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• W2913335974 abstract "R G Dalton (Feb 27, p 758)1Dalton RG Thromboprophylaxis for atrial fibrillation.Lancet. 1999; 353: 756Summary Full Text Full Text PDF PubMed Scopus (1) Google Scholar raises concerns about the risks of bleeding with anticoagulation for atrial fibrillation (AF), especially since the efficacy of warfarin in the clinical trials may not translate into benefit in practice. Indeed, these trials were never designed to provide anything more than an estimate of treatment efficacy, and although widely interpreted as being treatment studies of anticoagulation, these trials were essentially packages of care that included drugs, careful monitoring, and follow-up.Patients in these trials were highly selected, especially for contraindications to warfarin, and on average less than 10% (range 3–40%) of eligible patients were actually randomised. The frequent monitoring of warfarin therapy under trial conditions and motivation of patients and investigators was probably greater than that seen in usual clinical practice. Many patients were excluded after initial assessments for the absence of contraindications and physicians' refusal to enter their patients into the study. Hence, the ratio of antithrombotic benefit to bleeding risk may perhaps be lower in usual clinical practice than in the published trials. Nevertheless, similar arguments can be made for many intervention trials, especially with respect to the application to everyday clinical practice. However, many episodes of stroke in the groups treated by anticoagulation arose when the international normalised ratios (INR) were subtherapeutic; a counter argument may therefore be that the efficacy of warfarin was actually underestimated.The risk of bleeding associated with the use of warfarin in the elderly population is a major concern. Although some studies have suggested that the risk of bleeding with anticoagulation increases with age, this finding is not universal. Whereas stroke risk increases with age in AF (with this age group encompassing perhaps half the AF-associated stroke patients), the associated frailty, poor mobility, poor cognitive function, forgetfulness, or poor compliance with medication, polypharmacy (resulting in drug interactions), and frequent falls may jeopardise the benefits from warfarin. In the SPAF-II study, the benefits of warfarin were almost counteracted by an increased risk of intercranial haemorrhage in the warfarin group, which was unexpectedly high in patients over 75 years (1·8% per year); however, the rate of intracranial haemorrhage in this group was substantially higher than that reported in the original five trials (on average 0·3% per year), which probably relates to the higher intensity of anti-coagulation in the Stroke Prevention in Atrial Fibrillation II study2Stroke Prevention in Atrial Fibrillation InvestigatorsAdjusted-dose warfarin versus low-intensity, fixed-dose warfarin plus aspirin for high risk patients with atrial fibrillation; Stroke Prevention In Atrial Fibrillation III randomized clinical trial.Lancet. 1996; 348: 633-638Summary Full Text Full Text PDF PubMed Scopus (1092) Google Scholar (INR up to 4·5). Even aspirin can increase the risk of major haemorrhage by two-fold (0·5% per year in elderly people).In the trials, most strokes occur in patients assigned to warfarin therapy with INR values under 2·0.3Hylek EM Skates SJ Sheehan MA Singer DE An analysis of the lowest effective intensity of prophylactic anticoagulation for patients with non-rheumatic atrial fibrillation.N Engl J Med. 1996; 335: 540-546Crossref PubMed Scopus (757) Google Scholar At the other end of spectrum, the bleeding risk was higher in patients with INR values over 3·0.4The Stroke Prevention in Atrial Fibrillation InvestigatorsBleeding during antithrombotic therapy in patients with atrial fibrillation.Arch Intern Med. 1996; 156: 409-416Crossref PubMed Google Scholar The target INR for anticoagulation in non-valvular AF should therefore be between 2·0 and 3·0, providing maximum thromboprophylaxis with minimum bleeding risk. Maintenance of constant INR values between 2·0 and 3·0 is much more difficult than it seems, even in clinical trials. It has been suggested that INR between 1·6 and 2·5 can provide substantial, if partial, efficacy (nearly 90% of the highest intensities) for thromboprophylaxis.2Stroke Prevention in Atrial Fibrillation InvestigatorsAdjusted-dose warfarin versus low-intensity, fixed-dose warfarin plus aspirin for high risk patients with atrial fibrillation; Stroke Prevention In Atrial Fibrillation III randomized clinical trial.Lancet. 1996; 348: 633-638Summary Full Text Full Text PDF PubMed Scopus (1092) Google Scholar, 3Hylek EM Skates SJ Sheehan MA Singer DE An analysis of the lowest effective intensity of prophylactic anticoagulation for patients with non-rheumatic atrial fibrillation.N Engl J Med. 1996; 335: 540-546Crossref PubMed Scopus (757) Google Scholar With the uncertainty about the safety of INRs greater than 3·0, especially in elderly AF patients, a target INR of 2·0 (range 1·6–2·5) may be a reasonable compromise between efficacy and toxicity for the elderly.These concerns are why we should vigorously attempt risk stratification for thromboprophylaxis in AF;5Lip GYH Thromboprophylaxis for atrial fibrillation.Lancet. 1999; 353: 4-6Summary Full Text Full Text PDF PubMed Scopus (54) Google Scholar at least the patients at high risk who need warfarin most could be targeted for treatment, after careful assessment for contraindications to therapy. It is a question of risk-benefit ratio, as with many therapeutic decisions in clinical medicine. R G Dalton (Feb 27, p 758)1Dalton RG Thromboprophylaxis for atrial fibrillation.Lancet. 1999; 353: 756Summary Full Text Full Text PDF PubMed Scopus (1) Google Scholar raises concerns about the risks of bleeding with anticoagulation for atrial fibrillation (AF), especially since the efficacy of warfarin in the clinical trials may not translate into benefit in practice. Indeed, these trials were never designed to provide anything more than an estimate of treatment efficacy, and although widely interpreted as being treatment studies of anticoagulation, these trials were essentially packages of care that included drugs, careful monitoring, and follow-up. Patients in these trials were highly selected, especially for contraindications to warfarin, and on average less than 10% (range 3–40%) of eligible patients were actually randomised. The frequent monitoring of warfarin therapy under trial conditions and motivation of patients and investigators was probably greater than that seen in usual clinical practice. Many patients were excluded after initial assessments for the absence of contraindications and physicians' refusal to enter their patients into the study. Hence, the ratio of antithrombotic benefit to bleeding risk may perhaps be lower in usual clinical practice than in the published trials. Nevertheless, similar arguments can be made for many intervention trials, especially with respect to the application to everyday clinical practice. However, many episodes of stroke in the groups treated by anticoagulation arose when the international normalised ratios (INR) were subtherapeutic; a counter argument may therefore be that the efficacy of warfarin was actually underestimated. The risk of bleeding associated with the use of warfarin in the elderly population is a major concern. Although some studies have suggested that the risk of bleeding with anticoagulation increases with age, this finding is not universal. Whereas stroke risk increases with age in AF (with this age group encompassing perhaps half the AF-associated stroke patients), the associated frailty, poor mobility, poor cognitive function, forgetfulness, or poor compliance with medication, polypharmacy (resulting in drug interactions), and frequent falls may jeopardise the benefits from warfarin. In the SPAF-II study, the benefits of warfarin were almost counteracted by an increased risk of intercranial haemorrhage in the warfarin group, which was unexpectedly high in patients over 75 years (1·8% per year); however, the rate of intracranial haemorrhage in this group was substantially higher than that reported in the original five trials (on average 0·3% per year), which probably relates to the higher intensity of anti-coagulation in the Stroke Prevention in Atrial Fibrillation II study2Stroke Prevention in Atrial Fibrillation InvestigatorsAdjusted-dose warfarin versus low-intensity, fixed-dose warfarin plus aspirin for high risk patients with atrial fibrillation; Stroke Prevention In Atrial Fibrillation III randomized clinical trial.Lancet. 1996; 348: 633-638Summary Full Text Full Text PDF PubMed Scopus (1092) Google Scholar (INR up to 4·5). Even aspirin can increase the risk of major haemorrhage by two-fold (0·5% per year in elderly people). In the trials, most strokes occur in patients assigned to warfarin therapy with INR values under 2·0.3Hylek EM Skates SJ Sheehan MA Singer DE An analysis of the lowest effective intensity of prophylactic anticoagulation for patients with non-rheumatic atrial fibrillation.N Engl J Med. 1996; 335: 540-546Crossref PubMed Scopus (757) Google Scholar At the other end of spectrum, the bleeding risk was higher in patients with INR values over 3·0.4The Stroke Prevention in Atrial Fibrillation InvestigatorsBleeding during antithrombotic therapy in patients with atrial fibrillation.Arch Intern Med. 1996; 156: 409-416Crossref PubMed Google Scholar The target INR for anticoagulation in non-valvular AF should therefore be between 2·0 and 3·0, providing maximum thromboprophylaxis with minimum bleeding risk. Maintenance of constant INR values between 2·0 and 3·0 is much more difficult than it seems, even in clinical trials. It has been suggested that INR between 1·6 and 2·5 can provide substantial, if partial, efficacy (nearly 90% of the highest intensities) for thromboprophylaxis.2Stroke Prevention in Atrial Fibrillation InvestigatorsAdjusted-dose warfarin versus low-intensity, fixed-dose warfarin plus aspirin for high risk patients with atrial fibrillation; Stroke Prevention In Atrial Fibrillation III randomized clinical trial.Lancet. 1996; 348: 633-638Summary Full Text Full Text PDF PubMed Scopus (1092) Google Scholar, 3Hylek EM Skates SJ Sheehan MA Singer DE An analysis of the lowest effective intensity of prophylactic anticoagulation for patients with non-rheumatic atrial fibrillation.N Engl J Med. 1996; 335: 540-546Crossref PubMed Scopus (757) Google Scholar With the uncertainty about the safety of INRs greater than 3·0, especially in elderly AF patients, a target INR of 2·0 (range 1·6–2·5) may be a reasonable compromise between efficacy and toxicity for the elderly. These concerns are why we should vigorously attempt risk stratification for thromboprophylaxis in AF;5Lip GYH Thromboprophylaxis for atrial fibrillation.Lancet. 1999; 353: 4-6Summary Full Text Full Text PDF PubMed Scopus (54) Google Scholar at least the patients at high risk who need warfarin most could be targeted for treatment, after careful assessment for contraindications to therapy. It is a question of risk-benefit ratio, as with many therapeutic decisions in clinical medicine." @default.
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