You might think that blood pressure as a risk factor would be well understood. A paper just published in the prestigious British medical journal The Lancet points out that episodic surges in blood pressure and sharp changes recorded in sequential office visits, often dismissed as a concern, indicate high risk for vascular events. The authors state the background to their investigation:
“The mechanisms by which hypertension causes vascular events are unclear. Guidelines for diagnosis and treatment focus only on underlying mean [average] blood pressure. We aimed to reliably establish the prognostic significance of visit-to-visit variability in blood pressure, maximum blood pressure reached, untreated episodic hypertension, and residual variability in treated patients.”
An editorial in the same issue provides additional perspective:
“Although hypertension is the most prevalent treatable vascular risk factor, how it causes end-organ damage and vascular events is poorly understood. Yet, a widespread belief exists that underlying usual blood pressure can alone account for all blood-pressure-related risk of vascular events and for the benefits of antihypertensive drugs, and this notion has come to underpin all major clinical guidelines on diagnosis and treatment of hypertension. Other potentially informative measures, such as variability in clinic blood pressure or maximum blood pressure reached, have been neglected, and effects of antihypertensive drugs on such measures are largely unknown. Clinical guidelines recommend that episodic hypertension is not treated, and the potential risks of residual variability in blood pressure in treated hypertensive patients have been ignored. This Review discusses shortcomings of the usual blood-pressure hypothesis…“
(By the way, blood pressure variability is not the same as heart rate variability where, generally speaking, the more the better.) The study authors investigated the incidence of transient ischemic attack (TIA, ‘mini-stroke) in relation to changes in BP from visit to visit, maximum blood pressure in patients with previous TIA and in patients with treated high blood pressure. What did their data show?
“…visit-to-visit variability in systolic blood pressure (SBP) was a strong predictor of subsequent stroke, independent of mean SBP… Maximum SBP reached was also a strong predictor of stroke…residual visit-to-visit variability in SBP on treatment was also a strong predictor of stroke and coronary events…all measures of variability were most predictive in younger patients and at lower (<median) values of mean SBP in every cohort.”
In other words, a person’s average systolic blood pressure (‘the first number’) may be OK, but a lot of change from doctor visit to visit, episodic surges, must be recognized as a predictor for stroke. Variability persisting after treatment predicts both strokes and heart attacks. And all measures of variability in BP, at even lower average pressures, are a warning sign for younger people. Clinicians and patients managing their blood pressure can remember their concise summary:
“Visit-to-visit variability in SBP and maximum SBP are strong predictors of stroke, independent of mean SBP. Increased residual variability in SBP in patients with treated hypertension is associated with a high risk of vascular events.“