RATE OF VARIATION IN AMBULATORY BLOOD PRESSURE IS NOT A PREDICTOR OF CARDIOVASCULAR DEATH OR EVENTS IN THE OHASAMA POPULATION

Abstract

Objective: Patients with increased short term blood pressure (BP) variability have a poorer prognosis. In the Ohasama population study, standard deviation (SD) of BP has been shown to be a BP independent risk factor for cardiovascular death in an 8.5 year follow up. However, SD doesn’t distinguish between linear trends within the time period and measurement to measurement variability. Time rate of variability (TRV) is a novel measure of the latter and is independent of any linear trends. Design and method: We applied the TRV method to ambulatory BP measurements (ABPM) from the Ohasama outcome study to determine whether TRV is an independent predictor of cardiovascular mortality or morbidity. Results: Among 1522 subjects, there were 126 cardiovascular deaths and 165 cardiovascular events. When separated into quintiles, both day and night SD of mean BP were associated with 2–4-fold greater risk of CV death or cardiovascular event (highest versus lowest quintile). Average 24-hour TRV was 15.8+/−3.5 mmHg/hr (lowest quintile 11 and highest 21 mmHg/hr). The risk of death or cardiovascular event was 3-fold higher in the upper compared to the lower quintile (P < 0.05). Daytime TRV showed a 2.4-fold high risk of cardiovascular event or death (upper vs lower quintile, P < 0.001). However, night TRV was only predictive of CV events and not death. The strongest predictors of risk in this study were age and BP. The risk of death or CV events was eliminated when TRV was adjusted for age and 24-hour BP. Further adjustment for smoking status, sex, anti hypertensive therapy, body mass index, history of hypertension, history of heart disease or levels of plasma cholesterol made no further impact. Adjusting TRV by SD alone eliminated the association with risk as the two measured are highly correlated (r = 0.52, P < 0.001). Conclusions: We conclude that the apparent risk of measurement to measurement variability as assessed by TRV has no advantage over the simpler SD method and is not an independent risk factor in the Ohasama population of Japan since the associated risk is more related to being older and having higher blood pressure.