Programmed upper-rate limit dependent endless loop tachycardia.

In a patient with a VDD dual chamber pacemaker, an endless loop tachycardia (ELT) appeared spontaneously or could be provoked by magnet application and removal. The duration of the ELT was dependent on the programmed upper-rate limit of the pacemaker, ie, the higher it was set, the shorter the duration of the ELT. This was caused by the automatic variable pacemaker AV delay (the Wenckebach effect) which prolongs maintaining the programmed cycle length at each upper-rate limit during the tachycardia. This case illustrates the mechanism by which increasing the upper-rate setting of this unit prevents or restrains the ELT.