Download Predictors of Uncontrolled Hypertension in Ambulatory Patients

Predictors of Uncontrolled Hypertension in
Ambulatory Patients
Eric L. Knight, Rhonda L. Bohn, Philip S. Wang, Robert J. Glynn, Helen Mogun, Jerry Avorn
Abstract—Hypertension remains poorly controlled in the United States. Improvement of its management will require an
understanding of the patient characteristics and treatment factors associated with uncontrolled hypertension. We studied
antihypertensive medication use, comorbidity, and blood pressure measurements for 525 hypertensive patients in 3
different healthcare systems over a 1-year period. We concomitantly conducted comprehensive patient interviews
covering demographic factors, knowledge of hypertension and its treatment, and medication side effects. Ordinal logistic
regression was used to identify factors associated with poor blood pressure control. Mean age of the patients was 65⫾11
years. Mean systolic blood pressure (SBP) was 143⫾15 mm Hg; and mean diastolic blood pressure (DBP),
80⫾9 mm Hg. Only 39% (203/525) of patients had mean blood pressure ⬍140/90 mm Hg during the study period; about
half (257/525) had stage 1 hypertension (mean SBP 140 to 159 mm Hg and/or mean DBP 90 to 99 mm Hg), and 12%
(65/525) had stage 2 or greater hypertension (SBP ⬎160 mm Hgand/or DBP ⬎100 mm Hg). Multivariate analysis
revealed several independent predictors of poor control: older age, multi-drug regimens, lack of knowledge by the
patient of their target SBP, and a report of antihypertensive drug side effects. Patients with angina had a higher
likelihood of adequate blood pressure control. Fewer than 40% of the treated patients studied had a mean blood pressure
ⱕ140/90 mm Hg, and specific patient-related factors appear to predict poor control. Some of these may be amenable
to modification. Further identification of patients at risk of poor control can lead to targeted interventions to improve
management. (Hypertension. 2001;38:809-814.)
Key Words: hypertension 䡲 epidemiology 䡲 education
H
factors, including compliance behavior, the presence of comorbid illness, and patient knowledge, as well as patterns of
treatment and systems of care. Much of the literature on blood
pressure control is focused on antihypertensive medication
adherence, and good adherence has been associated with
good blood pressure control.7 However, blood pressure is also
determined by other factors, including age, severity of disease, health habits, and intensity of care.
The current study was designed to test several issues
related to blood pressure control that have not been extensively examined in prior studies. First, we sought to assess the
role of patient-specific factors in blood pressure control, as
well as to explore the relationship between age and blood
pressure control.8 –11 We also wanted to measure the relationship between patient knowledge of target blood pressure
goals and blood pressure control, as lack of such knowledge
has been associated with poor compliance with medications
and clinic visits.12
Second, we wished to examine the impact of different
healthcare systems on blood pressure control, an especially
important issue at a time when systems of care are in such
rapid flux. Systems that emphasize regular, ongoing primary
ypertension is the second most common reason for an
outpatient physician visit in the United States, accounting for approximately 30 million visits a year.1 However, in
a recent national study, only 29% of people with hypertension
had their blood pressure controlled ⬍140/90 mm Hg.2 A
study of older men at 5 Department of Veterans Affairs sites
found even worse blood pressure control, with fewer than
25% of patients having a blood pressure ⬍140/90 mm Hg,
despite an average of ⬎6 hypertension-related visits per
year.3 Similar results were found in a study of unionized
healthcare workers with hypertension.4 The reasons for this
epidemic of uncontrolled hypertension are unclear, and several explanations have been considered. In a study of innercity patients with uncontrolled hypertension, lack of a primary care physician and noncompliance were both associated
with poor blood pressure control.5 There is also some
evidence that intensity of medical therapy is related to blood
pressure control; however, this is difficult to measure accurately. The cost of antihypertensive medication has also been
linked to poor blood pressure control.6
In addition to the underlying pathophysiology, blood pressure control is potentially determined by multiple other
Received October 19, 2000; first decision November 13, 2000; revision accepted March 21, 2001.
From the Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical
School, Boston, Mass.
Correspondence to Jerry Avorn, MD, Chief, Division of Pharmacoepidemiology and Pharmacoeconomics, Brigham and Women’s Hospital, 221
Longwood Ave, Boston, MA 02115. E-mail [email protected]
© 2001 American Heart Association, Inc.
Hypertension is available at http://www.hypertensionaha.org
809
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Hypertension
October 2001
care and have blood pressure management guidelines in place
should, in theory, have more success at controlling hypertension than other forms of healthcare delivery. However, the
literature is unclear as to which systems of care provide
superior care for patients with hypertension.13
Third, we sought to explore the relationship between
comorbidity and blood pressure control. Patients with substantial comorbidity, especially when blood pressure is a
contributing factor, might be more likely to have better blood
pressure control because the impact of hypertension would be
more apparent to them compared with those with asymptomatic hypertension and no comorbidity. For example, we have
previously shown that patients with cardiac disease comply
better with antihypertensive regimens, which would be expected to lead to better blood pressure control.14 Significant
cardiac disease may also result in lower blood pressures
secondary to cardiac dysfunction.
Fourth, we wanted to explore whether perceived adverse
drug effects would influence blood pressure control, because
patients with side effects may be less likely to take their
medications as directed.15 This hypothesis is indirectly supported by studies showing poorer compliance with hypertension therapy in patients prescribed thiazides compared with
calcium channel blockers.14,16 In addition, patients who report
adverse effects may have other characteristics (eg, dissatisfaction with the healthcare system) that may influence their
blood pressure control.
Methods
The study was conducted at outpatient clinics in 3 sites: a not-forprofit managed care organization, a large tertiary care hospital, and
a Veterans Affairs Medical Center (VAMC). The managed care
organization provided comprehensive drug coverage with a $5 to $10
copayment. At the hospital clinic, most patients received drug
coverage through Medicaid or free care. At the VAMC site, all
patients received free prescription coverage.
Patients were identified on the basis of antihypertensive medication use and a diagnosis of hypertension. Letters were sent to
prospective subjects, inviting them to participate in the study and
enabling them to opt out. All traceable patient identifiers were
transformed to anonymous coded study numbers to protect confidentiality. Institutional review boards at all sites approved this study.
At the managed care site, 49% of patients (250/515) agreed to
participate, of whom 96% (240) had complete survey and chart data.
At the tertiary care site, 40% (63/157) agreed to participate, of whom
70% (44) had complete survey and chart data. At the VAMC, 38%
(247/658) agreed to participate, of whom 97% (241) had complete
survey and chart data. Study participants were quite similar to
nonparticipants for most characteristics, although participants at the
hospital clinic were more likely to be taking ACE inhibitors than
were nonparticipating patients, and participants at the VAMC site
were more likely to be taking ␤-blockers or ACE inhibitors than
were those who declined to participate.
We recorded information from all healthcare encounters during 1
calendar year, including date, systolic (SBP) and diastolic (DBP)
blood pressures, symptoms, diagnoses, and medication use. The
survey obtained data on age, race, gender, educational level, marital
status, education by the physician, use of medication reminders,
health habits, knowledge of target blood pressure, and side effects.
For Spanish-speaking patients, the survey instrument was translated
into Spanish, back-translated for accuracy, and administered by a
medical interpreter. For patients taking combination drugs, compliance was counted in terms of each constituent drug class.
Blood pressure categories were based on standard criteria17
(in mm Hg): (1) SBP ⬍140 and DBP ⬍90, (2) SBP ⱖ140 and ⬍160,
and/or DBP ⱖ90 and ⬍100 (stage 1 hypertension), and (3) SBP
ⱖ160 or DBP ⱖ100 (stage 2 or greater hypertension). A minimum
of 2 blood pressure readings were required to classify a study
subject.
The outcome variable was blood pressure control defined in the 3
ordered categories noted above; we used a proportional odds model
to evaluate potential determinants of blood pressure control.18
Univariate associations were tested by placing each variable into a
separate proportional odds model. For categorical variables, referent
variables were created. The proportional odds assumption was not
violated for any variables on univariate analysis at a P value ⱕ0.05.
Variables that were associated with the above-defined outcomes at a
P value ⬍0.2 were entered into the multivariate model. Variables
with a P value ⱕ0.05 were kept in the final multivariate model, as
were gender, race, and site of care. We also examined interaction
terms for potential entry into the model. All analyses were performed
using SAS software.
Results
A total of 525 subjects completed the survey and had data
available for a 1-year medical record review. Their mean age
was 65⫾11 years, 64% were male, and 89% were white.
Table 1 presents basic demographic information of the study
population and other descriptive statistics by site. The managed care population was remarkable for the number of
patients using only 1 antihypertensive medication during the
study period (49%, compared with ⬍30% for the other sites,
P⬍0.001). The VAMC site was notable for its expected
preponderance of males and for the number of patients using
multiple antihypertensive medications during the study period. The hospital clinic population was relatively young and
ethnically diverse (30% white, versus ⬎90% white for the
other sites, P⬍0.001).
A mean of 7.4⫾5.0 SBP and DBP recordings was obtained
for each subject. The mean SBP for the study population was
143⫾15 mm Hg , and the mean DBP was 80⫾9 mm Hg.
Based on the mean BP during the study year, 203 patients
were normotensive, 257 had stage I hypertension, and 65 had
stage 2 or higher blood pressure. Table 2 presents the mean
SBPs and DBPs in each category.
On univariate analysis, we found the following characteristics to be associated with poor blood pressure control (Table
3): older age, female gender, calcium channel blocker therapy, the use of ⱖ2 antihypertensive medications during the
study period, site of care, presence of arthritis, being widowed, lack of knowledge of appropriate target SBP, and
experience of an adverse effect of an antihypertensive medication. The presence of angina and a history of myocardial
infarction were both associated with better blood pressure
control.
With construction of a multivariable model as described
above, we found the following factors to be significantly and
independently associated with poor blood pressure control
after adjusting for all other significant predictors: age ⱖ65,
the use of ⱖ2 antihypertensive medications during the study
period, lack of knowledge of appropriate target SBP, and the
experience of a specific side effect attributed to an antihypertensive medication (see Table 4). Treated hypertensive
patients age ⱖ65 were 2.5 times more likely to have higher
blood pressure than patients ⬍55 years, patients on ⱖ4
hypertensive medications were almost 5 times as likely to
have higher blood pressure than patients on 1 antihypertensive medication, patients who were not aware that their target
Knight et al
TABLE 1.
Predictors of Uncontrolled Hypertension
811
Characteristics of Patients in the 3 Study Sites
Variable
Managed Care
(n⫽240)
VAMC
(n⫽241)
Hospital Clinic
(n⫽44)
66.5⫾12.0
65.4⫾10.3
59.1⫾11.7
Mean age, y⫾SD
Gender, % female
62
4
Mean SBP, mm Hg⫾SD
144⫾14.5
Mean DBP, mm Hg⫾SD
80
141.5⫾14.8
146.9⫾14.0
81.3⫾7.7
78.6⫾8.7
84.9⫾10.1
97
92
30
32
Race, % white
Antihypertensive drug class, %
Thiazide
38
27
␤-Blocker
43
59
75
Calcium channel blocker
29
53
34
ACE inhibitor
37
62
50
6
17
7
Other
No. of antihypertensive medication
classes during the study period, %
0
5
5
14
1
49
23
16
2
35
33
36
3
8
28
27
4 or 5
3
11
7
Angina, %
9
24
9
History of myocardial infarction, %
3
30
14
11
Congestive heart failure, %
5
14
History of stroke, %
6
14
9
Diabetes, %
20
37
32
Lack of knowledge of goal SBP, %
48
43
66
Reported side effects attributed to
antihypertensive medication, %
21
45
48
SBP should be ⱕ140 mm Hg were 1.5 times more likely to be
in a higher blood pressure category, and patients who attributed a side effect to a specific antihypertensive medication
were twice as likely to be in a higher blood pressure category.
There was a trend for managed care patients to have worse
control than VAMC patients, but there was no evidence of
any difference between the hospital clinic site and managed
care organization (however, small numbers at the hospital site
makes it difficult to assess this comparison). Angina was
associated with relatively better blood pressure control, with
these patients having only a third the risk of poor control
compared with patients without angina. Antihypertensive
drug class had no impact on blood pressure control. (Table 3).
Discussion
Only 39% of the 525 hypertensive patients we studied had a
mean blood pressure ⬍140/90 mm Hg, despite ongoing
TABLE 2.
Mean SBP and DBP by Hypertension Category
Blood Pressure
Category
No. of
Patients
Mean
SBP⫾SD
Mean
DBP⫾SD
Controlled hypertension
203
129⫾8
76⫾7
Stage 1 hypertension
261
148⫾6
82⫾8
61
170⫾7
85⫾11
Stage 2 hypertension or greater
medical treatment. Older age was associated with poorer
blood pressure control relative to that seen in younger treated
patients. SBP increases with age, but DBP tends to level off
at age 55 to 60.19 This increase in SBP is a strong predictor
of cardiovascular disease with advancing age.20 The clinical
benefits of treating systolic hypertension in older patients
have now been demonstrated in several randomized, placebocontrolled trials, yet the implications of these trials may not
be fully accepted in routine practice.8 –10 Even the oldest old,
age ⬎80, appear to benefit from antihypertensive therapy.21 It
is possible that despite the proven benefit of antihypertensive
therapy in this age group, older patients are still treated less
aggressively compared with younger patients.
Lack of knowledge of appropriate SBP was also found to
be a risk factor for poor blood pressure control. Patients who
indicated in the interview that they were not aware that their
target SBP should be ⱕ140 mm Hg were significantly more
likely to have a higher mean blood pressure documented in
their medical records. Such patients may have been less likely
to take their medication, adopt healthy lifestyle changes, or
see their physician if their blood pressure was outside the
ideal range. However, we did not observe a relation between
patient-reported education by their physician and blood pressure control. One explanation for this may be that physicians
are more likely to educate patients whose blood pressure is
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Hypertension
October 2001
TABLE 3.
Univariate Predictors of Poor Blood Pressure Control
Variable
Age
⬍55 y
55–64 y
65–74 y
ⱖ75 y
White
Female gender
Site
Managed care
VAMC
Hospital clinic
Antihypertensive drug class
Thiazide diuretic
␤-Blocker
Calcium channel blocker
ACE inhibitor
Other
Total No. of antihypertensive drugs
0
1
2
3
4 or 5
Alcohol abuse
Angina
History of myocardial infarction
Congestive heart failure
History of stroke
Diabetes
Arthritis
Highest educational level
Grade school or junior high school
High school or vocational school
College
Postgraduate
Marital status
Single
Married
Widowed
Divorced or separated
Provider explained hypertension (referent⫽yes)
Somewhat
No
Education about hypertension (referent⫽yes)
Somewhat
No
Used a reminder to take blood pressure pills
Exercise to lower blood pressure
Weight loss to lower blood pressure
Lack of knowledge of appropriate SBP
Lack of knowledge of appropriate DBP
Side effect attributed to antihypertensive medication
Number
(Total⫽525)
Odds of Poor
Control
95%
Confidence
Interval
98
111
205
111
468
194
referent
1.12
2.05
2.33
0.69
1.64
0.65–1.93
1.27–3.32
1.38–3.94
0.41–1.16
1.17–2.31
240
241
44
referent
0.71
1.86
0.50–1.00
1.03–3.37
171
280
212
261
59
referent
0.97
1.44
1.29
1.56
0.69–1.37
1.02–2.03
0.92–1.81
0.92–2.62
30
181
179
99
36
55
83
85
51
52
143
97
0.87
referent
1.63
1.83
3.31
0.69
0.44
0.55
0.62
1.40
0.86
1.64
77
284
137
27
0.93
referent
0.73
1.03
0.53–1.62
43
324
88
70
1.59
0.86–2.94
1.73
0.78
1.09–2.74
0.45–1.35
83
72
1.00
0.68
0.58–1.73
0.45–1.05
48
56
482
371
207
246
148
180
1.12
1.44
1.40
0.75
0.81
1.61
0.97
2.06
0.63–1.99
0.84–2.46
0.77–2.56
0.52–1.08
0.58–1.13
1.16–2.24
0.68–1.40
1.41–3.01
0.41–1.83
1.09–2.42
1.14–2.94
1.65–6.65
0.40–1.17
0.28–0.70
0.35–0.87
0.36–1.09
0.81–2.43
0.60–1.24
1.08–2.51
0.49–1.09
0.48–2.21
Knight et al
TABLE 4.
Multivariate Model of Poor Blood Pressure Control
Variable
Odds of
95% Confidence
Poor Control
Interval
Age group*
55– 64 y
1.26
65–74 y
2.50
0.71–2.24
1.49–4.19
ⱖ75 y
2.56
1.45–4.52
VAMC
0.63
0.40–1.01
Hospital
0.94
0.42–2.11
0
0.90
0.41–1.98
2
1.91
1.25–2.91
3
2.53
1.50–4.28
4 or 5
Site**
No. of antihypertensive drugs during the
study period***
4.70
2.22–9.95
Angina
0.33
0.20–0.56
Lack of knowledge of appropriate SBP
1.55
1.09–2.20
Attributed a specific side effect to a specific
antihypertensive medication
2.06
1.41–3.01
The odds ratio represents the likelihood of being in a higher blood pressure
category. The model is adjusted for gender and race.
*Referent group: age⬍55; **referent group: managed care site; ***referent
group: 1 antihypertensive drug during the study period.
out of control. In some controlled trials, educational interventions have been shown to be effective in improving blood
pressure control. In 1 study,22 patients in the intervention
group showed significant reductions in both SBP and DBP
compared with those of controls. Educational interventions
have also been shown to improve compliance with blood
pressure medication.23 However, not all trials of patient
education have improved compliance or blood pressure control.24 The same authors did find improvement in both
compliance and blood pressure control when patients were
taught to measure their own blood pressures and chart it,
along with their pill-taking schedule.25 The important difference between these 2 approaches may be the relevance of the
educational message to the patient’s specific blood pressure
levels (as opposed to general concepts about hypertension
and risk).
To assess the influence of the system of care, we controlled
for multiple factors which differed across the 3 sites studied,
including age, gender, race, antihypertensive medication
class, and number of antihypertensive medications used.
After adjusting for these and other factors, we found no
differences between the study sites in adequacy of blood
pressure control, though there was a trend for managed care
patients to have worse control than VAMC patients. Thus,
these findings provide no evidence that patients in managed
care systems have better blood pressure control than patients
in the VA system or patients in an urban, academic practice.
Other studies have found similar results. For example, in the
Medical Outcomes Study there was an equivalent lowering of
baseline SBP after 2 years in managed care patients versus
fee-for-service patients.13 In an earlier study, patients in a
managed care organization had slightly better blood pressure
Predictors of Uncontrolled Hypertension
813
control than patients receiving care in a fee-for-service
setting.26 However, this study was limited in that it excluded
patients with significant comorbidities such as ischemic heart
disease, diabetes, and chronic lung disease. In the present
study, which included patients with these common conditions, none of the 3 systems of care performed admirably well
in managing hypertension.
The impact of comorbidity on hypertension control has
not been examined extensively in large studies. We found
angina to be associated with better blood pressure control.
This may be due to improved compliance in these patients,
more aggressive treatment, or the direct effect of cardiovascular disease.14,27,28 There was also a trend for patients
with congestive heart failure or a history of myocardial
infarction to have better blood pressure control. Although
the study sample included a large number of diabetic
patients, diabetes was not associated with better control
despite published recommendations suggesting that these
patients should be particularly well controlled, with a
target of ⬍130/85 mm Hg.29
We also found a relationship between the number of
antihypertensive drugs used during the study period and
blood pressure control, although this measure has some
intrinsic limitations. For example, a patient who was switched
from thiazide monotherapy to ␤-blocker monotherapy after 1
month would have the same number of medications used
during the study year as a patient who was maintained on both
a thiazide and a ␤-blocker throughout the study period. The
observed relationship between increased number of antihypertensive drugs and poorer blood pressure control could be
explained by several factors. First, patients whose blood
pressure is more difficult to control are likely to be treated
with multiple drugs. Thus, this measurement may be a
consequence of poor blood pressure control. Second, patients
who frequently are switched from 1 drug class to another may
also have poorer blood pressure control, because they might
have a greater percentage of days uncovered. Third, frequent
switching could also be an effort to eliminate side effects,
though the identification of a specific side effect was not
highly correlated with the number of antihypertensive medications during the study period. Fourth, poor control may also
be a reason to switch medication class.
Another potentially important observation was the relationship between poor blood pressure control and adverse events
attributed to antihypertensive medications. We have shown
previously that patients initially prescribed ACE inhibitors or
calcium channel blockers for hypertension were more likely
to adhere to therapy than patients prescribed thiazides,
possibly because the former medications may have fewer side
effects.14 Patients who report adverse effects may also differ
in terms of unmeasured factors which are also associated with
uncontrolled hypertension.
In the present study, no specific medications were associated with poorer versus better blood pressure control on
multivariate analysis.
Several limitations of this study deserve mention. The
study design was observational, so each patient was managed
at the discretion of his or her physician. Therefore, based on
this study, it is difficult to impute causality with certainty for
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Hypertension
October 2001
any of the factors associated with poor blood pressure control.
In addition, despite the comparability of respondents and
nonrespondents in terms of basic demographic characteristics
and medication use, it is possible that the absence of data
from patients who declined to participate could have affected
the findings and their ability to be generalized.
This study provides a framework for identifying hypertensive patients who are at high risk of poor control, and many
of the factors identified may be amenable to improvement.
Older patients can be targeted for greater attention to blood
pressure control, particularly in light of the evidence for
improvement in clinical outcomes with hypertension therapy
in this population. Patients with poor knowledge of the goal
of their hypertension therapy should be informed about their
target blood pressure, to enable them to participate more fully
in their own management. Finally, clinicians should discuss
with patients the potential adverse effects of their hypertension therapy, seek out the presence of such symptoms in
routine follow-up history-taking, and when they occur, modify therapy.
These data provide further evidence that poor blood pressure control is common in a variety of health care settings,
and that patients at particular risk of poor control can be
identified. Targeted interventions to improve management in
such patients could make a substantial difference in stemming
the epidemic of poorly controlled hypertension in the United
States.
Acknowledgments
This work was funded by a research grant from the Outcomes
Research Department of the Bristol-Myers Squibb Pharmaceutical
Research Institute. Dr Knight was supported in part by grants from
The Medical Foundation and the Claude Pepper Older Americans
Independence Center (OAIC) at the Harvard Medical School Division on Aging. The authors would like to thank Sherry Hawley,
Laura Van Houten, and Asra Warsi for their extensive time and
effort performing the surveys and data collection and organizing the
data for these analyses.
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