To determine the minimum number and duration of blood pressure(BP) measurement needed to estimate long term visit-to-visit blood pressure variability (BPV) for predicting 10-year cardiovascular (CV) risk.Design and Method:
This is a 10-year retrospective cohort study of 1403 patients from a primary care clinic. Three monthly BP readings per year were retrieved from 10 years of clinic visits. Standard deviation (SD) of systolic blood pressure (SBP) was used as a measure of BPV. SD was calculated for each cumulative year of readings. CV events defined as fatal and nonfatal coronary heart disease and fatal and nonfatal stroke. We used Pearson's correlation to examine the concordance between the SD of each additional year of follow-up and SD at the end of 10 years. Multiple logistic regression was used to estimate the CV risk and compare the odd ratio (OR) between 10-year SD and SD of each additional year of follow-up.Results:
Mean SD increased with more SBP measurements for each increasing year. Pearson's correlation increased with the years of SBP measurements indicating increasing concordance with 10-year SD when more years of SBP readings was included from the baseline. With 10-year SD, the OR for CV risk was associated with an increase in SD (OR 1.121, 95% CI 1.057–1.188, p < 0.001) after adjusting for age, sex, race, smoking, diabetes mellitus, hypertension, HbA1c, total cholesterol and LDL cholesterol. Fewer years of SBP readings led to smaller ORs and, consequently, a weaker association between SD and 10-year CV risk. However, the ORs remained significant even with only 5-year of SBP measurements (adjusted OR 1.062 95% CI 1.009–1.117, p = 0.021).Conclusions:
Repeated BP measurements over a period of 5 years is sufficient to determine the long term visit-to-visit systolic BPV to predict the 10-year CV risk. Number and duration of BP readings to derive BPV should be taken into consideration when predicting long-term CV risk.