Cyclic appropriate mode switching and inappropriate back switching of a biventricular pacemaker during atrial tachyarrhythmia.

In patients with resynchronization devices and intact intrinsic AV conduction, atrial tachyarrhythmias may give rise to high ventricular rates, resulting in inhibition of (bi)ventricular pacing and concomitant lack of therapeutic effects of the device. This report presents a patient with atrial arrhythmias in whom mode switching and back switching of the biventricular pacemaker occurred, due to special timing of the atrial and ventricular deflections. This case report stresses the importance of strenuous treatment of atrial arrhythmias in patients with resynchronization devices.