Interaction between autonomic tone and the negative chrono tropic effect of adenosine in humans

Prior studies have demonstrated that sympathetic tone may influence the eff ects of adenosine on His-Purkinje automaticity, and that enhanced vagal ton e may influence its effects on the sinus node. However, the interaction bet ween autonomic tone and the effects of adenosine on the sinus node in human s remains unknown. Therefore, this study was designed to investigate the in teraction between different states of autonomic tone and the bradycardiac r esponse of the sinus node to adenosine. In 11 patients without structural h eart disease who underwent a clinically indicated electrophysiology procedu re, the sinus cycle length was measured before and after a 12-mg bolus of a denosine in the baseline state, during an infusion of 2 mcg/min of isoprote renol, after the administration of 0.2 mg/kg of propanolol, and again after the administration of 0.04 mg/kg of atropine. Adenosine significantly leng thened the sinus cycle length in the baseline state (760 +/- 165 vs 909 +/- 188 ms, P < 0.05), during isoproterenol infusion (516 +/- 67 vs 766 +/- 14 6 ms, P < 0.05), after propranolol (850 +/- 153 vs 924 +/- 143 ms, P < 0.05 ) and after the combination of propranolol and atropine (662 +/- 76 vs 801 +/- 121 ms, P < 0.05). The degree of lengthening in sinus cycle length was significantly greater (P < 0.05) during isoproterenol infusion (253 +/- 157 ms, or 51% +/- 40%) than in the baseline stale (149 +/- 85 ms, or 20% +/- 12%), after propranolol 188 +/- 53 ms, or 8% +/- 8%), and after propranolol and atropine (140 +/- 110 ms, or 21% +/- 18%). The negative chronotropic e ffect of adenosine is influenced by autonomic tone. The effect of adenosine on the sinus node is accentuated by beta-adrenergic stimulation and unaffe cted by beta-adrenergic blockade or combined beta-adrenergic and cholinergi c blockade.