The cardiovascular complications associated with hypertension are shown in Box 19.1. The most common and important of these are stroke and myocardial infarction. An increase of 5 mmHg in usual diastolic blood pressure is associated with a 35–40% increased risk of stroke. There is a similar but less steep association for coronary heart disease risk. The risk of heart failure is increased six-fold in hypertensive subjects. Meta-analysis of clinical trials has indicated that these risks are reversible with relatively modest reductions in blood pressure of 10/6 mmHg associated with a 38% reduction in stroke and 16% reduction in coronary events (Collins et al., 1990), while a 5 mmHg reduction in blood pressure is associated with a 25% reduction in risk of renal failure.

The absolute benefits of blood pressure lowering achieved as a result of these relative risk reductions depend on the underlying level of risk in an individual. High-risk subjects gain more benefit in terms of events saved per year of therapy. Absolute risk is highest in those who already have evidence of cardiovascular disease, such as previous myocardial infarction, transient ischaemic attack or stroke, or who have other evidence of cardiovascular dysfunction such as electrocardiogram (ECG) or echocardiograph abnormality. Risk is also increased in the elderly and in people with diabetes or renal failure and is further enhanced by other risk factors such as smoking, dyslipidaemia, obesity and sedentary lifestyle. In those under the age of 75, men are at greater risk than women. Cardiovascular risk in an individual who has no current cardiovascular disease can be estimated from coronary risk prediction charts (Joint British Societies, 2005; see Chapter 24).

Epidemiology

Between 10% and 25% of the population are expected to benefit from drug treatment of hypertension; the exact figure depending on the cut-off value for blood pressure and the age group considered for active treatment.

In 90–95% of cases of hypertension, there is no underlying medical illness to cause high blood pressure. This is termed ‘essential’ hypertension, so named because at one time it was erroneously believed to be an ‘essential’ compensation mechanism to maintain adequate circulation. The precise aetiology of essential hypertension is currently unknown. Genetic factors clearly play a part as the condition clusters in families, with hypertension being twice as common in subjects who have a hypertensive parent. Genetic factors account for about one-third of the blood pressure variation between individuals, although no single gene appears to be responsible except in some rare conditions such as polycystic kidney disease and other metabolic conditions such as Liddle’s syndrome (Beevers et al., 2001). The remaining 5–10% of cases are secondary to some other disease process (Box 19.2).

Hypertension is more common in black people of African Caribbean origin, who are also at particular risk of stroke and renal failure. Hypertension is exacerbated by other factors, for example, high salt or alcohol intake or obesity.

Regulation of blood pressure

The mean blood pressure is the product of cardiac output and total peripheral resistance. In most hypertensive individuals, cardiac output is not increased and high blood pressure arises as a result of increased total peripheral resistance caused by constriction of small arterioles.

Control of blood pressure is important in evolutionary terms and a number of homeostatic reflexes have evolved to provide blood pressure homeostasis. Minute-to-minute changes in blood pressure are regulated by the baroreceptor reflex, while the renin–angiotensin–aldosterone system is important for longer term salt, water and blood pressure control. Long-term increases in shear stress can cause vascular remodelling of the endothelium which lead to the formation of a procoagulant rather than anticoagulant surface. At the same time, systems that lead to vascular relaxation, for example nitric oxide, are overcome by increased sensitivity to vasoconstricter substances such as endothelin which predispose to vascular disease and further increases in peripheral resistance which lead to a vicious cycle increasing blood pressure further due to the increase in vascular resistance. Other substances with a role in controlling blood pressure include atrial natriuretic peptide, bradykinin and antidiuretic hormone. Some new therapies seek to treat high blood pressure by modifying responses to these substances, for example, the endothelin antagonist darusentan.

Clinical presentation

Hypertension is often an incidental finding when subjects present for screening or with unrelated conditions. Severe cases may present with headache, visual disturbances or evidence of target organ damage (stroke, ischaemic heart disease or renal failure). In the UK, all patients under 80 years of age should have their blood pressure checked at least every 5 years, with an annual review for those with high normal values in the range 135–139 mmHg systolic or 85–89 mmHg diastolic.

Malignant (accelerated) hypertension

Malignant or accelerated hypertension is an uncommon condition characterised by greatly elevated blood pressure (usually >220/120 mmHg) associated with evidence of ongoing small vessel damage. Fundoscopy may reveal papilloedema, haemorrhages and/or exudates, while renal damage can manifest as haematuria, proteinuria and impaired renal function. The condition may be associated with hypertensive encephalopathy, which is caused by small vessel changes in the cerebral circulation associated with cerebral oedema. The clinical features are confusion, headache, visual loss, seizures and coma. Brain imaging (particularly MRI) usually demonstrates extensive white matter changes. Malignant hypertension is a medical emergency that requires hospital admission and rapid control of blood pressure over 12–24 h towards normal levels.

Management of hypertension

In the UK, the management of hypertension is guided by consensus guidelines produced by the British Hypertension Society (BHS) and the National Institute for Health and Clinical Excellence (NICE). In 2004, there were significant differences between NICE and BHS guidance but these were addressed in the form of modified joint guidance issued in 2006 which specifically addressed the areas of controversy (National Collaborating Centre for Chronic Conditions: Hypertension, 2006). The European Society of Hypertension also published a task force discussion document in January 2009 and formal guidance in 2007 (Mancia et al., 2009).

Diagnosis of hypertension

In the UK, it is recommended that all adults have their blood pressure measured every 5 years. Those with high normal (130–139 mmHg systolic or 85–89 mmHg diastolic) or previous high readings should have annual measurement.

Blood pressure should be measured using a well-maintained sphygmomanometer of validated accuracy. Blood pressure should initially be measured in both arms and the arm with the highest value used for subsequent readings. The subject should be relaxed and, at least at the first presentation, blood pressure should be measured in both the sitting and the standing positions. An appropriate sized cuff should be used since one that is too small will result in an overestimation of the patient’s blood pressure. The arm should be supported level with the heart and it is important that the patient does not hold their arm out since isometric exercise increases blood pressure. Blood pressure is measured using the Korotkov sounds which appear (the first phase) and disappear (the fifth phase) over the brachial artery as pressure in the cuff is released. Cuff deflation should occur at approximately 2 mmHg/s to allow accurate measurement of the systolic and diastolic blood pressures. The fourth Korotkov phase (muffling of sound) has previously been used for diastolic blood pressure measurement but is not currently recommended unless Korotkov V cannot be defined. Having established that the blood pressure is increased, the measurement should be repeated several times over several weeks, unless the initial measurement is at dangerously high levels, in which case several measurements should be made during the same clinic attendance.

Home or ambulatory blood pressure measurements

Some people develop excessive and unrepresentative blood pressure rises when attending the doctor’s surgery, so-called ‘white coat’ hypertension. These patients can be diagnosed if they use a blood pressure machine themselves at home or by 24-h ambulatory blood pressure monitoring. Home blood pressure measurement is inexpensive but it is important to have a machine of validated accuracy that the patient can use properly. Ambulatory blood pressure monitoring over 24 h is also useful for patients who have unusual variability in blood pressure, resistant hypertension or symptoms suggesting hypotension. Home or ambulatory blood pressure measurements are usually lower than clinic recordings, on average by 12/7 mmHg.

Assessment of the hypertensive patient

Secondary causes

It is important to take a careful history checking for features that might suggest a possible secondary cause of hypertension. Examples would be symptoms of renal disease, for example, haematuria, polyuria, etc., or the paroxysmal symptoms that suggest the rare diagnosis of phaeochromocytoma and include headache, postural dizziness, syncope. A careful physical examination should be performed for abdominal bruits, which suggest possible renal artery stenosis, radiofemoral delay which suggest coarctation of the aorta and palpable kidneys which suggest polycysctic kidney disease. Laboratory analysis should include a full blood count, electrolytes, urea, creatinine and urinalysis. In some patients, further investigations may be appropriate, for example, ultrasound of the abdomen or isotope renogram where renal disease is suspected. A renin–angiotensin ratio is a useful screening test to investigate for possible hyperaldosteronism while serum metanephrine and urinary catecholamines may detect underlying phaeochromocytoma.

A low serum potassium may alert to the presence of hyperaldosteronism but it should be remembered that renin levels are suppressed by β-blockers and aldosterone by angiotensin converting enzyme inhibitors and receptor antagonists. A very high aldosterone/renin ratio may suggest Conn’s syndrome or primary hyperaldosteronism. This is usually caused by a benign adenoma or simple hyperplasia within the zona glomerulosa of the adrenal gland, the presence of which may be demonstrated by CT or MRI scanning. The tumours may be surgically resected, but where there is a suggestion of hyperaldosteronism and no obvious tumour on imaging, patients may still respond to spironolactone, an aldosterone antagonist, while remaining relatively resistant to other antihypertensives.

Contributing factors

The patient should also be assessed for possible contributory factors to hypertension such as obesity, excess alcohol or salt intake and lack of exercise. Occasionally, hypertension may be provoked by the use of drugs (see Box 19.2), including over-the-counter medicines used as cold and flu remedies. Other risk factors should also be documented and addressed, for example, smoking, diabetes and hyperlipidaemia. It is important to establish whether there is a family history of cardiovascular disease.

Evidence of end-organ damage

The patient should also be examined carefully for evidence of end-organ damage from hypertension. This should include examination of the optic fundi to detect retinal changes. An ECG should be performed to detect left ventricular hypertrophy or subclinical ischaemic heart disease. It is advisable to check the renal function and test the urine for signs of micro-albuminutria which may be an indicator of a higher risk of future end-stage renal disease and overall vascular risk.

Determination of cardiovascular risk

An accurate assessment of cardiovascular disease risk is essential before recommending appropriate management in hypertension. Patients with documented atheromatous vascular disease, for example, previous myocardial infarction or stroke, angina or peripheral vascular disease are at high risk of recurrent events. Those with type 2 diabetes over 40 years of age are also at high risk and can be regarded as ‘coronary equivalents’, that is, with risks similar to non-diabetic patients with previous myocardial infarction. For non-diabetic patients without vascular disease it is necessary to estimate cardiovascular risk (see Chapter 24). A 10-year cardiovascular disease risk of 20% (equivalent to a 15% coronary heart disease risk) is regarded as an appropriate threshold for antihypertensive therapy in patients with moderate hypertension, as well as for lipid-lowering therapy. Treatment decisions based on these tables will favour treatment in elderly subjects. While a younger patient may be at lower absolute risk over 10 years and may not meet the criteria for blood pressure and lipid treatment, they may be at higher lifetime and longer term risk of premature death and vascular disease and, thus, still merit risk factor intervention.

Other factors to consider include microalbuminuria which increases cardiovascular risk by a factor of 2–3 and the combination of reduced GFR and microalbuminuria may increase risk by as much as six-fold (Cirillo et al 2008; Sehestedt et al., 2009).

Treatment

Non-pharmacological approaches

Non-pharmacological management of hypertension is important, although the effects are often disappointing. Patients with mild hypertension in the range 140–159/90–100 mmHg can be assessed for levels of risk while offered lifestyle advice. General health education is important to allow patients to make informed choices about management. In order to maximise potential benefit, patients should receive clear and unambiguous advice, including written information they can digest in their own time. Written advice for patients can be downloaded from the BHS website (http://www.bhsoc.org/).

In patients who are overweight, weight loss results in reduction in blood pressure of about 2.5/1.5 mmHg/kg. The DASH diet (Dietary Approaches to Stop Hypertension) was evaluated in a clinical trial and found to lower blood pressure significantly (4.5/2.7 mmHg) compared with a typical US diet. This diet emphasises fruit, vegetables, and low-fat dairy produce in addition to fish, low-fat poultry and whole grains while minimising red meat, confectionary and sweetened drinks (Appel et al., 1997). Subjects should reduce their salt intake, for example, by not adding salt to food on the plate. A daily sodium intake of <100 mmol (i.e. 6 g sodium chloride or 2.4 g elemental sodium) should be the aim. There is a significant amount of hidden salt in processed meat, ready meals, cheese and even bread. A dietary assessment may be required to accurately quantify a patient’s salt intake and advise on how reductions might be made.

Most subjects will need to control their intake of calories and saturated fat. Regular aerobic exercise, at a level appropriate to the individual subject, at least 3 times a week for at least 30 min derives maximum benefit. This results in improved physical fitness as well as a reduction in blood pressure. Alcohol intake should be restricted to two (females) or three (males) units per day. Although smoking does not affect blood pressure, it increases cardiovascular risk and patients should quit or, if this is not possible, reduce their cigarette consumption.

Unless hypertension is severe, it is appropriate to observe the subject over several months while instituting non-pharmacological interventions. However, if there is a more urgent need for drug treatment, non-pharmacological interventions should occur in parallel.

Drug treatment

Treatment thresholds

Treatment thresholds are summarised in Table 19.1. Lifestyle advice should be provided to all patients with any degree of hypertension. Patients with severe hypertension (>220/120 mmHg confirmed on several readings on the same occasion) should be treated immediately and some guidance suggests that dual therapy should be commenced immediately in patients with blood pressure >20 mmHg above their target as monotherapy is unlikely to be fully effective (Mancia et al., 2007). Patients with blood pressures in the range 160–220/100–120 mmHg should be monitored over several weeks and treated if blood pressure remains in this range. The period of observation before starting treatment depends on the severity of the hypertension and the presence or absence of end-organ damage (see Table 19.1). Patients whose blood pressure is in the range 140–159/90–99 mmHg should be observed annually unless they have evidence of target organ damage, cardiovascular complications, diabetes or a calculated cardiovascular risk >20% over 10 years, in which case drug treatment should be offered. Patients with blood pressure in the range 135–139/85–89 mmHg should be reassessed annually, while those with blood pressure lower than this can be rechecked every 5 years.

Table 19.1 Threshold blood pressures for intervention

Initial blood pressure		Management
Systolic (mmHg)	Diastolic (mmHg)
Malignant hypertension		Admit and treat immediately
>220	>120	Repeat several times at the same attendance and treat immediately if blood pressure persists in this range
180–219	110–119	Confirm over 1–2 weeks and treat if blood pressure remains in this range
160–179	100–109	Repeat over 3–4 weeks (end-organ damage present) or 2–12 weeks (no end-organ damage), institute non-pharmacological measures and treat if blood pressure persists in this range
140–159	90–99	Repeat over several weeks. Institute non-pharmacological measures. Treat if remains in this range and patient has target organ damage, cardiovascular complications or an estimated 10-year cardiovascular risk >20%. Otherwise reassess annually
135–139	85–89	Reassess annually
<135	<85	Reassess in 5 years

Target blood pressures

Within the Hypertension Optimal Treatment (HOT) study (Hansson et al., 1998), patients were allocated diastolic target blood pressures of <90, 85, 80 mmHg. The study struggled to stratify patients effectively into these treatment groups but analysis suggested that the optimum target blood pressure was <140/85 mmHg with little benefit in lowering to lower levels of 120/70 mmHg but also little evidence of harm.

The UK Prospective Diabetes Study Group (1998a,b) suggested ‘tight’ blood pressure control was better than less tight in patients with non-insulin-dependent diabetes. The targets in the UK Prospective Diabetes Study were ‘tight’ <150/85 mmHg and ‘less tight’ <180/105 mmHg but the actually achieved blood pressures were lower, for example, 154/87 mmHg versus 144/82 mmHg. Recommendations in diabetics have, therefore, suggested treating to a target of 140/80 mmHg or less, although few studies have successfully lowered blood pressure to these levels.

A more recent study (Cardio-Sis) randomised non-diabetic subjects with systolic blood pressure >150 mmHg to target systolic blood pressure of <140 or <130 mmHg (Verdecchia et al., 2009). The primary end-point was left ventricular hypertrophy though the secondary end-point of a composite cardiovascular end-point was reduced (as well as the primary end-point) in the 130-mmHg group, with no increase in adverse events. This, however, is not robust enough evidence to recommend a reduction in blood pressure target levels and would require a larger study of hard clinical end-points to confirm these findings.

Achievement of target blood pressures is incorporated as a quality indicator for the General Medical Services Contract for primary care doctors in the UK. Diabetic patients are an exception and benefit from more aggressive blood pressure reduction. Target blood pressures for diabetic and non-diabetic subjects are summarised in Table 19.2. It should be emphasised that the audit standard will not be achieved in all patients.

Table 19.2 Target clinic blood pressures according to British Hypertension Society guidelines 2004 (Williams et al., 2004)

	Clinic blood pressure
	No diabetes (mmHg)	Diabetes (mmHg)
Optimal treated blood pressure	<140/85	<130/80
Audit standard	<150/90	<140/80

Antihypertensive drug classes

β-Adrenoreceptor antagonists

The mode of action of β-adrenoreceptor antagonists in hypertension is uncertain. β-Adrenoreceptor blockade reduces cardiac output in the short term and during exercise. They also reduce renin secretion by antagonising β-receptors in the juxtaglomerular apparatus. Central actions may also be important for some agents. Non-selective β-blockers may give rise to adverse effects as a result of antagonism of β₂-adrenoceptors, that is, asthma and worsened intermittent claudication. However, the so-called ‘cardioselective’ (β₁-selective) β-blockers are not entirely free of these adverse effects. Patients who develop very marked bradycardia and tiredness may tolerate a drug with partial agonist activity such as pindolol.

β-Adrenoreceptor antagonists also have substantial clinical trial evidence of benefit over placebo in hypertension, and are relatively inexpensive. However, their use is declining and they have been relegated to fourth-line therapy in the UK according to NICE guidance (Fig. 19.1). This recommendation largely stems from the evidence that they may be less effective at preventing stroke in conjunction with their diabetogenic effects. The Losartan For Endpoint reduction in hypertension (LIFE) study compared an atenolol/thiazide-based regime with a losartan-based regime and demonstrated equivalent levels of blood pressure reduction but with a small excess incidence of stroke in the atenolol arm (Dahlöf et al., 2002). In the Anglo Scandinavian Cardiac Outcomes Trial (ASCOT) study, the risk of diabetes was 2.5% higher in the atenolol arm compared with the amlodipine arm with similar increased risk of diabetes found within the atenolol arm of the LIFE study (Dahlöf et al., 2005). A Cochrane review warned of the excess risk in developing diabetes in patients prescribed combinations of thiazide diuretics and β-blockers. This would equate to one new case per 500 treated (Mason et al., 2004). The combination of thiazide and a β-blocker should, therefore, be avoided if possible, particularly in those who are at risk of developing diabetes (e.g. obese, strong family history of diabetes, South Asian origin).