Effect of Quaternary Nitrogen Compounds on the S.A. Node in Profound Hypothermia

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Abstract
Dogs anesthetized with sodium Pentothal and artificially respired with 100% oxygen characteristically go into a severe bradycardia when cooled to an average rectal temperature of 19°C. The onset of the severe bradycardia is usually quite abrupt (the ventricular rate dropping to a fifth of its former speed) and is associated with a change from sinus to nodal rhythm. This acute failure of sinus activity can be relieved by Q.N.C. injected i.v. The successful Q.N.C. are acetylcholine antagonists. These are either ganglionic blocking agents such as C.6., T.E.A., tetrabutylammonium iodide and WIN 2173 or neuromuscular blocking agents such as d-tubocurarine and Flaxedil. These drugs probably act directly on the sinus node. The unsuccessful Q.N.C. are either drugs such as thiamine whose ganglioplegic and curareform properties are weak or drugs such as choline and T.M.A. which mimic the action of acetylcholine. The restoration of sinus activity is frequently associated with ventricular extrasystoles and ventricular fibrillation. The drug with the lowest incidence of ventricular fibrillation is C.6, while WIN 2173 and T.E.A. have a high incidence.