VDD (R) PACING SYSTEM

A VDD-type pacing system which may have a floating atrial electrode analyzes P-wave events and absences of P-waves to determine data indicative of the likelihood of P-wave undersensing. The pacemaker logic chooses a reaction algorithm to respond to atrial events in accordance with whether an absence of a P-wave is more likely to have been an undersense or an incidence of bradycardia. Specific algorithms are presented which illustrate pacemaker reactions to probable undersense and brady occurrences. The pacemaker also incorporates a subsystem for detection of undersense events.