Hypertension

Introduction

Hypertension refers to a persistent increase in blood pressure (BP) and is associated with significant cardiovascular risk. A blood pressure above 140/90mmHg (150/90 if aged 80 years or older) is generally considered the cut-off for hypertension.

Epidemiology

1 in 4 adults in England have hypertension, including 31% of men and 25% of women in England. Hypertension is the largest single known risk factor for cardiovascular disease and related disability in the UK.

Causes

Essential hypertension

Essential (also known as primary) hypertension refers to when the cause of hypertension is unknown. It accounts for 95% of all cases of hypertension and is thought to be due to an interaction of a range of risk factors, including:

• Obesity
• Insulin resistance
• Excessive alcohol consumption
• Genetics
• Environment
• Foetal programming
• Low birth weight
• Salt sensitivity
• Age
• Ethnicity

Secondary hypertension

Secondary hypertension is rare and accounts for 5% of all cases. Causes include:

• Chronic kidney disease
• Renovascular disease e.g. renal artery stenosis, fibromuscular dysplasia
• Conn’s syndrome
• Cushing’s syndrome
• Acromegaly
• Hyperparathyroidism
• Phaeochromocytoma
• Gestational hypertension
• Drugs:
  • Corticosteroids
  • Sympathomimetics

Pathophysiology

The pathophysiology behind essential hypertension is unclear. However, it is thought to occur as a result of increasing arteriolar resistance and increased cardiac output. Hypertension can increase the risk of individuals developing atherosclerosis by causing damage to arterial walls resulting in atherosclerotic plaque formation and an inflammatory response. The formation of these plaques in coronary arteries can narrow their lumen, resulting in angina, myocardial infarction and stroke if these plaques rupture and occlude cerebral vessels.

Clinical features

Most patients with hypertension are asymptomatic but can suffer numerous complications because of long-term hypertension. Therefore, it is important to screen at-risk patients regularly, including patients who are obese and have other co-morbidities such as diabetes or hypercholesterolemia.

On the other hand, malignant/accelerated hypertension can present with symptoms. This is a serious condition where there is a rapid increase in BP to 180/120mmHg or higher (often over 220/120mmHg) which results in vascular damage, such as signs of bilateral retinal haemorrhages and exudates ± papilloedema.

Hypertensive retinopathy

Long-term hypertension can lead to vascular damage in the eye, resulting in retinopathy. The presence of stage 4 indicates malignant hypertension.

The Keith-Wagener Classification of hypertensive retinopathy is:

• Stage 1: Tortuous arteries with thick shiny walls (silver/copper wiring)
• Stage 2: AV nipping (narrowing where arteries cross veins)
• Stage 3: Flame haemorrhages and cotton-wool spots 
• Stage 4: Papilloedema

Investigations

Routine investigations include measuring blood pressure to confirm diagnosis and carrying out blood tests to help quantify the overall risk of cardiovascular disease development in the patient. Additional investigations may include urinalysis, ECG and echocardiogram to look for end-organ damage associated with hypertension.

Measure blood pressure

BP measurements above 140/90mmHg confirm a diagnosis of hypertension. It is important to take multiple readings to over a period of time to diagnose hypertension. BP readings between 120/80mmHg and 140/90mmHg indicate an increased risk of developing hypertension. To avoid the risk of white coat hypertension (high blood pressure in clinical settings because of stress), ensure that the patient is relaxed, seated and with their arm supported before taking their BP. If the patient has any pulse irregularities, such as concurrent atrial fibrillation, measure BP manually using a sphygmomanometer.

 If clinic BP is between 140/90mmHg – 180/120mmHg, ambulatory BP monitoring should be offered to confirm diagnosis and differentiate from white coat hypertension. If ambulatory BP monitoring is not suitable for the patient, offer home blood pressure monitoring to where measurements above 140/90mmHg confirm diagnosis.  

A BP recording greater than 180/120mmHg indicates malignant/accelerated hypertension and is associated with rapid development of end-organ damage, such as encephalopathy and myocardial infarction. Therefore, these patients require specialist referral and urgent treatment to try and reduce BP over a few days to reduce the risk of complications . 

Blood tests

These tests are carried out to indicate and identify risk factors for cardiovascular disease in the patient as concurrent type 2 diabetes and hypercholesterolaemia alongside hypertension are common. It can help identify metabolic syndrome which is a cluster of these risk factors for cardiovascular disease indication.

Urinalysis

An elevated albumin: creatinine ratio and haematuria indicate renal disease including glomerulonephritis and pyelonephritis.

12 lead ECG

Check for signs of left ventricular hypertrophy, which may occur as a consequence of hypertension.

Investigations for secondary hypertension

If essential hypertension is unlikely,  difficult to control with antihypertensives or other symptoms are present (e.g. nausea, weight change), it is important to investigate potential secondary causes. Investigations to consider include:

Management

Making lifestyle changes is the first step in the management of essential hypertension and is used alongside anti-hypertensive medication to control BP.

For secondary hypertension, management should also be directed towards treating the underlying cause of disease.

Lifestyle changes

Advise patient that they can reduce their overall cardiovascular risk through lifestyle modifications, including:

• Reducing alcohol consumption
• Weight reduction
• Avoid excess caffeine
• Reducing fat and salt intake
• Increasing fruit and oily fish in the diet
• Increasing exercise
• Smoking cessation

Anti-hypertensive drugs

Antihypertensive drugs are used to control BP. According to UK NICE guidelines, a step-up approach is used whereby you increase the step of the treatment if the patient’s hypertension is not controlled in the current step, starting from step 1 to step 4.

Step 1 treatment

Initially, choose either an ACEi/ARB or calcium channel blocker. The choice of drug depends on patient age, if they have concurrent diabetes and their ethnicity in order to maximise efficacy to these medications.

Use ACE inhibitor (ACEi) (or angiotensin II receptor blocker (ARB) if ACEi is not tolerated) first-line in the following groups:

• Type 2 diabetes and of any age or family origin
• Age <55 but not of black African or African-Caribbean family origin

Use calcium channel blocker (CCB) (or thiazide-like diuretic if CCB is not tolerated) first-line in the following groups:

• Age ≥55 and do not have type 2 diabetes
• Black African or African-Caribbean family origin and do not have type 2 diabetes

Step 2 treatment

• If BP is uncontrolled by ACEi/ARB, offer the addition of either a CCB or thiazide-like diuretic alongside the ACEi/ARB
• If BP uncontrolled by CCB, offer the addition of either an ACEi/ARB or thiazide-like diuretic alongside the CCB
• If uncontrolled in adults of black African or African-Caribbean family who do have diabetes, consider an ARB in addition to step 1 treatment

Step 3 treatment

Patient should receive a combination of all three drugs: ACEi/ARB, CCB and thiazide-like diuretic. In addition, consider testing for secondary hypertension.

Step 4 treatment

Measure potassium levels and consider adding further antihypertensives depending on the results:

• If potassium <4.5mmol/L: add low dose spironolactone
• If potassium >4.5mmol/L: add alpha or beta-blocker

Complications

There are numerous complications associated with hypertension, including:

• Ischaemic heart disease
• Atherosclerosis
• Heart failure
• Myocardial infarction
• Chronic renal failure
• Stroke
• Retinopathy
• Peripheral arterial disease
• Aortic aneurysm
• Vascular dementia

References

• Oxford Handbook of Clinical Medicine (10^th edition)
• https://www.nice.org.uk/guidance/ng136/chapter/Recommendations#measuring-blood-pressure
• https://www.nhs.uk/conditions/high-blood-pressure-hypertension/
• https://www.gov.uk/government/publications/health-matters-combating-high-blood-pressure/health-matters-combating-high-blood-pressure#:~:text=In%20the%20UK%2C%20high%20blood,heart%20failure
• https://www.saga.co.uk/magazine/health-wellbeing/conditions/cardiovascular/high-blood-pressure-atherosclerosis