Departments of Pharmacotherapy, Cardiology and Cardiothoracic Surgery, Academic Medical Centre, University of Amsterdam, Meibergdreef, Amsterdam, The Netherlands
Introduction
Until the 1980s diastolic blood pressure (DBP) was assumed to be the most relevant haemodynamic parameter as a predictor of prognosis in hypertensive patients. Accordingly, most clinical studies particularly addressed DBP, and DBP-values were put forward as goals for treatment [1]. Since then a radical change in thinking, based upon epidemiological studies has led to the recognition of elevated systolic blood pressure (SBP) as a risk factor at least as important as high DBP [15]. Certain studies would even indicate that SBP is a more relevant predictor of prognosis than DBP, in particular with respect to the risk of stroke [1]. For this and other reasons, the term isolated systolic hypertension (ISH) has been introduced for those subjects with elevated SBP and normal (or even lower) DBP. This condition is found particularly in elderly hypertensives, since SBP is known to rise with advancing age, whereas DBP usually levels off and then tends to decrease in the elderly. Consequently, pulse pressure (SBP minus DBP) will increase in such patients. It appears that elevated pulse pressure is an even better predictor of cerebro- and cardio-vascular events in elderly hypertensives than a high SBP as such [1,2]. Indeed, ISH is the most common type of hypertension in the elderly, and it is the most prevalent type of untreated hypertension among persons over 60 years of age.
According to modern definitions, expressed in the JNC-VI- [16] and 1999 WHO/ISH-Guidelines [7] ISH is now defined as BP >140/<90 mmHg. These criteria are more stringent than the older definition of ISH at >160/<90 mmHg. The development of ISH with increasing age is explained by a deterioration of arterial compliance, in particular that of the large conduit arteries. Such increasing arterial stiffness is caused by structural and functional changes in the vascular wall, affecting collagen, extracellular protein matrix, and elastin. The proliferation of connective tissue results in intimal thickening and fibrosis. The increasing vascular stiffness causes a reduction in arterial compliance and the decrease of the Windkessel function of the large arteries. Accordingly, pulse pressure and pulse wave velocity increase, associated with an earlier and enhanced reflection of pressure waves from the periphery [1,2], thus causing a disproportionate increase in SBP. DBP, however, does not increase and may even be lowered as a result of increased arterial stiffness.
Isolated systolic hypertension as a risk factor
The widened pulse pressure found so typically in the elderly reflects both an increase in systolic and a decrease in diastolic pressure. Several studies, including the Framingham study, documented the risk of high SBP in particular with respect to stroke and, less clearly, ischaemic heart disease [8]. Similarly, in the MRFIT study SBP was found to be a stronger predictor of outcome than DBP [9]. However, it should be realized that too low a DBP is also dangerous [1012]. These observations once more emphasize the important role of widened pulse pressure as a risk factor. Conversely, several intervention studies in patients with ISH, to be discussed in a subsequent paragraph, have demonstrated the beneficial effect of the treatment of ISH, and more generally of treatment of hypertension in the elderly. At least on theoretical grounds it seems desirable to lower SBP in such patients, without simultaneously lowering DBP, in order to avoid a further widening of pulse pressure.
Benefit of treatment of ISH
In general terms, the beneficial effect of treatment of ISH runs in parallel with that of the treatment of hypertension in the elderly. In general, this issue has been addressed since the 1990s by means of intervention trials. Several trials such as STOP-1, STOP-2, and MRC Elderly have clearly shown that treatment of hypertension in the elderly protects against the complications of hypertension, particularly stroke (for review see [13]). In most of these trials no clear distinction was made between ISH and ordinary hypertension. There is no doubt, however, that a major percentage of the elderly hypertensive patients enrolled in these studies displayed the haemodynamic characteristics of ISH. A few clinical trials have deliberately addressed a population of patients with ISH as such.
Systolic Hypertension in the Elderly Program (SHEP) ]14[
Patients with well-defined ISH were treated with low-dose chlorthalidone (with the option to add atenolol or reserpine), and this was compared with administration of placebo. Chlorthalidone treatment caused the following reductions: non-fatal stroke: -37%; non-fatal MI: -33%; LV failure: -54%. There were obvious trends for a decrease in TIAs (-25%) as well as in total (-13%), cardiovascular (-20%), cerebrovascular (-29%), and coronary (-15%) mortality.
Systolic Hypertension in Europe (SYST-EUR) [15]
In a large number of patients with ISH, the calcium antagonist nitrendipine (with optional add-on enalapril and/or hydrochlorothiazide) was compared in a double-blind randomized design with placebo. Active treatment with nitrendipine caused a significant and striking reduction in the incidence of stroke by 42%, and there was also a clear tendency towards a reduction of myocardial infarction. This reduction did not achieve statistical significance however, probably because the trial had been stopped prematurely for ethical reasons. Total mortality (all causes) was not influenced by active treatment. Interestingly, the rate of vascular dementia was reduced (by -50%) in the study area with nitrendipine treatment [16].
SYST-China trial [17]
Chinese patients with ISH were treated with nitrendipine or placebo. The trial design was very similar to that of SYST-EUR. Active treatment with nitrendipine significantly reduced the following endpoints: total stroke: -38%; stroke mortality: -58%; all cause mortality: -39%; cardiovascular mortality: -39%; fatal and non-fatal cv events: -37%.
INSIGHT study [18]
The INSIGHT study has dealt with a population of hypertensive patients with an additional risk factor, such as diabetes mellitus, hypercholesteraemia, etc. Treatment consisted of nifedipine (in the GITS form: Adalat-OROS®) vs hydrochlorothiazide. INSIGHT was not a selective ISH-trial, but it contained a subgroup of patients with ISH. This subgroup was analysed separately [19]. These patients appeared to be more responsive to treatment with nifedipine-GITS than those with ordinary hypertension. Interestingly, in this study patients with ISH whose DBP significantly decreased under treatment were smokers with evidence of atherosclerosis.
A series of outcome trials in patients with ISH was recently subjected to a meta-analysis [20]. Active treatment reduced total mortality by 13%, cardiovascular mortality by 18%, all cardiovascular complications by 26%, stroke by 30% and coronary events by 23%. Drug therapy appeared to offer better protection against stroke than against acute coronary syndromes. The absolute benefit was best in patients older than 70 years, and in those with a history of cardiovascular complications or a high pulse pressure (i.e. wide blood pressure amplitude).
In a series of smaller studies it has been shown that in ISH patients thiazide diuretics are more protective than ß-blockers [2123]. Newer drugs such as ACE-inhibitors [24] and AT1-blockers [25] are also suitable for blood pressure control in ISH, although data on an epidemiological scale are not yet available. Omapatrilat, a combined inhibitor of neutral endopeptidase and ACE showed a stronger effect on SBP than on DBP [26].
New approaches in the treatment of ISH
At least on theoretical grounds it would seem desirable to find antihypertensive drugs which reduce SBP more markedly than DBP:
Similar findings concerning systolic pressure have been obtained with transdermal nitroglycerine and molsidomine [2,28]. It is therefore believed that these beneficial effects are explained by the increased release of NO as the underlying principle. So far no data are available concerning the protective effects of long-term nitrate treatment on the sequelae of hypertension.
Conclusions and recommendations
Isolated systolic hypertension is characterized by a widened pulse pressure. It has been recognized as an important entity, which requires consistent treatment. Apart from the well-known advices for life-style modification, drug treatment is required in the majority of patients with ISH.
The data so far available indicate that low-dose thiazide diuretics and slow/long-acting calcium antagonists are the drugs of first choice. A slow reduction of systolic pressure in the mostly elderly patients is mandatory. A target level of SBP around 140 mmHg seems desirable. Newer drugs such as ACE-inhibitors, AT1-blockers and omapatrilat are effective in lowering SBP in ISH patients, but large-scale data concerning their protective effects are not available. Finally, aldosterone antagonists and nitrates (as NO generators) deserve further investigation as drugs which may reduce arterial stiffness, the pathogenetic mechanism underlying ISH.
Notes
Correspondence and offprint requests to: P. A. van Zwieten, Departments of Pharmacotherapy, Cardiology and Cardiothoracic Surgery, Academic Medical Centre, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
References