Clopidogrel plus aspirin versus oral anticoagulation for atrial fibrillation in the Atrial fibrillation Clopidogrel Trial with Irbesartan for prevention of Vascular Events (ACTIVE W): a randomised controlled trial

Oral anticoagulants versus antiplatelet therapy for preventing stroke in patients with non-valvular atrial fibrillation and no history of stroke or transient ischemic attacks

BACKGROUND

Non-valvular atrial fibrillation (AF) carries an increased risk of stroke mediated by embolism of stasis-precipitated thrombi originating in the left atrial appendage. Both oral anticoagulants and antiplatelet agents have proven effective for stroke prevention in most patients at high risk for vascular events, but primary stroke prevention in patients with non-valvular AF potentially merits separate consideration because of the suspected cardio-embolic mechanism of most strokes in AF patients.

OBJECTIVES

To characterize the relative effect of long-term oral anticoagulant treatment compared with antiplatelet therapy on major vascular events in patients with non-valvular AF and no history of stroke or transient ischemic attack (TIA).

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (June 2006). We also searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2006), MEDLINE (1966 to June 2006) and EMBASE (1980 to June 2006). We contacted the Atrial Fibrillation Collaboration and experts working in the field to identify unpublished and ongoing trials.

SELECTION CRITERIA

All unconfounded, randomized trials in which long-term (more than four weeks) adjusted-dose oral anticoagulant treatment was compared with antiplatelet therapy in patients with chronic non-valvular AF.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, assessed quality and extracted data. The Peto method was used for combining odds ratios after assessing for heterogeneity.

MAIN RESULTS

Eight randomized trials, including 9598 patients, tested adjusted-dose warfarin versus aspirin (in dosages ranging from 75 to 325 mg/day) in AF patients without prior stroke or TIA. The mean overall follow up was 1.9 years/participant. Oral anticoagulants were associated with lower risk of all stroke (odds ratio (OR) 0.68, 95% confidence interval (CI) 0.54 to 0.85), ischemic stroke (OR 0.53, 95% CI 0.41 to 0.68) and systemic emboli (OR 0.48, 95% CI 0.25 to 0.90). All disabling or fatal strokes (OR 0.71, 95% CI 0.59 to 1.04) and myocardial infarction (OR 0.69, 95% CI 0.47 to 1.01) were substantially but not significantly reduced by oral anticoagulants. Vascular death (OR 0.93, 95% CI 0.75 to 1.15) and all cause mortality (OR 0.99, 95% CI 0.83 to 1.18), were similar with these treatments. Intracranial hemorrhages (OR 1.98, 95% CI 1.20 to 3.28) were increased by oral anticoagulant therapy.

AUTHORS' CONCLUSIONS

Adjusted-dose warfarin and related oral anticoagulants reduce stroke, disabling stroke and other major vascular events for those with non-valvular AF by about one third when compared with antiplatelet therapy.

Combined antiplatelet and anticoagulant therapy: clinical benefits and risks

The combination of anticoagulant and antiplatelet therapy is more effective than antiplatelet therapy alone for the initial and long-term management of acute coronary syndromes but increases the risk of bleeding. Antiplatelet therapy is often combined with oral anticoagulants in patients with an indication for warfarin therapy (e.g. atrial fibrillation) who also have an indication for antiplatelet therapy (e.g. coronary artery disease) but the appropriateness of such an approach is unresolved. Anticoagulation appears to be as effective as antiplatelet therapy for long-term management of acute coronary syndrome and stroke, and possibly peripheral artery disease, but causes more bleeding. Therefore, in such patients who develop atrial fibrillation, switching from antiplatelet therapy to anticoagulants might be all that is required. The combination of anticoagulant and antiplatelet therapy has only been proven to provide additional benefit over anticoagulants alone in patients with prosthetic heart valves. The combination of aspirin and clopidogrel is not as effective as oral anticoagulants in patients with atrial fibrillation, whereas the combination of aspirin and clopidogrel is more effective than oral anticoagulants in patients with coronary stents. Whether the benefits of triple therapy outweigh the risks in patients with atrial fibrillation and coronary stents requires evaluation in randomized trials.

Risk of major bleeding with concomitant dual antiplatelet therapy after percutaneous coronary intervention in patients receiving long-term warfarin therapy

STUDY OBJECTIVES

To characterize the safety of concomitant aspirin, clopidogrel, and warfarin therapy after percutaneous coronary intervention (PCI), and to identify patient characteristics that increase the risk of hemorrhage.

DESIGN

Retrospective, matched cohort study.

SETTING

Academic medical center and affiliated outpatient offices.

PATIENTS

The active group consisted of 97 patients who underwent PCI from January 1, 2000-September 30, 2005, and received warfarin, aspirin, and clopidogrel; the control group consisted of 97 patients who were individually matched to patients in the active group by procedure type, procedure year, age, and sex. Control patients received aspirin and clopidogrel.

MEASUREMENTS AND MAIN RESULTS

Clinical data were collected from inpatient records, outpatient physician office records, and telephone surveys administered to patients or caregivers. The primary end point was major bleeding. The median duration of follow-up after index procedure was 182 days (range 0-191 days) in the active group and 182 days (range 0-213 days) in the control group. Fifty-seven (59%) of the 97 patients in the active group received warfarin for atrial fibrillation. There were 14 major bleeds in the active group (including 1 death) and 3 major bleeds in the control group during the study period. Mean international normalized ratio at the time of bleeding was 3.4. Hazard ratio for major bleeding was 5.0 in patients receiving warfarin therapy (95% confidence interval 1.4-17.8, p=0.012). Aspirin dose, age, sex, body mass index, history of hypertension, diabetes mellitus, intraprocedural glycoprotein IIb-IIIa or anticoagulant type, and postprocedural anticoagulant use did not have a significant effect on the risk of major bleeding.

CONCLUSION

Warfarin was an independent predictor of major bleeding after PCI in patients receiving dual antiplatelet therapy. Prospective data to further characterize the safety of concomitant warfarin and dual antiplatelet therapy after PCI are needed.

Frequency of adverse events in patients with poor anticoagulation: a meta-analysis

BACKGROUND

Patients taking anticoagulants orally over the long term have international normalized ratios (INRs) outside the individual therapeutic range more than one-third of the time. Improved anticoagulation control will reduce hemorrhagic and thromboembolic event rates. To gauge the potential effect of improved anticoagulation control, we undertook to determine the proportion of anticoagulant-associated events that occur when INRs are outside the therapeutic range.

METHODS

We conducted a meta-analysis of all studies that assigned hemorrhagic and thromboembolic events in patients taking anticoagulants to discrete INR ranges. We identified studies using the MEDLINE (1966-2006) and EMBASE (1980-2006) databases. We included studies reported in English if the majority of patients taking oral anticoagulants had an INR range with a lower limit between 1.8 and 2 and an upper limit between 3 and 3.5, and their INR at the time of the hemorrhagic or thromboembolic event was recorded.

RESULTS

The final analysis included results from 45 studies (23 that reported both hemorrhages and thromboemboli; 14 that reported hemorrhages only; and 8, thromboemboli only) involving a median of 208 patients (limits of interquartile range [25th-75th percentile] 131-523 subjects; total n = 71 065). Of these studies, 64% were conducted at community practices; the remainder, at anticoagulation clinics. About 69% of the studies were classed as having moderate or high quality. Overall, 44% (95% confidence interval [CI] 39%-49%) of hemorrhages occurred when INRs were above the therapeutic range, and 48% (95% CI 41%-55%) of thromboemboli took place when below it. The mean proportion of events that occurred while the patient's INR was outside the therapeutic range was greater for studies with a short mean follow-up (< 1 yr). Between-study heterogeneity was significant (p < 0.001).

INTERPRETATION

Improved anticoagulation control could decrease the likelihood of almost half of all anticoagulant-associated adverse events.

Atrial fibrillation in the elderly

Atrial fibrillation is increasingly prevalent among older adults. It causes approximately 24% of strokes in patients aged 80 to 89 years. The management of atrial fibrillation is directed at preventing thromboembolism and controlling the heart rate and rhythm. Stroke prevention is most effectively accomplished through administering anticoagulants such as warfarin, although older patients have higher hemorrhagic risk. Cognitive dysfunction, functional impairments, and increased fall risk further complicate warfarin management in elderly patients. The use of risk stratification schemes can help guide the anticoagulation decision, although the benefits of warfarin generally outweigh the risks in most older patients with atrial fibrillation. Pharmacologic rate control has been shown to result in similar outcomes compared with pharmacologic restoration of sinus rhythm and should be the initial therapy for elderly patients. Anti-arrhythmic medications should be selected based on an individual patient's coexisting medical conditions. In symptomatic patients who fail pharmacologic therapy, invasive strategies such as AV nodal ablation may help improve quality of life and symptoms, although such strategies do not obviate the need for antithrombotic therapy.

Major Hemorrhage and Tolerability of Warfarin in the First Year of Therapy Among Elderly Patients With Atrial Fibrillation

Background— Warfarin is effective in the prevention of stroke in atrial fibrillation but is under used in clinical care. Concerns exist that published rates of hemorrhage may not reflect real-world practice. Few patients ≥80 years of age were enrolled in trials, and studies of prevalent use largely reflect a warfarin-tolerant subset. We sought to define the tolerability of warfarin among an elderly inception cohort with atrial fibrillation.

Methods and Results— Consecutive patients who started warfarin were identified from January 2001 to June 2003 and followed for 1 year. Patients had to be ≥65 years of age, have established care at the study institution, and have their warfarin managed on-site. Outcomes included major hemorrhage, time to termination of warfarin, and reason for discontinuation. Of 472 patients, 32% were ≥80 years of age, and 91% had ≥1 stroke risk factor. The cumulative incidence of major hemorrhage for patients ≥80 years of age was 13.1 per 100 person-years and 4.7 for those <80 years of age ( P =0.009). The first 90 days of warfarin, age ≥80 years, and international normalized ratio (INR) ≥4.0 were associated with increased risk despite trial-level anticoagulation control. Within the first year, 26% of patients ≥80 years of age stopped taking warfarin. Perceived safety issues accounted for 81% of them. Rates of major hemorrhage and warfarin termination were highest among patients with CHADS 2 scores (an acronym for congestive heart failure, hypertension, age ≥75, diabetes mellitus, and prior stroke or transient ischemic attack) of ≥3.

Conclusions— Rates of hemorrhage derived from younger noninception cohorts underestimate the bleeding that occurs in practice. This finding coupled with the short-term tolerability of warfarin likely contributes to its underutilization. Stroke prevention among elderly patients with atrial fibrillation remains a challenging and pressing health concern.

Warfarin and Antiplatelet Combination Use Among Commercially Insured Patients Enrolled in an Anticoagulation Management Service

BACKGROUND

Although warfarin and antiplatelet medications have documented efficacy for prevention of primary and secondary cardiovascular events, the appropriateness of warfarin and antiplatelet combination therapy is not well described in national consensus guidelines.

METHODS AND RESULTS

Cross-sectional data from 4,557 Kaiser Permanente Colorado members > or = 18 years old who were receiving warfarin anticoagulation therapy were used to quantify the prevalence of warfarin and antiplatelet agent (ie, aspirin, clopidogrel, dipyridamole, and/or dipyridamole/aspirin) combination therapy as of September 30, 2005, and to identify characteristics of patients receiving combination therapy. The prevalence of warfarin and any antiplatelet combination therapy was 385/1,000 (95% confidence interval [CI], 371/1,000 to 399/1,000). The majority of combination therapy was warfarin and aspirin (prevalence, 378/1,000) with a daily dose of aspirin, 81 mg, being the most reported dose (prevalence, 328/1,000). Patients receiving combination therapy were more likely to be male (63.6% vs 46.4%; adjusted odds ratio, 1.5; 95% CI, 1.3 to 1.7) and have a comorbidity of heart failure (29.0% vs 15.6%; adjusted odds ratio, 1.2; 95% CI, 1.1 to 1.5), coronary artery disease (62.4% vs 17.5%; adjusted odds ratio, 7.6; 95% CI, 6.5 to 8.8), and/or stroke/transient ischemic attack (5.2% vs 1.6%; adjusted odds ratio, 3.5; 95% CI, 2.3 to 5.3).

CONCLUSION

Nearly 4 of 10 patients receiving warfarin management care were receiving warfarin and antiplatelet combination therapy. The findings suggest that this practice is widespread, especially among patients with established cardiovascular disease, and involves a substantially higher number of patients than previously reported. The clinical outcomes associated with this practice require further investigation.

Platelet Surface CD62P and CD63, Mean Platelet Volume, and Soluble/Platelet P-Selectin as Indexes of Platelet Function in Atrial Fibrillation

OBJECTIVES

The aim of this work was to comprehensively study the role of platelets in atrial fibrillation (AF), in relation to the underlying cardiovascular diseases and type of AF, and to analyze the effect of antithrombotic treatment on different aspects of platelet activation.

BACKGROUND

Platelet activation is present in nonvalvular AF, but there is debate whether this is due to AF itself and/or to underlying cardiovascular diseases.

METHODS

A total of 121 AF patients were compared with 65 "healthy control subjects" and 78 "disease control subjects" in sinus rhythm. Platelet activation was assessed using 4 different aspects of platelet pathophysiology: 1) platelet surface expression of CD62P (P-selectin) and CD63 (a lysosomal glycoprotein) (by flow cytometry); 2) mean platelet volume (MPV) (by flow cytometry); 3) plasma levels of soluble P-selectin (sP-selectin, enzyme-linked immunoadsorbent assay); and 4) total amount of P-selectin per platelet (pP-selectin) ("platelet lysis" assay).

RESULTS

Both AF patients and "disease control subjects" had higher levels of CD62P (p < 0.001), CD63 (p < 0.001), and sP-selectin (p < 0.001) compared with "healthy control subjects," with no difference between AF patients and "disease control subjects." Patients with permanent AF had higher levels of sP-selectin (p = 0.014) and MPV (p = 0.025) compared with those with paroxysmal AF. The presence of AF independently affected the levels of CD62P expression, while "high-risk" AF patients (CHADS score > or =2) had higher levels of CD62P compared with those with "low risk." Introducing warfarin resulted in a reduction of pP-selectin (p = 0.013).

CONCLUSIONS

There is a degree of excess of platelet activation in AF compared with "healthy control subjects," but no significant difference between AF patients and "disease control subjects" in sinus rhythm. Platelet activation may differ according to the subtype of AF, but this is not in excess of the underlying comorbidities that lead to AF. Platelet activation in AF may be due to underlying cardiovascular diseases, rather than due to AF per se.

Effects of blood pressure on the prothrombotic risk in 1235 patients with non-valvular atrial fibrillation

BACKGROUND

Increased levels of plasma von Willebrand factor (vWf, an index of endothelial damage/dysfunction) and soluble P-selectin (sP-sel, an index of platelet activation) concentrations have been reported as indices of the prothrombotic state in both non-valvular atrial fibrillation and hypertension separately. However, the effect of hypertension on the levels of these indices in the setting of atrial fibrillation, and whether increasing severity of hypertension presents an additive prothrombotic risk, is unclear.

METHODS

Plasma concentrations of vWf and sP-sel were measured by ELISA in 1235 patients with atrial fibrillation, and levels related to a history of hypertension and rising quartiles of systolic, diastolic and pulse pressure in those with and without diabetes mellitus and prior vascular events.

RESULTS

Mean plasma vWf was higher among patients with atrial fibrillation with a history of hypertension (149 vs 145 IU/dl, p = 0.005). Also, an increase in the levels of vWf with increasing quartiles of pulse pressure (p = 0.042) was noticed. However, on multivariate analysis, after adjusting for potential confounders, the effects of both hypertension and pulse pressure became non-significant (p = 0.261 and p = 0.5, respectively). Levels of sP-sel were unaffected by a history of hypertension and rising quartiles of systolic and diastolic blood pressure, or pulse pressure.

CONCLUSION

Among patients with atrial fibrillation, patients with hypertension have higher vWf levels, indicating endothelial damage/dysfunction, which is associated with increasing pulse pressure. However, these associations are probably owing to the presence of other associated cardiovascular disease, rather than hypertension itself. Furthermore, platelet activation (sP-sel) was unrelated to hypertension or blood pressure in this atrial fibrillation cohort. Hypertension or blood pressure levels do not seem to have an independent additive affect on the prothrombotic state in atrial fibrillation.

[Arrhythmias and cardiac electrophysiology]

In the past few months, numerous articles have been published on arrhythmias and cardiac electrophysiology. As in previous years, a substantial proportion of researchers have concentrated on atrial fibrillation, both on catheter ablation of chronic and paroxysmal atrial fibrillation and on the development of new approaches to thromboembolism prophylaxis. The feasibility of atrial fibrillation ablation by remote control has been demonstrated and a step-wise approach to ablation has been proposed, which appears to improve outcome and reduce lesion size. In addition, multicenter randomized trials have shown that the improvements in functional class and left ventricular ejection fraction achieved by ablation in patients with chronic atrial fibrillation are greater than those resulting from pharmacological treatment. New strategies are being developed to improve the selection of patients for defibrillator implantation and to decrease the number of high-energy discharges occurring during follow-up. Controlled trials continue to demonstrate that pharmacological therapy is of little value in preventing recurrence of vasovagal syncope compared with maneuvers involving isometric muscular contraction. Finally, one of the most significant events in the last year was the publication of new clinical practice guidelines by European and American societies of cardiology. These provide important recommendations on the treatment and prevention of ventricular arrhythmias and sudden death and on the management of and thromboembolic prophylaxis in atrial fibrillation.

Elevated Platelet Microparticle Levels in Nonvalvular Atrial Fibrillation

BACKGROUND

Platelet microparticles (PMPs), are procoagulant membrane vesicles that are derived from activated platelets, the levels of which are elevated in patients with hypertension, coronary artery disease (CAD), diabetes, and stroke, all of which are conditions that lead to (and are associated with) atrial fibrillation (AF). We hypothesized the following: (1) PMP levels are elevated in patients with AF compared to levels in both healthy control subjects (ie, patients without cardiovascular diseases who are in sinus rhythm) and disease control subjects (ie, patients with hypertension, CAD, diabetes or stroke, but who are in sinus rhythm); (2) PMP levels correlate with levels of soluble P-selectin (sP-selectin) [a marker of platelet activation]; and (3) PMP levels are related to the underlying factors in patients with AF that contribute to the overall risk of stroke secondary to AF.

METHODS

We performed a case-control study of 70 AF patients, 46 disease control subjects and 33 healthy control subjects. Peripheral venous levels of PMP and sP-selectin were analyzed by flow cytometry and enzyme-linked immunosorbent assay, respectively.

RESULTS

Both AF patients and disease control subjects had significantly higher levels of PMPs (p < 0.001) and sP-selectin (p = 0.001) compared to healthy control subjects, but there was no difference between AF patients and disease control subjects. There was no difference in PMP levels between patients with paroxysmal and permanent AF (p = 0.581), and between those receiving therapy with aspirin and warfarin (p = 0.779). No significant correlation was observed between PMP and sP-selectin levels (p = 0.463), and the clinical characteristics that contribute to increased stroke risk in patients with AF. On stepwise multiple regression analysis in the combined cohort of AF patients plus disease control subjects, the presence/absence of AF was not an independent determinant of PMP and sP-selectin levels.

CONCLUSION

There is evidence of platelet activation (ie, high PMP and sP-selectin levels) in AF patients, but this is likely to be due to underlying cardiovascular diseases rather than the arrhythmia per se.

Atrial fibrillation

The incidence and prevalence of atrial fibrillation are increasing because of both population ageing and an age-adjusted increase in incidence of atrial fibrillation. Deciding between a rate control or rhythm control approach depends on patient age and comorbidities, symptoms and haemodynamic consequences of the arrhythmia, but either approach is acceptable. Digoxin is no longer a first-line drug for rate control: beta-blockers and verapamil and diltiazem control heart rate better during exercise. Anti-arrhythmic drugs have only a 40%-60% success rate of maintaining sinus rhythm at 1 year, and have significant side effects. The selection of optimal antithrombotic prophylaxis depends on the patient's risk of ischaemic stroke and the benefits and risks of long-term warfarin versus aspirin, but is independent of rate or rhythm control strategy. Ischaemic stroke risk is best estimated with the CHADS2 score (Congestive heart failure, Hypertension, Age > or = 75 years, Diabetes, 1 point each; prior Stroke or transient ischaemic attack, 2 points). For patients with valvular atrial fibrillation or a CHADS(2) score > or = 2, anticoagulation with warfarin is recommended (INR 2-3, higher for mechanical valves) unless contraindicated or annual major bleeding risk > 3%. Aspirin or warfarin may be used when the CHADS(2) score = 1. Aspirin, 81-325 mg daily, is recommended in patients with a CHADS(2) score of 0 or if warfarin is contraindicated. Stroke rate is similar for paroxysmal, persistent, and permanent atrial fibrillation, and probably for atrial flutter.

Platelet P2 receptors: old and new targets for antithrombotic drugs

Platelets possess three P2 receptors for adenine nucleotides: P2Y1 and P2Y12, which interact with ADP, and P2X1, which interacts with ATP. The interaction of adenine nucleotides with their platelet receptors plays an important role in thrombogenesis. The thienopyridine ticlopidine, an antagonist of the platelet P2Y12 ADP receptor, reduces the incidence of vascular events in patients at risk, but it also has some important drawbacks: a relatively high incidence of toxic effects; delayed onset of action; high inter-individual variability in response. Another thienopyridine, clopidogrel, has superseded ticlopidine, because it is an efficacious antithrombotic drug and is less toxic than ticlopidine. However, the high inter-patient variability in response still remains an important issue. These drawbacks justify the continuing search for agents that can further improve the clinical outcome of patients with atherosclerosis through greater efficacy and/or safety. A new thienopyridyl compound prasugrel, which is characterized by higher potency and faster onset of action compared with clopidogrel, is currently under clinical evaluation. Two direct and reversible P2Y12 antagonists, cangrelor and AZD6140, have very rapid onset and reversal of platelet inhibition, which make them attractive alternatives to thienopyridines, especially when rapid inhibition of platelet aggregation or its quick reversal are required. Along with new P2Y12 antagonists, inhibitors of the other platelet receptor for ADP, P2Y1, and of the receptor for ATP, P2X1, are under development and may prove to be effective antithrombotic agents.

Infarctus cérébral: prise en charge en urgence et prévention secondaire

Stroke is a medical emergency. Intravenous administration of recombinant tissue-type plasminogen activator (rt-PA) within three hours of stroke onset is the only pharmacological treatment proven effective in ischemic stroke. Its efficacy is time dependent. Patients must be carefully selected and treated in dedicated stroke units to reduce the risk of hemorrhage. Early treatment in dedicated stroke units reduces mortality and disability, independent of any specific treatment. Secondary prevention includes antiplatelet therapy and successful control of all risk factors (hypertension, diabetes, tobacco use, and hyperlipidemia). Carotid endarterectomy may be considered if the residual disability is not serious. Lowering blood pressure is beneficial even when initial blood pressure is normal. Lowering LDL-C with statins after ischemic stroke reduces the risk of recurrent stroke and coronary events.

Clopidogrel

Clopidogrel (Plavix), Iscover) selectively and irreversibly inhibits adenosine diphosphate (ADP)-induced platelet aggregation. Long-term administration of clopidogrel was associated with a modest but statistically significant advantage over aspirin in reducing adverse cardiovascular outcomes in patients with established cardiovascular disease in the CAPRIE trial. In other large well designed multicentre trials, such as CURE, COMMIT and CLARITY-TIMI 28, the addition of clopidogrel to aspirin therapy improved outcomes in patients with acute coronary syndromes. However, some issues regarding the use of clopidogrel remain unresolved, such as the optimal loading dose in patients undergoing percutaneous coronary interventions (PCI) and the optimal treatment duration following drug-eluting intracoronary stent placement. Results of several large randomised trials, therefore, have established clopidogrel as an effective and well tolerated antiplatelet agent for the secondary prevention of ischaemic events in patients with various cardiovascular conditions, including those with ischaemic stroke or acute coronary syndromes. In addition, treatment guidelines from the US and Europe acknowledge the importance of clopidogrel in contemporary cardiovascular medicine.

Stroke in atrial fibrillation: update on pathophysiology, new antithrombotic therapies, and evolution of procedures and devices

Atrial fibrillation (AF) is said to be an epidemic, affecting 1%-1.5% of the population in the developed world. The clinical significance of AF lies predominantly in a 5-fold increased risk of stroke. Strokes associated with AF are usually more severe and confer increased risk of morbidity, mortality, and poor functional outcome. Despite the advent of promising experimental therapies for selected patients with acute stroke, pharmacological primary prevention remains the best approach to reducing the burden of stroke. New antithrombotic drugs include both parenteral agents (e.g. a long-acting factor Xa inhibitor idraparinux) and oral anticoagulants, such as oral factor Xa inhibitors and direct oral thrombin inhibitors (ximelagatran, dabigatran). Ximelagatran had shown significant potential as a possible replacement to warfarin therapy, but has been withdrawn because of potential liver toxicity. Its congener dabigatran appears to have a better safety profile and has recently entered a phase III randomized clinical trial in AF. Oral factor Xa inhibitors (rivaroxaban, apixaban, YM150) inhibit factor Xa directly, without antithrombin III mediation, and may prove to be more potent and safe. Selective inhibitors of specific coagulation factors involved in the initiation and propagation of the coagulation cascade (factor IXa, factor VIIa, circulating tissue factor) are at an early stage of development. Additional new agents with hypothetical, although not yet proven, anticoagulation benefits include nematode anticoagulant peptide (NAPc2), protein C derivatives, and soluble thrombomodulin. A battery of novel mechanical approaches for the prevention of cardioembolic stroke has recently been evaluated, including various models of percutaneous left atrial appendage occluders which block the connection between the left atrium and the left atrial appendage, minimally invasive surgical isolation of the left atrial appendage, and implantation of the carotid filtering devices which divert large emboli from the internal to the external carotid artery, preventing the embolic material from reaching intracranial circulation. Despite recent advances and promising new approaches, prevention of recurrent AF may be one of the best protections against AF-related stroke and may reduce the prevalence of stroke by almost 25%. Improved pharmacological and nonpharmacological rhythm control strategies for AF as well as primary prevention of AF with 'upstream' therapy and risk factor modification are likely to produce a larger effect on the reduction of stroke rates in the general population than will specific interventions.

Platelet adhesion in atrial fibrillation

BACKGROUND

Increased platelet activation has been reported in nonvalvular atrial fibrillation (AF) but it remains unclear whether or not this is due to the underlying cardiovascular diseases, clinical subtype of AF and the influence of anti-thrombotic therapy.

METHODS

Platelet adhesion in AF patients was assessed using a 'platelet adhesion assay', and compared to both 'healthy controls' and 'disease controls' (patients with hypertension, coronary artery disease, diabetes or stroke but in sinus rhythm).

RESULTS

AF patients on no anti-thrombotic treatment (N=20) had increased platelet adhesion compared to 'healthy controls' (N=57) (p=0.044). Initiating treatment with both aspirin and warfarin resulted in significant reduction in platelet adhesion in AF patients (p=0.014 and 0.019 respectively). AF patients on optimal anti-thrombotic therapy (N=98) had no significant difference in platelet adhesion compared to 'healthy controls' and 'disease controls' (p=0.312). Platelet adhesion failed to distinguish between 'high-risk' (i.e. CHADS score > or = 2) and 'low-risk' (i.e. CHADS score < 2) AF patients (p=0.352). Amongst the clinical parameters that contribute to increased stroke risk in AF, platelet adhesion was only correlated with age (r=0.215, p=0.034), and not with other stroke risk factors. There was no significant difference in platelet adhesion between paroxysmal and permanent AF (p=0.618).

CONCLUSION

There is a significant, albeit weak, excess of platelet adhesion in AF patients on no anti-thrombotic therapy compared to 'healthy controls'. In optimally treated AF patients, platelet adhesion is not different to both 'healthy' and 'disease controls'. It is possible that abnormal platelet adhesion does not significantly contribute to the increased risk of stroke and thromboembolism that persists despite anti-thrombotic treatment in AF or in identifying 'high-risk' AF patients.

Warfarin dose and the pharmacogenomics of CYP2C9 and VKORC1 - rationale and perspectives

Warfarin is the most widely prescribed oral anticoagulant, but there is greater than 10-fold interindividual variability in the dose required to attain a therapeutic response. Information from pharmacogenomics, the study of the interaction of an individual's genotype and drug response, can help optimize drug efficacy while minimizing adverse drug reactions. Pharmacogenetic analysis of two genes, the warfarin metabolic enzyme CYP2C9 and warfarin target enzyme, vitamin K epoxide reductase complex 1 VKORC1, confirmed their influence on warfarin maintenance dose. Possession of CYP2C9*2 or CYP2C9*3 variant alleles, which result in decreased enzyme activity, is associated with a significant decrease in the mean warfarin dose. Several single nucleotide polymorphisms (SNPs) in VKORC1 are associated with warfarin dose across the normal dose range. Haplotypes based on these SNPs explain a large fraction of the interindividual variation in warfarin dose, and VKORC1 has an approximately three-fold greater effect than CYP2C9. Algorithms incorporating genetic (CYP2C9 and VKORC1), demographic, and clinical factors to estimate the warfarin dosage, could potentially minimize the risk of over dose during warfarin induction.

Anticoagulation in atrial fibrillation: a contemporary viewpoint

Anticoagulation therapy in patients with atrial fibrillation is important. This review consists of three parts: chronic anticoagulation, anticoagulation for cardioversion, and a brief comment on anticoagulation around the time of left atrial radiofrequency ablation. The risk stratification scheme of the American College of Cardiology/American Heart Association/European Society of Cardiology (ACC/AHA/ESC) guidelines for chronic anticoagulation is briefly reviewed. Although there are several other similar schemes, they are not identical. The key point is the balance between benefit and risk. Some emerging controversies are outlined. Two specific questions explored are: is well-controlled hypertension a risk factor, and does paroxysmal atrial fibrillation confer the same risk as continuous atrial fibrillation? Differences in the risk of bleeding while taking a vitamin K antagonist noted in recent compared with older data are discussed. Risk of bleeding in the elderly and combined antithrombotic therapy with a vitamin K antagonist and an antiplatelet agent in high-risk patients are briefly discussed. Recent failures of studies attempting to find a suitable alternative to vitamin K antagonists are outlined. The treatment guidelines for anticoagulation for cardioversion are briefly reviewed. The risk of thromboembolism according to international normalized ratio and use of low-molecular-weight heparin as an alternative to warfarin are discussed. Anticoagulation before and after left atrial radiofrequency ablation is empirical, and long-term anticoagulation seems advisable for high risk patients at the present time. The two most pressing needs for further investigation are (1) clarification, simplification, and consolidated of risk stratification schemes and treatment recommendations and (2) discovery of alternatives to warfarin.

Drug Insight: antithrombotic therapy after percutaneous coronary intervention in patients with an indication for anticoagulation

Antiplatelet therapy with aspirin and clopidogrel is standard care following revascularization by percutaneous coronary intervention with stent insertion. This so-called dual therapy is recommended for up to 4 weeks after intervention for bare-metal stents and for 6-12 months after intervention for drug-eluting stents. Although it is estimated that 5% of patients undergoing percutaneous coronary intervention require long-term anticoagulation because of an underlying chronic medical condition, continuing treatment with triple therapy (warfarin, aspirin and clopidogrel) increases the risk of bleeding. In most patients triple antithrombotic therapy seems justified for a short period of time. In some patients, however, a more considered judgment based on absolute need for triple therapy, risk of bleeding and risk of stent thrombosis is required, but the optimum antithrombotic treatment for these patients who require long-term anticoagulation has not been defined. This Review summarizes the existing literature concerning antithrombotic therapy and makes recommendations for initiation and duration of triple therapy in the small proportion of patients already receiving anticoagulant therapy who require percutaneous coronary intervention.

Anticoagulant and Antiplatelet Therapy Use in Patients With Atrial Fibrillation Undergoing Percutaneous Coronary Intervention

BACKGROUND

There is a lack of published evidence on what is the optimal management strategy in anticoagulated patients with nonvalvular atrial fibrillation (AF) who undergo percutaneous coronary intervention (PCI) and, hence, need antiplatelet therapy.

AIMS

Review of cases of patients with nonvalvular AF undergoing PCI in our hospital, either as an elective case or following acute coronary syndrome (ACS).

METHODS

By means of our local West Midlands Regional Health Authority computerized Hospital Activity Analysis register, we obtained a list of all patients seen at our hospital with a diagnosis of AF in association with ACS or PCI between 2000 and 2005. Patient clinical details and antithrombotic therapy management during PCI were recorded.

RESULTS

Of the drugs prescribed on discharge, aspirin and clopidogrel were prescribed to 25 patients (71.4%), while 6 patients (17.1%) were discharged receiving triple therapy, 2 patients (5.7%) receiving clopidogrel alone, and 2 patients (5.7%) receiving warfarin plus one antiplatelet drug (either aspirin or clopidogrel). There was wide variability in the antithrombotic regime and duration of treatment used by the four interventionists in our unit.

CONCLUSION

This case series reveals the lack of any coordinated strategy in the prevention of thrombotic or thromboembolic events in patients with AF and a recent PCI. Further large studies are required to assess the bleeding and thrombotic risk with various post-PCI strategies in order to facilitate the development of guidelines. Suggested management guidelines are made in this article.

Enhanced thrombogenesis but not platelet activation is associated with transcatheter closure of patent foramen ovale in patients with cryptogenic stroke

BACKGROUND AND PURPOSE

No studies have yet determined whether antiplatelet or anticoagulant therapy is the more appropriate treatment after transcatheter closure of patent foramen ovale (PFO) in patients with cryptogenic stroke. The objective of this study was to prospectively evaluate the presence, degree, and timing of activation of the platelet and coagulation systems after transcatheter closure of PFO in patients with cryptogenic stroke.

METHODS

Twenty-four consecutive patients (mean age, 44+/-10 years; 11 men) with previous cryptogenic stroke who had undergone successful transcatheter closure of PFO were included in the study. Prothrombin fragment 1+2 (F1+2) and thrombin-antithrombin III (TAT) were used as markers of coagulation activation, and soluble P-selectin and soluble CD40 ligand were used as markers of platelet activation. Measurements of all hemostatic markers were taken at baseline just before the procedure and at 7, 30, and 90 days after device implantation.

RESULTS

F1+2 and TAT levels increased from 0.41+/-0.16 nmol/L and 2.34+/-1.81 ng/mL, respectively, at baseline to a maximal value of 0.61+/-0.16 nmol/L and 4.34+/-1.83 ng/mL, respectively, at 7 days, gradually returning to baseline levels at 90 days (P<0.001 for both markers). F1+2 and TAT levels at 7 days after PFO closure were higher than those obtained in a group of 25 healthy controls (P<0.001 for both markers). Levels of soluble P-selectin and soluble CD40 ligand did not change at any time after PFO closure.

CONCLUSIONS

Transcatheter closure of PFO is associated with significant activation of the coagulation system, with no increase in platelet activation markers. These findings raise the question of whether optimal antithrombotic treatment after PFO closure should be short-term anticoagulant rather than antiplatelet therapy.

Clopidogrel resistance?

Clopidogrel is an effective inhibitor of platelet activation and aggregation due to its selective and irreversible blockade of the P2Y(12) receptor. Combination antiplatelet therapy with clopidogrel and aspirin is an important strategy for patients with acute coronary syndromes and those undergoing percutaneous interventions. Despite significant benefits demonstrated with combination antiplatelet treatment in large clinical trials, the occurrence of adverse ischemic events, including stent thrombosis, remains a serious clinical problem. Recent studies have demonstrated distinct response variability and nonresponsiveness to clopidogrel therapy based on ex vivo platelet function measurements. Small scale investigations have suggested that nonresponsiveness may be associated with a heightened risk for adverse clinical events. The above findings have stimulated a close examination of clopidogrel metabolism.

Primary Stroke Prevention

The best way to prevent a first-time stroke is to identify at-risk patients and control as many risk factors as possible. Some risk factors, such as smoking, can be eliminated; others, such as hypertension and carotid artery stenosis, can be controlled or treated to reduce the risk of stroke. Nurses are encouraged to work with patients to identify all risk factors in order to reduce the prevalence of this medical condition that costs billions of dollars annually and results in significant disability.

Optimising stroke prevention in non-valvular atrial fibrillation

Atrial fibrillation is associated with substantial morbidity and mortality. Pooled data from trials comparing antithrombotic treatment with placebo have shown that warfarin reduces the risk of stroke by 62%, and that aspirin alone reduces the risk by 22%. Overall, in high-risk patients, warfarin is superior to aspirin in preventing strokes, with a relative risk reduction of 36%. Ximelagatran, an oral direct thrombin inhibitor, was found to be as efficient as vitamin K antagonist drugs in the prevention of embolic events, but has been recently withdrawn because of abnormal liver function tests. The ACTIVE-W (Atrial Fibrillation Clopidogrel Trial with Irbesartan for Prevention of Vascular Events) study has demonstrated that warfarin is superior to platelet therapy (clopidogrel plus aspirin) in the prevention af embolic events. Idraparinux, a Factor Xa inhibitor, is being evaluated in patients with atrial fibrillation. Angiotensin-converting enzyme inhibitors and angiotensin II receptor-blocking drugs hold promise in atrial fibrillation through cardiac remodelling. Preliminary studies suggest that statins could interfere with the risk of recurrence after electrical cardioversion. Finally, percutaneous methods for the exclusion of left atrial appendage are under investigation in high-risk patients.

Preadmission antithrombotic treatment and stroke severity in patients with atrial fibrillation and acute ischaemic stroke: an observational study

BACKGROUND

Vitamin K antagonists (eg, warfarin) substantially reduce the risk of ischaemic stroke in patients with atrial fibrillation. Additionally, therapeutic anticoagulation at time of acute stroke admission might reduce in-hospital mortality and disability. We assessed the association between preadmission antithrombotic treatment and initial stroke severity, neurological deterioration, major vascular events during hospital stay, and death or disability at discharge in patients with acute ischaemic stroke and atrial fibrillation.

METHODS

We identified consecutive patients with acute ischaemic stroke and atrial fibrillation, admitted to 11 hospitals in Ontario, Canada, from the Registry of the Canadian Stroke Network (2003-05). Logistic regression was used to assess the association between antiplatelet treatment, subtherapeutic warfarin treatment (admission international normalised ratio [INR] < 2), therapeutic warfarin treatment (admission INR > or = 2), and clinical outcome. Stroke severity was measured using the Canadian neurological scale (CNS) and was categorised into mild (CNS > 7) and severe stroke (CNS < or = 7). Disability was measured with the modified-Rankin scale (mRS) and was categorised into strokes associated with no or mild-moderate dependency (mRS 0-3) and with severe dependency or death (mRS 4-6).

RESULTS

Of 948 patients, 306 (32%) were not on antithrombotic treatment, 292 (31%) were receiving antiplatelet treatment, 238 (25%) were receiving warfarin with a subtherapeutic INR, and 112 (12%) were receiving warfarin with a therapeutic INR on admission. Compared with those not receiving antithrombotic therapy, antiplatelet therapy (odds ratio 0.7; 95% CI 0.5-0.995) and therapeutic warfarin (0.4; 0.2-0.6) were associated with a reduction in severe stroke at admission. Therapeutic warfarin was also associated with a reduction in the odds of severe disability or death at discharge (0.5; 0.3-0.9).

INTERPRETATION

Therapeutic warfarin is associated with reduced severity of ischaemic stroke at presentation and reduced disability or death at discharge in patients with atrial fibrillation. Antiplatelet treatment is associated with a more modest reduction than warfarin in baseline stroke severity.