http://www.medpagetoday.com/Cardiology/AcuteCoronarySyndrome/tb/6886

The Lancet 2007; 370:1219-1229

Prognostic accuracy of day versus night ambulatory blood pressure: a
cohort study

José Boggia MD b †,   Yan Li MD c †,   Lutgarde Thijs MSc a,   Tine W
Hansen MD d g,   Masahiro Kikuya MD e,   Kristina Björklund-Bodegård
MD f,   Tom Richart MD a,   Takayoshi Ohkubo MD e,   Tatiana
Kuznetsova MD a,   Prof Christian Torp-Pedersen MD g,   Prof Lars Lind
MD f,   Prof Hans Ibsen MD g,   Prof Yutaka Imai MD e,   Prof Jiguang
Wang MD c,   Prof Edgardo Sandoya MD h,   Prof Eoin O'Brien MD i
and   Prof Jan A Staessen MD  a ,   on behalf of the International
Database on Ambulatory blood pressure monitoring in relation to
Cardiovascular Outcomes (IDACO) investigators
†José Boggia and Yan Li contributed equally to this manuscript

‡IDACO investigators listed at end of article

Summary
Background
Few studies have formally compared the predictive value of the blood
pressure at night over and beyond the daytime value. We investigated
the prognostic significance of the ambulatory blood pressure during
night and day and of the night-to-day blood pressure ratio.

Methods
We did 24-h blood pressure monitoring in 7458 people (mean age 56·8
years [SD 13·9]) enrolled in prospective population studies in
Denmark, Belgium, Japan, Sweden, Uruguay, and China. We calculated
multivariate-adjusted hazard ratios for daytime and night-time blood
pressure and the systolic night-to-day ratio, while adjusting for
cohort and cardiovascular risk factors.

Findings
Median follow-up was 9·6 years (5th to 95th percentile 2·5–13·7).
Adjusted for daytime blood pressure, night-time blood pressure
predicted total (n=983; p<0·0001), cardiovascular (n=387; p<0·01), and
non-cardiovascular (n=560; p<0·001) mortality. Conversely, adjusted
for night-time blood pressure, daytime blood pressure predicted only
non-cardiovascular mortality (p<0·05), with lower blood pressure
levels being associated with increased risk. Both daytime and night-
time blood pressure consistently predicted all cardiovascular events
(n=943; p<0·05) and stroke (n=420; p<0·01). Adjusted for night-time
blood pressure, daytime blood pressure lost prognostic significance
only for cardiac events (n=525; p≥0·07). Adjusted for the 24-h blood
pressure, night-to-day ratio predicted mortality, but not fatal
combined with non-fatal events. Antihypertensive drug treatment
removed the significant association between cardiovascular events and
the daytime blood pressure. Participants with systolic night-to-day
ratio value of 1 or more were older, at higher risk of death, and died
at an older age than those whose night-to-day ratio was normal (≥0·80
to <0·90).

Interpretation
In contrast to commonly held views, daytime blood pressure adjusted
for night-time blood pressure predicts fatal combined with non-fatal
cardiovascular events, except in treated patients, in whom
antihypertensive drugs might reduce blood pressure during the day, but
not at night. The increased mortality in patients with higher night-
time than daytime blood pressure probably indicates reverse causality.
Our findings support recording the ambulatory blood pressure during
the whole day.

Affiliations

a. Studies Coordinating Centre, Division of Hypertension and
Cardiovascular Rehabilitation, Department of Cardiovascular Diseases,
University of Leuven, Leuven, Belgium
b. Departamento de Fisiopatología, Hospital de Clínicas, Universidad
de la República, Montevideo, Uruguay
c. Center for Epidemiological Studies and Clinical Trials, Ruijin
Hospital, Shanghai Jiaotong University School of Medicine, Shanghai,
China
d. Research Center for Prevention and Health, Copenhagen, Denmark
e. Tohoku University Graduate School of Pharmaceutical Sciences and
Medicine, Sendai, Japan
f. Section of Geriatrics, Department of Public Health and Caring
Sciences, Uppsala University, Uppsala, Sweden
g. Copenhagen University Hospital, Copenhagen, Denmark
h. Asociación Española Primera de Socorros Mutuos, Montevideo, Uruguay
i. Conway Institute of Biomolecular and Biomedical Research,
University College Dublin, Dublin, Ireland

Correspondence to: Prof Jan A Staessen, Studies Coordinating Centre,
Division of Hypertension and Cardiovascular Rehabilitation, Department
of Cardiovascular Diseases, University of Leuven, Campus Gasthuisberg,
Herestraat 49, Box 702, B-3000 Leuven, Belgium