STIMULUS CONDUCTION IN ATRIA STUDIED BY MEANS OF INTRACELLULAR MICROELECTRODE. I. THAT IN BACHMANN'S BUNDLE.

Abstract

In the present paper, the propagation process of the excitation in Bachmann's bundle was studied by means of the microelectrode method. The activation that was evoked in the sinus node was transmitted quickly through Bachmann's bundle toward the left atrium. The conduction rate was most rapid along the ridge of the bundle and became progressively less toward the periphery of the bundle. The conduction rate along the ridge of the bundle was about 1 M./sec. and in the trasverse direction to the bundle was about 0.2 M./sec.The membrane action potential from Bachmann's bundle showed a sharp upstroke followed by a spiked overshoot. After the overshoot, the action potential gradually returned to the membrane resting potential level via a short phase of plateau. There was no diastolic slow depolarization.From the fact that there was no diastolic slow depolarization in a trace from Bachmann's bundle, it was supposed that there was no specialized muscle fiber characterized by a slow diastolic depolarization in the bundle since the needle could reach through the epicardial membrane.The thickness of the muscle bundle was supposed to be very important for the accelerated conduction of the activation. That is, the thicker the bundle the quicker the transmission of the activation.