Guidelines from the British Hypertension Society

Hypertension represents a major public health concern. It affects about a billion people worldwide and is the most common treatable risk factor for cardiovascular disease in patients aged over 50. In the United Kingdom, the prevalence of hypertension (blood pressure more than 140/90 mm Hg) has been estimated to be 42% in people aged 35 to 64.¹ Large benefits, in terms of avoided cardiovascular disease, are expected from the treatment of hypertension. However, these benefits are low because the control of hypertension remains poor in European countries—particularly in the United Kingdom, where it is controlled in only 10% of the hypertensive population.²

These past years, a huge quantity of novel data has been published on the prominent role of lowering blood pressure in the reduction of cardiovascular disease and on the safety and effectiveness of antihypertensive drugs. Two guidelines for management of hypertension, updating previous ones, were published in 2003.³,⁴ They originate from the European Society of Hypertension/European Society of Cardiology⁵ and the US Joint National Committee.⁶

Is it worth having a third one, written by the British Hypertension Society?⁷ Although the major features of most of these recommendations are similar, they differ in some aspects; doctors may consider these guidelines as matters for specialists and may exaggerate the difficulty of treating hypertension. Thus we run the risk of dilution of the main message, which is to simplify the therapeutic approach, at a time where all efforts are needed to fight against the under diagnosis and under treatment of hypertension. However, tailoring guidelines for the United Kingdom has two advantages: these recommendations implement previous guidelines which doctors are familiar with,⁸ and they are adapted to the NHS.

The British guidelines, which are published as a summary in this issue (p 634), simplify the therapeutic approach by selecting a small number of evidence based key actions.⁷ Several boxes are added to give immediate answers to some key questions, for instance concerning the treatment target for antihypertensive drug therapy, or the contraindications for the major classes of antihypertensive drugs.

The strength of these guidelines is to delineate clearly the main objectives of the primary care physician, and the means for reaching these objectives. For instance, the choice of initial treatment has been facilitated by recent meta-analyses showing that overall most classes of drugs are similarly safe and effective. These include the diuretics and β blockers (older drugs) and calcium channel blockers, angiotensin converting enzyme inhibitors, and angiotensin II receptor blockers (newer drugs).⁹

The British guidelines remind us that “the main determinant of benefit from blood pressure lowering drugs is the achieved blood pressure, rather than the choice of therapy.” In other words, the lower the pressure the better. Worldwide, a common reason for poor control of blood pressure is that most doctors keep using monotherapy in patients who obviously need combination therapy to normalise blood pressure. The British guidelines insist on at least two blood pressure lowering drugs in most patients. A simple treatment algorithm, named AB/CD, is now formally incorporated into the guidelines and underscores the need for two or three drugs for most patients.¹⁰ Particularly, it states that drugs that inhibit the renin-angiotensin system—angiotensin converting enzyme inhibitors and angiotensin II receptor blockers (A) or β blockers (B)—should be logically combined with drugs which do not inhibit it—calcium channel blockers (C) or diuretics (D).¹¹ Although this therapeutic approach has yet to be validated by controlled trials, it illustrates the pharmacological synergy between drugs. By recommending the AB/CD algorithm, the British guidelines are more prescriptive than the European guidelines, which maintained α blockers as first line drug treatment and offered a larger possibility of drug combinations.

The British guidelines also differ from the US guidelines, which positioned thiazide-type diuretics in the centre of treatment strategy after the ALLHAT trial showed that a therapeutic strategy based on a thiazide-type diuretic was superior to strategies based on a calcium channel antagonist or an angiotensin converting enzyme inhibitor in preventing some major forms of cerebrovascular disease. These different therapeutic strategies should be compared for their effectiveness in lowering blood pressure and cerebrovascular disease.

“The lower the pressure the better” is particularly true for patients at high cardiovascular risk. The British guidelines provide simple means, like European guidelines and to a larger extent than US guidelines, for identifying hypertensive patients at high cardiovascular risk—diabetes, complications of hypertension, target organ damage, or a 10 year cerebrovascular disease risk of 20% or more. (A risk scoring system to detect these patients more precisely, jointly established by the British societies and adapted from epidemiological data recorded in the United Kingdom, is available in the full version of the British Hypertension Society's guidelines or on the society's website (www.bhsoc.org).¹²) The theoretical benefit in reducing cerebrovascular disease is largest in this high risk population. Unfortunately, this is precisely the population in which the rate of control of hypertension is one of the lowest.

In any case, adherence of primary care physicians to the British guidelines is key to successfully treating their individual patients, thus improving the rate of control of hypertension and reducing cardiovascular events.