McGill Case 293

This case report is kindly provided by Michael Rosengarten from McGill and is part of the McGill Cases. These cases come from the McGill EKG World Encyclopedia. Previous Case: McGill Case 292 | Next Case: McGill Case 294

This is an intra-atrial tracing recorded via the telemetry channel of a Medtronic Model 7077 pacemaker. The pacemaker was implanted in a patient who had a heart rate of 75/min. when the pacer was set to the DDD mode. For this tracing the pacer was programmed to VVI mode at a rate of 70/min. Why did the pacer pace at 75/min in the DDD mode and why is it not now pacing at 70/min ?