ABSTRACT
Pacemaker-mediated tachycardia (PMT) is a well-known complication of dual-chamber pacemaker with atrioventricular sensing and pacing (DDD) or atrial synchronous, ventricular demand pacemaker (VDD). PMT usually starts with sensing a retrograde P waves linked to ventricular extrasystole with retrograde ventriculoatrial conduction and forms reentrant or circus movement tachycardia with the pacemaker itself as an antegrade limb and the conducting tissue of the heart as a retrograde limb. Recently, a number of pacemaker manufactures have incorporated in their devices a variety of relatively complex algorithms to prevent PMT. Despite these measures, PMT may still occur because of inappropriate programming or unpredictable variations of ventri-culoatrial conduction. We report two cases of PMT in 78 year-old man and 60 year-old man who received DDD type pacemakers due to sick sinus syndrome, and a case of PMT in 69 year-old man who had suffered complete heart block and received a VDD type pacemaker. In these cases, we investigate symptoms, mechanism of PMT, programed parameters of pacemaker and treatments of PMT.