated inter-laboratory variability in the magnitude of the treatment effect (p = 0.004).

CONCLUSION

This study demonstrated the feasibility of performing a multicenter, preclinical, randomized, double-blinded cardiac arrest trials. Standard dose epinephrine by bolus or continuous infusion did not increase coronary perfusion pressure during CPR when compared to placebo.

Elevated prehospital point-of-care glucose is associated with worse neurologic outcome after out-of-hospital cardiac arrest

Objectives

Hyperglycemia is associated with poor outcomes in critically-ill patients. This has implications for prognostication of patients with out-of-hospital cardiac arrest (OHCA) and for post-resuscitation care. We assessed the association of hyperglycemia, on field point-of-care (POC) testing, with survival and neurologic outcome in patients with return of spontaneous circulation (ROSC) after OHCA.

Methods

This was a retrospective analysis of data in a regional cardiac care system from April 2011 through December 2017 of adult patients with OHCA and ROSC who had a field POC glucose. Patients were excluded if they were hypoglycemic (glucose <60 mg/dl) or received empiric dextrose. We compared hyperglycemic (glucose >250 mg/dL) with euglycemic (glucose 60–250 mg/dL) patients. Primary outcome was survival to hospital discharge (SHD). Secondary outcome was survival with good neurologic outcome (cerebral performance category 1 or 2 at discharge). We determined the adjusted odds ratios (AORs) for SHD and survival with good neurologic outcome.

Results

Of 9008 patients with OHCA and ROSC, 6995 patients were included; 1941 (28%) were hyperglycemic and 5054 (72%) were euglycemic. Hyperglycemic patients were more likely to be female, of non-White race, and have an initial non-shockable rhythm compared to euglycemic patients (p < 0.0001 for all). Hyperglycemic patients were less likely to have SHD compared to euglycemic survivors, 24.4% vs 32.9%, risk difference (RD) −8.5% (95 %CI −10.8%, −6.2%), p < 0.0001. Hyperglycemic survivors were also less likely to have good neurologic outcome compared to euglycemic survivors, 57.0% vs 64.6%, RD −7.6% (95 %CI −12.9%, −2.4%), p = 0.004. The AOR for SHD was 0.72 (95 %CI 0.62, 0.85), p < 0.0001 and for good neurologic outcome, 0.70 (95 %CI 0.57, 0.86), p = 0.0005.

Conclusion

In patients with OHCA, hyperglycemia on field POC glucose was associated with lower survival and worse neurologic outcome.

Prehospital Predictors of Atypical STEMI Symptoms

Introduction: Rapid prehospital identification of patients with ST-elevation myocardial infarction (STEMI) is a critical step to reduce time to treatment. Broad screening with field 12-lead ECGs can lead to a high rate of false positive STEMI activations due to low prevalence. One strategy to reduce false positive STEMI interpretations is to limit acquisition of 12-lead ECGs to patients who have symptoms strongly suggestive of STEMI, but this may delay care in patients who present atypically and lead to disparities in populations with more atypical presentations. We sought to assess patient factors associated with atypical STEMI presentation.Methods: We retrospectively analyzed consecutive adult patients for whom Los Angeles Fire Department paramedics obtained a field 12-lead ECG from July 2011 through June 2012. The regional STEMI receiving center registry was used to identify patients with STEMI. Patients were designated as having typical symptoms if paramedics documented provider impressions of chest pain/discomfort, cardiac arrest, or cardiac symptoms, otherwise they were designated as having atypical symptoms. We utilized logistic regression to determine patient factors (age, sex, race) associated with atypical STEMI presentation.Results: Of the 586 patients who had STEMI, 70% were male, 43% White, 16% Black, 20% Hispanic, 5% Asian and 16% were other or unspecified race. Twenty percent of STEMI patients (n = 117) had atypical symptoms. Women who had STEMI were older than men (74 years [IQR 62-83] vs. 60 years [IQR 53-70], p < 0.001). Univariate predictors of atypical symptoms were older age and female sex (p < 0.0001), while in multivariable analysis older age [odd ratio (OR) 1.05 per year, [95%CI 1.04-1.07, p < 0.0001] and black race (OR vs White 2.18, [95%CI 1.20-3.97], p = 0.011) were associated with atypical presentation.Conclusion: Limiting prehospital acquisition of 12-lead ECGs to patients with typical STEMI symptoms would result in one in five patients with STEMI having delayed recognition, disproportionally impacting patients of older age, women, and Black patients. Age, not sex, may be a better predictor of atypical STEMI presentation.

Variation in Post-Cardiac Arrest Care Within a Regional EMS System

Objective: Within Emergency Medical Systems (EMS) regional systems, there may be significant differences in the approach to patient care despite efforts to promote standardization. Identifying hospital-level factors that contribute to variations in care can provide opportunities to improve patient outcomes. The purpose of this analysis was to evaluate variation in post-cardiac arrest care within a large EMS system and explore the contribution of hospital-level factors.Methods: This was a retrospective analysis from a regional cardiac system serving over 10 million persons. Patients with out-of-hospital cardiac arrest (OHCA) with return of spontaneous circulation (ROSC) are transported to 36 cardiac arrest centers with 24/7 emergent coronary angiography (CAG) capabilities and targeted temperature management (TTM) policies based on regional guidelines. We included adult patients ≥18 years with non-traumatic OHCA from 2016-2018. Patients with a Do-Not-Resuscitate order and those who died in the emergency department (ED) were excluded. For the TTM analysis, we also excluded patients who were alert in the ED. The primary outcome was receiving CAG or TTM after cardiac arrest. The secondary outcome was neurologic recovery (dichotomized to define a "good" outcome as cerebral performance category (CPC) 1 or 2). We used generalized estimating equations including patient-level factors (age, sex, witnessed arrest, initial rhythm) and hospital-level factors (academic status, hospital size based on licensed beds, annual OHCA patient volume) to estimate the odds ratios associated with these variables.Results: There were 7831 patients with OHCA during the study period; 4694 were analyzed for CAG and 3903 for TTM. The median and range for treatment with CAG and TTM after OHCA was 23% (12-49%) and 58% (17-92%) respectively. Hospital size was associated with increased likelihood of CAG, adjusted odds ratio 1.71, 95% CI 1.05-2.86, p = 0.03. Academic status approached significance in its association with TTM, adjusted odds ratio 1.69, 95% CI 0.98-2.91, p = 0.06. Overall, 28% of patients survived with good neurologic outcome, ranging from 17 to 43% across hospitals.Conclusion: Within this regional cardiac system, there was significant variation in use of CAG and TTM after OHCA, which was not fully explained by patient-level factors. Hospital size was associated with increased CAG.

Emergency Medical Services Responses to Out-of-Hospital Cardiac Arrest and Suspected ST-Segment-Elevation Myocardial Infarction During the COVID-19 Pandemic in Los Angeles County

Background Public health emergencies may significantly impact emergency medical services responses to cardiovascular emergencies. We compared emergency medical services responses to out-of-hospital cardiac arrest (OHCA) and ST-segment‒elevation myocardial infarction (STEMI) during the 2020 COVID-19 pandemic to 2018 to 2019 and evaluated the impact of California's March 19, 2020 stay-at-home order. Methods and Results We conducted a population-based cross-sectional study using Los Angeles County emergency medical services registry data for adult patients with paramedic provider impression (PI) of OHCA or STEMI from February through May in 2018 to 2020. After March 19, 2020, weekly counts for PI-OHCA were higher (173 versus 135; incidence rate ratios, 1.28; 95% CI, 1.19‒1.37; P<0.001) while PI-STEMI were lower (57 versus 65; incidence rate ratios, 0.87; 95% CI, 0.78‒0.97; P=0.02) compared with 2018 and 2019. After adjusting for seasonal variation in PI-OHCA and decreased PI-STEMI, the increase in PI-OHCA observed after March 19, 2020 remained significant (P=0.02). The proportion of PI-OHCA who received defibrillation (16% versus 23%; risk difference [RD], -6.91%; 95% CI, -9.55% to -4.26%; P<0.001) and had return of spontaneous circulation (17% versus 29%; RD, -11.98%; 95% CI, -14.76% to -9.18%; P<0.001) were lower after March 19 in 2020 compared with 2018 and 2019. There was also a significant increase in dead on arrival emergency medical services responses in 2020 compared with 2018 and 2019, starting around the time of the stay-at-home order (P<0.001). Conclusions Paramedics in Los Angeles County, CA responded to increased PI-OHCA and decreased PI-STEMI following the stay-at-home order. The increased PI-OHCA was not fully explained by the reduction in PI-STEMI. Field defibrillation and return of spontaneous circulation were lower. It is critical that public health messaging stress that emergency care should not be delayed.

Mastering Electrocardiogram Interpretation Skills Through a Perceptual and Adaptive Learning Module

Although accurate interpretation of the standard 12-lead electrocardiogram (ECG) is fundamental to diagnosing heart disease, several prior studies report low accuracy rates among medical students, residents, and practicing physicians. The objective of this study was to determine if an online ECG Perceptual and Adaptive Learning Module (ECG PALM) is an efficient instrument to teach ECG interpretation. The ECG PALM consists of 415 unique ECG tracings with associated pretest, posttest, and delayed tests, each using 30 additional ECGs to gauge the effectiveness and durability of training. Between 2013 and 2015, a total of 113 third-year and 156 fourth-year medical students and 34 first-year, 41 second-year, and 37 third-year emergency medicine residents completed the PALM and associated tests. We measured two mastery criteria: accuracy, the percentage of correct interpretations, and fluency, the percentage of images interpreted accurately within 15 seconds. The ECG PALM produced statistically significant improvements (0.0001 < p < 0.0045) in student and resident performance for both accuracy (effect size = 0.9 to 3.2) and fluency (effect size = 2.5 to 3.1) following training ranging from 46 ± 24 minutes (R3s) to 88 ± 32 minutes (third-year medical students). Medical students and residents performed significantly better on a test the year following training (delayed test) than those without prior ECG PALM training (pretest). The fluency of R3 residents in classifying the 15 diagnostic categories was less than 60% for nine of the 15 diagnoses and greater than 80% for only one. Following PALM training, fluency was higher than 80% for seven of the 15 categories and less than 60% for only two categories. Accuracy in recognizing ST-elevation myocardial infarctions (STEMIs) was high both before and after PALM training for R3s, but fluency was only 64% for anterior STEMIs on the pretest, increasing to 93% following PALM training. These observations suggest that the ECG PALM is an effective and durable supplemental tool for developing mastery in interpreting common ECG abnormalities.

Implementation of Targeted Temperature Management After Out-of-Hospital Cardiac Arrest: Observations From the Los Angeles County Regional System

Background

Despite the benefits of targeted temperature management (TTM) for out‐of‐hospital cardiac arrest), implementation within the United States remains low. The objective of this study was to evaluate the prevalence and factors associated with TTM use in a large, urban‐suburban regional system of care.

Methods and Results

This was a retrospective analysis from the Los Angeles County regional cardiac system of care serving a population of >10 million residents. All adult patients aged ≥18 years with non‐traumatic out‐of‐hospital cardiac arrest transported to a cardiac arrest center from April 2011 to August 2017 were included. Patients awake and alert in the emergency department and patients who died in the emergency department before consideration for TTM were excluded. The primary outcome measure was prevalence of TTM use. The secondary analysis were annual trends in TTM use over the study period and factors associated with TTM use. The study population included 8072 patients; 4154 patients (51.5%) received TTM and 3767 patients (46.7%) did not receive TTM. Median age was 67 years, 4780 patients (59.2%) were men, 4645 patients (57.5%) were non‐White, and the most common arrest location was personal residence in 4841 patients (60.0%). In the adjusted analysis, younger age, male sex, an initial shockable rhythm, witnessed arrest, and receiving coronary angiography were associated with receiving TTM.

Conclusions

Within this regional system of care, use of TTM was higher than previously reported in the literature at just over 50%. Use of integrated systems of care may be a novel method to increase TTM use within the United States.

Regional "Call 911" Emergency Department Protocol to Reduce Interfacility Transfer Delay for Patients With ST-Segment-Elevation Myocardial Infarction

BACKGROUND

We evaluated the first-medical-contact-to-balloon (FMC2B) time after implementation of a "Call 911" protocol for ST-segment-elevation myocardial infarction (STEMI) interfacility transfers in a regional system.

METHODS AND RESULTS

This is a retrospective cohort study of consecutive patients with STEMI requiring interfacility transfer from a STEMI referring hospital, to one of 35 percutaneous coronary intervention-capable STEMI receiving centers (SRCs). The Call 911 protocol allows the referring physician to activate 911 to transport a patient with STEMI to the nearest SRC for primary percutaneous coronary intervention. Patients with interfacility transfers were identified over a 4-year period (2011-2014) from a registry to which SRCs report treatment and outcomes for all patients with STEMI transported via 911. The primary outcomes were median FMC2B time and the proportion of patients achieving the 120-minute goal. FMC2B for primary 911 transports were calculated to serve as a system reference. There were 2471 patients with STEMI transferred to SRCs by 911 transport during the study period, of whom 1942 (79%) had emergent coronary angiography and 1410 (73%) received percutaneous coronary intervention. The median age was 61 years (interquartile range [IQR] 52-71) and 73% were men. The median FMC2B time was 111 minutes (IQR 88-153) with 56% of patients meeting the 120-minute goal. The median STEMI referring hospital door-in-door-out time was 53 minutes (IQR 37-89), emergency medical services transport time was 9 minutes (IQR 7-12), and SRC door-to-balloon time was 44 minutes (IQR 32-60). For primary 911 patients (N=4827), the median FMC2B time was 81 minutes (IQR 67-97).

CONCLUSIONS

Using a Call 911 protocol in this regional cardiac care system, patients with STEMI requiring interfacility transfers had a median FMC2B time of 111 minutes, with 56% meeting the 120-minute goal.

Outcomes of ST Elevation Myocardial Infarction Complicated by Out-of-Hospital Cardiac Arrest (from the Los Angeles County Regional System)

The objective of this study was to evaluate the time to primary percutaneous coronary intervention (PCI) and the outcome for patients with ST elevation myocardial infarction (STEMI) complicated by out-of-hospital cardiac arrest (OHCA). In this regional system, all patients with STEMI and/or OHCA with return of spontaneous circulation were transported to STEMI Receiving Centers. The outcomes registry was queried for patients with STEMI with underwent primary PCI from April 2011 to December 2014. Patients with STEMI complicated by OHCA were compared with a reference group of STEMI without OHCA. The primary end point was the first medical contact-to-device time. Of 4,729 patients with STEMI who underwent primary PCI, 422 patients (9%) suffered OHCA. Patients with OHCA were on average 2 years (95% confidence interval 0.7 to 3.0) older and had a slightly higher male predominance. The first medical contact-to-device time was longer in STEMI with OHCA compared with STEMI alone (94 ± 37 vs. 86 ± 34 minutes, p < 0.0001). In-hospital mortality was higher after OHCA, 38% versus 6% in STEMI alone, odds ratio 6.3 (95% confidence interval 5.3 to 7.4). Among OHCA survivors, 193 (73%) were discharged with a cerebral performance category score of 1 or 2. In conclusion, despite longer treatment intervals, neurologic outcome was good in nearly half of the surviving patients with STEMI complicated by OHCA, suggesting that these patients can be effectively treated with primary PCI in a regionalized system of care.

Sex Differences in Survival From Out-of-Hospital Cardiac Arrest in the Era of Regionalized Systems and Advanced Post-Resuscitation Care

BACKGROUND

The purpose of this study was to evaluate sex differences in out-of-hospital cardiac arrest (OHCA) characteristics, interventions, and outcomes.

METHODS AND RESULTS

This is a retrospective analysis from a regionalized cardiac arrest system. Data on patients treated for OHCA are reported to a single registry, from which all adult patients were identified from 2011 through 2014. Characteristics, treatment, and outcomes were evaluated with stratification by sex. The adjusted odds ratio (OR) for survival with good neurological outcome (cerebral performance category 1 or 2) was calculated for women compared to men. There were 5174 out-of-hospital cardiac arrests (OHCAs; 3080 males and 2094 females). Women were older, median 71 (interquartile range [IQR], 59-82) versus 66 years (IQR, 55-78). Despite similar frequency of witnessed arrest, women were less likely to present with a shockable rhythm (22% vs 35%; risk difference [RD], 13%; 95% CI, 11-15), have ST-segment elevation myocardial infarction (23% vs 32%; RD, 13%; 95% CI, 7-11), or receive coronary angiography (11% vs 25%; RD, 14%; 95% CI, 12-16), percutaneous coronary intervention (5% vs 14%; RD, 9%; 95% CI, 7-11), or targeted temperature management (33% vs 40%; RD, 7%; 95% CI, 4-10). Women had decreased survival to discharge (33% vs 40%; RD, 7%; 95% CI, 4-10) and a lower proportion of good neurological outcome (16% vs 24%; RD, 8%; 95% CI, 6-10). In multivariable modeling, female sex was not associated with decreased survival with good neurological outcome (OR, 0.9; 95% CI, 0.8-1.1).

CONCLUSIONS

Sex-related differences in OHCA characteristics and treatment are predictors of survival outcome disparities. With adjustment for these factors, sex was not associated with survival or neurological outcome after OHCA.

High Serum Tumor Necrosis Factor Levels in the Early Post-Cardiac Arrest Period Are Associated with Poor Short-Term Survival in a Swine Model of Ventricular Fibrillation

Most resuscitated victims of out-of-hospital cardiac arrest who survive to hospital expire due to the postresuscitation syndrome. This syndrome is characterized by a sepsis-like proinflammatory state. The objective of this investigation was to determine whether a relationship exists between the rise of tumor necrosis factor (TNF), a proinflammatory cytokine, following return of spontaneous circulation (ROSC), and early postarrest survival in a clinically relevant animal model of spontaneous ventricular fibrillation (VF). Mixed-breed Yorkshire swine (n = 20), weighing 39 ± 5 kg, were anesthetized and catheters placed in the right atrium and left ventricle/ascending aorta for continuous pressure monitoring. VF was induced by occluding the left anterior descending coronary artery with an angioplasty balloon. After 7 min of untreated VF, advanced life support resuscitation attempts were made for up to 20 min. Animals achieving ROSC were monitored for 3 h and fluid and pressor support was administered as needed. TNF levels were measured before VF and at 0, 15, and 30 min after ROSC using quantitative sandwich enzyme-linked immunosorbent assay. Twelve (60%) animals experienced early death, expiring during the 3 hour postarrest period (9 pulseless electrical activity, 2 VF, and 1 asystole). The TNF level at 15 min post-ROSC was significantly associated with death within the first 3 h post-ROSC with a univariate odds ratio of 1.4 [95% confidence interval (CI) 1.05-2.2, P = 0.01]. Using a cutoff TNF level of 525 pg/mL at 15 min post-ROSC had 100% negative predictive value (95% CI 0%-37%) and 67% positive predictive value (95% CI 35%-90%) for early death with a hazard ratio of 6.6 (95% CI 1.9-23.5). TNF increases shortly after ROSC and is predictive of early death. Early identification of resuscitated victims at greatest risk for hemodynamic collapse and recurrent arrest might facilitate the use of early hospital-based interventions to decrease the likelihood of a poor outcome.

Predictors of neurologic outcome in patients resuscitated from out-of-hospital cardiac arrest using classification and regression tree analysis

The estimated survival rate of 8% to 10% after out-of-hospital cardiac arrest (OHCA) remains dismal. Few studies have addressed predictors of functional neurologic outcome after successful resuscitation. The objective of the study was to identify variables associated with favorable neurologic outcomes, defined by a Glasgow Coma Scale of 14 or 15, after OHCA. We used a propensity analysis and classification and regression tree model of 184 OHCA patients surviving to hospital admission at a cardiac arrest receiving center in Los Angeles County from 2008 to 2013. Forty-three patients (23%) had a favorable outcome, median age was 65 years (interquartile range [IQR] 54 to 76), and 98 (53%) were men. Sixty-six patients (36%) presented with a shockable rhythm. The majority were witnessed, either by a civilian (n=115, 63%) or a paramedic (n=25, 14%). Bystander cardiopulmonary resuscitation was performed on 84 patients (46%); median dose of epinephrine was 2 mg (IQR 1 to 3). Median time to return of spontaneous circulation was 21 minutes (IQR 16 to 29); the median lactate level was 5.2 mmol/L (IQR 2.8 to 9.2). Lower epinephrine doses (<1.5 mg) and lactate levels<5 mmol/L were predictive of a normal Glasgow Coma Scale, with 90.7% sensitivity (95% confidence interval [CI] 76.9% to 96.9%), 47.5% specificity (95% CI 39.1% to 56.1%), a positive predictive value of 34.5% (95% CI 31.6% to 46.1%), a negative predictive value of 94.4% (95% CI 85.5% to 98.2%), and an area under the curve of 0.89. The propensity score-adjusted logistic regression model demonstrated that receiving <1.5 mg of epinephrine was associated with a favorable neurologic outcome (odds ratio 3.3, 95% CI 1.1 to 10, p=0.04). In conclusion, for patients surviving to hospital admission, a good neurologic outcome was associated with having received <1.5 mg of epinephrine and a lactate level<5 mmol/L.

Administration of amiodarone during resuscitation is associated with higher tumor necrosis factor-α levels in the early postarrest period in the swine model of ischemic ventricular fibrillation

To compare the early postarrest inflammatory cytokine response between animals administered amiodarone (AMIO) and lidocaine (LIDO) intra-arrest during resuscitation from ventricular fibrillation (VF). Domestic swine (n=32) were placed under general anesthesia and instrumented before spontaneous VF was induced by balloon occlusion of the left anterior descending coronary artery. After 7 min of VF, standard ACLS resuscitation was performed and animals were randomized to either bolus AMIO (5 mg/kg, n=13) or LIDO (1 mg/kg, n=14) for recurrent or refractory VF. A non-antiarrhythmic (n=5) was also used for comparison. Following return of spontaneous circulation (ROSC), tumor necrosis factor (TNF)-α levels were drawn at 30 and 60 min. Groups were comparable with respect to prearrest hemodynamics and resuscitation variables. In the postarrest period, the LIDO and non-antiarrhythmic group demonstrated virtually identical TNF-α response trajectories. However, TNF-α levels were significantly higher in AMIO- than LIDO-treated animals at 30 min (geometric mean 539 versus 240 pg/mL, 2.2-fold higher, 95% confidence interval [CI] 1.3-3.8-fold higher, P=0.003) and at 60 min (geometric mean 570 versus 204 pg/mL, 2.8-fold higher, 95% CI 1.1-7.0-fold higher, P=0.03). Significant differences in the postarrest TNF-α levels were observed between animals treated with AMIO as compared to those treated with LIDO. Improved rates of ROSC seen with AMIO may come at the expense of a heightened proinflammatory state in the postcardiac arrest period.

A comparison of etanercept vs. infliximab for the treatment of post-arrest myocardial dysfunction in a swine model of ventricular fibrillation

AIMS

To compare the effects of two TNF-α antagonists, etanercept and infliximab, on post-cardiac arrest hemodynamics and global left ventricular function (LV) in a swine model following ventricular fibrillation (VF).

METHODS

Domestic swine (n=30) were placed under general anesthesia and instrumented before VF was induced electrically. After 7 min of VF, standard ACLS resuscitation was performed. Animals achieving return of spontaneous circulation (ROSC) were randomized to immediately receive infliximab (5 mg/kg, n=10) or etanercept (0.3 mg/kg [4 mg/m(2)], n=10) or vehicle (250 mL normal saline [NS], n=10) and LV function and hemodynamics were monitored for 3 h.

RESULTS

Following ROSC, mean arterial pressure (MAP), stroke work (SW), and LV dP/dt fell from pre-arrest values in all groups. However, at the 30 min nadir, infliximab-treated animals had higher MAP than either the NS group (difference 14.4 mm Hg, 95% confidence interval [CI] 4.2-24.7) or the etanercept group (19.2 mm Hg, 95% CI 9.0-29.5), higher SW than the NS group (10.3 gm-m, 95% CI 5.1-15.5) or the etanercept group (8.9 gm-m, 95% CI 4.0-14.4) and greater LV dP/dt than the NS group (282.9 mm Hg/s, 95% CI 169.6-386.1 higher with infliximab) or the etanercep group (228.9 mm Hg/s, 95% CI 115.6-342.2 higher with infliximab).

CONCLUSIONS

Only infliximab demonstrated a beneficial effect on post cardiac arrest hemodynamics and LV function in this swine model. Etanercept was no better in this regard than saline.

Coronary imaging and intervention during cardiovascular collapse: use of the LUCAS mechanical CPR device in the cardiac catheterization laboratory

The management of cardiac arrest during coronary angiography and intervention presents substantial challenges. Patients presenting with ST-segment elevation myocardial infarction or following resuscitation from cardiac arrest are at greatest risk and may represent a significant portion of patients in some centers. Timely and effective cardiopulmonary resuscitation (CPR), with manual chest compressions is the primary mode of support though novel circulatory assist devices may have some role. To this end, the use of mechanical compression devices provides multiple patient- and provider-level benefits. This series provides a description of the use of the LUCAS mechanical CPR device and examples of coronary imaging and intervention during mechanical CPR.

Endothelin-1 attenuates the hemodynamic response to exogenous epinephrine in a porcine ischemic ventricular fibrillation cardiac arrest model

Endothelin-1 (ET-1) increases in the ischemically induced ventricular fibrillation (VF) swine model of cardiac arrest and affects outcome by potentially attenuating the hemodynamic response to epinephrine. Fifty-one swine underwent percutaneous left anterior descending occlusion. Seven minutes postonset of ischemic VF, cardiopulmonary resuscitation (CPR) was initiated. If VF persisted after 3 shocks, 1 mg of epinephrine was given. ET-1 (collected at baseline and every 5 min until VF onset) was assayed with ELISA. Bayesian multivariate logistic regression analysis compared peak ET-1 levels with the binary outcome of a positive coronary perfusion pressure response of >20 mmHg following epinephrine. Sixteen animals (31%) failed to achieve a positive response. Restoration of spontaneous circulation (ROSC) was observed in 1/16 (6.3%) of epinephrine nonresponders and 20/35 (57.1%) of epinephrine responders (P = 0.0006). The median peak ET-1 level was 2.71 pg/mL [interquartile range (IQR) 1.06-4.40] in nonresponders and 1.69 pg/mL (IQR 0.99-2.35) in responders. ET-1 levels were inversely associated with epinephrine response with a median posterior odds ratio (OR) of a coronary perfusion pressure response of 0.72 (95% confidence interval [CI] 0.48-1.06) for each one-unit increase in ET-1 and a probability that the associated OR is <1 of 0.95. Peak ET-1 levels predict a lack of a hemodynamic response to epinephrine during treatment of cardiac arrest during ischemic VF.

Out-of-hospital cardiac arrest: early in-hospital hypotension versus out-of-hospital factors in predicting in-hospital mortality among those surviving to hospital admission

OBJECTIVE

The purpose of this study was to determine the prevalence of in-hospital hypotension in patients surviving to admission after resuscitation from out-of-hospital cardiac arrest and compare it to that of traditional Utstein factors in predicting in-hospital mortality.

METHODS

Single-center retrospective cohort of adult patients surviving to hospital admission after resuscitation from out-of-hospital sudden death between January 1, 2006 and October 31, 2009. Study variables included Utstein template data: age, sex, initial rhythm, witnessed or nonwitnessed arrest, presence or absence of bystander CPR, location of arrest, response time (time of 9-1-1 dispatch to first vehicle arrival), and hypotension (systolic pressure<90 or mean arterial pressure<60) within 24h of ROSC. Univariate comparisons of categorical variables were performed and the Wilcoxon rank-sum test was used to compare continuous variables. Multivariable logistic regression was then performed after inclusion of Utstein variables.

RESULTS

73 patients met the inclusion criteria, and in-hospital mortality occurred in 54 (74%). On univariate analysis, in-hospital hypotension (OR=3.5, 95%CI 1.1-10.0, p=0.02), pre-hospital rhythm other than VF/VT (OR 4.3, 95%CI 1.4-13.3, p=0.008), and an unwitnessed arrest (OR=6.9, 95%CI 0.8-56.5, p=0.04), were significant predictors of in-hospital mortality. On multivariable analysis, in-hospital hypotension (OR=9.8, 95%CI 1.5, 63.0, p=0.02), pre-hospital rhythm other than VT/VF (OR=8.5, 95%CI 1.3-58.8, p=0.03), and lack of bystander CPR (OR=13.2, 95%CI 1.6-111, p=0.02) remained statistically significant predictors of in-hospital mortality.

CONCLUSIONS

In-hospital hypotension was predictive of mortality, as was a pre-hospital nonshockable rhythm and lack of bystander CPR. In contrast, traditional pre-hospital risk factors: age, gender, public location of arrest, response time, and witnessed arrest, were not predictive.

Does early postresuscitation stress hyperglycemia affect 72-hour neurologic outcome? Preliminary observations in the Swine model

BACKGROUND

Hyperglycemia is common in the early period following resuscitation from cardiac arrest and has been shown to be a predictor of neurologic outcome in retrospective studies.

OBJECTIVE

To evaluate neurologic outcome and early postarrest hyperglycemia in a swine cardiac arrest model.

METHODS

Electrically induced ventricular fibrillation cardiac arrest was induced in 22 anesthetized and instrumented swine. After 7 minutes, cardiopulmonary resuscitation (CPR) and Advanced Cardiac Life Support were initiated. Twenty-one animals were resuscitated and plasma glucose concentration was measured at intervals for 60 minutes after resuscitation. The animals were observed for 72 hours and the neurologic score was determined at 24-hour intervals.

RESULTS

Ten animals had a peak plasma glucose value ≥ 226 mg/dL during the initial 60 minutes after resuscitation. The neurologic scores at 72 hours in these animals (mean score = 0, mean overall cerebral performance category = 1) were the same as those in the animals with a peak plasma glucose value <226 mg/dL. The end-tidal carbon dioxide (CO(2)) values measured during CPR, times to restoration of spontaneous circulation, and epinephrine doses were not significantly different between the animals with a peak glucose concentration ≥ 226 mg/dL and those with lower values. The sample size afforded a power of 95% to detect a 50-point difference from the lowest score (0 points) of the porcine neurologic outcome scale.

CONCLUSION

In this standard porcine model of witnessed out-of-hospital cardiac arrest, early postresuscitation stress hyperglycemia did not appear to affect neurologic outcome. During the prehospital phase of treatment and transport, treatment of hyperglycemia by emergency medical services providers may not be warranted.

Markers of progenitor cell recruitment and differentiation rise early during ischemia and continue during resuscitation in a porcine acute ischemia model

Clinical administration of bone marrow-derived stem cells in the setting of acute myocardial infarction (AMI) leads to improved left ventricular ejection fraction. Thymosin beta-4 (TB4) and vascular endothelial growth factor (VEGF) are linked to adult epicardial progenitor cell mobilization and neovascularization and is cardioprotective after myocardial ischemia. This study investigated the time course of TB4 and VEGF during AMI, cardiac arrest, and resuscitation. Fifteen anesthetized and instrumented domestic swine underwent balloon occlusion of the proximal left anterior descending coronary artery. During occlusion, venous blood samples were collected from the right atrium at 5-min intervals until 15 min after the onset of cardiopulmonary resuscitation (CPR). Plasma levels of TB4, VEGF, and matrix metalloproteinase-9 (MMP-9, selected as a marker for remodeling and repair) were measured by ELISA. Generalized linear mixed models were employed to model the time-dependent change in plasma concentration. All variables were natural log transformed, except TB4 values, to normalize distributions. Fifteen animals successfully underwent balloon occlusion of the left anterior descending coronary artery and samples were collected from these subjects. The average onset of spontaneous ventricular fibrillation was 28 min. TB4, VEGF, and MMP-9 demonstrated a statistically significant, time-dependent increase in concentration during ischemia. Following arrest and throughout the first 15 min of resuscitation, MMP-9 had an unchanged rate of rise when compared with the prearrest, ischemic period, with VEGF showing a deceleration in its time-dependent concentration trajectory and TB4 demonstrating an acceleration. Endogenous TB4 and VEGF increase shortly after the onset of AMI and increase through cardiac arrest and resuscitation in parallel to remodeling proteases. These markers continue to rise during successful resuscitation and may represent an endogenous mechanism to recruit undifferentiated stem cells to areas of myocardial injury.

Does prearrest adrenergic integrity affect pressor response? A comparison of epinephrine and vasopressin in a spontaneous ventricular fibrillation swine model

OBJECTIVES

Coronary perfusion pressure (CPP) during resuscitation from cardiac arrest has been shown to correlate with return of spontaneous circulation. Adrenergic blockade of beta-1 and alpha-1 receptors is common in the long-term management of ischemic heart disease and congestive heart failure. We sought to compare the CPP response to vasopressin vs. epinephrine in a swine model of cardiac arrest following pre-arrest adrenergic blockade.

METHODS

Eight anesthetized and instrumented swine were administered 0.1mg epinephrine and arterial pressure and heart rate response were measured. An infusion of labetalol was then initiated and animals periodically challenged with epinephrine until adrenergic blockade was confirmed. The left anterior descending coronary artery was occluded to produce ventricular fibrillation (VF). After 7min of untreated VF, mechanical chest compressions were initiated. After 1min of compressions, 1mg epinephrine was given while CPP was recorded. When CPP values had returned to pre-epinephrine levels, 40U of bolus vasopressin was given. Differences in CPP (post-vasopressor-pre-vasopressor) were compared within animals for the epinephrine and vasopressin response and with eight, non-adrenergically blocked, historical controls using Bayesian statistics with a non-informative prior.

RESULTS

The CPP response following epinephrine was 15.1mmHg lower in adrenergically blocked animals compared to non-adrenergically blocked animals (95% Highest Posterior Density [HPD] 2.9-27.2mmHg lower). CPP went up 18.4mmHg more following vasopressin when compared to epinephrine (95% HPD 8.2-29.1mmHg). The posterior probability of a higher CPP response from vasopressin (vs. epinephrine) in these animals was 0.999.

CONCLUSIONS

Pre-arrest adrenergic blockade blunts the CPP response to epinephrine. Superior augmentation of CPP is attained with vasopressin under these conditions.

Cardiac function and the proinflammatory cytokine response after recovery from cardiac arrest in swine

Increased levels of cytokines have been reported after resuscitation from cardiac arrest. We hypothesized that proinflammatory cytokines, released in response to ischemia/reperfusion, increase following resuscitation and play a role in post-cardiac arrest myocardial dysfunction. Ventricular fibrillation (VF) was induced by coronary occlusion in 20 swine. After 7 min of VF, resuscitation was performed as per guidelines. Plasma levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 were measured 15 min after the start of resuscitation in all animals and at intervals of 6 h in resuscitated animals. Intravascular pressures and cardiac output (CO) were also recorded. TNF-alpha abruptly increased after resuscitation, peaking at 15 min following return of spontaneous circulation, and declined to baseline levels after 3 h. IL-1beta increased more slowly, reaching a maximum 2 h after reperfusion. IL-6 concentrations were not significantly different from control values at any time point. Males demonstrated greater elevations of TNF-alpha and IL-1beta than females. Stroke work was significantly depressed at all time points with a nadir at 15-30 min after reperfusion, corresponding to the peak TNF-alpha values. The anti-TNF-alpha antibody infliximab attenuated the decrease in myocardial function observed 30 min after reperfusion. TNF-alpha increases during recovery from cardiac arrest are associated with depression of left ventricle (LV) function. The effect of TNF-alpha can be attenuated by anti-TNF-alpha antibodies.

Advanced airway management does not improve outcome of out-of-hospital cardiac arrest

BACKGROUND

The goal of out-of-hospital endotracheal intubation (ETI) is to reduce mortality and morbidity for patients with airway and ventilatory compromise. Yet several studies, mostly involving trauma patients, have demonstrated similar or worse neurologic outcomes and survival-to-hospital discharge rates after out-of-hospital ETI. To date, there is no study comparing out-of-hospital ETI to bag-valve-mask (BVM) ventilation for the outcome of survival to hospital discharge among nontraumatic adult out-of-hospital cardiac arrest (OOHCA) patients.

OBJECTIVES

The objective was to compare survival to hospital discharge among adult OOHCA patients receiving ETI to those managed with BVM.

METHODS

In this retrospective cohort study, the records of all OOHCA patients presenting to a municipal teaching hospital from November 1, 1994, through June 30, 2008, were reviewed. The type of field airway provided, age, sex, race, rhythm on paramedic arrival, presence of bystander cardiopulmonary resuscitation (CPR), whether the arrest was witnessed, site of arrest, return of spontaneous circulation (ROSC), survival to hospital admission, comorbid illnesses, and survival to hospital discharge were noted. A univariate odds ratio (OR) was first computed to describe the association between the type of airway and survival to hospital discharge. A multivariable logistic regression analysis was performed, adjusting for rhythm, bystander CPR, and whether the arrest was witnessed.

RESULTS

A cohort of 1,294 arrests was evaluated. A total of 1,027 (79.4%) received ETI, while 131 (10.1%) had BVM, 131 (10.1%) had either a Combitube or an esophageal obturator airway, and five (0.4%) had incomplete prehospital records. Fifty-five of 1,294 (4.3%) survived to hospital discharge; there were no survivors in the Combitube/esophageal obturator airway cohort. Even after multivariable adjustment for age, sex, site of arrest, bystander CPR, witnessed arrest, and rhythm on paramedic arrival, the OR for survival to hospital discharge for BVM versus ETI was 4.5 (95% confidence interval [CI] = 2.3-8.9; p<0.0001).

CONCLUSIONS

In this cohort, when compared to BVM ventilation, advanced airway methods were associated with decreased survival to hospital discharge among adult nontraumatic OOHCA patients.

Transthoracic defibrillation potential gradients in a closed chest porcine model of prolonged spontaneous and electrically induced ventricular fibrillation

OBJECTIVE

The purpose of this study was to measure the local electrical field or potential gradient, measured with a catheter-based system, required to terminate long duration electrically or ischaemically induced ventricular fibrillation (VF). We hypothesized that prolonged ischaemic VF would be more difficult to terminate when compared to electrically induced VF of similar duration.

METHODS

Thirty anesthetized and instrumented swine were randomized to electrically induced VF or spontaneous, ischaemically induced VF, produced by balloon occlusion of the left anterior descending coronary artery. After 7 min of VF, chest compressions were initiated and rescue shocks were attempted 1 min later. The potential gradient for each shock was measured and the mean values required for defibrillation compared for the VF groups.

RESULTS

The number of shocks and the shock strength required for termination of VF were not significantly different for the groups. The potential gradient of the first successful defibrillating shock was significantly greater in the spontaneous, occlusion-induced VF group (12.80+/-2.82 V/cm vs 9.60+/-2.48 V/cm, p=0.002). The number of refibrillations was greater in the ischaemic group than in the non-ischaemic electrical group (6+/-4 vs 1+/-1, p<0.001). The number of animals requiring a shock at 360J was 2.5 times greater for the ischaemic group.

CONCLUSIONS

Defibrillation of prolonged VF produced by acute myocardial ischaemia requires a significantly greater potential gradient to terminate than prolonged VF induced by electrical stimulation of the right ventricular endocardium. The VF duration used in this study approximates that occurring in victims of out-of-hospital cardiac arrest. Our findings may be of clinical importance in the management of such patients.

Hypocalcemia following resuscitation from cardiac arrest revisited

OBJECTIVE

Hypocalcemia associated with cardiac arrest has been reported. However, mechanistic hypotheses for the decrease in ionized calcium (iCa) vary and its importance unknown. The objective of this study was to assess the relationships of iCa, pH, base excess (BE), and lactate in two porcine cardiac arrest models, and to determine the effect of exogenous calcium administration on post-resuscitation hemodynamics.

METHODS

Swine were instrumented and VF was induced either electrically (EVF, n=65) or spontaneously, ischemically induced (IVF) with balloon occlusion of the LAD (n=37). Animals were resuscitated after 7 min of VF. BE, iCa, and pH, were determined prearrest and at 15, 30, 60, 90, 120 min after ROSC. Lactate was also measured in 26 animals in the EVF group. Twelve EVF animals were randomized to receive 1g of CaCl(2) infused over 20 min after ROSC or normal saline.

RESULTS

iCa, BE, and pH declined significantly over the 60 min following ROSC, regardless of VF type, with the lowest levels observed at the nadir of left ventricular stroke work post-resuscitation. Lactate was strongly correlated with BE (r=-0.89, p<0.0001) and iCa (r=-0.40, p<0.0001). In a multivariate generalized linear mixed model, iCa was 0.005 mg/dL higher for every one unit increase in BE (95% CI 0.003-0.007, p<0.0001), while controlling for type of induced VF. While there was a univariate correlation between iCa and BE, when BE was included in the regression analysis with lactate, only lactate showed a statistically significant relationship with iCa (p=0.02). Post-resuscitation CaCl(2) infusion improved post-ROSC hemodynamics when compared to saline infusion (LV stroke work control 8+/-5 gm vs 23+/-4, p=0.014, at 30 min) with no significant difference in tau between groups.

CONCLUSIONS

Ionized hypocalcemia occurs following ROSC. CaCl(2) improves post-ROSC hemodynamics suggesting that hypocalcemia may play a role in early post-resuscitation myocardial dysfunction.

Plasma endothelin-1 level at the onset of ischemic ventricular fibrillation predicts resuscitation outcome

BACKGROUND

Endogenous vasopressors, including endothelin-1 (ET-1), have been shown to be elevated in patients following resuscitation from out-of-hospital cardiac arrest and are likely a physiologic response to global ischaemia. The importance of ET-1 in the setting of arrest and resuscitation has not been established. Prior work has demonstrated that ET-1 increases significantly after coronary occlusion. The purpose of this study was to assess changes in ET-1 following induction of ischaemia and VF.

METHODS

VF was induced in 30 anesthetized and instrumented swine by balloon occlusion of the LAD. Blood was collected from the right atrium at baseline and at 5 min intervals following LAD occlusion until VF occurred. After 7 min of VF, resuscitation was attempted in accordance with guidelines. ET-1 and matrix metalloproteinase-9 (MMP-9), a measure of infarct size, were measured using ELISA.

RESULTS

ET-1 and MMP-9 levels increased significantly from baseline within 20 min of occlusion of the LAD. Animals that could not be resuscitated had a higher ET-1 (p=0.031) at VF onset but similar ischaemia time (time to VF) and MMP-9, reflecting infarct size. An ET-1 level >4 pg/ml had a likelihood ratio of 4 for predicting resuscitation failure.

CONCLUSIONS

Elevated levels of ET-1 during acute ischaemia predict resuscitation failure independent of the time to VF. This finding may be due to the known effect of ET-1 on coronary vascular resistance or ventricular compliance, resulting in early ischemic contracture.

Endothelin-1 is not predictive of ventricular ectopy or ventricular fibrillation during acute myocardial ischemia

Endothelin(ET)-1 (ET-1) increases after myocardial infarction and may have effects on myocardial function. ET-1 has also been shown to affect the action potential (AP) which may be arrhythmogenic and predispose to ventricular fibrillation (VF). The effects of ET-2 and ET-3 are uncertain. We hypothesized that the ETs increase during acute ischemia and that plasma levels are predictive of ischemically induced VF. Thirty-four domestic swine underwent balloon occlusion of the proximal LAD coronary artery. Occlusion was confirmed angiographically. Venous samples were collected from the right atrium at baseline and at 5 min intervals for 30 min or until VF induction. ET-1, ET-2, and ET-3 were measured using ELISA. Changes in plasma concentrations were assessed using repeated measures ANOVA with Dunnett's. A p < 0.05 was considered statistically significant. All animals had angiographic evidence of successful proximal LAD occlusion. ET-1 levels were significantly increased from a baseline at 20 min and remained elevated during 30 min of occlusion. ET-2 and ET-3 levels did not change from baseline values (figure, mean +/- SE). VF occurred in 60% of animals. Peak ET-1 values were not significantly different between VF and non-VF animals (6.2 +/- 2.2 vs. 4.8 +/- 2.3 pg/mL). No single ET-1 value had a VF predictive value >50%. There is a significant increase in ET-1 level within 20 min of acute myocardial ischemia. Despite known effects of ET-1 on the AP, this increase did not correlate with the occurrence of VF.

The central nervous system cytokine response to global ischemia following resuscitation from ventricular fibrillation in a porcine model

AIM OF THE STUDY

Pro-inflammatory cytokines have been implicated as culprits in neurotoxicity following ischemia in small animal models of stroke. The aim of this study was to measure the central nervous system (CNS) cytokine response following resuscitation from ventricular fibrillation (VF) in a porcine model of cardiac arrest and global hypoxic ischemia.

METHODS

VF was induced electrically in 11 anesthetized swine. Following 7 min of untreated VF, animals were resuscitated. Cerebrospinal fluid (CSF) and serum was sampled prior to VF and at 60, 120, and 180 min post-resuscitation from which levels of TNF-alpha, IL-1 beta, and IL-6 were measured. Levels were also drawn in three sham pigs, instrumented but not fibrillated.

RESULTS

CSF levels of TNF-alpha rose following resuscitation and were associated with CSF levels of IL-1 beta (p=0.0002). CSF levels of all cytokines except TNF-alpha were associated with their serum counterparts.

CONCLUSIONS

Measurable increases in pro-inflammatory cytokines in the CSF follow resuscitation from cardiac arrest in this porcine model. The CNS response TNF-alpha and IL-1 beta are associated. However, serum levels of TNF-alpha did not seem to predict CSF levels in this study, consistent with the concept of immune privilege of the CNS.

The proinflammatory cytokine response following resuscitation in the swine model depends on the method of ventricular fibrillation induction

OBJECTIVES

A systemic inflammatory response has been reported following resuscitation from cardiac arrest. The purpose of this study was to compare the magnitude of the tumor necrosis factor-alpha (TNF-alpha) response in two different swine models of ventricular fibrillation (VF) arrest.

METHODS

This was a randomized comparative trial conducted with domestic swine (N = 28, mean weight 40 kg, range 34-49 kg) of both genders. Anesthetized and instrumented swine were randomized to electrically induced VF (n = 14) or spontaneous VF induced by occlusion of a coronary artery (n = 14). After 8 minutes of VF, countershocks were given and standard advanced cardiac life support was initiated. Resuscitated animals were observed for 3 hours, and hemodynamics, base excess, and TNF-alpha concentrations were measured at intervals.

RESULTS

TNF-alpha concentrations were significantly greater in the ischemic VF group throughout the postresuscitation period. Multivariate modeling demonstrated that the TNF-alpha level was dependent on the method of VF induction and correlated with ischemia time (untreated VF period plus time to restoration of circulation) and the degree of postresuscitation hypoperfusion as reflected in base excess measurements.

CONCLUSIONS

This study demonstrates that TNF-alpha concentrations increase after resuscitation from cardiac arrest and that the TNF-alpha response is more profound in animals subjected to ischemic, spontaneous VF. The observed differences may be due to a longer resuscitation time and persistent postresuscitation hypoperfusion in the ischemic VF group. These differences need to be considered in studies evaluating mechanisms of postresuscitation organ dysfunction and defining mortality markers.

A comparison of door-to-balloon times and false-positive activations between emergency department and out-of-hospital activation of the coronary catheterization team

OBJECTIVES

The objectives were to compare the proportion of false-positive activations and intervention times between emergency department (ED) and field-based activation of the coronary catheterization laboratory (cath) team for emergency medical services (EMS) patients identified by out-of-hospital (OOH) 12-lead electrocardiogram (ECG) with ST-segment elevation myocardial infarction (STEMI).

METHODS

This was a retrospective review of prospectively collected continuous quality improvement data at a single, urban, academic medical center. By protocol, weekday activation of the cath team occurred based on OOH notification of a computer-interpreted OOH ECG indicating potential STEMI. Night and weekend activation occurred at the discretion of the attending emergency physician (EP) after advanced ED notification and after patient arrival and assessment. Basic demographic information and cardiac risk factors were recorded, as well as door-to-balloon (DTB) and ultimate diagnosis.

RESULTS

From May 2007 through March 2008, there were 23 field activations and 33 ED activations. There was no difference in demographic or clinical characteristics between the two groups. In the field activation group, 9/23 (39%) were false-positives, while 3/33 (9%) were false-positives in the ED activation group (30% higher absolute difference in the field activation group, 95% confidence interval [CI] = 8% to 52%, p = 0.02). OOH times and time spent in the ED were similar between the two groups. DTB times were 77 minutes for field activation and 68 minutes for ED activation, respectively (difference 9 minutes, 95% CI = -9 to 27).

CONCLUSIONS

Emergency physician activation of the cath team results in a lower proportion of false-positive activations without clearly sacrificing DTB time when compared to field activation based solely on the results of the OOH ECG.

Is the tumour necrosis factor-alpha response following resuscitation gender dependent in the swine model?

INTRODUCTION

Reperfusion results in a proinflammatory cytokine response, as has been observed following resuscitation from cardiac arrest. Variations in the inflammatory response have been shown to be gender dependent and mediated by steroid hormones. The purpose of this study was to determine whether the tumour necrosis factor-alpha response following resuscitation was gender dependent.

METHODS

Anaesthetized swine (15 males and 15 females, weighs 32-47 kg) underwent 7 min of electrically induced cardiac arrest, followed by conventional resuscitation and then measurement of tumour necrosis factor-alpha by enzyme-linked immunosorbent assay at intervals for up to 3h. Testosterone and 17-estradiol were measured in 8 males and 8 females.

RESULTS

In all animals 17-estradiol was undetectable. Testosterone exceeded the lower limit of detection in 3 females and 1 male. Levels of tumour necrosis factor-alpha were higher in males than females, from 30 min after resuscitation to 3h. In females, tumour necrosis factor-alpha levels were significantly higher than control values only at 15 min following restoration of circulation; the levels in males demonstrated marked inter-animal variation.

CONCLUSIONS

In this swine model, males demonstrated an augmented post-resuscitation tumour necrosis factor-alpha response when compared with females. This difference was not related to steroid hormone levels.

A Bayesian sensitivity analysis of out-of-hospital 12-lead electrocardiograms: implications for regionalization of cardiac care

BACKGROUND

The effectiveness of out-of-hospital regionalization of ST-elevation myocardial infarction (STEMI) patients to hospitals providing primary percutaneous coronary intervention depends on the accuracy of the out-of-hospital 12-lead electrocardiogram (PHTL). Although estimates of sensitivity and specificity of PHTL for STEMI have been reported, the impact of out-of-hospital STEMI prevalence on positive predictive value (PPV) has not been evaluated.

OBJECTIVES

To describe the relationship between varying population STEMI prevalences and PHTL predictive values, using ranges of PHTL sensitivity and specificity.

METHODS

The authors performed a Bayesian analysis using PHTL, where values for sensitivities (60%-70%), specificities (98%), and two prevalence ranges (0.5%-5% and 5%-20%) were derived from a literature review. PPV prediction intervals were compared with three months of prospective data from the Los Angeles County Emergency Medical Services Agency STEMI regionalization program.

RESULTS

When the estimated prevalence of STEMI in the out-of-hospital population is 5%-20%, the median PPV of the PHTL is 83% (95% credible interval [CrI] = 53% to 97%). However, if the population prevalence of STEMI is between 0.5% and 5%, the median PPV is 43% (95% CrI = 12% to 86%). When the PPV prediction intervals were incorporated with the Los Angeles County Emergency Medical Services Agency data, the PPV was 66%.

CONCLUSIONS

Even when assuming high specificity for PHTL, the false-positive rate will be considerable if applied to a population at low risk for STEMI. Before broadening application of PHTL to low-risk patients, the implications of a high false-positive rate should be considered.