IMPACT OF SEASONAL BLOOD PRESSURE CHANGES ON VISIT-TO-VISIT BLOOD PRESSURE VARIABILITY

Abstract

Objective: Visit-to-visit blood pressure (BP) variability (V) associates with an increased risk of cardiovascular events. Limited information is available, however, on the factors responsible for this phenomenon. We investigated the role of seasonal BP modifications on the magnitude of BPV and its impact on cardiovascular risk. Design and method: In 28365 patients included in the ONTARGET and TRANSCEND trials the on-treatment systolic (S) BP values were grouped according to the month in which they were obtained. SBP differences between winter and summer months were calculated for each BPV quintile (Q), quantified by the coefficient of variation (CV) of between-visits mean SBP. The differences in the risk of morbid and fatal cardiovascular events between Qs were assessed by the Cox regression model. Results: SBP was 4 mmHg lower in summer than in winter regardless of sex, age, diabetes, baseline SBP and achieved SBP of the patients. Winter/summer SBP differences contributed significantly to each SBP-CV and the contribution increased progressively from Q1 to 5. Increase of SBP-CV from Q1 to Q5 was associated with a progressive increase in the adjusted hazard ratio of the primary endpoint of the trials, i.e.morbid and fatal cardiovascular events (Q5 vs Q1: 1.51, 95% CI 1.36 - 1.67). A similar trend was observed for secondary endpoints. This was also the case after subtraction of the SBP seasonality. Conclusions: Winter/summer SBP differences significantly contribute to visit-to-visit SBP variability and more so as variability becomes greater. This contribution, however, does not explain the adverse prognostic significance of visit-to-visit BP variations.