The use of ambulatory blood pressure monitoring in ... - Nature

Journal of Human Hypertension (2001) 15, 535–538  2001 Nature Publishing Group All rights reserved 0950-9240/01 $15.00 www.nature.com/jhh

ORIGINAL ARTICLE

The use of ambulatory blood pressure monitoring in managing hypertension according to different treatment guidelines C Addison, S Varney and A Coats Imperial College of Science, Technology and Medicine, Dovehouse Street, London SW3 6LY, UK

Objective: To investigate the use of ambulatory blood pressure monitoring (ABPM) in identifying and managing a group of patients referred to a tertiary centre for the assessment of their blood pressure and to illustrate the importance of introducing standardised ABPM treatment guidelines. Patients and methods: We examined 2000 sequential ABP recordings, 1557 were first time referrals from General Practitioners, Consultants and other hospitals. All patients were referred with suspected hypertension, resistant hypertension, white coat hypertension and for investigations of secondary hypertension. Fully trained nurse specialists fitted the monitors in the hypertension clinic and recordings were performed for 24 h. The data was then analysed and stratified according to treatment guidelines and categorised according to different definitions. Results: The group of first time referrals (n ⴝ 1557) showed an even sex distribution of 789 men and 768 women, mean age 53 ± 13.8 (12–88 years). Of this group 542 patients (35%) exhibited a white coat effect (WCE),

526 (34%) had a daytime ABP ⭐139/89 mm Hg. Of these 81 (15%) had a high clinic blood pressure (ie, white coat hypertension (WCH)) according to our definition. Thirtyfive of these patients were not on treatment but may have had it initiated on the basis of their clinic pressures. According to the British Hypertension Society (BHS) guidelines on clinic readings 772 (45%) of our patients would be classified as hypertensive or inadequately treated, 509 (33%) borderline and 326 (21%) as normal. Using daytime ABP levels according to O’Brien: 1031 (67%) would be defined as abnormal, 192 (12%) as borderline and 334 (21%) as normal. Conclusion: These results illustrates how patient management may differ markedly when treating in accordance either with the BHS guidelines for clinic readings or the suggested levels for ABP. More patients had abnormal blood pressure levels according to ABPM, even though it is superior in detecting WCE and WCH. Clear guidelines for ABPM treatment levels need to be established. Journal of Human Hypertension (2001) 15, 535–538

Keywords: ambulatory blood pressure monitoring; white coat effect; treatment thresholds

Introduction Ambulatory blood pressure monitoring (ABPM) has proved to be useful in assessing levels of blood pressure away from hospital or a medical environment. It is of great importance in distinguishing between true hypertension and ‘white coat’ hypertension (WCH) and has proved to be uniquely successful in this area.1 It has long been established that ABPM is not only more reproducible than office measurements, but also more closely related to the incidence of cardiovascular events and the prevalence of end organ damage.2 There is substantial evidence that ABP correlates better with left ventricular mass index (LVMI) than casual readings. This is of Correspondence: C Addison, Heart Function Office, Royal Brompton & Harefield NHS Trust, Sydney Street, London SW3 6NP, UK. E-mail: c.addison 얀ic.ac.uk Received 27 October 2000; revised and accepted 1 March 2001

particular importance in deciding a level above which the chances of developing left ventricular hypertrophy (LVH) significantly increases and therefore establishing appropriate treatment levels.3 ABPM reduces variability introduced by the observer such as digit preference, threshold avoidance and bias, and increases reproducibility. One of the rationales for using 24-h monitoring is that it is thought to be more representative of a patient’s true blood pressure and is more reproducible than clinic readings.4 ABPM has advanced as a research instrument from assessing the efficacy of new treatments to a valuable accessory in the hypertension clinic and general practice. With the increasing use of ABPM in the clinical management of hypertensive patients, treatment levels are being reassessed and guidelines prepared. Although ABPM has been in widespread use there has not been a consensus on the levels that should be used as guidelines for treatment. Many studies

Use of ABPM in managing hypertension C Addison et al

536

Table 1 Data split according to definitions

Clinic readings (BHS guidelines) Daytime ABPM levels (O’Brien8)

Hypertensive/uncontrolled hypertension

Borderline between groups

Normal/well controlled blood pressure

⭓160 and/or ⭓100 mm Hg 722 (46%)

509 (33%)

⭐139 and/or ⭐89 mm Hg 326 (21%)

⭓140 and/or ⭓90 mm Hg 1031 (67%)

190 (12%)

⭐134 and/or ⭐84 mm Hg 336 (21%)

have been performed in selected tertiary centres and therefore potentially unrepresentative of the general hypertensive picture. General population studies have been underway for some time and their results that have been eagerly awaited are just emerging. We decided to see how our group of patients would fit into the current definitions and the impact that this could have on their treatment and possible management.

Patients and methods The patients in this study were a consecutive series of patients referred to our hypertension clinic for investigation of suspected or confirmed hypertension. They represent all patients referred to the Hypertension Clinic of the Royal Brompton & Harefield NHS Trust over a 5-year period. All patients had been referred primarily from primary care with smaller numbers from consultants or from other hospitals. There were no specific referral criteria required as this was at the discretion of the clinician. The main reasons for referrals were: suspected white coat hypertension, borderline hypertension, resistant hypertension, episodic hypertension and investigating causes of secondary hypertension. All patients wore an ABPM for 24 h. Hypertension nurse specialists, who have been extensively trained in ABPM, fitted each recorder. All patients were given written and oral information of the procedure and techniques to establish a good recording. Three clinic readings were taken after a seated period of at least 5 min and the same recorder was used as would be used for the 24-h recording. The monitor was programmed to measure the blood pressure every 15 min during the day and every 30 min at night. Sleep periods were programmed as suggested by the patient who were also asked to keep a simple diary confirming at what times they were awake and asleep. We required at least 20 awake readings to consider the recording satisfactory for analysis purposes. We used the TM 2420 (A&D, Tokyo, Japan), a microphonic monitor using Korotkoff sounds I and V to determine systolic and diastolic blood pressure (SBP/DBP). This monitor has been extensively validated and passes the AAMI criteria for ambulatory accuracy.5 Data was read automatically by proprietary Journal of Human Hypertension

software (A&D) and transferred to a dedicated computer program for analysis. Readings excluded as faulty by the monitors were excluded from the analysis, but no other data were rejected in order to exclude any subjective bias. The data was analysed to calculate averages for waking and sleeping SBP and DBP, and pulse rate (definitions were based on diary entries). We looked at 2000 sequential recordings and excluded those that were not first time referrals, which left 1557. The grouped data was then analysed and stratified according to different classifications (see definitions). We investigated what proportion of the total population of our patients would have had been classified as established hypertensives/borderline hypertensive or normotensive based on published criteria: for clinic readings using the BHS guidelines,6 and then for ABP levels using levels suggested by O’Brien7 (Table 1). In this particular patient population we analysed the prevalence of a significant white coat effect (WCE), (Table 2). We employed the definition used in the substudy of the Second Australian National Blood Pressure Study (ANBP2).8 A WCE is not exclusive to normotensive patients and can equally be present in those patients with hypertension. In this latter group however it might lead to excessive antihypertensive dose increases. We then divided the data by treatment groups (Table 3) to see how the different guidelines would effect treatment strategies. Definitions BHS Guidelines6: Established hypertension is defined as clinic SBP ⭓160 mm Hg and/or DBP ⭓100 mm Hg, normotensive clinic SBP ⭐139

Table 2 WCH (patients not receiving treatment) n = 35

Mean s.d. Range

Clinic readings (mm Hg)

Daytime ABP (mm Hg)

Systolic

Diastolic

Systolic

Diastolic

153.9 12.97 122.3–179

101.6 11.55 80.3–126.3

128.2 8.99 99.1–139.9

79 7.55 62.7–88.8


537

Table 3 Patients divided by treatment levels, according to their ABPM readings and clinic readings ABP Clinic

Treatment or increase in medication (⭓140/90 mm Hg)

Possible treatment (borderline)

No. Treatment/or change in treatment (⭐135/85 mm Hg)

Total

Definite treatment or increase in medication (⭓160/100 mm Hg)

641

38

43

722

Possible treatment (borderline) (140–160/90–99 mm Hg)

312

90

107

509

78

62

186

326

1031

190

336

1557

No treatment/no change in treatment (⭐139/89 mm Hg) Total

mm Hg and/or DBP ⭐89 mm Hg and borderline between these. 7

Guidelines after O’Brien et al : Daytime ABP levels were defined as blood pressures ⭓140 and/or 90 mm Hg being probably abnormal and blood pressures below ⭐135/85 mm Hg are probably normal White coat effect from Second Australian National Blood Pressure Study (ANBP2)8: Clinic SBP ⭓20 mm Hg higher than ABP or clinic DBP ⭓10 mm Hg. White coat hypertension: Daytime ABPM ⭐139/89 mm Hg and clinic readings ⭓160 and/or DBP ⭓100 mm Hg.

Results We examined 1557 ABPM recordings, which were all first time referrals for ABPM. We saw an even sex distribution of 789 men and 768 women with a mean age 53 ± 13.8 (12–88 years). White coat hypertension and white coat effect A total of 542 of all patients (35%) exhibited a WCE (SBP reduced by 20 mm Hg or DBP reduced by 10 mm Hg on ABPM compared with the average of three clinic readings). A total of 526 patients had a normal/borderline ABPM reading as defined by O’Brien7 (Table 1) eg, ⭐139/89 mm Hg. A total of 81 (15%) had a clinic reading average ⭓160 and/or ⭓100 mm Hg and so met our definition of WCH, 46 were receiving antihypertensive treatment and 35 were not receiving any treatment (Table 2). If we use broader definitions the prevalence of WCH increases. For those patients whose office blood pressure ⭓140 and/or ⭓90 mm Hg we stratified the patients according to the following subdivisions of daytime ABP levels to assess the proportions of patients that would meet this diagnosis: • ⭐139/89 mm Hg ⫽ 264 (17%) • ⭐135/85 mm Hg ⫽ 158 (10%)

• ⭐130/80 mm Hg ⫽ 72 (5%) Therefore using the broadest definition we can claim that 17% of our population had WCH. Of the 1031 patients whose blood pressure was not well controlled according to their ABP (Table 3), 78 (8%) would not have had treatment initiated or changed according to their clinic readings. A further 312 (30%) of this group were borderline for treatment according to their clinic readings. Of the 722 patients whose blood pressure was uncontrolled according to their clinic readings, 43 (6%) had good blood pressure control according to their ABPM.

Discussion This centre is unusual as it attracts referrals for patients who have already had cardiovascular problems identified. However, with that in mind and having introduced ABPM to this centre we are interested to see how it may influence the management of patients referred with ‘hypertension’. We are also aware that this is of particular relevance and interest given the current debate and controversy regarding levels of normality as published in the WHO/ISH guidelines9 and the consequent discussion in the Lancet.10 It is disappointing that these guidelines have not gone further in clarifying the issue of ABPM. Although recognising the benefits of ABPM they fall short of advocating its use in practice. On one hand they stress the need for more prognostic studies to confirm the advantages of ABPM and then appear to contradict this by confirming that ABPM does have a prognostic value and is superior in correlating high levels of blood pressure with target organ damage. In the light of these disparities it appears even more pressing to have a consensus over ‘normal’ ABP levels. In our discussion we have used the levels that have been advocated by Professor O’Brien. The 35 patients with white coat hypertension who were not receiving treatment would almost certainly have had treatment commenced on the basis of their clinic readings measured in the clinic setting. It is also likely that the 46 who were already receiving antihypertensive treatment may have had it Journal of Human Hypertension


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increased on the basis of these office measurements. This group of patients with highly divergent ABPM and clinic readings is relatively small (81 is only 5% of the total) (however this figure increases to 17% using broader definitions). Table 2 describes these 35 patients who would have been prescribed treatment on the basis of their clinic reading had they not been referred for ABP. Unfortunately we do not have follow-up details on this group of 35 patients as they come from such diverse referral sources. In Table 1, 67% of our group would be classified as hypertensive or having uncontrolled hypertension according to their daytime ABP levels, if the BHS guidelines are applied to their clinic readings this would have fallen to 46%. This means 309 patients possibly being under-treated or not treated at all. The results demonstrate the importance of establishing standard levels to use in managing and treating blood pressure, slight differences in groupings obviously result in large numbers of patients being mismanaged; either not being detected or being over-treated. Despite the difference in the number of patients in the hypertensive group and the borderline group an interesting point is that both definitions concur with each other with exactly the same number of patients (21%) having normal blood pressures. In Table 3 the same patient group of 1557 has been stratified according to treatment levels, and shows that 43 patients may have been started on antihypertensive therapy according to their clinic readings but would not have been according to their ABP results. The results in this table support those in Table 1. However, 78 patients with normal clinic readings would have had treatment indicated by their ABPM levels. This illustrates the disparity between the recommended guidelines for definite treatment between clinic and ABP, which is a difference of 20 mm Hg SBP and 10 mm Hg DBP. It appears from this table that if ABPM is performed it results in more patients being possibly treated if O’Brien’s guidelines are used. This is unsurprising as many more readings are taken during a 24-h per-

Journal of Human Hypertension

iod and therefore the averages that are used to define treatment levels are lower. We await with great interest the publication of the new guidelines from the British Hypertension Society (how will they differ from the WHO/ISH guidelines?) and hope that ABPM thresholds are not ignored.

References 1 Purcell H, Gibbs S, Coats A, Fox K. Ambulatory blood pressure monitoring and circadian variations of cardiovascular disease; clinical and research applications. Int J Cardiol 1992; 36: 135–149. 2 Mancia G et al. Blood pressure reduction and endorgan damage in hypertension. J Hypertens 1994; 12 (Suppl 8): S35–S40. 3 Verdecchia P et al. White-coat hypertension: not guilty when correctly defined. Blood Press Monit 1998; 3: 147–152. 4 Coats A. Reproducibility or variability of causal and ambulatory blood pressure data: implications for clinical trials. J Hypertens 1990; 8 (Suppl 6): S17–S20. 5 Clark S et al. Ambulatory blood pressure monitoring: validation of the accuracy and reliability of the TM 2420 according to the AAMI recommendations. Hum Hypertens 1991; 5: 77–82. 6 Ramsay L et al. Guidelines for the management of hypertension: report of the third working party of the British Hypertension Society. J Hum Hypertens 1999; 13: 569–592. 7 O’Brien E et al. What are the normal levels for ambulatory blood pressure measurement? Blood Press Monit 1998; 3: 131–132. 8 Management Committee on behalf of High Blood Pressure Research Council of Australia. Australian comparative outcome trial of angiotensin-converting enzyme inhibitor and diuretic-based treatment of hypertension in the elderly (ANBP2): objectives and protocol. Clin Exp Pharmacol Physiol 1997; 24: 188– 192. 9 Chalmers J et al. WHO-ISH Hypertension Guidelines Committee. 1999 World Health Organisation–International Society of Hypertension Guidelines for the Management of Hypertension. J Hypertens 1999; 17: 151–185. 10 O’Brien E, Staessen J. Commentary. What is ‘hypertension’? Lancet 1999; 353: 1541–1542.