Behind The Medical Headlines

Prehypertension and high normal blood pressure – a fundamental shift in the management of cardiovascular risk?

• Dr JJ Oliver, Clinical Pharmacology Unit and Research Centre, University of Edinburgh, Western General Hospital, Edinburgh, Scotland
• Professor DJ Webb, Clinical Pharmacology Unit and Research Centre, University of Edinburgh, Western General Hospital, Edinburgh, Scotland

Summary

Hypertension (high blood pressure) is a major risk factor for cardiovascular disease. Recent clinical guidelines have recommended a fundamental shift in the management of cardiovascular risk by recognising and treating ‘prehypertension’ - blood pressure levels which were previously considered to be safe. Dr James Oliver and Prof David Webb review the implications of the new guidelines.

Declaration of interests: No conflict of interests declared

Hypertension is a leading cause of the global disease burden, behind only malnutrition and unsafe sex. Although relatively more important in developed regions, it is also a major and growing cause of disease in the developing world.¹

Two major guidelines for the assessment and treatment of hypertension have been published this year, from the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure in the USA (JNC 7),² and the European Societies of Hypertension and Cardiology.³ While the recommendations in the two guidelines are similar in many respects, there are some differences. For example, the European guideline, but not JNC 7, emphasises the importance of overall cardiovascular risk assessment, rather than a strict focus on hypertension, when making treatment decisions.

The two guidelines classify blood pressure (BP) differently (Figure 1).

Perhaps the most controversial aspect of JNC 7 is that BP in the range 120-139/80-89 mmHg should be diagnosed as ‘prehypertension’. No longer will doctors be able to consider a BP of 120/80 mmHg either normal or completely safe! This is largely based on data from the Framingham Heart Study showing that, within four years, hypertension will develop in 39% of 35-64 year olds and 53% of 65-94 year olds if baseline BP is 130-139/85-89 mmHg, and 18% of 35-64 year olds and 29% of 65-94 year olds if baseline BP is 120-129/80-84 mmHg.⁴ The European guideline does not use the term prehypertension. It does, however, identify BP in the range 130-139/85-89 mmHg as ‘high normal’ BP. It then recommends that people with high normal BP initiate lifestyle measures, have other risk factors corrected and, if cardiovascular risk is high, start antihypertensive treatment. This approach is consistent with that recommended in JNC 7, indicating that this difference relates more to terminology than substance.

The European guideline categorises BP in the range 120-129/80-84 mmHg as normal, though not optimal. Therefore, it is really within these values that the approach to BP classification differs across the Atlantic. JNC 7, but not the European guideline, recommends that at this level of BP lifestyle measures should be instituted and treatment initiated for compelling indications, including high coronary risk.

Will targeting prehypertension or high normal BP reduce cardiovascular disease? Lifestyle measures can reduce BP in patients with hypertension.^2,3 Although reducing BP in this way might be expected to improve clinical outcome, direct evidence that lifestyle changes, even when they are adopted, ultimately reduce cardiovascular events or mortality is currently lacking. Also, there is no evidence that lifestyle measures prevent or delay hypertension in those with higher than optimal BP, let alone whether this approach will ultimately reduce the incidence of vascular disease. However, it is unlikely that direct evidence to support the guidance on prehypertension/high normal BP will be forthcoming. Some insight may be gained from observational data, but it would be impractical - and possibly unethical - to randomise people to lifestyle measures or no lifestyle measures prospectively. Furthermore, the benefits of targeting high normal BP or prehypertension would be expected to accrue over many years, possibly decades, a much longer time period than can be examined in clinical trials.

If the recommendations of the European guideline are adopted then full assessment of cardiovascular risk will be required in all patients with high normal BP. This would require formal diagnosis, after at least three separate BP measurements, an ECG, and measurement of abdominal circumference and plasma creatinine, lipids, C-reactive protein (a new development) and glucose. Lifestyle advice would then routinely be required, and some patients might need drug treatment. This is all likely to considerably increase clinical workload. In the US, 13% of the adult population have high normal BP.⁵ The burden of hypertension is greater in Europe than in the US.⁶ Therefore, while the increased workload might be greater here in Europe, we should probably take on board the prehypertension message even more seriously.

Will this approach to the prevention of cardiovascular disease be cost-effective? Cost-effectiveness will be difficult to measure, especially given that the benefits themselves are difficult to quantify. Nevertheless, in a resource-constrained healthcare system it is likely that widespread implementation will be at the expense of other, perhaps more cost-effective, healthcare measures.

Current practice in cardiovascular risk management is to target intervention at those at high risk of an event within ten years. Most people with high normal BP or prehypertension have a low ten-year risk. However, ten years is often not a relevant time frame for these people, especially when they are young. More relevant, is that they are at high risk relative to others of similar age. For some years the entire population has been encouraged to adopt a healthy lifestyle. In an attempt to combat cardiovascular disease in its early stages it seems rational that we should target this advice to people with high relative risk, even if this is a large group. Currently, however, we do not adequately manage patients at high risk. For example, in England, 46% of hypertensives were aware that they had hypertension. Of these, just over half were on treatment and, of those on treatment, just under a third were controlled to recommended values. Overall, just 9% of hypertensives had their BP controlled.⁷ Some would maintain that targeting intervention to those at high absolute risk should remain the priority.

The terms prehypertension and high normal BP are not supposed to suggest the presence of disease, at least not yet. Those with prehypertension, however, are referred to as patients in JNC 7. What will patients think of these BP categories? Many people previously considered entirely normal will now be labelled with a medical condition. Both guidelines appear to have been produced without wider consultation of the general public. Given the potential for widespread medicalisation this seems rather paternalistic. For example, public opinion might have been useful in deciding on terminology. Prehypertension has a more definitive ring to it; the patient is left with little doubt that they are no longer medically normal. This might have advantages. Perhaps it is more honest. Perhaps it will be more likely to provide the impetus for lifestyle change. Nevertheless, such an approach runs the risk of having a negative influence on perceptions of health in the population.

The identification and management of high normal BP has the potential to substantially improve the cardiovascular health of the nation. The principle, however, must first be accepted by the medical community, which will then have to take on the considerable challenge of implementation in clinical practice.

Prehypertension and high normal blood pressure – a paradigm shift in the management of cardiovascular risk?

References

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2. Chobanian AV, Bakris GL, Black HR et al. The seventh report of the joint national committee on prevention, detection, evaluation, and treatment of high blood pressure: The JNC 7 report. JAMA 2003; 289(19):2560-72.
3. 2003 European Society of Hypertension-European Society of Cardiology guidelines for the management of arterial hypertension. J Hypertens 2003; 21:1011-53.
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