Repetitive non-reentrant VA synchrony and pacemaker-mediated tachycardia induced by the AF suppression algorithm.

A 76-year-old man underwent implantation of a model 5386 Identity ADx XL DR pacemaker (St. Jude Medical, Sylmar, CA, USA) for intermittent, high-degree atrioventricular (AV) block. A model 4480 passive bipolar lead (St. Jude) was placed in the right atrial appendage, and a model 1688T active fixation lead (St. Jude) was placed on the right ventricular midseptum. The device was programmed in DDD mode, with a backup rate set at 50 bpm, maximum tracking rate and maximum sensor rate limit at 110 bpm, and AV/PV delays at 250/250 ms. The postventricular atrial refractory period (PVARP) and postventricular atrial blanking periods were set at 250 and 165 ms, respectively. The rate-responsive AV/PV delay and PVARP were set at MEDIUM level. The atrial fibrillation (AF) suppression algorithm was programmed ON. Since ventriculoatrial (VA) conduction during ventricular pacing at 70 ppm was observed neither at the time of device implantation nor at any of the follow-up visits, the pacemakermediated tachycardia (PMT) option was programmed OFF. The atrial high rate episodes (AHRE) function was activated for detection of rates >190 bpm. Far-field R-wave oversensing was excluded by setting of the postventricular atrial blanking. Since the bipolar atrial electrogram measured 2.3 mV and the capture threshold was 0.75 V/0.4 ms, the atrial sensitivity was set at 0.5 mV and atrial pulse amplitude at 2.5 V/0.4 ms. At the 1-year follow-up visit, the intracardiac electrograms (iEGM) of recorded AHRE were reviewed (Fig. 1). AF suppression, initiated by atrial premature complexes, increased the atrial pacing rate to the maximum tracking rate. Retrograde