Head To Head

Is systolic blood pressure all that matters? Yes

BMJ 2009; 339 doi: http://dx.doi.org/10.1136/bmj.b2665 (Published 10 July 2009) Cite this as: BMJ 2009;339:b2665
  1. Peter Sever, head of department
  1. 1International Centre for Circulatory Health, Imperial College London, London W2 1NY
  1. p.sever{at}imperial.ac.uk

    Peter Sever argues that abandoning diastolic measurements will improve control of blood pressure, but Eoin O’Brien (doi:10.1136/bmj.b2669) thinks that we should change the method of measurement instead

    Tradition invariably shackles progress: for almost 100 years the focus of blood pressure measurement has been on diastolic pressure. Now despite persuasive findings from observational studies and the results of trials of interventions to lower systolic pressure, we remain unable to accept the new model in which systolic pressure is pre-eminent. A continuing focus on diastolic pressure throughout adult life is arguably the most important factor contributing to poor control of blood pressure, high residual cardiovascular risk, and global morbidity and mortality.

    As recently as 2004, only 5-15% of people in Europe met the guideline targets for blood pressure (<140/90 mm Hg), with the proportion for high risk groups being even smaller.1 The switch in emphasis to the importance of systolic blood pressure is relatively recent, but many doctors who have achieved diastolic control in their patients still fail to modify treatment further to achieve systolic targets.2

    If at the time of the switch to the pre-eminence of systolic pressure we had abandoned diastolic pressure measurement, as I have advocated,3 the new focus on systolic pressure as a guide to therapeutic decision making would have been more successful and in all probability have led to better rates of control.

    Problems with diastolic pressure

    Preoccupation with diastolic pressure as the basis for the conduct of observational studies and intervention trials seems to have been an accident of history. An editorial insertion to a posthumous edition of MacKenzie’s classic book on the heart and circulation, published in 1926,4 led to the widespread misconception that increased diastolic pressure resulted from raised peripheral vascular resistance but that high systolic pressure was an indicator of a strong heart. As a result, generations of doctors embraced an all too simplistic explanation of blood pressure and were subsequently misguided in their assessment and treatment of patients with hypertension.

    Systolic pressure rises with age but diastolic pressure, which rises with age to around 50 years, thereafter falls. The prevalence of systolic hypertension, due to increased rigidity of large arteries,5 is high in people older than 50 years, and as age advances systolic pressure becomes a far more important determinant of future cardiovascular events.6 Thus therapeutic decisions should be based on systolic and not diastolic pressure, particularly in the light of the strong evidence for the benefits of reducing systolic pressure observed in two trials of isolated systolic hypertension; stroke and coronary events were reduced by active treatment by about 40% and 25% respectively.7 8

    On the other hand, when systolic pressure is at the lower end of the continuum (for example <140 mm Hg) the risks associated with raised diastolic pressure are small. So in the absence of systolic hypertension, how important is isolated diastolic hypertension? Over the age of 60 years isolated diastolic hypertension is rare.9 Although in younger people it occurs more commonly, its contribution to the disease burden is small. In the Health Survey for England, 2006, isolated diastolic hypertension was present in 1% and 2.7% of the untreated population aged 16-34 and 35-54 years respectively (E Falaschetta and N Poulter, personal communication), and in prospective studies involving 12.7 million person years of risk,10 raised diastolic pressure in isolation (>90 mm Hg) accounted for only 104 (0.9%) of all stroke deaths and 392 (1.2%) of all coronary deaths (S Lewington, personal communication). No intervention trials have been, nor could be, sufficiently large to evaluate the benefits of blood pressure lowering in isolated diastolic hypertension.

    Treatment decisions

    Isolated diastolic hypertension at a younger age can herald the subsequent development of combined systolic and diastolic hypertension, and its retention as a marker of future cardiovascular disease in younger subjects may therefore be justified. However, there is little justification for its retention as a determinant of treatment decisions. Its measurement is less accurate, and it is less powerful than systolic blood pressure as a predictor of future events; when both systolic and diastolic pressure are raised, systolic pressure should guide therapeutic decisions. Few doctors will treat isolated diastolic hypertension, not least in the UK because diastolic pressure is not incorporated into the charts for cardiovascular risk assessment.

    Following my proposal to abandon measuring diastolic pressure in1990,3 a large general practice in South Wales implemented a policy of treatment decisions based solely on systolic pressure. Over the following four years, repeated practice audits showed blood pressure control to targets increased by more than 20% in people over 60 years and by more than 30% in those less than 60 years (G Elwyn, personal communication). I therefore rest my case.

    The all important message to doctors and patients is for a renewed focus on systolic blood pressure and its control, without which there will remain unacceptable levels of poorly controlled hypertension and a high prevalence of largely preventable cardiovascular morbidity and mortality.11 As Geoffrey Rose said “One sometimes wishes that Nikolai Korotkoff had never described the fourth and fifth phases.”

    Notes

    Cite this as: BMJ 2009;339:b2665

    Footnotes

    • I thank Alun Hughes and Kennedy Cruickshank for their helpful comments and Bryan Williams and Lars Lindholm for earlier discussions on this subject. I thank the NIHR Biomedical Research Centre Funding Scheme for support.

    • Competing interests: None declared.

    References