With NICE set to change its hypertension diagnostic guidelines, cardiology GPSI Dr Chris Arden offers his tips on using ABPM effectively
1. Draft NICE guidance recommends we offer ABPM to anyone with two high clinic readings.
New NICE guidance on hypertension is due out later this year, and it's likely to recommend we offer ABPM to all patients who have had two clinic readings higher than 140/90mmHg. This may seem daunting for practices not currently doing it, but in the long run fewer patients will be wrongly diagnosed and treated.
2. It's not just useful for suspected white-coat hypertension.
White-coat hypertension is very common, with a prevalence of between 10-30%, and increases with age. There are no clearly identifiable predisposing factors, but there is increasing evidence that the prognosis for this group of patients is intermediate, between that of those with normotension and those with established hypertension. But ABPM is also useful in managing patients whose blood pressure is apparently poorly controlled, despite using appropriate antihypertensive therapy. It may also prove useful in assessing adequacy of
24-hour blood pressure control in patients at particularly high risk of cardiovascular events, and deciding on indications for treatment in elderly patients or for evaluation of patients with suspected orthostatic hypotension or syncope.
3. Remember, clinical end points are more tightly correlated with ABPM readings than they are with those taken in the clinic.
Many studies over the past 25 years have shown that end-organ damage associated with hypertension is more strongly correlated with ABPM readings than with clinic measurements.
Findings from prospective studies demonstrate that an ABPM profile better predicts cardiovascular morbidity and mortality, as well as other clinical outcomes – including left ventricular hypertrophy regression – as compared with conventional clinic measurements.
In addition, an ambulatory monitor provides a profile of blood pressure readings away from the medical environment.
4. ABPM is useful in hypotension too.
ABPM may be a useful investigation in patients with suspected orthostatic hypotension or syncope, as well as identifying any significant drug-induced hypotension. Establishing a relationship between antihypertensive medication and excessive blood pressure lowering is important, as it may result in untoward effects in patients with a compromised arterial circulation, including those with significant coronary or cerebrovascular disease.
5. It's especially useful in older patients.
Optimising antihypertensive therapy, and minimising potential adverse effects of pharmacotherapy, is an important consideration in the elderly. Evidence shows that clinic systolic blood pressure readings may average 20mmHg higher than daytime ABPM measurements – potentially leading to overestimation of isolated systolic hypertension in older patients, which may result in unnecessary treatment. The elderly experience hypotensive states, caused by baroreceptor or autonomic impairment, which may be detected on ABPM screening.
6. ABPM profiles should be interpreted with reference to diary information and timing of any antihypertensive drug treatment.
Normal (non-pregnant) adult ABPM values are <135/85 mmHg during the day, <120/75mmHg during the night and <130/80mmHg over 24 hours.
It is important to remember that blood pressure values obtained by either ABPM, or home blood pressure monitoring, are on average 10/5mmHg lower than those obtained by clinic measurements. This difference is even more exaggerated for systolic blood pressure in elderly patients with isolated systolic hypertension.
7. The nocturnal readings can be hugely informative.
The absence of nocturnal blood pressure ‘dipping' is strongly associated with target organ damage and may suggest the presence of underlying secondary hypertension. ABPM is the only non-invasive technique that permits measurement of blood pressure during sleep, and is generally well tolerated. The nocturnal fall in blood pressure (normally by more than 10% of the daytime average) is more a result of cessation of activity than of sleep itself. Patients with a ‘non-dipping' nocturnal profile have a significantly increased cardiovascular risk, even if they have an overall normotensive ABPM profile.
8. ABPM allows much more rational antihypertensive drug treatment.
Recent reviews have highlighted the benefits of ABPM in assessing an individual's response to antihypertensive therapy.
In particular, evidence shows that adjustment of treatment – based on either ABPM or clinic blood pressure measurements – results in less intensive drug treatment in the ABPM patients.
Importantly, individuals in this group had similar outcomes, and left ventricular mass measured by echocardiography, as patients receiving conventional care and more intensive treatment regimes.
9. Think carefully about equipment choice and training if you're planning to bring ABPM in-house.
Only ABPM equipment validated, to international standards, by the British Hypertension Society (www.bhsoc.org) should be used. The guidelines recommend observer training and assessment, calibration testing and an ongoing schedule of equipment evaluation.
Patients should ideally be monitored on a normal working day, rather than rest day, to provide a more representative blood pressure profile. The ABPM readings may be less reliable during exercise, driving or when the cardiac rate is irregular, as in atrial fibrillation.
A general rule is that an APBM 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 appropriate ABPM device, clinicians should refer to either the British Hypertension Society or the European Society of Hypertension (www.eshonline.org) recommendations. All ABPM devices are sold with individual software packages, which present the data in varying formats.
In the general practice setting, software which presents the day and night blood pressure averages, together with a visual plot, may be sufficient, although more complex analysis software is available, which may be useful for research purposes.
Dr Chris Arden is a GP in Southampton and is a GPSI in cardiology at NHS Southampton City
Competing interests None declaredAmbulatory blood pressure monitor Ambulatory blood pressure monitor