Atrial sensing failure

This tracing reveals an intermittent atrial undersensing. P wave sensing has certain peculiarities. Indeed, the amplitude of the sensed atrial signal can vary according to the position of the patient and as a function of the respiratory cycle. It is therefore necessary to set a sufficient margin to avoid atrial undersensing issues during exertion which, in a patient with atrioventricular block, can cause a sudden decrease in the ventricular pacing rate. In addition to the lack of proper monitoring of P waves during exertion, atrial undersensing may have a pro-arrhythmogenic effect if atrial pacing occurs in vulnerable atrial periods with a risk of atrial arrhythmia induction.