Prognostic relevance of masked hypertension in subjects with prehypertension

BACKGROUND The prognostic impact of masked hypertension is not yet completely clear. The aim of this study was to evaluate the prognostic relevance of masked hypertension in subjects with prehypertension. METHODS The occurrence of fatal and nonfatal cardiovascular events was evaluated in 591 subjects with prehypertension defined as clinic blood pressure (BP) in the range of 120-139 mm Hg for systolic 1313 and 80-89 mm Hg for diastolic BP. Among them, 471 were classified as having true prehypertension (clinic BP < 140/90 mm Hg and daytime BP < 135/85 mm Hg) and 120 as having masked hypertension (clinic BP < 140/90 mm Hg and daytime BP >= 135 or 85 mm Hg). RESULTS During the follow-up (6.6 +/- 4.3 years, range 0.5-15.5 years), 29 cardiovascular events occurred. In subjects with true prehypertension and masked hypertension the event-rates per 100 patient-years were 0.57 and 1.51, respectively. Event-free survival was significantly different between the groups (P < 0.005). After adjustment for other covariates, including clinic BP (forced into the model), Cox regression analysis showed that cardiovascular risk was significantly higher in masked hypertension than in true prehypertension (masked vs. true prehypertension, relative risk 2.65, 95% confidence interval 1.18-5.98, P = 0.018). CONCLUSIONS Among subjects with prehypertension, those with masked hypertension are at higher cardiovascular risk than those with true prehypertension. Out-of-office BP should be known in individuals with prehypertension, preferably by ambulatory BID monitoring or alternatively by home BP measurement, to obtain a better prognostic stratification.