The mechanisms by which raised blood pressure causes stroke and other vascular events are poorly understood.  Although substantial variability in clinical blood pressure is often noted, episodic hypertension tends not to be treated.  The prognostic value of visit-to-visit variability and episodic hypertension in the same setting has not been established.  Therefore in this study the risk of stroke in relation to visit-to-visit variability in blood pressure and maximum blood pressure was studied in patients who were participants in the UK-TIA (transient ischaemic attack) study and the Anglo-Scandinavian Cardiac Outcomes Trial Blood Pressure Lowering Arm (ASCOT-BPLA).

In patients in the UK-TIA study visit-to-visit variability in blood-pressure was a strong predictor of subsequent stroke (hazard ratio 6.22 in the top variability decile over seven visits, p<0.0001).  This effect was found to be independent of mean blood pressure, but dependent on the precision of measurement, and maximum blood pressure recorded at any stage was also found to be a strong predictor of stroke after adjustment for mean systolic blood pressure(hazard ratio for top-decile over seven visits, 15.01; p<0.0001).  In ASCOT-BPLA, residual visit-to-visit variability in SBP on treatment was also found to be a strong predictor of both stroke and coronary events, independent of mean systolic blood pressure in clinic or on ambulatory blood pressure monitoring (figure).Conclusions:Visit-to-visit variability in systolic blood pressure and maximum systolic blood pressure are strong predictors of stroke, indpendent of mean systolic blood pressure.  In patients with treated hypertension, residual variability is also associated with a high risk of vascular events.

• Rothwell PM, Howard SC, Dolan E, O’Brien E, Dobson JE, Dahlöf B, et al. Prognostic significance of visit-to-visit variability, maximum systolic blood pressure, and episodic hypertension. Lancet 2010, Mar 13;375(9718):895-905.

Hazard ratios for risk of stroke in ASCOT-BPLA patients with mean SBP during follow-up (less than the median value for the trial population) by deciles of variation independent of the mean (VIM) systolic blood pressure.