Historically, diastolic blood pressure has been considered the most important factor in adverse sequelae of hypertension. However, recent evidence has shown that systolic blood pressure has an equal or even greater role in cardiovascular risk. Kannel reviewed the evidence suggesting that systolic blood pressure plays a major role in determining cardiovascular risk.
Early investigations by insurance companies revealed that mortality rates increased more steeply in relation to systolic than to diastolic blood pressure. In the 1969 Framingham Heart Study, the involvement of systolic blood pressure in cardiovascular and stroke risk became evident. Results from later epidemiologic studies showed that systolic blood pressure had an equal, if not greater, effect than diastolic blood pressure in peripheral vascular disease and heart failure.
Data from clinical trials also showed that systolic blood pressure should be relied on more in evaluating hypertensive risk and used as a guide for control of hypertension. The Systolic Hypertension in the Elderly Program (SHEP) and the Systolic Hypertension in Europe (SYST-EUR) trial results demonstrated the clinical benefits of lowering elevated systolic blood pressure in elderly patients, including those more than 80 years of age. These data showed that treatment significantly reduced the risk of myocardial infarction and stroke, and, with later studies, also supported the clinical concept that the cardiovascular hazards of hypertension are derived from diastolic and systolic blood pressure.
Ongoing data collected from the Framingham Study show that higher blood pressure, even within the nonhypertensive range, causes an increased rate of cardiovascular disease. Most adverse cardiovascular events seem to occur in persons with high normal blood pressure (mild hypertension). In the past decade, the median blood pressure at which cardiovascular events occur is only 135/80 mm Hg. Because arterial compliance decreases with advancing age, systolic blood pressure continues to increase as the diastolic pressure levels off and then declines. This increase in pulse pressure appears to be associated with an increase in the risk of cardiovascular events.
The author concludes that systolic blood pressure is the principal cause of hypertension and its adverse cardiovascular sequelae. Physicians must be more aggressive in reducing systolic and diastolic blood pressure levels. The sixth report of the Joint National Committee on Detection, Evaluation and Treatment of High Blood Pressure recommends that systolic and diastolic pressures be used to stage and treat patients.
editor's note: Mounting evidence suggests that elevated systolic blood pressure and widened pulse pressure are associated with increased cardiovascular risk in the elderly. Age-related stiffening of the aorta is largely responsible for elevated systolic pressure and normal diastolic pressure. Smulyan and Safar discuss the indistensible aorta, which causes the pressure pulse to travel faster than normal to where it is quickly reflected off the peripheral resistance. The reflected wave returns to the aorta during systole rather than diastole, increasing systolic work even more and reducing diastolic pressure, on which coronary flow depends. They conclude that antihypertensive drugs are appropriate in older patients with widened pulse pressure, but that care is needed to avoid excessive lowering of the diastolic pressure with accompanying myocardial hypoperfusion. An agent that improves aortic distensibility would best decrease systolic blood pressure without greatly decreasing diastolic pressure. Nitrates appear to come close to doing this, but the ideal agent has yet to be discovered.—r.s.