Protective effects of therapeutic hypothermia in post-resuscitation myocardium

Effects of temperature control on hyperthermia-related cardiac dysfunction in a porcine model of cardiac arrest

The outcome of cardiac arrest is worse when there is fever after spontaneous circulation is restored (ROSC). The purpose of this study was to investigate the mechanism of post-ROSC cardiac dysfunction after hyperthermia treatment and the effects of temperature control. Twenty-four male Bama minipigs were randomized into 3 groups (8 per group): CPR + controlled normothermia (CN), CPR + hyperthermia (HT), and CPR + therapeutic mild hypothermia (TMH). Defibrillation was given to pigs with ventricular fibrillation after 8 min of untreated fibrillation. Subsequently, these animals received the post-ROSC treatments of hyperthermia (38 °C), controlled normothermia (37 °C) or hypothermia (33 °C) according to the groups. Hemodynamic parameters, left ventricular ejection fraction, blood samples and myocardial tissues were assessed. At 24 h after the post-ROSC treatments, the pigs treated with hyperthermia showed increments in heart rate and plasma cardiac troponin I, and decreases in mean arterial pressure, cardiac index, and left ventricular ejection fraction, compared to those with the controlled normothermia pigs. However, the deterioration of the above parameters can be attenuated by TMH. The pigs in the TMH group also had a reduced percentage of apoptotic cardiomyocytes, an increased anti-apoptotic Bcl-2/Bax ratio and a decreased caspase-3 activity in myocardium, as compared with both controlled normothermia and hyperthermia pigs. In conclusion, hyperthermia is associated with a worse myocardial dysfunction. TMH improves hyperthermia-induced myocardial dysfunction by attenuating apoptosis in a porcine model of cardiac arrest.

Cardiac Arrest in Pigs With 48 hours of Post-Resuscitation Care Induced by 2 Methods of Myocardial Infarction: A Methodological Description

Background

Systematic reviews have disclosed a lack of clinically relevant cardiac arrest animal models. The aim of this study was to develop a cardiac arrest model in pigs encompassing relevant cardiac arrest characteristics and clinically relevant post‐resuscitation care.

Methods and Results

We used 2 methods of myocardial infarction in conjunction with cardiac arrest. One group (n=7) had a continuous coronary occlusion, while another group (n=11) underwent balloon‐deflation during arrest and resuscitation with re‐inflation after return of spontaneous circulation. A sham group was included (n=6). All groups underwent 48 hours of intensive care including 24 hours of targeted temperature management. Pigs underwent invasive hemodynamic monitoring. Left ventricular function was assessed by pressure‐volume measurements. The proportion of pigs with return of spontaneous circulation was 43% in the continuous infarction group and 64% in the deflation‐reinflation group. In the continuous infarction group 29% survived the entire protocol while 55% survived in the deflation‐reinflation group. Both cardiac arrest groups needed vasopressor and inotropic support and pressure‐volume measurements showed cardiac dysfunction. During rewarming, systemic vascular resistance decreased in both cardiac arrest groups. Median [25%;75%] troponin‐I 48 hours after return of spontaneous circulation, was 88 973 ng/L [53 124;99 740] in the continuous infarction group, 19 661 ng/L [10 871;23 209] in the deflation‐reinflation group, and 1973 ng/L [1117;1995] in the sham group.

Conclusions

This article describes a cardiac arrest pig model with myocardial infarction, targeted temperature management, and clinically relevant post‐cardiac arrest care. We demonstrate 2 methods of inducing myocardial ischemia with cardiac arrest resulting in post‐cardiac arrest organ injury including cardiac dysfunction and cerebral injury.

Beneficial Effects of Ivabradine on Post-Resuscitation Myocardial Dysfunction in a Porcine Model of Cardiac Arrest

Background:

Ivabradine selectively inhibits the If current, reducing the heart rate and protecting against myocardial ischemia/reperfusion injury. We investigated the effects of ivabradine on post-resuscitation myocardial function in a porcine model of cardiopulmonary resuscitation.

Methods and Results:

Ventricular fibrillation was induced and untreated for 8 min while defibrillation was attempted after 6 min of cardiopulmonary resuscitation in anesthetized domestic swine. Then the animals were randomized into ivabradine and placebo groups (n = 5 each). Ivabradine and saline were administered at the same volume 5 min after Return of Spontaneous Circulation, followed by continuous intravenous infusion at 0.5 mg/kg for 480 min. Hemodynamic parameters were continuously recorded. Myocardial function was assessed by echocardiography at baseline and at 60, 120, 240, 480 min and 24 h after resuscitation. The serum levels of N-terminal pro-brain natriuretic peptide (NT-proBNP) and cardiac troponin I (cTnI) were measured by commercial enzyme-linked immunosorbent assay kits. Animals were killed 24 h after resuscitation, and all myocardial tissue was removed for histopathological analysis. The heart rate was significantly reduced from 1 h after resuscitation in the ivabradine group (all P < 0.05). The post-resuscitation mitral E/A and E/e′ velocity ratios and left ventricular ejection fraction were significantly better in the ivabradine than placebo group (P < 0.05). The serum levels of myocardial injury biomarkers (NT-proBNP, cTnI) and the myocardial biopsy scores were significantly lower in the ivabradine than placebo group (P < 0.05). Neurological deficit scores were lower in the IVA group at PR 24 h (P < 0.05).

Conclusions:

Ivabradine improved post-resuscitation myocardial dysfunction, myocardial injury, and post-resuscitation cerebral function, and also slowed the heart rate in this porcine model.

Impaired Right Ventricular Performance Is Associated with Adverse Outcome after Hypoxic Ischemic Encephalopathy

Rationale: Asphyxiated neonates with hypoxic ischemic encephalopathy (HIE) are at risk of myocardial dysfunction; however, echocardiography studies are limited and little is known about the relationship between hemodynamics and brain injury.Objectives: To analyze the association between severity of myocardial dysfunction and adverse outcome as defined by the composite of death and/or abnormal magnetic resonance imaging.Methods: Neonates with HIE undergoing therapeutic hypothermia were enrolled. Participants underwent echocardiography at 24 hours, 72 hours (before rewarming), and 96 hours (after rewarming). Cerebral hemodynamics were monitored by near-infrared spectroscopy and middle cerebral artery Doppler.Measurements and Main Results: Fifty-three patients with a mean gestation and birthweight of 38.8 ± 2.0 weeks and 3.33 ± 0.6 kg, respectively, were recruited. Thirteen patients (25%) had mild encephalopathy, 27 (50%) had moderate encephalopathy, and 13 (25%) had severe encephalopathy. Eighteen patients (34%) had an adverse outcome. Severity of cardiovascular illness (P < 0.001) and severity of neurologic insult (P = 0.02) were higher in neonates with adverse outcome. Right ventricle (RV) systolic performance at 24 hours was substantially lower than published normative data in all groups. At 24 hours, lower tricuspid annular plane systolic excursion (P = 0.004) and RV fractional area change (P < 0.001), but not pulmonary hypertension, were independently associated with adverse outcome on logistic regression. High brain regional oxygen saturation (P = 0.007) and low middle cerebral artery resistive index (P = 0.04) were associated with RV dysfunction on post hoc analysis.Conclusions: RV dysfunction is associated with the risk of adverse outcome in asphyxiated patients with HIE undergoing hypothermia. Echocardiography may be a valuable diagnostic and prognostic tool in this vulnerable population.

Transcriptome Analysis of Gene Expression Provides New Insights into the Effect of Mild Therapeutic Hypothermia on Primary Human Cortical Astrocytes Cultured under Hypoxia

Hypothermia is increasingly used as a therapeutic measure to treat brain injury. However, the cellular mechanisms underpinning its actions are complex and are not yet fully elucidated. Astrocytes are the most abundant cell type in the brain and are likely to play a critical role. In this study, transcriptional changes and the protein expression profile of human primary cortical astrocytes cultured under hypoxic conditions for 6 h were investigated. Cells were treated either with or without a mild hypothermic intervention 2 h post-insult to mimic the treatment of patients following traumatic brain injury (TBI) and/or stroke. Using human gene expression microarrays, 411 differentially expressed genes were identified following hypothermic treatment of astrocytes following a 2 h hypoxic insult. KEGG pathway analysis indicated that these genes were mainly enriched in the Wnt and p53 signaling pathways, which were inhibited following hypothermic intervention. The expression levels of 168 genes involved in Wnt signaling were validated by quantitative real-time-PCR (qPCR). Among these genes, 10 were up-regulated and 32 were down-regulated with the remainder unchanged. Two of the differentially expressed genes (DEGs), p38 and JNK, were selected for validation at the protein level using cell based ELISA. Hypothermic intervention significantly down-regulated total protein levels for the gene products of p38 and JNK. Moreover, hypothermia significantly up-regulated the phosphorylated (activated) forms of JNK protein, while downregulating phosphorylation of p38 protein. Within the p53 signaling pathway, 35 human apoptosis-related proteins closely associated with Wnt signaling were investigated using a Proteome Profiling Array. Hypothermic intervention significantly down-regulated 18 proteins, while upregulating one protein, survivin. Hypothermia is a complex intervention; this study provides the first detailed longitudinal investigation at the transcript and protein expression levels of the molecular effects of therapeutic hypothermic intervention on hypoxic human primary cortical astrocytes. The identified genes and proteins are targets for detailed functional studies, which may help to develop new treatments for brain injury based on an in-depth mechanistic understanding of the astrocytic response to hypoxia and/or hypothermia.

The Extent of Myocardial Injury During Prolonged Targeted Temperature Management After Out-of-Hospital Cardiac Arrest

AIM

The aim of this study is to evaluate the extent of myocardial injury by cardiac biomarkers during prolonged targeted temperature management of 24 hours vs 48 hours after out-of-hospital cardiac arrest.

METHODS

This randomized Scandinavian multicenter study compares the extent of myocardial injury quantified by area under the curve (AUC) of cardiac biomarkers during prolonged targeted temperature management at 33°C ± 1°C of 24 hours and 48 hours, respectively. Through a period of 2.5 years, 161 comatose out-of-hospital cardiac arrest patients were randomized to targeted temperature management for 24 hours (n = 77) or 48 hours (n = 84). The AUC was calculated using both high-sensitivity cardiac troponin T (hs-cTnT_AUC) and creatine kinase-myocardial band (CK-MB_AUC) that were based upon measurements of these biomarkers every 6 hours upon admission until 96 hours after reaching target temperature.

RESULTS

The median hs-cTnT_AUC of 33,827 ng/L/h (interquartile range [IQR] 11,366-117,690) of targeted temperature management at 24 hours did not differ significantly from that of 28,973 ng/L/h (IQR 10,656-163,655) at 48 hours. In contrast, the median CK-MB_AUC of 1829 μg/L/h (IQR 800-6799) during targeted temperature management at 24 hours was significantly lower than that of 2428 μg/L/h (IQR 1163-10,906) within targeted temperature management at 48 hours, P <.05.

CONCLUSION

This study of comatose out-of-hospital cardiac arrest survivors showed no difference between the extents of myocardial injury estimated by hs-cTnT_AUC of prolonged targeted temperature management of 48 hours vs 24 hours, although the CK-MB_AUC was significantly higher during 48 hours vs 24 hours. Hence, it seems unlikely that the duration of targeted temperature management has a beneficial effect on the extent of myocardial injury after out-of-hospital cardiac arrest, and may even have a worsening effect.

Chronic heart failure: Ca(2+), catabolism, and catastrophic cell death

Robust successes have been achieved in recent years in conquering the acutely lethal manifestations of heart disease. Many patients who previously would have died now survive to enjoy happy and productive lives. Nevertheless, the devastating impact of heart disease continues unabated, as the spectrum of disease has evolved with new manifestations. In light of this ever-evolving challenge, insights that culminate in novel therapeutic targets are urgently needed. Here, we review fundamental mechanisms of heart failure, both with reduced (HFrEF) and preserved (HFpEF) ejection fraction. We discuss pathways that regulate cardiomyocyte remodeling and turnover, focusing on Ca(2+) signaling, autophagy, and apoptosis. In particular, we highlight recent insights pointing to novel connections among these events. We also explore mechanisms whereby potential therapeutic approaches targeting these processes may improve morbidity and mortality in the devastating syndrome of heart failure.

Prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation model

BACKGROUND

Hypothermia when cardiopulmonary resuscitation begins may help achieve defibrillation and return of spontaneous circulation (ROSC), but few data are available.

OBJECTIVE

The objective of this study was to determine whether prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation (VF) model.

RESULTS

Thirty-six New Zealand rabbits were randomized equally to receive normothermia (Norm) (~39°C), post-ROSC hypothermia (~33°C), or prearrest hypothermia (~33°C). Ventricular fibrillation was induced by alternating current. After 4 minutes of VF, rabbits were defibrillated and given cardiopulmonary resuscitation until ROSC or no response (≥30 minutes). Hemodynamics and electrocardiogram were monitored; N-terminal pro-brain natriuretic peptideand troponin I were determined by enzyme-linked immunosorbent assay. Myocardial histology and echocardiographic data were evaluated. First-shock achievement of perfusion rhythm was more frequent in prearrest than normothermic animals (7/12 vs 1/12; P=.027). After ROSC, dp/dtmax was higher in prearrest than normothermic animals (P<.001). Left ventricular end-systolic pressure was higher in prearrest than normothermic animals (P=.001). At 240 minutes after ROSC, troponin I and N-terminal pro-brain natriuretic peptide were lower in prearrest than normothermic animals (15.74±2.26 vs 25.09±1.85 ng/mL and 426±23 vs 284±45 pg/mL, respectively), the left ventricular ejection fraction and cardiac output were lower in the Norm group than other 2 groups (P<.01). Myocardial histology was more disturbed in normothermic than post-ROSC and prearrest animals, but was not different in the latter 2 groups.

CONCLUSIONS

Induction of hypothermia before VF led to improved cardiac function in a rabbit VF model through improving achievement of perfusing rhythm by first-shock defibrillation and facilitating resuscitation.

Protective effects of the melanocortin analog NDP-α-MSH in rats undergoing cardiac arrest

We previously reported that melanocortins afford cardioprotection in conditions of experimental myocardial ischemia/reperfusion, with involvement of the janus kinases (JAK), extracellular signal-regulated kinases (ERK) and signal transducers and activators of transcription (STAT) signalings. We investigated the influence of the melanocortin analog [Nle(4), D-Phe(7)]α-melanocyte-stimulating hormone (NDP-α-MSH) on short-term detrimental responses to cardiac arrest (CA) induced in rats by intravenous (i.v.) administration of potassium chloride, followed by cardiopulmonary resuscitation (CPR) plus epinephrine treatment. In CA/CPR rats i.v. treated with epinephrine (0.1 mg/kg) and returned to spontaneous circulation (48%) we recorded low values of mean arterial pressure (MAP) and heart rate (HR), alteration of hemogasanalysis parameters, left ventricle low expression of the cardioprotective transcription factors pJAK2 and pTyr-STAT3 (JAK-dependent), increased oxidative stress, up-regulation of the inflammatory mediators tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and down-regulation of the anti-inflammatory cytokine IL-10, as assessed at 1h and 3h after CPR. On the other hand, i.v. treatment during CPR with epinephrine plus NDP-α-MSH (340 μg/kg) almost completely restored the basal conditions of MAP and HR, reversed metabolic acidosis, induced left ventricle up-regulation of pJAK2, pTyr-STAT3 and IL-10, attenuated oxidative stress, down-regulated TNF-α and IL-6 levels, and improved survival rate by 81%. CA/CPR plus epinephrine alone or in combination with NDP-α-MSH did not affect left ventricle pSer-STAT3 (ERK1/2-dependent) and pERK1/2 levels. These results indicate that melanocortins improve return to spontaneous circulation, reverse metabolic acidosis, and inhibit heart oxidative stress and inflammatory cascade triggered by CA/CPR, likely via activation of the JAK/STAT signaling pathway.

Effects of pretreatment hypothermia during resuscitated porcine hemorrhagic shock

OBJECTIVES

Accidental hypothermia increases mortality and morbidity after hemorrhage, but controversial data are available on the effects of therapeutic hypothermia. Therefore, we tested the hypothesis whether moderate pretreatment hypothermia would beneficially influence organ dysfunction during long-term, porcine hemorrhage and resuscitation.

DESIGN

Prospective, controlled, randomized study.

SETTING

University animal research laboratory.

SUBJECTS

Twenty domestic pigs of either gender.

INTERVENTIONS

Using an extracorporeal heat exchanger, anesthetized and instrumented animals were maintained at 38°C, 35°C, or 32°C core temperature and underwent 4 hours of hemorrhage (removal of 40% of the blood volume and subsequent blood removal/retransfusion to maintain mean arterial pressure at 30 mm Hg). Resuscitation comprised of hydroxyethyl starch and norepinephrine infusion titrated to maintain mean arterial pressure at preshock values.

MEASUREMENTS AND MAIN RESULTS

Before, immediately at the end of, and 12 and 22 hours after hemorrhage, we measured systemic and regional hemodynamics (portal vein, hepatic and right kidney artery ultrasound flow probes) and oxygen transport, and nitric oxide and cytokine production. Hemostasis was assessed by rotation thromboelastometry. Postmortem biopsies were analyzed for histomorphology (hematoxylin and eosin staining) and markers of apoptosis (kidney Bcl-xL and caspase-3 expression). Hypothermia at 32°C attenuated the shock-related lactic acidosis but caused metabolic acidosis, most likely resulting from reduced carbohydrate oxidation. Although hypothermia did not further aggravate shock-related coagulopathy, it caused a transitory attenuation of kidney and liver dysfunction, which was ultimately associated with reduced histological damage and more pronounced apoptosis.

CONCLUSIONS

During long-term porcine hemorrhage and resuscitation, moderate pretreatment hypothermia was associated with a transitory attenuation of organ dysfunction and less severe histological tissue damage despite more pronounced metabolic acidosis. This effect is possibly due to a switch from necrotic to apoptotic cell death, ultimately resulting from reduced tissue energy deprivation during the shock phase.

Induced hypothermia does not impair coagulation system in a swine multiple trauma model

BACKGROUND

Accidental hypothermia, acidosis, and coagulopathy represent the lethal triad in severely injured patients. Therapeutic hypothermia however is commonly used in transplantations, cardiac and neurosurgical surgery, or after cardiac arrest. However, the effects of therapeutic hypothermia on the coagulation system following multiple trauma need to be elucidated.

METHODS

In a porcine model of multiple trauma including blunt chest injury, liver laceration, and hemorrhagic shock followed by fluid resuscitation, the influence of therapeutic hypothermia on coagulation was evaluated. A total of 40 pigs were randomly assigned to sham (only anesthesia) or trauma groups receiving either hypothermia or normothermia. Each group consisted of 10 pigs. Analyzed parameters were cell count (red blood cells, platelets), pH, prothrombin time (PT), fibrinogen concentration, and analysis with ROTEM and Multiplate.

RESULTS

Trauma and consecutive fluid resuscitation resulted in impaired coagulation parameters (cell count, pH, PT, fibrinogen, ROTEM, and platelet function). During hypothermia, coagulation parameters measured at 37°C, such as PT, fibrinogen, thrombelastometry measurements, and platelet function, showed no significant differences between normothermic and hypothermic animals in both trauma groups. Additional analyses of thrombelastometry at 34°C during hypothermia showed significant differences for clotting time and clot formation time but not for maximum clot firmness. We were not able to detect macroscopic or petechial bleeding in both trauma groups.

CONCLUSION

Based on the results of the present study we suggest that mild hypothermia can be safely performed after stabilization following major trauma. Mild hypothermia has effects on the coagulation system but does not aggravate trauma-induced coagulopathy in our model. Before hypothermic treatment can be performed in the clinical setting, additional experiments with prolonged and deeper hypothermia to exclude detrimental effects are required.

Therapeutic mild hypothermia improves early outcomes in rabbits subjected to traumatic uncontrolled hemorrhagic shock

BACKGROUND

Survival benefits of mild hypothermia in animals suffering from uncontrolled hemorrhagic shock (HS) may be influenced by trauma severity. We hypothesized that mild hypothermia would improve early outcomes based on our rabbit model of severe traumatic HS.

MATERIALS AND METHODS

Fifty male New Zealand rabbits weighing between 1.6 and 2.2 kg were randomized into one of the five groups: group 1 (sham), group 2 (37°C/80 mm Hg), group 3 (37°C/40 mm Hg), group 4 (34°C/80 mm Hg), and group 5 (34°C/40 mm Hg). Under urethane anesthesia, animals that suffered fractures and uncontrolled HS received prehospital fluid resuscitation (aggressive or limited) with temperature controlled at normothermia or mild hypothermia, hemostasis, and hospital resuscitation followed by observation.

RESULTS

Mild hypothermia significantly improved cardiac systolic function and decreased lung wet-to-dry weight ratios and total injury score compared with normothermia. Group 5 manifested the best results in lung injury. The decreased base excess and pH and increased lactate levels during HS and limited fluid resuscitation were not exacerbated by mild hypothermia. Electrolytes including potassium and calcium and blood glucose levels as well as coagulation were not significantly influenced after mild hypothermia treatment. Seven-hour survival in the hypothermic groups was higher than that in the normothermic groups, although there was no significant difference in survival between groups 5 and 3.

CONCLUSIONS

Therapeutic mild hypothermia improves early outcomes through improving lung and cardiac performance without causing evident homeostasis disturbances in the rabbit model of traumatic uncontrolled HS. Animals may benefit most under the combination treatment with mild hypothermia and limited fluid resuscitation.

The implementation of therapeutic hypothermia in the emergency department: a multi-institution case review

BACKGROUND

The use of therapeutic hypothermia (TH) is a burgeoning treatment modality for post-cardiac arrest patients.

OBJECTIVES

We performed a retrospective chart review of patients who underwent post-cardiac arrest TH at eight different institutions across the United States. Our objectives were to assess how TH is currently being implemented in emergency departments and to examine the feasibility of conducting TH research using multi-institution prospective data.

METHODS

A total of 94 cases were identified in a 3-year period and submitted for review by participating institutions of the Peri-Resuscitation Consortium. Of those, seven charts were excluded for missing data. Two independent reviewers performed the data abstraction. Results were subsequently compared, and discrepancies were resolved by a third reviewer. We assessed patient demographics, initial presenting rhythm, time until TH initiation, duration of TH, cooling methods and temperature reached, survival to hospital discharge, and neurological status on discharged.

RESULTS

The majority of cases had initial cardiac rhythms of asystole or pulseless electrical activity (55.2%), followed by ventricular tachycardia or fibrillation (34.5%). The inciting cardiac rhythm was unknown in 10.3% of cases. Time to initiation of TH ranged from 0 to 783 minutes with a mean time of 99 minutes (SD=132). Length of TH ranged from 25 to 2,171 minutes with a mean time of 1,191 minutes (SD=536). The average minimum temperature achieved was 32.5°C, with a range from 27.6°C to 36.7°C (SD=1.5°C). Of the 87 charts reviewed, 29 (33.3%) of the patients survived to hospital discharge.

CONCLUSION

The implementation of TH across the country is extremely varied with no universally accepted treatment. While our study is limited by sample size, it illustrates some compelling trends. A large, prospective, multicenter trial or registry is necessary to elucidate further the optimal parameters for TH and its benefit in various population subsets.