Sites of Conduction Block in the Atria in Excess Potassium and a Doubt on the Existence of the Sino-atrial Block

Abstract

Employing microelectrodes and isolated rabbit right atrium, the sites of conduction block were examined by increasing the potassium content of the Tyrode solution.
The conduction block occurred first in the whole left atrium and the right atrial portions closer to the atrioventricular groove. Next conduction block appeared in the extension of the upper branch of the crista terminalis near the atrial septum. In the third stage of block it was seen on the atrial septum side and in the adjacent caval region, including the septal side of the upper and lower branches. In the terminal stage of block the excitation wave from the sinus node could reach the crista terminalis, but it could not go much farther.
The fact that the sinus node area was found to be the most resistant in these experiments suggests that the so-called sino-atrial block observed clinically in the electrocardiogram may actually be intra-atrial block.