I have always assumed that atrial fibrillation means that both atria are in a quiver. Is it possible for only one atrium to be in fibrillation while the other is in a normal sinus rhythm, atrial flutter, atrial standstill, or other rhythm?—Raymond Delille Sr, PA, Sanderson, Tex.

The faster rate of the atrial fibrillation overrides any rhythm in the other atrium. The only exception would be a case in which there was no electrical conduction pathway between the two atria. To illustrate, a heart-transplant patient could have residual tissue from his own atrium and the donor atrium. Proving the presence of two different rhythms (atrial fibrillation and possibly atrial flutter) would require placing a catheter in each atrium.
—Debra Kleinschmidt, PhD, PA