Murine Cardiac Arrest Model Research Articles

Neurovascular Hypoxia Trajectories Assessed by Photoacoustic Imaging in a Murine Model of Cardiac Arrest and Resuscitation.

Cardiac arrest is a common cause of death annually mainly due to postcardiac arrest syndrome that leads to multiple organ global hypoxia and dysfunction after resuscitation. The ability to quantify vasculature changes and tissue oxygenation is crucial to adapt patient treatment in order to minimize major outcomes after resuscitation. For the first time, we applied high-resolution ultrasound associated with photoacoustic imaging (PAI) to track neurovascular oxygenation and cardiac function trajectories in a murine model of cardiac arrest and resuscitation. We report the preservation of brain oxygenation is greater compared to that in peripheral tissues during the arrest. Furthermore, distinct patterns of cerebral oxygen decay may relate to the support of vital brain functions. In addition, we followed trajectories of cerebral perfusion and cardiac function longitudinally after induced cardiac arrest and resuscitation. Volumetric cerebral oxygen saturation (sO2) decreased 24 h postarrest, but these levels rebounded at one week. However, systolic and diastolic cardiac dysfunction persisted throughout and correlated with cerebral hypoxia. Pathophysiologic biomarker trends, identified via cerebral PAI in preclinical models, could provide new insights into understanding the pathophysiology of cardiac arrest and resuscitation.

Abstract 155: Intra-arrest Epinephrine Administration is Associated with Increased Myocardial Injury and Inflammation in a Novel Murine Model of Cardiac Arrest

Introduction: Epinephrine (EPI) is routinely administered in cardiac arrest resuscitation. Using a novel murine model of cardiac arrest, this study aims to assess the effects of epinephrine on myocardial inflammation and injury. Hypothesis: Intra-arrest epinephrine use is associated with increased myocardial injury, inflammation and fibrosis. Methods: A total of 56 mice were included in the study. Both cardiac arrest (CA) and sham (SHAM) groups received intravenous potassium chloride either as a bolus (CA) or slow infusion (SHAM), inducing ECG-confirmed asystole (CA only) for 4-minutes prior to delivery of intravenous epinephrine (250ul, 30ug/ml) or saline (250ul) and manual chest compressions (300BPM) for 4-minutes (Fig A). Mice were recovered for assessments at 24- or 72-hour timepoints. Results: Rates of successful ROSC (n=21(96%) vs. n=14(82%), P=0.18) and survival to recovery (n=11(50%) vs. n=12(71%),P=0.19) were similar in CA treated with (CA+EPI) and without (CA-Epi) EPI, respectively. Greater myocardial injury occurred in CA+EPI, compared to CA-Epi, with increased Hs-Troponin levels measured at 24- (26.0±0.9ng/mL vs. 9.4±5.3,P=0.015) and 72-hours (20.9±8.3ng/mL vs. 5.0±2.4,P=0.012) (Fig B). To examine mRNA expression in cardiac tissue, rt-PCR was performed. At 72-hours, CA+EPI, compared to CA-EPI, was associated with significantly increased expression of inflammatory (TNF-α, IL1β, IL10, F4-80 and CD68) and fibrotic (TGFβ, Col1 and Col3) genes. There was no difference between SHAM-EPI and SHAM+EPI at 72-hours (Fig C). Conclusion: In a mouse model of cardiac arrest, the use of epinephrine did not improve rates of ROSC and survival. However, epinephrine exposure was associated with increased biomarkers of myocardial injury, end-organ inflammation, and fibrosis. These findings underscore the need for further pre-clinical studies to assess alternate agents that confer protection to vital organs and improve rates of survival.

A randomised preclinical trial of adrenaline use during cardiac arrest in mice

BackgroundAdrenaline is routinely administered during cardiac arrest resuscitation. Using a novel murine model of cardiac arrest, this study evaluates the effects of adrenaline use on survival and end-organ injury. MethodsA total of 58 mice, including cardiac arrest (CA) and sham (SHAM) groups received intravenous potassium chloride either as a bolus (CA) or slow infusion (SHAM), inducing ECG-confirmed asystole (in CA only) for 4-minutes prior to intravenous adrenaline (+ADR;250 ul,32 ug/ml) or saline (-ADR;250 ul) and manual chest compressions (300 BPM) for 4-minutes. Mice with return of spontaneous circulation (ROSC) were assessed at 24- or 72-h timepoints. ResultsAmong animals that underwent CA, rates of ROSC (n = 21 (95 %) vs n = 14 (82 %), P = 0.18) and survival to the planned endpoint (n = 11 (50 %) vs n = 12 (71 %), P = 0.19) were similar when comparing those treated with (CA+ADR) and without (CA-ADR) adrenaline. However, in CA animals that initially achieved ROSC, subsequent mortality was approximately 3-fold greater with adrenaline treatment (48 % vs 14 %, P = 0.042). Among SHAM animals, adrenaline use had no impact on survival rates or other endpoints. Greater myocardial injury occurred in CA+ADR vs CA-ADR, with increased Hs-Troponin levels measured at 24- (26.0 ± 0.9 vs 9.4 ± 5.3 ng/mL, P = 0.015) and 72-h (20.9 ± 8.3 vs 5.0 ± 2.4 ng/mL, P = 0.012), associated with increased expression of pro-inflammatory and fibrotic genes within cardiac and renal tissue. ConclusionAdrenaline did not improve ROSC or overall survival but following successful ROSC, its use resulted in 3-fold greater mortality rates. Adrenaline was also associated with increased myocardial injury, end-organ inflammation, and fibrosis. These findings underscore the need for further preclinical evaluation of alternate pharmacologic adjuncts for cardiopulmonary resuscitation that improve survival and limit end-organ injury.

Abstract 10241: Single-Cell RNA-Sequencing Reveals Hyperacute NK Cell and Monocyte Cell States Correlating with Poor Neurological Outcomes After Cardiac Arrest

Background: Lymphopenia and elevated cytokine levels suggest a role for the systemic immune response after cardiac arrest (CA). However, little is known about the phenotypes and interactions of immune cells after CA. This study aimed to investigate the immunological network after CA and identify cell states correlating with poor neurological outcomes. Methods: Peripheral mononuclear blood cells of 11 post-out-of-hospital CA patients and 3 healthy subjects were analyzed by single-cell RNA-sequencing (scRNA-seq), with validation by flow cytometry, bulk RNA-seq of sorted cell subsets, plasma levels of cytokines, and the murine model of CA. Good and poor neurological outcomes at hospital discharge were defined by Cerebral Performance Category 1-2 and 3-5, respectively. Results: The scRNA-seq analysis of 96,179 cells revealed 6 major cell lineages with several subclusters. At 6h post-CA, cells of patients with good outcomes co-clustered with healthy subjects, while patients with poor outcomes formed distinct transcriptomic clusters. This distinction was lost by 48h post-CA. At 6h post-CA, we identified pro-inflammatory and hypoxia-responsive Tim-3 + NK cell and Nectin-2 + monocyte cell states specific to poor outcomes. In a validation cohort of post-CA patients, Tim-3 + NK cells and Nectin-2 + monocyte cell states were validated by flow cytometry. Bulk RNA-seq analysis of these sorted cells reproduced the transcriptomic profile determined by scRNA-seq. Interactome analysis identified NK cell-monocyte axes in poor outcomes, including IFNG-IFNGR2. Measurement of plasma cytokine levels revealed increased IFNγ levels at 6h post-CA that were associated with poor outcomes, but both poor and good outcomes had similarIFNγ levels by 48h. A murine model of CA demonstrated that IFNγ drives poor outcomes and mortality after CA. Conclusions: In clinical CA, transcriptomic analysis at single-cell resolution revealed hyperacute cell states of NK cells and monocytes associated with poor neurological outcomes. These hyperacute cell states interact by IFNγ-IFNγR2 axis, which is pathogenic in the murine model of CA. The immunophenotypes that distinguish patients with poor or good neurological outcomes are present at 6h but are no longer detectable by 48h post-CA.

Microglial Activation and Neurological Outcomes in a Murine Model of Cardiac Arrest

BackgroundNeurological injury following successful resuscitation from sudden cardiac arrest (CA) is common. The pathophysiological basis of this injury remains poorly understood, and treatment options are limited. Microglial activation and neuroinflammation are established contributors to many neuropathologies, such as Alzheimer disease and traumatic brain injury, but their potential role in post-CA injury has only recently been recognized. Here, we hypothesize that microglial activation that occurs following brief asystolic CA is associated with neurological injury and represents a potential therapeutic target.MethodsAdult C57BL/6 male and female mice were randomly assigned to 12-min, KCl-induced asystolic CA, under anesthesia and ventilation, followed by successful cardiopulmonary resuscitation (n = 19) or sham intervention (n = 11). Neurological assessments of mice were performed using standardized neurological scoring, video motion tracking, and sensory/motor testing. Mice were killed at 72 h for histological studies; neuronal degeneration was assessed using Fluoro-Jade C staining. Microglial characteristics were assessed by immunohistochemistry using the marker of ionized calcium binding adaptor molecule 1, followed by ImageJ analyses for cell integrity density and skeletal analyses.ResultsNeurological injury in post-cardiopulmonary-resuscitation mice vs. sham mice was evident by poorer neurological scores (difference of 3.626 ± 0.4921, 95% confidence interval 2.618–4.634), sensory and motor functions (worsened by sixfold and sevenfold, respectively, compared with baseline), and locomotion (75% slower with a 76% decrease in total distance traveled). Post-CA brains demonstrated evidence of neurodegeneration and neuroinflammatory microglial activation.ConclusionsExtensive microglial activation and neurodegeneration in the CA1 region and the dentate gyrus of the hippocampus are evident following brief asystolic CA and are associated with severe neurological injury.

Salvianolic Acid B Improves Postresuscitation Myocardial and Cerebral Outcomes in a Murine Model of Cardiac Arrest: Involvement of Nrf2 Signaling Pathway.

Survival and outcome of cardiac arrest (CA) are dismal despite improvements in cardiopulmonary resuscitation (CPR). Salvianolic acid B (Sal B), extracted from Salvia miltiorrhiza, has been investigated for its cardioprotective properties in cardiac remodeling and ischemic heart disease, but less is known about its role in CA. The aim of this study was to learn whether Sal B improves cardiac and neurologic outcomes after CA/CPR in mice. Female C57BL/6 mice were subjected to eight minutes of CA induced by an intravenous injection of potassium chloride (KCl), followed by CPR. After 30 seconds of CPR, mice were blindly randomized to receive either Sal B (20 mg/kg) or vehicle (normal saline) intravenously. Hemodynamic variables and indices of left ventricular function were determined before CA and within three hours after CPR, the early postresuscitation period. Sal B administration resulted in a remarkable decrease in the time required for the return of spontaneous circulation (ROSC) in animals that successfully resuscitated compared to the vehicle-treated mice. Myocardial performance, including cardiac output and left ventricular systolic (dp/dtmax) and diastolic (dp/dtmin) function, was clearly ameliorated within three hours of ROSC in the Sal B-treated mice. Moreover, Sal B inhibited CA/CPR-induced cardiomyocyte apoptosis and preserved mitochondrial morphology and function. Mechanistically, Sal B dramatically promoted Nrf2 nuclear translocation through the downregulation of Keap1, which resulted in the expression of antioxidant enzymes, including HO-1 and NQO1, thereby counteracted the oxidative damage in response to CA/CPR. The aforementioned antiapoptotic and antioxidant effects of Sal B were impaired in the setting of gene silencing of Nrf2 with siRNA in vitro model. These improvements were associated with better neurological function and increased survival rate (75% vs. 40%, p < 0.05) up to 72 hours postresuscitation. Our findings suggest that the administration of Sal B improved cardiac function and neurological outcomes in a murine model of CA via activating the Nrf2 antioxidant signaling pathway, which may represent a novel therapeutic strategy for the treatment of CA.

Neuroinflammation and Blood Brain Barrier Injury in a Murine Model of Cardiac Arrest

BackgroundNeurological injury is often evident following resuscitation from cardiac arrest and yet, the pathophysiology of this injury is not well understood. Moreover, treatment options are limited to targeted temperature management (TTM) and conservative care. We hypothesize that neuroinflammation and blood brain barrier (BBB) injury are associated with neurological injury following cardiac arrest and represent potential targets for therapeutic intervention.MethodsWe randomized adult C57BL/6 male/female mice to either a 12‐minute KCl‐induced asystolic CA ‐ under anesthesia and ventilation ‐ followed by CPR (N=12) or sham intervention (N=9). Neurological assessments of mice were performed using standardized neurological scoring, video motion tracking, and sensory/motor testing. BBB permeability was assessed by injection of fluorescein isothiocyanate (FITC) dextran beads. Changes to immune cell number in the brain was assessed by immunohistochemistry using the microglia marker (Iba1+).ResultsNeurological injury following cardiac arrest was evident by neurological scores (difference of 3.419 ± 0.5576, 95% CI 2.25–4.586), sensory scores (difference of −61.39 ± 16.65 seconds, 95% CI −97.10 to −25.67), motor scores (difference of −107.3 ± 6.503 seconds, 95% CI −121.2 to −93.35) and video analysis of distance (difference of 8.914 meters ± 1.411, 95% CI 4.425 −13.40) and speed (difference of 0.07428 m/s ±0.01175, 95% CI 0.03687 to 0.1117). Post‐CA brains demonstrated increased bead fluorescence compared to controls indicative of increased blood brain barrier injury. Moreover, Iba1+ cell number was approximately 2.47 times greater and integrity density was approximately 4.66 times greater post‐CA suggesting neuroinflammation following CA.ConclusionsGlobal neurological injury is evident following asystolic cardiac arrest in mice but is particularly prominent in regard to motor movements. This injury is associated with BBB injury and nueroinflammation. Ongoing studies are determining the mechanisms and possible therapeutic targets of this injury.Support or Funding InformationThe project described was supported by Grant Number T32HL007381 from the National Heart, Lung, and Blood Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Heart, Lung, and Blood Institute or the National Institutes of Health.

Toll-like receptor 4 deficiency or inhibition does not modulate survival and neurofunctional outcome in a murine model of cardiac arrest and resuscitation.

BackgroundPatients experiencing cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) often die or suffer from severe neurological impairment. Post resuscitation syndrome is characterized by a systemic inflammatory response. Toll-like receptor 4 (TLR4) is a major mediator of inflammation and TLR4 has been implicated in the pathogenesis of post-resuscitation encephalopathy. The aim of this study was to evaluate whether TLR4 deficiency or inhibition can modulate survival and neurofunctional outcome after CA/CPR.MethodsFollowing intubation and central venous cannulation, CA was induced in wild type (C57Bl/6J, n = 38), TLR4 deficient (TLR4-/-, n = 37) and TLR4 antibody treated mice (5mg/kg MTS510, n = 15) by high potassium. After 10min, CPR was performed using a modified sewing machine until return of spontaneous circulation (ROSC). Cytokines and cerebral TNFalpha levels were measured 8h after CA/CPR. Survival, early neurological recovery, locomotion, spatial learning and memory were assessed over a period of 28 days.ResultsFollowing CA/CPR, all mice exhibited ROSC and 31.5% of wild type mice survived until day 28. Compared to wild type mice, neither TLR4-/- nor MTS510 treated wild type mice had statistically significant altered survival following CA/CPR (51.3 and 26.7%, P = 0.104 and P = 0.423 vs. WT, respectively). Antibody-treated but not TLR4-/- mice had higher IL-1β and IL-6 levels and TLR4-/- mice had higher IL-10 and cerebral TNFalpha levels. No differences existed between mice of all groups in early neurological recovery, locomotion, spatial learning ability or remembrance.ConclusionTherapeutic strategies targeting TLR4 may not be suitable for the reduction of mortality or neurofunctional impairment after CA/CPR.

A comparison of therapeutic hypothermia and genetic mitochondrial permeability transition pore inhibition in a murine model of cardiac arrest

Recent evidence suggests that therapeutic hypothermia limits the severity of the post-cardiac arrest syndrome by inhibiting mitochondrial permeability transition pore (mPTP) opening through a Cyclophilin-D (CypD) dependent mechanism. We sought to compare the effects of genetic loss of CypD (CypD-KO) and therapeutic hypothermia on resuscitability and survival after cardiac arrest (CA). Adult mice underwent 5 minutes of asphyxial CA followed by resuscitation. Animals were assigned to one of the 5 following groups: Sham, Control (Ctrl): normothermic CA in wild-type mice, CypD-KO: normothermic CA in CypD-KO mice, therapeutic hypothermia (TH): CA in wild-type mice with fast hypothermia induced by external cooling at the onset of cardiac massage (33 °C for 1 hour) and CypD-KO + TH. Two hours after CA, left ventricle-shortening fraction, blood levels of S100B protein (a marker of brain injury) and troponin Ic, were assessed. Additional mice were included in the same 5 groups for survival follow-up. Baseline characteristics and characteristics of CA were similar among groups. Rate of restoration of spontaneous circulation (ROSC) was significantly higher in CypD-KO and TH groups compared to controls ( P < 0.05). Time to ROSC was significantly shorter in CypD-KO mice versus wild-type mice ( P < 0.05). Genetic loss of CypD and therapeutic hypothermia prevented to a similar extent CA-induced myocardial dysfunction, increase in S100B, troponin Ic and death within 24 hours after CA ( P < 0.05 versus Ctrl). Only therapeutic hypothermia applied to either wild-type or CypD-KO animals improved survival at day 7 ( P < 0.05 versus non-hypothermic groups). There were no additive beneficial effects in the combination of genetic loss of CypD and therapeutic hypothermia. In our CA model, genetic inhibition of CypD improved resuscitability and early cardiac dysfunction but, unlike therapeutic hypothermia, failed to improve 7-day survival.

Enhanced pyruvate dehydrogenase activity improves cardiac outcomes in a murine model of cardiac arrest.

RationalePost-ischemic changes in cellular metabolism alter myocardial and neurological function. Pyruvate dehydrogenase (PDH), the limiting step in mitochondrial glucose oxidation, is inhibited by increased expression of PDH kinase (PDK) during ischemia/reperfusion injury. This results in decreased utilization of glucose to generate cellular ATP. Post-cardiac arrest (CA) hypothermia improves outcomes and alters metabolism, but its influence on PDH and PDK activity following CA are unknown. We hypothesized that therapeutic hypothermia (TH) following CA is associated with the inhibition of PDK activity and increased PDH activity. We further hypothesized that an inhibitor of PDK activity, dichloroacetate (DCA), would improve PDH activity and post-CA outcomes.Methods and resultsAnesthetized and ventilated adult female C57BL/6 wild-type mice underwent a 12-minute KCl-induced CA followed by cardiopulmonary resuscitation. Compared to normothermic (37°C) CA controls, administering TH (30°C) improved overall survival (72-hour survival rate: 62.5% vs. 28.6%, P<0.001), post-resuscitation myocardial function (ejection fraction: 50.9±3.1% vs. 27.2±2.0%, P<0.001; aorta systolic pressure: 132.7±7.3 vs. 72.3±3.0 mmHg, P<0.001), and neurological scores at 72-hour post CA (9.5±1.3 vs. 5.4±1.3, P<0.05). In both heart and brain, CA increased lactate concentrations (1.9-fold and 3.1-fold increase, respectively, P<0.01), decreased PDH enzyme activity (24% and 50% reduction, respectively, P<0.01), and increased PDK protein expressions (1.2-fold and 1.9-fold, respectively, P<0.01). In contrast, post-CA treatment with TH normalized lactate concentrations (P<0.01 and P<0.05) and PDK expressions (P<0.001 and P<0.05), while increasing PDH activity (P<0.01 and P<0.01) in both the heart and brain. Additionally, treatment with DCA (0.2 mg/g body weight) 30 min prior to CA improved both myocardial hemodynamics 2 hours post-CA (aortic systolic pressure: 123±3 vs. 96±4 mmHg, P<0.001) and 72-hour survival rates (50% vs. 19%, P<0.05) in normothermic animals.ConclusionsEnhanced PDH activity in the setting of TH or DCA administration is associated with improved post-CA resuscitation outcomes. PDH is a promising therapeutic target for improving post-CA outcomes.

Abstract 13483: Peptide Inhibition of PTEN Improves Metabolic Recovery and Outcomes in a Murine Cardiac Arrest Model

Introduction: Recent work shows that PTEN inhibition protects against cardiomyocyte contractile dysfunction and death following ischemia/reperfusion. To further determine whether PTEN inhibition improves metabolic recovery and survival in a mouse model of cardiac arrest, we have designed a TAT fused cell-permeable peptide (TAT-PTEN9c) based on the c-terminal PDZ binding motif of PTEN for rapid tissue delivery. We hypothesized that TAT-PTEN9c interferes with endogenous PTEN binding to cell membrane adaptors resulting in increased Akt activation, causing Akt-enhanced glucose utilization (with decreased diversion of glucose via the alternate polyol pathway to sorbitol) and improved survival. Methods: Mouse cardiomyocytes were isolated from 1-3 day old mouse pups. Western blot was used to identify concentrations of TAT-PTEN9c that enhanced Akt phosphorylation in mouse cardiomyocytes exposed to oxidant stress. C57BL6 mice were then subjected to an established KCL-induced 8 min cardiac arrest protocol. 30 mice after CPR were randomly assigned to receive saline or TAT-PTEN9c. MAP, ETCO2, and ECG were recorded until 4 h after successful cardiopulmonary resuscitation (CPR). TAT-PTEN9c (7.8 mg/kg) was given intravenously (IV) after CPR (n=10). As a measure of impaired glucose utilization, sorbitol content in heart and brain was determined by a fluorescence assay of NADH formation using sorbitol dehydrogenase and NAD+. Results: TAT-PTEN9c peptide enhanced Akt activation in neonatal mouse cardiomyoctes in a concentration-dependent manner. Survival was significantly increased in the TAT-PTEN9c treated group compared to saline controls at 2 h (14/15, 93% vs. 9/15, 60%, P &lt; 0.05) and 4 h (10/15, 67% vs. 6/15, 40%, P &lt; 0.05) after CPR. Treated mice had increased Akt phosphorylation within 30 min after CPR in heart and brain tissues with significantly decreased sorbitol content, suggesting improved metabolic recovery and glucose utilization. Conclusion: TAT-PTEN9c can be used after CPR in a mouse SCA model to rapidly enhance Akt activation and decrease glucose shunting via the polyol pathway in critical organs, preventing early cardiovascular collapse and death. Further work exploring the role of tissue sorbitol in sudden cardiac arrest injury is needed.

Inhibition of the mitochondrial fission protein dynamin-related protein 1 improves survival in a murine cardiac arrest model.

Survival following sudden cardiac arrest is poor despite advances in cardiopulmonary resuscitation and the use of therapeutic hypothermia. Dynamin-related protein 1, a regulator of mitochondrial fission, is an important determinant of reactive oxygen species generation, myocardial necrosis, and left ventricular function following ischemia/reperfusion injury, but its role in cardiac arrest is unknown. We hypothesized that dynamin-related protein 1 inhibition would improve survival, cardiac hemodynamics, and mitochondrial function in an in vivo model of cardiac arrest. Laboratory investigation. University laboratory. Anesthetized and ventilated adult female C57BL/6 wild-type mice underwent an 8-minute KCl-induced cardiac arrest followed by 90 seconds of cardiopulmonary resuscitation. Mice were then blindly randomized to a single IV injection of Mdivi-1 (0.24 mg/kg), a small molecule dynamin-related protein 1 inhibitor or vehicle (dimethyl sulfoxide). Following resuscitation from cardiac arrest, mitochondrial fission was evidenced by dynamin-related protein 1 translocation to the mitochondrial membrane and a decrease in mitochondrial size. Mitochondrial fission was associated with increased lactate and evidence of oxidative damage. Mdivi-1 administration during cardiopulmonary resuscitation inhibited dynamin-related protein 1 activation, preserved mitochondrial morphology, and decreased oxidative damage. Mdivi-1 also reduced the time to return of spontaneous circulation (116 ± 4 vs 143 ± 7 s; p < 0.001) during cardiopulmonary resuscitation and enhanced myocardial performance post-return of spontaneous circulation. These improvements were associated with significant increases in survival (65% vs 33%) and improved neurological scores up to 72 hours post cardiac arrest. Post-cardiac arrest inhibition of dynamin-related protein 1 improves time to return of spontaneous circulation and myocardial hemodynamics, resulting in improved survival and neurological outcomes in a murine model of cardiac arrest. Pharmacological targeting of mitochondrial fission may be a promising therapy for cardiac arrest.

A COMPREHENSIVE STUDY OF SURVIVAL, TISSUE DAMAGE, AND NEUROLOGICAL DYSFUNCTION IN A MURINE MODEL OF CARDIOPULMONARY RESUSCITATION AFTER POTASSIUM-INDUCED CARDIAC ARREST

There are only few strategic and therapeutic options to improve the functional outcome of patients after cardiac arrest and resuscitation (CPR). The pathophysiology of reperfusion injury after global ischemia is not completely understood. We present here a murine model of cardiac arrest and resuscitation that allows an analysis of the pathophysiology of reperfusion injury, especially focusing on survival, tissue damage, and functional neurological parameters. Under systemic hemodynamic monitoring, male C57BL/6J mice were subjected to 3 min of a potassium-induced cardiac arrest. After resuscitation under controlled conditions, mice were observed and neurologically scored for 72 h post-CPR. As a control, sham-treated animals were provided. In addition, blood samples were drawn and organs were removed for a histological analysis. Here, global I/R led to functional and histological reperfusion damage. The overall mortality up to day 3 post-CPR was 54%. Resuscitated animals developed marked functional neurologic deficits, as assessed by Rotarod and elevated plus-maze testing. Histological examinations and blood analyses of CPR animals revealed significant leukocyte tissue infiltration and morphological damage of brain, lung, and kidneys. In summary, mice undergoing CPR after cardiac arrest present distinct neurological deficits, marked organ damage, and a 54% mortality rate. Our highly standardized and reproducible model of mice resuscitation provides a means for a better understanding of the post-CPR pathophysiology and thus opens new perspectives to develop relevant therapeutic approaches to minimize global I/R injury.

SOD1 Overexpression and Female Sex Exhibit Region-Specific Neuroprotection after Global Cerebral Ischemia Due to Cardiac Arrest

Cardiac arrest is often associated with poor neurologic outcome since therapeutic options are limited. We tested the hypothesis that overexpression of CuZn superoxide dismutase (SOD+/-) is neuroprotective in a new murine model of cardiac arrest and cardiopulmonary resuscitation (CPR). Second, we investigated if female and male mice sustain similar injury and if sex-specific outcomes are altered by SOD overexpression. Neuronal injury was quantified 3 days after 8 mins of KCl-induced cardiac arrest by calculating the percentage of ischemic neurons for caudoputamen and hippocampal CA1 region. In rostral caudoputamen, less neuronal cell loss was found for SOD+/- mice (31%+/-22%) when compared with wild-type (WT) mice (47%+/-31%, P<0.05). Superoxide dismutase overexpression did not reduce injury in the caudal caudoputamen. No sex-linked protection was evident in either genotype in the caudoputamen. Female WT mice had less CA1 injury than male WT mice (26%+/-31% versus 54%+/-30%, P<0.05), whereas no sex difference was found in SOD+/- mice (female: 42%+/-29%; male: 37%+/-37%). Comparison of hippocampal injury between genotypes revealed no differences for either males or females. In conclusion, SOD1 overexpression and female sex were associated with significant neuroprotection in this murine cardiac arrest model. However, no additive neuroprotection was observed, and these beneficial effects were restricted to specific brain regions.

Intra-arrest cooling improves outcomes in a murine cardiac arrest model.

Recent clinical studies have demonstrated that hypothermia to 32 degrees to 34 degrees C provides significant clinical benefit when induced after resuscitation from cardiac arrest. However, cooling during the postresuscitation period was slow, requiring 4 to 8 hours to achieve target temperatures after return of spontaneous circulation (ROSC). Whether more rapid cooling would further improve survival remains unclear. We sought to determine whether cooling during cardiac arrest before ROSC (ie, "intra-arrest" hypothermia) has survival benefit over more delayed post-ROSC cooling, using a murine cardiac arrest model. A model of potassium-induced cardiac arrest was established in C57BL/6 mice. After 8 minutes of untreated cardiac arrest, resuscitation was attempted with chest compression, ventilation, and intravenous fluid. Mice were randomized to 3 treatment groups (n=10 each): an intra-arrest hypothermia group, in which mice were cooled to 30 degrees C just before attempted resuscitation, and then rewarmed after 1 hour; a post-ROSC hypothermia group, in which mice were kept at 37 degrees C for 20 minutes after successful ROSC and then were cooled to 30 degrees C for 1 hour; and a normothermic control group, in which mice were kept at 37 degrees C. The intra-arrest hypothermia group demonstrated better 72-hour survival than delayed hypothermia and normothermia groups (6/10 versus 1/10 and 1/10 survivors, respectively, P<0.05), with similar differences seen at 6-hour survival and on neurological scoring. Timing of hypothermia is a crucial determinant of survival in the murine arrest model. Early intra-arrest cooling appears to be significantly better than delayed post-ROSC cooling or normothermic resuscitation.