What blood pressure should I treat?

Who to treat
The primary aim of blood pressure (BP) treatment is to reduce the risk of stroke and CHD. Assuming secondary causes of hypertension have been excluded, the decision to treat a particular level of BP is based on an assessment of the risk of stroke, coronary heart disease (CHD) and hypertensive renal disease in the individual patient. All patients with evidence of target organ damage (left ventricular hypertrophy, retinopathy, or hypertensive ephropathy) are considered to be at high risk and should receive treatment whatever the level of BP. Similarly, all patients who have previously suffered a stroke or CHD should have their BP lowered if it is above 140/90mmHg.

Difficulties arise in those without end-organ damage or a previous cardiovascular event. Guidelines in the UK have advocated antihypertensive treatment for sustained BP levels
above 160/100mmHg since in these individuals the risks of stroke and renal disease are unacceptably high. Absolute risk of stroke or CHD depends, however, not only on BP but also on the combination of other risk factors (age, gender, total cholesterol, HDLcholesterol, smoking, diabetes, and left ventricular hypertrophy). Their synergistic interaction in any individual makes universal application of BP thresholds perhaps inappropriate and some
individuals with BP >140/90mmHg will benefit from treatment. Recent guidelines on treatment have also advocated a global assessment of risk rather than focusing on individual risk factors. The risk of stroke or CHD in an individual can be calculated using tables1 or computer programmes2 based on a validated risk function (for example Framingham Risk Equation). Having calculated absolute risk (based on the variables above), one has to decide what level of risk is worth treating. A low threshold for treatment will result in a larger number of individuals exposed to antihypertensive drugs and a higher cost, but a greater number of cardiovascular events saved. Meta-analysis has shown that (for a given level of BP lowering) the relative reduction in stroke and CHD is constant whatever the starting level of BP. Thus, the absolute benefit from BP lowering depends on the initial level of risk. A threshold cardiovascular event risk of 2% per year has been advocated by some1 and equates to treating 40 individuals for five years to save one cardiovascular event (myocardial nfarction, stroke, angina or cardiovascular death).

Young patients
Since age is a major determinant of absolute risk, treatment thresholds based on absolute risk levels will tend to postpone treatment to older ages. However, younger patients with elevated BP who have a low absolute risk of stroke and CHD exhibit greatly elevated relative risks of these events compared to their normotensive age-matched peers. Deciding on the optimal age of treatment in such individuals presents some difficulty and the correct strategy has yet to be determined.

Elderly patients
The absolute risk of CHD and stroke in elderly hypertensive patients is high and, consequently, the absolute benefit from treatment is much greater than in younger patients. Decisions to treat based on absolute risk are therefore usually straightforward. However, there is little in the way of firm trial evidence for the benefits of treatment in individuals aged more than 80. In these patients, decisions could be made on a case-by-case basis taking
into account biological age.

What to aim for
Although it might be assumed that the lower the BP the lower the risk of stroke and CHD, some studies have described a Jshaped relationship between BP and cardiovascular events,
where the risk of an adverse outcome rises slightly at the lower end of the BP range. However, in the large Hypertension Optimal Treatment (HOT) study3 lowering BP to 130–140/80–85 mmHg was safe. While there was no additional advantage of lowering
BP below these levels (except possibly in diabetic subjects), there was also no evidence of a J-shaped phenomenon in this large trial.