“…The causes of this rare phenomenon are considered catecholamine-induced changes in the AP refractory period, pacing site–dependent conduction block, supernormal retrograde conduction, bradycardia-dependent block, 1 and phase 3 or phase 4 retrograde block. 2 In our case, further differentiation was difficult because we did not use catecholamines, change the RV pacing site, slow down the sinus rhythm, or evaluate VA conduction at slower rates before radiofrequency energy delivery.…”