A wide range of settings can be adjusted. Programming is done through an external device that communicates wirelessly with the pacemaker. The pacemaker software includes pre-programmed algorithms and settings, which can be tailored to the patient’s needs. The higher the resistance in the lead tip, the smaller the current used. Given that voltage (V) is constant and battery depletion must be minimized, most pacemakers use lead tips with high resistance (400 to 1200 Ω). The current that is delivered by the pulse generator can be calculated as follows: Pacemakers generate a constant voltage (V).
The relationship between current (I), voltage (V) and resistance (R) is described by Ohm’s law: Amplitudes are normally below 1.5 V and pulse duration (width) is usually set to 0.5 ms. The amplitude and duration of the pulse must be optimized to ensure depolarization while minimizing battery consumption. The intensity of the electrical stimulus is described by its amplitude (measured in volts) and duration (measured in milliseconds). Stimulation threshold is the minimum amount of energy required to reach threshold and evoke an action potential. As previously discussed, myocardium may be excited by external electrical stimuli that drive the cells to threshold.
