Non-central Nervous System Embolism Research Articles

Rivaroxaban—Once daily, oral, direct factor Xa inhibition Compared with vitamin K antagonism for prevention of stroke and Embolism Trial in Atrial Fibrillation: Rationale and Design of the ROCKET AF study

Atrial fibrillation (AF), the most common significant cardiac arrhythmia, increases the risk of stroke, particularly in the elderly. Warfarin is effective in reducing stroke risk but is burdensome to patients and is difficult to control. Rivaroxaban is an oral direct factor Xa inhibitor in advanced development as an alternative to warfarin for the prevention and treatment of thromboembolic disorders. ROCKET AF is a randomized, double-blind, double-dummy, event-driven trial, which aims to establish the noninferiority of rivaroxaban compared with warfarin in patients with nonvalvular AF who have a history of stroke or at least 2 additional independent risk factors for future stroke. Patients are randomly assigned to receive rivaroxaban, 20 mg once daily (od), or dose-adjusted warfarin titrated to a target international normalized ratio (INR) of 2.5 (range 2.0-3.0, inclusive) using point-of-care INR devices to receive true or sham INR values, depending on the study drug allocation. The primary efficacy end point is a composite of all-cause stroke and noncentral nervous system systemic embolism. The primary safety end point is the composite of major and clinically relevant nonmajor bleeding events. Over 14,000 patients have been randomized at 1,100 sites across 45 countries, and will be followed until 405 primary outcome events are observed. The ROCKET AF study will determine the efficacy and safety of rivaroxaban as an alternative to warfarin for the prevention of thromboembolism in patients with AF.

Effect of Clopidogrel Added to Aspirin in Patients with Atrial Fibrillation

Vitamin K antagonists reduce the risk of stroke in patients with atrial fibrillation but are considered unsuitable in many patients, who usually receive aspirin instead. We investigated the hypothesis that the addition of clopidogrel to aspirin would reduce the risk of vascular events in patients with atrial fibrillation. A total of 7554 patients with atrial fibrillation who had an increased risk of stroke and for whom vitamin K-antagonist therapy was unsuitable were randomly assigned to receive clopidogrel (75 mg) or placebo, once daily, in addition to aspirin. The primary outcome was the composite of stroke, myocardial infarction, non-central nervous system systemic embolism, or death from vascular causes. At a median of 3.6 years of follow-up, major vascular events had occurred in 832 patients receiving clopidogrel (6.8% per year) and in 924 patients receiving placebo (7.6% per year) (relative risk with clopidogrel, 0.89; 95% confidence interval [CI], 0.81 to 0.98; P=0.01). The difference was primarily due to a reduction in the rate of stroke with clopidogrel. Stroke occurred in 296 patients receiving clopidogrel (2.4% per year) and 408 patients receiving placebo (3.3% per year) (relative risk, 0.72; 95% CI, 0.62 to 0.83; P<0.001). Myocardial infarction occurred in 90 patients receiving clopidogrel (0.7% per year) and in 115 receiving placebo (0.9% per year) (relative risk, 0.78; 95% CI, 0.59 to 1.03; P=0.08). Major bleeding occurred in 251 patients receiving clopidogrel (2.0% per year) and in 162 patients receiving placebo (1.3% per year) (relative risk, 1.57; 95% CI, 1.29 to 1.92; P<0.001). In patients with atrial fibrillation for whom vitamin K-antagonist therapy was unsuitable, the addition of clopidogrel to aspirin reduced the risk of major vascular events, especially stroke, and increased the risk of major hemorrhage. (ClinicalTrials.gov number, NCT00249873.)

Rivaroxaban, an oral direct factor Xa inhibitor

Rivaroxaban is a small molecule, direct Factor Xa inhibitor and may be a potentially attractive alternative to vitamin K antagonists. Rivaroxaban is being investigated for the prevention and treatment of venous and arterial thrombosis. A broad search of Medline, clinicaltrials.gov and the annual proceedings of the American Society of Hematology and the International Society on Thrombosis and Hemostasis was conducted. This review addresses the findings of this systematic search, including the need for new oral anticoagulants, the development and pharmacology of rivaroxaban, and the results of completed as well as ongoing trials with rivaroxaban. At present, the safety and efficacy of rivaroxaban for the prophylaxis and treatment of venous thromboembolism has been evaluated in Phase II and Phase III trials involving over 24,000 patients. Additionally, rivaroxaban is being evaluated for the treatment of pulmonary embolism, secondary prevention after acute coronary syndromes and the prevention of stroke and non-central nervous system embolism in patients with non-valvular atrial fibrillation. The drug may have its greatest impact in providing a much-needed and attractive alternative to warfarin. Further data (especially large Phase III trials) are required.

Monitoring the ACTIVE-W trial: Some issues in monitoring a noninferiority trial

Noninferiority comparisons of new to current therapies and the use of composite outcomes represent significant advances in the design of clinical trials. They increasingly characterize trials of new cardiovascular agents, posing new challenges to Data Safety Monitoring Boards (DSMB) and principal investigators. The ACTIVE-W study was a noninferiority comparison of the combination of clopidogrel and acetylsalicylic acid versus oral anticoagulant among patients with atrial fibrillation. When unexpectedly high rates of stroke and then of the composite outcome of stroke, non-central nervous system systemic embolism, myocardial infarction, and vascular death emerged, the DSMB modified its monitoring plan and conducted its first formal interim analysis much earlier than had been planned in the DSMB charter. The study was terminated when only 27% of the anticipated outcomes had occurred. This paper discusses issues of appropriate stopping guidelines for noninferiority trials and the early emergence of significant harm in relation to one component (stroke) of a composite outcome. Conditional power was not determined concurrently with the HRs during the monitoring of ACTIVE-W; however, the members of the DSMB now believe that such calculations should be considered as useful adjuncts to the calculation of HRs and could lead to earlier termination of noninferiority trials whose interim results suggest futility, without the need for convincing proof of harm.

Canadian atrial fibrillation anticoaguiation (CAFA) study

The Canadian Atrial Fibrillation Anticoagulation Study was a randomized double-blind placebo-controlled trial to assess the potential of warfarin to reduce systemic thromboembolism and its inherent risk of hemorrhage. As a result of the publication of two other “positive” studies of similar design and objective, this study was stopped early before completion of its planned recruitment of 630 patients. There were 187 patients randomized to warfarin and 191 to placebo. Permanent discontinuation of study medication occurred in 26% of warfarin-treated and 23% of placebo-treated patients. The target range of the international normalized ratio was 2 to 3. For the warfarin-treated patients, the international normalized ratio was in the target range 43.7% of the study days, above it 16.6% of the study days and below it 39.6% of the study days. Fatal or major bleeding occurred at annual rates of 2.5% in warfarin-treated and 0.5% in placebo-treated patients. Minor bleeding occurred in 16% of patiente receiving warfarin and 9% receiving placebo. The primary outcome event cluster was nonlacunar stroke, noncentral nervous systemic embolism and fatal or intracranial hemorrhage. Events were included in the primary analysis of efficacy if they occurred within 28 days of permanent discontinuation of the study medication. The annual rates of the primary outcome event cluster were 3.5% in warfarin-treated and 5.2% in placebo-treated patients, with a relative risk reduction of 37% (95% confidence limits, −63.5%, 75.5%, p = 0.17). This esumate of benefit of anticoagulant therapy in atrial fibrillation is consistent with the estimates from previous reports and supports the use of warfarin in patients with nonrheumatic valvular atrial fibrillation for the prevention of systemic thromboembolism.