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Alan A Montgomery a Division of Primary Health Care, University of Bristol,
Bristol BS8 2PR, b Department of Social Medicine, University
of Bristol
Correspondence to: T Fahey tom.fahey{at}bristol.ac.uk
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Abstract |
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Objectives:
To investigate the effect of a computer
based clinical decision support system and a risk chart on absolute cardiovascular risk, blood pressure, and prescribing of cardiovascular drugs in hypertensive patients.
High blood pressure can no longer be viewed as an
isolated risk factor for cardiovascular disease. Guidelines from New
Zealand for the management of high blood pressure now reflect this view by explicitly including additional risk factors into an overall estimate of absolute cardiovascular risk.
1 2
These risk
charts are now available on the internet
(http://cebm.jr2.ox.ac.uk/docs/prognosis.html). However, accurate
estimation of cardiovascular risk without the use of explicit risk
charts or computer based clinical decision support systems is not easy.
Health professionals find it difficult to assimilate multiple risk
factors into an accurate assessment of cardiovascular
risk.
3 4
Computer based clinical decision support systems
have the advantage of being able to synthesise patient specific
information, perform complex evaluations, and present the results to
health professionals quickly.5 They have been shown to
enhance clinical performance in terms of drug dosing and preventive
care.5 However, their effect on patient outcomes, in
particular control of blood pressure, is unclear.
5 6
We evaluated the effect of a computer based clinical decision support
system and cardiovascular risk chart on patient centred outcomes of
absolute cardiovascular risk and blood pressure.
A computer based clinical decision support system was
written for the two most commonly used practice computing systems (EMIS and AAH Meditel) so that it could be incorporated into routine clinical
care. The system is identical to the New Zealand guidelines for the
management of hypertension,2 except that absolute risk is
presented numerically rather than pictorially. The following patient
information is required to ascertain absolute cardiovascular risk: sex,
age, diabetes, smoking, blood pressure, cholesterol, body mass index,
symptomatic cardiovascular disease, family history of ischaemic heart
disease, and familial hypercholesterolaemia. The system then
calculates the patient's five year risk of a fatal or non-fatal
cardiovascular event (newly diagnosed angina, myocardial infarction,
coronary heart disease, stroke, or transient ischaemic attack).
Practice randomisation
Patients
Protocol
Outcomes
Data analysis
Design:
Cluster randomised controlled trial.
Setting:
27 general practices in Avon.
Participants:
614 patients aged between 60 and 79 years with high blood pressure.
Interventions:
Patients were randomised to computer
based clinical decision support system plus cardiovascular risk chart; cardiovascular risk chart alone; or usual care.
Main outcome measures:
Percentage of patients in each
group with a five year cardiovascular risk
10%, systolic blood
pressure, diastolic blood pressure, prescribing of cardiovascular drugs.
Results:
Patients in the computer based clinical
decision support system and chart only groups were no more likely to
have cardiovascular risk reduced to below 10% than patients receiving usual care. Patients in the computer based clinical decision support group were more likely to have a cardiovascular risk
10% than chart
only patients, odds ratio 2.3 (95% confidence interval 1.1 to 4.8).
The chart only group had significantly lower systolic blood pressure
compared with the usual care group (difference in means
4.6 mm Hg
(95% confidence interval
8.4 to
0.8)). Reduction of diastolic
blood pressure did not differ between the three groups. The chart only
group were twice as likely to be prescribed two classes of
cardiovascular drugs and over three times as likely to be prescribed
three or more classes of drugs compared with the other groups.
Conclusions:
The computer based clinical decision
support system did not confer any benefit in absolute risk reduction or blood pressure control and requires further development and evaluation before use in clinical care can be recommended. Use of chart guidelines are associated with a potentially important reduction in systolic blood pressure.
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Introduction
Top
Abstract
Introduction
Participants and methods
Results
Discussion
References
![]()
Participants and methods
Top
Abstract
Introduction
Participants and methods
Results
Discussion
References
We invited all 96 practices in Avon using the EMIS and AAH
Meditel computing systems to participate in the study. Practices
agreeing to participate in the study were firstly stratified by
computer system and then assigned by simple random allocation to use
the computer based clinical decision support system and a
cardiovascular risk chart (which gives identical information about
risk), the risk chart alone, or usual care (no information given about
cardiovascular risk). Randomisation was performed with a table of
random numbers by a researcher not involved in the study and who was
blind to the identity of the practices.
All patients aged 60-80 years with a diagnosis of
hypertension and a record of having been prescribed antihypertensive drugs in the previous year were eligible. Thirty eligible patients were
randomly sampled from each practice list by using either the computer
system's built-in sampling facility (EMIS practices) or a random
sampling program on a personal computer (AAH Meditel practices).
The main study was performed by general practitioners (n=74) and practice nurses (n=11), depending on procedures for management of hypertensive patients within each practice. The general
practitioners and nurses were trained to use the computer based
clinical decision support system by one of us (AM). Each patient's
blood pressure was measured on the day of attendance. Other risk
factors were extracted from the patient's notes and cardiovascular
risk recorded either automatically (in computer practices) or manually
by the general practitioner or nurse (in chart practices). Data were
missing only for total and high density lipoprotein cholesterol
concentrations. The computer system assumed missing data to have a
value representing the lowest addition to absolute risk, and general
practitioners and nurses in the chart only practices were instructed to
do likewise. A sensitivity analysis was performed for the outcome of
absolute cardiovascular risk in which missing values were assigned the
median for each trial group. Follow up was at six and 12 months.
Because of the nature of the study, neither the doctors and nurses nor
the patients were blind to their study group. The study took place from
September 1996 to September 1998.
The primary outcome was the percentage of patients in each
group with five year cardiovascular risk
10%. Secondary outcomes
were systolic and diastolic blood pressure and prescribing of
cardiovascular drugs. Although follow up data were collected at six and
12 months, the primary follow up was at 12 months, and only these
results are presented here.
We managed and analysed data using Stata Statistical Software.7 Baseline comparability of the groups was
investigated by descriptive statistics. All analyses comparing the
groups at follow up were conducted on an intention to treat basis. We
used multivariable regression models and adjusted for the value of the
outcome variable at baseline and practice computer system. Since
randomisation was by practice, we also corrected for clustering using
procedures in Stata to derive robust estimates of standard error.
Lastly, we tested for an interaction effect of baseline risk level and
trial arm.
2 techniques and multinomial logistic
regression models that allowed for the corresponding distributions at baseline.
Sample size
The trial was designed principally to detect a difference
between the two intervention arms of the trial, computer based clinical
decision support system plus chart versus chart alone. Based on
previous work,8 we estimated that 55% of patients would
have an absolute cardiovascular risk over five years of
10%. The
sample size was designed to detect a difference between these two
groups of 20 percentage points in the proportion of patients with five
year risk
10%. To allow for randomisation by practice, the sample
size was inflated by a factor of two based on an intrapractice
correlation coefficient of 0.0551.
9 10
With this
inflation factor, 80% power and two tailed 5%
, the required
sample size was 190 in each of the two intervention groups. Twenty
seven practices agreed to participate in the trial: 10 were therefore
randomly allocated to each of the two intervention arms and seven to
the usual care arm. To ensure sufficient numbers of patients with
adequate follow up data, 30 patients were randomly sampled from each
practice.
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Results |
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Baseline comparability
Of 810 randomly selected patients, 95 were excluded before
invitation (non-ambulatory patients and those with life threatening
illness or who had recently had major surgery (figure)). A further 101 failed to attend the baseline consultation. Of the remaining 614 patients, 552 (90%) and 531 (86%) attended the six and 12 month
follow up respectively. Table 1 shows baseline descriptive statistics
for the three groups.
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Absolute cardiovascular risk
Table 2 shows unadjusted absolute cardiovascular risk at
baseline and 12 month follow up. Adjustment for the clustering effect
of using practices as the unit of randomisation did not materially
affect the findings and is not reported here. After practice computer
system and baseline absolute risk were adjusted for by multivariable
logistic regression, a significantly greater proportion of patients in
the computer based clinical decision support system group were at high
risk of a cardiovascular event at follow up compared with those in the
chart only group (adjusted odds ratio 2.3, 95% confidence interval 1.1 to 4.8; P=0.02). There were no significant differences compared with
usual care for either the computer based clinical decision support
group (1.7, 0.7 to 3.9; P=0.22) or chart only group (0.7, 0.3 to 1.6;
P=0.43).
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Blood pressure
Unadjusted means for systolic and diastolic blood pressures
at baseline and 12 months are given in table 2. After practice computer
system and baseline blood pressure were adjusted for, the only
significant difference was that the chart only group had a lower mean
systolic blood pressure (4.6 mm Hg, 95% confidence interval 0.8 to 8.4 mm Hg, P=0.02) compared with the usual care group.
Intensity of drug treatment
Sixteen (3%) patients had stopped blood pressure treatment
at follow up. Table 4 gives the distributions of the number of
cardiovascular drugs being prescribed to the patients at baseline and
the six month follow up. When multinomial logistic regression was used
to adjust for baseline prescribing, the difference between the trial
groups was highly significant (P=0.0078). Relative to 0-1 classes of
cardiovascular drugs, patients in the chart only group were about twice
as likely to be prescribed two classes of cardiovascular drugs and over
three times as likely to be prescribed three or more classes of drugs
(table 5).
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Discussion |
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This study shows that in terms of the percentage of patients with a five year cardiovascular risk greater than 10%, neither the computer based clinical decision support system plus chart or chart alone were any better than usual care. The observation that the computer support group had poorer cardiovascular risk reduction than the chart only group is difficult to explain and requires replication. There was some evidence that both the interventions worked more effectively in higher risk patients compared with usual care (table 3), although this depended on values assigned to missing cholesterol data. Systolic blood pressure was significantly reduced in the chart only group compared with usual care (4.6 mm Hg). This reduction in systolic blood pressure is consistent with significantly increased prescribing of cardiovascular drugs in the chart only group. We found no significant differences in diastolic blood pressure between any of the groups.
Interpretation of findings
Our results do not support the use of this computer based
clinical decision support system in the management of hypertension. The
findings are consistent with results of previous studies.
5 6 11
The benefits of computers are clearer
when they are used as administrative aids for detection, registration, and
recall.
6 11 12
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Study limitations
Our trial had several limitations. Firstly, the target
reduction of 20 percentage points in the proportion of patients at high
absolute risk was large, particularly as the only modifiable risk
factors are blood pressure, cholesterol, body mass index, and smoking.
For this reason, control of blood pressure may be a more suitable and
realistic outcome measure. Secondly, the outcome measures were patient
based but both interventions were aimed at health professionals.
Observational research has shown that health professionals are
reluctant to modify cardiovascular prescribing despite persistent high
blood pressure.16 Thirdly, the computer based clinical
decision support system that we used only estimated risk; other aspects
of hypertension management such as drug dose and treatment
recommendations were not included.17 Computer based
clinical decision support systems which combine risk estimation and
management recommendations for hypertension require further development
and evaluation.
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What is already known on this topic
Cardiovascular risk in hypertensive patients depends on a wide variety of factors Guidelines are being increasingly used to help assess risk Computer based clinical decision support systems have been shown to improve preventive care, but it is unclear whether they affect blood pressure and cardiovascular risk What this study addsNeither a risk chart alone nor a computer based clinical decision support system plus risk chart were any better than usual care in reducing absolute risk of cardiovascular disease Use of the risk chart alone was associated with a significant reduction in systolic blood pressure and increased prescribing of cardiovascular drugs Computer based clinical decision support systems require further development and evaluation before introduction into routine practice in primary care |
Conclusions
This randomised trial has shown that using a computer based
clinical decision support system did not confer any additional benefits
compared with chart guidelines and may have impaired the translation of
evidence to individual patients. Further studies are required on newer
computer based clinical decision support systems, on how the
understanding of absolute risk can influence health professionals'
decision making, and how interactive computers can assist patients in
decision making, treatment preferences, and adherence to treatment
schedules.
11 18 19
Developers of computer based clinical
decision support systems should remember that as well as technological
development, clinical understanding of the recommendations made by such
systems is required.
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Acknowledgments |
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We thank the 27 Avon practices for participating in this study and Shah Ebrahim for helpful comments on earlier drafts of this paper.
Contributors: The study was conceived and designed by TF, TP, and DS, with additional design input by AM. The computer based clinical decision support system was written by CM. Pilot work was done by AM, TF, and CM. Practices and patients were recruited by AM and TF. AM trained the health professionals in the use of the computer system and risk charts and collected the data. TP, AM, and TF performed the statistical analyses. AM, TF, and TP drafted the paper with contributions from DS and CM. AM, TF, and TP are the guarantors.
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Footnotes |
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Funding: NHS Wales Office of Research and Development, grant number RC016. TF is supported by an NHS R&D primary care career scientist award.
Competing interests: None declared.
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References |
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(Accepted 19 July 1999)
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