Paradoxical atrial undersensing: noise rate reversion or amplifier ringing?

Atrial tachy-arrhythmias may give rise to mode switching or noise rate reversion in dual-chamber pacemakers. In case of high amplitude of the atrial electrogram during tachycardia, a paradoxical behavior of atrial sensitivity programming can be observed. Two patients with implanted dual-chamber pacemakers showed intermittent and complete loss of atrial sensing during atrial tachycardia during device programming to a higher atrial sensitivity setting. This phenomenon is caused by amplifier ringing and can be considered as a state of amplifier saturation, which disables atrial sensing in spite of the high amplitude of the atrial signal. In patients with high amplitude of the atrial electrogram during atrial tachycardia, a paradoxical behavior of sensitivity programming resulting in atrial undersensing can be observed.