Sensing of 2 atrial rhythms by a pacemaker in a transplanted heart.

A patient who had undergone orthotopic heart transplantation received a VDD pacemaker for AV block. The pacemaker sensed both the recipient and donor atrial rhythms. The atrial lead must be implanted in the donor atrium: a double atrial electrogram requires a different atrial site unless programmable atrial sensitivity can establish preferential sensing of donor P waves.