Factors Affecting the Incidence of Atrial Fibrillation

¹ From the Department of Pharmacology, Vanderbilt Medical School, Nashville, Tennessee

A study of fibrillation induced in isolated rabbit atria by stimulating at high frequencies (600–1200 cycles/min.) in presence of acetylcholine revealed it to be dependent on the ionic composition of the medium. The effects of varying the Na, K and Ca ion content of the bath fluid on the incidence of fibrillation are interrupted on the basis that fibrillation only begins at a time when the transmembrane flux of Na and K ions exceeds a critical rate. Evidence is presented that the initiation and maintenance of fibrillation are governed by separate physico-chemical processes. The onset of fibrillation results from a sudden transient increase in cell membrane permeability. This latter reaction sets off other biochemical processes which maintain the phenomenon.