Ambulatory blood pressure monitoring

By Dr Raj Thakkar on the 14 September 2016

The benefits of in-house ambulatory blood pressure monitoring (ABPM), including the latest NICE guidelines for ABPM, and how to interpret results.

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Practices are increasingly offering in-house ambulatory blood pressure monitoring (ABPM). Commissioners should consider in-house ambulatory blood pressure monitoring as a means of releasing capacity in hospitals while reducing diagnostic costs.

Guidelines update

The European Society of Hypertension/European Society of Cardiology (ESH/ESC) 2013 hypertension guidelines stated that ‘out-of-office’ blood pressure monitoring is more reliable than office measurements.¹

Ambulatory results more consistently predict cardiovascular morbidity and mortality risk than office readings. Studies have shown that ambulatory readings correlate more reliably with end-organ damage and cardiovascular events than clinic BP monitoring (CBPM).^2,3

Despite this, the ESH/ESC guidelines suggest that office readings remain the gold standard from a practical perspective, and home readings are a valid alternative in appropriate patients.

Choice of device

There are many incentives to purchase ambulatory monitoring equipment for use within general practice, not least to align with the 2011 NICE guidelines (due to be updated in summer 2016).⁴ However, there are a number of issues to consider before setting up this service in primary care:

Capital and maintenance costs
Cost-effectiveness
Time required
Training needs
The clinical process of fitting and removing the device and analysing the data
Patient management
Clinical governance

The choice of device should not only be based on cost. Reliability, technical support, ease of use, quality of accompanying software, warranty, and approval by the British Hypertension Society are all equally important. Some GPs may wish to purchase equipment similar to that used by their local cardiology department.

When to use ABPM

Indications for monitoring are listed in table 1 below.¹

Table 1. Indications for monitoring
Clinical indications for home blood pressure monitoring (HBPM) or ABPM
Suspicion of white-coat hypertension - Grade 1 hypertension in the office - High office BP in individuals without asymptomatic organ damage and at low total CV risk Suspicion of masked hypertension - High normal BP in the office - Normal office BP in individuals with asymptomatic organ damage or at high total CV risk Identification of white-coat effect in hypertensive patients Considerable variability of office BP over the same or different visits Autonomic, postural, post-prandial, siesta- and drug-induced hypotension Elevated office BP or suspected pre-eclampsia in pregnant women Elevated office BP or suspected pre-eclampsia in pregnant women Identification of true and false resistant hypertension
Specific indications for ABPM
Marked discordance between office BP and home BP Assessment of dipping status Suspicion of nocturnal hypertension or absence of dipping, such as in patients with sleep apnoea, chronic kidney disease (CKD), or diabetes Assessment of BP variability

Practical hints

When using ambulatory monitors:

a manual BP should be within 5mmHg of the initial reading from the automated machine
usual daily activities are recommended while wearing the machine, but excessive exercise should be avoided
advise the patient to keep still, not to talk, and to ensure the arm is at the level of the heart when the cuff inflates
encourage the patient to keep an activity diary.

Interpretation

A number of clinically useful datasets are generated by ambulatory devices, including the BP profile over a 24-hour period, the overall mean, night and daytime BP readings, and pulse data.

The greatest differences between clinic and ambulatory readings are usually seen in patients with the highest clinic readings. It's essential to appreciate the nuances in interpreting results from ambulatory devices, depending on the device used. The ESC has published a useful table to help, below.¹

Table 2. Definitions of hypertension by office and out-of-office blood pressure levels¹
Category	Systolic BP (mmHg)		Diastolic BP (mmHg)
Office BP	≥140	and/or	≥90
Ambulatory BP
Daytime (or awake)	≥135	and/or	≥85
Nightime (or asleep)	≥120	and/or	≥70
24-hour	≥130	and/or	≥80
Home BP	≥135	and/or	≥85

Automated reports will usually comment on the ‘dipping status’ of a patient - that is, if the blood pressure drops sufficiently overnight.

Failure to adequately dip can confer a cardiovascular risk. Non-dipping may simply be caused by a disturbed night’s sleep. But other conditions can account for non-dipping, including, old age, obesity, obstructive sleep apnoea, orthostatic hypotension, autonomic dysfunction, and CKD.

Benefits for patients and practice

Effective hypertension control will help to reduce the burden of cardiovascular disease in the population. Hypertension is common, and efficiently diagnosing and treating it is a challenge that requires innovative solutions and systems.

Patients whose treatment has been based on ABPM rather than conventional blood pressure measurement (CBPM) require less intensive treatment which does not lead to an increase in left ventricular mass, a marker of end organ damage in hypertension.

ABPM also reflects treatment effect more accurately than CBPM. Given that studies have shown the correlation between CBPM and ABPM is poor,⁵ it may be argued that all hypertensive patients should have regular ABPM.

Blood pressure measurement often requires several appointments to diagnose, investigate, and stabilise, using valuable practice resources and disrupting patients' lives. ABPM can significantly reduce appointment pressure, which saves resources for the practice.

Compliance with the diagnostic process may also be improved because ambulatory monitoring is often more convenient for busy patients.

Ambulatory monitoring and QIPP

Quality, innovation, productivity, and prevention (QIPP) aims to reduce costs while improving services. Many areas rely on acute trusts to provide ABPM, which adds to CCGs’ costs and creates capacity problems in hospitals. A community service helps to alleviate this problem, as well as providing care closer to home for patients.

There is a strong clinical and business argument for using ABPM in primary care. Although an initial investment is required, the benefits for patients, practice resources, and the health economy are significant.

Dr Raj Thakkar is a GP in Buckinghamshire; commissioning director and cardiac lead of Thames Valley Strategic Cardiac Network; and planned care director, Chiltern CCG