Key result
Rabbit sinus nodes resist high-potassium conduction block, suggesting clinical SA block may actually be intra-atrial.
The finding that the sinus node area is highly resistant to excess potassium suggests that clinically observed sino-atrial block may actually represent intra-atrial block.
Does not yet inform clinical diagnosis of sinoatrial block; leaves open whether intra-atrial mechanisms predominate in hyperkalemia.
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.
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Sano et al. (1966) studied Conduction block. High potassium solution vs. Normal Tyrode solution was evaluated on Sites of conduction block. In isolated rabbit atria exposed to high potassium, the sinus node area was the most resistant to conduction block, suggesting that clinical sino-atrial block may actually be intra-atrial block.
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