Effects of digoxin on acute, atrial fibrillation-induced changes in atrialrefractoriness

Background-Atrial fibrillation (AF) shortens the atrial effective refractor y period (ERP) and predisposes to further episodes of AF. The acute changes in atrial refractoriness may be related to tachycardia-induced intracellul ar calcium overload. The purpose of this study was to determine whether dig oxin, which increases intracellular calcium, potentiates the acute effects of AF on atrial refractoriness in humans. Methods and Results-In 38 healthy adults, atrial ERP was measured at basic drive cycle lengths (BDCLs) of 350 and 500 ms after autonomic blockade. Nin eteen patients had been treated with digoxin for 2 weeks. After a several-m inute episode of AF, atrial ERP was measured serially at alternating BDCLs. Compared with pre-AF ERPs, the first post-AF ERPs were significantly short er in both the digoxin and the control groups (P<0.001), The post-AF ERP at a BDCL of 350 ms shortened to a greater degree in the digoxin group (37+/- 16 ms) than in the control group (20+/-13 ms, P<0.001); similar changes occ urred at a BDCL of 500 ms. During post-AF determinations of the atrial ERP, secondary AF episodes occurred significantly more often in the digoxin gro up (32% versus 16%; P<0.04). Conclusions-After a brief episode of AF, digoxin augments the shortening th at occurs in atrial refractoriness and predisposes to the reinduction of AF . These effects occur in the setting of autonomic blockade and therefore ar e more likely to be due to the effects of digoxin on intracellular calcium than to its vagotonic effects.