How Many Measurements Are Needed to Estimate Blood Pressure Variability Without Loss of Prognostic Information?

BACKGROUND Average real variability (ARV) is a recently proposed index for short-term blood pressure (BP) variability. We aimed to determine the minimum number of BP readings required to compute ARV without loss of prognostic information. METHODS ARV was calculated from a discovery dataset that included 24-hour ambulatory BP measurements for 1,254 residents (mean age 56.6 years; 43.5% women) of Copenhagen, Denmark. Concordance between ARV from full (80 BP readings) and randomly reduced 24-hour BP recordings was examined, as was prognostic accuracy. A test dataset that included 5,353 subjects (mean age 54.0 years; 45.6% women) with at least 48 BP measurements from 11 randomly recruited population cohorts was used to validate the results. RESULTS In the discovery dataset, a minimum of 48 BP readings allowed an accurate assessment of the association between cardiovascular risk and ARV. In the test dataset, over 10.2 years (median), 806 participants died (335 cardiovascular deaths, 206 cardiac deaths) and 696 experienced a major fatal or nonfatal cardiovascular event. Standardized multivariable-adjusted hazard ratios (HRs) were computed for associations between outcome and BP variability. Higher diastolic ARV in 24-hour ambulatory BP recordings predicted (P <0.01) total (HR 1.12), cardiovascular (HR 1.19), and cardiac (HR 1.19) mortality and fatal combined with nonfatal cerebrovascular events (HR 1.16). Higher systolic ARV in 24-hour ambulatory BP recordings predicted (P <0.01) total (HR 1.12), cardiovascular (HR 1.17), and cardiac (HR 1.24) mortality. CONCLUSIONS Forty-eight BP readings over 24 hours were observed to be adequate to compute ARV without meaningful loss of prognostic information.