The preeminence of systolic blood pressure measurement in the management of patients with high blood pressure




Peter SEVER

by P. Sever,United Kingdom

Recent years have seen a switch in the focus of blood pressure measurement from diastolic to systolic pressure. A historical review of the subject reveals that early statements about raised systolic pressure having no pathological significance led to erroneous beliefs that diastolic pressures were all-important and should form the basis of blood pressure assessment. However, an extensive evidence base exists that confirms that systolic pressure is a more important prognostic determinant of cardiovascular disease, particularly in those over the age of 50 years. Systolic hypertension is by far the most common type of hypertension in the middle-aged and elderly, in whom diastolic pressures are frequently not elevated. A focus on diastolic pressure and use of it to determine thresholds and goals for treatment in these age groups is therefore misleading and irrelevant, and leads to inadequate treatment of most hypertensive subjects. For the majority of people, thresholds for diagnosis and treatment should be based on a single number—the systolic pressure. This will help to communicate an important health message to patients and policy makers, simplify treatment decisions for physicians, and lead to improvements in blood pressure control with accompanying reductions in cardiovascular morbidity and mortality.

Medicographia. 2010;32:250-253 (see French abstract on page 253)

For almost 100 years of blood pressure measurement, the focus has been on diastolic blood pressure. This is clearly an accident of history: research into the writings of the teachers of the early 20th century revealed that an editorial insertion into the posthumous 3rd edition (1926) of MacKenzie’s classic book Principles of Diagnosis and Treatment in Heart Affections led to the widespread misconception that increased diastolic pressure resulted fromelevated peripheral vascular resistance, and that high systolic pressure was an indicator of the strength of the heart.1 In Nicholson’s text (1915), the author’s view was also that the maximum systolic pressure was believed to indicate the strength of the heart.2 In 1926, Halls Dally reported that:

It is of the greatest importance to remember that of the two pressures, the minimal pressure is the more valuable, in that it is a measure of the burden which the arteries and valves must continuously bear, and from which there is no escape…Records of systolic pressure alone are of no value…Transitory systolic elevations which form the pulse represent only an intermittent and superadded load.3

The consequence of these widely disseminated beliefs was that generations of physicians embraced the all-too-simple explanation of blood pressure and were subsequently misguided in their assessment and management of patients with hypertension, resulting in a continuous focus on diastolic pressure throughout adult life that has contributed to poor overall blood pressure control (in particular lack of systolic control) and high residual cardiovascular risk, and has been a major contributor to global morbidity and mortality.

Figure 1
Figure 1.
The changes in systolic and diastolic blood pressure with age in three North American
populations.

After reference 5: Burt et al. Hypertension. 1995;25:
305-313. © 1995, American Heart Association, Inc.

Switch from preeminence of diastolic pressure to systolic pressure

The switch to the preeminence of systolic pressure, which has occurred gradually over the past 10-15 years, has been brought about because of overwhelming evidence from observational studies that systolic pressure is a more important prognostic determinant of cardiovascular disease end points than diastolic pressure, particularly in those over the age of 50 years.4 Systolic pressure rises with age, but diastolic pressure, which rises with age until around 50 years, thereafter falls (Figure 1)5 during a time period when cardiovascular disease incidence rises (Figure 2).

The prevalence of systolic hypertension is high in those over the age of 50 years, and accounts for more than 80% of hypertension in the older age group.6 Any focus on diastolic pressure in the middle-aged and elderly is, therefore, totally misleading. Higher levels of blood pressure in younger people are largely accounted for by an increase in peripheral vascular resistance, which, in turn, is due to functional and structural narrowing of small arteries and arterioles. With advancing age, increasing rigidity in larger arteries generates higher levels of systolic pressure, but is associated with lower diastolic pressures.7,8

Whilst systolic and diastolic pressures are both strong predictors of cardiovascular morbidity and mortality, as age advances, systolic pressure becomes a far more important determinant of future cardiovascular events, and should thus be the figure upon which therapeutic decisions are made.

Figure 2
Figure 2. Prevalence of isolated systolic hypertension, systolicdiastolic
hypertension, and isolated diastolic hypertension in different
age groups.

After reference 6: Franklin et al. Hypertension. 2001;37:869-874. © 2001,
American Heart Association, Inc.

The switch to the preeminence of systolic pressure is also supported by overwhelming evidence from intervention trials that lowering systolic pressure confers substantial benefits on cardiovascular outcomes.9-12 Regrettably, this evidence base has been accompanied by a slow and disappointing rate of uptake in clinical practice in the management of raised systolic pressure and the achievement of systolic blood pressure targets. As recently as 2004, control of blood pressure to the target levels set by national and international guidelines (<140/90 mm Hg) was achieved in only 5%-15% of people in Europe, and even fewer in those at higher risk, such as those with diabetes, for whom a lower target is set (<130/ 80 mm Hg).13

Explanations for failure to achieve systolic blood pressure goals certainly include the historical focus on the physiology of the circulation and the perceived role of diastolic pressure, but this has been compounded by evidence from trials that have been mainly based on diastolic pressure thresholds for intervention and for treatment goals. Widespread teaching on the importance of diastolic pressure together with an outdated but long-held view that “normal” systolic pressure is “100 plus age” have also contributed. Such traditions have clearly shackled progress in this important field of medicine.

Current proposals

The current proposals, therefore, are that for the majority of people, thresholds for diagnosis and treatment should be based on a single number—the systolic blood pressure14-16— simply because systolic blood pressure is the defining feature of hypertension in those over the age of 50 years (when most hypertension occurs), and that a continuing focus on diastolic blood pressure is misleading and irrelevant and leads to inadequate treatment of most hypertensive subjects. Systolic pressure is easier to measure (and can be more accurately measured), and distilling the risk of high blood pressure into a single number will greatly assist communication of the all-important public health message to patients and policy makers and the simplification of thresholds and targets for physicians.

For those less than 50 years of age, diastolic blood pressure should be considered along with systolic blood pressure, but the latter should be the main target. One issue arising from this recommendation is whether those with isolated diastolic hypertension (diastolic blood pressure >90 mm Hg, systolic blood pressure <140 mm Hg) warrant therapeutic intervention in the light of the questionable benefits of treatment in this low-risk group. Concerns have been raised that a switch to a focus on systolic blood pressure and the abandonment of consideration of diastolic blood pressure levels could lead to harmful outcomes in selected patient subgroups. Such concerns have been largely ameliorated following observations in high-risk patients with isolated systolic hypertension undergoing antihypertensive treatment in placebo-controlled trials such as the Systolic Hypertension in the Elderly Programme,9 the Syst- EUR Trial,10 The Hypertension in the Very Elderly Trial,11 and the Medical Research Council Trial in Older Patients with Hypertension.12 In these studies, substantial reductions in systolic blood pressure were accompanied by falls in diastolic pressures to levels as low as 60 mm Hg, which were not associated with adverse outcomes. However, other studies that included patients with established coronary disease suggested that those achieving the lowest diastolic pressures (50-70 mm Hg) were at higher risk of subsequent ischemic coronary events (observations compatible with the “J-curve” hypothesis).17 Whilst these data are understandable, the extrapolation of the concept of a J-curve relationship to older hypertensive patients in general, and particularly those with isolated systolic hypertension, has led to the reluctance of some physicians to aggressively treat systolic blood pressure, with the result that the protection of a small minority of patients with established coronary disease is accompanied by failure to achieve systolic blood pressure goals in the vast majority for whom low diastolic pressures do not confer an additional risk.

The final issue concerns those patients in the younger age group (<50 years) in whom elevated diastolic pressure is not associated with raised systolic pressure (isolated diastolic hypertension). In some observational studies18 but not others,19 raised isolated diastolic pressure does confer an increased cardiovascular risk in the longer term, but the absolute risk associated with isolated diastolic hypertension is extremely small and would be far below any threshold advocated by contemporary guidelines for therapeutic intervention. It may be that in some patient subgroups, such as those with obesity, isolated diastolic hypertension predicts the development of combined systolic and diastolic hypertension in later years.20 However, for reasons stated above, the absolute risks in this group are very low, and nonpharmacological, ie, lifestyle,measures would be a more appropriate course of intervention.

Following “My Personal View” published in the BMJ in 1999,14 a large general practice in South Wales implemented a policy of treatment decisions based solely on systolic pressure measurements. Over the following 4 years, repeated practice audits showed blood pressure control to targets increased by more than 20% in those over 60 years, and by more than 30% in those less than 60 years (Glyn Elwyn personal communication).

Conclusion

Hypertension must be one of the most extensively studied areas of medicine, with a wealth of observational data and outcomes from randomized intervention trials establishing the risks and benefits of treatment. It is, therefore, a great disappointment that translation of this extensive database and its conclusions into better models of patient care has not been achieved. Whilst those of us involved in producing national and international guidelines must bear some responsibility for ignoring the all-important question of why guidelines have not been implemented (too long, too detailed, too complicated, and at times inconsistent), it is likely that difficulties associated with managing two numbers—systolic blood pressure and diastolic blood pressure—have led to uncertainties and confusion in the minds of practicing physicians, with the inevitable outcome of poor systolic control and high residual cardiovascular morbidity and mortality. As the late Geoffrey Rose once stated, “One sometimes wishes that Nikolai Korotkov had never described the fourth and fifth phases…” _

References
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Keywords: systolic; diastolic; blood pressure; measurement; treatment guideline; cardiovascular disease; predictor