Antithrombotic therapy in the acute phase: new approaches.

Both anticoagulants and antiplatelet agents have been advocated, used and studied for the treatment of acute ischemic stroke. Randomized trials of unfractionated heparin, low-molecular-weight heparin and heparinoids have failed to show an overall benefit to these agents largely because the benefits in reducing thromboembolic events are offset by the increased risk of bleeding complications. The International Stroke Trial, the Trial of ORG 10172 Acute Stroke Treatment and studies of fraxaripine all failed to show an overall benefit to anticoagulation in the patients studied. Aspirin has been shown to offer a modest benefit when studied in patients treated within 48 h of stroke onset. Ancrod is an antithrombotic agent that acts by reducing circulating fibrinogen levels. Patients treated within 3 h of stroke symptom onset had a better functional outcome at 90 days compared to placebo-treated patients with both the benefits and the risk of intracerebral bleeding related to the fibrinogen lowering achieved. Abciximab is a blocker of the platelet GPIIb/IIIa receptor. A dose finding safety study suggests that in doses up to that typically given in patients with acute coronary occlusion syndromes, there is no increased risk of symptomatic intracerebral bleeding and suggestions of potential benefits on neurological outcome.

Intravenous ancrod for treatment of acute ischemic stroke: the STAT study: a randomized controlled trial. Stroke Treatment with Ancrod Trial.

CONTEXT: Approved treatment options for acute ischemic stroke in the United States and Canada are limited at present to intravenous tissue-type plasminogen activator, but bleeding complications, including intracranial hemorrhage, are a recognized complication. OBJECTIVE: To evaluate the efficacy and safety of the defibrinogenating agent ancrod in patients with acute ischemic stroke. DESIGN: The Stroke Treatment with Ancrod Trial (STAT), a randomized, parallel-group, double-blind, placebo-controlled trial conducted between August 1993 and January 1998. SETTING: Forty-eight centers, primarily community hospitals, in the United States and Canada. PATIENTS: A total of 500 patients with an acute or progressing ischemic neurological deficit were enrolled and included in the intent-to-treat analysis. INTERVENTIONS: Patients were randomly assigned to receive ancrod (n=248) or placebo (n =252) as a continuous 72-hour intravenous infusion beginning within 3 hours of stroke onset, followed by infusions lasting approximately 1 hour at 96 and 120 hours. The ancrod regimen was designed to decrease plasma fibrinogen levels to 1.18 to 2.03 micromol/L. MAIN OUTCOME MEASURES: The primary efficacy end point was functional status, with favorable functional status defined as survival to day 90 with a Barthel Index of 95 or more or at least the prestroke value, compared by treatment group. Primary safety variables included symptomatic intracranial hemorrhage and mortality. RESULTS: Favorable functional status was achieved by more patients in the ancrod group (42.2%) than in the placebo group (34.4%; P=.04) by the prespecified covariate-adjusted analysis. Mortality was not different between treatment groups (at 90 days, 25.4% for the ancrod group and 23% for the placebo group; P=.62), and the proportion of severely disabled patients was less in the ancrod group than in the placebo group (11.8% vs 19.8%; P=.01). The favorable functional status observed with ancrod vs placebo was consistent in all subgroups defined for age, stroke severity, sex, prestroke disability, and time to treatment (< or = 3 or > 3 hours after stroke onset). There was a trend toward more symptomatic intracranial hemorrhages in the ancrod group vs placebo (5.2% vs 2.0%; P=.06), as well as a significant increase in asymptomatic intracranial hemorrhages (19.0% vs 10.7%; P=.01). CONCLUSION: In this study, ancrod had a favorable benefit-risk profile for patients with acute ischemic stroke.

Heparin and heparinoids in stroke.

Anticoagulation with heparin has a valuable place in prevention and management of deep venous thrombosis. However, the benefit of heparin in acute ischemic stroke and transient ischemic attack remains unclear despite its widespread use for these indications. Heparin also carries several risks, including unpredictable anticoagulation effects, bleeding, and thrombocytopenia. Low-molecular-weight heparins (LMWHs) and heparinoids have several advantages over heparin, such as higher bioavailability, more predictable anticoagulant effects, and less interaction with platelets. Heparin, LMWHs, and heparinoids have been studied in acute ischemic stroke with variable results. Of three recent, large, controlled clinical trials, only one documented a net benefit of treatment. Fewer patients treated with an LMWH within 48 hours of stroke were dead or disabled at 6 months compared with placebo-treated patients. The largest randomized clinical trial of heparin in acute stroke (the International Stroke Trial) showed that heparin was associated with a significant excess in bleeding complications but no clinical benefit at 6 months. Interim analysis of the TOAST (Trial of ORG 10172 in Acute Stroke Treatment) study also showed an excess number of bleeding complications in the treated group without a corresponding benefit on stroke outcome at 3 months. Therefore, although heparin, LMWHs, and heparinoids continue to be used in the management of patients with acute ischemic stroke, their value in recurrent stroke prevention and in the treatment of stroke-in-progress remains unsettled. Ongoing studies may help to clarify the use of LMWHs and heparinoids in these patients.

Prevention of stroke in patients with nonvalvular atrial fibrillation.

OBJECTIVE: To review the risk and pathogenesis of stroke associated with nonvalvular atrial fibrillation (AF) and the efficacies and risks of stroke prevention strategies. BACKGROUND: About 16% of ischemic strokes are associated with AF; AF is an independent risk factor for stroke. METHODS: Review of the literature, focusing on 13 randomized trials of antithrombotic therapy. RESULTS: The overall risk of stroke in AF patients averages about 5%/y, but with wide variation depending on the presence of coexistent thromboembolic risk factors. AF patients with low (about 1% per year), moderate (about 3% per year), and high (about 6% per year) stroke risks have been identified, but the generalizability of risk stratification schemes to clinical practice has not been fully assessed. AF patients with prior stroke or transient ischemic attack, even if remote, are at highest risk (about 12% per year). Adjusted-dose warfarin (target International Normalized Ratio [INR] 2-3) is highly efficacious for preventing stroke in AF patients (about 70% risk reduction) and is safe for selected patients, if carefully monitored. Aspirin has a modest effect on reducing stroke (about 20% risk reduction). The numbers of AF patients that would need to be treated with warfarin instead of aspirin for 1 year to prevent one ischemic stroke are about 200, 70, and 20 for those with low, moderate and high risk, respectively. CONCLUSIONS: Many patients with nonvalvular AF have substantial rates of ischemic stroke. Stratification of stroke risk identifies AF patients who benefit most and least from lifelong anticoagulation. Warfarin is recommended for high-risk AF patients who can safely receive it. Aspirin may be indicated for those with a low stroke risk and for those who cannot receive warfarin. For AF patients considered to have a moderate risk of stroke, individual bleeding risk during anticoagulation and patient preference should particularly influence the choice of antithrombotic prophylaxis.

Introduction to PCR/OLA/SCS, a multiplex DNA test, and its application to cystic fibrosis.

The field of medical, molecular diagnostics has grown rapidly over the last few years, becoming increasingly informative to both clinician and patient. As genes associated with specific diseases have been discovered and sequenced, many genotype-phenotype relationships have been defined. For those genetic diseases with associated, defined, gene mutations, sophisticated DNA diagnostic tests are being developed. As an example, the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene, is associated with Cystic Fibrosis (CF). We have developed a new molecular diagnostic technology, PCR/OLA/SCS, and applied it first to the diagnosis of CF. Test design in the field of molecular diagnostics must consider such characteristics as specificity, sensitivity, ease and speed of protocol, multiplex capacity, and cost. PCR/OLA/SCS addresses these requirements. Polymerase Chain Reaction (PCR) is widely used in both diagnostics and research. We have combined well established PCR technology with Oligonucleotide Ligation Assay (OLA) and Sequence-Coded Separation (SCS), two relatively new technologies.

Pathophysiology and treatment of acute ischemic stroke.

Risk factors, pathogenesis, clinical manifestations, diagnosis, and surgical and pharmacological treatment of ischemic stroke are reviewed. Risk factors play an important part in the pathogenesis of ischemic stroke. Knowledge of the complex metabolic and cellular changes that occur during ischemic stroke is rapidly growing. Choosing the correct treatment is dependent upon obtaining a thorough and accurate clinical assessment of the patient. Diagnostic tests help in determining the size, location, etiology, and characteristics of the lesion. Currently no single agent or mode of therapy appears to be most efficacious. Many drugs are still in the human clinical testing stage; promising agents include thrombolytics, low-molecular-weight heparin, and heparinoids. Hemodilution, pentoxifylline, epoprostenol, nimodipine, naloxone, and GM1 therapy have had mixed results in clinical trials, partly because some of these agents were not tested in enough patients to provide an accurate assessment of their efficacy. Atenolol and propranolol are ineffective. Ticlopidine and aspirin decrease the incidence of subsequent stroke but have not been tested in acute ischemic stroke. Heparin may be effective in preventing further cardioembolic stroke or in treating stroke in progress. Nondrug therapies include carotid endarterectomy and surgical decompression for cerebellar stroke. No single agent can be recommended for treatment of ischemic stroke at this time. Promising regimens include ancrod, low-molecular-weight heparin and heparinoids, or thrombolytics.

Strategies for preventing stroke.

The limited effectiveness of any therapy for acute stroke dictates that emphasis be placed on strategies for preventing stroke. The identification and management of risk factors is paramount. Modifiable risk factors include hypertension, smoking, hyperlipidemia, and diabetes. Patients with transient ischemic attacks or stroke are at risk for recurrent stroke and should be considered for antithrombotic therapy and carotid endarterectomy. Patients with nonvalvular atrial fibrillation should also be treated with antithrombotic therapy. The proper management of other cardiac, malignant, and hematologic disorders is important in preventing stroke in these high-risk patients.

Solid-phase time-resolved fluorescence detection of human immunodeficiency virus polymerase chain reaction amplification products.

A new assay system for the detection of polymerase chain reaction (PCR) amplification products is presented. This single-pot sandwich assay system employs solid-support oligonucleotide-coated capture beads, a rare earth metal chelate-labeled probe, and a time-resolved fluorescence detection. The new assay system was evaluated for various reaction conditions including, DNA denaturation time, hybridization salt concentration, probe concentration, and hybridization time, all of which are important in designing an assay with a high level of sensitivity for the detection of duplex DNA. This nonisotopic assay system was applied to the detection of purified human immunodeficiency virus (HIV) DNA and sensitivity was compared with agarose gel electrophoresis and slot blot hybridization using a 32P-labeled probe. We were able to detect the amplified product from one copy of HIV DNA after 35 cycles of PCR amplification in less than 30 min using this assay, which compared with one copy by gel electrophoresis after 40 cycles of PCR amplification and one copy by slot blot hybridization after 35 cycles of PCR amplification and an overnight exposure of the autoradiogram. Thus, this assay is rapid, sensitive, and easy to use.

Detection of human immunodeficiency virus type 1 RNA in plasma samples from high-risk pediatric patients by using the self-sustained sequence replication reaction.

There is an urgent need for rapid and sensitive methods to assess human immunodeficiency virus (HIV) infection in infants and children. We evaluated an approach by using the self-sustained sequence replication reaction (3SR) to amplify HIV type 1 (HIV-1) RNA directly. The amplified RNA product was then detected by bead-based sandwich oligonucleotide capture hybridization and rare earth metal chelate time-resolved fluorescence. The sensitivity of this technology was determined to be less than 12 HIV-1 RNA copies with an amplification level of 10(10)-fold with purified HIV-1 RNA. Plasma samples from 19 high-risk pediatric patients younger than 5 years of age were examined, and results were compared with viral culture of patient plasma. Results from plasma culture and 3SR amplification agreed for 14 of these patients and disagreed for 5. Of the five samples which did not agree, four were positive by 3SR and negative by culture and one was positive by culture and negative by 3SR but became positive by 3SR at a subsequent testing. We conclude that 3SR amplification coupled with time-resolved fluorescence is a promising technology for investigating the relationship between the presence of HIV-1 RNA in plasma and progression of disease in HIV-infected pediatric patients. This technology should be important in the assessment of HIV-1 infection, in evaluating drug therapies, and in understanding the pathogenesis and transmission of the virus.