Cross-stimulation: the unexpected stimulation of the unpaced chamber.

The ability to stimulate one chamber through a lead or output circuit to the opposite cardiac chamber is termed cross-stimulation. Three examples of this phenomenon are presented. The first involves the close proximity of the atrial lead to the ventricular myocardium with ventricular capture occurring at sufficiently high outputs; the second is due to the basic design of dual unipolar pacing systems which have output circuits that share a common anode; the third is a self-limited eccentricity of one device that occurs only during the first phase of magnet-induced asynchronous pacing. The mechanism and clinical significance of these observations are discussed.