undersensing

Non-sensing of the intracardiac atrial or ventricular depolarization signal by a pacemaker.

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un·der·sens·ing (unґdər-sens″ing) missed sensing of cardiac electrical signals by an artificial cardiac pacemaker, resulting in too frequent or irregular delivery of stimuli; causes include head dislodgment, malfunctioning of the pulse generator, fibrosis, infarct, and drugs.