Nuclear magnetic resonance spectroscopy study of human brain after cardiac resuscitation

Value of assessment of multivoxel proton chemical shift imaging to predict long term outcome in patients after out-of-hospital cardiac arrest: A preliminary prospective observational study

BACKGROUND

Existing methods to predict recovery after out-of-hospital cardiac arrest (OHCA) lack of accuracy. The aim of this study was to determine whether quantitative proton chemical shift imaging (¹H-CSI) during the subacute stage of OHCA can predict neurological outcome of such patients.

METHODS

This monocentric prospective observational study was conducted in a Intensive Care Unit of a teaching hospital. Forty consecutive patients with OHCA were enrolled between January 1st 2011-December 31st 2013. Multivoxel ¹H-CSI values were compared to structural magnetic resonance imaging (MRI) sequences (fluid-attenuated inversion recovery and diffusion-weighted imaging). Ratios of N-acetyl-aspartate (NAA) to creatine (Cr) and choline compounds were analyzed using region of interest in bilateral lenticular cores and thalami. The outcome evaluated was the Cerebral Performance Category (CPC) at 6 months, dichotomized as favorable (CPC 1-2) and unfavorable outcome (CPC 3-5). The performance was compared by area under the receiver operating characteristic (ROC_AUC) curves analysis.

RESULTS

Twenty nine OHCA had an interpretable MRI. Eight patients (28%) had favorable outcome at 6 months. The worst NAA/Cr in lenticular cores was the best ¹H-CSI marker, with 80% sensitivity (95% confidence interval (CI), 57-94) and a 100% specificity (95% CI, 63-100) with a positive predictive value of 100%. Prognostic accuracy, as quantified by the ROC_AUC, was higher with the worst NAA/Cr in lenticular cores (ROC_AUC 0.88; 95% CI, 0.70-0.97) than with the structural MRI sequences.

CONCLUSION

In this preliminary study we found that multivoxel ¹H-CSI in lenticular cores was highly predictive of unfavorable outcome at 6 months.

Prognostication in Anoxic Brain Injury

Cardiac arrest is a common cause of coma with frequent poor outcomes. Palliative medicine teams are often called upon to discuss the scope of treatment and future care in cases of anoxic brain injury. Understanding prognostic tools in this setting would help medical teams communicate more effectively with patients’ families and caregivers and may promote improved quality of life overall. This article reviews multiple tools that are useful in determining outcomes in the setting of postarrest anoxic brain injury.

Post-cardiac arrest syndrome: Epidemiology, pathophysiology, treatment, and prognostication: A scientific statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke (Part 1)

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the postcardiac arrest syndrome are potentially treatable.

Post-cardiac arrest syndrome: epidemiology, pathophysiology, treatment, and prognostication. A Scientific Statement from the International Liaison Committee on Resuscitation; the American Heart Association Emergency Cardiovascular Care Committee; the Council on Cardiovascular Surgery and Anesthesia; the Council on Cardiopulmonary, Perioperative, and Critical Care; the Council on Clinical Cardiology; the Council on Stroke

AIM OF THE REVIEW

To review the epidemiology, pathophysiology, treatment and prognostication in relation to the post-cardiac arrest syndrome.

METHODS

Relevant articles were identified using PubMed, EMBASE and an American Heart Association EndNote master resuscitation reference library, supplemented by hand searches of key papers. Writing groups comprising international experts were assigned to each section. Drafts of the document were circulated to all authors for comment and amendment.

RESULTS

The 4 key components of post-cardiac arrest syndrome were identified as (1) post-cardiac arrest brain injury, (2) post-cardiac arrest myocardial dysfunction, (3) systemic ischaemia/reperfusion response, and (4) persistent precipitating pathology.

CONCLUSIONS

A growing body of knowledge suggests that the individual components of the post-cardiac arrest syndrome are potentially treatable.

Intracellular pH-dependent peroxynitrite-evoked synergistic death of glucose-deprived astrocytes

Previously, we reported that glucose-deprived astrocytes were highly vulnerable to peroxynitrite (ONOO-). Here we demonstrate that the increased vulnerability caused by glucose deprivation and ONOO- depends on intracellular pH. The ONOO- releasing reagent 3-morpholinosydnonimine (SIN-1) markedly induced the release of lactate dehydrogenase (LDH, the marker of cytotoxicity) in glucose-deprived astrocytes. Morphological studies and caspase activity assay showed that astrocytes treated together with glucose deprivation and ONOO- died mostly in a necrotic mode. Alkalinization of pH from 7.4 to 7.8 increased LDH release, whereas acidification from pH 7.4 to 7.0 decreased it. However, intracellular pH (pHi), not extracellular pH (pHe), appeared to play a critical role in the synergistic death. Thus, without a change in pHe (7.4) cytosolic acidification by a weak acid salt, sodium acetate, and a Na+/H+ antiporter inhibitor, amiloride, reduced LDH release. In contrast, a weak base, NH4Cl, and a Na+/H+ antiporter stimulator, monensin, increased pHi and greatly enhanced LDH release. The augmented death was found to be due, in part, to the preceding decrease in the level of reduced glutathione, the ONOO- scavenger, and collapse of the mitochondrial transmembrane potential at alkaline pH.

Analysis of magnetic resonance imaging (MRI) morphometry and cerebral blood flow in patients with hypoxic-ischemic encephalopathy

The aim of this study was to analyze magnetic resonance imaging (MRI) morphometry and cerebral blood flow (CBF) in patients with hypoxic-ischemic encephalopathy, and determine the viability of such measurements for predicting cerebral outcome. The subjects were 26 patients with histories of cardiopulmonary resuscitation who had subsequently developed encephalopathy. We examined the CBF using stable xenon-computed tomography (Xe-CT) and MR images in the subacute period (8-20 days). Three signal-change patterns in the basal ganglia emerged in the MRI study. The first pattern, isointense areas evident in both the T1-weighted image (T1WI) and the T2-weighted image (T2WI), was observed in four patients with favorable outcomes. The second pattern, iso- or hypointense areas evident in the T1WI and hyperintense areas evident in the T2WI, was observed in six patients with favorable outcomes and three patients with poor outcomes. The third pattern, hyperintense areas evident in both the T1WI and T2WI, was observed in 13 patients with poor outcomes. Hemispheric CBFs were 38.9+/-4.6 (mean (SD)) ml/100 g/min in patients with favorable outcomes and 25.3+/-4.3 ml/100 g/min in patients with poor outcomes (p < 0.01). The CBF increase after acetazolamide administration was 13.3+/-3.4 ml/100 g/min in patients with favorable outcomes and 6.8+/-5.6 ml/100 g/min in patients with poor outcomes ( p < 0.05). The presence of hyperintense lesions in the basal ganglia in T1WI, low hemispheric CBF ( < 30 ml/100 g/min), and low acetazolamide reactivity ( < 10 ml/100 g/min) are all factors associated with poor outcome in patients with hypoxic-ischemic encephalopathy.

Cerebral perfusion and metabolism in resuscitated patients with severe post-hypoxic encephalopathy

Positron emission tomography (PET) was used for the study of regional cerebral perfusion and metabolism in eight patients with severe post-hypoxic encephalopathy, caused by cardiac arrest and resulting in a coma lasting for at least 24 h. Using this method, we aimed to identify regional vulnerability, which was hypothesized to provide (i) insight in pathogenic mechanisms and (ii) early prognostic parameters. On day 1 post-resuscitation, 18-Fluor deoxyglucose ([F18]-FDG) indicated a marked decrease of cerebral metabolic activity. Gray matter glucose consumption was 54% of normal values, whereas white matter uptake was 70% of normal. Regional differences followed a pattern of neuronal density rather than specific patterns of functionally or biochemically defined regions or of vascular territories. In contrast to [F18]-FDG, the distribution of 15-oxygen labeled water ([O-15]-water) showed a better demarcation between gray and white matter, whereas focal deficit was not observed. In some patients, hyperperfusion relative to regional glucose consumption was observed in the occipital poles and basal ganglia. This suggests loss of vascular tone, i.e. vascular paralysis, in the basilar artery territory. CT and MRI scanning did not show any major change with respect to the hypoxic injury. In the small group studied, all patients had a poor outcome. The comparison between survivors and nonsurvivors did not reveal obvious differences in PET data, suggesting that this technique does not provide major prognostic clues adding to the prognostic information derived from serial neurological assessment in the restricted patient group characterized by prolonged coma.

Improved outcome prediction in unconscious cardiac arrest survivors with sensory evoked potentials compared with clinical assessment

OBJECTIVE

To compare the prognostic ability of sensory evoked potentials in cardiac arrest survivors with the outcome predicted by a panel of experienced emergency physicians based on detailed prehospital, clinical, and laboratory data.

DESIGN

Inception cohort study.

SETTING

Medical intensive care unit and department of emergency medicine at a university hospital.

PATIENTS

A total of 162 unconscious, mechanically ventilated patients who survived > or =24 hrs after resuscitation from cardiac arrest.

INTERVENTIONS

Recording of sensory evoked potentials and outcome prediction after review of detailed clinical and laboratory data by emergency physicians within 24 hrs after cardiac arrest.

MEASUREMENTS AND MAIN RESULTS

At 6 months, the outcome of 36 patients was classified as favorable and 126 patients were rated as poor. After review of prehospital data, emergency physicians predicted favorable vs. poor outcome with a sensitivity of 70% and a specificity of 65%. After additional assessment of data 1 hr after cardiac arrest, the sensitivity of emergency physician predictions increased to 80%, whereas the specificity decreased to 48%. Outcome prediction by emergency physicians was most accurate after obtaining detailed patient data 24 hrs after cardiac arrest (sensitivity, 81%; specificity, 58%). In 35 of 36 patients with favorable outcomes, the cortical evoked potential N70 peak was detected between 72 and 128 msec. Of 113 patients with an N70 peak latency >130 msec or an absent N70 peak, all except one had a poor outcome. By using a cutoff of 130 msec, the N70 peak latency alone had a sensitivity of 94% and a specificity of 97%. The predictive accuracy of the N70 peak latency was significantly higher than the clinical assessment 24 hrs after cardiac arrest (91% vs. 76%, p = .0003).

CONCLUSION

In unconscious cardiac arrest survivors, a recording of long-latency sensory evoked potentials is more accurate in predicting individual outcome than an emergency physician review of clinical data.

Quantitative analysis of synaptophysin immunoreactivity in human neocortex after cardiac arrest: confocal laser scanning microscopy study

Transient global ischaemia caused by cardiac arrest results in lesions that involve all brain structures. The aim of this study was to investigate the condition of synapses in patients surviving, but remaining in a persistent vegetative state, following resuscitation after cardiac arrest. We performed a quantitative analysis of the distribution and density of elements containing a synaptic vesicle protein--synaptophysin (p38)--in human neocortex in cases which survived for 1 week, 2 months, and 1 year after the cardiac arrest. Neurologically healthy cases that died following an accident served as control. Dual-channel confocal laser scanning microscopy (CLSM) was used to image p38-immunoreactivity (IR) and lipofuscin autofluorescence. In control cases no statistically significant differences were found for p38-IR between layers II-III and V-VII. However, the temporal cortex had a higher density of p38-immunoreactive structures than the motor cortex. In postischaemic cases a reduction in the density of p38-IR elements was apparent, mainly in the frontal and motor cortices and less pronounced in the temporal cortex. The least decrease compared with controls was observed in the visual cortex. In the 1 week survival case, a maximal decrease in p38-IR (35% below control) was found. In this case, the number of p38-IR elements per visual field was decreased, and big aggregates of p38-IR structures were observed. In general, the amounts of p38-IR structures were higher in all of the control cases compared with the postischaemic cases.

pH-associated Brain Injury in Cerebral Ischemia and Circulatory Arrest

Neuronal injury remains a major limitation in therapies directed toward cardiopulmonary resuscitation and cerebral ischemia. We summarize clinical and experimental information regarding pH-modulated mechanisms of cerebral ischemic injury and the status of antiacidosis therapies relative to the brain. A large body of evidence in animals and humans indicates that cerebral pH can modulate, and perhaps mediate, ischemic brain pathology and influence functional outcome. The importance of low pH and brain bicarbonate levels during reperfusion as a secondary injury remains an open question of therapeutic importance. Under specific conditions, acidosis may be neuroprotective, but this is an area of current controversy. Effective antiacidosis therapy must address the possibility of synergism and competition among multiple injury mechanisms.

Optimal defibrillation strategy and follow-up of out-of-hospital cardiac arrest. The Belgian CPCR Study Group

In the current climate of rising healthcare cost, resuscitation efforts performed outside the hospital are critically evaluated because of their limited success rate in some settings. As part of a quality assurance program between the 1st January 1991 and 31st December 1993, six centres of the Belgian CPCR study group prospectively registered cardiac arrest (CA) patients and their treatment according to the Ustein Style recommendations. In the group (n = 511) of patients initially found in ventricular fibrillation (VF) a significantly better survival rate was observed for those patients who received a 1st defibrillatory shock by the 1st tier (n = 142 (27.8%)) as compared to those defibrillated after arrival of the 2nd tier (n = 369 (72.2%)). Median time to delivery of the first shock was significantly shorter (5 min) in the 1st tier group. In a second part of the study we describe long-term management of the 28 surviving VF patients, treated by the single EMS system of Brugge between 1st January 1991 and 30th April 1995: only 6 patients eventually received an implantable cardioverter defibrillator (ICD), whereas coronary revascularization was performed in 9 patients, and 3 patients were discharged on amiodarone only. Satisfactory long-term survival after out-of-hospital VF can be achieved by an early shock followed by advanced life support and appropriate definitive treatment.

What might be the impact on neurology of the analysis of brain metabolism by in vivo magnetic resonance spectroscopy?

In vivo nuclear magnetic resonance spectroscopy (MRS) of the human brain is a recently developed technique which allows to assay noninvasively in vivo key molecules of brain metabolism. After a review of the origin of the signals detected by phosphorus and proton MRS of human brain, the impact of MRS on clinical neurology is examined. MRS of the brain does not purport to be a metabolic "biopsy", but unique applications for brain MRS are (1) quantitating the oxidative state of the brain and defining neuronal death, (2) assessing and mapping neuron damage, (3) evaluating membrane alterations, and (4) characterizing encephalopathies. In the near future brain MRS will be performed routinely after conventional MRI, as a valuable metabolic (and functional) complement to the anatomical evaluation of cerebral pathologies, particularly the toxic, metabolic and infectious encephalopathies.

Sequential change of heterogeneous cerebral blood blow patterns after diffuse brain ischemia

In order to provide an insight into the basic nature of ischemic brain injury, we sequentially studied cerebral blood flow with [99mTc]hexamethylpropyleneamine oxime single photon emission computed tomography (CBF imaging) in a patient with diffuse brain ischemia due to prolonged cardiac arrest. On the 10th postarrest day, concentrated blood flow over superior-medial portion of the occipital lobe was demonstrated. On the 18th postarrest day, the same region became high density on a CT scan, while the concentrated flow on the CBF imaging had diminished. Thus, an abnormal cerebral blood flow (CBF) pattern preceded the density change on CT scan. On the 23rd postarrest day, remarkably concentrated flow over the brainstem was demonstrated. This might have illustrated the reduced metabolic demand of the damaged tissue over the cerebral and cerebellar hemispheres with relative preservation of brainstem perfusion. In patients with diffuse brain ischemia, a CBF imaging may be a useful tool for clarifying pathological process and prognosis.

Vascular dementia: neuropathologic alterations and metabolic brain changes

After reviewing the concepts of dementia, in general, and vascular dementia, in particular, this review discusses potential future approaches that may contribute to an improved definition of the clinical syndrome and the neuropathological features of vascular dementia. Specific brain alterations in high-energy phosphate compounds, as measured by nuclear magnetic resonance, may contribute to the separation between dementias with neurodegenerative diseases and those with ischemic (vascular or hemodynamic) disorders.