Optimal thrombolytic strategies for acute myocardial infarction--bolus administration.
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Optimal strategies for thrombolysis in myocardial infarction (TIMI) are still being sought because the TIMI 3 flow rates achievable using standard regimens average approximately 60%. Double bolus administration of recombinant tissue plasminogen activator (tPA) is a novel approach with potential for earlier patency combined with ease of administration. We reviewed total patency rates, TIMI 3 patency rates, mortality, stroke and intracranial haemorrhage rates in the major trials of accelerated infusion tPA/bolus tPA/reteplase in acute myocardial infarction. A direct comparison was performed with results of two recent trials of double bolus (two 50 mg boli, 30 min apart) vs. accelerated infusion tPA: the Double Bolus Lytic Efficacy Trial (DBLE), an angiographic study, and the COBALT Trial, a mortality study. The DBLE trial showed equivalent patency rates for accelerated infusion and double bolus administration of tPA. Reviewing other angiographic trials, total patency and TIMI 3 patency rates achievable with double bolus tPA were comparable to those with accelerated infusion tPA or bolus reteplase administration. The COBALT study demonstrated a 30-day mortality of 7.53% in patients treated with accelerated infusion tPA compared with 7.98% for double bolus tPA treated patients. The small excess in mortality with double bolus treatment was confined to the elderly; in those < or = 75 years, mortality rates were 5.6% and 5.7%, for double bolus and accelerated infusion, respectively, and rates for death or non-fatal stroke were 6.35% and 6.3%, respectively. Comparison with other trials demonstrated mortality, stroke and intracranial haemorrhage rates with double bolus treatment similar to those associated with either accelerated infusion tPA or bolus reteplase treatment. Double bolus administration of tPA to patients with acute myocardial infarction is associated with total patency, TIMI 3 patency, mortality, stroke and intracranial haemorrhage rates similar to those associated with either accelerated infusion of tPA or bolus reteplase. (+info)
Arterial flow conditions downregulate thrombomodulin on saphenous vein endothelium.
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BACKGROUND: The antithrombogenic properties of venous endothelium may be attenuated when vein is implanted in the arterial circulation. Such changes may facilitate thrombosis, which is the final common pathway for saphenous vein arterial bypass graft occlusion. METHODS AND RESULTS: Using human saphenous vein in a validated ex vivo flow circuit, we investigated (1) the possibility that arterial flow conditions (mean pressure, 100 mm Hg, 90 cpm, approximately 200 mL/min) alter the concentration of proteins involved in regulating thrombosis at the vessel wall and (2) the influence of ion channel blockade on such effects. Concentrations of thrombomodulin and tissue factor were quantified by Western blotting (ratio of von Willebrand factor staining) and immunohistochemistry (as a percentage of CD31-staining area). Thrombomodulin concentrations after 90 minutes of venous and arterial flow conditions were quantified by immunostaining (68.9+/-4.8% and 41.0+/-3.0% CD31, respectively; P<0.01) and by Western blotting (1.35+/-0.20 and 0. 15+/-0.03 ratio of von Willebrand factor, respectively; P<0.01). The ability of endothelial cells to generate activated protein C also decreased from 62+/-14 to 19+/-10 ng. min-1. 1000 cells-1 (P=0.01). The significant reduction in thrombomodulin was attenuated if calcium was removed from the perfusate but not by external vein stenting. Inclusion in the vein perfusate of drugs that reduce calcium entry (including Gd3+, to block stretch-activated ion channels, and nifedipine) abolished the reduction in thrombomodulin concentration observed after arterial flow conditions. In freshly excised vein, negligible concentrations of tissue factor were detected on the endothelium and concentrations did not increase after 90 minutes of arterial flow conditions, although the inclusion of nifedipine caused the immunostaining to increase from 3.0+/-0.4% to 8.5+/-0.7% CD31 (P<0.02). CONCLUSIONS: In saphenous vein endothelium exposed to arterial flow conditions, there is rapid downregulation of thrombomodulin, sufficient to limit protein C activation, by a calcium-dependent mechanism. (+info)
Distinct contributions of residue 192 to the specificity of coagulation and fibrinolytic serine proteases.
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Archetypal members of the chymotrypsin family of serine proteases, such as trypsin, chymotrypsin, and elastase, exhibit relatively broad substrate specificity. However, the successful development of efficient proteolytic cascades, such as the blood coagulation and fibrinolytic systems, required the evolution of proteases that displayed restricted specificity. Tissue-type plasminogen activator (t-PA), for example, possesses exquisitely stringent substrate specificity, and the molecular basis of this important biochemical property of t-PA remains obscure. Previous investigations of related serine proteases, which participate in the blood coagulation cascade, have focused attention on the residue that occupies position 192 (chymotrypsin numbering system), which plays a pivotal role in determining both the inhibitor and substrate specificity of these enzymes. Consequently, we created and characterized the kinetic properties of new variants of t-PA that contained point mutations at position 192. These studies demonstrated that, unlike in coagulation serine proteases, Gln-192 does not contribute significantly to the substrate or inhibitor specificity of t-PA in physiologically relevant reactions. Replacement of Gln-192 with a glutamic acid residue did, however, decrease the catalytic efficiency of mature, two-chain t-PA toward plasminogen in the absence of a fibrin co-factor. (+info)
Cerebral venous thrombosis: combined intrathrombus rtPA and intravenous heparin.
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BACKGROUND AND PURPOSE: We chose to evaluate the safety and efficacy of combined intrathrombus rtPA and intravenous heparin in cerebral venous thrombosis (CVT). METHODS: We treated 12 patients with symptoms of 1 to 40 days' duration (eg, headache, somnolence, focal deficits, seizures, and nausea and vomiting). Pretreatment MRI disclosed subtle hemorrhagic venous infarction in 4 patients, obvious hemorrhagic infarction in 2, small parenchymal hemorrhage from recent pallidotomy in 1, and no focal lesion in 5. Magnetic resonance venography and contrast venography identified thrombi in the superior sagittal sinus (SSS) in 3 patients; transverse/sigmoid sinus (TS/SS) in 2; SSS and both TS/SS in 1; SSS and 1 TS/SS in 5; and SSS, 1 TS/SS, and straight sinus in 1 patient. A loading dose of rtPA was instilled throughout the clot at 1 mg/cm, followed by continuous intrathrombus infusion at 1 to 2 mg/h. Intravenous heparin was infused concomitantly. RESULTS: Flow was restored completely in 6 patients and partially in 3, with a mean rtPA dose of 46 mg (range, 23 to 128 mg) at a mean time of 29 hours (range, 13 to 77 hours). Symptoms improved in these 9 patients concomitantly with flow restoration. Flow could not be restored in 3 patients. In 1 of them, treatment was stopped when little progress had been made, and fibrinogen level dropped to 118 mg/dL. In the other 2 patients, hemorrhagic worsening occurred, and treatment was abbreviated after initial rtPA dosing. In 1 of these, the hematoma was evacuated. CONCLUSIONS: Our experience with intrathrombus rtPA in conjunction with intravenous heparin in patients with CVT is encouraging. This therapy should probably be regarded as unsafe in patients with obvious hemorrhage. Time to restore flow may be faster than with urokinase (an average of 71 hours has been reported for 29 documented patients). Further evaluation of rtPA with heparin in CVT is warranted. (+info)
Delayed increase in infarct volume after cerebral ischemia: correlations with thrombolytic treatment and clinical outcome.
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BACKGROUND AND PURPOSE: Growing experimental evidence indicates that the development of cerebral ischemic damage is slower than previously believed. The aims of this work were (1) to study the evolution of CT hypoattenuation between 24 to 36 hours and 7 days in ischemic stroke patients; (2) to evaluate whether thrombolytic treatment given within 6 hours of stroke affects delayed infarction evolution; and (3) to investigate possible correlations between lesion volume changes over time and clinical outcome. METHODS: Of 620 patients included in the European Cooperative Acute Stroke Study 1 (ECASS1), we selected 450 patients whose control CT scans at day 1 (CT1) and day 7 (CT7) were available. They had been randomly divided into 2 groups: 206 patients had been treated with rtPA and 244 with placebo. CT1 and CT7 were classified according to the location of the infarct. The volume of CT hypoattenuation was measured using the formula AxBxC/2 for irregular volumes. The 95% confidence interval of inter- and intrarater variability was used to determine whether significant changes in lesion volume had occurred between CT1 and CT7. Clinical severity was evaluated by means of the Scandinavian Stroke Scale (SSS) at entry (SSS0) and at day 30 (SSS30). RESULTS: Mean lesion volumes were significantly (P<0.0001) higher at day 7 than at day 1 in all the subgroups of patients and particularly in patients with a subcortical lesion. Of the 450 patients studied, 287 (64%) did not show any significant change in lesion volume between CT1 and CT7, 143 (32%) showed a significant increase and the remaining 20 (4%) a significant decrease. No significant correlation was observed between treatment and lesion evolution between CT1 and CT7. Both clinical scores (SSS0 and SSS30) and degree of neurological recovery were significantly (P<0.05) lower in the subgroup of patients with a significant lesion volume increase than in the other 2 groups. CONCLUSIONS: In approximately two thirds of patients, infarct size is established 24 to 36 hours after stroke onset, whereas in the remaining one third, changes in lesion volume may occur later than the first 24 to 36 hours. Many factors may be responsible for delayed infarct enlargement and for a lower degree of clinical recovery, both of which may occur despite early recombinant tissue plasminogen activator treatment. (+info)
Thrombolysis with tissue plasminogen activator alters adhesion molecule expression in the ischemic rat brain.
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BACKGROUND AND PURPOSE: We tested the hypothesis that treatment of embolic stroke with recombinant human tissue plasminogen activator (rhtPA) alters cerebral expression of adhesion molecules. METHODS: Male Wistar rats were subjected to middle cerebral artery occlusion by a single fibrin-rich clot. P-selectin, E-selectin, and intercellular adhesion molecule-1 (ICAM-1) immunoreactivity was measured at 6 or 24 hours after embolic stroke in control rats and in rats treated with rhtPA at 1 or 4 hours after stroke. To examine the therapeutic efficacy of combined rhtPA and anti-ICAM-1 antibody treatment at 4 hours after embolization, ischemic lesion volumes were measured in rats treated with rhtPA alone, rats treated with rhtPA and anti-ICAM-1 antibody, and nontreated rats. RESULTS: Administration of rhtPA at 1 hour after embolization resulted in a significant reduction of adhesion molecule vascular immunoreactivity after embolization in the ipsilateral hemisphere compared with corresponding control rats. However, when rhtPA was administered to rats at 4 hours after embolization, significant increases of adhesion molecule immunoreactivity in the ipsilateral hemisphere were detected. A significant increase of ICAM-1 immunoreactivity was also detected in the contralateral hemisphere at 24 hours after ischemia. A significant reduction in lesion volume was found in rats treated with the combination of rhtPA and anti-ICAM-1 antibody compared with rats treated only with rhtPA. CONCLUSIONS: The present study suggests that the time of initiation of thrombolytic therapy alters vascular immunoreactivity of inflammatory adhesion molecules in the ischemic brain and that therapeutic benefit can be obtained by combining rhtPA and anti-ICAM-1 antibody treatment 4 hours after stroke. (+info)
Intra-arterial rtPA treatment of stroke assessed by diffusion- and perfusion-weighted MRI.
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BACKGROUND: Diffusion-weighted MRI (DWI) and perfusion-weighted MRI (PWI) are new techniques that can be used for the evaluation of acute ischemic stroke. However, their potential role in the management of patients treated with recombinant tissue plasminogen activator (rtPA) has yet to be determined. CASE DESCRIPTION: The authors present the case of a 73-year-old man who was treated with intra-arterial rtPA, and they compare findings on DWI and PWI scans with angiography. PWI revealed decreased cerebral perfusion corresponding to an area that was not successfully recanalized, but revealed no abnormality in regions in which blood flow was restored. DWI was unremarkable in the region that was reperfused early (3 hours) but revealed hyperintensity in an area that was reperfused 3. 5 hours after symptom onset and in the area that was not reperfused. CONCLUSIONS: Findings on PWI correlated well with angiography, and DWI detected injured tissue in the hyperacute stage, whereas conventional MRI findings were negative. This suggests that these techniques may be useful to noninvasively evaluate the success of thrombolytic therapy. (+info)
Recombinant soluble form of PSGL-1 accelerates thrombolysis and prevents reocclusion in a porcine model.
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BACKGROUND: We investigated whether administration of a soluble recombinant P-selectin glycoprotein ligand-1 chimera (rPSGL-Ig) in conjunction with thrombolytic therapy would enhance thrombolysis by preventing ongoing interactions of leukocytes with platelets and the injured arterial wall. METHODS AND RESULTS: An occlusive thrombus was formed in an internal iliac artery of Yorkshire pigs by placement of a copper coil in the artery under fluoroscopic guidance. Pigs then received heparin and, 15 minutes later, either vehicle or rPSGL-Ig followed by infusion with 25 mg tissue plasminogen activator according to the 90-minute regimen. Blood flow through the artery was monitored by angiography and scored on a scale of 0 to 3. Lysis of the thrombus was accelerated by 70% in pigs treated with rPSGL-Ig 250 microg/kg compared with control (13.3+/-5.0 versus 44. 4+/-13.3 minutes; n=9 each). Eight of 9 control pigs reoccluded in 13.8+/-16.9 minutes after the end of tissue plasminogen activator infusion, whereas no reocclusion was observed in 8 of 9 pigs in the rPSGL-Ig group. When the dose of rPSGL-Ig was increased to 500 microg/kg, time to lysis was shortened by 61% from control (18.0+/-8. 4 versus 46.0+/-8.9 minutes). Reocclusion occurred in 6.0+/-15.2 minutes in control but not in any rPSGL-Ig-treated pig (n=5 each). In addition, near-normal flow (score 2 or 3) after thrombolysis was achieved 59% and 58% faster in the 2 rPSGL-Ig groups than in their respective controls. CONCLUSIONS: Inhibition of leukocyte accumulation at the site of thrombosis with rPSGL-Ig may represent a safe therapeutic intervention that could be important in accelerating thrombolysis, achieving optimal reperfusion, and reducing incidence of acute reocclusion. (+info)