Pacemakers are amongst the most reliable of medical devices, but problems do occur. These can be broken down in a number of ways, but it is probably most convenient to consider them in the following fashion.
Device failure: failure to sense and/or pace appropriately. This may happen at any stage after implant. In some situations problems can be overcome with adjustments to programming, but in other cases the device may need replacement.
Lead failure: in the immediate post-implant period the leads may displace. This may be fairly subtle, and manifest with a change in the parameters detected at device interrogation. In some cases the displacement can be much more obvious, with a marked shift in position within the desired chamber, or displacement into another chamber. It is relatively unusual for displacement to occur later, unless there has been significant chest trauma or cardiac surgery.
Pocket problems: The pacemaker itself is implanted in a pocket created within the deep tissues of the anterior chest wall, and is conducted as an aseptic procedure; infection does still occur however. This may be related to the incision, the pocket, or the device/leads. Although it may be reasonable to try and treat these infections conservatively with antibiotics, the system often has to be revised or extracted. Patients with convincing signs of infection should be admitted for treatment and expert evaluation.
The pacemaker box may cause problems with its site. Patients may find it uncomfortable, or occasionally it may erode towards the surface, threatening the viability of the overlying tissue. This usually requires operative revision. Certainly any patient with tissue breakdown over the site of the box should be admitted for specialist evaluation.