Effects of Digoxin on Acute, Atrial Fibrillation–Induced Changes in Atrial Refractoriness

Background—Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The acute changes in atrial refractoriness may be related to tachycardia-induced intracellular calcium overload. The purpose of this study was to determine whether digoxin, 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. Nineteen patients had been treated with digoxin for 2 weeks. After a several-minute episode of AF, atrial ERP was measured serially at alternating BDCLs. Compared with pre-AF ERPs, the first post-AF ERPs were significantly shorter 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 occurred a...