Purpose: This study evaluated the effect of neostigmine on heart rate in cardiac transplant patients.
Methods: Neostigmine (2.5-50 micrograms.kg-1) was administered to ASA 1 or 2 patients with normally innervated hearts (controls), and to patients who had undergone recent (< six months before study) or remote (> six months before study) cardiac transplantation.
Results: Baseline heart rate was 66 +/- 3 beats.min-1 in controls (n = 10, mean +/- SEM), which was slower than that observed in recently (95 +/- 4 beats.min-1, n = 15, P < 0.001) and in remotely (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 rate produced by an estimated dose of 5.0 +/- 1.0 micrograms.kg-1. The recently transplanted group was the least sensitive, with the maximum dose producing only an 8.3 +/- 0.9% reduction. The response to neostigmine of the remotely transplanted patients was variable. The estimated dose to produce a 10% decrease in heart rate in this group was 24 +/- 6 micrograms.kg-1 which was greater than that for controls (P = 0.008). Administration of atropine (1.2 mg) reversed the neostigmine-induced bradycardia in all three groups. Reversal of the bradycardia consisted of a transient peak increase in heart rate in controls to 145 +/- 6% of baseline, a value which was greater than that observed 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 neostigmine.