Heart 1998;79:153-160 ( February )
Lipophilic versus hydrophilic 
1 blockers and the
cardiac sympatho-vagal balance during stress and daily activity in
patients after acute myocardial infarction
Department of Cardiovascular Medicine, John
Radcliffe Hospital, Headington, Oxford OX3
9DU, UK
Correspondence to: Dr Casadei. email: barbara.casadei{at}cardiov.ox.ac.uk
Accepted for publication 1 October 1997
Objective
To compare the effects of a lipophilic
and a hydrophilic 
1 blocker on cardiac sympatho-vagal
balance during daytime activity and stress in patients four to six
weeks after myocardial infarction.
DesignRandomised, double blind, crossover
study comparing the effect of atenolol (50 mg once daily) with
metoprolol CR (100 mg once daily) with treatment periods of four weeks.
SettingLarge teaching hospital.
Patients50 patients (45 male, 5 female, age range
40 to 75 years), four to six weeks after an acute myocardial infarction.
MethodsAt the end of each treatment period the 24 hour heart rate variability, heart rate variability power spectra
during head up tilt and mental stress, baroreflex sensitivity, and
exercise performance were evaluated.
ResultsDuring daytime activity and during
orthostatic and mental stress, both heart rate and the ratio between
the low and high frequency spectral components of the heart rate
variability were significantly lower with atenolol. Conversely, there
was no difference between treatments in baroreflex sensitivity and
resting plasma catecholamines. Exercise duration and peak oxygen
consumption did not differ between treatments, but the heart rate
during submaximal and peak exercise was significantly lower with atenolol.
ConclusionsAt the doses used in this study,
atenolol achieved greater 1 adrenergic blockade than
metoprolol CR and this was associated with significant inhibition of
vagal withdrawal during stress. This suggests that peripheral blockade
of 1 adrenergic receptors may be more important than
central blockade in preventing stress induced vagal withdrawal in
patients after myocardial infarction.
© 1998 by Heart
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