Thrombolysis in acute ischemic stroke: does it work?

Systematic review of evidence on thrombolytic therapy for acute ischaemic stroke

BACKGROUND

Recent trials of thrombolytic therapy in acute ischaemic stroke have given apparently conflicting results. Only one trial, the National Institute of Neurological Disorders and Stroke trial of tissue plasminogen activator (tPA), suggested that thrombolysis was definitely beneficial. To make sense of these results, we have done a systematic review of all available randomised trials of thrombolysis in acute ischaemic stroke.

METHODS

From all available completed randomised trials of thrombolytic therapy compared with control in acute ischaemic stroke (with prerandomisation CT), we checked tabular data on deaths during roughly the first 2 weeks, deaths from all causes and functional outcome (disability) at the end of the trial follow-up period, and early symptomatic and fatal intracranial haemorrhages.

FINDINGS

12 trials included 3435 patients, of whom 694 (20%) were dead and 1001 (39%) of 2567 were functionally dependent at the end of follow-up (duration of follow-up varied between trials, but the longest was 6 months). 214 (6%) of the 3435 patients had early symptomatic or fatal intracranial haemorrhages. Thrombolytic therapy was associated with a significant excess of early deaths (91 per 1000 patients treated [95% CI 54-134]), and total deaths (37 per 1000 [20-83]), but there was nevertheless a significant reduction in the number of patients in the combined outcome of dead or dependent (65 fewer per 1000 patients treated [28-107]). There was a substantial and significant excess of symptomatic and fatal intracranial haemorrhages with thrombolysis-which was similar in all recent trials-of about 70 extra symptomatic intracranial haemorrhages per 1000 patients treated (of which 51 per 1000 were fatal). In the cohort of patients randomised within 3 h of stroke, there was a significant reduction in the number of patients who were dead or dependent at the end of follow-up (141 fewer dead or dependent per 1000 patients treated [75-206] and a non-significant increase in the number dead (nine per 1000 treated [-39 to 70]). There was significant heterogeneity between the trials for total deaths at the end of follow-up, which may be partly explained by differences in the use of antithrombotic drugs within the first 24 h of thrombolysis; the variation in severity of strokes included: the time window to thrombolytic treatment; and the dose of thrombolytic drug used. There were no direct comparisons of tPA with streptokinase or urokinase: much of the poor outcome in the streptokinase-treated patients might be explained by the inclusion of more severe strokes, greater use of antithrombotic drugs, higher doses, and the longer time to treatment compared with the trials that used tPA.

INTERPRETATION

Thrombolysis requires further testing in large randomised trials because the risks seem substantial, and the benefit uncertain. The time window for effective treatment remains unclear. There is no objective evidence to suggest that tPA is safer than streptokinase; the apparent hazards and benefits may be similar when differences in trial design and baseline variables are accounted for.

Delayed adjuvant therapy with the 21-aminosteroid U74006F and the anion channel blocker L644-711 does not improve outcome following thrombolytic therapy in a rabbit model of thromboembolic stroke

BACKGROUND

Both the 21-aminosteroid U74006F, a potent inhibitor of lipid peroxidation, and L644-711, an anion channel blocker that inhibits both neutrophil and astrocyte function, have been previously shown to reduce brain injury in pretreatment paradigms of cerebral ischemia. It was therefore of interest to examine the effect of these agents in combination, when given on a delayed basis as adjuvants to thrombolytic therapy in a rabbit model of thromboembolic stroke.

METHODS

Animals were mechanically ventilated and arterial blood gases controlled. Core and brain temperature, intracranial pressure, and mean arterial pressure were continuously monitored. Regional cerebral blood flow and hematocrit were measured hourly. Blood samples were taken to measure neutrophil (aggregation and chemiluminescence) and platelet (aggregation) activity. Following delivery of an autologous clot via the carotid artery, all experiments were continued for an 8-hour period. U74006F (3 mg/kg I.V.) and L644,711 (12 mg/kg I.V.) or their vehicle control (n = 8, each group) were given 3.5 hours following autologous clot embolization. Both groups received tissue-type plasminogen activator (t-PA) (6.3 mg/kg I.V.), beginning 4 hours following thromboembolic stroke and continuing over a 2-hour infusion period. Infarct size was determined following staining and image analysis.

RESULTS

In the L644,711/U74006F group, neutrophil chemiluminescence was reduced following drug therapy; however, there were no significant differences between groups regarding infarct size (50.3 +/- 8.7 vs. 49.9 +/- 10.6, treatment vs. t-PA control, mean +/- SEM), or in regional cerebral blood flow or intracranial pressure over time.

CONCLUSIONS

It is concluded that prolonged (3.5 hours) delay of the initiation of therapy with the anion channel blocker L644,711 and the 21-aminosteroid U74006F fails to further reduce brain injury when given in combination with tissue plasminogen activator in a rabbit model of thromboembolic stroke.

Thrombolytic therapy in neurointensive care

Thrombolytic therapy has been studied in acute ischemic stroke, intracranial hemorrhage, intraventricular hemorrhage, subarachnoid hemorrhage, and sagittal sinus thrombosis. This form of therapy has an evolving role in contemporary neurologic practice, and increased investigational fervor will ensure more exacting therapeutic alternatives for stroke victims in the future.

Thrombolytic Therapy for Acute Ischemic Stroke: What Cardiac Physicians Need to Know

The current status of thrombolytic therapy for acute ischemic stroke is reviewed in relation to early work and to the use of thrombolytic agents in acute myocardial infarction. The case of a patient treated with recombinant tissue plasminogen activator for acute ischemic stroke is described to illustrate the improvement in outcome that can be achieved with this therapy in selected patients. A number of recommendations are included for cardiologists on the use of plasminogen activator in acute ischemic stroke regarding the timing, dosage, selection, and monitoring of patients.

Radiologic intervention in the acute stroke patient

Overall, stroke is a common disease that can have devastating results. Treatment of stoke has been, for the most part, supportive in nature. Recently, more aggressive intervention has been used, particularly thrombolysis. Although such intervention can have devastating consequences, it has shown some promise, particularly in the arena of intraarterial administration. Although much work is needed to find the ideal agents and methods of administration, screening of patients may hold the key to success and the limitations of complications. Determination of exactly which patients will benefit and which will not and which will have complications and which will not, remains for the most part an enigma. Only through further investigation in a controlled, collaborative manner can such information be obtained.

The effect of oral antiplatelet agents on tissue plasminogen activator-mediated thrombolysis in a rabbit model of thromboembolic stroke

OBJECTIVE

The success of thrombolytic therapy in acute stroke relies on timely reperfusion. The current study examines the efficacy of antiplatelet agents as adjuvants for thrombolytic therapy.

METHODS

Using an established rabbit model of clot embolization and a randomized blinded design, rabbits (n = 8 in each group) were orally pretreated daily for 5 days with adjuvant aspirin (1 mg/kg of body weight or 20 mg/kg), ticlopidine (100 mg/kg), or vehicle (sodium carbonate). On the 6th day, tissue plasminogen activator (6.3 mg/kg administered intravenously over 2 h), was initiated 1 hour after embolization.

RESULTS

In all groups, cerebral blood flow (CBF) was reduced to < 10 ml/100 g/min immediately after clot embolization. After the initiation of tissue plasminogen activator (t-PA), there was significant restoration of CBF in the control (t-PA only) and ticlopidine groups (P < 0.05) only. Restoration of CBF generally correlated with brain infarct size (percent hemisphere, mean +/- standard error of the mean), which was 18.0 +/- 7.0 in the t-PA only group versus 11.0 +/- 3.3, 26.5 +/- 5.8, and 21.5 +/- 3.4 in the ticlopidine, low-dose aspirin, and high-dose aspirin groups, respectively (ticlopidine versus aspirin, P < 0.05). Clot lysis was identical in the control and ticlopidine groups, with 6 of 8 animals demonstrating complete clot lysis. Aspirin antagonized clot lysis in a dose-related manner, with low-and high-dose aspirin groups noting clot lysis in four of eight and two of eight animals, respectively.

CONCLUSIONS

Pretreatment with ticlopidine significantly reduced brain infarct size when compared with aspirin treatment (P < 0.05). Moreover, whereas ticlopidine treatment did not affect clot lysis or CBF relative to t-PA alone, aspirin therapy resulted in antagonism of clot lysis and was associated with a more modest restoration of blood flow. This study provides a background for a more comprehensive understanding of the balance of thrombogenicity and thrombolysis and may assist in the development of novel therapies to expedite cerebrovascular patency and reduce ischemic and reperfusion-mediated neuronal injury.

Thrombolytic therapy with streptokinase in acute ischemic stroke

BACKGROUND

In patients with acute ischemic stroke, early treatment with thrombolytic agents is thought to permit reperfusion of ischemic neurons and to promote recovery of function. The Multicenter Acute Stroke Trial-Europe (MAST-E) was designed to assess the efficacy and safety of streptokinase in patients with acute ischemic stroke.

METHODS

Patients with moderate-to-severe ischemia in the territory of the middle cerebral artery were randomly assigned to receive streptokinase (1.5 million units over a period of one hour) or placebo within six hours after the onset of stroke. The primary efficacy outcome was a binary criterion combining mortality and severe disability at six months, with severe disability defined as a score of 3 or higher on the Rankin scale. The primary safety outcomes were mortality at 10 days and cerebral hemorrhage.

RESULTS

All randomized patients (156 in the streptokinase group and 154 in the placebo group) were evaluated at six months. The incidence of the primary efficacy outcome was similar in the two groups (124 patients in the streptokinase group and 126 in the placebo group died or had a Rankin score > or = 3). However, the mortality rate at 10 days was significantly higher in the streptokinase group than in the placebo group (34.0 percent vs. 18.2 percent, P = 0.002). The higher rate in the streptokinase group was mainly due to the hemorrhagic transformation of ischemic cerebral infarcts. At six months, more deaths had occurred in the streptokinase group than in the placebo group (73 vs. 59, P = 0.06).

CONCLUSIONS

In patients with acute ischemic stroke, treatment with streptokinase resulted in an increase in mortality. The routine use of streptokinase cannot be recommended in acute ischemic stroke.

Effects of acute percutaneous transluminal recanalization on cerebral embolism

The effects of percutaneous transluminal recanalization (PTR) on critical hemodynamics of cerebral embolism were studied using stable xenon-enhanced computed tomography in patients within 6 hours after onset. PTR was conducted in 10 cases (PTR group) and not conducted 8 cases (non-PTR group). The development of infarction was followed by CT scan. In the cortical arterial regions, the lowest cerebral blood flow (CBF) value in regions of interests (ROIs) without development of infarction was 12.9 ml/100 g/min in the PTR group and 17.0 ml/100 g/min in the non-PTR group. In ROIs with a cerebrovascular reserve capacity (CRC) less than 0 ml/100 g/min, even with a CBF greater than 12.9 ml/100 g/min, 3 of 4 ROIs underwent cerebral infarction. PTR conducted within 6 hours after onset of cerebral embolism would prevent the cortical regions with a CBF greater than 12.9 ml/100 g/min and with a CRC greater than 0 ml/100 g/min from undergoing cerebral infarction.

Intra-arterial thrombolysis in acute ischaemic stroke: experience with a superselective catheter embedded in the clot

OBJECTIVES

To report experience of intra-arterial thrombolysis for acute stroke, performed with a microcatheter navigated into the intracranial circulation to impale the clot.

METHODS

Patients were selected on the following criteria: (1) clinical examination suggesting a large vessel occlusion in stroke patients between 18 and 75 years; (2) no radiographic signs of large actual ischaemia on CT at admission; (3) angiographically documented occlusion of the middle cerebral artery (MCA) stem or of the basilar artery (BA), without occlusion of the ipsilateral extracranial internal carotid artery or of both the vertebral arteries; (4) end of the entire procedure within six hours of stroke. 12 patients with acute stroke were recruited, eight of whom had occlusion of the MCA stem and four of the BA. Urokinase was used as the thrombolytic agent.

RESULTS

Complete recanalisation in six MCA stem and in two BA occurred, and partial recanalisation in two MCA stem and one BA. There was no recanalisation in one BA. A clinically silent haemorrhage occurred in two patients, and a parenchymal haematoma in one patient, all in MCA occlusions. At four months five patients achieved self sufficiency (four with MCA and one with BA occlusion). Six patients were dependent (three totally), and one died.

CONCLUSIONS

The strict criteria of eligibility allowing the enrollment of very few patients and the procedure itself, requiring particular neuroradiological expertise, make this procedure not routine. Nevertheless, the approach can be considered a possible option for patients with acute ischaemic stroke.

Intracranial intraarterial thrombolysis facilitated by microcatheter navigation through an occluded cervical internal carotid artery

This report covers a series of four patients with acute cervical carotid occlusion and profound neurological deficits who were treated with intracranial intraarterial thrombolysis. All of the patients presented with arm plegia with variable leg involvement and two of them had global aphasia. Angiography identified occlusion of the proximal internal carotid artery (ICA) in each case and intracranial thromboembolus of the supraclinoid ICA and/or its branches. Catheter navigation through the occluded ICA segment was straightforward in three patients and somewhat difficult in one patient with an 80% ICA stenosis. Intraarterial urokinase infusion along with mechanical clot disruption was performed at the clot site in the middle cerebral artery, supraclinoid ICA, and/or anterior cerebral artery. All patients had recanalization of the treated artery after urokinase infusion. Antegrade flow through the ICA was reestablished in two patients, and good collateral filling across the anterior communicating artery was established in the other two. All patients had major pretreatment deficits (mean National Institutes of Health (NIH) Stroke Score 24 +/-4) with significant improvement noted at 3 months posttreatment (NIH Stroke Score 7 +/-6;p=0.03). Two patients made a dramatic early recovery. Postprocedure computerized tomography revealed no abnormality in one and asymptomatic basal ganglia high density from repeated local contrast injections in two patients. On the basis of their findings in this small study group the authors suggest that catheter navigation through a presumably occluded carotid artery is feasible and possibly effective in thrombolytic therapy of intracranial thrombolysis. Further study with clinical trials is necessary to determine the safety and efficacy of this technique.

Thrombolytic therapy. From myocardial to cerebral infarction. The MAST-I Group. Multicentre Acute Stroke Trial

Thrombolysis is proposed for the acute treatment of cerebral infarction as it is able to recanalize occluded arteries and thus potentially restore normal perfusion of the cerebral parenchyma, but the results concerning the efficacy of this treatment are still inconclusive. However, it has been fully demonstrated that thrombolytic treatment, leads to a significant reduction in mortality, in patients with acute myocardial infarction. Data from all of the pilot studies using SK or tPA treatment in acute stroke are described in this review, which underlines the incidence of hemorrhagic transformation (hemorrhagic infart and parenchymal hematoma) and its possible correlation to clinical worsening. Pharmacological, experimental and clinical studies encourage the carrying out of large-scale clinical trials using thrombolytics in patients with acute cerebral infarction. Significant data relating to ongoing controlled clinical trials will be available in the near future; only after the analysis of these results will it be possible to confirm the efficacy of thrombolytics in acute stroke.

Lys-plasminogen as an adjunct to local intra-arterial fibrinolysis for carotid territory stroke: laboratory and clinical findings

To improve the efficacy of local intraarterial fibrinolysis (LIF), we compared different fibrinolytic drugs in a cerebral circulation model in the laboratory. The technical efficacy of fibrinolysis, defined as the clot volume lysed per unit time, was found to be optimal with r-tissue plasminogen activator (TPA) activated lys-plasminogen (= plasmin). Subsequently, 20 patients with stroke due to carotid artery territory occlusion were treated by local intraarterial fibrinolysis using the plasmin regimen. The angiographic data and clinical outcome of these patients were compared with those of 40 patients who received plasminogen activators (urokinase or r-TPA) only. Laboratory and clinical data confirmed that plasmin lysis is superior to treatment using only plasminogen activators.

Acute stroke

Disruption of cerebral blood flow may influence brain energy metabolism to produce reversible or irreversible neurologic deficits. The emergency physician is in a unique position to provide timely treatment during the first few hours of an acute stroke. He or she must be facile with unique pharmacologic and non-pharmacologic treatment designed for the stroke patient concerning ventilation, blood pressure, and circulation.

Thrombolysis acute ischemic stroke

Thrombolysis is an attractive but potentially dangerous they for cerebral ischemia: it is capable of dissolving an arterial thrombus, but can also transform a pale infarct into a hematoma and/or may cause severe oedema and herniation. The safety and efficacy of the treatment critically depend on the timing of intervention ad on patient selection. In recent studies on ischemic stroke, spontaneous hemorrhagic transformation of an infarct seems to be related to the size of the lesion, and can be reliably predicted as early as five hours from stroke onset by the presence of focal hypodensity in the CT scan. That is why in the European Co-operative Acute Stroke (ECASS), a randomised, double blind trial on intravenous rt-PA in hemispheric stroke, patients showing, on the admission CT scan, extended early hypodensity, involving more than one third of the territory of the middle cerebral artery, were excluded from the day. Other ongoing trials on thrombolytic agents are expected to provide further indications on how to identify those patients most likely to benefit and least likely to experience adverse effects from this treatment.

Local thrombolytic therapy for cerebrovascular disease: current Oregon Health Sciences University experience (July 1991 through April 1995)

PURPOSE

This report details experience with local intraarterial or intradural sinus thrombolytic therapy for cerebrovascular thromboembolic occlusions in 40 patients.

PATIENTS AND METHODS

Between July 1991 and April 1995, intracranial local thrombolytic therapy with urokinase was used to treat 40 patients with occlusive vascular disease. Twenty-six patients had acute occlusions of the central retinal artery, middle cerebral artery, basilar artery, or combined internal carotid and middle cerebral arteries. Three patients had embolic complications related to cerebral vascular embolization procedures. Five patients were undergoing intracranial angioplasty procedures for occlusive atheromatous disease. Six patients had dural sinus thrombosis.

RESULTS

Local intraarterial thrombolytic therapy for acute thromboembolic arterial occlusions resulted in excellent restoration of perfusion in 18 patients, partial restoration of flow in four patients, and no effect in five patients. Fourteen of these patients had excellent clinical outcomes, seven made moderate improvements, and six died. In the two patients with central retinal arterial occlusions, no angiographic or clinical response to thrombolytic therapy could be ascertained. There was no angiographic improvement response from thrombolytic therapy in five patients with primary intracranial atheromatous stenosis, and one patient may have had an embolic complication related to this therapy. Three of six patients with dural sinus thrombosis had clearing of the thrombus and an excellent clinical result. The remaining three with extensive dural thrombosis did not have clearing of the thrombus; one patient became blind, and two patients died. Among the 40 patients treated, significant cerebral hemorrhage occurred after therapy in four.

CONCLUSION

Local thrombolytic therapy for thromboembolic occlusive cerebrovascular disease is useful in restoring perfusion of acutely occluded vessels. Further experience is needed to fully identify the most appropriate patients for therapy, dose of thrombolytic agent, timing and length of therapy, and risk factors for hemorrhage.

Thrombolytic therapy for basilar artery thrombosis in the puerperium

A case is presented of a woman in whom basilar artery thrombosis developed 14 days post partum. She was successfully treated with intraarterial urokinase. This case demonstrates that complete neurologic recovery can be achieved after recanalization of the basilar artery with thrombolytic therapy.

Color-coded ultrasound diagnosis of vascular occlusion in acute ischemic stroke

A combination of extracranial and transcranial color-coded sonography was used to identify the patterns of vascular occlusion in 47 patients with acute ischemic stroke. Total anterior circulation infarction (n = 20) was associated with internal carotid artery (ICA) or middle cerebral artery (MCA) occlusion (n = 8 and 9, respectively), or with significant reduction in ipsilateral MCA velocities (n = 5). Patients with partial anterior circulation (n = 22) infarction had patency of the ipsilateral ICA and MCA. In this group, significant reduction of ipsilateral MCA velocities (n = 7) was associated with more extensive infarcts on conventional neuroimaging (n = 6), suggesting multiple MCA branch occlusions. Ultrasound imaging was unable to identify underlying vascular pathology in patients with posterior circulation infarction or with lacunar infarction (n = 5). An ultrasound-based approach enables noninvasive identification of major vascular pathology of the anterior cerebral circulation in patients with acute cerebral infarction. It may be useful for the rapid identification of patients most and those least likely to benefit from acute intervention, and for monitoring their response.

Thrombolytic therapy of non-cardiac disorders

Patients with a recent (less than 10 days) proximal deep vein thrombosis of the leg or pelvis are candidates for thrombolysis as the major benefit over heparin seems to be the prevention of the postphlebitic limb, an aim which is still not proven in a satisfactory manner. Nonocclusive thrombi appear to lyse more readily than occlusive thrombi. For this indication the optimal dose regimens for the three thrombolytic drugs (streptokinase, urokinase, alteplase) are not established. Acute massive pulmonary embolism with hypotension or shock should be treated with thrombolytic drugs and, pending the outcome in the first hour, be considered for pulmonary embolectomy. Major acute pulmonary embolism with haemodynamic instability responds well to thrombolysis. Whether thrombolysis is superior to heparin in subacute intermediate pulmonary embolism has not been proven unequivocally in terms of mortality or clinically important endpoints. Systemic administration of thrombolytic drugs for peripheral arterial occlusion has been abandoned for catheter-directed and intraoperative intra-arterial repeated bolus or short-term infusions. The efficacy and safety of intravenous thrombolytic treatment following a major ischaemic stroke is presently being tested in large scale trials; its use must be restricted to experimental protocols.

Antithrombotic agents in cerebral ischemia

The choice of antithrombotic agent in cerebral ischemia depends on the pathogenesis: thrombosis, embolism, or hemorrhage. Antiplatelet agents are considered most beneficial in thrombotic stroke, anticoagulants are most effective in cardioembolic stroke; antithrombotic agents are generally contraindicated in hemorrhagic stroke. A meta-analysis of 18 trials documented a 23% reduction in stroke risk with antiplatelet agents; aspirin is typically the antiplatelet agent of choice for stroke prevention. There are no definitive data regarding the optimal aspirin dose for stroke prevention and this issue remains controversial. Ticlopidine is the most effective antiplatelet agent, but its adverse effect profile restricts its use. Anticoagulants are highly effective for preventing cardioembolic stroke, but their effectiveness in non-cardioembolic stroke is uncertain because of lack of trial data. Results of the ongoing Warfarin/Aspirin Recurrent Stroke Study (warfarin [INR 1.8-2.8] vs aspirin [325 mg/day]) may clarify this issue. There is renewed interest in thrombolytics because recent data indicate that reperfusion within a few hours of stroke onset appears to be effective in preventing neuronal damage. In addition, when given within 6 hours of stroke onset, thrombolytics appear to be relatively safe. Several direct thrombin inhibitors are being evaluated. Experimentally, hirudin, hirulog, D-Phe-L-Pro-L-Arg-CH2Cl (PPACK), and argatroban are clearly more effective than heparin in inhibiting platelet deposition and thrombus formation, and also show promise in preventing reocclusion after thrombolysis for both experimental thrombotic and embolic stroke. However, the risk of hemorrhage in patients with cerebrovascular disease is unknown for these agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Archie Cochrane's challenge: can periodically updated reviews of all randomised controlled trials relevant to neurology and neurosurgery be produced?

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Carotid endarterectomy for unstable and compelling neurologic conditions: do results justify an aggressive approach?

PURPOSE

In a retrospective study the outcome of 70 carotid endarterectomies (CEA) in 68 patients with neurologically unstable conditions or anatomically compelling findings on carotid angiography was examined to more accurately identify patients who might benefit from CEA in this setting.

METHODS

Out of a total of 1734 CEAs performed from 1978 to 1992, five groups of patients were selected: group A, stroke in evolution with tight stenosis (n = 5); group C, crescendo transient ischemic attacks (CTIA) continuing despite heparin (n = 14); group D, CTIA (above criteria) ceasing with heparin (n = 21); and group E, anatomically compelling situation on carotid angiography (n = 13). Data collected included preoperative and postoperative Neurologic Event Severity Score (NESS), CHAT classification, arteriosclerosis risk factors, demographics, and long-term overall and transient ischemic attack/stroke-free survival rates.

RESULTS

Risk factors and demographics were similar in all groups. By NESS criteria the conditions of 97.3% of patients in the neurologically unstable groups A to C were improved or stabilized after operation, with one deterioration (2.7%). All patients in group B either stabilized or improved. In group D, one patient's NESS deteriorated, resulting in 3.5% overall morbidity rate and no deaths for groups A to D. Follow-up showed an overall survival rate by Kaplan-Meier analysis equivalent to a matched control population, with 85% alive at 5 years. The cumulative TIA/stroke-free survival rate at 5 years was 75%.

CONCLUSIONS

In this retrospective series, CEA performed for compelling or unstable neurologic findings carried low morbidity and mortality rates. Early aggressive surgical therapy of neurologically unstable patients may be warranted because our results improved on the anticipated natural history of the conditions studied. Further clarification of proper patient selection is necessary before this principle can be applied broadly.

The complex role of nitric oxide in the pathophysiology of focal cerebral ischemia

Nitrogen monoxide (NO) has recently emerged as an important mediator of cellular and molecular events which impacts the pathophysiology of cerebral ischemia. Although tempting to ask whether NO is "good or bad" for cerebral ischemia, the question underestimates the complexities of NO chemistry and physiology as well as oversimplifies the pathophysiology of focal cerebral ischemia. Important vascular and neuronal actions of NO have been defined which both enhance tissue survival and mediate cellular injury and death, and these will be reviewed. Strategies which modify NO synthesis and/or metabolism may someday assume therapeutic importance, but not until the tissue compartments generating NO, the activities of the enzymes that are inducibly and constitutively expressed, and the redox state of NO during the stages of ischemic injury, are defined with greater precision. Our knowledge of these processes is rudimentary. This review will summarize the evidence from animal models which supports an emerging role for NO in ischemic pathophysiology. Important aspects of NO synthesis and inhibitors of this process will also be discussed.

Magnetic resonance angiography monitoring of streptokinase in occlusion of the middle cerebral artery

A 77 year old woman was hospitalized one hour after the onset of right hemiplegia and aphasia. Magnetic resonance imaging (MRI) examination was negative and MRA indicated occlusion of the left middle cerebral artery. Treatment with streptokinase was instituted (a 60 minute intravenous infusion of 1.5 MU of streptokinase in 100 ml of saline solution). Two hours after infusion, the patient's motor function clearly improved. An MRA examination performed six hours later showed partial recanalization of the obstructed vessel. Our report demonstrates the potential usefulness of MRA monitoring during thrombolytic therapy.

Intracerebral hematoma related to thrombolysis for myocardial infarction

The incidence of intracerebral hematomas after myocardial infarction increases after thrombolysis. As noted in the case described, clots formed after the administration of thrombolytic agents may remain liquid, and this blood can be drained by a catheter. However, in this case, the patient continued to bleed locally. This problem requires the development of methods to stop such ongoing local bleeding. It may be prevented in the future by improved thrombolytic drugs.

PET imaging of cerebral perfusion and oxygen consumption in acute ischaemic stroke: relation to outcome

We used positron emission tomography (PET) to assess the relation between combined imaging of cerebral blood flow and oxygen consumption 5-18 h after first middle cerebral artery (MCA) stroke and neurological outcome at 2 months. All 18 patients could be classified into three visually defined PET patterns of perfusion and oxygen consumption changes. Pattern I (7 patients) suggested extensive irreversible damage and was consistently associated with poor outcome. Pattern II (5) suggested continuing ischaemia and was associated with variable outcome. Pattern III (6), with hyperperfusion and little or no metabolic alteration, was associated with excellent recovery, which suggests that early reperfusion is beneficial. This relation between PET and outcome was highly significant (p < 0.0005). The results suggest that within 5-18 h of stroke onset, PET is a good predictor of outcome in patterns I and III, for which therapy seems limited. The absence of predictive value for pattern II suggests that it is due to a reversible ischaemic state that is possibly amenable to therapy. These findings may have important implications for acute MCA stroke management and for patients' selection for therapeutic trials.