Purpose: This study evaluated the effect of neostigmine on heart rate
in cardiac transplant patients. Methods: Neostigmine (2.5-50 mu g . kg
(-1)) was administered to ASA I or 2 patients with normally innervated
hearts (controls), and to patients who had undergone recent (<six mon
ths before study) or remote (>six months before study) cardiac transpl
antation. Results: Baseline heart rate was 66 +/- 3 beats . min(-1) in
controls (n = 10, mean +/- SEM) which was slower than that observed i
n recently (95 +/- 4 beats . min(-1), n = 15, P < 0.001) and in remote
ly (88 +/- 3 beats . min(-1), n = 16, P < 0.001) transplanted patients
. Neostigmine produced a dose-dependent decrease in heart rate in all
patients. Controls were the most sensitive to neostigmine, with a 10%
decrease in heart rare produced by an estimated dose of 5.0 +/- 1.0 mu
g . kg(-1). The recently transplanted group was the least sensitive,
with the maximum dose producing only all 8.3 +/- 0.9% reduction The re
sponse to neostigmine of the remotely transplanted patients was variab
le. The estimated dose to produce a 10% decrease in heart rate in this
group was 24 +/- 6 mu g . kg(-1) which was greater than that for cont
rols (P = 0.008). Administration of atropine (1.2 mg) reversed the neo
stigmine-induced bradycardia in all three groups. Reversal of the brad
ycardia consisted of a transient peak increase in heart rate in contro
ls to 145 +/- 6% of baseline, a value which was greater than that obse
rved in recent (103 +/- 1%, P < 0.001) and in remote (109 +/- 3%, P <
0.001) transplants. Conclusions: Neostigmine produces a dose-dependent
bradycardia in heart transplant patients. Some remotely transplanted
patients may be particularly sensitive to the bradycardic effects of n
eostigmine.