(Circulation. 1996;93:697-703.)
© 1996 American Heart Association, Inc.
Articles |
From the Framingham Heart Study, Framingham, Mass (P.A.S., R.B.D., A.J.B., W.B.K.); the Statistics and Consulting Unit, Department of Mathematics, Boston (Mass) University (P.A.S., R.B.D., A.J.B.); and Section of Preventive Medicine, Department of Medicine, Boston University School of Medicine (W.B.K.).
| Abstract |
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Methods and Results Trends in the prevalence of LTS
hypertension and its treatment were assessed in 1950, 1960, and 1970
among three cohorts of men and women in the Framingham Heart Study
(Mantel-Haenszel test). Cardiovascular disease (CVD)
incidence and mortality were compared between patients with LTS
hypertension with and without long-term treatment by use of the
2 test. Cox proportional hazards regression
analysis was used to estimate 10-year risk of death as a
function of risk factor levels and treatment. Prevalence of LTS
hypertension rose from 138 to 208 per 1000 between the 1950 and 1970
male cohorts (P<.01), while prevalence fell from 253 to 198
per 1000 between the female cohorts (P<.02). Long-term
treatment increased 51% between the male cohorts and 45% between the
female cohorts (both P<.001). While CVD incidence was
similar (26% versus 25%), all-cause mortality was significantly
lower among men with long-term treatment (31% versus 43%;
P<.05), and CVD mortality was less than half (13% versus
28%; P<.01). Among treated women, all-cause mortality
was 21% (versus 34%; P<.01), and CVD mortality was 9%
(versus 19%; P<.01). Ten-year risk of CVD death for
patients with LTS hypertension with long-term treatment compared
with those without was 0.40 (95% CI, 0.27 to 0.60).
Conclusions This investigation of LTS hypertension, its treatment, and its sequelae in a free-living general population confirms the reduction in CVD mortality demonstrated in more short-term clinical trials of hypertension therapy in select patient groups.
Key Words: trials hypertension risk factors mortality cardiovascular diseases
| Introduction |
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A number of surveys and studies have reported trends over time in
the prevalence and control of
hypertension.14 15 16 17 In
these
reports, the hypertensive status of a subject is assessed on a single
occasion. Similarly, reports from clinical trials identify subjects as
hypertensive at the start of the study and compare morbidity and
mortality between treatment groups during the subsequent follow-up
period.9 10 11 12 13
There have been no reports of secular trends
in the treatment and control of hypertension sustained for long
durations, even though it is the chronic nature of hypertension that
gives rise to many of its cardiovascular sequelae. The
objectives of the present study were (1) to describe trends in the
prevalence of LTS (
6 of 10 years) hypertension and its treatment at
time points bridging the introduction and widespread use of
antihypertension medications and (2) to assess the impact of
long-term treatment on 10-year CVD incidence and mortality.
| Methods |
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Study Design and Definitions
This study uses a modified
cross-sectional cohort design
that measures differences over time among successive cohorts of men and
women of similar ages. This report focuses on the prevalence of
hypertension in 1950, 1960, and 1970 among three independent and
mutually exclusive cohorts of men and women from the Framingham Heart
Study. There were 589 men and 719 women 50 to 59 years old as of
January 1, 1950 (the 1950 cohorts), 596 men and 799 women 50 to 59
years old as of January 1, 1960 (the 1960 cohorts), and 655 men and 830
women 50 to 59 years old as of January 1, 1970 (the 1970 cohorts). The
study population totaled 4188: 1840 men and 2348 women.
Prevalence of
hypertension in each cohort is presented in terms
of point prevalence (hypertensive at baseline examination in 1950,
1960, or 1970) and period prevalence (hypertensive status during 1950
to 1960, 1960 to 1970, and 1970 to 1980). Hypertension is defined as
SBP
160 mm Hg and/or DBP
95 mm Hg or the patient taking
antihypertension medication.14 15 Hypertension is
considered to be controlled if SBP is <160 mm Hg and DBP is <95 mm Hg
while the patient is taking antihypertension medication and is
uncontrolled if SBP is
160 mm Hg and/or DBP is
95 mm Hg regardless
of treatment.14 15
The analysis of LTS hypertension is based on subjects in the 1950, 1960, and 1970 cohorts who attended the baseline examination for their cohort and at least three of the five subsequent biennial examinations, including the examination at the end of 10 years of follow-up. Of the 1950 cohorts, 434 men (74%) and 581 women (81%) met these criteria; of the 1960 cohorts, 442 men (74%) and 625 women (78%); and of the 1970 cohorts, 505 men (77%) and 708 women (85%).
A subject has LTS hypertension if he or she is hypertensive at
the
baseline examination plus a minimum of three of the five subsequent
biennial examinations, including the examination 10 years after
baseline (ie, hypertensive
6 of 10 years). Anyone who missed two
consecutive examinations or died within 10 years of baseline is
excluded. Those LTS hypertensive patients receiving antihypertension
medication at four or more biennial examinations (
6 years) are
considered to have long-term treatment. LTS hypertension is
considered to be controlled if SBP is <160 mm Hg and DBP is <95 mm Hg
for
6 of 10 years while the patient is taking antihypertension
medication and is uncontrolled if SBP is
160 mm Hg and/or DBP is
95
mm Hg for
6 of 10 years regardless of treatment.
Other Risk Factor Data
Methods of risk factor measurement and
laboratory
analysis are described elsewhere.19 SBP and DBP,
cholesterol, glucose intolerance, and LVH at baseline of
each cohort and 10 years after baseline are reported for all LTS
hypertensive patients. In the 1970s, plasma cholesterol
measurements were substituted for serum cholesterol in the
Framingham Study. Since plasma cholesterol values have been
shown to be systematically lower than those from serum,20
plasma values for the 1970 cohort were inflated by
3%.21
End-Point Definition and Ascertainment
Cardiovascular and
vital status information was
available for all subjects included in this report. Throughout the
Framingham Study, cardiovascular events have been dated
and assigned a diagnosis based on medical record review and
standard criteria for each outcome18 22
consistently applied at regular meetings of a panel of
physicians. CVD includes coronary heart disease (myocardial
infarction, angina and coronary insufficiency, sudden and
nonsudden coronary death), stroke, and other CVD (transient
ischemic attacks, congestive heart failure, intermittent
claudication, and other cardiovascular death).
Each cohort was followed for 20 years from baseline (1950 cohort, 1950 to 1970; 1960 cohort, 1960 to 1980; and 1970 cohort, 1970 to 1990). CVD incidence among LTS hypertensive patients was ascertained during the first 10 years of follow-up of each cohort, and mortality (all-cause and CVD) was assessed during the second 10 years of follow-up.
Statistical Methods
Trends in rates of hypertension,
treatment, and
cardiovascular events were analyzed by the
Mantel-Haenszel test for trend.23 Student's t
test23 was used to compare baseline risk factor levels
between LTS hypertensive patients in the three cohorts with and without
long-term treatment and to compare changes in risk factors after 10
years between those with and without long-term treatment. The
2 test23 was used to compare 10-year
incidence of CVD and 10-year mortality (all-cause and
cardiovascular) between those with and without
long-term treatment. Cox proportional hazards regression
analysis24 was used to determine the risk of death
in 10 years for those LTS hypertensive patients with and without
long-term treatment while controlling for other risk factors. A
significance level of P
.05 was used to test hypotheses,
and all significance tests were two-tailed.
| Results |
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The prevalence of uncontrolled hypertension was
significantly lower in
the 1970 male and female cohorts compared with the 1950 cohorts
(P<.001 for both male and female cohorts). More women than
men with uncontrolled hypertension had elevated SBP in the cohorts:
25% compared with 15% in the 1950 cohorts (P<.05) and
32% compared with 20% in the 1970 cohorts (P<.01). In
contrast, more men than women with uncontrolled hypertension in each
cohort had elevated DBP: 30% compared with 12% in the 1950 cohorts
(P<.001), 35% compared with 23% in the 1960 cohorts
(P<.01), and 24% compared with 15% in the 1970 cohorts
(P<.05). Treatment rates for uncontrolled hypertension,
whether due to elevated SBP or elevated DBP, were
20% among the
male cohorts and 30% among the female cohorts.
Trends in Period Prevalence of LTS Hypertension
Trends in
prevalence of LTS hypertension over 10-year
periods are presented in Table 2
. Period
prevalence was 208 per 1000 in the 1970 male cohort compared with 138
in the 1950 cohort (P<.01), while it was 198 per 1000 in
the 1970 female cohort compared with 253 in the 1950 cohort
(P<.02). Even though long-term treatment and control
increased between the 1960 and 1970 male cohorts (P<.001
for each), more women than men with LTS hypertension in each cohort
received treatment: 63% of women compared with 27% of men in the 1960
cohorts (P<.001) and 89% compared with 78% in the 1970
cohorts (P<.05). More women than men with LTS hypertension
also had their hypertension controlled: 33% of women compared with
14% of men in the 1960 cohorts (P<.01) and 78% compared
with 66% in the 1970 cohorts (P<.05).
|
The rate of uncontrolled LTS hypertension was 23% in the 1970 male cohort compared with 85% in the 1950 cohort (P<.001) and 15% in the 1970 female cohort compared with 92% in the 1950 cohort (P<.001). The percent who were uncontrolled and untreated was 4% in the 1970 male cohort compared with 35% in the 1950 cohort (P=.03) and 1% in the 1970 female cohort compared with 31% in the 1950 cohort (P<.001).
Risk Factors Among LTS Hypertensive Patients With and Without
Long-term Treatment
Age and blood pressure levels at initiation of
antihypertensive
therapy were compared for those LTS hypertensive patients with
long-term treatment identified in each cohort (Table 3
).
Treatment was initiated at younger ages
(P<.001) and at lower SBP and DBP (both P<.001)
in each successive cohort.
|
Risk factor levels at baseline of each
cohort were compared for LTS
hypertensive patients with and without long-term treatment (Table
4A
). Among men and women in the 1950 cohorts, baseline
SBP was higher for those with treatment (195 mm Hg compared with 177 mm
Hg, P<.01), as was DBP (113 mm Hg compared with 101 mm Hg,
P<.001). However, this situation was reversed in the 1970
cohort, when those with long-term treatment had a baseline SBP of
156 mm Hg compared with 163 mm Hg among those without treatment
(P<.05 for difference). This is consistent with the
trend to initiate treatment earlier noted in Table 3
. More LTS
hypertensive patients with LVH received long-term treatment.
Baseline prevalence of LVH (by ECG) among those with long-term
treatment was approximately twice the prevalence of those without
treatment. This difference was not statistically significant because of
sample size.
|
Changes in baseline risk factor levels over 10 years of
follow-up
of each cohort were compared for LTS hypertensive patients with and
without long-term treatment (Table 4B
). Mean
changes in SBP were similar, but DBP dropped an average of 10.2 mm Hg
over 10 years among those with long-term treatment compared with
7.6 mm Hg among those without (P=.01).
Cholesterol fell 4.6 mg/dL and glucose intolerance rose
12% among those with long-term treatment compared with a 2-mg/dL
rise in cholesterol and a 7% rise in glucose intolerance
among those without (P<.03 and P<.06,
respectively). The prevalence of LVH rose only 0.3% over 10 years
among those with long-term treatment compared with a 4.4% rise
among those without. This difference was not statistically
significant.
|
Cardiovascular Morbidity and Mortality Among LTS
Hypertensive Patients
CVD incidence during the first 10 years of
follow-up of the
three cohorts was 29% among men with LTS hypertension, 24% among
women, and 26% among men and women combined (Table 5
).
There was no significant difference in CVD incidence among LTS
hypertensive men with and without long-term treatment (30% versus
27%), among hypertensive women (24% versus 24%), or among
hypertensive men and women combined (26% versus 25%).
|
Table
6
compares trends in all-cause and CVD
mortality between LTS hypertensive patients with and without
long-term treatment in each cohort. In the combined cohorts,
all-cause mortality was 40% for men with long-term treatment
compared with 49% for men without (P<.05), while CVD
mortality was 14% among men with long-term treatment compared with
30% among men without (P<.01). Twenty-seven percent of
LTS hypertensive women with long-term treatment died during 10
years of follow-up compared with 36% without long-term
treatment (P<.01). Of those with long-term treatment,
9% died of CVD compared with 20% without
(P<.01). When the male and female cohorts were combined,
the differences in mortality rates between those LTS hypertensive
patients with and without long-term treatment were significant at
the P<.001 level: All-cause mortality was 31% for
those with long-term treatment compared with 41% for those
without, and CVD mortality was 11% for those LTS hypertensive patients
with long-term treatment compared with 24% for those without.
|
Cox proportional hazards regression analyses were performed using risk factor levels 10 years after baseline to predict mortality during the second 10 years of follow-up. After age, sex, smoking, cholesterol level, and glucose intolerance status were controlled for, the risk of death among those LTS hypertensive patients with long-term treatment compared with those without was 0.69 (95% CI, 0.53 to 0.89), and the risk of death from CVD was 0.40 (95% CI, 0.27 to 0.60).
| Discussion |
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6 of 10 years,
its treatment, and sequelae. The study of LTS hypertension is important
because the prevalence rates it provides are not affected by random
fluctuations in blood pressure measurements. More importantly, since
many of the sequelae of hypertension reflect chronic processes that
mediate the effects of blood pressure,7 9 it is
essential
that hypertension and treatment sustained for long periods of time be
the focus of evaluation research. Trends in the treatment and control
of sustained hypertension are, thus, appropriate outcome measures for
hypertension detection programs.
In the present report, the prevalence of LTS hypertension increased
between the 1950 and 1970 male cohorts, while prevalence decreased
between the female cohorts. Since hypertension in this study is defined
by SBP and DBP levels as well as the use of antihypertension
medication, higher prevalence can reflect increased use of medications
due to initiation of treatment at younger ages or at lower blood
pressuresboth trends noted in this report. On the other hand, the
lower prevalence of LTS hypertension in the 1970 female cohort compared
with the 1950 cohort cannot be explained by changes in the use of
medications. Elsewhere,27 however, we have reported a
significant reduction in the prevalence of obesity (defined as weight
120% of the US mean for sex, age, and height) among women in the
Framingham Heart Study. Prevalence dropped from 62% of women in 1950
to 44% in 1970 (P<.001). The average body mass index [ie,
weight (kg)/height (m)2] declined from 27.1 to 25.5
(P<.001). If we estimate that a 10-pound difference in
weight results in a 4.5 mm Hg average change in SBP,28
secular trends in obesity may offer an explanation for the lower
prevalence of LTS hypertension in women in 1970 reported here.
Major gains were made in the long-term treatment and control of LTS hypertension between 1960 and 1980. Among men, long-term treatment increased 51%. In the 1960 cohort, one half of men with long-term treatment had their hypertension controlled; by the end of follow-up of the 1970 cohort, 84% of those treated were controlled. Long-term treatment of LTS hypertension increased 45% between the female cohorts, and control of LTS hypertension rose from 50% of those treated in the 1960 cohort to 88% in the 1970 cohort. Uncontrolled LTS hypertension declined by 77% between the female cohorts, and only 1% of all LTS hypertensive patients in the 1970 cohort remained untreated during follow-up.
While three clinical trials of antihypertension drugs in older persons found significantly lower relative risk of CVD events (0.60 to 0.83) among those on active treatment compared with those on placebo,11 12 13 we did not observe a significant difference in 10-year incidence of CVD between those LTS hypertensive patients with and without long-term treatment in the three cohorts. This is not surprising, given the limited sample size and the high prevalence of LVH, a major risk factor for CVD,29 among those with long-term treatment in the present study. Although we did not assess physicians' reasons for initiating therapy, logistic regression analysis indicated that presence of LVH was a significant predictor of hypertension therapy among LTS hypertensive patients in these cohorts.
The beneficial effects of long-term treatment of LTS hypertension on mortality end points were evaluated during the second 10 years of follow-up of each cohort. When other risk factors were controlled, risk of death was 31% lower and risk of CVD death was 60% lower among those with long-term treatment compared with those without. This finding is consistent with decreased total and vascular mortality reported in clinical trials of the pharmacological treatment of hypertension.9 11 12 13 That mortality should have been affected 10 to 20 years after baseline speaks to the chronic processes involved in hypertension and its cardiovascular sequelae. A recent report after 10.5 years of follow-up of the MRFIT study30 also indicated a delayed effect of risk factor changes on mortality end points.
Study Strengths and Limitations
This study evaluates the
impact over time of the introduction of
intensive antihypertension therapy for LTS hypertension in a
free-living general population. It is an observational study and
not a clinical trial: comparison groups were not matched, treatment was
not randomly assigned, and therapies were not administered according to
strict protocols. In the general population, many factors contribute to
the physician's decision to administer therapy, and compliance is less
certain than in clinical trials. For these reasons, results from
population-based studies may provide more realistic evaluations of
therapeutic interventions.
The methods used in this report differ from those of prior evaluations of hypertension therapy from the Framingham Heart Study. Using a person-examination approach that pooled examinations over a 30-year period, Cupples and D'Agostino19 reported that for any given blood pressure, those receiving treatment had a higher risk of death in 2 years than those not receiving treatment. In contrast, we identified subjects with LTS hypertension in 1950, 1960, and 1970. We followed each of these subjects for 20 years from their baseline examination to assess CVD incidence and mortality. Relative risk of death in 10 years was estimated for those with and without long-term treatment while risk factors other than blood pressure were controlled for, since comparing risks between treated and untreated hypertensive patients with the same blood pressure levels ignores the benefit of treatment. It assumes that a blood pressure attained on medication is the same as an untreated blood pressure.31
Bias may have entered our analysis of incidence through the "healthy survivor effect," since to be defined as a LTS hypertensive patient, the subject had to be alive and had to attend the examination at the end of his or her cohort's first 10-year follow-up period. If more of the untreated patients died of CVD before the end of this first period and were therefore excluded from the analysis of incidence, our finding of no difference in incidence between the two groups underestimates the protective effect of long-term treatment.
The decline in cardiovascular mortality among men and women in this study was concomitant with increased treatment of LTS hypertension. Because of small sample size in each cohort, we combined the cohorts for the statistical analysis of mortality. Whether in doing so we overestimated the effect of treatment or whether, as has been suggested,28 32 there was a causal relation between hypertension treatment and the decline in cardiovascular mortality cannot be definitively answered through these analyses.
| Selected Abbreviations and Acronyms |
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| Acknowledgments |
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| Footnotes |
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Received August 14, 1995; revision received October 26, 1995; accepted October 31, 1995.
| References |
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