Fact Sheet: Isolated Hypertension (ISH) by Dr. Peter Sleight

Peter Sleight, M.D., F.R.C.P, F.A.C.C.
Professor Emeritus of Cardiovascular Medicine
University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, UK

The World Hypertension League is planning a new survey on ISH in selected countries.

Definition: Systolic blood pressure > 160 mmHg with diastolic blood pressure <90-95 mmHg (more usually <90 mm Hg).

Prevalence: Strongly related to age, around 5% in populations aged 60-69, 10% for age 70-79, and 20% aged 80+ years. It is more common in women, especially if obese.

Pathophysiology: Rigidity and loss of elasticity of large arteries due to aging +/ - atherosclerosis exaggerates the systolic peak in pressure and the lack of elastic recoil in diastole reduces diastolic pressure. This results in a wide pulse pressure and increasing impedance to left ventricular ejection, which leads to increasing hypertrophy (LVH) and increasing shear stress in arteries. The circulation is increasingly sensitive to sodium and fluid loading, with exaggerated and more rapid diuresis in response.

Prognostic Importance: Although at one time it was thought that the low diastolic pressure might be a favourable feature, it is now realized that the reverse is the case. The presence of ISH indicates, not only the presence of hypertension, but also the presence of diseased vessels and hence the worse prognosis.

Importance of Treatment of ISH: Some years ago physicians were cautious in advising treatment for ISH believing, erroneously, that lowering pressure might compromise coronary and cerebral flow and precipitate myocardial infarction or stroke. We now know from large randomized trials such as the Systolic Hypertension in the Elderly Programme (SHEP), the European Working Party on Hypertension in the Elderly (EWPHE), and the more recent SYST-EUR trial, that treatment of such patients with ISH gives greater absolute benefits than any other group of patients so far, with large reductions in both stroke and coronary events.

Which Drugs Are Best for Patients With ISH?: Diuretics are without doubt the best proven drugs for the treatment of ISH. As well as being particularly effective in elderly patients they also increase aortic compliance and help control heart failure and reduce the risk of development of heart failure. In comparison there is little or no evidence of benefit from beta blockers in elderly subjects, or in patients with ISH. This was clearly seen in the MRC trial of elderly hypertension, where diuretics were superior. I prefer potassium-sparing combinations of a thiazide with amiloride, or a diuretic with less potassium loss and proven increase in vascular compliance, such as indapamide, in order to reduce the metabolic and arrhythmic side effects seen with high dose. ACE inhibitors and calcium antagonists also increase compliance and are useful second to a diuretic when needed.

There has been some recent anxiety (from observational studies) about short acting dihydropyridine calcium channel blockers (particularly nifedipine) increasing coronary events, but the recent SYST-EUR trial was reassuring for nitrendipine. Longer acting calcium blockers which do not cause reflex increases in sympathetic tone, such as diltiazem or particularly verapamil, seem preferable.

What Target Level of BP, and What Dose of Drug?: We now realize that diuretics have rather flat dose response curves and so start with a low dose. Always check the standing blood pressure in patients with ISH, to avoid too much postural drop as a result of the reduced baroreflex response in the elderly, which may lead to falls or fractures. A target of 140 mmHg SBP when standing is usually low enough.

The Swedish Trial in Old People (STOP Hypertension) showed benefit in patients aged 70-84 years. We have not much evidence of benefit over this age, largely because so few patients in the late eighties or nineties have been studied in trials. However, since they continue to be a high risk of stroke and coronary events, I continue to advise treatment in fit, very elderly patients if the treatment is well tolerated.

Conclusions: Isolated systolic hypertension is a common and serious condition. Do not be falsely reassured (or reassuring!) by the low diastolic pressure. Treatment of ISH gives even better results (in reducing stroke and coronary events) than in conventional hypertension. Treatment is important because elderly subjects with ISH are increasing in numbers as the population ages. Diuretics remain the first choice of treatment in these elderly people. There is now good evidence of benefit, certainly up to the age of 84 years.