Abstract
The authors have studied the participation of the sinus node in the occurrence of atrial fibrillation.
In the experiments on dog hearts in situ, an electrical stimulation given to the right atrium easily induced atrial fibrillation in the presence of the normal sinus node.
When the sinus node was injured, atrial fibrillation was very much reduced in frequency of occurrence and duration.
Also in the case of aconitine induced atrial fibrillation, the occurrence of fibrillation was very late when the sinus node had been injured.
Application of aconitine on preparations of the rabbit's right atrium including the sinus node easily induced fibrillation, but by application of aconitine on preparation of right and left atrial common muscle devoid of spontaneous activity fibrillatory contraction has never been observed.
Recently, we have made the studies on aconitine-fibrillation of the right atrium of the rabbit with 2 microelectrodes by means of the isolation technique.
In them, aconitinc was administered to the common muscle chamber in which the solution had been separated from the sinus node chamber with glycerin-soaked cotton. An ectopic pacemaker was produced after aconitine administration. Then the sinus node became a latent pacemaker. As the ectopic impulses increased in frequency, the action potential of the sinus node was a little more reduced in duration than that of the pectinate muscle, showed a marked decrease, and could not synchronize with that of the pectinate muscle, then changed into the fibrillatory potential. Subsequently, the fibrillation occurred to the common muscle.
Authors further demonstrated a clinical case report. The patient was 23 years old male, whose cardiac rhythm alternated to atrial fibrillation with A-V nodal rhythm. We have observed successively ECG alternation by the system of long term recording. It was found that the sinus rhythm apparently appeared every time before the onset of atrial fibrillation.
From the results mentioned above, it oas considered that the sinus node dominantly participates in the occurrence and the duration of atrial fibrillation.
