One of the greatest advances in medicine over the past half century is the recognition of hypertension as a major cardiovascular risk factor and the awareness of the benefits of treatment. Cardiac death rate has fallen 30 percent and stroke death rate, 50 percent, in large part, because of the more aggressive and more effective treatment of high blood pressure.
Diagnosing and treating hypertension is clearly sound preventative medicine; but, as with so many areas of health care, too much of a good thing is often not good!
Blood pressure (BP) is measured using two numbers: an upper number, called the systolic pressure, and a lower number, the diastolic pressure. Hypertension, or high blood pressure, is generally defined as a systolic pressure over 140 and a diastolic pressure over 90 (BP>140/90). For certain patients -- such as diabetics, those with very weakened hearts, or those with kidney failure -- the upper limit of normal is lower, 130/85.
The benefit of lowering elevated blood pressure into the normal range is irrefutable, with the usual treatment consisting of diet, exercise, and a large choice of effective medications. However, once the BP is in the normal range, further lowering it with medications may be risky, especially for those with heart disease.
Lowering elevated blood pressure and its effect on cardiovascular complications was reviewed by Dr. Bangalore and associates and published in the respected cardiology journal, Circulation, in 2010. This review involved 4,162 patients with pre-existing heart problems and investigated the relationship between lowering blood pressure with medications and the occurrence of serious cardiac events.
The events the investigators documented were heart attacks, hospitalizations for worsening angina, heart surgery, strokes and death. When the incidence of these cardiovascular complications was graphed against BP readings, a strange finding was observed. As elevated BP was lowered into the normal level, those complications decreased. As BP was further lowered through the range of normal blood pressure, the incidence of complications flattened, that is, they did not further decrease. When the BP was lowered into the low normal range, however, the cardiovascular complications actually started to increase again!
The continued lowering of BP with medications in hypertensive patients through the low normal range, resulted in more heart attacks, angina, and death. The graph of complications versus BP was not a line with a straight downward slope, rather a "J" curve with an upturn of cardiac problems and death at low BP readings. The investigators found that the best cardiac outcomes were achieved with a BP of 136/85 with a further lowering presenting significant increased cardiac risk.
Dr. Bangalore's study was not the only one to discover these disturbing findings. Dr. Messerli and his colleagues presented a secondary analysis of two large studies including 22,576 patients in 14 countries with hypertension and coronary heart disease. Their findings were reported in The Annals of Internal Medicine in 2006. They, too, found that all-cause mortality and heart attacks were increased when blood pressure was lowered into the low normal range, especially in people who had undergone revascularization to their coronary arteries.
The relationship between increasing mortality and lower blood pressure was more dramatic with low diastolic pressure than with low systolic pressure, although it was present with both. The authors postulate that since the coronary arteries, which supply the heart muscle with oxygen and nutrients, receive most of their blood during diastole; the lower diastolic pressures were particularly damaging to the heart.
For the brain, though, the story is quite different than for the heart. There, continuously lowering blood pressures continuously lowers stroke risk. Since heart disease is much more common than strokes, the increased cardiac mortality more than offsets any improvement in stroke risk and overall mortality increases at low normal blood pressure levels. Messerli, et al, found that blood pressure levels below 119/84 were associated with an increased death rate.
These studies do not negate the importance of diagnosing hypertension and treating it with lifestyle changes and medications. High blood pressure is appropriately termed "the silent killer" since symptoms caused by hypertension often do not appear until irreversible damage is already done to the body.
What these studies do show is that lowering blood pressure excessively with medications can be dangerous. The national belief that more and newer in health care always represents improvement is not only expensive, but dangerous. In medicine, too much of a good thing can be bad.
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