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Mercedes R.
Carnethon, Duanping Liao, Gregory W. Evans, Wayne E. Cascio, Lloyd
E. Chambless, Wayne D. Rosamond, Herman A. Tyroler, and Gerardo
Heiss
Heart rate variability
(HRV) indices can estimate the cardiac autonomic shift from parasympathetic
to sympathetic control when combined with a postural change from
supine to standing. We evaluated whether low HRV or a small change
in HRV with standing was prospectively associated with the risk
of incident cardiac and non-cardiac events in a sample of adults
free of clinical coronary heart disease (CHD). This study included
9,267 black and white men and women aged 45-64 from the Atherosclerosis
Risk in Communities Study. Participants were followed through 1997
for myocardial infarction (MI) (n=296), fatal CHD (n=63), and non-CHD
mortality (n=533). At baseline (1987-1989), supine and standing
R-R intervals were continuously recorded for 2 minutes in each position.
Mean R-R interval length, the standard deviation of normal R-R intervals,
and high frequency (0.15-0.40 Hz) power were used to estimate heart
rate, overall modulation of autonomic tone, and parasympathetic
input, respectively. Cox Proportional Hazards regression was used
to compare the risk of events over follow-up between participants
in the each of the lower three quartiles of the distribution to
those in the uppermost quartile for each index and event separately.
After adjustment for age, race, gender, heart rate, and medication
use, supine and standing HRV indices were inversely associated with
the events, but the change in HRV with standing was not, with the
one exception of R-R interval change and MI (hazard ratio = 1.42,
95% CI: 1.02-1.98, for smallest quartile of change v. largest).
In this healthy population sample, postural changes in HRV did not
predict events better than HRV captured in the supine or standing
position.
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