The effect of nimodipine on the evolution of human cerebral infarction studied by PET

Effect of drug interventions on cerebral hemodynamics in ischemic stroke patients

The ischemic penumbra is sensitive to alterations in cerebral perfusion. A myriad of drugs are used in acute ischemic stroke (AIS) management, yet their impact on cerebral hemodynamics is poorly understood. As part of the Cerebral Autoregulation Network led INFOMATAS project (Identifying New Targets for Management and Therapy in Acute Stroke), this paper reviews some of the most common drugs a patient with AIS will come across and their potential influence on cerebral hemodynamics with a particular focus being on cerebral autoregulation (CA). We first discuss how compounds that promote clot lysis and prevent clot formation could potentially impact cerebral hemodynamics, before focusing on how the different classes of antihypertensive drugs can influence cerebral hemodynamics. We discuss the different properties of each drug and their potential impact on cerebral perfusion and CA. With emerging interest in CA status of AIS patients, either during or soon after treatment when timely reperfusion and salvageable tissue is at its most critical, the properties of these pharmacological agents may be relevant for modelling cerebral perfusion accuracy and for setting individualised treatment strategies.

Nitroglycerin Is Not Associated with Improved Cerebral Perfusion in Acute Ischemic Stroke

OBJECTIVE

The study was conducted to test the hypothesis that nitroglycerin (NTG) increases cerebral perfusion focally and globally in acute ischemic stroke patients, using serial perfusion-weighted imaging (PWI) magnetic resonance imaging measurements.

PATIENTS AND METHODS

Thirty-five patients underwent PWI immediately before and 72 h after administration of a transdermal NTG patch or no treatment. Patients with baseline mean arterial pressure (MAP) > 100 mmHg (NTG group, n = 20) were treated with transdermal NTG (0.2 mg/h) for 72 h, without a nitrate-free interval. Patients with MAP ≤ 100 mmHg (untreated group, n = 15) were not treated. The primary outcome measure was absolute cerebral blood flow (CBF) in the hypoperfused region at 72 h.

RESULTS

The mean baseline absolute CBF in the hypoperfused region was similar in the NTG group (33.3 ± 10.2 ml/100 g/min) and untreated (32.7 ± 8.4 ml/100 g/min, p = 0.4) groups. The median (IQR) baseline infarct volume was 10.4 (2.5-49.3) ml in the NTG group and 32.6 (8.6-96.7) ml in the untreated group (p = 0.09). MAP change in the NTG group was 1.2 ± 12.6 and 8 ± 20.7 mmHg at 2 h and 72 h, respectively. Mean absolute CBF in the hypoperfused region at 72 h was similar in the NTG (29.9 ± 12 ml/100 g/min) and untreated groups (24.1 ± 10 ml/100 g/min, p = 0.8). The median infarct volume increased in untreated (11.8 (5.7-44.2) ml) than the NTG group (3.2 (0.5-16.5) ml; p = 0.033) on univariate analysis, however, there was no difference on regression analysis.

CONCLUSION

NTG was not associated with improvement in cerebral perfusion in acute ischemic stroke patients.

Nimodipine Reappraised: An Old Drug With a Future

Nimodipine is a dihydropyridine calcium channel antagonist that blocks the flux of extracellular calcium through L-type, voltage-gated calcium channels. While nimodipine is FDAapproved for the prevention and treatment of neurological deficits in patients with aneurysmal subarachnoid hemorrhage (aSAH), it affects myriad cell types throughout the body, and thus, likely has more complex mechanisms of action than simple inhibition of cerebral vasoconstriction. Newer understanding of the pathophysiology of delayed ischemic injury after a variety of acute neurologic injuries including aSAH, traumatic brain injury (TBI) and ischemic stroke, coupled with advances in the drug delivery method for nimodipine, have reignited interest in refining its potential therapeutic use. In this context, this review seeks to establish a firm understanding of current data on nimodipine's role in the mechanisms of delayed injury in aSAH, TBI, and ischemic stroke, and assess the extensive clinical data evaluating its use in these conditions. In addition, we will review pivotal trials using locally administered, sustained release nimodipine and discuss why such an approach has evaded demonstration of efficacy, while seemingly having the potential to significantly improve clinical care.

MRI-based mismatch detection in acute ischemic stroke: Optimal PWI maps and thresholds validated with PET

Perfusion-weighted (PW) magnetic resonance imaging (MRI) is used to detect penumbral tissue in acute stroke, but the selection of optimal PW-maps and thresholds for tissue at risk detection remains a matter of debate. We validated the performance of PW-maps with 15O-water-positron emission tomography (PET) in a large comparative PET-MR cohort of acute stroke patients. In acute and subacute stroke patients with back-to-back MRI and PET imaging, PW-maps were validated with 15O-water-PET. We pooled two different cerebral blood flow (CBF) PET-maps to define the critical flow (CF) threshold, (i) quantitative (q)CBF-PET with the CF threshold <20 ml/100 g/min and (ii) normalized non-quantitative (nq)CBF-PET with a CF threshold of <70% (corresponding to <20 ml/100 g/min according to a previously published normogram). A receiver operating characteristic (ROC) curve analysis was performed to specify the accuracy and the optimal critical flow threshold of each PW-map as defined by PET. In 53 patients, (stroke to imaging: 9.8 h; PET to MRI: 52 min) PW-time-to-maximum (Tmax) with a threshold >6.1 s (AUC = 0.94) and non-deconvolved PW-time-to-peak (TTP) >4.8 s (AUC = 0.93) showed the best performance to detect the CF threshold as defined by PET. PW-Tmax with a threshold >6.1 s and TTP with a threshold >4.8 s are the most predictive in detecting the CF threshold for MR-based mismatch definition.

Effects of Acute Stroke Serum on Non-Ischemic Cerebral and Mesenteric Vascular Function

We investigated the effects of circulating factors in serum obtained from patients in the acute phase of different subtypes of ischemic stroke on non-ischemic cerebral and mesenteric arteries, as a potential mechanism involved in influencing regional perfusion and thus clinical evolution. Posterior cerebral arteries (PCAs) and mesentery arteries (MAs) isolated from Wistar Kyoto rats were perfused with serum from acute stroke patients with large vessel disease without (LVD) or with hypertension (LVD + HTN), cardioembolism with hypertension (CE + HTN), or physiologic saline as controls. Myogenic activity and nitric oxide-dependent vasorelaxation were assessed after 2 h of intraluminal exposure to serum. Vascular function was differentially affected by sera. Exposure to LVD serum increased myogenic tone and produced endothelial dysfunction in both PCAs and MAs. However, CE + HTN serum increased tone and decreased smooth muscle sensitivity to NO in vessels from both vascular beds. LVD + HTN serum was associated with reduced smooth muscle sensitivity to NO in vessels from both vascular beds but increased tone only in PCAs. Inflammation and oxidative stress, determined by measurement of high sensitivity C-reactive protein, uric acid, and free 8-isoprostane, were enhanced in all the serum groups. These results demonstrate vasoactive properties of acute stroke serum related to stroke subtypes that could potentially contribute to the pathogenesis of early hemodynamic-based clinical events.

Susceptibility-diffusion mismatch predicts thrombolytic outcomes: a retrospective cohort study

BACKGROUND AND PURPOSE

Asymmetric hypointensity of cerebral veins on susceptibility-weighted imaging has been shown to indirectly reflect tissue hypoxia after cerebral ischemia. We therefore investigated whether patients with prominent asymmetry of the cerebral veins on SWI and a relatively small diffusion-weighted imaging lesion (SWI-DWI mismatch), representing the presence of salvageable tissue, were more likely to benefit from thrombolytic therapy.

MATERIALS AND METHODS

We conducted a retrospective study of the anterior circulation of patients with ischemic stroke with SWI/DWI acquired before thrombolysis. The asymmetry index was defined as the ratio of cerebral vein voxel count between the ischemic and normal hemisphere on the SWI phase map. We defined SWI-DWI mismatch as an asymmetry index score of ≥1.75 with a DWI lesion volume of ≤25 mL. Favorable outcome was defined as modified Rankin Scale 0-2 at 3 months. Univariate and multivariate logistic regression analyses were used to examine the association between the mismatch profile and favorable outcome.

RESULTS

Fifty-four patients undergoing thrombolytic treatment were enrolled in this study. The rate of favorable outcome was significantly higher among patients with baseline SWI-DWI mismatch compared with those without (78% versus 44%; adjusted odds ratio, 6.317; 95% CI, 1.12-35.80; P = .037). Patients with SWI-DWI mismatch were also more likely to have a favorable outcome from reperfusion (91% versus 43%, P = .033) or recanalization (100% versus 40%, P = .013). The accuracy of SWI-DWI mismatch for predicting favorable outcome was higher than that of perfusion-diffusion mismatch (63% versus 48.1%).

CONCLUSIONS

The presence of SWI-DWI mismatch may identify patients with ischemia who would benefit from early reperfusion therapy.

Translational Perspectives on Perfusion–Diffusion Mismatch in Ischemic Stroke

Magnetic resonance imaging has tremendous potential to illuminate ischemic stroke pathophysiology and guide rational treatment decisions. Clinical applications to date have been largely limited to trials. However, recent analyses of the major clinical studies have led to refinements in selection criteria and improved understanding of the potential implications for the risk vs. benefit of thrombolytic therapy. In parallel, preclinical studies have provided complementary information on the evolution of stroke that is difficult to obtain in humans due to the requirement for continuous or repeated imaging and pathological verification. We review the clinical and preclinical advances that have led to perfusion–diffusion mismatch being applied in phase 3 randomized trials and, potentially, future routine clinical practice.

Nuclear medicine in cerebrovascular disease

Stroke and cerebrovascular diseases are major causes of mortality, morbidity, and disability. Nuclear Medicine, primarily via tomographic methods, has made significant contributions to the understanding of the hemodynamic and metabolic consequences of cerebrovascular diseases. In this review, the findings in acute, subacute, and chronic cerebrovascular diseases are described. Many of the pathophysiologic processes and consequences that follow stroke, including completed infarct core, adjacent penumbra, and diaschisis, have been investigated with Nuclear Medicine, and stroke outcome may be related to these phenomena. Additional topics included in this review are cerebrovascular reserve tests and multi-infarct dementia. Finally, Nuclear Medicine investigations of stroke recovery and cerebral plasticity appear to indicate that enhanced activity of preexisting networks, rather than substitution of function, represents the most important mechanism of improvement in chronic stroke rehabilitation.

Cerebral autoregulation and acute ischemic stroke

Cerebral autoregulation tightly controls blood flow to the brain by coupling cerebral metabolic demand to cerebral perfusion. In the setting of acute brain injury, such as that caused by ischemic stroke, the continued precise control of cerebral blood flow (CBF) is vital to prevent further injury. Chronic as well as acute elevations in blood pressure are frequently associated with stroke, therefore, understanding the physiological response of the brain to the treatment of hypertension is clinically important. Physiological data obtained in patients with acute ischemic stroke provide no clear evidence that there are alterations in the intrinsic autoregulatory capacity of cerebral blood vessels, except perhaps in infarcted tissue. While it is likely safe to modestly reduce blood pressure by 10-15 mm Hg in most patients with acute ischemic stroke, to date, there are no controlled trial data to indicate that reducing blood pressure is beneficial. There may be subgroups, such as those with persistent large vessel occlusion, large infarcts with edema causing increased intracranial pressure or local mass effect, or chronic hypertension, in which blood pressure reduction may lead to impaired cerebral perfusion in noninfarcted tissue.

Calcium antagonists for acute ischemic stroke

BACKGROUND

The sudden loss of blood supply in ischemic stroke is associated with the increase of calcium ions within neurons. Inhibiting this increase could protect neurons and hence might reduce neurological impairment, disability and handicap after stroke.

OBJECTIVES

To determine whether calcium antagonists reduce the risk of death or dependency after acute ischemic stroke. To investigate the influence of different drugs, dosages, routes of administration, time intervals after stroke and trial design on the risk of a primary outcome.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (January 2012), MEDLINE (1950 to December 2011), EMBASE (1980 to December 2011), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2011 issue 4) and four Chinese databases (December 2011): Chinese Biological Medicine Database (CBM-disc), China National Knowledge Infrastructure (CNKI), Chinese scientific periodical database of VIP information and Wanfang Data. We also contacted trialists and researchers.

SELECTION CRITERIA

All truly randomized trials comparing a calcium antagonist with control in patients with acute ischemic stroke.

DATA COLLECTION AND ANALYSIS

Two authors assessed all trials and extracted the data. We used death or dependency at the end of long-term follow-up (at least three months) in activities of daily living as the primary outcome. Analyses were, if possible, intention-to-treat.

MAIN RESULTS

We included 34 trials including 7731 patients. There was no effect of calcium antagonists on the primary outcome (risk ratio (RR) 1.05; 95% confidence interval (CI) 0.98 to 1.13), or on death at the end of follow-up (RR 1.07, 95% CI 0.98 to 1.17). Comparisons of different doses of nimodipine suggested that the highest doses were associated with poorer outcome.

AUTHORS' CONCLUSIONS

No evidence is available using calcium antagonists in patients with acute ischemic stroke is effective.

Elevated T2-values in MRI of stroke patients shortly after symptom onset do not predict irreversible tissue infarction

Distinct from signal alterations in diffusion-weighted images, T(2)-values are also dependent on tissue water content and known to increase with time from symptom onset in acute ischaemic stroke. The purpose of this study was to evaluate whether there is a detectable increase of T(2)-values in different regions in acute ischaemic stroke in the acute and subacute situation and to study the effect of recanalization on the evaluation of T(2)-values in the subacute phase. In addition, we sought to evaluate whether this increase in T(2)-values is reversible. For this purpose, 22 patients with acute ischaemic stroke in the territory of the middle cerebral artery underwent magnetic resonance imaging including diffusion-weighted imaging, perfusion-weighted imaging, fluid-attenuated inversion recovery to determine final infarct size, time-of-flight-angiography (acute and on day 1 or 2) and a triple echo-T(2)-sequence (calculation of T(2) maps) within 6 h after symptom onset. Images were co-registered and regions of diffusion restriction and prolonged time-to-peak as well as surviving tissue (surviving tissue = time-to-peak - final infarct size) and lesion growth (lesion growth = final infarct size-diffusion restriction) were defined and superimposed onto the quantitative T(2) map. In addition, patients were dichotomized according to recanalization information. Mean quantitative T(2)-values were derived for each patient within each region of interest. Mean T(2)-values for patients with recanalization (n = 15) in surviving tissue region of interest were 115.8 ± 7.2 ms (mean ± SD) and in the lesion growth region of interest 114.6 ± 7.0 ms. T(2)-values for patients without recanalization (n = 7) were 117.7 ± 11.4 ms in surviving tissue region of interest and 117.3 ± 12.1 ms in lesion growth region of interest. There was no significant difference between T(2)-values measured in lesion growth and surviving tissue region of interest for patients with or without recanalization. Even though it has been shown that T(2)-values increase with time from symptom onset within the infarct core, increased T(2)-values in areas of perfusion impairment do not identify irreversible damaged brain tissue and high T(2)-values are even found in tissue that is not part of the final infarct lesion and can therefore normalize. In conclusion, this study suggests that T(2)-values are not a valid imaging biomarker in acute stroke to predict tissue outcome.

Comparison of increased venous contrast in ischemic stroke using phase-sensitive MR imaging with perfusion changes on flow-sensitive alternating inversion recovery at 3 Tesla

BACKGROUND

Increased venous contrast in ischemic stroke using susceptibility-weighted imaging has been widely reported, although few reports have compared increased venous contrast areas with perfusion change areas.

PURPOSE

To compare venous contrast on phase-sensitive MR images (PSI) with perfusion change on flow-sensitive alternating inversion recovery (FAIR) images, and to discuss the clinical use of PSI in ischemic stroke.

MATERIAL AND METHODS

Thirty patients with clinically suspected acute infarction of the middle cerebral artery (MCA) territory within 7 days of onset were evaluated. Phase-sensitive imaging (PSI), flow-sensitive alternating inversion recovery (FAIR), diffusion-weighted imaging (DWI) and magnetic resonance angiography (MRA) were obtained using 3 Tesla scanner. Two neuroradiologists independently reviewed the MR images, as well as the PSI, DWI, and FAIR images. They were blinded to the clinical data and to each other's findings. The abnormal area of each image was ultimately identified after both neuroradiologists reached consensus. We analyzed areas of increased venous contrast on PSI, perfusion changes on FAIR images and signal changes on DWI for each case.

RESULTS

Venous contrast increased on PSI and hypoperfusion was evident on FAIR images from 22 of the 30 patients (73%). The distribution of the increased venous contrast was the same as that of the hypoperfused areas on FAIR images in 16 of these 22. The extent of these lesions was larger than that of lesions visualized by on DWI in 18 of the 22 patients. Hypointense signals reflecting hemorrhage and no increased venous contrast on PSI and hyperperfusion on FAIR images were found in six of the remaining eight patients (20%). Findings on PSI were normal and hypoperfusion areas were absent on FAIR images of two patients (7%).

CONCLUSION

Increased venous contrast on PSI might serve as an index of misery perfusion and provide useful information.

Spatiotemporal characteristics of postischemic hyperperfusion with respect to changes in T1, T2, diffusion, angiography, and blood-brain barrier permeability

The spatiotemporal dynamics of postischemic hyperperfusion (HP) remains incompletely understood. Diffusion, perfusion, T2, T1, angiographic, dynamic susceptibility-contrast magnetic resonance imaging (MRI) and magnetic resonance angiography were acquired longitudinally at multiple time points up to 7 days after stroke in rats subjected to 30-, 60-, and 90-minutes middle cerebral artery occlusion (MCAO). The spatiotemporal dynamics of postischemic HP was analyzed and compared with T1, T2 and blood-brain barrier (BBB) changes. No early HP within 3 hours after recanalization was observed. Late (12 hours) HP was present in all animals of the 30-minute MCAO group (N=20), half of the animals in the 60-minute MCAO group (N=8), and absent in the 90-minute MCAO group (N=9). Dynamic susceptibility-contrast MRI and magnetic resonance angiography corroborated HP. Hyperperfusion preceded T2 increase in some animals, but HP and T2 changes temporally coincided in others. T2 peaked first at 24 hours whereas HP peaked at 48 hours after occlusion, and HP resolved by day 7 in most animals at which point the arteries became tortuous. Pixel-by-pixel tracking analysis showed that tissue did not infarct (migrated from core or mismatch at 30 minutes to normal at 48 hours) showed normal cerebral blood flow (CBF), whereas infarct tissue (migrated from core or mismatch at 30 minutes to infarct at 48 hours) showed exaggerated CBF, indicating that HP was associated with poor outcome.

Quantitative T2 Values Predict Time From Symptom Onset in Acute Stroke Patients

Background and Purpose— We hypothesize that in comparison to diffusion-weighted imaging, quantitative T2 values (qT2) are more directly related to water uptake in ischemic tissue, depending on time from symptom onset. We measured the increase of qT2 in the infarct core to quantify the correlation between time from symptom onset and change in qT2.

Methods— Thirty-six patients with acute ischemic stroke in the territory of the proximal middle cerebral artery underwent MRI including diffusion-weighted imaging, fluid-attenuated inversion recovery, and a triple-echo T2 sequence (calculation of T2 maps) within 6 hours after symptom onset. Regions of decreased apparent diffusion coefficient <550×10 −9 mm 2 /sec were defined and superimposed onto the corresponding T2 map and the unaffected side in the horizontally flipped maps. Differences of T2/apparent diffusion coefficient values between affected and unaffected side were calculated (differences of T2/differences of apparent diffusion coefficient). Fluid-attenuated inversion recovery images were rated for lesion visibility.

Results— Differences of T2 showed a significant correlation with time from symptom onset ( R =0.580; P <0.001). T2 values measured in patients with visible fluid-attenuated inversion recovery lesions were significantly higher than in those without visible hyperintensity ( P <0.001). The accuracy of qT2 to predict a time from symptom onset <3 hours was 0.794, whereas the corresponding accuracy for visual assessment of fluid-attenuated inversion recovery images was 0.676.

Conclusions— T2 values demonstrated a strong correlation with time from onset, suggesting different pathophysiologic mechanisms than diffusion restriction. Whereas fluid-attenuated inversion recovery only provides binary information on lesion visibility, T2 values correlate well with time from symptom onset, and are free from operator bias, increasing reproducibility to determine time from symptom onset.

Interventions for deliberately altering blood pressure in acute stroke

BACKGROUND

It is unclear whether blood pressure should be altered actively during the acute phase of stroke. This is an update of a Cochrane review first published in 1997, and previously updated in 2001.

OBJECTIVES

To assess the effect of altering blood pressure in people with acute stroke, and the effect of different vasoactive drugs on blood pressure in acute stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (last searched July 2007), the Cochrane Database of Systematic Reviews and Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 2 2008), MEDLINE, EMBASE and other databases, reference lists of relevant publications and contacted researchers in the field.

SELECTION CRITERIA

Randomised controlled trials of interventions that aimed to alter blood pressure in patients within one week of acute ischaemic or haemorrhagic stroke.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria, assessed trial quality and extracted data.

MAIN RESULTS

Twelve trials involving 1153 participants were included (603 participants were assigned active therapy and 550 participants received placebo/control). The trials tested angiotensin converting enzyme inhibitors (ACEI), angiotensin receptor antagonists (ARA), calcium channel blockers (CCBs), clonidine, glyceryl trinitrate (GTN), thiazide diuretic and mixed antihypertensive therapy. One trial tested phenylephrine. At 24 hours after randomisation ACEIs reduced systolic blood pressure (SBP, mean difference, MD -6 mmHg, 95% confidence interval, CI -22 to 10) and diastolic blood pressure (DBP, MD -5 mmHg, 95% CI -18 to 7), ARA reduced SBP (MD -3, 95% CI -7 to 2) and DBP (MD -3, 95% CI -6 to 0.4), iv CCBs reduced SBP (MD -32 mmHg, 95% CI -65 to 1) and DBP (MD -13 mmHg, 95% CI -31 to 6), oral CCBs reduced SBP (MD -13 mmHg, 95% , CI -43 to 17) and DBP (MD -6 mmHg, 95% CI -14 to 2), GTN reduced SBP (MD -10 mmHg, 95% CI -18 to -3) and DBP (MD -1 mmHg, 95% CI -5 to 3) while phenylephrine, non-significantly increased SBP (MD 21 mmHg, 95% CI -13 to 55) and DBP (MD 1 mmHg, 95% CI -15 to 16). Functional outcome and death were not altered by any of the drugs.

AUTHORS' CONCLUSIONS

There is insufficient evidence to evaluate the effect of altering blood pressure on outcome during the acute phase of stroke. In patients with acute stroke, CCBs, ACEI, ARA and GTN each lower blood pressure while phenylephrine probably increases blood pressure.

T2' imaging predicts infarct growth beyond the acute diffusion-weighted imaging lesion in acute stroke

PURPOSE

To show that measurement of the transverse relaxation time that characterizes signal loss caused by local susceptibilities (T2') is sensitive to an increased deoxyhemoglobin concentration in the brain, indicating tissue at risk for infarction.

MATERIALS AND METHODS

The study was approved by the local institutional review board; patients or their guardians provided informed consent. Magnetic resonance (MR) imaging was performed within 6 hours of symptom onset and again 1-11 days thereafter in 100 consecutive stroke patients, all of whom received intravenous thrombolytic therapy (mean age, 67 years). The MR imaging protocol included diffusion- and perfusion-weighted imaging for determination of apparent diffusion coefficient (ADC) and time to peak (TTP), along with quantitative T2 and T2* imaging. T2' maps were calculated and visually compared with ADC and TTP lesions by two independent observers.

RESULTS

A T2'>ADC mismatch was observed by reader 1 in 73 (73%) of 100 patients, and by reader 2 in 65 (65%) patients. Respective sensitivities of T2'>ADC and of TTP>ADC mismatches for later infarct growth were 0.87 and 0.98 for reader 1 and 0.78 and 0.98 for reader 2, with respective specificities of 0.42 and 0.04 for reader 1 and 0.46 and 0.04 for reader 2. The odds ratios for infarct growth in the presence of a T2'>ADC mismatch were 4.59 (reader 1 P = .002) and 3.10 (reader 2 P = .012), while the odds ratios for TTP>ADC mismatch were 2.22 (reader 1 P = .606) and 1.73 (reader 2 P > .999).

CONCLUSION

The presence of a T2'>ADC mismatch is a more specific predictor of infarct growth than is TTP>ADC mismatch and hence may be of clinical value in patient selection for acute stroke therapies in the future.

Voltage-gated calcium channels provide an alternate route for iron uptake in neuronal cell cultures

Recent studies suggest that iron enters cardiomyocytes via the L-type voltage-gated calcium channel (VGCC). The neuronal VGCC may also provide iron entry. As with calcium, extraneous iron is associated with the pathology and progression of neurodegenerative diseases such as Parkinson's and Alzheimer's disease. VGCCs, ubiquitously expressed, may be an important route of excessive entry for both iron and calcium, contributing to cell toxicity or death. We evaluated the uptake of (45)Ca(2+) and (55)Fe(2+) into NGF-treated rat PC12, and murine N-2alpha cells. Iron not only competed with calcium for entry into these cells, but iron uptake (similar to calcium uptake) was inhibited by nimodipine, a specific L-type VGCC blocker, and enhanced by FPL 64176, an L-VGCC activator, in a dose-dependent manner. Taken together, these data suggest that voltage-gated calcium channels are an alternate route for iron entry into neuronal cells under conditions that promote cellular iron overload toxicity.

Evolving therapeutic approaches to treating acute ischemic stroke

Stroke contributes significantly to death, disability, and healthcare costs; however, recombinant tissue plasminogen activator (rt-PA) is the only approved thrombolytic therapy for acute ischemic stroke. One area of development for new ischemic stroke treatment options is focused on neuroprotection of viable tissue in the ischemic vascular bed. The ischemic penumbra is recognizable on MRI by decreased perfusion, in contrast to the core area of ischemia, which includes diffusion and perfusion abnormalities. Understanding the mechanisms of neuronal death, including the role of excitotoxic neurotransmitters, free radical production, and apoptotic pathways, is important in developing new therapies for stroke. This article reviews these causes and results of stroke, as well as current and future neuroprotective treatment options. Several compounds have shown neuroprotective effects in animal studies, but have failed to be effective in human clinical trials. Several promising therapeutic areas include targeting of free radicals, modulation of glutamatergic transmission, and membrane stabilization via ion channels.

The role of PET imaging in the management of patients with central nervous system disorders

PET will continue to play a critical role in both clinical and research applications with regard to CNS disorders. PET is useful in the initial diagnosis of patients presenting with CNS symptoms and can help clinicians determine the best course of therapy. PET studies can also be useful for studying the response to therapy. From the research perspective, the various neurotransmitter and other molecular tracers currently available or in development will provide substantial information about pathophysiologic process in the brain. As such applications become more widely tested, their introduction into the clinical arena will further advance the use of PET imaging in the evaluation and management of CNS disorders.

Penumbral topography in human stroke: methodology and validation of the 'Penumbragram'

The location as well as the volume of the ischemic penumbra in human stroke is likely to influence the outcome of therapeutic intervention but its spatial extent is poorly characterized. Based on the observation that infarct expansion progresses from the center to the periphery of the penumbra in animal stroke models, we describe a method of mapping the three-dimensional spatial extent of the penumbra relative to the infarct in a 'Penumbragram'. Central, peripheral and external zones of the final infarct were defined according to median voxel distance from the infarct center (IC) and were further subdivided by coronal, sagittal and axial planes through the IC. In 10 patients with hypoxic, viable (penumbral) tissue identified by (18)F-Fluoromisonidazole positron emission tomography within 48 h of stroke onset, 'Penumbragrams' displaying the percentage of penumbra in each region were generated using anatomically co-registered data sets. The correlation between penumbral percentage and time from stroke onset was negative in the central (P < 0.05) and peripheral (P > 0.05) zones of the infarct and positive in external zones (P < 0.05). The validity of infarct segmentation was assessed by factor analysis with no a priori grouping of regions. Negative and positive correlations of penumbra volume and time from stroke onset were observed in seven (five corresponding to central zone of the infarct) and four (all in external zone) infarct regions and were measured reliably (Cronbach's alpha 0.84 and 0.9, respectively). The 'Penumbragram' is a valid method for objectively mapping the spatial extent of the penumbra, which is applicable to other imaging modalities.

Probability of cortical infarction predicted by flumazenil binding and diffusion-weighted imaging signal intensity: a comparative positron emission tomography/magnetic resonance imaging study in early ischemic stroke

BACKGROUND AND PURPOSE

The differentiation of reversible from irreversible ischemic damage is essential for identifying patients with acute ischemic deficits who may benefit from therapeutic interventions. Diffusion-weighted imaging (DWI) has become the method of choice to detect ischemic lesions. Positron emission tomography (PET) of the central benzodiazepine receptor ligand 11C flumazenil (FMZ) has been shown to be a reliable marker of neuronal integrity. These 2 imaging parameters were compared with respect to the probability to predict cortical infarction in early ischemic stroke.

METHODS

In 12 patients with acute stroke, results from DWI (median, 6.5 hours after symptom onset) and FMZ-PET (interval, 85 minutes between DWI and PET) were compared with infarct extension 24 to 48 hours after onset of stroke on T2-weighted magnetic resonance imaging (T2-MRI). Probability curves predictive of eventual infarction were computed using respective DWI, FMZ, and apparent diffusion coefficient (ADC) values for voxels of interest (VOI) later classified as representing infarcted or noninfarcted tissue.

RESULTS

Ninety-five percent limits predictive of cortical infarction were determined for relative FMZ binding (< or =3.2), DWI signal intensity (> or =1.18), and ADC values (< or =0.83). Cortical regions with values beyond these 95% limits did not necessarily overlap with nor were fully congruous with final cortical infarct volumes. The respective median volumes for these regions were FMZ median 10.9, range 0 to 99.7 cm3; DWI median 15.2, range 0 to 116.0 cm3; ADC median 12.4, range 0 to 112.7 cm3; and final infarct median 14.9, range 0 to 114.7 cm(3). Overall, 83.5% of the final infarct, on average, was predicted by decreased FMZ binding, 84.7% by increased DWI signal intensity, and 70.9% by a decreased ADC value. The portions of the final infarct not predicted in the early investigation (false-negatives) were 4.8 cm3 (median) for FMZ, 3.7 cm3 for DWI, and 6.0 cm3 for ADC. The false-positive volumes not included in the final infarct were 0 cm3 (median) for FMZ, 5.1 cm3 for DWI, and 3.6 cm3 for ADC.

CONCLUSIONS

These results indicate that FMZ-PET and DWI are comparable in the prediction of probability of ischemic cortical infarction, but FMZ-PET carries a lower probability of false-positive prediction. The final infarcts include tissue not identified by these imaging modalities; at the time of the study, these tissue compartments are viable and could benefit from treatment. The discrepancy in predictive probability could be related to the fundamental difference of the measured variables: benzodiazepine receptor activity is a reliable marker of neuronal integrity in the cortex, and movement of water molecules in the extracellular space might be a more variable indicator of tissue damage.

The use of positron emission tomography in cerebrovascular disease

Even with rapid development of other neuroimaging modalities such as MR imaging and CT, PET is the only technique that provides accurate, quantitative measurements of regional hemodynamics and metabolism in human subjects. Through the use of these combined measurements, we have greatly expanded our knowledge of the pathophysiology of cerebrovascular disease of different types. It has been possible to document the compensatory responses of the brain to reductions in perfusion pressure and to directly relate these responses to prognosis. PET measurements of OEF identify a subgroup of patients who have carotid occlusion and who are at increased risk for recurrent stroke who cannot be identified by any other clinical or arteriographic means. These measurements of OEF are being used to identify high-risk patients for inclusion in a clinical trial to assess the efficacy of surgical revascularization in reducing the subsequence of ipsilateral ischemic stroke. In acute ischemic stroke, attempts have been made to define the "ischemic penumbra" and to predict tissue viability and clinical outcome, although the reliability of PET markers of ischemia in distinguishing viable from irreversibly damaged tissue needs to be confirmed with independent data sets. Much work has been devoted to the investigation of the metabolic effects of infarcts and hemorrhages on remote areas of the brain; the clinical importance of such findings appears to be minimal. Early studies of recovery from stroke suggested functional reorganization of the brain, but further investigations with more rigorous experimental design need to be performed. Given the case of performing such studies with functional MR imaging, it is likely that this technology will supplant PET for this specific indication. The importance of ischemia as a secondary mechanism of brain injury has been addressed in ICH and SAH. PET demonstrated that hematomas exert a primary depression of metabolism rather than inducing ischemia in the surrounding tissue. It also documented the integrity of autoregulation and provided clinically useful information regarding the safety of blood pressure reduction after ICH. Studies in SAH have differentiated the primary effects of the hemorrhage on cerebral hemodynamics and metabolism from those of vasospasm. PET studies are time-consuming, expensive, and require extensive facilities and technical support. In the field of cerebrovascular disease, PET has served as a specialized research tool at a few centers to help elucidate the pathophysiology of stroke. Up until now, however, PET scans in individual patients have not been demonstrated to be necessary for making patient care decisions. Whether the role of PET expands to impact the management of individual patients will depend on the results of investigations like the Carotid Occlusion Surgery Study that directly assess the ability of PET to influence patient outcome.

Effect of calcium antagonist on cerebral blood flow and oxygen metabolism in patients with hypertension and chronic major cerebral artery occlusion: a positron emission tomography study

To evaluate the effect of a calcium antagonist, nilvadipine, on cerebral blood flow and oxygen metabolism, we prospectively examined five ischaemic stroke patients, with both hypertension and chronic major cerebral artery occlusion, using positron emission tomography. The blood pressure showed a significant decrease after 3 months of nilvadipine treatment, the cerebral blood flow in the affected regions showed a significant increase and the oxygen extraction fraction showed a significant decrease. We conclude that nilvadipine is a safe and effective anti-hypertensive agent for patients with both hypertension and chronic major cerebral artery occlusion.

Cerebral blood flow predicts lesion growth in acute stroke patients

BACKGROUND AND PURPOSE

We sought to study the role of MRI-derived cerebral blood flow (CBF) measurements for the prediction of lesion development in acute stroke patients.

METHODS

Thirty-two patients were treated with tissue plasminogen activator. Diffusion-weighted (DWI) and perfusion-weighted MRI, T2-weighted imaging, and MR angiography were performed before treatment (2.8+/-0.9 hours after symptom onset) and on follow-up (days 1 and 7). CBF thresholds (12 and 22 mL/100 g per minute) were applied to bolus tracking MRI maps to determine predictive cutoff levels.

RESULTS

In 21 patients (group A), the terminal lesion volume (T2-weighted imaging) was larger than the initial DWI lesion volume (89+/-93 versus 21+/-38 mL). In 11 patients (group B), the terminal lesion volume was smaller than the initial DWI lesion volume (7+/-27 versus 15+/-29 mL). The initial DWI lesion volume did not differ between both groups. The presence of a tissue volume > or =50 mL with a CBF value < or =12 mL/100 g per minute was predictive for lesion enlargement to day 7 in T2-weighted imaging (positive predictive value, 0.80).

CONCLUSIONS

The presence of a tissue volume > or =50 mL with a CBF value < or =12 mL/100 g per minute predicts further lesion growth in hyperacute stroke patients. MRI-derived CBF values, with all their present limitations, are valuable in early estimation of prognosis of stroke patients.

Calcium modulation of adherens and tight junction function: a potential mechanism for blood-brain barrier disruption after stroke

BACKGROUND

This review deals with the role of calcium in endothelial cell junctions of the blood-brain barrier (BBB). Calcium is critical for adherens junction function, but it appears that calcium is also important in regulating tight junction function necessary for the barrier characteristics of cerebral microvessels.

SUMMARY OF REVIEW

The BBB is critical for brain homeostasis and is located at the cerebral microvessel endothelial cells. These endothelial cells maintain their barrier characteristics via cell-cell contacts made up of adherens and tight junctions. Adherens junctions are calcium dependent; recent evidence suggests that calcium also affects tight junctions. After stroke, there is a disruption of the BBB. Interfering with calcium flux under hypoxic conditions can prevent BBB breakdown. Calcium may alter BBB junction integrity by a number of different signal transduction cascades, as well as via direct interaction of calcium ions with junction proteins. It remains to be determined whether clinical use of calcium channel antagonists is a viable means to reduce BBB disruption after stroke.

CONCLUSIONS

With the widespread use of calcium channel blockers as clinical treatments for hypertension, which is a risk factor for stroke, the exact role of calcium in modulating BBB integrity needs to be elucidated.

Detection of deoxygenation-related signal change in acute ischemic stroke patients by T2*-weighted magnetic resonance imaging

BACKGROUND AND PURPOSE

Acute decreases in the MR T2*-weighted signal have been reported in experimental models of middle cerebral artery occlusion. This has been attributed to blood deoxygenation in association with an increased brain oxygen extraction fraction. The aim of this study was to detect this signal by susceptibility-weighted MR imaging in acute ischemic stroke patients.

METHODS

Dynamic susceptibility contrast-enhanced MR (DSC-MR) imaging was performed within 4 hours of stroke onset in 6 patients with unilateral cerebral artery occlusion (middle cerebral artery, n=5; internal carotid artery, n=1). Cerebral blood volume was estimated on a pixel-by-pixel basis. DSC-MR images taken before arrival of the contrast medium were examined visually to identify hypointense areas. Bilateral regions of interest were set in the middle cerebral artery territory for comparison of the mean signal intensity. A semilogarithmic plot of signal intensity versus cerebral blood volume for every pixel in the region of interest was also analyzed.

RESULTS

The side on which the hypointense area was seen was significantly correlated with the side of arterial occlusion. The mean signal intensity was significantly smaller on the affected side than on the contralateral side. The semilogarithmic plot of signal intensity versus cerebral blood volume indicated greater deoxyhemoglobin concentrations for the ipsilateral than for the contralateral region of interest.

CONCLUSIONS

DSC-MR images allow detection of hypointensity in the affected cerebral hemisphere in acute ischemic stroke patients. Such hypointensity may indicate increased oxygen extraction fraction (misery perfusion) and may provide information valuable to patient care.

Reversible ischemia around intracerebral hemorrhage: a single-photon emission computerized tomography study

OBJECT

A zone of perilesional ischemia has been demonstrated around intracerebral hemorrhage (ICH) in numerous experimental models and in human studies. There is potential for perfusion recovery in the zone of perilesional oligemia around ICH. The authors sought to demonstrate, quantify, and study the chronological evolution of perilesional ischemic change in ICH in humans by measuring cerebral blood flow.

METHODS

Eleven patients with spontaneous supratentorial ICH underwent two technetium-99m hexamethylpropyleneamine oxime single-photon emission computerized tomography (SPECT) scanning, one in the acute stage (within days of ictus) and the other in the late stage (6-9 months postictus). All patients in this study were treated nonsurgically. Methods of SPECT data analysis based on count differences in regions of interest can be difficult to apply to images with large space-occupying lesions such as ICH, because of the distortion of intracranial anatomy, midline shift, and alterations in the three-dimensional (3D) characteristics of the lesion over time (that is, absorption of the hematoma on the later studies). The authors used the following method: the late and early images were registered and aligned to a common 3D orientation and were normalized to maximal counts. The late images were then compared voxel by voxel with the early ones. The region-growing algorithm was used to discern the difference between the two images, outlining voxels in the perihematoma region, with a signal improvement of at least 15% on the late image. Discrete brain regions around the hematoma with at least a 15% improvement in radiotracer uptake (and hence perfusion) in the late images were observed in all cases. The mean volume of brain with a greater than 15% improvement in perfusion between the two studies was 34.8 cm3 (range 7.2-71.3 cm3). These volumes represent regions of the brain that were poorly perfused in the initial studies. This may represent a zone of reversible perilesional oligemia (penumbra) in ICH in humans.

CONCLUSIONS

This is the first study in which it is documented that some of the perilesional hypoperfused tissue around human ICH regains its perfusion in the long term, leading the authors to suggest that there may be a penumbra in human ICH. Medical or surgical therapeutic interventions could increase the volume of perilesional brain that recovers after the initial insult. The results of this study therefore support the concept that intervention in ICH has the potential to reduce the ultimate neurological deficit and improve outcome.

Time evolution of cerebral perfusion and apparent diffusion coefficient measured by magnetic resonance imaging in a porcine stroke model

PURPOSE

To demonstrate the feasibility of sequential diffusion-weighted (DW) and perfusion-weighted (PW) magnetic resonance imaging (MRI) of a recently developed porcine stroke model and to evaluate the evolution of cerebral perfusion and the apparent diffusion coefficient (ADC) over time. Materials and Methods In five pigs, DW imaging (DWI) and PW imaging (PWI) was carried out for 7 hours after stroke onset, starting 1 hour after middle cerebral artery occlusion (MCAO).

RESULTS

The DWI lesion volume increased significantly with time, and final DWI lesion volume correlated well with lesion area on histological sections (r = 0.910). T2 changes could be recognized 3 hours after stroke onset. At 1 hour the ADC ratio (ischemic lesion/contralateral side) was reduced to 0.81 in the caudate-putamen and to 0.87 in the cortex, and the cerebral blood flow ratio was reduced to 0.40 in the caudate-putamen and 0.51 in the cortex.

CONCLUSION

The level of flow reduction in the caudate-putamen and the cortex after 1 hour is in good correlation with human thresholds of irreversible and reversible ischemic damage, and accordingly, this model might be a model for mechanisms of infarct evolution and therapeutic intervention.

Calcium antagonists for ischemic stroke: a systematic review

BACKGROUND AND PURPOSE

Stroke is a common disease, and many trials with calcium antagonists as possible neuroprotective agents have been conducted. The aim of this review is to determine whether calcium antagonists reduce the risk of death or dependency after acute ischemic stroke.

METHODS

Acute stroke trials were identified with help of the Cochrane Collaboration Stroke Group and personal contacts. All randomized trials (published and unpublished) investigating a calcium antagonist (acting on voltage-sensitive calcium channels) were included. Poor outcome, defined as death or dependency in activities of daily living, was used as main outcome. Analyses were, if possible, "intention-to-treat"; pooled relative risks with 95% CIs were calculated.

RESULTS

Forty-seven trials were identified, of which 29 were included (7665 patients). No effect of calcium antagonists on poor outcome at the end of follow-up (relative risk, 1.04; 95% CI, 0.98 to 1.09) or on death at end of follow-up (relative risk, 1.07; 95% CI, 0.98 to 1.17) was found. Sensitivity analyses on route of administration and time interval between stroke and start of treatment showed no effect on outcome. In subgroups of unpublished and methodologically sound trials, a statistically significant negative effect for calcium antagonists was found. This contrasts with results of published trials and trials of moderate or poor methodological quality.

CONCLUSIONS

The presented evidence rules out a clinically important effect of calcium antagonists after ischemic stroke. The large amount of data leads to narrow CIs with no significant heterogeneity, and the overall results are therefore likely to be statistically robust.

Penumbral probability thresholds of cortical flumazenil binding and blood flow predicting tissue outcome in patients with cerebral ischaemia

Active treatment of acute ischaemic stroke can only be successful as long as tissue in the area of ischaemic compromise is still viable. Therefore, the identification of the area of irreversible damage, and its distinction from the penumbral zone, may improve the estimation of the potential efficacy of various therapeutic strategies. Ten patients (seven male, three female, aged 52-75 years) with acute ischaemic stroke, in whom MRI delineated an infarct involving the cortex 3 weeks after the attack, were studied by [(11)C]flumazenil (FMZ) PET to assess their neuronal integrity, and regional cerebral blood flow (CBF) was measured by H(2)(15)O PET 2-12 h (median interval 6 h) after onset of symptoms. Cortical volumes of interest (3 mm radius) were placed on co-registered CBF, FMZ and on late MRI scans. Using initial CBF and FMZ binding data from volumes of interest finally located within or outside the cortical infarct, cumulative probability curves were computed to predict eventual infarction or non-infarction. Positive (at least 95% chance of infarct) and negative (at least 95% chance of non-infarct) prediction limits for CBF (4.8 and 14.1 ml/100 g/min, respectively) and for FMZ binding (3.4 and 5.5 times the mean of normal white matter, respectively) were determined to define the penumbral range. Using the lower FMZ binding threshold of 3.4 for irreversible tissue damage and the upper CBF value of 14.1 ml/ 100 g/min for the threshold of critical perfusion at or above which tissue will likely be preserved, various cortical subcompartments were identified: of the final cortical infarct (median size 25.7 cm(3)) a major portion comprising, on average, 55.1% showed FMZ binding critically decreased, thus predicting necrosis. In 20.5% of the final infarct, on average, CBF was in the penumbral range (<14.1 ml/100 g/min) and FMZ binding was above the critical threshold of irreversible damage. Only 12.9% of the final infarct exhibited neuronal integrity and CBF values above the penumbral range. Therefore, most of the final infarct is irreversibly damaged already at the time of the initial evaluation, when studied several hours after stroke onset. A much smaller portion is still viable but suffers from insufficient blood supply: this tissue may be salvaged by effective reperfusion. Only an even smaller compartment is viable and sufficiently perfused, but eventually becomes necrotic, mainly owing to delayed mechanisms, and may benefit from neuroprotective or other measures targeted at secondary damage. Therefore, early reperfusion is crucial in acute ischaemic stroke.

Diffusion- and perfusion-weighted magnetic resonance imaging in human acute ischemic stroke: technical considerations

Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) are recently developed yet steadily evolving magnetic resonance techniques. DWI and PWI typically interrogate the microscopic diffusion and microcirculatory perfusion, and they can provide early, highly sensitive, and specific delineation of ischemic tissue. These techniques also can play a role in selecting patients who may benefit from thrombolytic therapy. This article reviews physical, technical, and pathophysiological background material that can be helpful in the acquisition and interpretation of DWI and PWI.

Ischemic penumbra: evidence from functional imaging in man

The ischemic penumbra is defined as tissue with flow within the thresholds for maintenance of function and of morphologic integrity. Penumbra tissue has the potential for recovery and therefore is the target for interventional therapy in acute ischemic stroke. The identification of the penumbra necessitates measuring flow reduced less than the functional threshold and differentiating between morphologic integrity and damage. This can be achieved by multitracer positron emission tomography (PET) and perfusion-weighted (PW) and diffusion-weighted magnetic resonance imaging (DW-MRI) in experimental models, in which the recovery of critically perfused tissue or its conversion to infarction was documented in repeat studies. Neuroimaging modalities applied in patients with acute ischemic stroke--multitracer PET, PW- and DW-MRI, single photon emission computed tomography (SPECT), perfusion, and Xe-enhanced computed tomography (CT)-- often cannot reliably identify penumbra tissue: multitracer studies for the assessment of flow and irreversible metabolic damage usually cannot be performed in the clinical setting; CT and MRI do not reliably detect irreversible damage in the first hours after stroke, and even DW-MRI may be misleading in some cases: determinations of perfusion alone yield a poor estimate of the state of the tissue as long as the time course of changes is not known in individual cases. Therefore, the range of flow values in ischemic tissue found later, either within or outside the infarct, was rather broad. New tracers--for example, receptor ligands or hypoxia markers--might improve the identification of penumbra tissue in the future. Despite these methodologic limitations, the validity of the concept of the penumbra was proven in several therapeutic studies in which thrombolytic treatment reversed critical ischemia and decreased the volume of final infarcts. Such neuroimaging findings might serve as surrogate targets in the selection of other therapeutic strategies for large clinical trials.

Cerebral hemodynamics in human acute ischemic stroke: a study with diffusion- and perfusion-weighted magnetic resonance imaging and SPECT

Nineteen patients with acute ischemic stroke (<24 hours) underwent diffusion-weighted and perfusion-weighted (PWI) magnetic resonance imaging at the acute stage and 1 week later. Eleven patients also underwent technetium-99m ethyl cysteinate dimer single-photon emission computed tomography (SPECT) at the acute stage. Relative (ischemic vs. contralateral control) cerebral blood flow (relCBF), relative cerebral blood volume, and relative mean transit time were measured in the ischemic core, in the area of infarct growth, and in the eventually viable ischemic tissue on PWI maps. The relCBF was also measured from SPECT. There was a curvilinear relationship between the relCBF measured from PWI and SPECT (r = 0.854; P < 0.001). The tissue proceeding to infarction during the follow-up had significantly lower initial CBF and cerebral blood volume values on PWI maps (P < 0.001) than the eventually viable ischemic tissue had. The best value for discriminating the area of infarct growth from the eventually viable ischemic tissue was 48% for PWI relCBF and 87% for PWI relative cerebral blood volume. Combined diffusion and perfusion-weighted imaging enables one to detect hemodynamically different subregions inside the initial perfusion abnormality. Tissue survival may be different in these subregions and may be predicted.

Neuroprotection and the ischemic cascade

Brain ischemia is a process of delayed neuronal cell death, not an instantaneous event. The concept of neuroprotection is based on this principle. Diminished cerebral blood flow initiates a series of events (the "ischemic cascade") that lead to cell destruction. This ischemic cascade is akin to a spreading epidemic starting from a hypothesized core of ischemia and radiating outward. If intervention occurs early, the process may be halted. Interventions have been directed toward salvaging the ischemic penumbra. Hypothermia decreases the size of the ischemic insult in both anecdotal clinical and laboratory reports. In addition, a wide variety of agents have been shown to reduce infarct volume in animal models. Pharmacologic interventions that involve thrombolysis, calcium channel blockade, and cell membrane receptor antagonism have been studied and have been found to be beneficial in animal cortical stroke models. Human trials of neuroprotective therapies have been disappointing. Other than thrombolytics, no agents have shown an unequivocal benefit. The future of neuroprotection will require a logical extension of what has been learned in the laboratory and previous human trials. A sensible approach to the use of multiple-agent cocktails used in combination with thrombolytics is likely to offer the highest chance for benefit.

Early [(11)C]Flumazenil/H(2)O positron emission tomography predicts irreversible ischemic cortical damage in stroke patients receiving acute thrombolytic therapy

BACKGROUND AND PURPOSE

Central benzodiazepine receptor ligands, such as [(11)C]flumazenil (FMZ), are markers of neuronal integrity and therefore might be useful in the differentiation of functionally and morphologically damaged tissue early in ischemic stroke. We sought to assess the value of a benzodiazepine receptor ligand for the early identification of irreversible ischemic damage to cortical areas that cannot benefit from reperfusion.

METHODS

Eleven patients (7 male, 4 female, aged 52 to 75 years) with acute, hemispheric ischemic stroke were treated with alteplase (recombinant tissue plasminogen activator; 0.9 mg/kg according to National Institute of Neurological Disorders and Stroke protocol) within 3 hours of onset of symptoms. At the beginning of thrombolysis, cortical cerebral blood flow ([(15)O]H(2)O) and FMZ binding were assessed by positron emission tomography (PET). Those early PET findings were related to the change in neurological deficit (National Institutes of Health Stroke Scale) and to the extent of cortical damage on MRI or CT 3 weeks after the stroke.

RESULTS

Hypoperfusion was observed in all cases, and in 8 patients the values were below critical thresholds estimated at 12 mL/100 g per minute, comprising 1 to 174 cm(3) of cortical tissue. Substantial reperfusion was seen in most of these regions 24 hours after thrombolysis. In 4 cases, distinct areas of decreased FMZ binding were detected. Those patients suffered permanent lesions in cortical areas corresponding to their FMZ defects (112 versus 146, 3 versus 3, 2 versus 1, and 128 versus 136 cm(3)). In the other patients no morphological defects were detected on MRI or CT, although blood flow was critically decreased in areas ranging in size up to 78 cm(3) before thrombolysis.

CONCLUSIONS

These findings suggest that imaging of benzodiazepine receptors by FMZ PET distinguishes between irreversibly damaged and viable penumbra tissue early after acute stroke.

Calcium antagonists for acute ischemic stroke

BACKGROUND

The sudden loss of blood supply in ischemic stroke is associated with increased levels of calcium ions within neurones. Inhibiting this increase could protect neurones and is thought to reduce neurological impairment, disability and handicap after stroke.

OBJECTIVES

The aim of this review is to determine whether calcium antagonists reduce the risk of death or dependency after acute ischemic stroke. The influence of different drugs, dosages, routes of administration, time intervals after stroke and trial design on the risk of poor outcome was investigated.

SEARCH STRATEGY

Relevant trials were identified in the Specialised Register of Controlled Trials (last searched: March 1999).

SELECTION CRITERIA

All truly randomised trials comparing a calcium antagonist with control in patients with acute ischaemic stroke were included.

DATA COLLECTION AND ANALYSIS

Two authors assessed all trials and extracted the data. Poor outcome, defined as death or dependency in activities of daily living, was used as the main outcome. Analyses were, if possible, "intention-to-treat".

MAIN RESULTS

46 trials were identified of which 28 were included (7521 patients). No effect of calcium antagonists on poor outcome at the end of follow-up (OR 1.07, 95% CI 0.97/1.18), or on death at end of follow-up (OR 1.10, 95% CI 0.98/1.24) was found. Intravenous administration (i.v.) of calcium antagonists was associated with an increase in the number of patients with poor outcome compared to oral administration (indirect comparisons). Comparisons of different doses of nimodipine suggested that the highest doses were associated with poorer outcome. Administration within 12 hours of onset was associated with an increase in the proportion of patients with poor outcome, but this effect was largely due to the poor results associated with i.v. administration. A subgroup analysis on nimodipine (oral, 120 mg/day) started within 12 hours of stroke onset, did not show a beneficial effect.

REVIEWER'S CONCLUSIONS

No evidence is available to justify the use of calcium antagonists in patients with acute ischaemic stroke.

Brain acidosis, cerebral blood flow, capillary bed density, and mitochondrial function in the ischemic penumbra

Within the ischemic penumbra, there is a heterogeneous development of cortical intracellular acidosis that is associated with selective neuronal injury. This experiment, which used a rabbit model of moderate focal cerebral ischemia, examined the time course for changes in intracellular brain pH, cortical blood flow, capillary bed density, and mitochondrial function in the ischemic penumbra. After cortical annotation of regions of intracellular acidosis in the ischemic penumbra, the animals underwent transcardiac carbon black perfusion for measurement of capillary bed density. Analysis of variance and Pearson's correlation coefficients were used to determine the relationship between capillary bed density, brain intracellular pH, mitochondrial function, and cortical blood flow. Thirty minutes after the onset of ischemia, cortical blood flow declined from 46+/-2 to 22+/-1 mL/100gm/min (P<.01) in all groups. The overall cortical intracellular brain pH measured 6.78+/-.01 compared with a preischemic value of 6.98+/-.01 (P<.05). Within this moderately ischemic cortex, there were small regions (1,000 to 45,000 mum(2)) of increased acidosis, meauring 6.68+/-.01, not associated with focal changes in cortical blood flow, occurring within 15 minutes of ischemia and persisting throughout the ischemic period. Capillary bed density progressively declined with ongoing ischemia occurring after the development of acidosis. For example, capillary bed density in preischemic controls was 338+/-6/mm(2), whereas after 1 hour of ischemia, it measured 147+/-12/mm(2), at 3 hours 97+/-23/mm(2), and at 6 hours 92+/-16/mm(2). Mitochondrial function was reduced coinciding with the decrease in capillary bed density. These data support the hypothesis that cortical acidosis in the ischemic penumbra facilitates the development of perfusion defects that subsequently lead to mitochondrial dysfunction.

Longitudinal magnetic resonance imaging study of perfusion and diffusion in stroke: evolution of lesion volume and correlation with clinical outcome

A prospective longitudinal diffusion-weighted and perfusion-weighted magnetic resonance imaging (DWI/PWI) study of stroke patients (n = 21) at five distinct time points was performed to evaluate lesion evolution and to assess whether DWI and PWI can accurately and objectively demonstrate the degree of ischemia-induced deficits within hours after stroke onset. Patients were scanned first within 7 hours of symptom onset and then subsequently at 3 to 6 hours, 24 to 36 hours, 5 to 7 days, and 30 days after the initial scan. Lesion evolution was dynamic during the first month after stroke. Most patients (18 of 19, 95%) showed increased lesion volume over the first week and then decreased at 1 month relative to 1 week (12 of 14, 86%). Overall, lesion growth appeared to depend on the degree of mismatch between diffusion and perfusion at the initial scan. Abnormal volumes on the acute DWI and PWI (<7 hours) correlated well with initial National Institutes of Health (NIH) stroke scale scores, outcome NIH stroke scale scores, and final lesion volume. DWI and PWI can provide an early measure of metabolic and hemodynamic insufficiency, and thus can improve our understanding of the evolution and outcome after acute ischemic stroke.

Nimodipine and perfusion changes after stroke

BACKGROUND AND PURPOSE

Meta-analysis of previous trials of oral nimodipine in acute stroke has suggested a benefit when commenced within 12 hours of onset. We sought to study the effect of oral nimodipine on reperfusion after acute stroke and the relation between reperfusion and outcome.

METHODS

Fifty patients with acute middle cerebral artery territory cortical infarction were blindly randomized within 12 hours of onset to either oral nimodipine (30 mg every 6 hours) or placebo. Treatment was continued for 2 weeks. Cerebral blood flow was assessed with the use of 99mTc-hexamethylpropyleneamine oxime single-photon emission CT before therapy, 24 hours later, and at 3 months. Hypoperfusion was measured by a validated volumetric technique. Neurological impairment and functional outcome were assessed with the Canadian Neurological Scale and Barthel Index, respectively. Tissue loss was measured with CT at 3 months. Four patients were excluded from analysis for technical reasons.

RESULTS

Twenty-three patients received nimodipine, and 23 received placebo. In the nimodipine group, there was early reperfusion that was not maintained at outcome (P=0.01). In the placebo group, mean infarct hypoperfusion volumes showed no overall change. Nonnutritional reperfusion in nimodipine-treated patients was associated with adverse neurological (P=0.05) and functional outcome (P=0.06). There was, however, no difference in clinical outcome between the 2 groups.

CONCLUSIONS

Oral nimodipine administered within 12 hours enhanced acute reperfusion, but this was largely nonnutritional. Larger studies using a shorter treatment delay are required to evaluate the clinical efficacy of nimodipine in acute ischemic stroke.

Which targets are relevant for therapy of acute ischemic stroke?

BACKGROUND

The efficiency of various strategies of neuroprotection is well documented in animal experiments but is thus far disappointing in ischemic stroke, for which only early reperfusion induced by thrombolysis has improved clinical outcome. This discrepancy between expectation from experimental research and clinical reality may be related to differences in the pathogenetic factors contributing to infarction.

SUMMARY OF COMMENT

Positron emission tomography cerebral blood flow studies within 3 hours of onset were used to identify the various compartments of the infarct outlined on MRI 2 to 3 weeks after a hemispheric stroke in 10 patients. Critical hypoperfusion below the viability threshold accounted for the largest proportion (mean, 70%) of the final infarct, whereas penumbral tissue (18%) and initially sufficiently perfused tissue (12%) were responsible for considerably smaller portions of the final infarct.

CONCLUSIONS

These results indicate that early critical flow disturbance leading to rapid cell damage is the predominant cause of infarction, while secondary and delayed pathobiochemical processes in borderline or initially sufficiently perfused regions contribute only little to the final infarct. Therefore, emerging therapeutic strategies should be targeted to the initially critically perfused tissue subcompartments. Clinical drug trials might benefit from stratification of patients for target tissue compartments applying functional imaging.

The effect of reperfusion therapy on cerebral blood flow in acute stroke

The effect of reperfusion therapy on cerebral blood flow (CBF) in acute cerebral ischemia was studied using xenon-enhanced computed tomography (XeCT). The XeCT CBF studies of 10 patients were evaluated before and after thrombolytic therapy. CBF evidence of reperfusion was evaluated in relation to the angiographic results and the clinical outcomes. Six patients had occlusions of the middle cerebral artery and four of the internal carotid artery. The mean CBF of the ischemic areas before attempted reperfusion was 9 +/- 3 mL/100g/min compared with 34 +/- 9 mL/100g/min in the contralateral asymptomatic region (P<.001). Intra-arterial-thrombolysis was performed in nine patients, and in one patient the intravenous route was used. Reperfusion of the ischemic region was shown in 9 of 10 patients, both angiographically and with the XeCT CBF studies (the mean CBF increased from 9 +/- 3 mL/100g/min to 32 +/- 10 mL/100g/min, P<.001). Among the nine successfully reperfused patients, seven were neurologically improved, one was unchanged, and one died. The mean National Institutes of Health stroke scale in the eight reperfused survivors was 12 on admission and decreased to 6 on discharge. XeCT CBF measurements are correlated with the angiographic results and can assist in the understanding of the effects of thrombolytic therapy on CBF in acute stroke. Re-establishment of CBF is associated with an improved clinical outcome but exceptions can be found. Reperfusion can occur in ischemic brain regions even with very low CBF (approaching 0 mL/100g/min) although it is not associated with prevention of infarction.