EFFECTS OF BETA-BLOCKADE WITH BISOPROLOL ON HEART-RATE-VARIABILITY INADVANCED HEART-FAILURE - ANALYSIS OF SCATTERPLOTS OF R-R INTERVALS ATSELECTED HEART-RATES

The effect of beta-blockade on heart-rate variability was assessed at different heart rates in 52 patients with heart failure included in th e randomized, placebo-controlled, Cardiac Insufficiency Bisoprolol Stu dy (CIBIS). Scatterplots of R-R intervals display beat-to-beat variabi lity by plotting each R-R interval against the preceding interval. Sca tterplot dispersion at different R-R intervals provides a measure of b eat-to-beat heart-rate variability at different heart rates. A 24-hour Holter tape was performed at baseline and after 2 months of treatment with bisoprolol or matched placebo. Geometric measurements of scatter plots were used to determine beat-to-beat dispersion for different R-R intervals. Bisoprolol and placebo groups were well matched at baselin e. After 2 months of treatment, bisoprolol significantly increased bea t-to-beat variability at the longest R-R intervals (p < 0.05); however , there was no change in scatterplot dispersion at the shortest R-R in tervals. This suggests that beta-blockade increases parasympathetic or decreases sympathetic tone or both in heart failure patients only at the slowest heart rates.