The spread of sinus activation during potassium administration.

fibers • In 1907, Keith and Flack 1 desc; rect muscular bundle connecting the and atrio-ventricular nodes a it was "therefore possible ular rhythm to occur in t' Two years later Thorel 2 publish^ communication in which he a direct path between the n the cells constituting this thought to be specialized Purkinje type. Since then, although many studies have been devoted to the subject, the results obtained have failed to settle the question (see Discussion and Schiitz 3). A step forward was permitted by the introduction of the intracellular microelectrode. By use of this method, electrophysiologically specialized fibers were found to form a bundle along the margin of the caval region. 4 These specialized cells, as well as those of the nodes, subsequently were shown to be particularly resistant to the depolarizing action of a high potassium concentration. 5 ' 6 As result of this property, the specialized fibers develop action potentials in the presence of an elevated extracellular [K*] when atrial muscle fibers are no longer excitable. The latter observation suggested that it might be possible loy induced hyperkalemia as a means liflestigate the spread of sinus impulses to in^th^atria. If excitation followed special-the sinus impulses would be ex-each the ventricles in spite of the oduced inexcitability of atrial ibers. On the other hand, if sinus propagate only through nonspecial-al muscle fibers, the inexcitability of ers would functionally isolate the sinus node from the rest of the heart. To test this hypothesis several electrodes were implanted on atria of intact dogs and local activity was recorded during administration of potassium. The results obtained show that during hyper-kalemia sinus activity does propagate to the ventricles when atrial muscle fibers are no longer active. Methods Surgical preparation of animals was made under thiopental (Pentothal) anesthesia in ten mongrel dogs, weighing 18 to 27 kg. Electrodes were implanted on the epicardial surface of the sinus region and the ventricles; in nine of these animals an electrode was placed also in the coronary sinus area and/or over the His bundle. In seven of these same dogs other electrodes were attached on the muscular wall of either the left, right, or both atria. The technique of chronic implanta-tion has been described in detail. 7 ' 8 Four days to several weeks after implantation of the electrodes , the animals were anesthetized with sodium pentobarbital (30 mg/kg, intravenously). Additional amounts of this anesthetic were …