Understanding High Blood Pressure

All patients with high blood pressure should be fully evaluated: this should include taking a medical history, doing a physical examination, running blood tests, doing a urine analysis, heart electrical tracing (electrocardiogram) and, possibly, carrying out an ultrasound scan of the heart (echocardiogram). This type of thorough examination looks for additional risk factors as well as high blood pressure, and any evidence of organ damage and should pick up any possible secondary causes of hypertension.

Your doctor should check for additional cardiovascular risk factors such as diabetes, smoking, and a family history of premature cardiac disease or hypertension. You are more likely to be started on treatment earlier if you are considered to have multiple risk factors for hypertension. Ideally, the treatment prescribed should be holistic and address all risk factors, rather that just aiming for better blood pressure control.

Family history is a significant risk factor in high blood pressure. A positive family history is having a first-degree family member who was diagnosed with hypertension or had a heart attack before the age of 60. A significant number of people with high blood pressure have a strong family history of hypertension, suggesting an underlying genetic cause. Hypertension is about twice as common in people who have one or two hypertensive parents. The genetics of hypertension is complex and single gene mutations causing elevation in blood pressure are rare. This means that genetic testing is not a useful tool, as multiple genes contribute to the development of hypertension. The medications that you are taking should be reviewed, as several treatments can increase blood pressure (see Chapter 5). Excessive alcohol intake and a high-salt diet are known to contribute to hypertension and correcting these is a priority (see Chapter 9).

Symptoms of chest tightness or breathlessness on exertion should be screened for, as these may point to an underlying heart disease. Any past medical history of heart disease or stroke suggests the need for blood pressure better control. Another common cause of blood pressure elevation is interrupted breathing during sleep (obstructive sleep apnoea), which has troublesome symptoms such as poor concentration, daytime sleepiness, and snoring. If this is suspected, you should be referred for specialist sleep studies, as obstructive sleep apnoea is treatable.

Your doctor will want to check whether your high blood pressure has affected any part of your body, and will take your general health into account when assessing this. For example, obesity is a common cause of high blood pressure and your doctor may want to measure your height, weight and body mass index (BMI). Your general appearance can sometimes offer other clues of underlying endocrine abnormalities that can cause high blood pressure, such as thyroid disease, acromegaly and Cushing’s disease. Bulbous eyes are a well-known sign of an overactive thyroid (hyperthyroidism), for example, but your doctor will also be alert for more subtle signs of illness, such as thinning or missing eyebrows, or rough, dry skin caused by an underactive thyroid (hypothyroidism), or the typical moon face of Cushing’s syndrome, caused by high levels of the hormone cortisol.

Your doctor will want to check for signs of heart failure, including swelling of the neck veins and ankles, and hearing crackles in the chest. He or she may also listen to your heart with a stethoscope, which could reveal additional heart sounds (murmurs) suggesting abnormal function of the heart valves. In this case, you may be referred for a special ultrasound scan of the heart, known as an echocardiogram, which will look in detail at the structural aspects of the heart. Your doctor may also test the pulse in your groin. Absent or weak pulses here may suggest a congenital narrowing of the aorta (coarctation) as the cause of hypertension. This is more common in young male patients. Your doctor may also want to examine your eyes. As explained above, severe hypertension can cause changes in the blood vessels at the back of the eye, and your doctor may use an ophthalmoscope to examine the retina.

When you are diagnosed with high blood pressure, your doctor or nurse may carry out routine blood tests to check how well your body is coping, and to help plan your treatment. Routine blood tests include tests for:

•anaemia;

•kidney function;

•diabetes;

•cholesterol levels;

•low blood potassium levels;

•excluding the possibility of thyroid disease.

If you have hypertension and ischaemic heart disease, you will need to take a statin to lower cholesterol levels and reduce the risk of a heart attack. If you have high blood pressure and low blood potassium levels, you may need additional blood tests to look for a rare endocrine disorder of the adrenal glands called Conn’s syndrome, which causes the excess production of a hormone called aldosterone.

A urine test with a dipstick is swift, painless and useful. It will detect any blood or protein in the urine, which can be a sign of chronic kidney disease (see Chapter 3). A simple urine test can be performed rapidly at the GP surgery, using indicator sticks that change colour when exposed to protein or blood in the urine. The colour change can be read off a scale to quantify the amount of protein or blood present. Sometimes your doctor will need more information, in which case a more detailed assessment is obtained by sending a urine sample to the laboratory to measure protein levels. Occasionally, 24-hour urine collection in special containers is required to calculate kidney function. The urine will be assessed for protein excretion and used to measure hormone levels.

An electrocardiogram, or ECG, records your heart rhythm. This non-invasive procedure detects the electrical activity of the heart muscle and shows an electrical tracing of the heart. Patients with hypertension are more likely to develop an irregular heart rhythm (such as atrial fibrillation), which is detected on the ECG. Long-standing high blood pressure can cause thickening of the heart muscle (hypertrophy), which can also cause high voltages on the ECG. In addition, an ECG can show signs of a previous heart attack, due to changes in electrical conduction, which indicate underlying structural heart disease.

This is an ultrasound examination of the heart, taken through the chest, in which sound waves transmit images to a video monitor. This is a useful test that looks for structural heart disease. If the ECG is abnormal, or there are signs of heart disease, an echocardiogram is often performed. The echocardiogram is more accurate than an ECG at detecting hypertrophy. It can also assess the function of the heart valves, look at the force of heart contractions, and measure the size of the heart chambers. High blood pressure can cause dilatation of the main artery arising from the heart (ascending aorta) and incompetence of the aortic valve. Both of these conditions can be detected by an echocardiogram.

Hypertension specialists may refer some patients with high blood pressure for a cardiac magnetic resonance imaging (MRI) scan, in which the patient lies inside a large circular magnetic scanner. The scan may last for up to an hour. The magnetic field causes the cells in the body to emit radiation waves, which are detected by the scanner to produce images of the heart. Cardiac MRI scans can show secondary causes of hypertension, such as narrowing of the kidney arteries, congenital narrowing of the aorta, kidney cysts or tumours of the adrenal glands. The cardiac MRI also enables the recording of precise measurements of the strength of heart contractions, thickness of heart muscle and chamber size.

Everyone with hypertension should be carefully screened for asymptomatic organ damage – that is, damage that you may not be aware of – and established cardiovascular or renal disease. Asymptomatic organ damage can be diagnosed as described below.

•Thickening of the heart muscle (left ventricular hypertrophy) seen on the ECG or echocardiogram.

•A wide pulse pressure (more than 60 mmHg difference in systolic and diastolic blood pressure) in the elderly.

•An ankle brachial pressure index (ABPI) of less than 0.9 in patients with impaired circulation in the legs. ABPI is a test used to diagnose significant narrowing of the arteries in the lower limbs (peripheral vascular disease). In healthy people the systolic pressure in the ankle is the same as the systolic pressure in the arm. The ABPI is the ratio between these two systolic blood pressures. An ABPI of less than 0.9 indicates significant peripheral vascular disease.

•Having a blood test showing moderate chronic kidney disease with estimated glomerular filtration rates (eGFR) of 30–60 mL/min/1.73 m² (the normal eGFR is ≥90 mL/min/1.73 m²).

•Having significant protein in the urine. This can be tested by urine dip stick, spot urine analysis or 24-hour urine collection. Microalbuminuria (small amounts of protein) is defined as 30–300 mg protein per 24 hours or a morning spot sample of urine with an albumen:creatinine ratio of >2.5 mg/mmol (for men) and >3.5 mg/mmol (for women). An albumen:creatinine ratio of >30 mg/mmol is defined as significant proteinuria and is no longer in the range for microalbuminuria.

•coronary artery disease with angina, a previous heart attack, a history of coronary angioplasty and stents or coronary artery bypass surgery;

•heart failure;

•cerebrovascular disease (stroke or transient ischaemic attack or brain haemorrhage);

•symptomatic peripheral vascular disease;

•chronic kidney disease with an eGFR of less than 30 mL/min/1.73 m² or severe protein loss in the urine (that is, more than 300 mg per 24 hours);

•significant damage to the retina with retinal bleeds or leaking of protein.

For practical reasons a single threshold is used above which the diagnosis of hypertension is made. This level is based on the results of clinical trials that have shown the benefits of blood-pressure lowering treatment. There is general agreement that people with sustained readings of systolic blood pressure equal to or higher than (≥) 140 and/or diastolic pressure ≥90 have hypertension. This value is used in all adults irrespective of age and gender. However, in young children and adolescents there is no single cut-off at which hypertension is diagnosed and high blood pressure is defined according to normal values found in that age group. Both systolic and diastolic readings are important and hypertension is diagnosed if the diastolic reading is high even when the systolic is below 140 mmHg.

There are three grades of hypertension that are based either on clinic, ambulatory or home blood pressure readings. Stage 1 is mild hypertension with a clinic blood pressure ≥140 systolic and/or a diastolic pressure ≥90 mmHg. On home or AMBP monitoring stage 1 hypertension corresponds to an average daytime systolic pressure ≥135 and/or diastolic ≥85 mmHg. Stage 2 hypertension is diagnosed when the clinic systolic blood pressure is ≥160 and/or diastolic is ≥100 mmHg. Stage 3, or severe hypertension, is diagnosed when systolic blood pressure is ≥180 and/or diastolic ≥ 110 mmHg. Some national guidelines have now incorporated stage 3 hypertension in with stage 2. However, some clinicians still refer to stage 3, or severe hypertension, for patients with blood pressure of more than 180/110 mmHg.

Isolated systolic hypertension is found mainly in those over the age of 65, with elevated systolic blood pressure (140 mmHg) and normal diastolic blood pressure (less than 90 mmHg) (Table 5).

Table 5 Stages of hypertension

Definition of hypertension stages	Clinic blood pressure	Ambulatory or home blood pressure (daytime average)
Not hypertensive	< 140/90	< 135/85
Stage 1	≥ 140/90	≥ 135/85
Stage 2	≥ 160/100	≥ 150/95
Stage 3 – severe	≥ 180/110
Isolated systolic hypertension	Systolic ≥ 140 and diastolic <90

An ideal blood pressure is considered to be below 120/80, with intermediate systolic blood pressure levels of 120–139 mmHg and diastolic pressure of 80–89 mmHg being classed as pre-hypertension. People with pre-hypertension are at increased risk of developing hypertension and should be advised on lifestyle changes and the need for careful follow up. Increased physical activity, weight loss, reduced salt intake and switching to a healthy diet can prevent the development of overt hypertension (see Chapters 10 and 11). At present, there is no evidence to suggest the need to treat pre-hypertension with blood-pressure lowering medications.

It is estimated that up to one-third of people with elevated (≥140/90) clinic blood pressure readings will have normal blood pressure when checked outside the doctor’s surgery (office), using either ambulatory or home blood pressure monitors. This is known as white coat or isolated-office hypertension. Blood pressure tends to be higher when recorded outside the home, due to a combination of anxiety and an alert response to an unfamiliar hospital or clinic environment. People who experience white coat hypertension are more likely to have mild hypertension, be female, non-smokers and have no target organ damage. ABPM or HBPM is used to detect white coat hypertension.