We check all pacemakers at least once a year.
The amount of energy that the pacemaker uses up is determined by how often it is called upon to work and how much energy is needed to cause the heart muscle to contract when paced.
Some people only need the pacemaker very rarely - perhaps a few beats each month when their own rhythm goes particularly slowly. Others are pacing continuously day and night from the moment the pacemaker is inserted. Clearly the latter will use up the pacemaker's battery life much quicker than the former.
In some people the contact between the tip of the pacing wire and the inside of the heart chamber is very good and the electrical current flows from the wire into the muscle with very little resistence. In these circumstances a lower voltage, using less energy, can be used. In others higher pacing voltages are required and this is another factor that determines the battery life. We attempt to individually program each person's pacemaker to maximise the battery life.
The large device that we use for programming the pacemaker 'reads' the pacemaker from outside the body and can be used to change various aspects of its setup - rather like using a very sophisticated television remote control! It will also tell us how much battery life is left in the pacemaker enabling us to judge when it is best to bring the patient in for a replacement