Journal of Human Hypertension (2014) 28, 731–735 & 2014 Macmillan Publishers Limited All rights reserved 0950-9240/14 www.nature.com/jhh
How many clinic BP readings are needed to predict cardiovascular events as accurately as ambulatory BP monitoring? K Eguchi1, S Hoshide1, K Shimada2 and K Kario1 We tested the hypothesis that multiple clinic blood pressure (BP) readings over an extended baseline period would be as predictive as ambulatory BP (ABP) for cardiovascular disease (CVD). Clinic and ABP monitoring were performed in 457 hypertensive patients at baseline. Clinic BP was measured monthly and the means of the ﬁrst 3, 5 and 10 clinic BP readings were taken as the multiple clinic BP readings. The subjects were followed up, and stroke, HARD CVD, and ALL CVD events were determined as outcomes. In multivariate Cox regression analyses, ambulatory systolic BP (SBP) best predicted three outcomes independently of baseline and multiple clinic SBP readings. The mean of 10 clinic SBP readings predicted stroke (hazards ratio (HR) ¼ 1.39, 95% conﬁdence interval (CI) ¼ 1.02–1.90, P ¼ 0.04) and ALL CVD (HR ¼ 1.41, 95% CI ¼ 1.13–1.74, P ¼ 0.002) independently of baseline clinic SBP. Clinic SBPs by three and ﬁve readings were not associated with any CVD events, except that clinic SBP by three readings was associated with ALL CVD (P ¼ 0.015). Besides ABP values, the mean of the ﬁrst 10 clinic SBP values was a signiﬁcant predictor of stroke and ALL CVD events. It is important to take more than several clinic BP readings early after the baseline period for the risk stratiﬁcation of future CVD events. Journal of Human Hypertension (2014) 28, 731–735; doi:10.1038/jhh.2014.8; published online 20 February 2014 Keywords: multiple clinic BP readings; ambulatory BP; stroke; cardiovascular disease (CVD) events
INTRODUCTION Ambulatory blood pressure (ABP) has been reported to be a better predictor of hypertensive target organ damage1–3 and cardiovascular events4–9 than clinic BP. ABP monitoring (ABPM) can assess BP and its variations in daily life without white-coat effects.10 It is thus an essential tool for the management of drugresistant hypertension, hypertension with large BP variation11 and the assessment of BP levels during antihypertensive drug therapy.12 Therefore, the British Hypertension Guidelines stipulate that BP should be evaluated by ABPM before the start of therapy in order to risk stratify for hypertension.13 Clinic BP has long been the most commonly used measure for assessing BP. Most epidemiological studies14 and clinical trials of hypertension15 have adopted clinic BP measurement to evaluate BP levels. However, recent studies and guidelines have revealed several shortcomings of clinic BP, such as mechanical defects of measurement devices, inappropriate measurement methods not following ofﬁcial guidelines and the white-coat phenomenon.16,17 Recent clinical guidelines have recommended that both home BP monitoring18,19 and ABPM13,19 be employed, as home BP monitoring and ABPM are considered more predictive of cardiovascular events than clinic BP. However, most of the studies that compared clinic BP with ABPM or home BP monitoring adopted only a few clinic BP readings at baseline.4,7,9,20–22 Because BP varies throughout the day, multiple measurements of BP are important to improve the reproducibility of BP levels and the predictability of outcomes.23 Actually, one of the main reasons for the better predictability of outcomes by out-of-ofﬁce BP monitoring has been the higher numbers of BP readings in those settings. In this regard, the number of BP measurements is an
essential consideration for the appropriate evaluation of BP. Furthermore, early achievement of target BP level has been demonstrated to predict good prognosis.24 However, to the best of our knowledge, none of the reports comparing the predictive abilities of clinic BP, ABPM and home BP monitoring have used the mean of multiple clinic BP readings over an extended baseline period as the clinic BP measure. Therefore, we tested the hypothesis that the mean of multiple clinic BP values taken over several months would be able to predict a given outcome measure as effectively as ABP at baseline. MATERIALS AND METHODS This prospective study was performed in a sample of 457 asymptomatic subjects with (n ¼ 202) or without (n ¼ 255) type 2 diabetes who were seen for the evaluation of hypertension at three institutes (one clinic and two hospitals) that participated in the Karatsu–Nishiarita Study.3
Subjects and deﬁnitions The subjects and methods in this study were essentially the same as in our previous publications.11,25 Brieﬂy, hypertensive or potentially hypertensive subjects who agreed to undergo ABPM were enrolled consecutively at general internal medicine clinics in Japan. Hypertension was diagnosed when the clinic systolic BP (SBP) was X140 and/or diastolic BP was X90 mm Hg on at least two occasions according to current guidelines,16 or by a previous diagnosis of hypertension with current antihypertensive medication use. Type 2 diabetes was diagnosed according to the guidelines of the American Diabetes Association26 or by a previous diagnosis and current use of antidiabetic medication. We excluded subjects with type 1 or secondary diabetes, renal dysfunction (serum creatinine 41.9 mg dl 1), hepatic damage, ischemic heart disease or other
1 Division of Cardiovascular Medicine, Department of Medicine, Jichi Medical University School of Medicine, Tochigi, Japan and 2Department of Cardiovascular Medicine, ShinOyama City Hospital, Oyama, Japan. Correspondence: Dr K Eguchi, Division of Cardiovascular Medicine, Department of Medicine, Jichi Medical University School of Medicine, 3311-1 Shimotsuke, Tochigi, Japan. E-mail: [email protected]
Received 13 October 2013; revised 6 December 2013; accepted 6 January 2014; published online 20 February 2014
Prediction of cardiovascular events K Eguchi et al
732 cardiac diseases, congestive heart failure, arrhythmias (including atrial ﬁbrillation), stroke (including transient ischemic attacks) or other major concomitant non-cardiovascular diseases (CVDs). Body mass index was calculated as weight (kg)/height2 (m2). Smoking was deﬁned as current smoking. This study was approved by the Institutional Review Board of each participating hospital or clinic. All the subjects studied were ambulatory and gave their informed consent to participate.
Clinic BP measurement At baseline and in the follow-up periods, clinic BP was measured with a mercury sphygmomanometer. At baseline, at least two out of three clinic BP readings were taken on each of two separate occasions after at least 5 min of rest in the sitting position (a total of four readings at baseline); for subjects who had stopped medication for ABPM, these occasions included before and after being ﬁtted with an ABPM. After the baseline, clinic BP was measured once each month. At each of these measurements, clinic BP was measured three times after a 5-min rest, and the average of the second and third readings was recorded. All available BP readings were adopted for each patient.
ABP monitoring Noninvasive ABPM was performed at baseline for the evaluation of BP level and dipping patterns. No additional ABPM was performed after these baseline measurements. ABPM was performed on a weekday with an automatic system (either TM2421 or TM2425; A&D, Tokyo, Japan) that recorded BP using the oscillometric method, and pulse was recorded every 30 min for 24 h. These devices have been previously validated.27 A minimum of six valid awake readings and four valid sleep readings were required for the computation of wake and sleep averages, but all subjects had many more valid readings. A reading was accepted as valid if it was nonartifactual and within a physiological range. Awake and sleep times were deﬁned based on the subjects’ written diaries recorded during ABPM. Mean awake, sleep and 24-h levels of SBP and diastolic BP were computed.1,7,28
Follow-up and events During follow-up, standard medical treatment for hypertension was performed on the basis of current guidelines.29,30 The target clinic BP was 140/90 mm Hg, and drugs were titrated to achieve this goal. The subjects’ medical records were reviewed periodically after ABPM to identify incident CVD. Follow-up examination was performed for all participants in the Karatsu–Nishiarita Study from March 2004 to October 2007. Participants who died from non-cardiovascular causes were censored as of the time of their death. The mean follow-up period was 66±27 months. We analyzed three categories of CVD outcome—stroke, HARD CVD events and ALL CVD events—as described in our recent publication.11 Brieﬂy, stroke was diagnosed on the basis of the sudden onset of a neurological deﬁcit that persisted for 424 h in the absence of any other disease process that could explain the symptoms.7 Stroke events were diagnosed by the physician caring for the patient at the time of the event, and independent neurologists reviewed the cases and conﬁrmed the diagnosis by referrals or medical records including computed tomography scan and magnetic resonance imaging. In this study, stroke events were limited to only the ﬁrst reported stroke event. Stroke events included ischemic stroke, hemorrhagic stroke and undeﬁned types of stroke. In this study, transient ischemic attacks (TIA) in which the neurological deﬁcit cleared completely in o24 h7 were also treated as stroke events. HARD CVD events included stroke (other than TIA), fatal or nonfatal myocardial infarction and sudden cardiac death. Participants who became dependent on others for their daily living, those who died or suffered from non-cardiovascular causes (such as malignant disease, accident or neurologic disorders) and those who moved or changed their telephone number were censored as of the time each such event took place (n ¼ 26 subjects in total). ALL CVD events included the HARD CVD events plus angina requiring revascularization, congestive heart failure requiring hospitalization, end-stage renal disease with hemodialysis, peripheral artery disease conﬁrmed by objective tests such as ankle-brachial index o0.931 and transient ischemic attacks.
Statistical analyses All statistical analyses were carried out with SPSS/Windows, version 19.0 (IBM-SPSS, Armonk, NY, USA). The data are expressed as means (±s.d.) or Journal of Human Hypertension (2014) 731 – 735
as percentages. Mean clinic BP during follow-up and BP values by ABPM were tested to determine whether they could be predictors for subsequent CVD events. As baseline clinic BP values, the ﬁrst 3, 5 and 10 clinic BP readings after the ABPM were also analyzed. Baseline clinic BP readings, and BP readings after the onset of CVD events, were not included in this study. Because most of the patients were elderly and the predictability of diastolic BP was low, we analyzed only SBP in this study. Adjusted hazards ratios (HRs) with 95% conﬁdence intervals (95% CI) were based on multivariate Cox regression analysis. Because the number of CVD events was limited, age (years), sex (male ¼ 1, female ¼ 0), body mass index (kg m 2), diabetes (yes or no), serum creatinine (mg dl 1) and current smoking status (yes or no) were treated as potential covariates and controlled only if they signiﬁcantly predicted the outcome. The null hypothesis was rejected when two-tailed P o0.05.
RESULTS Table 1 shows the baseline characteristics of subjects. The mean age was 67.0±9.2 years, 38% of the subjects were male and 44% of the subjects were diabetic. The high prevalence of diabetes reﬂects the accumulation of diabetic patients in regional center hospitals. For 457 patients baseline clinic BP and ABPM data were available: there were 3 and 5 clinic BP readings for 452 patients and 10 clinic BP readings for 412 patients. The average numbers of ABP measurements were 30.9±2.9 (range 22–39) in the daytime, 16.6±2.7 (range 8–24) in the nighttime and 47.5±1.1 (39–48) over a 24-h period. During the follow-up period, there were 30 stroke events, including 4 cerebral bleedings, 20 cerebral infarcts, 2 subarachnoid hemorrhages and 4 transient ischemic attacks. There were 34 HARD CVD events (not including TIA), and 58 events included as ALL CVD events. Table 2 shows the results of univariate analyses of outcomes. The following clinic and ambulatory SBP measures (for 10-mm Hg increases) were all signiﬁcantly associated with stroke events: baseline clinic SBP, clinic SBP 10 readings and all ABP values. For HARD CVD events, baseline clinic SBP was marginally associated with the outcome, but the ﬁrst 3–10 readings of clinic BP were not.
Baseline characteristics of subjects mean±s.d. or percentages
N Age, years Sex, male % Body mass index, kg m 2 Current smoking, % Type 2 diabetes, % Duration of hypertension, years Antihypertensive medications, % Total cholesterol, mg dl 1 Triglycerides, mg dl 1 Creatinine, mg dl 1 Clinic SBP at baseline, mm Hg Clinic DBP at baseline, mm Hg 24-h SBP, mm Hg 24-h DBP, mm Hg 24-h pulse rate, b.p.m. Awake SBP, mm Hg Awake DBP, mm Hg Awake pulse rate, b.p.m. Sleep SBP, mm Hg Sleep DBP, mm Hg Sleep pulse rate, b.p.m. Follow-up clinic SBP, mm Hg Follow-up clinic DBP, mm Hg
457 67±9.2 37.6 23.9±3.5 24.9 44.2 6.2±7.4 55.6 204±35 124±65 0.8±0.2 154±20 84±12 140±17 79±10 68±9 146±18 83±10 72±9 129±19 73±10 61±9 140±13 76±8
Abbreviations: BP, blood pressure; DBP, diastolic BP; SBP, systolic BP.
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Prediction of cardiovascular events K Eguchi et al
733 Table 2.
Univariate analyses of clinic and ambulatory BP for outcomes Stroke
Baseline clinic SBP, 10 mm Hg Clinic SBP three readings, 10 mm Hg Clinic SBP five readings, 10 mm Hg Clinic SBP 10 readings, 10 mm Hg 24-h SBP, 10 mm Hg Awake SBP, 10 mm Hg Sleep SBP, 10 mm Hg
1.20 1.16 0.98 1.43 1.53 1.42 1.41
(1.01–1.43)* (0.96–1.40) (0.88–1.08) (1.09–1.87)** (1.25–1.87)*** (1.17–1.73)*** (1.19–1.67)***
HARD CVD 1.19 1.10 0.95 1.19 1.45 1.35 1.39
(1.01–1.40)* (0.93–1.29) (0.87–1.03) (0.92–1.54) (1.20–1.75)*** (1.12–1.62)** (1.18–1.63)***
ALL CVD 1.19 1.23 1.01 1.44 1.43 1.35 1.34
(1.04–1.35)** (1.08–1.42)** (0.93–1.10) (1.19–1.74)*** (1.24–1.65)*** (1.17–1.55)*** (1.19–1.52)***
Abbreviations: BP, blood pressure; CVD, cardiovascular disease; SBP, systolic BP. Values are hazards ratio (95% confidence interval). *Po0.05, **Po0.01, ***Po0.001.
Figure 1. Pairwise comparisons of baseline clinic vs 10 clinic BP readings for outcomes of multivariate Cox regression analyses for stroke events, HARD CVD events and all CVD events based on a comparison of the baseline clinic BP values and 10 clinic BP readings. Values are the hazard ratios and 95% confidence intervals. Two BP variables were entered together in each model with adjustment for age, sex and serum creatinine.
Figure 2. Pairwise comparisons of 10 clinic BP readings vs ambulatory 24-h SBP for outcomes of multivariate Cox regression analyses for stroke events, HARD CVD events and all CVD events based on a comparison of the 10 clinic BP readings and ambulatory 24-h SBP. Values are the hazard ratios and 95% confidence intervals. Two BP variables were entered together in each model with adjustment for age, sex and serum creatinine.
On the other hand, all ABP values were signiﬁcantly associated with the outcome. For ALL CVD events, baseline clinic SBP, clinic SBP 3 and 10 readings and all ABPM values were signiﬁcantly associated with the outcome. On the basis of preliminary Cox regression analyses including only essential variables (age, sex, body mass index, smoking, diabetes and serum creatinine) as univariates, we selected age (Po0.001), sex (P ¼ 0.09) and serum creatinine (P ¼ 0.006) as covariates for adjustment together with clinic and ABP measures. The results of multivariate Cox regression analyses, which controlled for age, sex and serum creatinine, are shown in Figures 1 and 2. Figure 1 shows the comparison between baseline clinic SBP and clinic SBP by 10 readings adjusting for covariates. Although neither measure was a predictor of HARD CVD, clinic SBP by 10 readings was a predictor of stroke and of ALL CVD independently of baseline clinic SBP. With regard to the other numbers of readings, clinic SBP by three readings was associated with ALL CVD (HR ¼ 1.21, 95% CI ¼ 1.04–1.40, P ¼ 0.015) when analyzed in the same model, but clinic SBP by ﬁve readings was not associated with ALL CVD (HR ¼ 1.01, 95% CI ¼ 0.93–1.09, P ¼ 0.87). Figure 2 shows the comparison between clinic SBP by 10 readings and 24-h SBP adjusting for covariates. Ambulatory 24-h SBP was a potent predictor of stroke, HARD CVD and ALL CVD independently of clinic SBP by 10 readings. On the other hand, clinic SBP by 10 readings was associated with ALL CVD independently of 24-h SBP. However, clinic SBPs by three and ﬁve readings were not associated with ALL CVD in the same model.
DISCUSSION In this study, the multiple measurement of clinic SBP readings following the baseline BP measurement was a signiﬁcant predictor of stroke events and ALL CVD events in hypertensive subjects. Furthermore, this relationship was independent of baseline ABP value in cases of ALL CVD events. This is the ﬁrst study to show the importance of clinic BP early after the baseline measurement as a predictor of vascular events.
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Clinic BP and CVD events In this study, the multiple measurement of clinic BP values after the baseline period was associated with stroke and ALL CVD events. Numerous studies have shown that high clinic BP is associated with the future incidence of CVD events, including stroke. In epidemiological studies such as the Framingham study14 and the Hisayama study, BP values derived from screening BP were associated with cardiovascular outcomes. Almost all clinical trials of hypertension management have used a few readings of clinic BP measurement to predict CVD events. In most of the international BP guidelines, clinic BP measurements are described ﬁrst and out-of-ofﬁce BP comes next. In large clinical trials, clinic BP levels have been reported to be closely associated with stroke and CVD events.15,32,33 The preponderance of evidence regarding treatment of hypertension in subjects with hypertension is based on clinic measurements. It has been recommended that clinic BP measurements be performed twice and averaged.16 However, it has not been well established how many times clinic BP should be measured to predict CVD. Powers et al.34 have shown that more Journal of Human Hypertension (2014) 731 – 735
Prediction of cardiovascular events K Eguchi et al
734 than several clinic BP measurements are required for conﬁdent decision making. Therefore, clinic BP measured more than several times is fundamental for the assessment of BP and is the most important tool for the prediction of stroke or CVD events. ABP and CVD events In the present study, the measurement of ABPM at baseline as well as that of clinic BP were associated with future stroke and CVD events. Many studies have shown a signiﬁcant relationship between ABP level and CVD events. In many observational studies, higher ABP levels were associated with CVD events.6,7,35,36 Morning BP37 and sleep BP38 in particular have been associated with CVD events. Sleep BP levels are the most important component of ABPM.9 However, most ABPM studies were performed at baseline in subjects not receiving antihypertensive treatments. Even so, ABP levels in these studies were closely associated with stroke and CVD events, independent of baseline clinic BP levels. Recent hypertension guidelines have emphasized that ABPM has a higher predictive value than other BP measures.13,16,17 Most previous studies of ABPM looked at baseline values measured only a few times, without taking into account clinic BP measured several times over several months. Exceptions were studies of ABPM that considered both treated clinic and ABP,8 and a substudy of the ASCOT-BPLA that used 10 clinical BP and 3.5 ABP measurements during the follow-up period.36 In the latter study, the predictive value of clinic SBP was similar to that of 24-h SBP for total cardiovascular events, but clinic SBP was a bit less predictive for stroke events. These results agree with those of the present study, in which the 10 clinic BP readings were less predictive than the 24-h ABPM but more predictive than baseline clinic SBP. To improve the prediction of outcome, one of the best strategies could be baseline ABPM and subsequent measures of multiple clinic BP early after ABPM. Head-to-head comparison of clinic SBP and ABP In the present study, more than ﬁve clinic BP readings were associated with stroke and ALL CVD events. Multiple BP measurements are important to assure reproducibility and predictability.23 In our previous study, multiple measurements were important to achieve good reproducibility in the assessment of inter-arm differences in BP.39 Furthermore, multiple measurements of BP were essential for predicting events even in the case of home BP monitoring.40 In previous studies comparing clinic BP and ABP, the number of measurements used has varied widely. Indeed, some studies have compared data based on a few clinic BP readings at baseline with data from multiple BP measurements by ABPM at baseline.4,7,9,20–22 Because these clinic BPs reﬂect only one time point in the full spectrum of BP variation over the course of a day, they cannot be used to represent actual BP loads. Even in the situation where repeated measurements are not available, after correction for regression dilution bias, the associations between BP and stroke risk got 60% greater than in uncorrected analyses.41 Without the correction for this bias, many individuals in the cohorts would have been misclassiﬁed at artiﬁcial higher risks of exposure, which is what happens with just one or two ofﬁce readings—multiple ofﬁce readings may lessen the inﬂuence of alert reaction and regression to the mean.42 In clinical practice, not all hypertensive subjects can perform repeated ABPM for the assessment of antihypertensive therapy. Although the British Hypertension Guidelines recommended the use of ABPM for risk stratiﬁcation, they also recommend the use of clinic BP measurements to monitor the response to antihypertensive treatment.13 Our analyses of the independent association between ambulatory SBP or multiple clinic BP readings and future stroke and CVD events support this strategy. Therefore, in addition to baseline ABPM, it is very important to use subsequent multiple clinic BP readings for the assessment of antihypertensive Journal of Human Hypertension (2014) 731 – 735
therapy. Of note, use of automated monitor-based clinic BP was also supported in our previous publications.43,44 Clinical implications In treated hypertensive patients, the ABPM or home BP monitoring would be better markers than clinic BP for the assessment of BP. However, the results in the present study imply that carefully measured clinic BP over an extended period after the baseline visits can be an alternative marker of future stroke and CVD events. Therefore, primary care physicians should measure clinic BP carefully and the average of multiple clinic readings can be used for the assessment of antihypertensive treatment. Study limitations There were several limitations in this analysis. The sample size was moderate, and the numbers of events were small because of the study design. A study in which all subjects undergo both ABPM and multiple clinical readings is needed. Second, the inter-visit variability of clinic BP and circadian BP patterns was not reported in this paper, because it was reported in our recent publication.11 Third, because some antihypertensive drug regimens had been changed during the course of the treatments, the differential effects of antihypertensive medications could not be analyzed. CONCLUSIONS In addition to ABP values, the mean of more than several clinic SBP values early in the follow-up period was an important predictor of stroke and ALL CVD events in routine clinical practice. These results imply that carefully measured clinic BP over an extended period after the baseline visits can be a marker of future stroke and CVD events.
What is known about the topic Clinic BP is most commonly used measure for assessing BP, but there are several shortcomings such as white-coat phenomenon. Ambulatory BP monitoring (ABPM) has been reported to be a better predictor of hypertensive target organ damage and cardiovascular events than clinic BP, but only a few clinic BP readings were used for the comparisons. There have been few studies comparing the predictive abilities of clinic BP and ABPM using the mean of multiple clinic BP readings over an extended baseline period as the clinic BP measure. What this study adds In addition to ABP values, the mean of 10 clinic SBP values early in the follow-up period was an important predictor of stroke and ALL CVD events. Clinic SBPs by three and ﬁve readings were not associated with any CVD events, except that clinic SBP by three readings was associated with ALL CVD. These results imply that carefully measured clinic BP over an extended period after the baseline visits can be a marker of future stroke and CVD events.
CONFLICT OF INTEREST The authors declare no conﬂict of interest.
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