Original Articles

Original Articles
Appropriate Time Interval to Repeat Ambulatory Blood
Pressure Monitoring in Patients With White-Coat
Resistant Hypertension
Elizabeth S. Muxfeldt, Roberto Fiszman, Fabio de Souza, Bianca Viegas,
Fernanda C. Oliveira, Gil F. Salles
Abstract—Resistant hypertension is defined as uncontrolled office blood pressure, despite the use of ⱖ3 antihypertensive
drugs. Ambulatory blood pressure monitoring (ABPM) is mandatory to diagnose 2 different groups, those with true and
white-coat resistant hypertension. Patients are found to change categories between controlled/uncontrolled ambulatory
pressures without changing their office blood pressures. In this way, ABPM should be periodically repeated. The aim
of this study was to evaluate the most appropriate time interval to repeat ABPM to assure sustained blood pressure
control in patients with white-coat resistant hypertension. This prospective study enrolled 198 patients (69% women;
mean age: 68.9⫾9.9 years) diagnosed as white-coat resistant hypertension on ABPM. Patients were submitted to a
second confirmatory examination 3 months later and repeated twice at 6-month intervals. Statistical analyses included
Bland-Altman repeatability coefficients and multivariate logistic regression. Mean office blood pressure was 163⫾20/
84⫾17 mm Hg, and mean 24-hour blood pressure was 118⫾8/66⫾7 mm Hg. White-coat resistant hypertension
diagnosis presented a moderate reproducibility and was confirmed in 144 patients after 3 months. In the third and fourth
ABPMs, 74% and 79% of patients sustained the diagnosis. In multivariate regression, a daytime systolic blood pressure
ⱕ115 mm Hg in the confirmatory ABPM triplicated the chance of white-coat resistant hypertension status persistence
after 1 year. In conclusion, a confirmatory ABPM is necessary after 3 months of the first white-coat–resistant
hypertension diagnosis, and the procedure should be repeated at 6-month intervals, except in patients with daytime
systolic blood pressure ⱕ115 mm Hg, in whom it may be repeated annually. (Hypertension. 2012;59[part 2]:384-389.)
Key Words: ambulatory blood pressure monitoring 䡲 resistant hypertension 䡲 white-coat effect 䡲 reproducibility
R
esistant hypertension (RH) is defined as an uncontrolled
office blood pressure (BP), despite the use of an optimal
regimen with ⱖ3 antihypertensive drugs, ideally including a
diuretic.1 Even with a reported prevalence as high as 30% of
general hypertensives,1– 4 RH is still an understudied clinical
condition with a high cardiovascular morbidity and mortality,1,5 in whom the performance of ambulatory BP monitoring
(ABPM) is well established to guide diagnosis,1,2,4,6 – 8
therapy,9 and prognosis.5,10 –12 The ABPM classifies RH
patients into 2 groups, true (uncontrolled) RH (office BP
ⱖ140/90 mm Hg and 24-hour BP ⱖ130/80 mm Hg) and
white-coat (controlled) RH (WC-RH; office BP ⱖ140/
90 mm Hg and 24-hour BP ⬍130/80 mm Hg).6 The prevalence of WC-RH varies in different series, reaching 40%
of all RH patients.1,6,7,12,13
In patients with white-coat hypertension (WCH), it is
advisable to confirm this diagnosis by repeating ABPM
within 3 to 6 months.8 Although the diagnosis of WCH was
shown to be reasonably reproducible in a median interval
between 2 ABPMs of 1.5 years,14 there is no evidence in the
literature about the reproducibility on the needs of this
confirmatory ABPM in patients with WC-RH. Furthermore,
WC-RH had been demonstrated to have a lower cardiovascular risk than true RH,5 but resistant hypertensives are found
to change status between white-coat/true RH without changing office BPs. Therefore, the aim of this study was to
evaluate the most appropriate time interval to repeat ABPM
to assure persistence of BP control in resistant hypertensives
with a first ABPM diagnosis of white-coat RH.
Methods
Subjects and Baseline Procedures
This was a longitudinal observational study with 198 consecutive
patients diagnosed as WC-RH on the first ABPM, enrolled from
January 2006 to May 2010, entering a cohort of resistant hypertensive patients in the hypertension outpatient clinic of a university
hospital. All of the participants gave a written informed consent, and
the local ethics committee had previously approved the study
protocol. Compliance to antihypertensive treatment was evaluated in
the first interview by a validated standard questionnaire.15 Only
patients considered moderate or highly adherent to treatment were
Received October 10, 2011; first decision October 25, 2011; revision accepted November 30, 2011.
From the Department of Internal Medicine, University Hospital Clementino Fraga Filho, Medical School, Federal University of Rio de Janeiro, Rio
de Janeiro, Brazil.
Correspondence to Elizabeth S. Muxfeldt, Rua Homem de Melo, 150/102 Tijuca, Rio de Janeiro-RJ, Brazil. E-mail [email protected]
© 2012 American Heart Association, Inc.
Hypertension is available at http://hyper.ahajournals.org
DOI: 10.1161/HYPERTENSIONAHA.111.185405
384
Muxfeldt et al
PATIENTS DIAGNOSED AS RESISTANT HYPERTENSION
1st phase
ABPM Time Interval in White-Coat RH
Table 1. Baseline Characteristics and BP Measurements in
Patients Grouped According to the Diagnosis of White-Coat or
True RH on the Confirmatory ABPM
White-coat RH diagnosis in the 1st ABPM
(N=198)
3 months
54 true RH (27.3%)
2nd phase
136 (68.7)
Body mass index, kg/m
Third ABPM
(N=144)
6 months
12 missing
17 true RH (20.7%)
Sex, % women
2
6 months
17 missing
33 true RH (26.0%)
Characteristics
All Patients
(n⫽198)
Age, y
Second ABPM
Fourth ABPM
((N=94))
Figure 1. The flowchart of the study.
enrolled. In clinical interview, demographic and anthropometric
characteristics (sex, age, race, weight, height, and waist circumference), cardiovascular risk factors (diabetes mellitus, dyslipidemia,
smoking, physical inactivity, and obesity), and target-organ damage
(coronary heart disease, heart failure, cerebrovascular disease, advanced retinopathy, and peripheral arterial disease) were recorded.2
BP Measurements
Office BP was measured twice in the sitting position by the assisting
physician using a digital oscillometric BP monitor (HEM-907 XL,
Omron Healthcare, Kyoto, Japan) with a suitably sized cuff, and the
BP considered was the mean between the 2 readings.2 ABPM was
recorded using Mobil-O-Graph (version 12, DynaMAPA, Cardios,
São Paulo, Brazil) equipment, approved by the British Society of
Hypertension.16 Readings were taken every 15 minutes throughout
the day and every 30 minutes at night. The procedure was considered
satisfactory if at least two thirds of systolic (SBP) and diastolic BP
(DBP) measurements during the daytime and nighttime periods were
recorded. ABPM with no valid readings for ⱖ2 hours were also
excluded from the analysis.8 Parameters evaluated were mean
24-hour, daytime, and nighttime SBP and DBP, as well as the
magnitude of the white-coat effect (WCE), estimated as the difference between office and ambulatory daytime measurements. The
nighttime period was ascertained for each individual patient from
registered diaries. All of the patients used their prescribed antihypertensive medications during ABPM. After ABPM, patients were
classified as white-coat RH if mean 24-hour BP was ⬍130/
80 mm Hg.1,6 Daytime BP was considered controlled if ⬍135/
85 mm Hg and nighttime BP if ⬍120/70 mm Hg.8
The study was divided into 2 phases (Figure 1). At the first phase,
all of the patients diagnosed as WC-RH repeated ABPM after 3
months to confirm the diagnosis. On the second phase, all of the
patients with confirmed WC-RH diagnosis repeated the procedure
twice in intervals of 6 months. All of the patients used the same
antihypertensive therapeutic regimen during the whole study. Patients who became true RH on any follow-up ABPM had their
antihypertensive treatment immediately intensified and were
dropped out from the following ABPMs.
Patients With
Confirmed
WC-RH
(n⫽144)
97 (67.4)
Patients
With True
RH (n⫽54)
39 (72.2)
P
0.32
68.9 (9.8)
70.0 (9.4)
66.1 (10.7)
0.014
29.3 (5.0)
28.8 (4.7)
29.0 (5.2)
0.85
Diabetes mellitus, %
68 (34.3)
44 (30.6)
24 (44.4)
Current smoking, %
12 (6.1)
5 (3.5)
7 (13.0)
0.02
Dyslipidemia, %
150 (75.8)
107 (74.3)
43 (79.6)
0.28
Physical inactivity, %
0.049
128 (64.6)
95 (66.0)
33 (61.1)
0.32
Coronary heart disease,
%
51 (25.8)
36 (25.0)
15 (27.8)
0.41
Cerebrovascular disease,
%
27 (13.6)
18 (12.5)
9 (16.7)
0.29
7 (3.5)
4 (2.8)
3 (5.6)
0.29
27 (13.6)
20 (13.9)
7 (13.0)
0.54
4 (3–7)
4 (3–7)
4 (3–7)
0.81
Heart failure, %
Peripheral arterial
disease, %
65 patients sustained
white-coat RH diagnosis
385
No. of antihypertensive
drugs
Office SBP, mm Hg
163 (20)
161 (19)
168 (22)
0.04
Office DBP, mm Hg
84 (17)
82 (16)
88 (19)
0.04
24-h SBP, mm Hg
118 (8)
117 (8)
121 (7)
0.001
24-h DBP, mm Hg
66 (7)
66 (7)
68 (8)
0.036
Daytime SBP, mm Hg
120 (9)
119 (9)
123 (9)
0.003
Daytime DBP, mm Hg
68 (8)
67 (8)
70 (9)
0.041
Nighttime SBP, mm Hg
108 (11)
107 (12)
112 (8)
0.002
Nighttime DBP, mm Hg
60 (7)
59 (7)
61 (7)
0.06
Values are mean (SD) or proportion, except No. of antihypertensive drugs
that are median (range). WC-RH indicates white-coat resistant hypertension;
RH, resistant hypertension; SBP, systolic blood pressure; DBP, diastolic blood
pressure; BP, blood pressure; ABPM, ambulatory blood pressure monitoring.
Statistical Analysis
The statistical analyses were performed in SPSS 19.0. Continuous
variables were described as means (SDs) when normally distributed
or as medians (range) when asymmetrically distributed. The first
phase of the study evaluated the reproducibility of the diagnosis of
WC-RH in the first 2 ABPM exams. The use of correlation
coefficients for this purpose is misleading.17 So, we used the Bland
and Altman graphic approach and calculated the repeatability coefficients (twice the SDs of the differences between duplicate measurements)17 for office and ambulatory BPs and for the magnitude of
systolic and diastolic WCEs. The repeatability coefficients were also
expressed as a percentage of nearly maximal variation, that is, the
interval encompassing 4 times the SD of the averaged duplicate
measurements.17,18 Patients who confirmed or not the diagnosis of
WC-RH on the second ABPM were compared by unpaired t test,
Mann-Whitney test, or ␹2 test, when appropriate. The second phase
of the study evaluated who among those with confirmed WC-RH
would sustain this diagnosis after 2 additional ABPMs performed at
6-month intervals and which were the office and ambulatory BP
cutoff values on the confirmatory ABPM that best predict the
persistence of the WC-RH diagnosis after 1 year. BP measurements
on the second ABPM were compared between patients who sustained or not the WC-RH diagnosis at the end of the study by
unpaired t test. Office and ambulatory SBPs and DBPs of the second
ABPM (the confirmatory one) were categorized at the mean BP
386
Hypertension
February 2012, Part 2
Table 2. SBPs and DBPs and Magnitude of the WCE of the First and the Second ABPMs and Repeatability
Coefficient Between the 2 Exams
BPs
First ABPM
Second ABPM
SBP, mm Hg
163 (20)
157 (19)
DBP, mm Hg
84 (17)
80 (14)
Bland-Altman Repeatability
Coefficient
% of Near Maximal
Variability
0,30*
47
64
0.52*
31
56
Correlation Coefficient
Office BP
Average 24-h BP
SBP, mm Hg
118 (8)
123 (13)
0.44*
24
36
DBP, mm Hg
66 (7)
69 (10)
0.66*
15
32
SBP, mm Hg
120 (9)
125 (14)
0.44*
26
39
DBP, mm Hg
68 (8)
71 (11)
0.64*
17
34
SBP, mm Hg
108 (11)
115 (14)
0.29*
30
41
DBP, mm Hg
60 (7)
63 (10)
0.57*
17
30
SBP, mm Hg
46 (21)
35 (22)
0.22†
53
67
DBP, mm Hg
18 (15)
11 (14)
0.25*
35
45
Average daytime BP
Average nighttime BP
Magnitude of WCE
Values are mean (SD). BP indicates blood pressure; ABPM, ambulatory blood pressure monitoring; SBP, systolic blood pressure;
DBP, diastolic blood pressure; WCE, white-coat effect (difference between office and daytime BP).
*P⬍0.001.
†P⬍0.01.
value found in patients who sustained WC-RH diagnosis at the end
of the study, office SBP and DBP (155 and 80 mm Hg, respectively)
and ambulatory SBP and DBP (24-hour BP: 115 and 65 mm Hg;
daytime BP: 115 and 65 mm Hg; nighttime BP: 105 and 60 mm Hg,
respectively). Multivariate logistic regression analysis was performed to evaluate the association of each BP measurement and the
diagnosis of WC-RH at the end of the study (the dependent variable).
It was adjusted for age, sex, and number of antihypertensive drugs in
use, which is a surrogate for hypertension severity.
Results
At the first phase, 198 patients (68.7% women; mean age:
68.9 years; SD: 9.8 years) with a first ABPM diagnosis of
WC-RH were included in the study, and 144 (73%) confirmed the WC-RH status on a second ABPM performed 3
months later (Figure 1). From the 54 patients with true RH on
the second ABPM, 9% had isolated daytime hypertension,
37% had isolated nocturnal hypertension, and 54% had both
daytime and nighttime uncontrolled hypertension. The baseline characteristics of patients grouped according to the
diagnosis of WC-RH or true RH on the confirmatory second
ABPM are outlined in Table 1. Patients who became true RH
were younger, more frequently diabetics and current smokers,
and had higher office and ambulatory BPs than those with
confirmed WC-RH.
The second ABPM presented higher mean BPs in the 3
periods but lower office BPs and, consequently, lower extent
of the WCE in comparison with the first ABPM (Table 2).
Figure 2 showed Bland and Altman graphics for 24-hour BP.
The second ABPM had a mean 5-mm Hg higher 24-hour SBP
(95% of the differences were between ⫺19 and 29 mm Hg [2
SDs]) and a 3-mm Hg higher 24-hour DBP (95% of the
differences: ⫺13 and 18 mm Hg). As determined by correlation coefficients, SBPs were less reproducible than DBPs,
and the magnitude of WCEs showed a poor reproducibility.
However, correlation coefficients may not accurately assess
reproducibility.17,18 Assessing the agreement between the 2
exams with Bland-Altman repeatability coefficients corrected
for near-maximal variability, both SBPs and DBPs presented
moderate agreement between the first and second ABPMs. A
lower reproducibility was observed in the magnitude of
systolic WCEs, similar to office BPs (Table 2). Very low and
nonsignificant correlations between differences and mean
values of 24-hour SBPs and DBPs were found (0.034 for
SBP, P⫽0.63, and ⫺0.066 for DBP, P⫽0.35).
A total of 144 patients continued on the second phase. In
the third and fourth ABPMs, 74% and 79% of patients
sustained the WC-RH diagnosis, respectively. Twenty-nine
patients did not perform 1 of the follow-up ABPMs (Figure 1). These patients had lower prevalence of dyslipidemia
and physical inactivity, but they had other characteristics
similar to those who completed the study, including office
and ambulatory BPs (data not shown). Patients who sustained
the WC-RH diagnosis on the fourth ABPM had lower office
and ambulatory SBPs on the confirmatory ABPM than those
who became true RH (Table 3). Number and class of
antihypertensive drugs in use were the same during the whole
study. In multivariate regression analysis, we found that a
daytime SBP ⱕ115 mm Hg in the confirmatory second
ABPM was the best predictor of WC-RH status persistence; its
presence triplicated the chance of WC-RH persistence after 1
year (Table 4). Based on these results we proposed an algorithm
to guide the follow-up of WC-RH patients (Figure 3).
Discussion
The main finding of our study is the proposal of an algorithm
with great clinical applicability to follow-up white-coat re-
Muxfeldt et al
40
SBP differences
387
Table 3. Comparisons of BP Measurements on the
Confirmatory ABPM in Patients Who Persisted or Not With
WC-RH at the End of the Study
A
Patients Who
Persisted
WC-RH (n⫽65)
Patients Who
Became True
RH (n⫽50)
P
Office SBP, mm Hg
156 (17)
162 (18)
0.04
Office DBP, mm Hg
79 (16)
80 (13)
Mean + 2SD
20
BP Parameters
Mean
0
-20
Mean - 2SD
Difference SBP mean = 5.16 ± 12.14
90
100
110
120
130
140
0.81
24-h SBP, mm Hg
115 (9)
119 (7)
0.004
24-h DBP, mm Hg
64 (7)
66 (7)
0.12
Daytime SBP, mm Hg
117 (10)
122 (8)
0.002
Daytime DBP, mm Hg
66 (7)
68 (8)
0.09
Nighttime SBP, mm Hg
106 (8)
109 (8)
0.03
Nighttime DBP, mm Hg
58 (7)
61 (8)
0.14
Values are mean (SD). BP indicates blood pressure; WC-RH, white-coat
resistant hypertension; RH, resistant hypertension; SBP, systolic blood pressure; DBP, diastolic blood pressure; ABPM, ambulatory blood pressure
monitoring.
24-hour SBP means
B
ABPM Time Interval in White-Coat RH
40
DBP differences
30
20
Mean + 2SD
10
0
Mean
-10
Mean - 2SD
-20
Difference DBP mean = 2.68 ± 7.70
40
50
60
70
80
90
24-hour DBP means
Figure 2. Bland-Altman scatter plot of repeatability of 24-hour
systolic blood pressure (SBP; A) and diastolic blood pressure
(DBP; B) measured on 2 ambulatory blood pressure monitoring
(ABPM) exams performed 3 months apart.
sistant hypertensives, an understudied subgroup of patients,
for ascertaining the persistence of optimal BP control. A
confirmatory ABPM is necessary after at most 3 months of
the first diagnosis, and the procedure should be repeated at
every 6-month intervals, except in patients with daytime SBP
ⱕ115 mm Hg, who can repeat it annually. Moreover, more
than half of the patients with a first ABPM diagnosis of
white-coat RH became true RH after a 15-month period,
indicating that white-coat RH patients should not be considered less severe hypertensives but at high risk of developing
true RH over a relatively short time period.
The WCE was described in 1983 as a phenomenon that
occurs in normotensive and hypertensive subjects when BP
increases immediately in the presence of a doctor. Large
differences between individuals were observed, and the
repeated visits with the same doctor did not seem to attenuate
the pressure response.19 The physiological, psychological,
and behavioral factors involved in the white-coat phenomenon are still controversial.2,20 The prevalence of the WCE
ranges from 18% to 60% according to different definitions,2,21–23 and many studies showed that WCH has lower
cardiovascular risk than sustained hypertension but higher
than sustained normotensives.22,24,25 Resistant hypertensive
patients have a high cardiovascular risk5,10 –12 and usually
present a large magnitude of the WCE, reaching
ⱕ50 mm Hg,7 and also a high prevalence of masked hypertension,26 emphasizing the need to repeat ABPM frequently
to ensure BP control.
The principal question to establish the clinical significance
of the WCE is defining whether it is a persistent condition or
whether it becomes attenuated over time. In some studies, a
progressive reduction of office BP was observed and consequently a decrease in the WCE,21,27–29 suggesting that isolated
office hypertension could be only a transitional prehypertensive state.28 Otherwise, in a longitudinal study with a median
follow-up of 2.5 years evaluating 83 individuals with WCH,
37% shifted to the ambulatory hypertension category without
changing office BPs but increasing left ventricular mass.25
Similar to our study, the principal determinant of progression
to uncontrolled ambulatory hypertension was average daytime BP levels.25 However, it was suggested that these
findings may merely be a regression toward the mean and that
the definition of WCH is subject to selection bias.30 In this
study, 90 patients with WCH underwent 2 ABPMs 3 months
Table 4. Multivariate Logistic Regression Analysis for
Ambulatory Blood Pressure Monitoring Parameters Associated
With Persistence of the White-Coat Resistant Hypertension
Diagnosis After 1 y
Covariates
OR
95% CI
P
Female sex
0.76
0.32–1.77
0.51
Age, y
1.02
0.98–1.06
0.40
No. of antihypertensive drugs
0.76
0.48–1.20
0.25
Office SBP ⱕ155 mm Hg
2.19
0.97–4.96
0.06
24-h SBP ⱕ115 mm Hg
2.15
0.11–3.92
0.64
Daytime SBP ⱕ115 mm Hg
3.19
1.36–7.46
0.007
Nighttime SBP ⱕ105 mm Hg
1.88
0.73–4.90
0.19
OR indicates odds ratio; SBP, systolic blood pressure.
388
Hypertension
February 2012, Part 2
most 3 months and repeating the procedure afterward in short
intervals of 6 months for most of resistant hypertensive
patients, except for those with low daytime SBP levels (ⱕ
115 mm Hg), who can repeat ABPM on an annual basis.
RESISTANT HYPERTENSION
ABPM
True RH
White-coat RH
Perspectives
3 months
Confirmatory ABPM
True RH
White-coat RH
Daytime SBP > 115 mm Hg
Daytime SBP < 115 mm Hg
Repeat ABPM in 6 months
Repeat ABPM yearly
Figure 3. Algorithm for follow-up of patients with white-coat resistant hypertension.
This study provides a useful algorithm to guide clinical
practice on the appropriate diagnostic and therapeutic approach for white-coat RH patients to assuring sustained
ambulatory BP control. However, repeating ABPM periodically is costly and uncomfortable for patients, resulting in low
cost-effectiveness and low acceptance. So, other methods of
out-of-office BP assessment should be evaluated in RH
management, such as home BP monitoring. Furthermore,
serial changes in office and ambulatory BPs during follow-up
of RH patients should be addressed in future prospective
studies to evaluate whether this tight BP control in WC-RH
patients would translate into better cardiovascular outcomes.
Sources of Funding
apart, and 58% became sustained hypertensives. Office SBP
and DBP decreased, respectively, 5 and 3 mm Hg, whereas
24-hour SBP and DBP rose by 4 and 3 mm Hg. These
findings are similar to ours (Table 2). In another retrospective
study,14 196 subjects underwent repeated ABPM for clinical
indications, with a mean interval of 1.5 years; WCH was
diagnosed in 31 individuals in first ABPM, and it was
confirmed in only 14 of them. Both office and ambulatory
BPs decreased in the second ABPM and office and daytime
DBP showed good reproducibility, whereas systolic WCE
was more reproducible than office and daytime SBPs. Nevertheless, to the best of our knowledge, neither reproducibility nor ABPM follow-up of white-coat resistant hypertensives
has been evaluated before.
RH is a clinical diagnosis established in the office,1 and it
is well accepted that ABPM is mandatory after RH diagnosis
to classify patients as true or white-coat RH.1,4,6,7,13 Nevertheless, patients are found to change categories between
controlled/uncontrolled ambulatory BPs without changing
office readings, sometimes within a very short period of time,
and this issue had never been studied before. WC-RH was
first described in 1997.13 ABPM pattern in RH patients is well
established,4,6 but it is recognized that WC-RH diagnosis in
the office is not possible.7 This diagnosis is clearly important
because it avoids overtreatment, untoward drug adverse
effects; and unnecessary, costly, and sometimes invasive
investigations for secondary hypertension.1,2,6 Moreover, the
large WCE in WC-RH is also found in patients with true RH,
and it is maintained despite pharmacological therapy.4,6,7
Because the WC-RH diagnosis at baseline implied a lower
cardiovascular risk than true RH,5 it is important to assure the
adequate BP control during follow-up. In this way, it is
necessary to repeat ABPM periodically, but the most appropriate time interval to repeat the procedure should be clearly
defined to guide clinical practice. In this way, our study has
important clinical implications, showing a moderate WC-RH
diagnosis reproducibility (Table 2 and Figure 2), reinforcing
the importance of performing a confirmatory ABPM after at
This study was supported by grants from Conselho Nacional de
Desenvolvimento Científico e Tecnológico (CNPq) and Fundação
Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de
Janeiro (FAPERJ).
Disclosures
None.
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