Cardiology GPSI Dr Chris Arden on when to order ambulatory blood pressure monitoring and how to interpret the results
1 It's not just useful for white coat hypertension. Consider ambulatory blood pressure monitoring (ABPM) in patients with suspected white coat hypertension (with no evidence of end-organ damage) but also in those with borderline or labile hypertension, and to assist in management of patients whose blood pressure is apparently poorly controlled, despite using appropriate antihypertensive therapy. ABPM may also be useful in assessing control throughout the day in patients at high risk of cardiovascular events, and deciding on treatment in elderly patients or for evaluation of patients with suspected orthostatic hypotension or syncope.
2 Clinical endpoints are more tightly correlated with ABPM readings than clinic readings. Data from prospective studies demonstrate that an ABPM profile better predicts cardiovascular morbidity and mortality, as well as other outcomes, including LVH regression, than conventional clinic measurements. In addition an ambulatory monitor provides a profile of BP readings away from the medical environment.
3 White coat hypertension is very common. The prevalence is between 10-30% and increases with age. There are no clearly identifiable predisposing factors although there is evidence the prognosis is between that of normotensive patients and those with established hypertension.
4 ABPM helps in hypotension too. ABPM may be a useful investigation in patients with suspected orthostatic hypotension or syncope, as well as identifying any drug-induced hypotension. Establishing a link between antihypertensive medication and excessive BP lowering is key, as it may result in adverse effects in patients with a compromised arterial circulation, including those with coronary or cerebrovascular disease.
5 It's especially useful in older patients. Optimising antihypertensive therapy, and minimising adverse effects of pharmaocotherapy, is a key consideration in the elderly. Evidence shows that clinic systolic BP readings may average 20mmHg higher than daytime ABPM readings, potentially leading to overestimation of isolated systolic hypertension in the elderly, which may result in unnecessary treatment.
6 ABPM profiles should be interpreted with reference to diary information and timing of any antihypertensive drug treatment. It is important to remember that BP values obtained by either ABPM or home monitoring are on average 10/5mmHg lower than those obtained by clinic measurements. This difference is even more exaggerated for systolic BP in elderly patients with isolated systolic hypertension.
7 Nocturnal readings can be hugely informative. The absence of nocturnal blood pressure ‘dipping' is strongly associated with target organ damage and may suggest secondary hypertension. ABPM is the only non-invasive technique that measures BP during sleep, and is generally well tolerated. Patients with a ‘non-dipping' nocturnal profile have a significantly raised cardiovascular risk, even if they have an overall normotensive ABPM profile.
8 ABPM allows more rational antihypertensive drug treatment. Evidence shows that adjustment of medication based on either ABPM or clinic BP measurements results in less intensive treatment in ABPM patients. Importantly, patients in this group had similar outcomes, and left ventricular mass measured by echocardiography, as patients receiving more intensive treatment regimes.
9 Think carefully about equipment and training if bringing ABPM in-house. Only use equipment validated by the British Hypertension Society (www.bhsoc.org). The guidelines recommend observer training and assessment, calibration testing and ongoing equipment evaluation. Patients should ideally be monitored on a normal working day, rather than a day off. An ABPM recording is acceptable if more than 85% of readings are suitable for analysis.
10 Make sure the software meets your needs too. In considering an ABPM device, refer to either the British Hypertension Society or the European Society of Hypertension (www.eshonline.org) recommendations. All ABPM devices are sold with software packages, which present the data in varying formats. A setting software that presents day and night BP averages together with a visual plot may be sufficient, although more complex analysis software programmes are available, which may be useful for research purposes.
Dr Chris Arden is a GP in Chandlers Ford, Hampshire, and a cardiology GPSI at Solent Healthcare
Competing interests: none declared
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