Effect of atenolol and diltiazem on heart period variability in normal persons.
Several time and frequency domain measures of heart period variability are reduced 1 to 2 weeks after myocardial infarction, and a reduced standard deviation of normal RR intervals over a 24 h period (SDNN) is associated with increased mortality. The predictive accuracy of heart period variability may be reduced by drugs used to treat patients after myocardial infarction. Accordingly, a randomized, three period, placebo-controlled, crossover (Latin square) design was used to determine the effect of atenolol and diltiazem on time and frequency measures of heart period variability calculated from 24 h continuous electrocardiographic recordings during treatment with atenolol, diltiazem and placebo in 18 normal volunteers. During atenolol treatment, the 24 h average normal RR (NN) interval increased 24% (p less than 0.001). The three measures of tonic vagal activity were significantly increased (p less than 0.001) during atenolol treatment: percent of successive normal RR intervals greater than 50 ms = 69%, root mean square successive difference of normal RR intervals = 61% and high frequency power in the heart period power spectrum = 84%. Low frequency power also increased 45% (p less than 0.01), indicating that this variable also is an indicator of tonic vagal activity over 24 h. Diltiazem had no significant effect on the 24 h average NN interval or on any measure of heart period variability. The decreased mortality rate after myocardial infarction associated with beta-adrenergic blocker but not calcium channel blocker therapy may be attributed in part to an increase in vagal tone caused by beta-blockers.
Cook
J R
JR
Department of Medicine, School of Public Health, Columbia University, New York, New York 10032.
Bigger
J T
JT
Kleiger
R E
RE
Fleiss
J L
JL
Steinman
R C
RC
Rolnitzky
L M
LM
D000328:Adult; D001262:Atenolol / Q000494:pharmacology*; D004110:Diltiazem / Q000494:pharmacology*; D015716:Electrocardiography, Ambulatory; D005260:Female; D006321:Heart / Q000187:drug effects* / Q000294:innervation; D006801:Humans; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D009203:Myocardial Infarction / Q000188:drug therapy; D010275:Parasympathetic Nervous System / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects
D001262:Atenolol; D004110:Diltiazem