Comparative Effectiveness of Amiodarone and Lidocaine for the Treatment of In-Hospital Cardiac Arrest.

BACKGROUND: American Heart Association Advanced Cardiac Life Support (ACLS) guidelines support the use of either amiodarone or lidocaine for cardiac arrest caused by ventricular tachycardia or ventricular fibrillation (VT/VF) based on studies of out-of-hospital cardiac arrest. Studies comparing amiodarone and lidocaine in adult populations with in-hospital VT/VF arrest are lacking. RESEARCH QUESTION: Does treatment with amiodarone vs lidocaine therapy have differential associations with outcomes among adult patients with in-hospital cardiac arrest from VT/VF? STUDY DESIGN AND METHODS: This retrospective cohort study of adult patients receiving amiodarone or lidocaine for VT/VF in-hospital cardiac arrest refractory to CPR and defibrillation between January 1, 2000, and December 31, 2014, was conducted within American Heart Association Get With the Guidelines-Resuscitation (GWTG-R) participating hospitals. The primary outcome was return of spontaneous circulation (ROSC). Secondary outcomes were 24 h survival, survival to hospital discharge, and favorable neurologic outcome. RESULTS: Among 14,630 patients with in-hospital VT/VF arrest, 68.7% (n = 10,058) were treated with amiodarone and 31.3% (n = 4,572) with lidocaine. When all covariates were statistically controlled, compared with amiodarone, lidocaine was associated with statistically significantly higher odds of the following: (1) ROSC (adjusted OR [AOR], 1.15, P = .01; average marginal effect [AME], 2.3; 95% CI, 0.5 to 4.2); (2) 24 h survival (AOR, 1.16; P = 004; AME, 3.0; 95% CI, 0.9 to 5.1); (3) survival to discharge (AOR, 1.19; P < .001; AME, 3.3; 95% CI, 1.5 to 5.2); and (4) favorable neurologic outcome at hospital discharge (AOR, 1.18; P < .001; AME, 3.1; 95% CI, 1.3 to 4.9). Results using propensity score methods were similar to those from multivariable logistic regression analyses. INTERPRETATION: Compared with amiodarone, lidocaine therapy among adult patients with in-hospital cardiac arrest from VT/VF was associated with statistically significantly higher rates of ROSC, 24 h survival, survival to hospital discharge, and favorable neurologic outcome.

"All citizens of the world can save a life" - The World Restart a Heart (WRAH) initiative starts in 2018.

"All citizens of the world can save a life". With these words, the International Liaison Committee on Resuscitation (ILCOR) is launching the first global initiative - World Restart a Heart (WRAH) - to increase public awareness and therefore the rates of bystander cardiopulmonary resuscitation (CPR) for victims of cardiac arrest. In most of the cases, it takes too long for the emergency services to arrive on scene after the victim's collapse. Thus, the most effective way to increase survival and favourable outcome in cardiac arrest by two- to fourfold is early CPR by lay bystanders and by "first responders". Lay bystander resuscitation rates, however, differ significantly across the world, ranging from 5 to 80%. If all countries could have high lay bystander resuscitation rates, this would help to save hundreds of thousands of lives every year. In order to achieve this goal, all seven ILCOR councils have agreed to participate in WRAH 2018. Besides schoolchildren education in CPR ("KIDS SAVE LIVES"), many other initiatives have already been developed in different parts of the world. ILCOR is keen for the WRAH initiative to be as inclusive as possible, and that it should happen every year on 16 October or as close to that day as possible. Besides recommending CPR training for children and adults, it is hoped that a unified global message will enable our policy makers to take action to address the inequalities in patient survival around the world.

Endoplasmic reticulum stress-induced cysteine protease activation in cortical neurons: effect of an Alzheimer's disease-linked presenilin-1 knock-in mutation.

Endoplasmic reticulum (ER) stress elicits protective responses of chaperone induction and translational suppression and, when unimpeded, leads to caspase-mediated apoptosis. Alzheimer's disease-linked mutations in presenilin-1 (PS-1) reportedly impair ER stress-mediated protective responses and enhance vulnerability to degeneration. We used cleavage site-specific antibodies to characterize the cysteine protease activation responses of primary mouse cortical neurons to ER stress and evaluate the influence of a PS-1 knock-in mutation on these and other stress responses. Two different ER stressors lead to processing of the ER-resident protease procaspase-12, activation of calpain, caspase-3, and caspase-6, and degradation of ER and non-ER protein substrates. Immunocytochemical localization of activated caspase-3 and a cleaved substrate of caspase-6 confirms that caspase activation extends into the cytosol and nucleus. ER stress-induced proteolysis is unchanged in cortical neurons derived from the PS-1 P264L knock-in mouse. Furthermore, the PS-1 genotype does not influence stress-induced increases in chaperones Grp78/BiP and Grp94 or apoptotic neurodegeneration. A similar lack of effect of the PS-1 P264L mutation on the activation of caspases and induction of chaperones is observed in fibroblasts. Finally, the PS-1 knock-in mutation does not alter activation of the protein kinase PKR-like ER kinase (PERK), a trigger for stress-induced translational suppression. These data demonstrate that ER stress in cortical neurons leads to activation of several cysteine proteases within diverse neuronal compartments and indicate that Alzheimer's disease-linked PS-1 mutations do not invariably alter the proteolytic, chaperone induction, translational suppression, and apoptotic responses to ER stress.

Calpain activity in the rat brain after transient forebrain ischemia.

Activity of the Ca(2+)-dependent protease calpain is increased in neurons after global and focal brain ischemia, and may contribute to postischemic injury cascades. Understanding the time course and location of calpain activity in the post-ischemic brain is essential to establishing causality and optimizing therapeutic interventions. This study examined the temporal and spatial characteristics of brain calpain activity after transient forebrain ischemia (TFI) in rats. Male Long Evans rats underwent 10 min of normothermic TFI induced by bilateral carotid occlusion with hypovolemic hypotension (MABP 30 mm Hg). Brain calpain activity was examined between 1 and 72 h after reperfusion. Western blot analysis of regional brain homogenates demonstrated a bimodal pattern of calpain-mediated alpha-spectrin degradation in the hippocampus, cortex, and striatum with an initial increase at 1 h followed by a more prominent secondary increase at 36 h after reperfusion. Immunohistochemical analysis revealed that calpain activity was primarily localized to dendritic fields of selectively vulnerable neurons at one hour after reperfusion. Between 24 and 48 h after reperfusion neuronal calpain activity progressed from the dorsal to ventral striatum, medial to lateral CA1 hippocampus, and centripetally expanded from watershed foci in the cerebral cortex. This progression was associated with fragmentation of dendritic processes, calpain activation in the neuronal soma and subsequent neuronal degeneration. These observations demonstrate a clear association between calpain activation and subsequent delayed neuronal death and suggest broad therapeutic window for interventions aimed at preventing delayed intracellular Ca(2+) overload and pathologic calpain activation.

Molecular mechanisms of ischemic neuronal injury.

Brain ischemia triggers a complex cascade of molecular events that unfolds over hours to days. Identified mechanisms of postischemic neuronal injury include altered Ca(2+) homeostasis, free radical formation, mitochondrial dysfunction, protease activation, altered gene expression, and inflammation. Although many of these events are well characterized, our understanding of how they are integrated into the causal pathways of postischemic neuronal death remains incomplete. The primary goal of this review is to provide an overview of molecular injury mechanisms currently believed to be involved in postischemic neuronal death specifically highlighting their time course and potential interactions.

Brain ischemia and reperfusion: molecular mechanisms of neuronal injury.

Brain ischemia and reperfusion engage multiple independently-fatal terminal pathways involving loss of membrane integrity in partitioning ions, progressive proteolysis, and inability to check these processes because of loss of general translation competence and reduced survival signal-transduction. Ischemia results in rapid loss of high-energy phosphate compounds and generalized depolarization, which induces release of glutamate and, in selectively vulnerable neurons (SVNs), opening of both voltage-dependent and glutamate-regulated calcium channels. This allows a large increase in cytosolic Ca(2+) associated with activation of mu-calpain, calcineurin, and phospholipases with consequent proteolysis of calpain substrates (including spectrin and eIF4G), activation of NOS and potentially of Bad, and accumulation of free arachidonic acid, which can induce depletion of Ca(2+) from the ER lumen. A kinase that shuts off translation initiation by phosphorylating the alpha-subunit of eukaryotic initiation factor-2 (eIF2alpha) is activated either by adenosine degradation products or depletion of ER lumenal Ca(2+). Early during reperfusion, oxidative metabolism of arachidonate causes a burst of excess oxygen radicals, iron is released from storage proteins by superoxide-mediated reduction, and NO is generated. These events result in peroxynitrite generation, inappropriate protein nitrosylation, and lipid peroxidation, which ultrastructurally appears to principally damage the plasmalemma of SVNs. The initial recovery of ATP supports very rapid eIF2alpha phosphorylation that in SVNs is prolonged and associated with a major reduction in protein synthesis. High catecholamine levels induced by the ischemic episode itself and/or drug administration down-regulate insulin secretion and induce inhibition of growth-factor receptor tyrosine kinase activity, effects associated with down-regulation of survival signal-transduction through the Ras pathway. Caspase activation occurs during the early hours of reperfusion following mitochondrial release of caspase 9 and cytochrome c. The SVNs find themselves with substantial membrane damage, calpain-mediated proteolytic degradation of eIF4G and cytoskeletal proteins, altered translation initiation mechanisms that substantially reduce total protein synthesis and impose major alterations in message selection, down-regulated survival signal-transduction, and caspase activation. This picture argues powerfully that, for therapy of brain ischemia and reperfusion, the concept of single drug intervention (which has characterized the approaches of basic research, the pharmaceutical industry, and clinical trials) cannot be effective. Although rigorous study of multi-drug protocols is very demanding, effective therapy is likely to require (1) peptide growth factors for early activation of survival-signaling pathways and recovery of translation competence, (2) inhibition of lipid peroxidation, (3) inhibition of calpain, and (4) caspase inhibition. Examination of such protocols will require not only characterization of functional and histopathologic outcome, but also study of biochemical markers of the injury processes to establish the role of each drug.

Eukaryotic initiation factor 2alpha kinase and phosphatase activity during postischemic brain reperfusion.

When ischemic brain is reperfused, there is in vulnerable neurons immediate inhibition of protein synthesis associated with a large increase in phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 [eIF2alpha, phosphorylated form eIF2alpha(P)]. We examined eIF2alpha kinase and eIF2alpha(P) phosphatase activity in brain homogenate postmitochondrial supernatants obtained from rats after 3 to 30 min of global brain ischemia (cardiac arrest), after 5 min of ischemia and 5 min of reperfusion (5R), and after 10 min of ischemia and 90 min reperfusion (90R). Because it has been suggested that PKR might be specifically responsible for producing eIF2alpha(P) during reperfusion, we also examined in brain homogenates from wild-type and PKR0/0 C57BL/6J x 129/SV mice the effect of 5 min of ischemia and 5 min of reperfusion on eIF2alpha(P). Cytosolic brain eIF2alpha(P) in the 5R and 90R rats was 18- and 23-fold that of nonischemic controls without any change in the rate of eIF2alpha(P) dephosphorylation. There was no change in eIF2alpha kinase activity between 3 and 30 min of ischemia but an 85% decrease in the 5R group; the 90R group was similar to controls. In wild-type and PKR0/0 mice total eIF2alpha was identical, and there was an identical 16-fold increase in eIF2alpha(P) at 5 min of reperfusion. Our observations contradict hypotheses that PKR activation, loss of eIF2alpha(P) phosphatase activity, or any general increase in eIF2alpha kinase activity are responsible for reperfusion-induced phosphorylation of eIF2alpha, and we suggest that the mechanism may involve regulation of the availability of eIF2alpha to a kinase.

Calpain mediates eukaryotic initiation factor 4G degradation during global brain ischemia.

Global brain ischemia and reperfusion result in the degradation of the eukaryotic initiation factor (eIF) 4G, which plays a critical role in the attachment of the mRNA to the ribosome. Because eIF-4G is a substrate of calpain, these studies were undertaken to examine whether calpain I activation during global brain ischemia contributes to the degradation of eIF-4G in vivo. Immunoblots with antibodies against calpain I and eIF-4G were prepared from rat brain postmitochondrial supernatant incubated at 37 degrees C with and without the addition of calcium and the calpain inhibitors calpastatin or MDL-28,170. Addition of calcium alone resulted in calpain I activation (as measured by autolysis of the 80-kDa subunit) and degradation of eIF-4G; this effect was blocked by either 1 micromol/L calpastatin or 10 micromol/L MDL-28,170. In rabbits subjected to 20 minutes of cardiac arrest, immunoblots of brain postmitochondrial supernatants showed that the percentage of autolyzed calpain I increased from 1.9% +/- 1.1% to 15.8% +/- 5.0% and that this was accompanied by a 68% loss of eIF-4G. MDL-28,170 pretreatment (30 mg/kg) decreased ischemia-induced calpain I autolysis 40% and almost completely blocked eIF-4G degradation. We conclude that calpain I degrades eIF-4G during global brain ischemia.

Effect of brain ischemia and reperfusion on the localization of phosphorylated eukaryotic initiation factor 2 alpha.

Postischemic brain reperfusion is associated with a substantial and long-lasting reduction of protein synthesis in selectively vulnerable neurons. Because the overall translation initiation rate is typically regulated by altering the phosphorylation of serine 51 on the alpha-subunit of eukaryotic initiation factor 2 (eIF-2 alpha), we used an antibody specific to phosphorylated eIF-2 alpha [eIF-2(alpha P)] to study the regional and cellular distribution of eIF-2(alpha P) in normal, ischemic, and reperfused rat brains. Western blots of brain postmitochondrial supernatants revealed that approximately 1% of all eIF-2 alpha is phosphorylated in controls, eIF-2(alpha P) is not reduced by up to 30 minutes of ischemia, and eIF-2(alpha P) is increased approximately 20-fold after 10 and 90 minutes of reperfusion. Immunohistochemistry shows localization of eIF-2(alpha P) to astrocytes in normal brains, a massive increase in eIF-2(alpha P) in the cytoplasm of neurons within the first 10 minutes of reperfusion, accumulation of eIF-2(alpha P) in the nuclei of selectively vulnerable neurons after 1 hour of reperfusion, and morphology suggesting pyknosis or apoptosis in neuronal nuclei that continue to display eIF-2(alpha P) after 4 hours of reperfusion. These observations, together with the fact that eIF-2(alpha P) inhibits translation initiation, make a compelling case that eIF-2(alpha P) is responsible for reperfusion-induced inhibition of protein synthesis in vulnerable neurons.

Global brain ischemia and reperfusion: modifications in eukaryotic initiation factors associated with inhibition of translation initiation.

We used in vitro translation and antibodies against phosphoserine and the eukaryotic initiation factors elF-4E, elF-4G, and elF-2 alpha to examine the effects of global brain ischemia and reperfusion on translation initiation and its regulation in a rat model of 10 min of cardiac arrest followed by resuscitation and 90 min of reperfusion. Translation reactions were performed on postmitochondrial supernatants from brain homogenates with and without aurintricarboxylic acid to separate incorporation due to run-off from incorporation due to peptide synthesis initiated in vitro. The rate of leucine incorporation due to in vitro-initiated protein synthesis in normal forebrain homogenates was approximately 0.4 fmol of leucine/min/microgram of protein and was unaffected by 10 min of cardiac arrest, but 90 min of reperfusion reduced this rate 83%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blots of these homogenates showed that neither 10 min of global brain ischemia nor 90 min of reperfusion induced significant alterations in the quantity or serine phosphorylation of elF-4E. However, we observed in all 90-min-reperfused samples elF-4G fragments that also bound elF-4E. The amount of elF-2 alpha was not altered by ischemia or reperfusion, and immunoblotting after isoelectric focusing did not detect serine-phosphorylated elF-2 alpha in normal samples or in those obtained after ischemia without reperfusion. However, serine-phosphorylated elF-2 alpha was uniformly present after 90 min of reperfusion and represented 24 +/- 3% of the elF-2 alpha in these samples. The serine phosphorylation of elF-2 alpha and partial fragmentation of elF-4G observed after 90 min of reperfusion offer an explanation for the inhibition of protein synthesis.

Global brain ischemia and reperfusion.

Brain damage accompanying cardiac arrest and resuscitation is frequent and devastating. Neurons in the hippocampus CA1 and CA4 zones and cortical layers III and V are selectively vulnerable to death after injury by ischemia and reperfusion. Ultrastructural evidence indicates that most of the structural damage is associated with reperfusion, during which the vulnerable neurons develop disaggregation of polyribosomes, peroxidative damage to unsaturated fatty acids in the plasma membrane, and prominent alterations in the structure of the Golgi apparatus that is responsible for membrane assembly. Reperfusion is also associated with vulnerable neurons with prominent production of messenger RNAs for stress proteins and for the proteins of the activator protein-1 complex, but these vulnerable neurons fail to efficiently translate these messages into the proteins. The inhibition of protein synthesis during reperfusion involves alteration of translation initiation factors, specifically serine phosphorylation of the alpha-subunit of eukaryotic initiation factor-2 (elF-2 alpha). Growth factors--in particular, insulin--have the potential to reverse phosphorylation of elF-2 alpha, promote effective translation of the mRNA transcripts generated in response to ischemia and reperfusion, enhance neuronal defenses against radicals, and stimulate lipid synthesis and membrane repair. There is now substantial evidence that the insulin-class growth factors have neuron-sparing effects against damage by radicals and ischemia and reperfusion. This new knowledge may provide a fundamental basis for a rational approach to "cerebral resuscitation" that will allow substantial amelioration of the often dismal neurologic outcome now associated with resuscitation from cardiac arrest.

Brain mu-calpain autolysis during global cerebral ischemia.

Proteolytic degradation of numerous calpain substrates, including cytoskeletal and regulatory proteins, has been observed during brain ischemia and reperfusion. In addition, calpain inhibitors have been shown to decrease degradation of these proteins and decrease postischemic neuronal death. Although these observations support the inference of a role for mu-calpain in the pathophysiology of ischemic neuronal injury, the evidence is indirect. A direct indicator of mu-calpain proteolytic activity is autolysis of its 80-kDa catalytic subunit, and therefore we examined the mu-calpain catalytic subunit for evidence of autolysis during cerebral ischemia. Rabbit brain homogenates obtained after 0, 5, 10, and 20 min of cardiac arrest were electrophoresed and immunoblotted with a monoclonal antibody specific to the mu-calpain catalytic subunit. In nonischemic brain homogenates the antibody identified an 80-kDa band, which migrated identically with purified mu-calpain, and faint 78- and 76-kDa bands, which represent autolyzed forms of the 80-kDa subunit. The average density of the 80-kDa band decreased by 25 +/- 4 (p = 0.008) and 28 +/- 9% (p = 0.004) after 10 and 20 min of cardiac arrest, respectively, whereas the average density of the 78-kDa band increased by 111 +/- 50% (p = 0.02) after 20 min of cardiac arrest. No significant change in the density of the 76-kDa band was detected. These results provide direct evidence for autolysis of brain mu-calpain during cerebral ischemia. Further work is needed to characterize the extent, duration, and localization of mu-calpain activity during brain ischemia and reperfusion as well as its role in the causal pathway of postischemic neuronal injury.

Eukaryotic initiation factor 4E degradation during brain ischemia.

Suppression of protein synthesis in the brain following an ischemic insult has been thought to occur because of inhibition of translation initiation. All eukaryotic mRNAs, with the exception of heat-shock transcripts, require the activity of eukaryotic initiation factor (eIF) 4E for formation of the translation initiation complex, and eIF-4E availability is rate-limiting. The response of brain eIF-4E concentration and phosphorylation following decapitation ischemia was studied in rat brain homogenates after electrophoresis and western blotting with antibodies against eIF-4E and phosphoserine, respectively. There was no change in level of eIF-4E after 5 min of ischemia (p = 0.82 vs. time 0), but it had decreased 32 (p = 0.01) and 57% (p = 0.006) after 10 and 20 min of ischemia, respectively. There was no loss of serine phosphorylation on eIF-4E beyond signal loss observed due to degradation of the protein itself (p = 0.31). In vitro exposure of eIF-4E to activated mu-calpain resulted in a 50% loss in 10 min of eIF-4E on western blots. If active eIF-4E is required for translation of its own mRNA, degradation of this protein during ischemia, possibly by activated mu-calpain, could be a direct mechanism of irreversible neuronal injury, and the rate of proteolysis of eIF-4E could place an upper time limit on the maximal duration of global brain ischemia compatible with neurologic recovery.

Epinephrine and sodium bicarbonate during CPR following asphyxial cardiac arrest in rats.

Although high-dose epinephrine during CPR improves coronary perfusion pressure (CoPP) and rate of return of spontaneous circulation (ROSC) in some models, its impact on long term outcome (> or = 72 h) has not been evaluated. Previous studies of sodium bicarbonate (NaHCO3) therapy during CPR indicate that beneficial effects may be dependent on epinephrine (EPI) dose. We hypothesized that EPI and NaHCO3 given during CPR have a significant impact on long term outcome. One hundred male Sprague-Dawley rats were prospectively studied in a block randomized placebo controlled trial. Rats were anesthetized, paralyzed, mechanically ventilated, instrumented, and each underwent 10 min of asphyxia, resulting in 6.8 +/- 0.4 min of circulatory arrest. Resuscitation was performed by mechanical ventilation and manual external chest compressions. EPI 0.0 (placebo), 0.01, 0.1, or 1.0 mg/kg IV was given at the onset of CPR, followed by NaHCO3 0.0 (placebo) or 1.0 mEq/kg IV. Successfully resuscitated rats were monitored and ventilated for 1 h without hemodynamic support. Neurologic deficit scores (NDS), cerebral histopathologic damage scores (CHDS) and myocardial histopathologic damage scores (MHDS) were determined in rats that survived 72 h. EPI improved CoPP and ROSC in a dose-dependent manner up to 0.1 mg/kg. Rats receiving EPI 0.1 and 1.0 mg/kg during CPR exhibited prolonged post-ROSC hypertension and metabolic acidemia, increased A-a O2 gradient, and an increased incidence of post-ROSC ventricular tachycardia or fibrillation. Overall survival was lower with EPI 0.1 and 1.0 mg/kg compared to 0.01 mg/kg. Although NDS was significantly less with EPI 0.1 mg/kg compared to placebo, there was no difference in CHDS between groups. In contrast, MDS was significantly higher with EPI 0.1 mg/kg compared to placebo or EPI 0.01 mg/kg. There was an overall trend toward improved survival at 72 h in rats that received NaHCO3 which was most evident in the EPI 0.1 mg/kg group. We conclude that (1) EPI during CPR has a biphasic dose/response curve in terms of survival, when post-resuscitation effects are left untreated and (2) NaHCO3 doses greater than 1.0 mEq/kg may be necessary to treat the side-effects of high-dose EPI. Further work is needed to determine if treating the immediate post-resuscitation effects of high-dose EPI can prevent detrimental effects on long-term outcome.

Global brain ischemia and reperfusion: Golgi apparatus ultrastructure in neurons selectively vulnerable to death.

The neocortex and the hippocampus were examined for lipid peroxidation products and ultrastructural alterations by fluorescence and electron microscopy, respectively, in rats subjected to 10 min of cardiac arrest or 10 min cardiac arrest and either 90 or 360 min reperfusion. Lipid peroxidation products were observed after 90 min reperfusion in the perikarya and proximal dendrites of neocortical pyramidal neurons and in the hippocampal hilar cells and CA1, region; the fluorescence was most intense at the base of the apical dendrite, the region of the Golgi apparatus. After 90 min of reperfusion, the CA1, showed considerable stretches of rough endoplasmic reticulum devoid of ribosomes and the Golgi cisternae were shorter and widely dilated. The neocortex showed similar endoplasmic reticulum changes, but no significant alterations to the Golgi were noted. In addition there were areas where strings of ribosomes appear to be detaching from the endoplasmic reticulum. After 360 min reperfusion in both the neocortex and the hippocampus, the damage appeared more severe. The Golgi was fragmented into vacuoles, membranous whorls had appeared, and dense aggregates of smooth vesicles were seen coalescing with each other and the vacuoles. These observations suggest that early Golgi involvement is a more important marker of lethal injury than ribosome release from the endoplasmic reticulum. The areas of disturbed Golgi ultrastructure correspond to those areas that show evidence of lipid peroxidation and imply that lipid peroxidation may be causally related to the disturbance in Golgi ultrastructure.

Estimation of myocardial ischemic injury during ventricular fibrillation with total circulatory arrest using high-energy phosphates and lactate as metabolic markers.

STUDY OBJECTIVE: To define the time course of myocardial ischemic injury using high-energy phosphate (HEP) depletion and the cessation of lactate production as metabolic markers. SETTING: Data were collected in a laboratory animal model. TYPE OF PARTICIPANTS: Ten immature mixed breed swine weighing 23.2 +/- 3.5 kg. DESIGN: After thoracotomy, transmural myocardial biopsies were taken in vivo during normal sinus rhythm and at designated times during ventricular fibrillation with total circulatory arrest (VF-TCA). MEASUREMENTS AND MAIN RESULTS: Frozen tissue samples were analyzed for adenine nucleotides, by high-performance liquid chromatography, and lactate by enzymatic assay. At five minutes of VF-TCA, myocardial adenosine triphosphate averaged 50% of control. At 15 minutes of VF-TCA, 89% of animals had myocardial adenosine triphosphate levels above 20% of control and adenylate charge ratio above 0.60. With more than 30 minutes of VF-TCA, all animals had adenosine triphosphate levels below 10% of control and adenylate charge ratio below 0.30. In addition, myocardial lactate levels plateaued after 30 minutes of VF-TCA, indicating the cessation of lactate production. CONCLUSION: These results suggest that the myocardium can tolerate VF-TCA for as long as 15 minutes without irreversible injury; however, post-ischemic myocardial dysfunction may occur after as little as five minutes of VF-TCA. With more than 30 minutes of VF-TCA, myocardial injury is likely to be irreversible.