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Prevalence and Quality of Warfarin Use for Patients With Atrial Fibrillation in the Long-term Care Setting
Danny McCormick, MD, MPH;
Jerry H. Gurwitz, MD;
Robert J. Goldberg, PhD;
Richard Becker, MD;
Janet P. Tate, MPH;
Anne Elwell, RN;
Martha J. Radford, MD
Arch Intern Med. 2001;161:2458-2463.
ABSTRACT
| |
Background Evidence-based clinical practice guidelines recommend the use of warfarin
sodium for stroke prevention in most patients with atrial fibrillation (AF)
who do not have risk factors for hemorrhagic complications, irrespective of
age.
Methods The medical records of all residents of a convenience sample of long-term
care facilities in Connecticut (n = 21) were reviewed. The percentages of
all patients with AF (AF patients) and ideal candidates for warfarin therapy
(ie, AF patients with no risk factors for hemorrhage) who received warfarin
were determined; for patients receiving warfarin, the percentage of days spent
in the therapeutic range of international normalized ratio (INR) values (2.0-3.0)
was also assessed. The relationship between receipt of warfarin and the presence
of stroke and bleeding risk factors was assessed in multivariate models.
Results Atrial fibrillation was present in 429 (17%) of the 2587 long-term care
residents. Overall, 42% of AF patients were receiving warfarin. However, only
44 (53%) of 83 ideal candidates were receiving this therapy. In residents
who received warfarin therapy, the therapeutic range of INR values was maintained
only 51% of the time. The odds of receiving warfarin in the study sample decreased
with increasing number of risk factors for bleeding and increased (nonsignificant
trend) with increasing number of stroke risk factors present.
Conclusions Atrial fibrillation is very common among residents of long-term care
facilities. Even among apparently ideal candidates, warfarin therapy is underused
for stroke prevention in patients with AF. Prescribing decisions and monitoring
related to warfarin therapy in the long-term care setting warrant improvement.
INTRODUCTION
ATRIAL FIBRILLATION (AF) is the most common cause of embolic stroke,
an event that produces high rates of neurologic disability and death.1-2 The prevalence of AF increases substantially
as patients age, with half of all patients with AF being age 75 years and
older.3 Because AF is more common among older
individuals, and because the risk of stroke associated with AF increases dramatically
with advancing age,4 the risk of thromboembolic
stroke in elderly AF patients is an important public health issue.
Six randomized controlled clinical trials have demonstrated that warfarin
sodium is highly effective in the prevention of stroke, and death due to stroke,
in AF patients,5-11
including the elderly.12 In patients with nonvalvular
AF, anticoagulation therapy with warfarin reduces the risk of ischemic stroke
by approximately two thirds.12 The reduction
in the risk of stroke afforded by aspirin, although less pronounced than that
of adjusted-dose warfarin,10, 13
is still significant.5, 7, 12
Based on these findings, evidence-based, authoritative, and widely disseminated
clinical practice guidelines14-16
recommend the use of low-intensity warfarin therapy (international normalized
ratio [INR], 2.0-3.0) for AF patients who are at highest risk for stroke,
ie, patients with a previous stroke or transient ischemic attack, hypertension,
structural heart disease, or left ventricular dysfunction, or in patients
aged 75 years or older.15, 17 For
patients with AF who are 65 to 75 years old and who have 1 of these risk factors
for stroke, warfarin therapy is recommended. For patients in this age group
without risk factors for stroke, warfarin or aspirin therapy should be used,
depending on a patient's risk of bleeding. For AF patients in whom warfarin
therapy is declined, contraindicated, or not tolerated, use of aspirin is
recommended.
Despite the publication of 5 of the 6 randomized controlled trials of
warfarin for stroke prevention in patients with AF during or before 1992,
several observational studies using data collected from the early to mid-1990s
have suggested that warfarin therapy has been substantially underused in eligible
AF patients, particularly among the elderly.18
This pattern of care has been documented among patients residing in the long-term
care setting,19-21
in teaching and community hospital patients,22-26
and among community-dwelling outpatients.27-29
Although recent evidence indicates that the use of warfarin therapy
for AF has been increasing throughout the 1990s in the outpatient setting,30-31 no evidence currently exists regarding
trends in the use of warfarin for AF patients in the long-term care setting.
In addition, little is known regarding physicians' current knowledge of or
use of information about risk factors for stroke and bleeding in deciding
whether to prescribe warfarin for AF patients in the long-term care setting.
The purposes of this observational study were to assess the following
in 2587 residents of 21 long-term care facilities: (1) the prevalence of AF
and the percentage of AF patients who receive therapy with warfarin or aspirin;
(2) the relationship between the presence of known risk factors for stroke
and bleeding complications among individuals with AF and their receipt of
warfarin; and (3) the quality of warfarin prescribing and monitoring in nursing
home residents with AF.
SUBJECTS AND METHODS
STUDY CONTEXT AND DEVELOPMENT
As a continuation of ongoing initiatives to measure and improve the
quality of stroke prevention care for Medicare beneficiaries,23, 32
Qualidigm Inc, Middletown, Conn, in partnership with the University of Massachusetts
Medical School and the Meyers Primary Care Institute, Worcester, Mass, developed
a quality performance measurement and improvement project directed at stroke
prevention care for Medicare beneficiaries in long-term care facilities. This
study was approved by the Institutional Review Board at the University of
Massachusetts Medical Center.
STUDY SETTING
We studied patients residing in a convenience sample of 21 community-based
long-term care facilities located throughout the state of Connecticut. The
mean ± SD number of beds among these institutions was 146 ±
81 (range, 60-382). All participating institutions were certified by Medicare
and Medicaid.
STUDY POPULATION
The medical records of all residents in each participating facility
were reviewed by trained nurse abstractors for possible study inclusion. Patients
were included if a diagnosis of AF during the study period was confirmed in
the medical record by means of an interpretable electrocardiogram (ECG) or
written documentation by the resident's treating physician. We did not attempt
to discriminate between patients with rheumatic and nonrheumatic AF, although
the presence or absence of a mechanical heart valve was recorded. Residents
whose length of stay in the long-term care facility was less than 30 days
of the study period or who had end-stage renal disease were excluded.
DATA COLLECTION
For patients satisfying the study entry criteria, we collected information
from the medical record about age, sex, race, duration of AF, comorbid illnesses,
and medical history. Other features that might constitute risk factors for
hemorrhage during warfarin therapy were recorded from physician notes (eg,
frequent falls). Use of warfarin or aspirin (and other antiplatelet agents)
and all INR values (and the dates on which they were obtained) during the
12-month study period were also determined.
STATISTICAL ANALYSES
We categorized all study subjects according to their receipt of warfarin,
aspirin, both, or neither of these medications. For purposes of these analyses,
the 3 patients who received antiplatelet agents other than aspirin were combined
with those receiving aspirin. We calculated the percentage of residents in
each of these treatment categories for the entire study sample and for a restricted
group of ideal candidates for receipt of warfarin therapy. Ideal candidates
were defined as AF patients who had no documented potential contraindication
to warfarin therapy. Potential contraindications to warfarin therapy included
history of or current bleeding, blood dyscrasia, active cancer or terminal
illness, vascular malformation, dementia, seizure disorder, liver disease,
inability to cooperate with therapy, or frequent falls. We also repeated these
calculations according to whether a patient received an AF diagnosis on the
basis of an ECG tracing or physician documentation of the AF diagnosis in
the medical record only.
To assess the quality of treatment with warfarin for residents who received
this medication for at least 2 weeks during the 12 months immediately before
the date of record abstraction, we examined all INR values obtained during
this period. Each resident-day of warfarin therapy was characterized as being
below, within, or above the recommended therapeutic range of INR. Using the
method of Rosendaal et al,33 we divided in
half the time interval between 2 INR measurements. Days in the first half
of the interval were assigned to the first INR value; days in the second half,
to the second INR value. Using published guidelines of the American College
of Chest Physicians, we considered the appropriate therapeutic range of INR
to be 2.0 to 3.0 for patients without a mechanical heart valve and 2.5 to
3.5 for patients with a mechanical heart valve.15
To calculate the percentage of time below, within, or above the therapeutic
range of INR for the study population, each resident's experience was weighted
according to the total time receiving warfarin therapy during the 12-month
observation.
Finally, using a multivariable logistic regression model, we assessed
the impact of known risk factors for stroke and bleeding on receipt of warfarin
therapy for nursing home residents with AF. The dependent variable was receipt
of warfarin during the previous 12 months. Independent variables were numbers
of bleeding risk factors (categorized as 0, 1, or  2) and stroke risk factors
(categorized as 0, 1, 2, 3, or 4). Residents were considered to have a
stroke risk factor if any of the following conditions were documented in the
medical record: hypertension, coronary artery disease, congestive heart failure,
previous stroke or transient ischemic attack, diabetes mellitus, previous
arterial thrombosis, or mechanical heart valve placement.34
Regression models also included terms for factors, which were believed, a
priori, to be potential confounders. The controlling variables included patient
age, sex, aspirin use, facility bed size, and whether a facility was operated
as a for-profit or not-for-profit enterprise.
RESULTS
We reviewed a total of 2858 medical records of residents of the 21 participating
long-term care facilities. We excluded 266 records because the length of stay
in the facility was less than 30 days of the study period, and 5 records because
of the presence of end-stage renal disease. Of the remaining 2587 records,
study criteria indicated AF was present in 429 patients (17%), who constituted
the principal study population of interest.
CHARACTERISTICS OF THE STUDY POPULATION
The clinical and demographic characteristics of study patients are shown
in Table 1. The mean ±
SD age was 87.0 ± 7.1 years (range, 60-107 years), and most patients
were women. Risk factors for stroke were present in 400 (93%) of 429, and
risk factors for bleeding were present in 345 (80%). Of the 84 patients with
no documented risk factors for bleeding, 1 patient had a documented warfarin
allergy.
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Characteristics of Long-term Care Facility Residents With Atrial Fibrillation
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WARFARIN AND ASPIRIN USE FOR AF
Overall, 180 (42%) of 429 patients with AF received warfarin therapy
for at least 2 weeks during the 12-month observation. Of those not receiving
warfarin, 136 (55%) of 249 also did not receive aspirin (Figure 1A). In the restricted group of 83 ideal candidates, 44 (53%)
received warfarin (Figure 1B). Of
the 39 ideal candidates not receiving warfarin, 21 (54%) also did not receive
aspirin, thereby leaving 25% of patients without bleeding risk factors who
received no form of stroke prevention therapy for their AF.
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Figure 1. A, Distribution of all study patients
with atrial fibrillation (AF) according to treatment received (n = 429). B,
Distribution of ideal candidates for warfarin sodium therapy (no documented
contraindications to warfarin use) with AF according to treatment received
(n = 83).
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We also determined that 100 (51%) of all 196 patients with and 80 (34%)
of 233 patients without an ECG documenting AF in the medical record received
warfarin therapy for at least 2 weeks during the 12-month observation. Among
ideal candidates, 25 (64%) of 39 patients with and 19 (43%) of 44 patients
without an ECG documenting AF in the medical record received warfarin therapy.
The results of the multivariable regression model assessing the relationship
between bleeding and stroke risk factors and the receipt of warfarin are shown
in the following tabulation:
The adjusted odds of receiving warfarin decreased as the number of risk
factors for bleeding increased, although this difference was not statistically
significant for patients with 1 bleeding risk factor compared with patients
with none. Conversely, the adjusted odds of receiving warfarin increased with
increasing number of stroke risk factors present, although this did not reach
statistical significance.
QUALITY OF MONITORING OF INR
Of the 180 patients who received warfarin therapy, 6 (3%) had no INR
data available for assessment. For the remaining 174, the interval between
INR determinations was no longer than 7 days for 45% of INRs, 8 to 30 days
for 45% of INRs, and longer than 30 days for 5% of INRs. On average, in these
174 patients, the therapeutic range of INR was maintained 51% of the time,
was below the therapeutic range 36% of the time, and was above the therapeutic
range 13% of the time (Figure 2).
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Figure 2. Proportion of days below, within,
and above the therapeutic range of values of the international normalized
ratio (2.0-3.0) for all monitored patients receiving warfarin sodium.
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COMMENT
We found that AF was quite common in the long-term care setting, being
present in approximately one sixth of all residents. Despite the presence
of additional risk factors for stroke in most AF patients, warfarin was prescribed
to only 42%. Among AF patients aged 65 years and older with no contraindications
to warfarin therapy (ideal candidates), and for whom authoritative, widely
disseminated practice guidelines14-16,35
recommend treatment with warfarin (or potentially aspirin for those aged 65-75
years), less than half were prescribed this medication. More than half of
these patients who did not receive warfarin also did not receive aspirin,
despite its proven effectiveness in stroke prevention in AF patients.10-11,13 When warfarin was
prescribed, the recommended therapeutic range of INR was maintained approximately
half of the time.
The prevalence of AF in the sample of patients we studied was considerably
higher than in 2 previous studies of AF in the long-term care setting.19-20 Lackner and Battis20
found an AF (rheumatic and nonrheumatic) prevalence of 9.4% among residents
of 5 long-term care facilities in Minnesota, whereas Gurwitz and colleagues19 found that 7.6% of residents of 30 long-term care
facilities in New England and Canada had AF. The reasons for these differences
are not clear, but may be related to more stringent requirements for AF documentation
in the 2 previous studies. In the present study, residents were considered
to have AF if it was indicated by an ECG or included in written documentation
by the treating physician; each of the other cited studies required an ECG
in the medical record indicating that AF was present. Because many residents
with AF may not have an ECG in their long-term care facility medical record,
to include only those patients with ECG-documented AF may significantly underestimate
the prevalence of AF. Although we cannot confirm that patients in our study
without an ECG have AF, physician documentation of AF in the absence of an
ECG in the ambulatory medical record has been shown to be a sensitive indicator
of AF.36 In addition, our finding that physicians
prescribed warfarin to patients with (51%) and without (34%) an ECG showing
AF in the medical chart suggests that both groups were likely to have AF and
that physicians did not prescribe warfarin only in cases of ECG-documented
AF. Furthermore, although there was a modest difference in receipt of warfarin
between these groups, we suspect that this difference is the result of increased
physician surveillance with ECG among AF patients receiving warfarin than
among those not receiving warfarin. If our results were generalized to the
entire US long-term care population, a conservative estimate of the number
of AF patients residing in long-term care facilities would exceed 250 000.37
Two previous studies of warfarin use for AF in the long-term care setting
conducted with a small number of patients in 1993 and 1994 indicated that
warfarin was prescribed for only 17% (12/69) and 25% (17/67), respectively,
of all patients with nonrheumatic AF and 18% (9/49) and 71% (25/35), respectively,
of AF patients without contraindications to warfarin use.20-21
In a larger study conducted from 1993 to 1995 that included patients from
30 nursing homes in different geographic areas, only one third of all AF patients
were prescribed warfarin.19 Our data (from
1997 and 1998) indicating that 42% of AF patients (53% of ideal candidates)
were receiving warfarin suggest that this therapy continues to be used at
low levels for stroke prevention in the long-term care setting, long after
publication of the randomized controlled trials demonstrating the effectiveness
of warfarin for stroke prevention in AF.
It is difficult to quantify accurately the levels of potential underuse
of warfarin in the long-term care setting for residents with AF. In some cases,
information relevant to the decision to prescribe warfarin might not be documented
in the medical record, such as resident preference regarding this therapy.
Second, each of the 6 randomized controlled trials of warfarin had stringent
inclusion criteria for study subjects, and thus, final study cohorts consisted
of highly selected patients. To the extent that the sociodemographic and clinical
characteristics of AF patients in long-term care facilities differ from those
of patients enrolled in clinical trials, applying the results of such trials
to the care of individual elderly patients can be challenging. Nonetheless,
elderly patients are at considerably increased risk for stroke and would therefore
potentially benefit the most from warfarin therapy.
Several previous studies have examined barriers to appropriate warfarin
use across different health care settings, particularly among elderly patients.38-41 By
using physician surveys that included clinical vignettes, these studies have
identified several reasons for physicians' tendency to prescribe warfarin
less often to older AF patients. These reasons include the perceived difficulty
in monitoring anticoagulation therapy,39-41
the tendency for concern about the risk for bleeding complications of warfarin
therapy to outweigh concern regarding the risk for stroke in untreated AF
patients,38-39,41-42
and knowledge deficits regarding risk factors for stroke38
and the effectiveness of warfarin therapy for stroke prevention in older patients
with AF.38-39,41-42
In the present study, we found a graded, inverse relationship between
increasing number of bleeding risk factors and use of warfarin, and, although
not statistically significant, a similar graded relationship between increasing
stroke risk factors and increased use of warfarin. Similar relationships have
been described in a large, recent cohort of community-dwelling AF patients.36 Although we did not directly interview physicians
in this study, these data suggest that physicians in long-term care facilities
may have systematically incorporated patient risk factors for bleeding and
stroke into their decision-making process regarding warfarin use. Despite
this, the low percentage of residents who received warfarin still suggests
that physicians may weigh more heavily the risk for bleeding complications
of warfarin therapy than the risk for stroke in patients with untreated AF.
Alternatively, our findings may suggest that physicians do not have confidence
regarding the benefits of warfarin for stroke prevention in long-term care
residents with AF. A significant proportion of patients, however, rate occurrence
of a major stroke as a health outcome "worse than death."43
The low proportion of time that the therapeutic range of INR was maintained
in patients in our study (51%) was only slightly greater than that observed
in 2 earlier studies of anticoagulation monitoring in the long-term care setting
(45% and 37%).19-20 It is difficult
to determine what percentage of the time the therapeutic range of INR could
be maintained in AF patients in long-term care facilities under optimal conditions.
When patients are cared for in the long-term care setting, problems with patient
adherence to medications and INR monitoring are largely eliminated. Use of
medications that may interact with warfarin to increase or lower the INR,
and variations in diet, are potentially easier to control in the supervised
setting of a long-term care facility. Given this, the quality of prescribing
of warfarin and monitoring of the INR that we observed appears to be less
than optimal. It is not clear whether the physicians treating the patients
we studied were intentionally using a different (predominantly lower) target
INR range than 2.0 to 3.0, which is suggested by the medical literature44-49
and the American College of Chest Physicians,15
or were not aware of this recommended target INR range.
Warfarin is highly effective in reducing the risk for stroke in patients
with AF, particularly older patients. Few conclusions in clinical medicine
are as well supported by the results of randomized controlled clinical trials.
However, we have shown that 4 to 10 years after the publication of these randomized
controlled trials, warfarin continues to be used at low rates among elderly
AF patients who reside in long-term care facilities, even among ideal candidates
for this therapy. Given the high prevalence of AF in this population, a large
number of elderly residents of long-term care facilities appear to remain
at greater risk for ischemic stroke than is necessary.
CONCLUSIONS
Our study suggests that substantial opportunities exist to improve provision
of health care to these patients. The use of dedicated anticoagulation clinics
may be an option to allow physicians to use and safely monitor warfarin therapy
for elderly AF patients in the long-term care setting. In such clinics, anticoagulation
therapy can be comprehensively managed through evaluation of patient-specific
risks and benefits; through monitoring of INRs, diet, and concomitant drug
therapy; and by making appropriate warfarin dosage adjustments. Several nonrandomized
retrospective analyses have suggested that the use of an anticoagulation clinic
in the outpatient setting reduces the number of thromboembolic and major bleeding
complications for patients receiving warfarin.50-51
The use of such clinics may improve outcomes in the long-term care setting
as well, which in turn might increase physicians' comfort with prescribing
warfarin for their eligible AF patients who currently do not receive any stroke-prevention
therapy.
AUTHOR INFORMATION
Accepted for publication March 13, 2001.
The analyses on which this publication is based were performed under
contract 500-96-P549, entitled "Utilization and Quality Control Peer Review
Organization for the State of Connecticut," sponsored by the Health Care Financing
Administration, Department of Health and Human Services, Washington, DC.
Supplementary analyses by Drs Gurwitz, Goldberg, and Becker, not part
of the peer review and quality performance measurement and improvement work,
were supported in part by an unrestricted educational grant from Dupont Pharma,
Wilmington, Del.
Presented at the 22nd Annual Meeting of the Society of General Internal
Medicine, Washington, DC, May 1, 1999.
The authors' sponsoring health care systems assume full responsibility
for the accuracy and completeness of the ideas presented. This article is
a direct result of the Health Care Quality Improvement Program initiated by
the Health Care Financing Administration, which has encouraged identification
of quality improvement projects derived from analysis of patterns of care,
and therefore required no special funding on the part of this contractor.
Ideas and contributions to the authors concerning experience in engaging with
issues presented are welcomed.
The content of this publication does not necessarily reflect the views
or policies of the Department of Health and Human Services, nor does mention
of trade names, commercial products, or organizations imply endorsement by
the US government.
Corresponding author and reprints: Danny McCormick, MD, MPH, Department
of Medicine, Cambridge Hospital, 1493 Cambridge St, Cambridge, MA 02139 (e-mail: Danny_McCormick{at}HMS.Harvard.edu).
From the Department of Medicine, Cambridge Hospital, Cambridge, Mass,
and Harvard Medical School, Boston, Mass (Dr McCormick); Meyers Primary Care
Institute (Drs Gurwitz and Goldberg) and the Department of Cardiology (Drs
Goldberg and Becker), University of Massachusetts Medical School, Worcester;
the Fallon Healthcare System, Worcester (Drs Gurwitz and Goldberg); Qualidigm
Inc, Middletown, Conn (Mss Tate and Elwell and Dr Radford); and the Yale Health
System, New Haven, Conn (Dr Radford).
REFERENCES
| |
1. Lin HJ, Wolf PA, Kelly-Hayes M, et al. Stroke severity in atrial fibrillation: the Framingham Study. Stroke. 1996;27:1760-1764.
FREE FULL TEXT
2. Fisher CM. Reducing the risks of cerebral embolism. Geriatrics. 1979;34:59-66.
ISI
| PUBMED
3. Feinberg WM, Blackshear JL, Laupacis A, Kronmal R, Hart RG. Prevalence, age distribution, and gender of patients with atrial fibrillation. Arch Intern Med. 1995;155:469-473.
ABSTRACT
4. Wolf PA, Abbott RD, Kannel WB. Atrial fibrillation: a major contributor to stroke in the elderly:
the Framingham Study. Arch Intern Med. 1987;147:1561-1564.
ABSTRACT
5. Peterson P, Boysen G, Gotfriedsen J, Andersen ED, Anderson B. Placebo-controlled, randomized trial of warfarin and aspirin for prevention
of thromboembolic complications in chronic atrial fibrillation: the Copenhagen
AFASAK Study. Lancet. 1989;1:175-179.
ISI
| PUBMED
6. The Boston Area Anticoagulation Trial for Atrial Fibrillation Investigators. The effect of low-dose warfarin on the risk of stroke in patients with
nonrheumatic atrial fibrillation. N Engl J Med. 1990;323:1505-1511.
ABSTRACT
7. Stroke Prevention in Atrial Fibrillation Investigators. Stroke Prevention in Atrial Fibrillation Study: final results. Circulation. 1991;84:527-539.
FREE FULL TEXT
8. Connolly SJ, Laupacis A, Gent M, Roberts RS, Cairns JA, Joyner C. Canadian Atrial Fibrillation Anticoagulation (CAFA) Study. J Am Coll Cardiol. 1991;18:349-355.
ABSTRACT
9. Ezekowitz MD, Bridgers SL, James KE, et al. Warfarin in the prevention of stroke associated with nonrheumatic atrial
fibrillation. N Engl J Med. 1992;327:1406-1412.
ABSTRACT
10. Stroke Prevention in Atrial Fibrillation Investigators. Warfarin versus aspirin for prevention of thromboembolism in atrial
fibrillation: Stroke Prevention in Atrial Fibrillation II Study. Lancet. 1994;343:687-691.
FULL TEXT
|
ISI
| PUBMED
11. Hart RG, Benavente O, McBride R, Pearce LA. Antithrombotic therapy to prevent stroke in patients with atrial fibrillation:
a meta-analysis. Ann Intern Med. 1999;131:492-501.
FREE FULL TEXT
12. Atrial Fibrillation Investigators. Risk factors for stroke and efficacy of antithrombotic therapy in atrial
fibrillation. Arch Intern Med. 1994;154:1449-1457.
ABSTRACT
13. Stroke Prevention in Atrial Fibrillation Investigators. Adjusted-dose warfarin vs low-intensity, fixed-dose warfarin plus aspirin
for high risk patients with atrial fibrillation: Stroke Prevention in Atrial
Fibrillation III randomized clinical trial. Lancet. 1996;348:633-638.
FULL TEXT
|
ISI
| PUBMED
14. Laupacis A, Albers G, Dunn M, Feinberg W. Antithrombotic therapy in atrial fibrillation. Chest. 1992;102(suppl):426S-433S.
15. Laupacis A, Albers G, Dalen J, Dunn M, Feinberg W, Jacobson A. Antithrombotic therapy in atrial fibrillation. Chest. 1995;108(suppl 4):352S-359S.
16. American Geriatrics Society Clinical Practice Committee. The use of oral anticoagulants (warfarin) in older people. J Am Geriatr Soc. 1996;44:1112-1113.
ISI
| PUBMED
17. Laupacis A, Albers G, Dalen J, Dunn MI, Jacobson AK, Singer DE. Antithrombotic therapy in atrial fibrillation. Chest. 1998;114(suppl 5):579S-589S.
18. McCormick D, Gurwitz JH, Goldberg RJ, Ansell J. Long-term anticoagulation therapy for atrial fibrillation in elderly
patients: efficacy, risk and patterns of use. J Thromb Thrombolysis. 1999;7:157-163.
FULL TEXT
|
ISI
| PUBMED
19. Gurwitz JH, Monette J, Rochon PA, Eckler MA, Avorn J. Atrial fibrillation and stroke prevention with warfarin in the long-term
care setting. Arch Intern Med. 1997;157:978-984.
ABSTRACT
20. Lackner TE, Battis GN. Use of warfarin for nonvalvular atrial fibrillation in nursing home
patients. Arch Fam Med. 1995;4:1017-1026.
ABSTRACT
21. Lawson F, McAlister F, Ackman M, Ikuta R, Montague T. The utilization of antithrombotic prophylaxis for atrial fibrillation
in a geriatric rehabilitation hospital. J Am Geriatr Soc. 1996;44:708-711.
ISI
| PUBMED
22. Albers GW, Yim JM, Belew KM, et al. Status of antithrombotic therapy for patients with atrial fibrillation
in university hospitals. Arch Intern Med. 1996;156:2311-2316.
ABSTRACT
23. Brass LM, Krumholz HM, Scinto JM, Radford M. Warfarin use among patients with atrial fibrillation. Stroke. 1997;28:2382-2389.
FREE FULL TEXT
24. Antani MR, Beyth RJ, Covinsky KE, et al. Failure to prescribe warfarin to patients with nonrheumatic atrial
fibrillation. J Gen Intern Med. 1996;11:713-720.
ISI
| PUBMED
25. Whittle J, Wickenheiser L, Venditti LN. Is warfarin underused in the treatment of elderly persons with atrial
fibrillation? Arch Intern Med. 1997;157:441-445.
ABSTRACT
26. Flaker GC, McGowen DJ, Boechler M, Fortune G, Gage B. Underutilization of antithrombotic therapy in elderly rural patients
with atrial fibrillation. Am Heart J. 1999;137:307-312.
FULL TEXT
|
ISI
| PUBMED
27. Mendelson G, Aronow WS. Underutilization of warfarin in older persons with chronic nonvalvular
atrial fibrillation at high risk for developing stroke. J Am Geriatr Soc. 1998;46:1423-1424.
ISI
| PUBMED
28. Stafford RS, Singer DE. National patterns of warfarin use in atrial fibrillation. Arch Intern Med. 1996;156:2537-2541.
ABSTRACT
29. White RH, McBurnie MA, Manolio T, et al. Oral anticoagulation in patients with atrial fibrillation: adherence
to guidelines in an elderly cohort. Am J Med. 1999;106:165-171.
FULL TEXT
|
ISI
| PUBMED
30. Stafford RS, Singer DE. Recent national patterns of warfarin use in atrial fibrillation. Circulation. 1998;97:1231-1233.
FREE FULL TEXT
31. Smith NL, Psaty BM, Furberg CD, White R, Lima JAC, Newman AB. Temporal trends in the use of anticoagulants among older adults with
atrial fibrillation. Arch Intern Med. 1999;159:1574-1578.
FREE FULL TEXT
32. Brass LM, Krumholtz HM, Scinto JD, Mathur D, Radford MJ. Warfarin use following ischemic stroke among Medicare patients with
atrial fibrillation. Arch Intern Med. 1998;158:2093-2100.
FREE FULL TEXT
33. Rosendaal FR, Cannegieter SC, van der Meer FJM, Briet E. A method to determine the optimal intensity of oral anticoagulant therapy. Thromb Haemost. 1993;69:236-239.
ISI
| PUBMED
34. Ezekowitz MD, Levine JA. Preventing stroke in patients with atrial fibrillation. JAMA. 1999;281:1830-1835.
FREE FULL TEXT
35. Matchar DB, McCroy DC, Barnett HJM, Feussner JR. Guidelines for medical treatment for stroke prevention. Ann Intern Med. 1994;121:54-55.
FREE FULL TEXT
36. Go AS, Hylek EM, Borowsky LH, Phillips KA, Selby JV, Singer DE. Warfarin use among ambulatory patients with nonvalvular atrial fibrillation:
the AnTicoagulation and Risk Factors in Atrial Fibrillation (ATRIA) Study. Ann Intern Med. 1999;131:927-934.
FREE FULL TEXT
37. Kemper P, Murtaugh CM. Lifetime use of nursing home care. N Engl J Med. 1991;324:595-600.
ABSTRACT
38. Monette J, Gurwitz JH, Rochon PA, Avorn J. Physician attitudes concerning warfarin for stroke prevention in atrial
fibrillation: results of a survey of long-term care practitioners. J Am Geriatr Soc. 1997;45:1060-1065.
ISI
| PUBMED
39. McCrory DC, Matchar DB, Samsa G, Sanders LL, Pritchett ELC. Physician attitudes about anticoagulation for nonvalvular atrial fibrillation
in the elderly. Arch Intern Med. 1995;155:277-281.
ABSTRACT
40. Beyth RJ, Antani MR, Covinsky KE, et al. Why isn't warfarin prescribed to patients with nonrheumatic atrial
fibrillation? J Gen Intern Med. 1996;11:721-728.
ISI
| PUBMED
41. Kutner M, Nixon G, Silverstone F. Physicians' attitudes toward oral anticoagulants and antiplatelet agents
for stroke prevention in elderly patients with atrial fibrillation. Arch Intern Med. 1991;151:1950-1953.
ABSTRACT
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