Tackling The Risk Of Heart Disease And Stroke - Hypertension

12.12.05

What is hypertension?
• Increased blood volume, which increases risk of cardiovascular disease.
-Blood pressure is a continuous variable - not dichotomous.
-Continuous relationship between level of blood pressure and risk of cardiovascular disease.
-No level with no risk.
-Ie. level of blood pressure selected for treatment is arbitrary.
-Different guidelines use different thresholds.
-Morbidity and mortality concentrated in elderly.
-Should interventions concentrated in that group?
• Risk factors summate.

What harm does it do?
• Shearing forces lead to the development of atherosclerosis.
• Increased risk of coronary events.
• Increased risk of stroke (by up to 4 times).
• Compounds other cardiovascular risk factors.
• Risk of heart failure.
• Risk of renal failure.

What causes it?
• 90% idiopathic (=I DON'T KNOW) - primary.
-Abnormalities of sodium flux across cell membranes?
• 10% secondary.
-Cushing's syndrome - secrete excessive amounts of glucocorticoids.
-Conn's syndrome - secrete aldosterone.
-Phaeochromocytoma - tumour of adrenal gland - secrete adrenaline.
-Renal disease (renal artery stenosis, renal failure etc.)
-Coarctation of the aorta - congenital narrowing.
-Alcohol.

How big a problem is it?
• Cardiovascular atherosclerosis common.
-Major cause of disability and death.
-Thrombotic (70%), haemorrhagic (15%), embolic (atrial fibrillation - 15%).
-But decrease in frequency.
• Increased risk of myocardial infarction.
• Hypertensive renal failure/heart failure unusual today.
• Depending on level defined, maybe 20% of adult population have hypertension.

How do we measure it?
• Sphygmanometer.

Measuring blood pressure
• Badly done, badly recorded.
• Digit preference - 5s and 10s.
• "Rule of halves."
-Of all hypertensive patients…
-…Half have ever had blood pressure measured.
-…Of whom half have been treated.
-…Of whom half are controlled.

British Hypertension Society Guidelines BMJ 2004.

Targets for blood pressure control
• Both systolic and diastolic values should be attained.
• Not diabetic - <140/85.
• Diabetic - <130/80.
• Many argue lower for diabetes sufferers eg. 120/70 if proteinuria - controversial.
• Also in secondary prevention eg. post cardiovascular atherosclerosis - very aggressive blood pressure lowering needed.

Benefits of treating blood pressure
• 5-year decrease of 5-6 mmHg in diastolic blood pressure:
-35-40% relative risk reduction in stroke.
-20-25% relative risk reduction in coronary heart disease.
• 1000 person years of drug treatment in older adults (>60 years old) prevents:
-5 strokes (95% confidence intervals 2-8).
-3 coronary events.
-4 cardiovascular deaths.

How do we lower blood pressure?
• Non-drug interventions.
-Exercise (5/3 mmHg).
-Diet.
-Obesity (3/3 mmHg).
-Salt restriction (2/4 mmHg).
-Food supplements (4/2 mmHg).
• Anti-hypertensive drugs.
-Most evidence-based.
-Single drug usually decreases blood pressure by around 10/6 mmHg.
-Multiple drug therapy common.

Classes of drugs to test hypertension (may have other uses also)
• Thiazide diuretics eg. bendrofluazide (smooth muscle relaxation - reduces pressure on arterioles).
-Cheap, easy to use.
-Best evidence behind it.
-20 or more different drugs in class.
• Beta blockers eg. atenolol.
-Less effective than other therapies.
• Calcium channel blockers eg. nifedipine.
-Cause vasodilation of arterioles.
-15 or more.
• Angiotensin converting enzyme inhibitors eg. enalapril.
-12 or more.
• Others…

Drug treatment to decrease blood pressure - heavily studied, very commercial
• Best evidence for thiazides.
• Other drugs as effective, but evidence not as good.
• Tolebility similar (but differs between patients) - match drug to patient profile.
• To cost-effectiveness.

How are we doing?
• Rule of halves - now rule of around 60%.
• Stroke rate declining.
• Barriers to controlling blood pressure.
-Nonadherence.
-White coat hypertension.
-Ageist prejudice.
-Organisational.

Conclusions
• Tackling risk of cardiovascular disease requires multifaceted approach.
• Risk factors known and can be treated.
• Hypertension major risk factor.