Functional atrial undersensing associated with device algorithm promoting AV conduction.

A 58-year-old woman received a dual chamber pacemaker (Medtronic) for sick sinus syndrome. Given intact AV conduction the Managed Ventricular Pacing mode algorithm (MVP) was programmed. The day after, she suffered from palpitations. Her ECG showed a possible loss of atrial capture accompanied by atrial undersensing. Telemetry-supported pacemaker control confirmed the loss of capture. Undersensing of atrial signal was functional, related to long atrial refractory period in MVP mode algorithm. Device algorithms could induce false suspicions. Awareness about the different pacing algorithms can be useful in order to avoid erroneous interpretations and to correct potential malfunctioning.