Pacemaker for terminating pacemaker-mediated tachycardia

Claim 1

A pacer for pacing a patient's heart comprising: atrial sensing means for generating an atrial sensed event in response to a depolarization of atrial tissue; AV delay timer means for defining an AV delay interval, said AV delay timer means coupled to said atrial sensing means, said AV delay interval initiated by the occurrence of an atrial sensed event; ventricular pace stimulator means coupled to said AV delay timer means for generating a ventricular pacing stimulus at the conclusion of said AV delay interval; post ventricular atrial refractory period (PVARP) means coupled to said ventricular pacing stimulator means for defining a first predefined post ventricular atrial refractory period extending for a first predefined interval after the generation of said ventricular pacing stimulus; retrograde sense window timing means for defining a retrograde sense window after said PVARP; retrograde sensed event counter means for counting atrial sensed events occurring during retrograde sense windows defining a retrograde sense count; post ventricular atrial refractory period extension means for defining an extended PVARP in response to a predetermined count of said retrograde sensed event counter means, said extended PVARP including said first predefined interval plus an extension; retrograde sense window disable means for defining a disable time interval during which possible extended PVARPs are inhibited, said retrograde sense window disable means coupled to said retrograde sense counter means and invoked immediately following an initiation of an extended PVARP when said counter means reaches said predetermined count of said retrograde sensed event counter; and means for resetting said retrograde sense count after said predetermined count has been reached.