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 for stroke.
Peter Rothwell, MD, PhD, a professor of neurology at the University of Oxford, is the lead author of four papers published in the journals
The Lancer and The Lancet Neurology, which examined variable blood pressure and stroke risk.
Study On Variable Blood Pressure
One paper looked at high blood pressure and blood pressure variability in four groups of 2,000 people, each of who had minor strokes, known as transient ischemic attacks (TIA), or "mini-strokes." These are warning signs of stroke risk.
They found that people with the greatest variation in systolic blood pressure (the top number in a blood pressure reading 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.
Implications
Underdiagnosis and undertreatment of hypertension is a major problem, Dr. Rothwell said. "The new research shows that part of the problem is likely to have been underrecognition 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," Dr. 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."
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.
Best Medications For Blood Pressure Variability
Other papers by Dr. 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," Dr. 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," Dr Rothwell theorized.
Expert Reaction
"I think these findings are very important and very compelling, and may revolutionize how we treat blood pressure in the future," said Philip B. Gorelick, MD, 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."
Dr. Rothwell's findings already are starting to affect Dr. 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," Dr. 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," Dr. Gorelick said.
