Cardiac Arrhythmias Produced by Catecholamines in Anesthetized Dogs.

• The phenomenon of "sensitization" of the heart to sympathomimetic amines by hydrocarbon anesthetics has been the subject of numerous investigations. Early studies concerned mainly the development of ventricular fibrillation as a result of sensitization of the heart by chloroform. More recently, interest has centered around the less severe cardiac arrhythmias resulting from small doses of sympathomimetic amines in the presence of cyclopropane. The characteristic arrhythmias observed under these conditions are coupled bigeminal rhythms and monofocal tachycardias.' Dresel suggested, on the basis of indirect evidence, that both the bigeminal coupled rhythms and monofocal tachycardias result from re-entry and that they "originate in the A-V node or the bundle of His." With the use of mircoelectrode recordings and the recent methods developed by Hoffman and co-workers for recording from different regions of the specialized conduction system in situ, it has been possible to obtain more direct evidence concerning the origin of these arrhythmias. In the present studies monofocal tachycardia and bigeminal coupled rhythms always originated distal to the bundle of His electrode.