Hypertension (HT)

Definition:

• Very hard to define as it is varies from individual to individual and within individuals
• In a patient <50 years: 140/90mmHg
• In patient >50 years: 165/95mmHg
• Hypertension can be either primary (‘essential) or secondary

Primary (‘essential’) hypertension:

• Unknown aetiology
• >90% of cases of hypertension are primary

Secondary hypertension:

Renal causes:

• >80% of the cases of secondary HT
• Diabetic nephropathy
• Chronic glomerulonephritis
• Polycystic kidney disease
• Renovascular disease

Endocrine causes:

• Conn’s syndrome (hypersecretion of aldosterone)
• Adrenal hyperplasia
• Phaeochromocytoma
• Cushing’s syndrome
• Acromegaly

CVS causes:

• Coarctation of the aorta

Drugs:

• OCP
• Steroids

Complications of hypertension:

• Cerebrovascular disease (e.g. CVA)
• Coronary artery disease
• Renal failure
• Peripheral vascular disease

Malignant hypertension:

• Is said to occur when BP rises rapidly and is considered with severe HT (diastolic BP >140mmHg)
• Are changes in the renal circulation resulting in rapidly progressive renal failure, proteinuria and haematuria
• High risk of cerebral oedema and haemorrhage
• Marked changes in the retinal vessels (characteristic of malignant HT)
• Without effective treatment, there is a 1 year survival of <20%

Investigations:

Routine investigation of the hypertensive patient should include:

• CXR
• ECG
• Echocardiogram
• Urinalysis
• Fasting blood for lipids and glucose
• U&Es

General treatment measures for HT:

• Weight reduction
• Decrease alcohol consumption
• Salt restriction
• Regular exercise
• Cessation of smoking

Drug therapy:

The decision to commence specific drug therapy should usually be made only after a careful period of assessment (of up to 6 months) with repeated measurements of BP

Diuretics:

Thiazide diuretics:

• E.g. bendrofluazide (2.5-5mg daily)
• Duration of 12-24 hours
• Side-effects include:
• Hyperlipidaemia
• Hyperglycaemia
• Hyperuricaemia
• Hypokalaemia

Loop diuretics:

• E.g. Frusemide (40mg daily)
• Have a hypotensive effect and are not routinely used in essential HT

Potassium-sparing diuretics:

• E.g. Spironolactone (50-200mg daily) or amiloride (5-10mg daily)
• Not effective when used on their own, need to be used in combination with another diuretic

Β-blockers:

• Decrease force of cardiac contraction
• Reduce renin secretion
• Reduce anxiety (as anxiety increases BP)

There are major differences between the agents:

• Cardioselectivity:
• Some have less effect on B₂-receptors
• E.g. atenolol, bisoprolol

• Intrinsic sympathomimetic activity:
• Some agents have partial agonist activity and cause less Bradycardia
• E.g. pindolol, oxprenolol

• Lipid solubility:
• The agents that are less lipid-soluble are less likely to cause CNS effects
• E.g. atenolol

Side-effects:

• Bradycardia
• Bronchospasm (avoid in asthmatics)
• Cold extremities
• Fatigue
• Nightmares

ACE inhibitors:

• E.g. captopril (50-150mg daily in divided doses), enalapril (10-20mg daily)
• Block production of angiotensin II (potent vasoconstrictor)
• Inhibit degradation of bradykinin (potent vasodilator)
• Side-effects include severe hypotension on first administration and a dry cough (caused by the accumulation of bradykinin)

Angiotensin II receptor antagonists:

• E.g. losartan (50-100mg daily)
• Very similar actions to ACE inhibitors except they have no effect on bradykinin (therefore, do not cause a cough)
• Currently used for patients who cannot tolerate ACEIs because of a persistent cough

Calcium channel blockers:

• E.g. amlodipine (5-10mg daily), nifedipine (10-20mg TID)
• Reduce BP by causing arteriolar vasodilatation
• Major side-effects include:
• Headache
• Sweating
• Palpitations
• Flushing

• Side-effects can be lessened by the co-administration of a B-blocker

α-blockers:

• E.g. doxazosin (1-4mg daily)
• Cause postsynaptic α₁-receptor blockade
• Results in vasodilatation and a fall in BP

Drug selection:

• Treatment is normally commenced with a single agent (monotherapy)
• The target of therapy should be to maintain:
• Diastolic BP in the range 80-90mmHg
• Systolic BP <160mmHg

• Conventionally, thiazide diuretics and B-blockers have been used as a first line treatment, with the other agents reserved for those in whom these prove ineffective

Management of severe/malignant Hypertension:

• Admitted to hospital for immediate treatment
• Unwise to reduce the BP too rapidly as this may lead to myocardial/cerebral/retinal or renal infarction
• The aim is to reduce diastolic BP to 100-110mmHg over 24-48 hours
• The BP can then be normalised over the next few days