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Sensing and stimulation of the myocardium demands a closed electrical circuit. A pacemaker can sense and stimulate in a unipolar and bipolar fashion:
Sensing and stimulation of the myocardium demands a closed electrical circuit. A pacemaker can sense and stimulate in a unipolar and bipolar fashion:
* Unipolar: Pacemaker circuit between 1 electrode at the distal end of lead and the pacemaker pulse generator (large circuit ± 40-60 cm).
* Unipolar: Pacemaker circuit between 1 electrode at the distal end of lead and the pacemaker pulse generator (large circuit ± 40-60 cm).
- Advantage: large pacemaker spikes (easier interpretation pacemaker ECG)
** Advantage: large pacemaker spikes (easier interpretation pacemaker ECG)
- Disadvantage: extracardiac stimulation (pectoral muscle), sensing of extracardiac signals (such as ventricular depolarisations in the atrial sensing channel (far field R waves) or non-physiological noise)
** Disadvantage: extracardiac stimulation (pectoral muscle), sensing of extracardiac signals (such as ventricular depolarisations in the atrial sensing channel (far field R waves) or non-physiological noise)
* Bipolar: Pacemaker circuit between 2 electrodes at the distal end of the lead (small circuit ± 10-15 mm)
* Bipolar: Pacemaker circuit between 2 electrodes at the distal end of the lead (small circuit ± 10-15 mm)
- Advantage: more reliable sensing
** Advantage: more reliable sensing
- Disadvantage: small pacemaker spikes (difficult interpretation pacemaker ECG)
** Disadvantage: small pacemaker spikes (difficult interpretation pacemaker ECG)
 
===Follow up===
 
The first 6-8 weeks after implantation, patients are advised not to over-stretch their arm on the same side as the pacemaker (such as golf, swimming etc.) to allow time for the lead to mature.
 
Control visits for pacemakers are usually every 6 months. During this visit several electrical parameters are measured: battery status, stimulation thresholds and impedance.
 
===Complications===
 
* Undersensing: An intrinsic depolarization that is present, is not sensed by the pacemaker. This can be due to:
** Inappropriately programmed sensitivity
** Lead dislodgement
** Lead failure, such as lead fracture or insulation failure
** Lead maturation: the amplitude may abruptly decline during the first week after implantion, but these values return to the implantation values after about 6-8 weeks as the lead “matures”
 
 
* Oversensing: The pacemakers senses signals on the marker channel that do not correspond to the ECG pattern. This can be physiologic (e.g. ventricular pulse or myopotentials) or non-physiologic (e.g. lead fracture or if the lead is loose from the pacemaker pulse generator or outside interference such as TENS therapy or surgical diathermy).


==ICD==
==ICD==
*Overzicht trials met link naar pubmed
*Overzicht trials met link naar pubmed
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