Risk assessment and anticoagulation for primary stroke prevention in atrial fibrillation

Clinical factors in patients with ischemic versus hemorrhagic stroke in East China

BACKGROUND

Stroke is one of the leading causes of mortality and morbidity of vascular diseases, and its incidence maintains at a high level around the world. In China, stroke has been a major public health problem. Because the pathogenesis of ischemic stroke is different from that of hemorrhagic stroke, their clinical factors would not be the same. Therefore to investigate the different effects of various effect factors on ischemic versus hemorrhagic stroke and then to enhance the prevention are crucial to decrease the incidence.

METHODS

A total of 692 patients, consisting of 540 ischemic stroke patients and 152 hemorrhagic stroke patients from East China, were included in this study. The related factors of stroke subtypes were collected and analyzed.

RESULTS

The factors significantly associated with ischemic stroke as opposed to hemorrhagic stroke were family history of stroke, obesity, atherosclerotic plaque of the common carotid artery, atrial fibrillation, hyperfibrinogenemia, transient ischemic attack (TIA), atherosclerotic plaque of the internal carotid artery, coronary heart, lower high-density lipoproteins (lower HDL), increasing age, diabetes mellitus, and gender (male) (P<0.05). Leukocytosis, hypertension and family history of hypertension were the significant factors associated with hemorrhagic stroke versus ischemic stroke. Smoking, drinking, kidney diseases and lower HDL-C were the significant factors contributing to ischemic stroke in man. Obesity, family history of hypertension, family history of stroke, hypercholesteremia and myocardial ischemia were the significant factors for females with ischemic stroke.

CONCLUSIONS

The most prominent factors for overall stroke in East China were hypertension, followed by higher pulse pressure and hypercholesteremia. The factors for ischemic and hemorrhagic stroke are not the same. Different effects of risk factors on stroke are found in male and female patients.

Stroke and Death Prediction with the Impact of Vascular Disease in Patients with Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia encountered in the U.S. and the growing burden of AF has profound health implications due to the association of AF with an increased risk of stroke, heart failure, and mortality. AF is a significant risk factor for thromboembolic stroke; and also independently increases total mortality in patients with and without cardiovascular disease. Various risk stratification schemes such as CHADS₂ and CHA₂DS₂-VASc have been implemented in clinical practice to determine the risk of cardio-embolic stroke, and need for thrombo-prophylaxis in patients with AF. AF is also closely related to the pathophysiology of other cardiovascular and peripheral vascular disease. Many patients with AF have associated atherosclerosis given that many risk factors for atherosclerosis also predispose to AF. Myocardial infarction (MI) is also closely related to AF and its clinical course is affected by new onset AF. This review elucidates the impact of AF on major adverse cardiovascular events and mortality outcomes in relation to stroke, coronary artery disease and peripheral vascular disease.

Rationale and design of ACTIVE: the atrial fibrillation clopidogrel trial with irbesartan for prevention of vascular events

BACKGROUND

Atrial fibrillation (AF) is the most frequently occurring cardiac arrhythmia with often serious clinical consequences. Many patients have contraindications to anticoagulation, and it is often underused in clinical practice. The addition of clopidogrel to aspirin (ASA) has been shown to reduce vascular events in a number of high-risk populations. Irbesartan is an angiotensin receptor-blocking agent that reduces blood pressure and has other vascular protective effects.

METHODS AND RESULTS

ACTIVE W is a noninferiority trial of clopidogrel plus ASA versus oral anticoagulation in patients with AF and at least 1 risk factor for stroke. ACTIVE A is a double-blind, placebo-controlled trial of clopidogrel in patients with AF and with at least 1 risk factor for stroke who receive ASA because they have a contraindication for oral anticoagulation or because they are unwilling to take an oral anticoagulant. ACTIVE I is a partial factorial, double-blind, placebo-controlled trial of irbesartan in patients participating in ACTIVE A or ACTIVE W. The primary outcomes of these studies are composites of vascular events. A total of 14000 patients will be enrolled in these trials.

CONCLUSIONS

ACTIVE is the largest trial yet conducted in AF. Its results will lead to a new understanding of the role of combined antiplatelet therapy and the role of blood pressure lowering with an angiotensin II receptor blocker in patients with AF.

Atrial fibrillation, stroke and anticoagulant use

BACKGROUND

Ischaemic stroke is reduced by anticoagulant therapy in high-risk patients with atrial fibrillation. Evidence however, suggests patients are under treated.

AIM

To assess anticoagulant use in patients with ischaemic stroke and atrial fibrillation in Waikato Hospital.

METHODS

A retrospective review of all patients admitted with stroke over a one-year period.

RESULTS

Ischaemic stroke occurred in 189 patients with atrial fibrillation noted in 21% (39/189) of this group. The majority were female, 59% (23/39) with a mean age of 79.8 years. A total of 84% (33/39) were considered high risk for thromboembolic complications but only 18% (6/33) were anticoagulated prior to the stroke. Following the cerebrovascular accident all patients were considered to be at high risk but only a further 25% (10/39), were anticoagulated. In the remaining 55% (21/39) anticoagulant therapy was not commenced with age alone cited as a contraindication in 8% (3/39). At a mean follow-up of 10 months no complications of anticoagulant therapy were reported.

CONCLUSIONS

A significant proportion of patients with atrial fibrillation and high-risk characteristics are not anticoagulated prior to ischaemic stroke. These findings reflect overseas experience. Reasons are unknown but may in part relate to physician reluctance to anticoagulate elderly patients.

A randomised controlled trial and cost effectiveness study of systematic screening (targeted and total population screening) versus routine practice for the detection of atrial fibrillation in the over 65s: (SAFE) [ISRCTN19633732]

Background

Atrial fibrillation (AF) has been recognised as an important independent risk factor for thromboembolic disease, particularly stroke for which it provides a five-fold increase in risk. This study aimed to determine the baseline prevalence and the incidence of AF based on a variety of screening strategies and in doing so to evaluate the incremental cost-effectiveness of different screening strategies, including targeted or whole population screening, compared with routine clinical practice, for detection of AF in people aged 65 and over. The value of clinical assessment and echocardiography as additional methods of risk stratification for thromboembolic disease in patients with AF were also evaluated.

Methods

The study design was a multi-centre randomised controlled trial with a study population of patients aged 65 and over from 50 General Practices in the West Midlands. These purposefully selected general practices were randomly allocated to 25 intervention practices and 25 control practices. GPs and practice nurses within the intervention practices received education on the importance of AF detection and ECG interpretation. Patients in the intervention practices were randomly allocated to systematic (n = 5000) or opportunistic screening (n = 5000). Prospective identification of pre-existing risk factors for AF within the screened population enabled comparison between high risk targeted screening and total population screening. AF detection rates in systematically screened and opportunistically screened populations in the intervention practices were compared to AF detection rate in 5,000 patients in the control practices.

Prevention of vascular events in patients with atrial fibrillation: evidence, guidelines, and practice

Atrial fibrillation (AF) is a common arrhythmia that is associated with an increased risk for vascular events, particularly stroke. Two different therapies have been extensively evaluated for prevention of vascular events in AF: oral anticoagulation (such as warfarin), and aspirin. Placebo-controlled trials of warfarin have been performed and summarized in a meta-analysis. There is clear evidence of a benefit, with a relative risk reduction in stroke of 67% and in total vascular events of 42%. Aspirin also has been studied and is effective, but with a more modest benefit (relative risk reduction of 22%). Several studies have compared warfarin and aspirin, and showed a clear benefit in favor of warfarin for reduction of vascular events and stroke. Compared to aspirin, the risk of major hemorrhage with oral anticoagulation is increased by 70% to 100%. Current practice guidelines recommend oral anticoagulation therapy for high-risk patients with AF, unless there is an increased risk for bleeding. Nonetheless, oral anticoagulation therapy with drugs such as warfarin is difficult for both patients and physicians because of the increased risk for bleeding and the need for ongoing monitoring of coagulation status. Many patients do not receive anticoagulation therapy despite its proven benefits.

Atrial fibrillation: relation between clinical risk factors and transoesophageal echocardiographic risk factors for thromboembolism

OBJECTIVE

To correlate clinical risk factors for thromboembolism with transoesophageal echocardiography (TOE) markers of a thrombogenic milieu.

DESIGN

Clinical risk factors for thromboembolism and TOE markers of a thrombogenic milieu were assessed in consecutive patients with non-rheumatic atrial fibrillation. The following TOE parameters were assessed: presence of spontaneous echo contrast, thrombi, and left atrial appendage blood flow velocities. A history of hypertension, diabetes mellitus, or thromboembolic events, patient age > 65 years, and chronic heart failure were considered to be clinical risk factors for thromboembolism.

SETTING

Tertiary cardiac care centre.

PATIENTS

301 consecutive patients with non-rheumatic atrial fibrillation scheduled for TOE.

RESULTS

255 patients presented with clinical risk factors. 158 patients had reduced left atrial blood flow velocities, dense spontaneous echo contrast, or both. Logistic regression analysis showed that a reduced left ventricular ejection fraction and age > 65 years were the only independent predictors of a thrombogenic milieu (both p < 0.0001). The probability of having a thrombogenic milieu increased with the number of clinical risk factors present (p < 0.0001). 17.4% of the patients without clinical risk factors had a thrombogenic milieu whereas 41.2% of the patients presenting one or more clinical risk factors had none.

CONCLUSION

There is a close relation between clinical risk factors and TOE markers of a thrombogenic milieu. In addition, TOE examination allows for the identification of patients with a thrombogenic milieu without clinical risk factors.

A review of anticoagulation with warfarin in patients with nonvalvular atrial fibrillation

BACKGROUND

Warfarin therapy has proved safe and effective in a number of randomized controlled trials of stroke prophylaxis in patients with nonvalvular atrial fibrillation (NVAF), reducing the risk of stroke in these patients by two thirds. However, participants in the clinical trials were carefully selected and younger than patients in actual clinical practice.

OBJECTIVE

This analysis sought to determine whether the results of clinical trials in patients with NV can be extrapolated to the general population seen in clinical practice.

METHODS

A MEDLINE search from 1966 to the present was used to identify observational trials of anticoagulation in patients with NVAF that addressed warfarin use, anticoagulation control, efficacy, and complications. The search terms used were atrial fibrillation and anticoagulation.

RESULTS

Although warfarin prophylaxis against stroke in patients with NVAF appeared to be as well tolerated and effective in clinical practice as in clinical trials, it was generally underused, particularly in the elderly. Anticoagulation control was not as good in clinical practice as in clinical trials, although the rates of stroke and major bleeding were comparable.

CONCLUSIONS

Judicious use of warfarin, tailored to individual stroke risk, seems to be a reasonable policy. Warfarin therapy increases quality-adjusted survival in patients at high risk for stroke, and it is recommended for medium-risk patients unless their risk of bleeding is high or their quality of life while taking warfarin would be poor. Patients at a low risk for stroke will have equivalent health outcomes and incur lower costs if treated with aspirin. Despite the increased risk of hemorrhage in elderly patients, the net benefit of warfarin therapy is greater in this age group because of the higher risk of stroke. Active involvement of patients and their caregivers in an anticoagulation service setting may improve outcomes of anticoagulation therapy.

Oral anticoagulants. Pharmacologic issues for use in the elderly

There has been a marked expansion of the indications for oral anticoagulant therapy, particularly among the elderly. Despite the documented benefits, the use of warfarin remains strikingly low among patients 80 years of age and older. Elderly patients often exhibit an enhanced dose response to warfarin. On average, steady-state warfarin doses decrease by 11% per decade of age. Pharmacokinetic changes in the elderly are negligible. Pharmacodynamic differences have not been well characterized. Initiating warfarin dosing in the elderly should be done cautiously, with doses of 5 mg or less. Doses should be adjusted downward in the presence of congestive heart failure, advanced obstructive lung disease, liver disease, malignancy, protracted diarrhea, enteral feedings, or concurrent potentiating medications. Numerous medications interfere with the anticoagulant response of warfarin. The most powerful potentiating drugs are those that interfere with the metabolism of (S)-warfarin. Examples include amiodarone, trimethoprim-sulfamethoxazole, and metronidazole. These drugs should be prescribed with caution in the elderly and mandate frequent INR monitoring during the induction period. An extensive assessment of patient-specific factors that might increase the hazards related to warfarin therapy needs to be conducted and documented before initiating oral anticoagulant therapy. Patients and their caregivers need to understand the risks and benefits, and to recognize signs of abnormal bleeding and the need for frequent monitoring. Patients should be encouraged to maintain consistency in their vitamin K intake and should strive to meet the recommended dietary allowance for vitamin K. To improve anticoagulation control, physicians and other health care providers need to be aware of the many warfarin drug interactions and be cognizant of the increased dose response of warfarin seen in the elderly. Concurrent prescription of multiple drugs known to affect warfarin's anticoagulant response should be minimized and use of nonselective nonsteroidal anti-inflammatory drugs should be limited given their deleterious effects on the gastric mucosa. Transitions from inpatient care to subacute care and back to outpatient care are particularly vulnerable periods for patients' anticoagulation control. Enhanced provider communication and more seamless transitions help to ensure optimal INR follow-up and timely warfarin dose adjustment if indicated.

Antithrombotic therapy in atrial fibrillation

Atrial fibrillation is a common condition affecting elderly individuals; as many as 10% of people older than age 80 years have AF. AF is also a potent risk factor for ischemic stroke, raising the risk of stroke fivefold. A set of consistent randomized controlled trials has demonstrated that long-term anticoagulation can largely reverse the risk of stroke attributable to AF. In these trials, anticoagulation generally proved quite safe, raising the risk of intracranial hemorrhage by less than 0.5% per year. The anticoagulation target for AF is INR 2 to 3 with INR 2.5 as the specific goal. The trials were much less consistent about the efficacy of aspirin, although it seems that aspirin has a small stroke-preventive effect. The recommended dose of aspirin is 325 mg per day. Because it raises the risk of hemorrhage and adds the burden of frequent monitoring of INR values, anticoagulation is recommended for those patients with AF at higher risk of stroke. Such higher risk is conferred by the following risk factors: (1) a history of a prior stroke, TIA, or other systemic embolic event; (2) a history of hypertension; (3) diabetes mellitus; (4) left ventricular dysfunction; (5) mitral stenosis; and (6) older age. The exact age threshold conferring sufficiently increased risk is uncertain, with some research indicating the threshold should be age 65 years, and other research indicating the threshold should be age 75 years. For lower-risk patients, aspirin is recommended. Future research should focus on the oldest patients with AF. These individuals face the highest risk of ischemic stroke without anticoagulation and the highest risk of major hemorrhage with anticoagulation. Only small numbers of such elderly patients were included in the randomized trials. Future research should also focus on improved risk stratification, allowing better targeting of anticoagulation. Discoveries of new antithrombotic agents and new drugs and devices for preservation of sinus rhythm could radically improve stroke-preventive strategies for AF.

Assessment of three schemes for stratifying stroke risk in patients with nonvalvular atrial fibrillation

PURPOSE

The risk of ischemic stroke varies widely among patients with nonvalvular atrial fibrillation, influencing the choice of prophylactic antithrombotic therapy. We assessed three schemes for stroke risk stratification in these patients who were treated with aspirin and who did not have prior cerebral ischemia.

SUBJECTS AND METHODS

Criteria from three schemes of risk stratification were applied to a longitudinally observed cohort of patients with atrial fibrillation who did not have prior cerebral ischemia and who were treated with aspirin alone or aspirin combined with low, ineffective doses of warfarin in a multicenter clinical trial. The ability of the schemes to identify patients at high (>/=6%), low (</=2%), and intermediate annual risks of ischemic stroke was assessed.

RESULTS

During a mean follow-up of 1.8 years, 48 ischemic strokes occurred among 1,073 patients with atrial fibrillation who were taking aspirin (rate = 2.5 per 100 person-years). Each of the three schemes predicted stroke and disabling stroke, and successfully identified patients at low risk (observed stroke rates of 0.3 to 1.1 per 100 person-years), although the fractions of the cohort that were categorized as low risk varied from 14% to 45%. The observed rates of ischemic stroke among patients categorized as high risk ranged from 3.5 to 7.2 per 100 person-years among the stratification schemes. Two schemes considered all patients >75 years old as high risk (observed stroke rate 4.2 per 100 person-years), while the remaining scheme classified one third of patients in this age group as low risk (observed stroke rate 0.6 per 100 person-years).

CONCLUSIONS

When tested in a large cohort of patients with atrial fibrillation who were treated with aspirin, available risk-stratification schemes successfully identified patients with low rates of ischemic stroke, but less consistently identified high-risk patients.

Use of oral anticoagulants in older patients

Recently published American and British guidelines have comprehensively reviewed the indications for long term anticoagulation. The best evidence currently available supports the use of long term oral anticoagulants in patients with nonvalvular atrial fibrillation (NVAF), venous thromboembolic disease, ischaemic heart disease, mural thrombi, and mechanical heart valves. Selected patients with valvular heart disease, cerebral vascular disease, and peripheral arterial disease may also benefit from the use of these drugs. When no specific contraindications are present, elderly patients with either paroxysmal or persistent NVAF should be considered candidates for treatment with anticoagulants. Pooled analyses of the results from 9 randomised trials demonstrate that warfarin significantly reduces the risk of ischaemic stroke in patients with NVAF, particularly those in a 'high risk' category defined by the presence of additional clinical or echocardiographic risk factors. Long term anticoagulation does not appear to be justified in patients with NVAF considered to be at 'low risk' for stroke. Because the prevalence of NVAF and most other cardiovascular conditions increases with advancing age, many elderly patients will be candidates for thromboprophylaxis. The potential benefit of long term anticoagulation must be carefully weighed against the risk of serious haemorrhage in such patients. Bleeding complications with anticoagulant drugs appear to occur more frequently in older patients than in younger individuals. Advanced age (>75 years), intensity of anticoagulation [International Normalised Ratio (INR) >4.0], history of cerebral vascular disease (recent or remote), and concomitant use of drugs that interfere with haemostasis [aspirin (acetylsalicylic acid) or nonsteroidal anti-inflammatory drugs] are among the most important variables in determining an individual's risk for major bleeding with anticoagulants. Older patients often display increased sensitivity to the effects of warfarin, both in the early induction phase and during the long term maintenance phase of therapy. Conditions such as congestive heart failure, malignancy, malnutrition, diarrhoea and unsuspected vitamin K deficiency, enhance the prothrombin time response. The decision to interrupt anticoagulant therapy before elective surgery in elderly patients should evaluate the thrombotic risk of such a manoeuvre versus the risk of bleeding if anticoagulants are continued. In non-surgical patients, excessively elevated INRs without associated haemorrhage can usually be managed by simply witholding one or several doses of warfarin. If more rapid reversal is needed, small doses of phytomenadione (vitamin K1) can be administered safely without overcorrection or the development of vitamin K-induced warfarin resistance.

Prospective cohort study to determine if trial efficacy of anticoagulation for stroke prevention in atrial fibrillation translates into clinical effectiveness

OBJECTIVE

To determine whether trial efficacy of prophylaxis with warfarin for patients with atrial fibrillation at high risk of stroke translates into effectiveness in clinical practice.

DESIGN

Two year prospective cohort study.

SETTING

District general hospital.

PARTICIPANTS

167 patients with atrial fibrillation and at high stroke risk who were eligible for anticoagulation.

INTERVENTIONS

Long term anticoagulation with warfarin at adjusted doses to maintain an international normalised ratio of 2.0-3.0.

MAIN OUTCOME MEASURES

Comparison of patient characteristics, comorbidity, anticoagulation control, stroke rate, and haemorrhagic complications with pooled data from five randomised controlled trials.

RESULTS

Patients in the study group were seven years older (95% confidence interval 4 to 10) and comprised 33% more women than patients in the pooled trials. The international normalised ratio was in the target range for 61% of the time (range 37%-85%), below for 26% of the time (range 8%-32%), and above for 13% of the time (range 6%-26%). The time that patients in the study group spent in the target range was significantly less than in the pooled analysis. The incidence of stroke in the study group (2.0% per year, 0.7% to 4. 4%) was comparable to that of patients receiving warfarin in pooled studies (1.4%, 0.8% to 2.3%). Per year the incidence of major (1.7% v 1.6%) and minor (5.4% v 9.2%) bleeding complications was also similar.

CONCLUSION

Rates of stroke and major haemorrhage after anticoagulation in clinical practice were comparable to those obtained from pooled data from randomised controlled studies for patients with atrial fibrillation at high risk of stroke.

Atrial fibrillation and thromboembolism: a decade of progress in stroke prevention

Atrial fibrillation is associated with a sixfold increased risk for stroke. More than a dozen published randomized trials of anticoagulants or antiplatelet agents for stroke prevention provide solid evidence on which to base antithrombotic prophylaxis. Adjusted-dose warfarin reduces risk for stroke by about 60% compared with placebo, aspirin reduces this risk (primarily for nondisabling stroke) by about 20% compared with placebo, and warfarin reduces it by about 40% compared with aspirin. Warfarin provides maximal protection against stroke at international normalized ratios of 2.0 to 3.0. Risk stratification of patients with atrial fibrillation identifies those who potentially benefit most or least from anticoagulation; this is important because a substantial percentage of patients with atrial fibrillation have relatively low rates of stroke if they are given aspirin. Many elderly patients with recurrent intermittent atrial fibrillation experience high rates of stroke and benefit from anticoagulation. The value of precordial or transesophageal echocardiography in addition to clinical risk stratifiers for stratifying stroke risk is controversial. Altered hemostasis favoring thrombosis may contribute to formation of atrial appendage thrombus, but these conditions remain ill defined. The past decade has brought unprecedented progress toward understanding thromboembolism in patients with atrial fibrillation and has changed the clinical perspective of a prevalent cardiac arrhythmia into an important opportunity for stroke prevention. Making the most of this promise calls for appreciation of the epidemiology of atrial fibrillation and the concept of risk specificity in the face of diverse therapeutic options.