Update on hypertension; EPCCS 2011

Update on Hypertension 2011
Diagnosis, monitoring and guidelines treatment targets

Prof. Richard McManus, Birmingham

Stroke risk increases with age and usual blood pressure. For a 10mmHg increase in systolic blood pressure, stroke risk increases by 38% and CHD risk by 18%. Meanwhile, the prevalence of hypertension is known to increase with age, and since Western populations are getting older, overall rates of hypertension are likely to increase. However, blood pressure changes continuously and it is known to vary both during the day and between seasons: indeed, it is generally lower in summer than in winter. Because of this variation, error can “drown out” the truth and it is possible to get false positive readings. Even on a single occasion, blood pressure has been shown to fall with an increasing number of measurements: indeed, a 12mmHg systolic drop has been found between the 1st and 5th blood pressure measurements taken sequentially, though readings generally stabilise after this point.

Ambulatory blood pressure monitoring is an alternative to usual measurements taken in the clinic environment. In the UK, the threshold for diagnosing hypertension via ambulatory monitoring is a day time average blood pressure of 135/85mmHg (National Institute of Clinical Excellence, 2011). Clinic thresholds can be converted to ambulatory equivalents by adjusting downwards by 5/5mmHg at lower blood pressures (<140/90mmHg) and 10/5mmHg at higher blood pressures (>140/90mmHg). Ambulatory monitoring has been shown to offer both improved sensitivity and specificity relative to clinic blood pressures. It is also better correlated with end-organ damage and outcome.

Where ambulatory monitoring cannot be tolerated, home blood pressure monitoring has also been shown to be superior to clinic measurements though it is not as prognostically accurate as ambulatory. Financial modelling recently undertaken has demonstrated the cost effectiveness of ambulatory monitoring: this is thanks to the savings achieved through improved cardiovascular outcomes and the reduced prescribing of anti-hypertensives which outweigh the additional equipment costs.

Home monitoring has also been shown to reduce blood pressure when combined with a co-intervention such as access to a nurse or patient education. Meanwhile, the costs of this are comparable to usual care. If home monitoring, then at least 4 days of readings are required and the first should be discarded. In some instances, this can also be extended to self management where the patient modifies their own treatment. The theoretical basis for this is in bypassing the clinical inertia of doctors whilst empowering patients to take action, improving their adherence to treatment and modifying their behaviours. The benefits of self management were demonstrated in the TASMINH study: this showed that systolic blood pressure was reduced after both 6 and 12 months of self management whilst diastolic blood pressure was reduced at 12 months only. Those in the intervention group were also able to reduce their treatment by 0.5 of an anti-hypertensive. The benefits of self-monitoring are therefore evident.

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