(Stroke. 1997;28:2382-2389.)
© 1997 American Heart Association, Inc.
Articles |
Warfarin Use Among Patients With Atrial Fibrillation
From the Center for Outcomes Research and Evaluation, Yale–New Haven Hospital, New Haven, Conn (L.M.B., H.M.K.); Neurology Service, VA Connecticut Healthcare System, West Haven (L.M.B.); Yale Stroke Program, Department of Neurology (L.M.B.), Section of Chronic Disease Epidemiology, School of Epidemiology and Public Health (L.M.B., H.M.K.), and Department of Cardiology (H.M.K.), Yale University School of Medicine, New Haven, Conn; Connecticut Peer Review Organization, Middletown (L.M.B., H.M.K., J.M.S., M.R.); and Department of Cardiology (M.R.), University of Connecticut Health Sciences Center, Farmington.
Correspondence to Lawrence M. Brass, MD, Yale Stroke Program, Department of Neurology, LCI-700, Yale University School of Medicine, 15 York St, PO Box 208018, New Haven, CT 06520-8018. E-mail lawrence.brass{at}yale.edu
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Abstract |
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 Top Abstract IntroductionSubjects and MethodsResultsDiscussionAppendix 1References |
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Background and Purpose Warfarin reduces the rate of stroke among patients with atrial fibrillation. We sought to determine warfarin use within a population sample of elderly patients with atrial fibrillation.
Methods The Connecticut Peer Review Organization conducted a
chart review of Medicare patients aged 
65 years with a history of
atrial fibrillation before a hospitalization during the first 6 months
of 1994.
Results Among 488 patients (308 women; 457 white; 173 aged 85
years), 38% (184/488) had a relative contraindication to
anticoagulation (history of bleeding, dementia, alcohol use, falls,
cancer, or the need for nonsteroidal anti-inflammatory drugs). Among
the remaining patients (with known atrial fibrillation, but without a
contraindication), only 38% (117/304) had been prescribed warfarin. Of
those not prescribed warfarin, 63% (117/187) were also not taking
aspirin. There were 272 patients with at least one additional vascular
risk factor and no contraindication to anticoagulation. Among these
patients at moderate to high risk for stroke, anticoagulation had been
prescribed in 40% (109/272). Overall, among those not prescribed
warfarin, 58% (95/163) were not taking aspirin. Patients admitted with
a stroke were more likely to be significantly underanticoagulated (with
international normalized ratio <1.5) (43.5% versus 20.9% for those
without stroke; P<.005). Anticoagulation was most
effective for those with an international normalized ratio 2.0.
Conclusions Warfarin anticoagulation with atrial fibrillation, even among "ideal" candidates, appears dramatically underutilized. In addition, among those prescribed warfarin, patients are often undertreated. Increased warfarin use among patients with atrial fibrillation represents an excellent opportunity for stroke prevention in the elderly.
Key Words: anticoagulants • atrial fibrillation • stroke prevention • warfarin
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Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAppendix 1References |
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Over the past decade, great advances have been made in stroke prevention and treatment.1 2 3 4 5 6 Among the most potent therapies for stroke prevention is the use of anticoagulation therapy for patients with atrial fibrillation. Atrial fibrillation, with a prevalence of 6% among those older than 65 years,7 is a common cause of stroke, accounting for approximately 10% to 15% of all ischemic strokes and nearly a quarter of strokes for those older than 80 years.8 Among those with atrial fibrillation, the stroke rate is approximately five times higher than for those without atrial fibrillation.8 9 Stroke in patients with atrial fibrillation is also more severe and the outcome markedly poorer than in patients with sinus rhythm.10 11 The rate of death or significant neurological disability is as high as 71%,11 12 and the annual rate of recurrent stroke is over 10%.13 Since stroke is often the initial manifestation of embolism, prevention is critical to reducing death and disability.
Warfarin is effective in reducing the rate of stroke and safe to use in the treatment of atrial fibrillation.14 Six randomized clinical have demonstrated its effectiveness for primary prevention of stroke14 15 16 17 18 19 20 with a two-thirds reduction in the risk of stroke.21 A similar risk reduction has also been shown for secondary prevention.13 The use of warfarin has also been demonstrated to be cost-effective,22 especially for those at moderate to high risk.23
The use of warfarin for stroke prevention is part of standard recommendations for the management of patients with atrial fibrillation.24 25 It is estimated that tens of thousands of strokes could be prevented if these guidelines were implemented in clinical practice.26
Studies of practice patterns for cardiovascular disease indicate that recommended therapies for myocardial infarction are often underutilized.27 28 29 For patients with atrial fibrillation, despite the importance of anticoagulation, evidence from physician surveys suggests that not all appropriate candidates receive warfarin.30 31 32 In an investigation of anticoagulation for patients undergoing elective cardioversion of atrial fibrillation, in one third of cases physicians failed to follow the widely applied American College of Chest Physicians' recommendations regarding anticoagulation.33 Little information is available, however, on the actual use of warfarin for primary and secondary prevention of stroke among patients with atrial fibrillation. A recent study limited to six university hospitals demonstrated underutilization of antithrombotic therapy,34 as did a report of patient visits to office-based physicians from the National Ambulatory Medical Care Survey35 and another hospital-based study limited to only four hospitals.36 As part of the ongoing efforts by the Connecticut Peer Review Organization (CPRO) to improve the quality of care for Medicare beneficiaries, we performed an in-depth evaluation of the current patterns of warfarin use among patients with atrial fibrillation across a broad range of practice settings.37
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Subjects and Methods |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAppendix 1References |
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Study Population
The CPRO conducted a retrospective study to examine warfarin use among patients with atrial fibrillation with stroke and an equal number without stroke. The cohort consisted of Medicare patients aged 65 years or older discharged from Connecticut hospitals between January 1, 1994, and June 30, 1994. Using reliable techniques previously described for related projects, trained nurses and medical record technicians obtained information from medical charts.29 38
To identify potentially eligible patients, we determined the diagnosis of atrial fibrillation by examining principal and secondary discharge diagnoses using the MEDPAR (Medicare Part A claims) files. Those with a principal diagnosis of acute myocardial infarction were excluded. For this analysis of the use of warfarin among patients from the community, only patients with an established diagnosis of atrial fibrillation before the index hospitalization were included.
Stroke patients were selected with a principal diagnosis (reason in retrospect for which the patient was admitted) of ischemic stroke according to ICD-9 codes. The codes used for all diagnoses are listed in the "Appendix." Atrial fibrillation was required as a secondary diagnosis. For patients with multiple admissions meeting these criteria, the first admission was selected. Only patients admitted to one of Connecticut's 33 nongovernmental, acute care hospitals were included.
Patients without stroke were selected with a primary or secondary discharge diagnosis of atrial fibrillation. We also sought to eliminate those with a primary diagnosis of embolic events; additional excluded diagnoses were retinal vascular occlusion, peripheral vascular disease, vascular insufficiency of the intestine, and vascular disorders of the kidney. Each patient selected without a primary diagnosis of stroke was matched to one with stroke for age (within 1 year), sex, and secondary diagnoses of hypertension, non–insulin-dependent diabetes, insulin-dependent diabetes, congestive heart failure, angina, and myocardial infarction as a nonprimary diagnosis.
Collection of Data
Variables examined in this study include age, sex, race,
stroke risk factors, classes of medication, possible contraindications
to anticoagulation, and functional ability.
Past medical history of a medical or surgical diagnosis refers to a condition that was present in the recent or distant past before the current admission that prompted the patient to seek medical attention. These were abstracted from the coded discharge diagnoses and other sources including physician admission notes, history and physical, emergency department physician notes, consultation notes, and the discharge summary. In addition, nursing notes were used for items related to smoking history, alcohol use, or a fall within the past 2 years.
The principal outcome, warfarin use, was determined by medications that had been prescribed at the time of admission regardless of whether the patient had been taking warfarin or the effectiveness of the anticoagulation.
Laboratory variables used here—PT and INR—were taken as the first determination during the index hospital admission. The primary source was an official report. If this was not available, admission notes, emergency department notes, or progress notes documenting laboratory results were used.
Records were copied in their entirety by each hospital and sent to the CPRO. Trained abstractors reviewed each record and determined whether atrial fibrillation was noted in the official interpretation of any ECG. When atrial fibrillation was not noted in any official ECG interpretation, a board-certified cardiologist reviewed the record. ECGs and ECG rhythm strips were reviewed to identify atrial fibrillation. A history of atrial fibrillation was determined by the cardiologist's review of physician admission notes, consultation notes, progress notes, or discharge summary. A history of atrial fibrillation was defined as "detailed" if any physician's note included a date of atrial fibrillation or specific treatments. A history of atrial fibrillation was defined as "vague" if only "history of atrial fibrillation" or "hx afib" was noted by one or more physicians and no clinical details were provided. This information was combined with discharge diagnoses. As with previous studies done by CPRO, reabstraction was performed in 4% of cases.28 38 The interabstractor agreement was greater than 96% for among all abstracted items.
Analysis
First, we evaluated the bivariate association between the use of
warfarin and a family of variables that included demographic
factors (age, sex, and race), clinical factors (stroke risk factors
such as rheumatic heart disease, hypertension, and prior stroke or
TIA), medications, and possible contraindications to anticoagulation
(such as prior bleeding, falling, or alcohol use). For each
variable, a 
2 test was used to determine whether the
proportion of patients prescribed warfarin before admission differed
significantly from those not prescribed warfarin.
Variables that were associated with the use of warfarin with a value of P<.10 in the bivariate analysis were entered into a multivariate logistic regression model. For each association of interest, an adjusted OR and 95% CI were calculated.
Patients with a documented PT or INR were grouped by warfarin and stroke status. The mean, 95% CI, percent subtherapeutic (PT <14 seconds or INR >1.5), and percent supratherapeutic (PT >21 seconds or INR >3.5) were calculated with the first recorded result in the chart. In addition, the distribution of INR values for patients prescribed warfarin among those with stroke and control subjects was plotted. The unadjusted OR was calculated for each category by dividing the number of patients with a stroke within a given INR range by the number of nonstroke patients within the same INR range.
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Results |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAppendix 1References |
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A total of 707 of 710 charts identified and requested for review were abstracted. Twenty-one records were excluded because the hospital record had no documented history of or ECG demonstrating atrial fibrillation, and 51 records were excluded because the diagnosis was considered vague. The remaining 635 patients (233 men, 402 women) constituted the main study cohort. After 147 patients with a new diagnosis of atrial fibrillation made during the index hospitalization were excluded, the remaining 488 patients (180 men, 308 women), with a history of prior atrial fibrillation documented in the medical record, constituted the study cohort for this report.
Table 1
presents the patient
characteristics that were abstracted, including demographic
information, vascular risk factors, potential contraindications to
anticoagulation, and other common medical conditions. The results of
the bivariate analysis of these factors with the use of
warfarin before the index hospital admission are also shown in Table 1.
Overall, 34% (166/488) of patients had been prescribed warfarin at the
time of admission to the hospital. Of those not taking warfarin, 65%
(210/322), or 43% (210/488) of all patients, were also not taking
aspirin. The use of warfarin was also examined in a more restricted
cohort of 304 patients who did not have relative contraindications to
anticoagulation. There was a significantly higher rate of warfarin use
(P=.003); 38% (116/304) were on warfarin, and of those not
taking warfarin, 63% (119/188) were also not taking aspirin.
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Next, the use of warfarin was examined in the subcohort of patients who had additional risk factors for stroke. Among the 433 patients with at least one additional stroke risk factors (beyond atrial fibrillation), there was a higher rate of warfarin use compared with those without additional risk factors (P=.001); 36% (156/433) were on warfarin, and of those not taking warfarin, 66% (182/277) were also not taking aspirin.
Last, among the 272 patients with an additional stroke risk factor and without a contraindication, 40% (109/272) were on warfarin, and of those not taking warfarin, 58% (95/163) were also not taking aspirin.
As presented in Table 1
, differences by demographic and
clinical characteristics exist. Patients who were older, had possible
contraindications, and were limited in their activities of daily living
(before admission) were all less likely to receive warfarin. Patients
who had no contraindication to anticoagulation, rheumatic heart
disease, prior stroke or TIA, coronary artery disease, were
admitted from home, or had been prescribed certain classes of
medication (digoxin, ß-adrenergic blocking agents, ACE
inhibitors, or diuretics) were more likely to be
prescribed warfarin.
In the multiple logistic regression analysis, seven
variables were strongly associated with the use of warfarin (Table 2). The variables associated with the
use of warfarin were younger age groups, prior stroke or TIA, and the
use of ß-blockers, ACE inhibitors, or diuretics.
Those with limited activities of daily living or using aspirin had a
lower rate of warfarin use. For those with coronary disease,
there was a trend toward a higher rate of warfarin use.
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Coagulation parameters were available for 410 patients who
had a PT documented and 337 patients with an INR. Nearly a third of
patients taking warfarin were subtherapeutic on admission; 30.1%
(49/163) had a PT <14 seconds and 32.4% (44/136) had an INR <1.5.
Patients prescribed warfarin and admitted with a stroke were more
likely to be subtherapeutic than those without a stroke (Table 3).
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Patients admitted with a stroke were more likely to be significantly
underanticoagulated (with INR <1.5): 43.5% (30/69) versus 20.9%
(14/67) for those without stroke (P<.005). The level of
anticoagulation was a inversely associated with stroke. Anticoagulation
was most effective for those with an INR 2.0. There were 136 patients
prescribed warfarin with admission INRs recorded in the chart (69
admitted with stroke; 68 without stroke) (Table 3). Among the 69 stroke
patients prescribed warfarin, there were 43% (30/69) with an INR <1.5
compared with 21% (14/68) of those prescribed warfarin but admitted
without a stroke; there were 32% (22/69) with INR range of 1.5 to 1.9
compared with 24% (16/68) for those on warfarin but admitted without a
stroke. Similarly, the percentages were 12% (8/69) for those with
stroke compared with 22% (15/68) for the INR range of 2.0 to 2.4; 7%
(6/69) for those with stroke compared with 16% (11/68) for the INR
range of 2.5 to 2.9; 1.4% (1/69) for those with stroke compared with
6% (4/68) for the INR range of 3.0 to 3.9; and 2.9% (2/69) for those
with stroke compared with 12% (8/68) for the INR 4. The OR for
stroke rose sharply as INRs fell below 2.0 (Figure
); among patients with an INR <1.5, the
OR for stroke was nearly quadruple that of those with an INR in the
range of 2.0 to 2.9 (OR=4.13; 95% CI=1.5 to 11.38). The ORs among the
other INR ranges were as follows: for 1.5 to 1.9, OR=2.69, 95% CI=0.97
to 7.34; for 3.0 to 3.9, OR=0.64, 95% CI=0.06 to 6.8; and for 4,
OR=0.55, 95% CI=0.10 to 3.01. The 2 for linear trend
was 14.69 (P=.00013).
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAppendix 1References |
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Most current treatment guidelines recommend warfarin therapy for patients with atrial fibrillation who are older than 60 years.24 25 In our study only 11% of patients did not have at least one additional vascular risk factor beyond atrial fibrillation and age. This means that most of our patients were at moderate to high risk for stroke.21 This finding is similar to the Cardiovascular Health Study, in which only 8% of patients with atrial fibrillation older than 65 years did not have evidence of cardiovascular disease,39 and the pooled data from the atrial fibrillation trials, in which 15% of patients had no vascular risk factors other than atrial fibrillation.21 Our primary analysis was based on those at moderate to high risk for stroke. Among these patients, there is little controversy among consensus statements and guidelines.14 25 40
Our principal finding is that 60% of patients with atrial fibrillation who are good candidates for anticoagulation (atrial fibrillation plus at least one other stroke risk factor and no strong contraindications to anticoagulation) were not prescribed warfarin therapy. We also report that among those not on warfarin, more than half were also not on aspirin.
Our results were based on a cohort of hospitalized Medicare patients. Nearly all individuals older than 65 years used Medicare during the time of this study. Our data are consistent with other reports from more restricted cohorts indicating that the results of clinical trials do not necessarily translate into changes in clinical practice.41 42 This is true for hospital-based acute therapies such as those for myocardial infarction,38 42 43 cardioversion for atrial fibrillation,33 and simple therapies such as aspirin for secondary prevention of vascular disease.29 When changes in practice occur, there is often a several-year lag, significant geographic variation in practices, and an underutilization in the steady state.35 43
McCrory and colleagues30 performed a nationwide survey of physicians and found nearly unanimous agreement that anticoagulation treatment was effective. In another survey more than 95% of physicians recommended therapy to prevent thromboembolic complications; among patients with atrial fibrillation, warfarin therapy was favored by over 80%, and nearly all others recommended antiplatelet therapy.32
Self-reported use is higher than in actual practice. Albers et al34 reported that among academic centers, only a third of patients admitted with atrial fibrillation, at least one other risk factor for stroke, and no contraindication to warfarin were prescribed anticoagulation at the time of admission. Munschauer et al36 demonstrated both an underutilization of antithrombotic therapy at hospital discharge and a lack of influence of some important risk factors known to increase the risk of embolization in the setting of atrial fibrillation. Our results suggest that similar rates of underutilization exist across a broader range of clinical settings in the community before admission.
In the office-based survey reported by Stafford and Singer,35 anticoagulation was given to approximately a third of patients with atrial fibrillation, but there was only limited information reported on comorbid conditions and concomitant therapies that may help explain the underutilization of anticoagulation. Our study did include information on comorbid conditions, which allowed us to examine potential reasons and contraindications for anticoagulation therapy; however, the influence of commonly cited indications and contraindication was less than expected, accounting for a small portion of practice variation.
In their survey, McCrory and colleagues30 identified the three most common reasons for physicians not using anticoagulation as follows: (1) increased risk of hemorrhage, (2) patient refusal, and (3) low risk of embolus. Although these factors influence the use of warfarin, they seem unlikely to account for the low rate of warfarin use.
Risk of Hemorrhage
The major risks for bleeding with anticoagulation are advancing
age, more intense anticoagulation, and an increasing number of
prescription medications (independent of degree of
anticoagulation).44 In our study the presence of risk
factors for hemorrhage was associated with a statistically
significant reduction in the rate of warfarin use; however, the
absolute reduction was less than 10%. In addition, there was still a
low rate of warfarin use among those with no documented risk for
bleeding.
Approximately half of the patients with atrial fibrillation in the United States are older than 75 years.7 Our results reflect survey and practice data which demonstrate that physicians are less likely to recommend anticoagulation in older patients.30 35 It is not clear whether this trend is justified. The overall relative benefit of anticoagulation for people older than 75 years is currently in debate. The risk of bleeding complications may be increased,45 but so is the risk of thromboembolic stroke among those with atrial fibrillation.
With proper management, however, age alone may not be a major determinant of bleeding for those younger than 80 years.46 Bleeding complications may remain acceptably low as patients enter the eight and ninth decades of life, especially with close monitoring to prevent overdosing.45 47 A combined analysis of four of the primary prevention trials found warfarin to be safe and effective for those older than 75 years.48 49
Patient Refusal
Factors such as patients' perceptions of inconvenience and
compliance can influence the use of medications.50
Information on this was not available in our study but seems unlikely
to explain the magnitude of our results. Even among those taking other
cardiovascular medications, the overall use of warfarin
was low.
Among patients informed of the risk of stroke and its consequences, the large willingness to initiate therapy, high perceived value, and low discontinuance rate suggest that many physicians may underestimate patients' perception of the clinical importance of anticoagulation therapy.51 Improved methods for educating patients about atrial fibrillation, its consequences, and available treatments could help to further reduce patient refusal and increase compliance.
Risk of Embolization
In our study the use of warfarin was only slightly higher among
those with vascular risk factors than in those without these risk
factors. Among the stroke risk factors we investigated, only rheumatic
heart disease and prior cerebrovascular disease were associated with a
significantly higher rate of warfarin use. However, even for these
groups, the rate of warfarin use was low. For those with prior
cerebrovascular disease, the rate of stroke is increased by twofold to
threefold.13 Rheumatic heart disease is associated with a
similar increase. Even so, approximately half of patients with these
risk factors were not anticoagulated.
Medication Use
Among patients prescribed other cardiac medications, there was a
higher rate of warfarin use; however, this may simply be a marker for a
more aggressive management style or the recognition of more severe
cardiac disease and an increased risk of
cardioembolism.
Degree of Anticoagulation
Although the most commonly recommended target range for
anticoagulation is an INR of 2.0 to 3.0,24 47 we used a
more liberal therapeutic range based on those used among the major
anticoagulation trials of an INR of 1.4 to 4.5 (PT range of 1.2 to
2.0). Because control values were not always available in the chart, we
elected to analyze absolute PT (in seconds).
Even with a very wide therapeutic range for anticoagulation, among
those on anticoagulation therapy, just over 40% were out of
therapeutic range on admission to the hospital (Table 3). This provides
a practical estimate of the effectiveness of routine use of warfarin in
the community. In the setting of clinical trials, 9% to 40% of days
had anticoagulation levels that fell below the lower limit for the
planned intervention.44 52
We found that among those admitted with a stroke, the level of
anticoagulation was significantly lower, and the portion of
subtherapeutic patients higher, than the patients without a stroke
(Table 3). This association was seen in the clinical
trials.26 Our results extend this association and suggest
that the risk of stroke rises dramatically for those with an INR <2.0
(Figure), corroborating results from a recent case-control study of
Hylek and colleagues.47
Overall, nearly 9% of the patients on anticoagulation in our cohort were supratherapeutic. This is similar to the Stroke Prevention in Atrial Fibrillation Trial, in which anticoagulation exceeded the upper limit of the therapeutic range in 5% (INR=4.5; PT=1.8).44 Among the major clinical trials, the range of patients who were supratherapeutic was 0.6% to 17%.52 For those with hemorrhage, 40% were above the trial's therapeutic range, and excessive anticoagulation has been identified as a risk factor for intracranial hemorrhage.53 54
Among those not prescribed warfarin, approximately 10% had a first
recorded INR of 1.5 (Table 3). The reasons for this are unclear.
Few studies have reported INR testing across a wide range of clinical
settings. In limited studies, significant mismatching was found,
including those with INRs within the normal range.55 The
patients with an increased INR reported in the medical record in
our study do not cluster at a small number of institutions, nor do they
appear to be associated with the use of anticoagulant or antithrombotic
therapy during hospitalization or procoagulant depletion.56
Reabstraction of the medical records did not change the finding.
Although the use of the INR system for monitoring patients receiving
oral anticoagulation is widely endorsed and is an improvement over the
PT, it is not without concerns about reliability.57 58 This
will be addressed in a future quality improvement monitoring
project that includes more detailed abstraction of possible
procoagulant depletion such as hepatic disease.59
Conclusions
Although it might be suggested that the low rate of warfarin use
could be due in part to patients who decline anticoagulation therapy or
other physician-patient preferences, the surprisingly large portion of
individuals receiving neither aspirin nor warfarin suggests an
underutilization of stroke prevention therapies. In addition, among
those prescribed warfarin, patients are often undertreated, and low
levels of anticoagulation are associated with a greatly increased risk
of stroke.
Our study spans a broad range of patients and clinical settings and contains more clinical information than studies relying on self-report or discharge data. It was limited, however, by its retrospective nature and its reliance on documentation in the medical record. Even with these potential limitations, our findings suggest that efforts to develop programs that will ensure that patients with atrial fibrillation are evaluated for warfarin anticoagulation and are maintained in a therapeutic range represent a strong opportunity for stroke prevention.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This study was funded as part of the ongoing quality improvement programs of the CPRO with the assistance of a supplemental grant from DuPont Merck Pharmaceutical, Wilmington, Del.
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Footnotes |
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Presented in part at the 69th Scientific Sessions of the American Heart Association, New Orleans, La, November 10-13, 1996.
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Appendix 1 |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAppendix 1References |
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Diagnostic Criteria
Discharge diagnoses were based on ICD-9 codes and included the following: atrial fibrillation (427.31); stroke (ischemic stroke: 433.01, 433.11, 433.21, 433.31, 433.81, 433.91, 434.01, 434.11, 434.91, 436); prior stroke (late effects: 438); angina (411.1, 411.81, 411.89, 413.1, 413.9); acute myocardial infarction (410.01 to 410.91); history of myocardial infarction (412); congestive heart failure (402.01, 402.11, 402.91, 404.01, 404.03, 404.11, 404.13, 404.91, 404.93, 428.0, 428.1); hypertension (diagnosed as hypertensive disease excluding secondary hypertension: 401.0 to 404.93); diabetes, non–insulin dependent (250.00, 250.02, 250.10, 250.12, 250.20, 250.22, 250.30, 250.32, 250.40, 250.42, 250.50, 250.52, 250.60, 250.62, 250.70, 250.72, 250.80, 250.82, 250.90, 250.92); diabetes, insulin dependent (250.01, 250.03, 250.11, 250.13, 250.21, 250.23, 250.31, 250.33, 250.41, 250.43, 250.51, 250.53, 250.61, 250.63, 250.71, 250.73, 250.81, 250.83, 250.91, 250.93); retinal vascular occlusion (362.3); peripheral vascular disease (440 to 444.9); vascular insufficiency of the intestine (557); and vascular disorders of the kidney (593.81).
Received May 16, 1997; revision received September 8, 1997; accepted September 8, 1997.
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References |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAppendix 1References |
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S. J. Connolly Preventing stroke in atrial fibrillation: Why are so many eligible patients not receiving anticoagulant therapy? Can. Med. Assoc. J., September 1, 1999; 161(5): 533 - 534. [Full Text] [PDF]
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N. L. Smith, B. M. Psaty, C. D. Furberg, R. White, J. A. C. Lima, A. B. Newman, and T. A. Manolio Temporal Trends in the Use of Anticoagulants Among Older Adults With Atrial Fibrillation Arch Intern Med, July 26, 1999; 159(14): 1574 - 1578. [Abstract] [Full Text] [PDF]
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L. Kalra, I. Perez, and A. Melbourn Risk Assessment and Anticoagulation for Primary Stroke Prevention in Atrial Fibrillation Stroke, June 1, 1999; 30(6): 1218 - 1222. [Abstract] [Full Text] [PDF]
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K. N. Vemmos, M. L. Bots, P. K. Tsibouris, V. P. Zis, D. E. Grobbee, G. S. Stranjalis, and S. Stamatelopoulos Stroke Incidence and Case Fatality in Southern Greece : The Arcadia Stroke Registry Stroke, February 1, 1999; 30(2): 363 - 370. [Abstract] [Full Text] [PDF]
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L. M. Brass, H. M. Krumholz, J. D. Scinto, D. Mathur, and M. Radford Warfarin Use Following Ischemic Stroke Among Medicare Patients With Atrial Fibrillation Arch Intern Med, October 26, 1998; 158(19): 2093 - 2100. [Abstract] [Full Text] [PDF]
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G. W. Albers Choice of Antithrombotic Therapy for Stroke Prevention in Atrial Fibrillation: Warfarin, Aspirin, or Both? Arch Intern Med, July 27, 1998; 158(14): 1487 - 1491. [Full Text] [PDF]
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L. A. Simons, J. McCallum, Y. Friedlander, and J. Simons Risk Factors for Ischemic Stroke : Dubbo Study of the Elderly Stroke, July 1, 1998; 29(7): 1341 - 1346. [Abstract] [Full Text] [PDF]
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