Paradoxical under-sensing of atrial lead at high sensitivity setting in dual chamber pacemaker during atrial flutter - What is the mechanism?

The causes of atrial undersensing in a dual chamber pacemaker include true undersensing (low amplitude electrogram), functional undersensing (related to the effect of special timing cycles in the presence of an adequate signal) and paradoxical undersensing. This case report describes paradoxical atrial undersensing at a higher programmed atrial sensitivity and with the return of normal atrial sensing at a lower programmed sensitivity.