Doctors treating high blood pressure rely on the wrong methods to measure blood pressure, a Belgian study has discovered.

The study, from the University of Leuven, Belgium, was a meta analysis of major blood pressure studies and found that doctors can misjudge a patient's need for antihypertensive therapy as well as the risk of fatal and non fatal complications because they focus almost exclusively on diastolic blood pressure measurements those measuring the pressure of blood returning to the heart.

To examine the importance of diastolic, systolic and mean BP measurements on the risk of fatal and non fatal coronary and vascular events, the Belgian team carried out a meta analysis of eight trials involving 15,693 patients aged 60 years or more. The study included patients with systolic hypertension (a systolic BP of 160 mmHg or greater and a diastolic BP less than 95 mmHg), who were followed up for an average of 3.8 years.

Overall, the Belgian researchers found that, in untreated patients, systolic blood pressure was a more accurate predictor of fatal and non fatal complications than diastolic blood pressure.

The researchers concluded that a 10-mmHg increase in systolic BP was significantly linked with increases of nearly 10 per cent in the risk of all fatal and non fatal complications, except coronary events.

In contrast, lower diastolic BP measurements were associated with an increase in total and cardiovascular mortality. Nevertheless, diastolic BP did not prove to have a significant influence on deaths from all causes.

What was significant, say the authors, was the pulse pressure in each of the patients. This proved to be useful in targeting those who might benefit from antihypertensive treatment. A pulse pressure of 90 mmHg or more proved protective.

If only those with a lower pulse pressure were treated, the number of patients needed to be treated in order to prevent one cardiovascular death would be reduced by nearly half.

Across all the trials reviewed, antihypertensive therapy was less effective than many would imagine. Overall, drugs only reduced fatal and non fatal events by 26 per cent for all cardiovascular complications, 30 per cent for stroke and 23 per cent for coronary events.

The meta analysis concluded that those most likely to benefit from antihypertensive therapy were men, older patients and those with previous cardiovascular complications (Lancet, 2000; 355: 865-72).