Reed switch in a pacemaker / ICD

Reed switch in a pacemaker / ICD

Reed switch is used to activate the magnet mode in pacemaker / ICD (implantable cardioverter-defibrillator). It is basically a collection of two strips of magnetic material enclosed in a glass capsule. Application of a magnetic field closes the switch by making contact between the two metal strips. This changes the sensed voltage in a sensing amplifier, triggering a circuit controlling the magnet mode functional status. Reed switch can malfunction if the glass capsule is broken, remaining in same position regardless of the applied magnetic field. This situation is called ‘sticky reed switch’.

Reed switch has been replaced by Hall sensor in MRI conditional devices.