BP variability a powerful stroke predictor

VARIABILITY in blood pressure readings, commonly regarded as being ‘uninformative and random’, is actually highly predictive for stroke and other adverse outcomes and should be more widely considered when assessing cardiovascular risk, experts say.

European researchers found visit-to-visit variability in systolic blood pressure (SBP) was "a powerful predictor of stroke and coronary events independent of mean SBP, and maximum SBP is more predictive than mean SBP".

A review of four cohort studies, including around 7000 patients with previous hypertension or transient ischaemic attack, found variability was independently a strong predictor of stroke, heart failure, angina and myocardial infarction, both in clinic or in 24-hour ambulatory blood-pressure monitoring.

Patients with the greatest variation in BP over seven clinic visits were six times more likely to have a stroke, while those with the highest BP over seven visits were 15 times more likely to have a stroke.

Lead author, Professor Peter Rothwell of Oxford University, said "the usual blood-pressure hypothesis is inconsistent with much of the epidemiology of hypertension and stroke, and its clinical application is questionable in patients with variable blood pressure".

Dr Fiona Turnbull, acting director of the cardiovascular division at The George Institute for International Health in Sydney, said variability "looks like [it] may be an important prognostic indicator for stroke, it’s less clear for other outcomes like coronary heart disease and heart failure."

Professor Garry Jennings, cardiologist and director of the Baker IDI Heart and Diabetes Institute in Melbourne, agreed that current guidelines didn’t address variability and that it could be used in conjunction with average BP. However, he said it was not conclusive that BP variability related to cardiovascular outcomes and suspected it could be driven by lifestyle and environmental changes.

Meanwhile, a meta-analysis by Professor Rothwell and colleagues of 389 randomised trials of hypertension treatment also revealed class-specific effects of antihypertensive drugs on BP variation and risk of stroke.  

Calcium channel blockers and diuretics were associated with the greatest reduction in visit-to-visit BP variability and were also most effective in stroke prevention. In contrast, beta blockers were the least effective for stroke prevention and increased BP variability, though this was dose-dependent. 

Dr Turnbull said the study provided a plausible explanation for why “certain classes of blood pressure drugs like calcium antagonists appear better at protecting against stroke than other agents like beta blockers, because… [they] reduce that BP variability.”

However, Professor Jennings believed it was a “huge assumption… The differences are small, I don’t think they are nearly as important as getting good blood pressure control”, he said.

Dr Turnbull said the George Institute was coordinating an international Blood Pressure Lowering Treatment Trialists’ Collaboration that would extend the present meta-analysis using patient-level data rather than aggregate data.

Data from over 200,000 patients was expected to confirm the relationship between visit-to-visit BP variability and stroke, coronary heart disease, heart failure and dementia, and its role alongside average BP.

References:

Lancet 2010; 375:867-68, 895-915, 938-48