Sinus Node Impulses and Atrial Fibrillation

Abstract

In atrial muscle strips from rabbits, fibrillation occurred in a solution low in potassium, with or without a high calcium content, and the role of the sinus node in inducing atrial fibrillation was examined by microelectrodes and by direct close bipolar lead electrocardiograms. In right atrial strips that included the sinus node, the sinus node action potential often just preceded spontaneous fibrillation or premature beats. In left atrial strips in a similar condition, the incidence of spontaneous fibrillation or premature beats was very low. However, when electrical stimulation simulating sinus node impulses was applied, fibrillation or the premature beat frequently appeared immediately after the stimulating pulse waves, and its incidence was also remarkably increased, being fairly close to that of the right atrial strip. These findings suggest that "the sinus node impulses occasionally caused fibrillation or premature beats during these experiments in a medium low in potassium. In addition, fibrillation was frequently induced even when the impulse fell outside the vulnerable period of the preceding beat.

Decreased intercellular coupling after prolonged rapid stimulation in rabbit atrial muscle.

“…Our results provide support for this view since the maximum response rate (present results) is in the range of firing (8-20 Hz) observed during atrial fibrillation (Sano et al, 1967;Kositsky et al, 1972a). Disturbances of intercellular electrical coupling during fibrillation contribute to disturbances of circular pathways of propagation and elimination of reentry.…”

Cardiac Lesions in Dairy Cows with Idiopathic Atrial Fibrillation.

“…It is therefore possible that in cattle AF is a cause of histopathological changes in the SA node. Intriguingly, it has been reported that, in experiments on dog hearts, AF was easily produced by some drugs when the SA node was intact, but was difficult to produce when the SA node was injured [30].…”

Anatomy of the sinus node, av node, and his bundle of the heart of the sperm whale (Physeter macrocephalus), with a note on the absence of an os cordis

“…It is well established that it is easier to produce either atrial or ventricular fibrillation in large than small hearts and that therapeutic termination of either form of fibrillation is more difficult in large hearts. Both experimental and clinical evidence furthermore indicates that presence or absence of continued activity by the sinus node influences whether or not atrial fibrillation will occur (Sano et al, 1967;Azuma et al, 1972;Kirchhof, 1989;Page, 1992), and default of the sinus node may help fibrillation to begin andlor be perpetuated. A sinus node as large and well organized as that of the sperm whale may be more difficult to unstabilize or suppress.…”