Predicting Cardiovascular Risk Using Ambulatory Blood Pressure

hour ambulatory systolic blood pressure (BP) was linearly related to cardiovascular risk in older patients with untreated isolated systolic hypertension. In a previous study of 1542 residents aged 40 years or older in a rural Japanese community, we found that the relationship between 6-year total mortality risk and 24-hour BP was significantly better fitted to a second-degree equation than to a linear equation model, and that this curvilinear relationship persisted after cumulative adjustment for possible cardiovascular risk factors. 2 We also reported that the right and left sides of the curvilinear relationship were related to increased risk of cardiovascular and noncardiovascular mortality, respectively. With regard to our study, Staessen et al commented, “. . . the Japanese group did not report whether the correlation remained after adjusting for the conventional BP at baseline or after excluding the noncardiovascular deaths.” 1 Therefore, we further analyzed the relationship using the latest follow-up data for the same 1542 residents (mean duration of follow-up: 8 years, 166 total deaths). The curvilinear relationship between total mortality and the 24-hour BP persisted after the data had been further adjusted for the conventional BP at baseline (systolic BP: ˛2 log likelihood in a seconddegree equation, 230.896; in a first-degree equation, 217.989; likelihood ratio, 12.907, P,.001; diastolic BP: ˛2 log likelihood in a second-degree equation, 224.054; in a first-degree equation, 217.733; likelihood ratio, 6.321, P,.02). After excluding noncardiovascular deaths, the 24-hour BP was linearly and significantly related to cardiovascular mortality risk. A 10-mm Hg increase in the 24-hour systolic BP and diastolic BP was related to relative hazards for cardiovascular mortality of 1.33 (95% confidence interval [CI], 1.07-1.64; P = .009) and 1.44 (95% CI, 1.01-2.6; P = .05), respectively. These results strongly suggest that the 24-hour BP, which is a more representative BP for each individual than conventional BP, is linearly related to cardiovascular disease risk, irrespective of the population studied.