Causes of "failure to output" (absence of pacemaker spike)

  Oversensing (most frequent).

  End of life of pacemaker battery.

  Defect in pacemaker battery.

  Fracture of the electrode.

  Insulation defect of the electrode.

  Faulty connection of pacemaker electrode to the battery (inadequate squeezing of the screw, etc.).

  Oversensing.



Causes of "Failure to Capture"
(although pacemaker gives stimulus, the cardiac chamber cannot be depolarized)

  Elevated threshold (due to displacement of the electrode tip, myocardial infarction, myocardial fibrosis or cardiac perforation)

  Excessive use of antiarrhythmic drugs.

  Electrolyte disturbances.

  Insulation defect of the electrode.

  Electrode fracture.

  Presence of air in the pacemaker pocket (only in pacemakers with unipolar leads).



Causes of oversensing

  Sensing of the T wave at the ventricular channel.

  Sensing of the skeletal muscle activity.

  Defective connection of the electrode to the battery.

  Lead fracture.

  Electromechanical interference.



Causes of undersensing

  Improper positioning of the electrode tip (most frequent).

  Displacement of the electrode tip after proper initial positioning.

  Improper adjustment of the sensitivity.

  Myocardial fibrosis or infarction.

  Defective insulation of the electrode.

  Electrode fracture.

  Electrolyte disturbances.