Oversensing refers to inappropriate sensing of electrical stimuli by pacemaker leads. Atrial and ventricular leads are both susceptible to this phenomenon and the inciting electrical stimuli may be a normal physiological event (e.g. P, R or T wave), a pacemaker discharge, muscular contraction, or Electro-Magnetic Interference (EMI) from electrical phenomena outside the body (cautery, arc-welding, etc.)

Oversensing can be a medical emergency resulting in underpacing (bradycardia), triggered pacing (tachycardia), or inappropriate delivery of arrhythmia treatment in patients with ICDs.

Some of the most frequently encountered clinical examples of over-sensing are Far Field R Wave (FFRW) sensing in the atrium, T wave over-sensing in the atrium or ventricle , and P wave over-sensing in the ventricle.

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