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Michael W Muscholl a Klinik und Poliklinik für Innere Medizin II,
University of Regensburg, D-93042 Regensburg, Germany, b Institut für
Epidemiologie und Sozialmedizin, University of Münster, Münster,
Germany, c Institut für
Epidemiologie, GSF Forschungszentrum, Munich-Neuherberg, Germany
Correspondence to: Dr Schunkert
heribert.schunkert{at}klinik.uni-regensburg.de
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Abstract |
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Objectives: To assess the relation between white coat
hypertension and alterations of left ventricular structure and
function.
Design: Cross sectional survey.
Setting: Augsburg, Germany.
Subjects: 1677 subjects, aged 25 to 74 years, who
participated in an echocardiographic substudy of the monitoring of trends and determinants in cardiovascular disease Augsburg study during
1994-5.
Outcome measures: Blood pressure measurements and M
mode, two dimensional, and Doppler echocardiography. After at least 30 minutes' rest blood pressure was measured three times by a technician,
and once by a physician after echocardiography. Subjects were
classified as normotensive (technician <140/90 mm Hg, physician <160/95 mm Hg; n=849), white coat hypertensive (technician
<140/90 mm Hg, physician
160/95 mm Hg; n=160), mildly
hypertensive (technician
140/90 mm Hg, physician <160/95 mm Hg;
n=129), and sustained hypertensive (taking antihypertensive drugs or
blood pressure measured by a technican
140/90 mm Hg, and physician
160/95 mm Hg; n=538).
Results: White coat hypertension was more common in
men than women (10.9% versus 8.2% respectively) and positively related to age and body mass index. After adjustment for these variables, white coat hypertension was associated with an increase in
left ventricular mass and an increased prevalence of left ventricular hypertrophy (odds ratio 1.9, 95% confidence interval 1.2 to 3.2; P=0.009) compared with normotensive patients. The increase in left
ventricular mass was secondary to significantly increased septal and
posterior wall thicknesses whereas end diastolic diameters were similar
in both groups with white coat hypertension or normotension. Additionally, the systolic white coat effect (difference between blood
pressures recorded by a technician and physician) was associated with
increased left ventricular mass and increased prevalence of left
ventricular hypertrophy (P<0.05 each). Values for systolic left
ventricular function (M mode fractional shortening) were above normal
in subjects with white coat hypertension whereas diastolic filling and
left atrial size were similar to those in normotension.
Conclusion: About 10% of the general population show
exaggerated inotropic and blood pressure responses when mildly stressed. This is associated with an increased risk of left ventricular
hypertrophy.
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Key messages
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Introduction |
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A physical examination by a physician may cause a rise in the patient's blood pressure. Individuals showing such responses are considered to have white coat hypertension if their blood pressure reaches a hypertensive level when measured in the doctor's practice but remains normal in an informal setting.1 The clinical implications of white coat hypertension are unclear and the subject of an ongoing debate.2 Compared with patients with sustained hypertension, individuals with white coat hypertension have less end organ damage 3 4 and a better prognosis.5 It should not, however, be assumed that white coat hypertension is similar to normotension and therefore harmless to the heart.6 In fact more recent studies including larger numbers of normotensive individuals have raised doubts about white coat hypertension as a benign condition.7-10 This is supported by an epidemiological study that showed an unfavourable risk profile in young adults with white coat hypertension including a high prevalence of familial, haemodynamic, and metabolic risk factors.11
Cardiac structure and function in subjects with white coat hypertension have not been studied at a population based level. Previous studies on this topic are not conclusive, probably because (a) the study population was small, 12 13 (b) analyses did not adjust for anthropometric characteristics of subjects with white coat hypertension, and, (c) different definitions of white coat hypertension were used. 3 4 6 8-10 Perhaps most importantly these studies did not address the risk of left ventricular hypertrophy in patients with white coat hypertension. As echocardiographic evidence of left ventricular hypertrophy is an independent predictor of overall mortality,14 it has been proposed as a pathophysiological marker for white coat hypertension.2 We investigated the association of white coat hypertension with left ventricular hypertrophy, and echocardiographic variables of left ventricular systolic and diastolic function, in a population based setting.
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Subjects and methods |
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Augsburg study
The monitoring of trends and determinants in cardiovascular
disease (MONICA) Augsburg study was conducted as part of the
international collaborative World Health Organisation MONICA project.
This study investigated cardiovascular risk factors of randomly
selected subjects from Augsburg in cross sectional
surveys.15 We performed echocardiographic examinations in
845 men and 832 women, aged 25 to 74 years, who participated in an
echocardiographic substudy of the third Augsburg survey during 1994-5 (participation rate 70.6%).
140/90 mm Hg when measured by a technician and
<160/95 mm Hg when measured by a physician, and subjects as white
coat hypertensive if their blood pressure was <140/90 mm Hg when
measured by a technician and systolic or diastolic blood pressure was
160/95 mm Hg when measured by a physician. Subjects were classed as
sustained hypertensive if they were taking an antihypertensive drug or
had a systolic or diastolic blood pressure
140/90 mm Hg when
measured by a technician and
160/95 mm Hg when measured by a
physician.
Echocardiography
Two dimensional and two dimensionally guided M mode
echocardiography (Hewlett Packard, Sonos 1500, Andover, MA) were
performed on each subject by two sonographers with a 2.5 or 3.5 MHz
transducer. M mode tracings were recorded at 50 mm/s. M mode
echocardiograms were only suitable for analysis in 1404 (84%)
participants. To reduce interobserver variability all M mode tracings
were analysed by a single cardiologist. Measurements of left
ventricular mass were taken just below the tips of the mitral valve.
Internal end diastolic and end systolic diameters and septal and
posterior wall thicknesses of the left ventricle were measured
according to the guidelines of the Penn convention.19
Relative wall thickness was calculated at end diastole as the ratio of
2 × (posterior wall thickness/end diastolic diameter). Left
ventricular mass was calculated according to the formula of Penn as
left ventricular mass (g)=1.04 ((end diastolic diameter+septal wall
thickness+posterior wall thickness)3
(end diastolic
diameter)3)
13.6 g.17 Left ventricular mass
was indexed to height in grams per metre.20 Left
ventricular hypertrophy was defined as a left ventricular mass
>138 g/m for men and >106 g/m for women. These partition values are
close to the Framingham criteria and represent 2 SDs above the mean of
healthy subjects in the Augsburg echocardiographic substudy of MONICA.
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Statistical methods
Crude baseline data in each hypertensive group were compared with
normotensive subjects, and the statistical significance of differences
assessed by unpaired t tests. The mean values of echocardiographic variables in the three hypertensive groups were compared with normotensive subjects after adjustment for the covariates of age, sex, and body mass index in multiple linear regression analyses. Other factors such as physical activity, alcohol consumption, and diabetes mellitus had no major impact on left ventricular mass and
were excluded from further analyses. Hypertensive groups were included
as a four level class variable, and adjusted means obtained with
PROC GLM (version 6.11, SAS Institute, Cary, NC). Means for
variables of diastolic filling were additionally adjusted for heart
rate. Differences in cardiac size were further analysed for magnitude
of the white coat effect. Multiple logistic regression was applied to
estimate the odds ratio of left ventricular hypertrophy in hypertensive
groups compared with the normotensive group. P values <0.05 were
considered statistically significant.
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Results |
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Anthropometry
Table 1 and the figure show the anthropometric data and mean
technician and physician blood pressure measurements for the blood
pressure groups. Subjects were classed as white coat hypertensive if
they had normotensive blood pressure measurements when taken by a
technician and hypertensive measurements when taken by a physician.
Although both systolic and diastolic blood pressures measured by a
technician were in the normotensive range they were slightly higher in
subjects with white coat hypertension compared with normotensive
individuals. Mean technician and physician blood pressure readings were
similar in men and women. Compared with normotensive subjects, patients
with hypertension, and white coat hypertension in particular, were
older and had high body mass indices. Furthermore, more men than women
had white coat hypertension or mild hypertension, and more women than
men had normotension. Consequently, the prevalence of white coat
hypertension was higher in men than in women in this cross sectional
sample (10.9% versus 8.2%; P<0.01).
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Cardiac structure
Because of variations in anthropometry between the blood pressure
groups, structural and functional variables of the left ventricle were
adjusted for age, sex, and body mass index to analyse whether
differences were related to blood pressure groups independently of
these potential confounders (table 2). Analyses showed that subjects
with white coat hypertension or sustained hypertension had increased
left ventricular mass indices. The increase in cardiac mass in subjects
with white coat hypertension (7.0 g/m, 95% confidence interval 1.8 to
12.2; P=0.009) was similar for both sexes (data not shown) and due to
an increase of left ventricular septal (0.4 mm, 0.2 to 0.7; P=0.004)
and posterior (0.4 mm, 0.2 to 0.6; P=0.001) wall thicknesses. Diastolic
diameters of the left ventricle were similar in all blood pressure
groups; accordingly, relative wall thicknesses were increased in the
hypertensive groups.
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Systolic function of the left ventricle,
assessed by M mode fractional shortening, was within normal limits for
both sexes in each blood pressure group. Fractional shortening was,
however, enhanced in subjects with white coat hypertension (1.3%, 0.2 to 2.4; P=0.017) (table 2). In the white coat hypertensive group significantly increased fractional shortening persisted after adjustment for age, sex, and body mass index, and systolic blood pressure measured by a technician (table 3). However, a systolic or
diastolic white coat effect of 10 mm Hg was not associated with a
significant increase in fractional shortening (data not shown).
Diastolic filling
Compared to normotensive or mildly
hypertensive subjects, variables of diastolic filling were similar in
subjects with white coat hypertension when adjusted for sex, age, and
body mass index (table 2). In contrast, subjects with sustained
hypertension had a prolonged isovolumetric relaxation time and a
decreased E/A ratio due to an increase in atrial filling velocity
(table 2). An increase of 10 mm Hg for systolic or diastolic white
coat effects had no impact on variables of diastolic filling (data not
shown).
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Discussion |
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An exaggerated rise in a patient's blood pressure seems to be a common phenomenon after an echocardiographic examination by a physician. This response to mild stress was found to be related to structural alterations of the heart including a significant increase in left ventricular mass and an increased prevalence of left ventricular hypertrophy. Moreover, the extent of blood pressure rise seems to be independently associated with left ventricular mass and left ventricular hypertrophy.
As previous studies have shown that left ventricular hypertrophy may lead to increased morbidity and mortality in both patients with uncomplicated essential hypertension and the general population,20 the present data may indicate that white coat hypertension confers an increased cardiovascular risk. The increased risk of left ventricular hypertrophy may add to the poor haemodynamic and metabolic profiles reported in subjects with white coat hypertension.11 White coat hypertension has also been shown to advance frequently into sustained hypertension.7 Taken together, these data raise doubts about white coat hypertension as a benign condition.6 Rather, white coat hypertension may identify those individuals at increased risk of cardiovascular disease who may benefit from primary preventive strategies such as non-pharmacological intervention to lower blood pressure.
White coat hypertension and left ventricular mass
Our study does not explain the underlying mechanism between white
coat hypertension and left ventricular hypertrophy, but the literature
does provide substantial evidence for left ventricular hypertrophy not
being confined to subjects with sustained
hypertension.
24 25
In fact, transient increases in blood
pressure, such as during physical exercise, may have an independent
effect on left ventricular mass.26 One study in dogs
showed that concentric left ventricular hypertrophy could be produced
by intermittently compressing the dogs' hindlimbs to increase blood
pressure.27 Likewise, in our study relative wall thickness
was increased in subjects with white coat hypertension suggesting the
predominance of a concentric pattern of hypertrophy. Furthermore,
experimental studies have shown that short episodes of cardiac pressure
overload are sufficient to induce growth related genes and protein
synthesis in the heart.28 Thus it may be speculated that
intermittent blood pressure spikes caused by exaggerated responses to
mild stress may augment mechanisms of cardiac growth and thus the risk
of hypertrophy.
White coat effect and left ventricular mass
To further analyse this hypothesis, we correlated the white coat
effect
that is, the absolute difference in systolic or diastolic blood
pressure as measured by a technician and physician
with variables of
cardiac mass and function. The association between white coat effect
and left ventricular mass persisted after adjustment for age, sex, body
mass index, and blood pressure levels as measured by a technician. Thus
the rise in blood pressure in a situation of mild stress may be as
informative as the diagnosis of white coat hypertension. This finding
is highly relevant as the term white coat hypertension lacks defined
diagnostic criteria.2 Most clinical investigators have
contrasted ambulatory blood pressure measurements taken automatically
with those taken by the physician,2 whereas population
based surveys have contrasted blood pressure measurements taken by
a nurse,29 or self measurements,7 with measurements taken by a physician. Neither ambulatory blood pressure measurements nor those taken in the doctor's practice have been performed uniformly,2 and definitions of the upper normal
limits of daytime blood pressure or physician blood pressure in white coat hypertensive subjects greatly vary between studies.2
As a result some investigators have proposed that the association between left ventricular mass and white coat hypertension is largely affected by cut off points of baseline blood pressure.2
Our study of a large sample size does not concur with this as it shows that a rise in blood pressure by itself is related to left ventricular hypertrophy. We used a standardised triple sphygmomanometric
measurement to assess baseline systolic and diastolic blood pressure
values after an extensive resting period. These values were compared with a single sphygmomanometric measurement taken by a physician within 60 minutes of the baseline measurement. We believe this method
validly reflects the individual's blood pressure response to mild
stress and avoids misinterpretations caused by diurnal blood pressure
variation and different measurement techniques.
Potential limitations
Our study may be challenged as baseline systolic and diastolic
blood pressure measurements were already higher in the white coat
hypertensive patients compared with normotensive subjects. Previous
investigators have made similar observations.
4 8-10 30
As even a slightly higher blood pressure than normal may result in a
chronic increase in haemodynamic load of the heart26 it may be hypothesised that the increase in left ventricular mass in the
white coat hypertensive group is exclusively related to differences in
baseline blood pressure rather than related to the white coat effect.
However, in contrast to previous studies we corrected for the baseline
(technician) blood pressure by multivariate analysis. We also observed
that the white coat effect was related to left ventricular mass and
hypertrophy independent of differences in baseline blood pressure. We
therefore believe that stress related increases in blood pressure can
be regarded as an independent determinant of left ventricular mass.
White coat hypertension and left ventricular function
Our study agrees with previous investigations of reported normal
left ventricular systolic function in subjects with white coat
hypertension.26 In fact we observed left ventricular
function slightly above normal in the white coat hypertensive group. It may be hypothesised that in addition to reduced peripheral arterial compliance,13 enhanced left ventricular contractility may
contribute to the increase in blood pressure observed in white coat
hypertensive patients. The findings are consistent with enhanced
activity or sensitivity, or both, of the sympathetic nervous system
resulting in increases in blood pressure and augmented left ventricular contractility during mild stress. We were, however, unable to detect
any independent association between white coat hypertension and
variables of diastolic filling or left atrial size.
Conclusion
Our study shows that white coat hypertension is common in the
general population and that it may be associated with an increased risk
of left ventricular hypertrophy and concentric remodelling of the
heart. It would seem premature to dismiss white coat hypertension as a
benign variant of blood pressure regulation, rather it may indicate the
need for intensified monitoring and control of cardiovascular risk
factors.
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Acknowledgments |
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Contributors: MWM, H-WH, UB, AD, GAJR, and HS conceived and designed the study, collected, analysed, and interpreted the data, and helped draft and revise the manuscript. MWM will act as guarantor for the paper.
Funding: The investigation was supported by grants from the Deutsche Forschungsgemeinschaft (672/3-1, 672/9-1, and 672/10-1) and the Bundesministerium für Forschung und Technologie (HS and HWH). This paper was presented in part at the 46th scientific sessions of the American College of Cardiology.
Conflict of interest: None.
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References |
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(Accepted 13 May 1998)
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