Effects of halothane with and without histamine and/or epinephrine on automaticity, intracardiac conduction times, and development of dysrhythmias in the isolated guinea pig heart.

Histamine is released during allergic reactions, and is known to produce cardiac dysrhythmias. The authors compared the cardiac effects of histamine and epinephrine during exposure to halothane in the isolated perfused guinea pig heart. Responses studied were spontaneous sinus rate, intra-atrial conduction time, atrial-septal conduction time (ASCT), intraventricular conduction time (IVCT), and left ventricular pressure (LVP). The incidence and type of dysrhythmias with histamine and halothane and with epinephrine and halothane were analyzed from electrograms. The authors found that halothane alone (0.7 to 2.1 vol%) causes dose-dependent depressions of sinus rate and LVP, prolongs ASCT and IVCT, and produces atrioventricular (AV) block with junctional bradycardia. Histamine alone (.01-10 microM) increases sinus rate and LVP but, like halothane, prolongs ASCT. Halothane antagonizes the inotropic and chronotropic effects of histamine, but enhances ASCT compared with histamine alone. Histamine with halothane greatly increases the incidence of junctional tachycardia with AV dissociation from 0% with histamine alone up to 48%. Epinephrine alone (0.1-5 microM), like histamine, increases sinus rate and LVP, but does not cause a relative increase in ASCT. Halothane antagonizes the inotropic and chronotropic effects of epinephrine, but increases the incidence of ventricular tachycardia from 6% to 28%, and the incidence of premature ventricular excitations from 0% to 40%, compared with epinephrine alone. The authors' in vitro findings show that histamine and halothane, like epinephrine and halothane, can cause dysrhythmias, but that the genesis and type of dysrhythmias induced by these agents are dissimilar. Consequently, the release of histamine with an anaphylactoid reaction during halothane anesthesia, and the treatment of the reaction with epinephrine, could result in dangerous ventricular tachydysrhythmias.