Pacemaker syndrome induced by the mode switching algorithm of a DDDR pacemaker

A patient with marked first-degree AV block and a DDDR pacemaker presented with a history of paroxysmal narrow QRS tachycardia, subsequently identifie d as sinus tachycardia (with a very long PR interval), causing a clinical p roblem similar to pacemaker syndrome because of loss of AV synchrony. The l atter resulted from an excessively long postventricular atrial refractory p eriod (PVARP) that prevented sensing of sinus P waves, The unfavorable hemo dynamics caused reflex sinus tachycardia. The long PVARP was mandated by th e mode switching algorithm of this particular device and was automatically set according to the selected tachycardia detection rate. The patient becam e asymptomatic when the mode switching function was turned off and the PVAR P shortened.