Audit of ambulatory blood pressure monitoring in the ... - Nature

Journal of Human Hypertension (1998) 12, 249–252  1998 Stockton Press. All rights reserved 0950-9240/98 $12.00

ORIGINAL ARTICLE

Audit of ambulatory blood pressure monitoring in the diagnosis and management of hypertension in practice A Zawadzka, R Bird, B Casadei and J Conway Department of Cardiovascular Medicine, John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK

This study was carried out to ascertain the value of ambulatory blood pressure monitoring (ABPM) in the diagnosis and treatment of hypertension in routine clinical practice. ABPM was performed during the daytime hours in 410 patients believed to be hypertensive after at least three measurements by their physician and one measurement by a nurse in a hypertension clinic. The diagnosis was confirmed in 70% of patients when 90 mm Hg diastolic blood pressure (BP) was used as the upper limit of normal, and 86.3% when 85 mm Hg was used. In 204 patients who were reviewed 5 years later there were 108 on medical treatment. This reduced dias-

tolic pressure from a mean of 100.6 ± 8.8 to 85.7 ± 8.8 mm Hg. However, in 30% of patients the diastolic pressure was still above 90 mm Hg. In the 49 patients with isolated clinic hypertension (ICH), who had remained untreated, diastolic pressure increased from 84.0 ± 4.8 to 88.1 ± 8.4 mm Hg over the 5 years. In 19 of these the level exceeded 90 mm Hg. ABPM therefore improves diagnostic accuracy and prevents treatment of patients with ICH. This condition, however, requires follow-up since BP tends to rise with time in some patients. The audit also identified patients who had had a suboptimal response to medical treatment.

Keywords: diagnosis; treatment; isolated clinic hypertension

Introduction The variability in blood pressure (BP) level has always presented a problem for the diagnosis of hypertension and many different strategies have been adopted to cope with it.1–4 All of these rely essentially upon multiple BP recordings to arrive at a reasonable estimate of the true mean BP. They also remove the patient from the stressful medical environment and diminish the alerting response which is a major source of error. Ambulatory BP monitoring (ABPM) provides an accurate and reproducible estimate of the usual BP level5–7 and has now been introduced into clinical practice. We assess its value in the management of patients who had been diagnosed as hypertensive from clinic BP readings.

Materials and methods An ‘open access’ service for ABPM has been available for general practitioners and hospital physicians in Oxford since 1985. We report here on the experience with 410 consecutive untreated patients who were believed to have hypertension on referral, since both the mean of three diastolic BP measurements on different occasions by the referring physician and the clinic nurse exceeded 90 mm Hg.

Correspondence: Dr James Conway Received 4 August 1997; revised 12 October 1997; accepted 5 November 1997

The apparatus used for ABPM was the TM2420 device (A&D Co, Tokyo, Japan). This used the Korotkoff sounds with the 1st and 5th phases indicating systolic and diastolic pressure, respectively. The device was validated by ourselves8,9 and others10–12 and found to be satisfactory according to the criteria of the American Association for Medical Instrumentation.13 Two investigators, however, have reported reservations regarding the device.14,15 The machine emitted a warning bleep 20 secs before a measurement was to be made and the subjects were then asked to sit quietly with the arm supported until the measurement was complete. A BP measurement was recorded every half-hour during the waking day and at least 20 satisfactory readings were required to derive the mean value for the day. Definitions For the purposes of this study, hypertension was defined arbitrarily as a mean daytime diastolic BP exceeding 90 mm Hg on ambulatory monitoring. To take account of later attempts to define ‘normality’ by ABPM an upper limit of 85 mm Hg for the diastolic BP was examined.16 Isolated clinic hypertension (ICH),16 or white coat hypertension, is defined as a diastolic pressure exceeding 90 mm Hg on clinic measurements and a value below this level on ABPM. The referring physician was advised to treat patients classified as hypertensive by an ABP of 90 mm Hg or more. At

Blood pressure audit A Zawadzka et al

250

least 5 years after the first recording the hypertensives and those with ICH were invited to return for repeat ABPM. This was achieved in 204 subjects who were still living in the area. Data are presented as means and standard deviations and relationships between the different BP recordings were assessed by linear regression. Diagnosis Of the 410 patients believed to have hypertension on the basis of their clinic readings, the diagnosis was confirmed in 286 (69.7%) by the daytime ABPM, whereas 124 (30.2%) were classified as ICH. Their mean clinic BP was 168.4 ± 21.8/106.8 ± 10.1 mm Hg and the mean fall in BP on monitoring was 11.5 ± 13.4/5.8 ± 8.5 mm Hg. This fall in BP was not related to the initial BP level. When the lower limit of 85 mm Hg diastolic was used the incidence of ICH fell to 13.7%. Follow-up Of the 204 patients followed up for a mean of 5.7 years, 60 (29.4%) had ICH when 90 mm Hg was used as the cut-off point but this figure fell to 25 (12.3%) when 85 mm Hg was used. Of the hypertensive patients, 36 subjects had received no medical treatment in spite of the recommendation that they should have it. The mean BP in this group had been 148.3 ± 11.9/97.8 ± 6.7 mm Hg on recruitment and on follow-up it was 152.4 ± 12.1/98.2 ± 12 mm Hg. This difference was not statistically significant. For the remaining 108 hypertensive patients the treatment choices had been made by the individual practititioners and the majority (68%) were managed with a single drug. Thirty-one per cent were on beta-blockers, 17% on angiotensin-converting enzyme inhibitors, 11% on calcium antagonists and 7% diuretics. Dual therapy was used in 30% and 4% were on triple therapy. Treatment lowered the ambulatory diastolic BP from a mean of 100.6 ± 8.8 mm Hg to 85.7 ± 8.8 mm Hg (Figure 1). Although this was satisfactory, the distribution of diastolic pressures reveals that BP reduction was less than optimal in 33 (30%) patients in whom the ambulatory diastolic pressure still exceeded 90 mm Hg and, in 13 of these it exceeded 95 mm Hg (Figure 1). Half of the patients who were poorly controlled were on more than one anti-hypertensive drug. The fall in diastolic BP with treatment was related to the initial diastolic BP level (r = 0.55), but the BP level in the patients who failed to achieve an adequate response was distributed throughout the range of the initial diastolic pressures. Of the 60 patients with ICH, 49 had received no anti-hypertensive drugs. Their ABP level increased modestly with time. The initial ABP was 132.2 ± 12.3/84.0 ± 4.8 and on repeat it was 139.5 ± 16.7/88.1 ± 8.4 mm Hg (P ⬍ 0.001 for systolic and diastolic pressures). This rise was linearly related to the initial BP level (r = 0.5 P ⬍0.001) for systolic pressure whereas for diastolic pressure the relationship was weaker (R = 0.33, P ⬍ 0.02). From the individual data it was apparent that 19 patients (39%)

Figure 1 Frequency distribution of the level of ambulatory diastolic pressure before treatment (upper graph) and at follow-up (lower graph) when the patients were on anti-hypertensive treatment for at least 5 years.

had a diastolic BP exceeding 90 mm Hg on repeat ABPM.

Discussion Although the number of patients in this study is not large and a period of follow-up of 5.7 years is quite modest for hypertension, three points have emerged which have a bearing on the diagnosis and management of the condition. First, of those who were believed to have hypertension on referral, about 30% had an ABPM below 90 mm Hg and 13.7% were below 85 mm Hg. Secondly, some patients with ICH experienced a modest increase in pressure over the period of observation. Thirdly, while anti-hypertensive therapy guided


by clinic BP measurements is generally effective in lowering BP in hypertensive patients there remains a substantial proportion of patients in whom diastolic pressure is not adequately controlled. Isolated clinic hypertension The proportion of ICH observed in this study is similar to that found by others.17,18 The number of subjects detected has important implications for the management of this condition. It indicates that those who are believed to have uncomplicated hypertension on the basis of clinic readings require additional measures to establish the diagnosis properly. Treatment of ICH is not only wasteful of resources but it often leads to side effects.19 There is also a psychological burden of a false diagnosis in individuals who may not require treatment and are essentially normal. The level of diastolic pressure increased with time in some patients and 40% of the subjects with ICH had diastolic pressures above 90 mm Hg on review. It is not yet clear whether this rise in pressure is greater than one would expect in truly normal subjects. This finding is similar to that of Bidlingmeyer et al20 who followed a group of ICHs over the same period of time although the proportion of subjects who crossed the threshold of 90 mm Hg was 75% in their study. Thus it is apparent that, in spite of some evidence to the contrary,17,21 ICH may not be an entirely benign condition.22–24 Since the morbidity and mortality of ICH is not clearly established, it would seem prudent that these patients should have their BP monitored periodically. Treatment of hypertension Although treatment by doctors was assessed entirely by clinic readings its efficacy was impressive and in the majority of patients the diastolic BP fell within the normal range. Nevertheless there was a substantial proportion of patients who were poorly controlled. Though not unexpected,24,25 this is worrisome. Failure to control BP was not particularly evident amongst those with the highest initial BP levels but they were scattered throughout the initial BP level. However, it was clear that the problem of BP control had been recognised by their physicians since half of the patients were on more than one agent.

Conclusions The use of ABPM more than justifies itself in the detection of ICH, although it has to be said, that other methods of obtaining multiple recordings of BP would suffice.26 The average control of BP by physicians is good but the individual data show that there is an uncomfortable proportion of patients who are poorly controlled. These non-responders are not necessarily the most severely hypertensive patients to start with, but there is clearly a need for the accurate assessment of BP in hypertensive patients on treatment in order to identify these poor responders and bring the BP under proper control.

Acknowledgement This project was supported by a Locally Organised Research Grant from the Oxford Regional Health Authority.

References 1 Freis ED. The discrepancy between home and office recordings of blood pressure in patients under treatment with pentopyrolidinium. Importance of home readings in adjusting dosage. Med Ann DC 1954; 23: 363–367. 2 Smirk FH. Casual and basal blood pressures. Their relationship to supplemental pressure with a note on statistical implications. Br Med J 1949; i: 791–793. 3 Guidelines sub-committee of the WHO/ISH mild hypertension liaison committee. 1993 guidelines for the management of mild hypertension: memorandum from a World Health Organisation/International Society of Hypertension meeting. J Hypertens 1993; 11: 905–918. 4 Sever P et al. Management guidelines in essential hypertension: report of the second working party of the British Hypertension Society. Br Med J 1993; 306: 983–987. 5 James GD et al. The reproducibility of average ambulatory, home, and clinic pressures. Hypertension 1988; 11: 545–549. 6 Waeber B et al. Ambulatory blood pressure measurement and antihypertensive therapy. J Hypertens 1989; 7 (Suppl 3): S33–S39. 7 Mansoor GA, McCabe EJ, White WB. Long-term reproducibility of ambulatory blood pressure. J Hypertens 1994; 12: 703–708. 8 Clark S et al. Age and blood pressure measurement experience with the TM2420 ambulatory blood pressure monitor and elderly people. Age and Aging 1992; 21: 398– 403. 9 Clark S, Hofmeyer GJ, Conway J, Redman CWG. Ambulatory blood pressure monitoring during pregnancy: validation of TM2420 monitor. Obstet Gynecol 1991; 77: 152–155. 10 Russell AE et al. Accuracy of the Takeda TM-2420 ambulatory blood pressure monitor. Clin Exp Pharmac Physiol 1989; 16: 253–256. 11 White WB et al. A multicenter evaluation of the A & D TM2420 ambulatory blood pressure recorder. Am J Hypertens 1991; 4: 890–896. 12 Palatini P, Penzo M, Canali C. Validation of the A & D TM-2420 model 7 for ambulatory monitoring and effect of microphone replacement on its performance. J Ambulat Monit 1991; 4: 281–288. 13 Association for the Advancement of Medical Instrumentation (AAMI). Proposed standard for electronic or automated sphygmomanometers. Arlington Va: 1986. 14 O’Brien E, Mee F, Atkins N, O’Malley K. Accuracy of the Takeda TM-2420.2020 determined by the British Hypertension Society Protocol. J Hypertens 1991; 9: 571–572. 15 Jamieson MJ, Fowler G, MacDonald TM. Bench and ambulatory field automated field evaluation of A & D automated sphygmomanometer. J Hypertens 1990; 8: 599–605. 16 World Health Organisation: Hypertension control. WHO Technical Report Series 1996; 862: 7–8. 17 Pickering TG et al. How common is white coat hypertension? JAMA 1988; 259: 225–228. 18 Krakoff LR et al. Effect of ambulatory blood pressure monitoring on the diagnosis and cost of treatment for mild hypertension. Am Heart J 1988; 116: 1152–1154.

251


252

19 Waeber B et al. Are some hypertensive patients overtreated? A prospective study of ambulatory blood pressure recording. Lancet 1987; 2: 732–734. 20 Bidlingmeyer I et al. Isolated office hypertension: a prehypertensive state? J Hypertens 1996; 14: 327–332. 21 White WB, Schulman P, McCabe EJ, Dey HM. Average daily blood pressure, not office blood pressure, determines cardiac function in patients with hypertension. JAMA 1989; 261: 873–877. 22 Kuwajima I, Suzuhi Y, Fujisawa A, Kuramoto K. Is white coat hypertension innocent? Structure and function of the heart in the elderly. Hypertension 1993; 22: 826–831. 23 Hoegholm A et al. Microalbuminuria in 411 untreated

individuals with established hypertension, white coat hypertension, and normotension. Hypertension 1994; 24: 101–105. 24 Samuelson O. Hypertension in middle-aged men. Management, morbidity and prognostic factors during long-term hypertensive care. Acta Med Scand 1985; Suppl 702: 1–79. 25 Attwood S et al. Within-patient correlation between the antihypertensive effects of atenolol, lisinopril and nifedipine J Hypertens 1994; 12: 1053–1060. 26 Chatallier G et al. Decision to treat mild hypertension after assessment by ambulatory monitoring and World Health Organisation recommendations. Br Med J 1992; 305: 1062–1066.