"There is a point at which blood pressure lowering becomes counterproductive," says Franz H. Messerli, MD, a professor of clinical medicine at Columbia University College of Physicians and Surgeons and director of the hypertension program in the division of cardiology at St. Luke's-Roosevelt Hospital in New York.
Messerli is the senior author on the report linking very low pressures with a higher risk of heart attack and stroke, scheduled to be presented today at the annual meeting of The American Society of Hypertension in San Francisco.
The "danger" points, according to Messerli's analysis, are 110 or lower for systolic pressure (the top number of the reading) and 60 or lower for diastolic pressure (the bottom number).
For the general population, a blood pressure of 140/90 or above is considered high; blood pressure between 120/80 and 139/89 is considered prehypertension, according to the National Institutes of Health.
But another hypertension expert criticized the study on a number of fronts. "In my opinion this analysis should be ignored," says Henry Black, MD, a nephrologist and clinical professor of internal medicine at New York University School of Medicine.
Blood Pressure: The Lower the Better?
Messerli and colleagues extracted data from the Treating to New Targets (TNT) trial, which enrolled 10,001 patients with known coronary artery disease and assigned them to two different doses of Lipitor, trying to evaluate whether aggressive lowering of LDL "bad" cholesterol would reduce heart attacks and strokes. The patients were followed for nearly five years.
"If you go down to 130, 120, it's no big deal," Messerli tells WebMD. But in his analysis, he found that reducing systolic blood pressure to 110 was associated with a 3.1-fold increased risk of major cardiovascular events.
As for diastolic pressure, those in the group with diastolic pressures of 60 or less had a 3.3-fold increased risk of heart attack and stroke.
In the study, a pressure of 140.6/79.8 was linked with the lowest rate of heart attack and stroke.
In general, Messerli says, doctors have long believed "the lower the better" when it comes to blood pressure. His study suggests that may not be so for those with known coronary artery disease. "The dictum 'the lower the better' does not apply for the TNT coronary heart disease population," he tells WebMD.
He concludes that a so-called J-curve relationship exists -- that is, pressures either too high or too low adversely affect the risk of heart attack and stroke. Why low pressure would do that is not certain, he says.
Blood Pressure: Study Details 'Sketchy'
Much more study is needed on the proposed relationship between very low blood pressure and the risk of cardiovascular events, says Black.
"The details are too sketchy to make any recommendation at all," he says. The J curve, he adds, has been discussed for decades among high blood pressure experts. He says most cardiology experts don't believe it exists.
The original intent of the TNT study, he says, was not to look at blood pressure but to look at aggressive lowering of LDL cholesterol and its effects on heart attacks and strokes in patients with coronary artery disease.
"This data needs to be dissected," agrees Ravi Dave, MD, a cardiologist at Santa Monica-UCLA and Orthopaedic Hospital and clinical associate professor of medicine at the University of California Los Angeles David Geffen School of Medicine, who also reviewed the analysis for WebMD.
In clinical practice, Dave says, he tends to keep patients with coronary artery disease at systolic pressures higher than 100. "Once patients' systolic pressure gets lower than 100, they will have side effects of fatigue, dizziness, tiredness, and they may even lose consciousness," he says.
The findings apply only to those with known coronary artery disease, Messerli cautions, and not to the general population.
His advice? If someone has known coronary artery disease, ''you want to be a bit careful in lowering the blood pressure."
Black cautions that patients on blood pressure lowering drugs should never stop or adjust their doses without consulting the doctor who prescribed them.