The incentive to purchase equipment for ambulatory BP monitoring (ABPM) for use within general practice has never been greater. However, there are a number of key elements to consider before setting up such a service.
Perhaps the most important is to understand the indications for the use of ABPM and the fundamental differences between clinic readings and that of ABPM readings.
Of course, prior to any purchase, consideration of capital and maintenance costs, cost-effectiveness, time required, training needs and the clinical process of fitting and removing the device, analysing the data, managing the patient and clinical governance should not be underestimated.
The choice of device should not only be based on cost as 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.
1. When to use ABPM
A number of different and clinically useful datasets are generated by ambulatory devices, including the BP profile over a 24-hour period and the mean overall, night and daytime BP readings.
Measurements preand post-treatment may also be taken if the patient is willing. The combined European Society of Cardiology and European Society of Hypertension guidelines suggest ABPM should be considered when clinic readings vary considerably between clinic visits, when there is a large discrepancy between home and clinic readings, in a patient with an otherwise low cardiovascular risk presenting with consistently high clinic readings, where drug resistance or poor adherence is suspected, in patients with pre-syncope or syncope, or in pregnant women with high clinic readings where pre-eclampsia is suspected.
In addition, patients with a borderline-high clinic BP may benefit from ABPM. Also, the management of disease in the elderly, in whom isolated systolic hypertension is often over-diagnosed and hypotension is common, may be greatly improved by ABPM.
ABPM significantly reduces the 'white coat effect' of the clinician on the patient and may prevent the over-diagnosis and subsequent unnecessary treatment of hypertension.
Given that most cardiovascular events occur in the morning, ABPM readings may change management and reduce risks of adverse outcomes in high-risk patients.
Graph of the BP of a man with mild hypertension (over 24 hours) (Photograph: SPL)
2. Predicting cardiovascular events
Studies, including Office Versus Ambulatory blood pressure (OvA)1 and Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA),2 have shown ambulatory readings correlate more reliably with end-organ damage and cardiovascular events compared with clinic BP monitoring (CBPM).
ABPM also reflects treatment effect more accurately than CBPM. Data have shown patients whose treatment has been based on ABPM rather than CBPM have required less intensive treatment without an increase in left ventricular mass, which is a marker of end-organ damage in hypertension.
Night-time BP has been shown to be prognostically more significant than daytime readings. Failure or blunted reduction in night-time BP as shown by ABPM, so called 'non-dipping' status, has been shown by some studies to be a risk factor for end-organ damage and hence guides treatment strategies, although some researchers have refuted this.
Given studies, including Hypertension Optimal Treatment (HOT),3 have shown the correlation between CBPM and ABPM is poor, it may be argued that all hypertensive patients should have regular ABPM.
While this may allow clinicians to predict cardiovascular disease more accurately in both treated and untreated patients, such a programme would not be practical or affordable. In addition, the device is inconvenient for patients.
3. Monitor readings
When fitting a monitor, as with CBPM, a correct-sized cuff should be used. The initial reading should also be checked against a standard sphygmomanometer and the device set to take readings no more frequently than every 30 minutes.
Patients should carry on with normal daily activities and should ensure their arm is straight during inflations.
In addition, they should keep a diary to record events that may correlate to an unexpected rise in BP, or indeed episodes of light-headedness.
While a persistent BP above 140/90mmHg is considered abnormal and given ambulatory readings are on average between 10-20/5-10mmHg lower, average ABPM readings of above 125-130/80mmHg, night readings of above 120/70mmHg and day readings of above 130-135/85mmHg are considered abnormal.
ABPM in primary care is in its infancy but its use is growing fast. When applied effectively, ABPM may dramatically reduce hospital referrals, enhance the patient experience and ultimately reduce morbidity and mortality from cardiovascular disease.
- Dr Thakkar is a GP in Wooburn Green, Buckinghamshire
1. Clement DL. Office versus ambulatory recordings of blood pressure (OvA): a European multicenter study. The Steering Committee. J Hypertens Suppl 1990; 8(6): S39-41.
2. Grassi G, Bombelli M, Sega R et al. The PAMELA (Pressioni Arteriose Monitorate E Loro Associazioni) study: main features and results. High blood pressure and cardiovascular prevention 2007; 14(2): 83-8.
3. Hansson L, Zanchetti A, Carruthers SG et al. Effects of intensive blood pressure lowering and low-dose aspirin in patients with hypertension: principal results of the Hypertension Optimal Treatment (HOT) randomised trial. Lancet 1998; 351: 1755-62.
- NICE. Hypertension. Management of hypertension in adults in primary care. CG34. London, NICE, 2006.
- European Society of Hypertension and European Society of Cardiology. 2007 Guidelines for the management of arterial hypertension. Eur Heart J 2007; 28: 1462-536.