Both nighttime and daytime blood pressure values were predictive, depending on whether fatal endpoints, fatal outcomes combined with non-fatal outcomes, or the part played by hypertension medication were being studied, according to study results in the Oct. 6 issue of The Lancet.
Prior to the results of the study, it was commonly believed that the failure of blood pressure to dip at night heralds cardiovascular complications.
Jan Staessen, MD, of the University of Leuven, and colleagues, analyzed the records of 7,458 people with a mean age of 56.8. The median follow-up was 9.6 years.
Adjusted for daytime blood pressure, nighttime blood pressure predicted total mortality in 983 patients – cardiovascular mortality in 387 and non-cardiovascular mortality in 560. Conversely, adjusted for nighttime blood pressure, daytime blood pressure in 525 patients lost prognostic significance for cardiac events and predicted only non-cardiovascular mortality with lower blood pressure levels associated with increased risk.
Both daytime and nighttime blood pressure consistently predicted cardiovascular events and stroke. The researchers also found that participants with a systolic night-to-day ratio of 1.0 or more were older, at higher risk of death, but died at an older age than those whose night-to-day ratio was normal
Staessen and his colleagues reported that daytime blood pressure adjusted for nighttime blood pressure predicted events in the combined category of fatal and non-fatal cardiovascular events.
Antihypertensive drug treatment removed the association between cardiovascular events and the daytime blood pressure.
The increased patient mortality with higher nighttime than daytime blood pressure probably indicates reverse causality, and the findings support recording the ambulatory blood pressure during the whole day.