THURSDAY, March 11, 2010 (HealthDay News) -- Challenging established medical wisdom about blood pressure and stroke, new British research suggests that extremely variable blood pressure, and not just high blood pressure, can greatly increase a person's risk of stroke.
"Some people have very stable hypertension, in which case simple hypertension is all that matters, but variability and episodic hypertension is very common and matters much more than mean blood pressure in some patients," said Dr. Peter Rothwell, a professor of neurology at the University of Oxford and lead author of four papers in the March 13 issues of The Lancet and The Lancet Neurology.
One paper looked at high blood pressure and blood pressure variability in four groups of 2,000 people, each of who had minor strokes called transient ischemic attacks (TIAs), or "mini-strokes." These are warning signs of stroke risk.
They found that people with the greatest variation in systolic blood pressure (the higher of the 120/80 readings) over seven visits to their doctor were six times more likely to have a major stroke. People with the highest blood pressure readings were 15 times more likely to have a stroke.
"Under-diagnosis and under-treatment of hypertension is a major, seemingly intractable problem in all health-care systems," Rothwell said. "The new research shows that part of the problem is likely to have been under-recognition of the impact of variability in blood pressure on diagnosis in routine clinical practice in primary care. It shows that doctors have to make diagnoses on the basis of blood pressure measurements that vary substantially from visit to visit."
The message for doctors is that they have to change the way they view high blood pressure, he said.
"All current clinical guidelines encourage doctors to ignore variability and occasional high readings and to rely exclusively on the average blood pressure from multiple visits or 24-hour monitoring," Rothwell said. "The new research shows that increased variability in blood pressure, a high maximum blood pressure and episodic hypertension are associated with high risks of stroke and other vascular events, and emphasize that any comfort taken from the fact blood pressure is sometimes normal is false."
Other papers by Rothwell and his colleagues indicated that doctors should consider blood pressure variability when they choose among the many drugs now prescribed to control high blood pressure. A meta-analysis of 389 controlled trials found that effects on blood pressure variability explained why some classes of blood pressure drugs were more effective than others in preventing stroke. Another paper looked at the greater effectiveness of calcium channel blockers and thiazide diuretics vs. beta blockers in reducing stroke risk.
The result: "Calcium channel blockers and thiazide diuretics reduce [blood pressure] variability and beta blockers increase it," Rothwell concluded.
He called for development of new drugs that would stabilize and lower blood pressure at the same time. "Drugs that reduced variability without reducing average blood pressure should still prevent stroke and would be likely to be helpful in patients who cannot tolerate reductions in their average blood pressure," Rothwell theorized.
Variability can easily be measured when people visit their doctors, although "the fact that many people now monitor their blood pressure at home will be helpful in identifying variability," he said.
"I think these findings are very important and very compelling, and may revolutionize how we treat blood pressure in the future," said Dr. Philip B. Gorelick, director of the Center for Stroke Research at the University of Illinois, and a leading American expert on blood pressure and stroke. "They provide a very important foundation for change in future treatment."
Rothwell's findings already are starting to affect Gorelick's practice, he said.
"First, we may begin to screen patients with blood pressure measurements for variability to see if we can select for classes of drugs that reduce variability," Gorelick said. "And we can certainly adopt an at-home program to detect blood pressure variability, although within-visit variability seems to be a more important factor."
The findings may also affect the choice of the first drugs prescribed for blood pressure control, he said. "We would consider calcium channel blockers and diuretics for initial use," Gorelick said.
There's more on spotting and controlling high blood pressure at the American Heart Association.