Isolated systolic hypertension-its pathophysiology, clinical significance and management (Abstract)
Professor of Department of Medicine, National Taiwan University Hospital, Taipei, Taiwan
Historically, diastolic blood pressure (DBP) has been regarded as the most importand factor for the adverse sequelae of hypertension. For example, in 1977, the first report of the Joint National Committee (JNC I) recommended DBP as the basis for the diagnosis and treatment of hypertension. However, the importance of systolic blood pressure (SBP) has been recognized as equal to, if not greater than, that of DBP in the treatment of hypertension based on several prospective population-based studies. In 1980, after 38 years of follow-up, Framingham Heart Study concluded that SBP has a greater influence than DBP on cardiovascular mortality and morbidity. It is not until 1990's that the effect of lowering SBP on cardiovascular mortality was proved. Two studies: Systolic Hypertension in the Elderly Program, SHEP (1991) and systolic Hypertension in Elderly in Europe trial, Syst-Europe (1997) showed that the clinical benefits of lowering elevasted SBP to reduce the risk of cardiovascular events in elderly patients, includig those aged>=80 years. In the newest report of the Joint National Committee (JNC VI, 19970), SBP has been incoporated to stage and justify the treatment high blood pressure effectively.
Isolated systolic hypertension (ISH) is defined as a SBP over 140mmHg with a DBP below 90mmHg. In elderly, the arterial compliance is decreased due to the fatigue of elastic fiber and increased synthesis of collagen fiber in arterial media layer. The decrease in arterial compliance also causes a faster pulse wave velocity. A more rapid return of reflexion pulse wave can result in augmentation of systole rather diastole blood pressure, which causes a widening pulse pressure. Therefore, the
SBP continues to increase while the diastolic pressure declines with advancing age. In USA, one study showed that poor SBP control was overwhelmingly responsible for poor rates of overall control to goal in participants followed between 1990 and 1995. Framingham Heart Study also found that ISH comprised 87% frequency for subjects in the sixth decade of life, and required greater reduction in systolic blood pressure in these subjects to reach treatment goal compared with subjects in the younger group. In Taiwan, 10 year follow-up in Chin-Shan Community also concluded that ISH and pulse pressure are important determinants of cerebral vascular accidents and carotid intimal thickening.
Treatment of ISH in elderly is based on two important randomized controlled studies : SHEP (thiazide) and Syst-Europe (nitredipine). In older patients with ISH, diuretics (thiazide) and calcium-channel blocker (nitredipine) are preferred because they have significantly reduced multiple end-point events such as stroke, heart failure and ischemic heart disease. Recently, candesartan cilexetil as monotherapy or add-on therapy to various background therapies, has been shown to consistently reduce mean SBP/DBP further. All the studies have shown that aggressive treatment of ISH could reduce stroke (36-42%) and cardiovascular events (30-33%).
In conclusion, ISH caused by decreased compliance of the large arteries is a strong survival determinant especially in elderly. Aggressive treatment of ISH with thiazide and nitrendipine can reduce cardiovascular morbidity and mortality.