Orthodromic pacemaker circus movement tachycardia.

We report on the case of a 33-year-old woman with sick sinus syndrome who had an orthodromic pacemaker circus movement tachycardia (PCMT), with antegrade atrioventricular (AV) conduction and a retrograde pathway by means of a DDD (AV universal) pacemaker. This PCMT was provoked and sustained by premature ventricular contraction-synchronous atrial stimulation (PVC-SAS), which is a new feature for the prevention of antidromic PCMTs. The conditions for occurrence of this tachycardia were: PVC-SAS; atrial undersensing; first degree AV block. Recommendations for prevention of this pacemaker-mediated tachycardia are given.