Nighttime dipping status and risk of cardiovascular events in patients with untreated hypertension: A systematic review and meta-analysis

The objective of this systematic review and meta-analysis is to determine whether nocturnal blood pressure fall, expressed by dipping patterns according to ambulatory blood pressure monitoring (ABPM), is a risk factor for cardiovascular events (CVEs) in untreated hypertensives. Alpha thorough systematic literature search at MEDLINE, Embase, Cochrane Library, and gray literature was conducted through March 2020. Two reviewers screened studies and assessed dipping patterns of untreated hypertensives using ABPM with a follow-up >6 months. Newcastle-Ottawa scale was used for risk of bias assessment. We initially identified 463 reports; of which, seven cohort studies were eligible for meta-analysis enrolling 10 438 untreated hypertensives. Untreated patients classified as dippers at baseline (n = 7081) had significant lower risk of CVEs and total mortality compared to non-dippers (n = 3,357) [RR = 0.67, 95% CI (0.49, 0.92); RR = 0.71, 95% CI (0.59, 0.86)]. However, when patients were further classified into four dipping groups, only reverse dippers, yet not extreme dippers or non-dippers, were at increased risk for CVEs compared to dippers [RR = 0.47, 95% CI (0.33, 0.66)]. Likewise, only reverse dippers had a higher stroke risk than dippers [RR = 0.39, 95% CI (0.22, 0.72)]. When compared with the whole group of dippers (including extreme dippers), non-dipping alone (excluding reverse dipping) was not a significant risk factor for CVEs [RR = 0.84, 95% CI (0.61, 1.16)] or total mortality [RR = 0.84, 95% CI (0.61, 1.16); RR = 0.78, 95% CI (0.53, 1.13), respectively]. Untreated hypertensives may benefit more from the evaluation of reverse dipping rather than the non-dipping phenomenon in general.