Pathoaetiology, Epidemiology and Diagnosis of Hypertension

Hypertension is currently defined in terms of levels of blood pressure associated with increased cardiovascular risk. A cut-off of 140/90mm Hg is accepted as a threshold level above which treatment should at least be considered. This would give a prevalence of hypertension of about 20% of the adult population in most developed countries. Hypertension is associated with increased risk of stroke, myocardial infarction, atrial fibrillation, heart failure, peripheral vascular disease and renal impairment. Hypertension results from the complex interaction of genetic factors and environmental influences. Many of the genetic factors remain to be discovered, but environmental influences such as salt intake, diet and alcohol form the basis of nonpharmacological methods of blood pressure reduction.

Investigation of the individual hypertensive patient aims to identify possible secondary causes of hypertension and also to assess the individual’s overall cardiovascular risk, which determines the need for prompt and aggressive therapy. Cardiovascular risk can be determined from (i) target organ damage to the eyes, heart and kidneys; (ii) other medical conditions associated with increased risk; and (iii) lifestyle factors such as obesity and smoking. Secondary causes of hypertension are individually rare. Screening tests should be initially simple, with more expensive and invasive tests reserved for those in whom a secondary cause is suspected or who have atypical features to their presentation.

The main determinants of blood pressure are cardiac output and peripheral resistance. The typical haemodynamic finding in patients with established hypertension is of normal cardiac output and increased peripheral resistance. Treatment of hypertension should initially use nonpharmacological methods. Selection of initial drug therapy should be based upon the strength of evidence for reduction of cardiovascular mortality in controlled clinical trials, and should also take into account coexisting medical conditions that favour or limit the usefulness of any given drug. Given this approach, it would be reasonable to use a thiazide diuretic and/or a β-blocker as first-line therapy unless there are indications to the contrary. Individual response to given drug classes is highly variable and is related to the underlying variability in the abnormal pathophysiology.

There are data to suggest that the renin-angiotensin system is more important in young patients. The targeting of this system in patients under the age of 50 years with a β-blocker (or ACE inhibitor), and the use of a thiazide diuretic (or calcium antagonist) in patients over 50 years, may enable blood pressure to be controlled more quickly.