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Excessive reduction of diastolic pressure may be harmful in some elderly hypertensives

By: Thomas Pickering, MD, DPhil, FRCP, Director of Integrative and Behavioral Cardiology Program
of the Cardiovascular Institute at Mount Sinai School of Medicine, New York.

Systolic hypertension of the elderly is characterized by a high systolic and normal or low diastolic pressure. This is thought to be a consequence of the increased stiffness of the arteries that occurs with aging, and also the effects of atherosclerosis. An idea that has been around for a long time is the possibility that in people who have narrowed arteries, excessive reduction of blood pressure may lead to impaired blood flow to the tissue supplied by the artery, and hence cause damage that results in a stroke or heart attack. Some studies have concluded that there is a 'J-curve' phenomenon, that is the relationship between blood pressure and its consequences (strokes and heart attacks) is not a straight line, but J- or tick-shaped, such that when blood pressure goes below a certain level, the risk starts to increase again.

An analysis of the data from the SHEP study (Systolic Hypertension of the Elderly Program) has provided some important new information on this point. There were 4736 patients all over the age of 65, and all had systolic pressure of 160 or higher, and a diastolic pressure of 90 or lower to enter the study. Half were treated with blood pressure lowering medications and half got placebo. In both treatment groups, the patients who had a cardiovascular event (stroke or heart attack) had a higher systolic pressure than the ones who had no event (no surprise here). But in the active treatment group, the people who had an event had lower diastolic pressures than the ones who had none. This could not be explained by these people being sicker to begin with, leading the authors to conclude that it was a consequence of the treatment itself. Further analysis showed that the risk starts to increase when diastolic pressure is lowered to less than 70 mmHg, and any further reduction below this level becomes increasingly harmful.

Doctor’s comments

The main finding here is that elderly people with systolic hypertension are at increased risk of a stroke or a heart attack if their diastolic pressure is lowered to less than 70 mmHg by treatment. Reduction of systolic pressure to low levels reduced risk, however. Another study, the HOT (Hypertension Optimal Treatment) study was designed to see if aggressive reduction of blood pressure (to a diastolic pressure of 80 mmHg or lower) had any adverse effects, and concluded that lowering blood pressure below 138 mmHg systolic and 83 mmHg diastolic produced no further benefit, but also no harm. However, the patients in the HOT study did not have isolated systolic hypertension as in the SHEP study, and were younger. Furthermore, HOT was not able to say what would happen at diastolic pressures below 70 mmHg.

The authors of the study noted that the overwhelming effect of treatment was to reduce the number of strokes and heart attacks, and that the increased risk for very low diastolic pressures only occurred in a minority of patients.

Where it was published

GW Somes and colleagues. The role of diastolic blood pressure when treating isolated systolic hypertension. Archives of Internal Medicine 1999; 159:2004.