Sleep-Time Blood Pressure: Prognostic Value and Relevance as a Therapeutic Target for Cardiovascular Risk Reduction

Abstract

Correlation between blood pressure (BP) level and target organ damage, cardiovascular disease (CVD) risk, and long-term prognosis is greater for ambulatory BP monitoring (ABPM) than clinical BP measurements. Nevertheless, the latter continue to be the "gold standard" to diagnose hypertension, assess CVD risk, and evaluate hypertension treatment. Independent ABPM studies have found that elevated sleep-time BP is a better predictor of CVD risk than either the awake or 24-h BP mean. A major limitation of all previous ABPM-based prognostic studies is the reliance only upon a single baseline profile from each participant at the time of inclusion, without accounting for potential changes in the level and pattern of ambulatory BP thereafter during follow-up. Accordingly, impact of the alteration over time, i.e., during long-term follow-up, of specific features of the 24-h BP variation on CVD risk has never been properly investigated. We evaluated the comparative prognostic value of (i) clinic and ambulatory BP; (ii) different ABPM-derived characteristics, e.g., asleep or awake BP mean; and (iii) specific changes in ABPM characteristic during follow-up, mainly whether reduced CVD risk is more related to the progressive decrease of asleep or awake BP. We prospectively studied 3344 subjects (1718 men/1626 women), 52.6 ± 14.5 (mean ± SD) yrs of age, during a median follow-up of 5.6 yrs. Those with hypertension at baseline were randomized to ingest all their prescribed hypertension medications upon awakening or ≥1 of them at bedtime. At baseline, BP was measured at 20-min intervals from 07:00 to 23:00 h and at 30-min intervals at night for 48-h, and physical activity was simultaneously monitored every min by wrist actigraphy to accurately derive awake and asleep BP means. Identical assessment was scheduled annually and more frequently (quarterly) if treatment adjustment was required. Data collected either at baseline or the last ABPM evaluation per participant showed that the asleep systolic BP mean was the most significant predictor of both total CVD events and major CVD events (a composite of CVD death, myocardial infarction, and stroke). Moreover, when the asleep BP mean was adjusted by the awake mean, only the former was a significant independent predictor of outcome in a Cox proportional-hazard model adjusted for sex, age, diabetes, anemia, and chronic kidney disease. Analyses of changes in ambulatory BP during follow-up revealed 17% reduction in CVD risk for each 5 mm Hg decrease in the asleep systolic BP mean (p < .001), independent of changes in any other clinic or ambulatory BP parameter. The increased event-free survival associated with the progressive reduction in the asleep systolic BP mean during follow-up was significant for subjects with either normal or elevated BP at baseline. The ABPM-derived asleep BP mean was the most significant prognostic marker of CVD morbidity and mortality. Most important, the progressive decrease in asleep BP mean, a novel therapeutic target that requires proper patient evaluation by ABPM and best achieved by ingestion of at least one hypertension medication at bedtime, was the most significant predictor of event-free survival.