The risk of death, stroke and coronary heart disease (CHD) increases continuously with increasing BP with no evidence of a threshold. The excess risk of stroke and CHD associated with BP differences of varying degrees is illustrated in Table 1.1.

Table 1.1 Effect of a sustained difference in BP on risk of stroke and
CHD






























Difference in usual
% increase in risk of
SBP (mmHg)
DBP (mmHg)
Stroke
CHD
9
5
34
21
14
7.5
46
29
19
10
56
37

Meta-analysis of outcome trials shows that the reduction in risk achieved by ntihypertensive treatment is approximately constant whatever the starting BP. Antihypertensive treatment
producing a 5–6mmHg fall in DBP results in an approximately 36% reduction in stroke and a 16% reduction in CHD. Greater BP lowering would be expected to achieve greater risk reductions. Although the observed reduction in stroke risk from intervention trials is commensurate with that predicted by observational studies, the observed reduction in CHD risk is less than that expected (see Table 1.2). The reason for this discrepancy is unclear but might reflect: a clustering of additional cardiovascular risk factors (for example diabetes and hypercholesterolaemia) in hypertensive subjects; an adverse effect of some antihypertensive drugs (e.g. thiazides and ß blockers) on plasma lipids; or the effect of pre-existing end-organ damage.

Table 1.2 Reductions in stroke and CHD risk resulting from a 5–6 mmHg reduction in BP




















Reduction in risk (%)

Expected
Observed
Stroke
35–40
31–45
CHD
20–25
8–23

No comments: