THE EFFECTS OF HALOTHANE ON ABNORMAL AUTOMATICITY IN CANINE CARDIAC PURKINJE-FIBERS

Abnormal automaticity is the spontaneous beating of cardiac cells with abnormally depolarized resting membrane potentials. The effects of ha lothane on cardiac arrhythmias caused by abnormal automaticity are con troversial, with either antiarrhythmic effects or enhancement of abnor mal automaticity reported by different authors. The goal of the presen t investigation was to clarify the effects of halothane on abnormal au tomaticity induced by superfusing excised canine Purkinje fibers (PF) with barium chloride. Intracellular microelectrodes recorded action po tentials from fibers superfused with buffer solution in a tissue bath. Barium chloride 0.25 mM reduced maximal diastolic potential from -82. 1 +/- 5.6 mV to -67.4 +/- 9.4 mV (mean +/- so, P < 0.05). Fibers devel oped abnormal automatic rhythms at a rate of 47.1 +/- 5.9 bpm. Halotha ne, 0.5%-4%, was added to the superfusate. Halothane reduced the rate of firing in a dose-dependent manner, so that abnormal automaticity wa s abolished by 4% halothane and reduced by lesser concentrations. Sere ndipitously, during barium superfusion, two additional fibers develope d early afterdepolarizations, a cause of triggered arrhythmias in pati ents with long Q-T syndrome. Halothane abolished early afterdepolariza tions in each. In this model of barium toxicity in excised canine PF, halothane antagonized both abnormal automaticity and early afterdepola rizations. Implications: Life-threatening cardiac arrhythmias may occu r during anesthesia. An arrhythmia called abnormal automaticity occurs after heart attacks and can be mimicked by adding barium to small seg ments of heart tissue. Halothane abolished abnormal automaticity in th ese tissues, which suggests that it or similar agents may benefit pati ents prone to developing such abnormal rhythms during surgery.